The work was supported by projects: "Research Centre of University of &#381;ilina - 2nd phase", ITMS 313011D011, Scientific Grant Agency of the Ministry of Education, Science and Sports of the Slovak Republic and Slovak Academy of Sciences, grants No.: 1/0045/17, 1/0951/17 and 1/0123/15 and Slovak Research and Development Agency, grant No. APVV-16-0276.

Note: Each specimen&#39;s geometry has to be selected and calculated according to the mechanical and physical properties of the tested material, so that it has an identical resonance frequency as the ultrasonic testing system.

1. Determination of the Fatigue Test Specimen Dimensions
Note: The standard &#34;hourglass&#34; tension-compression specimen geometry, with defined main dimensions, is shown in Figure 1. Dimensions d, D, and r are user defined (independent), while l and L dimensions have to be calculated, according to the conditions of the correct resonance frequency (dependent). The gauge length l results only from the geometry ratio between d, r, and D, and can be calculated easily or obtained from a component model; thus, it will not be an object of further discussion.
<ol>
	<li>Determination of Independent Dimensions 
	Note: The main dimensions of the specimen (d, D, r) are chosen according to the material parameters and the test conditions.
	<ol>
		<li>Determine the gauge diameter d according to the required volume of material for testing. In the case of a homogenous microstructure with no internal defects, a smaller gauge diameter is preferred. In the case of a material with significant internal defects (such as voids and shrinkages in cast materials), a bigger gauge diameter is necessary. The gauge diameter d is usually from 3&#160;mm to 5 mm.</li>
		<li>Determine the head diameter D according to available experimental material size. The used head diameter D is usually from 10 mm to 15 mm. 
		Note: The larger the D is, the shorter the head length (L) will be.</li>
	</ol>
	</li>
	<li>Determine the gauge radius r according to the required mechanical stress distribution in the specimen&#39;s gauge length. The larger the gauge diameter r is, the smoother is the mechanical stress distribution. A commonly used gauge radius is r = 20 mm or r = 32 mm. 
	Note: The larger the r is, the longer the specimen will be.</li>
	<li>Determination of Dependent Dimensions
	<ol>
		<li>Determine the wave number K according to the following formula9,18: 
		<img alt="Equation 1" src="/files/ftp_upload/57007/57007eq1.jpg" /> 
		Note: Here the fr is the resonance frequency of the ultrasonic system (Hz), &#961; is the volume density (kg m-3), and Ed is the dynamic modulus of elasticity (kg m-3).</li>
		<li>Determine the hyperbolic approximation of the gauge radius, according to the following formula9,19: 
		<img alt="Equation 2" src="/files/ftp_upload/57007/57007eq2.jpg" /> 
		Note: Here l is the gauge length (m), D is the head diameter (m), and d is the gauge diameter (m) (Figure 1).</li>
		<li>Determine the effective eccentricity according to following formula9,18: 
		<img alt="Equation 3" src="/files/ftp_upload/57007/57007eq3.jpg" /> 
		Note: Here A is the hyperbolic approximation (m-1) determined by equation (2), and K is the wave number (-) determined according to expression (1).</li>
		<li>Determine the length of head (L) according to the following equation9,18: 
		<img alt="Equation 4" src="/files/ftp_upload/57007/57007eq4.jpg" /> 
		Note: Here K is the wave number (-) determined according to expression (1) in point 1.2.1, &#946; is the effective eccentricity (m-1) determined by equation (3), and l is the gauge length (m) (Figure 1).</li>
	</ol>
	</li>
</ol>
2. Calculation of the Mechanical Stress in the Gauge Length of the Specimen
<ol>
	<li>Determine the norming geometrical factor <img alt="Equation 5" src="/files/ftp_upload/57007/57007eq5.jpg" /> according to the following equation9,18: 
	<img alt="Equation 6" src="/files/ftp_upload/57007/57007eq6.jpg" /></li>
	<li>Determine the deformation amplitude &#603; according to the following equation9,18: 
	<img alt="Equation 7" src="/files/ftp_upload/57007/57007eq7.jpg" /> 
	Note: Here&#160;<img alt="Equation 5" src="/files/ftp_upload/57007/57007eq5.jpg" /> is the geometrical factor (-) and u is the required displacement amplitude of the free end of the specimen (m).</li>
	<li>Determine the mechanical stress amplitude &#963;a according to the following equation9,18: 
	<img alt="Equation 8" src="/files/ftp_upload/57007/57007eq8.jpg" /> 
	Note: Here &#603; is the deformation amplitude (-) determined according to expression (5), and Ed is the dynamic modulus of elasticity (kg m-3). If the calculated mechanical stress is too low, it is necessary to increase the displacement amplitude u (m), and vice versa.</li>
</ol>
3. Manufacturing of the Specimen with Machining Operations
<ol>
	<li>Due to various small deviations of the machined specimens from an ideal shape, manufacture specimens with longer heads, usually L + 0.5 mm.</li>
</ol>
4. Harmonizing of the Resonance Frequency of the Specimen with the Ultrasonic System
Note: Harmonizing is the process of compensating various small deviations of the real specimen from the ideal, calculated shape, to obtain the correct resonance frequency, which is in harmony with the ultrasonic acoustic sonotrode.
<ol>
	<li>Choose the proper type of acoustic sonotrode, according to the required displacement range, which is able to provide proper mechanical stress in the specimen. 
	Note: Each type of sonotrode is designed and calibrated for a different displacement range, thus the proper sonotrode is chosen according to the required displacement amplitude calculated according to section 2.</li>
	<li>Mount the sonotrode on the piezo-electric converter.
	<ol>
		<li>Screw the connection screw inside the central hole on the sonotrode until it reaches the bottom.</li>
		<li>Spread acoustic gel on the face of the sonotrode. 
		Note: A small amount of gel is used, just enough to fill the irregularity of the surfaces, which improves the transfer of the mechanical wave between piezo-electric converter and the sonotrode.</li>
		<li>Screw the sonotrode into the piezo-electric converter.</li>
	</ol>
	</li>
	<li>Run the ultrasonic system with a piezo electric converter with mounted sonotrode to measure the resonance frequency of the particular system at actual temperature.
	<ol>
		<li>Run the ultrasonic testing software (e.g., Win20k).</li>
		<li>Choose the type of the used sonotrode in the drop-down menu in the &#34;Model&#34; box.</li>
		<li>Enter the lowest possible displacement amplitude for the particular sonotrode into the &#34;Amplitude&#34; box.</li>
		<li>Click the &#34;Start&#34; button.</li>
		<li>Read the actual resonance frequency of the system in the &#34;Frequency&#34; box.</li>
		<li>Click the &#34;Stop&#34; button.</li>
	</ol>
	</li>
	<li>Mount the specimen at the end of the sonotrode.
	<ol>
		<li>Screw the connection screw into the central hole of the specimen until it reaches the bottom.</li>
		<li>Screw the specimen to the sonotrode.</li>
	</ol>
	</li>
	<li>Run the ultrasonic system with a piezo electric converter with mounted sonotrode and specimen to measure the resonance frequency of the particular system at actual temperature.
	<ol>
		<li>Run the ultrasonic testing software.</li>
		<li>Choose the type of sonotrode used in the drop-down menu in the &#34;Model&#34; box.</li>
		<li>Enter the lowest possible displacement amplitude for the particular sonotrode into the &#34;Amplitude&#34; box.</li>
		<li>Click the &#34;Start&#34; button.</li>
		<li>Read the actual resonance frequency of the system in the &#34;Frequency&#34; box.</li>
		<li>Click the &#34;Stop&#34; button.</li>
	</ol>
	</li>
	<li>When the resonance frequency of the system with mounted specimen is lower than that without the specimen, reduce the mass of the specimen by cutting off the faces of the specimen&#39;s head. 
	Note: If the resonance frequency with a mounted specimen is higher, it would be necessary to reduce the gauge diameter d, which would change the conditions of the test. This is the reason 0.5 mm is added to length of the heads in the manufacturing process.
	<ol>
		<li>Dismount the specimen from the sonotrode.</li>
		<li>Mount the specimen into a lathe and turn down 0.1 mm of the face of the first head.</li>
		<li>Mount the specimen into a lathe and turn down 0.1 mm of the face of the second head.</li>
		<li>Repeat step 4.6 until the resonance frequency is within tolerance of &#177; 10 Hz.</li>
	</ol>
	</li>
</ol>
5. Final Mounting of the Specimen to the Sonotrode before the Fatigue Test
<ol>
	<li>Apply acoustic gel on the faces to create connections between the sonotrode and the specimen.
	<ol>
		<li>Screw the connection screw into the central hole of the specimen until it reaches the bottom.</li>
		<li>Spread the acoustic gel on the face of the specimen. 
		Note: Just a small amount of acoustic gel is used to fill in the irregularities on the surface to improve the acoustic wave transfer from the sonotrode to the specimen.</li>
		<li>Screw the specimen to the sonotrode.</li>
	</ol>
	</li>
</ol>
6. Run the Cooling System for Specimen
<ol>
	<li>If air cooling is used, focus the air stream directly on the middle of the gauge length of the specimen, and wait for about 20 s, so the flow of the air stream saturates the specimen.</li>
	<li>If water cooling is used, focus the water nozzles at the top head of the specimen, and adjust the stream intensity so the water flows smoothly along the gauge length, to avoid cavitation. 
	Note: Submerging the specimen into water or oil is possible as well, however this can be used only for short time tests due to the significant cavitation effect, which accelerates the fatigue crack initiation process.</li>
</ol>
7. Run the Cooling System of the Piezo Electric Converter
<ol>
	<li>Open the valve of the air stream and adjust the pressure in the interval between 0.5 and 1 bar.</li>
</ol>
8. Run the Test at Required Displacement Amplitude
<ol>
	<li>Run the ultrasonic testing software.</li>
	<li>Choose the type of the used sonotrode in the drop-down menu in the &#34;Model&#34; box.</li>
	<li>Enter the requested displacement amplitude for the particular sonotrode into the &#34;Amplitude&#34; box.</li>
	<li>Click the &#34;Start&#34; button.</li>
</ol>
9. Fatigue Crack Initiation and Propagation
<ol>
	<li>Observe that after the fatigue crack initiation and propagation through a part of the cross section, the system is shifted out of the resonance frequency and the test is naturally terminated.</li>
	<li>If the test does not end with a fracture, after reaching requested number of loading cycles, (the test is a run-out) terminate using the &#34;Stop&#34; button in the ultrasonic testing software.</li>
</ol>
10. Dismount the Specimen from the Sonotrode
<ol>
	<li>Screw off the specimen from the ultrasonic sonotrode.</li>
</ol>
11. Static Loading Force Fracturing
<ol>
	<li>Use static loading force to fracture the rest of the cross section with use of a static loading machine. 
	Note: The vector and type of the loading force for the static fracture should correspond with the type of the fatigue loading so that the fracture surface has consistent character.</li>
</ol>

<ol>
	<li>Moore, H. F., Kommers, J. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> The fatigue of metals. , 321 (1927).</li><li>Nicholas, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> High Cycle Fatigue: A Mechanics of Materials Perspective. , (2006).</li><li>Schijve, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Fatigue of Structures and Materials. , (2008).</li><li>Murakami, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Metal Fatigue: Effects of Small Defects and Nonmetallic Inclusions. , (2002).</li><li>Trsko, L., Bokuvka, O., Novy, F., Guagliano, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+severe+shot+peening+on+ultra-high-cycle+fatigue+of+a+low-alloy+steel.">Effect of severe shot peening on ultra-high-cycle fatigue of a low-alloy steel.</a> Mater. Design. 57, 103-113 (2014).</li><li>Stanzl, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fracture+mechanisms+and+fracture+mechanics+at+ultrasonic+frequencies.">Fracture mechanisms and fracture mechanics at ultrasonic frequencies.</a> Fatigue. Fract. Eng. M. 22 (7), 567-579 (1999).</li><li>Bathias, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=There+is+no+infinite+fatigue+life+in+metallic+materials.">There is no infinite fatigue life in metallic materials.</a> Fatigue. Fract. Eng. M. 22 (7), 559-565 (1999).</li><li>Ritchie, R. O., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-cycle+fatigue+of+Ti-6Al-4V.">High-cycle fatigue of Ti-6Al-4V.</a> Fatigue. Fract. Eng. M. 22 (7), 621-631 (1999).</li><li>Bathias, C., Paris, P. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Gigacycle Fatigue in Mechanical Practice. , (2004).</li><li>Bokuvka, O., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Ultrasonic Fatigue of Materials at Low and High Frequency Loading. , (2015).</li><li>Almaraz, G. M. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrasonic+Fatigue+Testing+on+the+Polymeric+Material+PMMA,+Used+in+Odontology+Applications.">Ultrasonic Fatigue Testing on the Polymeric Material PMMA, Used in Odontology Applications.</a> Procedia Structural Integrity. 3, 562-570 (2017).</li><li>Flore, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Investigation+of+the+high+and+very+high+cycle+fatigue+behaviour+of+continuous+fibre+reinforced+plastics+by+conventional+and+ultrasonic+fatigue+testing.">Investigation of the high and very high cycle fatigue behaviour of continuous fibre reinforced plastics by conventional and ultrasonic fatigue testing.</a> Compos. Sci. Technol. 141, 130-136 (2017).</li><li>Tr&#353;ko, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Influence+of+Severe+Shot+Peening+on+the+Surface+State+and+Ultra-High-Cycle+Fatigue+Behavior+of+an+AW+7075+Aluminum+Alloy.">Influence of Severe Shot Peening on the Surface State and Ultra-High-Cycle Fatigue Behavior of an AW 7075 Aluminum Alloy.</a> J. Mater. Eng. Perform. 26 (6), 2784-2797 (2017).</li><li>Mayer, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cyclic+torsion+very+high+cycle+fatigue+of+VDSiCr+spring+steel+at+different+load+ratios.">Cyclic torsion very high cycle fatigue of VDSiCr spring steel at different load ratios.</a> Int. J. Fatigue. 70, 322-327 (2015).</li><li>Bathias, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Piezoelectric+fatigue+testing+machines+and+devices.">Piezoelectric fatigue testing machines and devices.</a> Int. J. Fatigue. 28 (11), 1438-1445 (2006).</li><li>Mayer, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrasonic+torsion+and+tension-compression+fatigue+testing:+Measuring+principles+and+investigations+on+2024-T351+aluminium+alloy.">Ultrasonic torsion and tension-compression fatigue testing: Measuring principles and investigations on 2024-T351 aluminium alloy.</a> Int. J. Fatigue. 28 (11), 1446-1455 (2006).</li><li>Brugger, C., Palin-Luc, T., Osmond, P., Blanc, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+new+ultrasonic+fatigue+testing+device+for+biaxial+bending+in+the+gigacycle+regime.">A new ultrasonic fatigue testing device for biaxial bending in the gigacycle regime.</a> Int. J. Fatigue. 100, Part 2, 619-626 (2017).</li><li>Wagner, D., Cavalieri, F. J., Bathias, C., Ranc, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrasonic+fatigue+tests+at+high+temperature+on+anaustenitic+steel.">Ultrasonic fatigue tests at high temperature on anaustenitic steel.</a> J. Propul. Power. 1 (1), 29-35 (2012).</li><li>Kohout, J., Vechet, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+new+function+for+fatigue+curves+characterization+and+its+multiple+merits.">A new function for fatigue curves characterization and its multiple merits.</a> Int. J. Fatigue. 23 (2), 175-183 (2001).</li></ol>

We have nothing to disclose.

Ultrasonic fatigue testing is one of the few methods which allows testing of the structural materials in the ultra-high cycle region. However, the specimen shape and size are very limited with respect to the resonance frequency. For instance, testing of thin sheets in the mode of axial loading is generally not possible. In addition, testing of large specimens is usually not possible, because the testing machines do not provide such power and it would require the design of a special ultrasonic system. 
The proper design, calculation, and harmonizing of the specimen should not be underestimated, even when modern ultrasonic generators are able to modulate the ultrasonic wave and successfully resonate a specimen with slightly different dimensions. However, this causes a shift of the node of the ultrasonic wave away from the middle part of the gauge length, and then the specimen is not correctly loaded in the gauge length. For the same reason, great care has to be taken to ensure the symmetry of the test specimen with respect to both axes. 
A big discussion was held about the correlation of the test results performed at high frequencies with data obtained on conventional testing devices with the low frequency loading. Many tests have shown that results of the high frequency tests fluently extended results obtained at low frequencies, and also some part of the results have overlapped, when the same loading mode was considered10. Later, it was generally understood that the frequency of loading is not the parameter determining the fatigue properties, but the deformation rate is, and large deformations at low frequency of loading provide similar deformation rates as loading with small deformations at high frequency. However, this is the main reason why this technique can be used for tests in the range of high and mainly ultra-high cycle region, where the deformation amplitudes are small. An increase of the operation frequencies of various components made this discussion less important, as well, since this method provides more similar loading conditions than the ones in the high-speed operation.
The internal damping ability of the tested material determines the amount of heat produced during the test (internal damping is the ability of material to convert mechanical energy to heat). In the case of insufficient cooling, the gauge length is significantly heated, which accelerates initiation of a fatigue crack due to the lower mechanical properties of the tested material at elevated temperatures. In case of most aluminum and magnesium alloys, a stream of cold air is sufficient to cool down the specimen during the test. For materials with higher internal damping capacity such as steel, nickel, and titanium alloys, a stream of liquid coolant is used. During the cooling with liquid coolant, the cavitation in the middle part of the gauge length has to be avoided, because cavities accelerate initiation of the crack, which may invalidate the test results. 
Fatigue tests on most of the conventional testing devices end with a complete fracture of the cross section. After the cross section of the specimen is reduced by the continuously growing crack to a so-called "critical cross section", the specimen is then fractured in one cycle and has a character of a static fracture. In the process of ultrasonic testing, when the crack length reaches a critical length which shifts the stiffness of the system out of the resonance frequency, the vibrating stops causing a natural termination of the test. This means that it is not possible to reach the critical cross section and the test does not end with a full fracture, which is later performed artificially. Since the fatigue crack initiation in smooth fatigue specimens (without an artificial notch) represents more than 95% of the number of cycles to fracture, when such a high number of cycles is considered, the difference is considered negligible.
Ultrasonic fatigue testing is a very important method, which allows the simulation of conditions of high-speed loading, and reduces testing time. In this protocol, we highlighted the most critical points, possibilities, and limitations of the method for successful applications in material research and safety verification in industrial operation.

Fatigue damage of structural materials is strongly connected with industrialization and mainly with use of steam engine and steam locomotives for railway transport, where a lot of metal components, mainly iron based, have been used and had to withstand various types of cyclic loading. One of the earliest tests was done by Albert (Germany 1829)1 on welded chains for mine hoists. The loading frequency was 10 bends per minute, and the maximal tests recorded reached 100,000 loading cycles1. Another important work was carried out by William Fairbairn in 1864. Tests were performed on wrought-iron girders with use of a static load, which was lifted by a lever and then dropped causing vibrations. The girder was loaded with gradually increasing loading stress amplitude. After reaching several hundred thousand cycles on various loading stress amplitudes, in the end the girder failed after just about five thousand loading cycles at a loading amplitude of two fifths of the ultimate tensile strength. The first comprehensive and systematic study of the influence of repeated stress on structural materials was done by August W&#246;hler in 1860-18701. For these tests, he was using torsion, bending, and axial loading modes. W&#246;hler designed many unique fatigue testing machines, but their disadvantage was low operation speeds, for example the fastest rotating bending machine operated at 72 rpm (1.2 Hz), thus completion of the experimental program took 12 years1. After performing these tests, it was considered that after reaching a loading amplitude at which the material withstands 107 cycles, the fatigue degradation is negligible and the material can withstand an infinite number of loading cycles. This loading amplitude was named the &#34;fatigue limit&#34; and became the main parameter in industrial design for many years2,3.
Further development of new industrial machines, which required higher efficiency and cost savings, had to provide the possibility of higher loading, higher operation speeds, higher durations, and high reliability with low maintenance requirements. For example, components of the high-speed train Shinkanzen, after 10 years of operation, have to withstand approximately 109 cycles and failure of a main component can have fatal consequences4. Furthermore, components of jet engines often operate at 12,000 rpm, and components of turbo blowers often exceed 17,000 rpm. Those high operation speeds increased requirements for fatigue life testing in the so-called ultra-high cycle region, and to assess if the fatigue strength of a material could be really considered constant for more than 10 million cycles. After the first tests performed by exceeding this endurance, it was obvious that fatigue failures can occur even at applied stress amplitudes lower than the fatigue limit, after a number of cycles much more than 107, and that the damage and failure mechanism could be different from the usual ones5.
Creating a fatigue test program aimed at investigating the ultra-high cycle region required the development of new testing devices to strongly increase the loading frequency. A symposium focused on this topic was held in Paris in June 1998, where experimental results were presented which were obtained by Stanzl-Tschegg6 and Bathias7 at 20 kHz loading frequencies, by Ritchie8 with the use of 1 kHz closed loop servo-hydraulic testing machine, and by Davidson8 with a 1.5 kHz magneto-strictive testing machine4. From that time, many solutions were proposed, but still the most commonly used machine for this kind of test is based on the concept of Manson from 1950 and uses frequencies close to 20 kHz9. These machines exhibit a good balance between strain rate, the determination accuracy of the number of cycles, and the time of the fatigue test (1010 cycles are achieved in approximately 6 days). Other devices were able to provide even higher loading frequencies, like the one used by Girald in 1959 - 92 kHz and Kikukawa in 1965 - 199 kHz; however, these are rarely used because they create extremely high deformation rates and, since the test lasts for only few minutes, a remarkable error in the cycle counting is expected. Another important factor limiting the loading frequency of resonance devices for fatigue testing is the size of the specimen, which is in direct relation with the resonance frequency. The larger the requested loading frequency, the smaller the specimen. This is the reason why frequencies above 40 kHz are rarely used10.
Since the displacement amplitude is usually limited within the interval between 3 and 80 &#181;m, ultrasonic fatigue testing can be successfully applied on most metallic materials, though techniques for the testing of polymeric materials such as PMMA11 and composites12 were also developed. Generally, ultrasonic fatigue testing is possible to perform in modes of axial loading: tensile - compression symmetrical cycle13,14, tension - tension cycle15, three-point bending15, and there are also a few studies with special modifications of the system for torsion testing15,16 and biaxial bending17. It is not possible to use arbitrary specimens, because for this method, the geometry is strictly related to achieving the resonance frequency of 20 kHz. For the axial loading, several types of specimens have been commonly used, usually with an hour-glass shape with a gauge length diameter from 3 to 5 mm. For the three-point bending, thin sheets are commonly used, and for other methods special types of specimens are designed, according to the method type and testing conditions. The method was designed for evaluation of fatigue life in the high and ultra-high cycle region, and this means that at 20 kHz loading, a million cycles is obtained in 50 s; therefore, this is usually considered the bottom limit of loading cycles which can be investigated with reasonable accuracy, with respect to the number of cycle determination. Each specimen has to be harmonized with the ultrasonic horn by changing the specimen&#39;s mass to provide the right resonance frequency of the system: ultrasonic horn with specimen.

<table border="0" cellpadding="0" cellspacing="0" width="665">
	<tbody>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Ultrasonic fatigue testing device</td>
			<td style="width:71px;">Lasur</td>
			<td style="width:119px;">-</td>
			<td style="width:259px;">20 kHz, used for fatigue tests</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Nyogel 783</td>
			<td style="width:71px;">Nye Lubricants</td>
			<td style="width:119px;">-</td>
			<td>Used as acoustic gel for connection of the parts of the ultrasonic system</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Win 20k software</td>
			<td style="width:71px;">Lasur</td>
			<td style="width:119px;">-</td>
			<td>Software for operation of the Lasur fatigue testing machine</td>
		</tr>
	</tbody>
</table>

ultrasonic fatigue testing in the tension-compression mode

Ultrasonic fatigue testing is one of a few methods which allow investigating fatigue properties in the ultra-high cycle region. The method is based on exposing the specimen to longitudinal vibrations on its resonance frequency close to 20 kHz. With use of this method, it is possible to significantly decrease the time required for the test, when compared to conventional testing devices usually working at frequencies under 200 Hz. It is also used to simulate loading of material during operation in high speed conditions, such as those experienced by components of jet engines or car turbo pumps. It is necessary to operate only in the high and ultra-high cycle region, due to the possibility of extremely high deformation rates, which can have a significant influence on the test results. Specimen shape and dimensions have to be carefully selected and calculated to fulfill the resonance condition of the ultrasonic system; thus, it is not possible to test the full components or specimens of arbitrary shape. Before each test, it is necessary to harmonize the specimen with the frequency of the ultrasonic system to compensate for deviations of the real shape from the ideal one. It is not possible to run a test until a total fracture of the specimen, since the test is automatically terminated after initiation and propagation of the crack to a certain length, when the stiffness of the system changes enough to shift the system out of the resonance frequency. This manuscript describes the process of evaluation of materials' fatigue properties at high-frequency ultrasonic fatigue loading with use of mechanical resonance at a frequency close to 20 kHz. The protocol includes a detailed description of all steps required for a correct test, including specimen design, stress calculation, harmonizing with the resonance frequency, performing the test, and final static fracture.

Fatigue test results include loading stress, number of loading cycles, and the test termination character (fracture or run-out) can be seen in Table 1, where results of fatigue life of the 50CrMo4 quenched and tempered steel are provided. The most common interpretation of the fatigue life test results is the so-called S - N plot (S - stress, N - number of cycles), also known as the W&#246;hler&#39;s plot. The dependence of fatigue life on the applied loading stress is plotted in a diagram with historically given inverted axis, where the independent value (loading stress) is on the y axis and the dependent value (number of cycles) is on the x axis. Various types of regression analysis are applied19 on the fatigue life results and, in case a fit is added to the diagram, it is commonly called the S - N curve. However, there was no difference with the original plot, which includes just a data fit. If the test does not end with a fracture, and it is terminated after reaching the required number of loading cycles without damage, this result is called a run-out and in the S-N plot usually marked by arrow. Figure 2 shows a typical S - N plot of three tested steels: Hardox 450, Strenx 700 MC, and S355 J2.
In addition, the fracture surfaces of the specimens are analyzed, usually with use of scanning electron microscopy (SEM), where the character of the fatigue crack initiation and propagation is identified and interpreted. Figure 3 shows a fatigue fracture surface after ultrasonic fatigue testing of 50CrMo4 quenched and tempered steel. The crack was initiated on a free surface of the specimen and then propagated through the cross section until the ultrasonic system was shifted out of the resonance frequency (dark area). Consequently, the rest of the cross section was fractured by static loading that created the lighter area on the top of the figure. Figure 4 shows the area of the fatigue crack propagation in extruded AW 7075 - T6511 aluminum alloy. Figure 5 shows a cavity created on the surface due to submerging of the specimen into cooling liquid (distilled water with anti-corrosive inhibitor at room temperature) for a long-time test (several hours). The cavity accelerated the fatigue crack initiation and the result of this test cannot be considered as valid.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/57007/57007fig1.jpg" /> 
Figure 1: Drawing of the standard tension-compression ultrasonic fatigue test specimen. The&#160;dimensions are defined as follows: d - gauge diameter, D - head diameter, r - gauge radius, L - head length, l - gauge length. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57007/57007fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/57007/57007fig2.jpg" /> 
Figure 2: The S - N plot of the Hardox 450, Strenx 700 MC and S355 J2 steel. Run-out test is marked by arrow. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57007/57007fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/57007/57007fig3.jpg" /> 
Figure 3: Fracture surface character of the 50CrMo4 steel specimen loaded at 365 MPa and fractured after 1.97 &#215; 108 loading cycles. The fracture initiated on the free surface of the specimen. The fracture surface consists of the area of stable fatigue crack propagation (dark area) and the area of the unstable crack propagation, the so called static fracture (light area). <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57007/57007fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/57007/57007fig4.jpg" /> 
Figure 4: Area of the fatigue crack propagation in the AW 7075 aluminum alloy specimen loaded at 203 MPa and fractured after 8.3 &#215; 106 loading cycles. The crack propagated with a transcrystalline fatigue mechanism and the band-kind character of the fracture surface is a result of the strong deformation texture after extrusion of the material in the manufacturing process. The arrow shows the direction of fatigue crack propagation. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57007/57007fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/57007/57007fig5.jpg" /> 
Figure 5: Cavity on a surface of the 50CrMo4 steel specimen when an improper cooling process was used. The specimen was submerged in the liquid (distilled water with anti-corrosive inhibitor at room temperature). Cavities accelerate the fatigue crack initiation process because they serve as stress concentration notches, thus the result of this fatigue test is not valid. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57007/57007fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td rowspan="2">Specimen No.</td>
			<td>Stress amplitude</td>
			<td rowspan="2">Number of loading cycles</td>
			<td rowspan="2">Result</td>
		</tr>
		<tr>
			<td>&#160;(MPa)</td>
		</tr>
		<tr>
			<td>1</td>
			<td>449</td>
			<td>1.22 &#215; 107</td>
			<td>Fracture</td>
		</tr>
		<tr>
			<td>2</td>
			<td>505</td>
			<td>4.87 &#215; 106</td>
			<td>Fracture</td>
		</tr>
		<tr>
			<td>3</td>
			<td>421</td>
			<td>2.08 &#215; 107</td>
			<td>Fracture</td>
		</tr>
		<tr>
			<td>4</td>
			<td>449</td>
			<td>8.50 &#215; 106</td>
			<td>Fracture</td>
		</tr>
		<tr>
			<td>5</td>
			<td>421</td>
			<td>1.59 &#215; 107</td>
			<td>Fracture</td>
		</tr>
		<tr>
			<td>6</td>
			<td>393</td>
			<td>8.90 &#215; 107</td>
			<td>Fracture</td>
		</tr>
		<tr>
			<td>7</td>
			<td>365</td>
			<td>1.22 &#215; 108</td>
			<td>Fracture</td>
		</tr>
		<tr>
			<td>8</td>
			<td>337</td>
			<td>2.39 &#215; 108</td>
			<td>Fracture</td>
		</tr>
		<tr>
			<td>9</td>
			<td>337</td>
			<td>5.55 &#215; 108</td>
			<td>Fracture</td>
		</tr>
		<tr>
			<td>10</td>
			<td>309</td>
			<td>7.28 &#215; 108</td>
			<td>Fracture</td>
		</tr>
		<tr>
			<td>11</td>
			<td>365</td>
			<td>1.97 &#215; 108</td>
			<td>Fracture</td>
		</tr>
	</tbody>
</table>
Table 1: Results of the 50CrMo4 steel fatigue life analysis by ultrasonic fatigue testing. Fatigue life results represent the dependence of&#160;the number of loading cycles on the applied loading stress. The test can end with fracture, or by a run-out when no fatigue fracture occurs after the requested number of loading cycles.

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Ultrasonic Fatigue Testing in the Tension-Compression Mode

A protocol for ultrasonic fatigue testing in the high and ultra-high cycle region in axial tension-compression loading mode.

Ultrasonic fatigue testing is one of a few methods which allow investigating fatigue properties in the ultra-high cycle region. The method is based on ...

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10.6K Views.  University of Žilina. A protocol for ultrasonic fatigue testing in the high and ultra-high cycle region in axial tension-compression loading mode.

Video: Ultrasonic Fatigue Testing in the Tension-Compression Mode

Development of Whispering Gallery Mode Polymeric Micro-optical Electric Field Sensors

Optical modes of dielectric micro-cavities have received significant attention in recent years for their potential in a broad range of applications. The optical modes are frequently referred to as "whispering gallery modes" (WGM) or "morphology dependent resonances" (MDR) and exhibit high optical quality factors. Some proposed applications of micro-cavity optical resonators are in spectroscopy1, micro-cavity laser technology2, optical communications3-6 as well as sensor technology. The WGM-based sensor applications include those in biology7, trace gas detection8, and impurity detection in liquids9. Mechanical sensors based on microsphere resonators have also been proposed, including those for force10,11, pressure12, acceleration13 and wall shear stress14. In the present, we demonstrate a WGM-based electric field sensor, which builds on our previous studies15,16. A candidate application of this sensor is in the detection of neuronal action potential.
The electric field sensor is based on polymeric multi-layered dielectric microspheres. The external electric field induces surface and body forces on the spheres (electrostriction effect) leading to elastic deformation. This change in the morphology of the spheres, leads to shifts in the WGM. The electric field-induced WGM shifts are interrogated by exciting the optical modes of the spheres by laser light. Light from a distributed feedback (DFB) laser (nominal wavelength of ~ 1.3 &mu;m) is side-coupled into the microspheres using a tapered section of a single mode optical fiber. The base material of the spheres is polydimethylsiloxane (PDMS). Three microsphere geometries are used: (1) PDMS sphere with a 60:1 volumetric ratio of base-to-curing agent mixture, (2) multi layer sphere with 60:1 PDMS core, in order to increase the dielectric constant of the sphere, a middle layer of 60:1 PDMS that is mixed with varying amounts (2% to 10% by volume) of barium titanate and an outer layer of 60:1 PDMS and (3) solid silica sphere coated with a thin layer of uncured PDMS base. In each type of sensor, laser light from the tapered fiber is coupled into the outermost layer that provides high optical quality factor WGM (Q ~ 106). The microspheres are poled for several hours at electric fields of ~ 1 MV/m to increase their sensitivity to electric field.

A high-sensitivity photonic micro sensor was developed for electric field detection. The sensor exploits the optical modes of a dielectric sphere. Changes in the external electric field perturb the sphere morphology leading to shifts in its optical modes. The electric field strength is measured by monitoring these optical shifts.

Optical modes of dielectric micro-cavities have received significant attention in recent years for their potential in a broad range of applications. The ...

Microwave Photonics Systems Based on Whispering-gallery-mode Resonators

Microwave photonics systems rely fundamentally on the interaction between microwave and optical signals. These systems are extremely promising for various areas of technology and applied science, such as aerospace and communication engineering, sensing, metrology, nonlinear photonics, and quantum optics. In this article, we present the principal techniques used in our lab to build microwave photonics systems based on ultra-high Q whispering gallery mode resonators. First detailed in this article is the protocol for resonator polishing, which is based on a grind-and-polish technique close to the ones used to polish optical components such as lenses or telescope mirrors. Then, a white light interferometric profilometer measures surface roughness, which is a key parameter to characterize the quality of the polishing. In order to launch light in the resonator, a tapered silica fiber with diameter in the micrometer range is used. To reach such small diameters, we adopt the "flame-brushing" technique, using simultaneously computer-controlled motors to pull the fiber apart, and a blowtorch to heat the fiber area to be tapered. The resonator and the tapered fiber are later approached to one another to visualize the resonance signal of the whispering gallery modes using a wavelength-scanning laser. By increasing the optical power in the resonator, nonlinear phenomena are triggered until the formation of a Kerr optical frequency comb is observed with a spectrum made of equidistant spectral lines. These Kerr comb spectra have exceptional characteristics that are suitable for several applications in science and technology. We consider the application related to ultra-stable microwave frequency synthesis and demonstrate the generation of a Kerr comb with GHz intermodal frequency.

The customized techniques developed in our lab to build microwave photonics systems based on ultra-high Q whispering gallery mode resonators are presented. The protocols to obtain and characterize these resonators are detailed, and an explanation of some of their applications in microwave photonics is given.

Microwave photonics systems rely fundamentally on the interaction between microwave and optical signals. These systems are extremely promising for various ...

Fabrication of VB2/Air Cells for Electrochemical Testing

A technique to investigate the properties and performance of new multi-electron metal/air battery systems is proposed and presented. A method for synthesizing nanoscopic VB2 is presented as well as step-by-step procedure for applying a zirconium oxide coating to the VB2 particles for stabilization upon discharge. The process for disassembling existing zinc/air cells is shown, in addition construction of the new working electrode to replace the conventional zinc/air cell anode with a the nanoscopic VB2 anode. Finally, discharge of the completed VB2/air battery is reported. We show that using the zinc/air cell as a test bed is useful to provide a consistent configuration to study the performance of the high-energy high capacity nanoscopic VB2 anode.

Fabrication of VB2/Air Cells for Electrochemical Testing

A protocol is presented to study multi-electron metal/air battery systems by using previous technology developed for the zinc/air cell. Electrochemical testing is then performed on fabricated batteries to evaluate performance.

A technique to investigate the properties and performance of new multi-electron metal/air battery systems is proposed and presented. A method for ...

Experiments on Ultrasonic Lubrication Using a Piezoelectrically-assisted Tribometer and Optical Profilometer

Friction and wear are detrimental to engineered systems. Ultrasonic lubrication is achieved when the interface between two sliding surfaces is vibrated at a frequency above the acoustic range (20 kHz). As a solid-state technology, ultrasonic lubrication can be used where conventional lubricants are unfeasible or undesirable. Further, ultrasonic lubrication allows for electrical modulation of the effective friction coefficient between two sliding surfaces. This property enables adaptive systems that modify their frictional state and associated dynamic response as the operating conditions change. Surface wear can also be reduced through ultrasonic lubrication. We developed a protocol to investigate the dependence of friction force reduction and wear reduction on the linear sliding velocity between ultrasonically lubricated surfaces. A pin-on-disc tribometer was built which differs from commercial units in that a piezoelectric stack is used to vibrate the pin at 22 kHz normal to the rotating disc surface. Friction and wear metrics including effective friction force, volume loss, and surface roughness are measured without and with ultrasonic vibrations at a constant pressure of 1 to 4 MPa and three different sliding velocities: 20.3, 40.6, and 87 mm/sec. An optical profilometer is utilized to characterize the wear surfaces. The effective friction force is reduced by 62% at 20.3 mm/sec. Consistently with existing theories for ultrasonic lubrication, the percent reduction in friction force diminishes with increasing speed, down to 29% friction force reduction at 87 mm/sec. Wear reduction remains essentially constant (49%) at the three speeds considered.

We present a protocol for using a piezoelectrically-assisted tribometer and optical profilometer to investigate the dependence of ultrasonic wear and friction reduction on linear velocity, contact pressure, and surface properties.

Friction and wear are detrimental to engineered systems. Ultrasonic lubrication is achieved when the interface between two sliding surfaces is vibrated at ...

Ultrasonic Welding of Thermoplastic Composite Coupons for Mechanical Characterization of Welded Joints through Single Lap Shear Testing

This paper presents a novel straightforward method for ultrasonic welding of thermoplastic-composite coupons in optimum processing conditions. The ultrasonic welding process described in this paper is based on three main pillars. Firstly, flat energy directors are used for preferential heat generation at the joining interface during the welding process. A flat energy director is a neat thermoplastic resin film that is placed between the parts to be joined prior to the welding process and heats up preferentially owing to its lower compressive stiffness relative to the composite substrates. Consequently, flat energy directors provide a simple solution that does not require molding of resin protrusions on the surfaces of the composite substrates, as opposed to ultrasonic welding of unreinforced plastics. Secondly, the process data provided by the ultrasonic welder is used to rapidly define the optimum welding parameters for any thermoplastic composite material combination. Thirdly, displacement control is used in the welding process to ensure consistent quality of the welded joints. According to this method, thermoplastic-composite flat coupons are individually welded in a single lap configuration. Mechanical testing of the welded coupons allows determining the apparent lap shear strength of the joints, which is one of the properties most commonly used to quantify the strength of thermoplastic composite welded joints.

A straightforward procedure for ultrasonic welding of thermoplastic composite coupons for basic mechanical testing is described. Key characteristics of this ultrasonic welding process are the use of flat energy directors for simplified process preparation and the use of process data for the fast definition of optimum processing conditions.

This paper presents a novel straightforward method for ultrasonic welding of thermoplastic-composite coupons in optimum processing conditions. The ...

Automation of Mode Locking in a Nonlinear Polarization Rotation Fiber Laser through Output Polarization Measurements

When a laser is mode-locked, it emits a train of ultra-short pulses at a repetition rate determined by the laser cavity length. This article outlines a new and inexpensive procedure to force mode locking in a pre-adjusted nonlinear polarization rotation fiber laser. This procedure is based on the detection of a sudden change in the output polarization state when mode locking occurs. This change is used to command the alignment of the intra-cavity polarization controller in order to find mode-locking conditions. More specifically, the value of the first Stokes parameter varies when the angle of the polarization controller is swept and, moreover, it undergoes an abrupt variation when the laser enters the mode-locked state. Monitoring this abrupt variation provides a practical easy-to-detect signal that can be used to command the alignment of the polarization controller and drive the laser towards mode locking. This monitoring is achieved by feeding a small portion of the signal to a polarization analyzer measuring the first Stokes parameter. A sudden change in the read out of this parameter from the analyzer will occur when the laser enters the mode-locked state. At this moment, the required angle of the polarization controller is kept fixed. The alignment is completed. This procedure provides an alternate way to existing automating procedures that use equipment such as an optical spectrum analyzer, an RF spectrum analyzer, a photodiode connected to an electronic pulse-counter or a nonlinear detecting scheme based on two-photon absorption or second harmonic generation. It is suitable for lasers mode locked by nonlinear polarization rotation. It is relatively easy to implement, it requires inexpensive means, especially at a wavelength of 1550 nm, and it lowers the production and operation costs incurred in comparison to the above-mentioned techniques.

A protocol to detect and automate mode locking in a pre-adjusted nonlinear polarization rotation fiber laser is presented. The detection of a sudden change in the output polarization state when mode locking occurs is used to command the alignment of an intra-cavity polarization controller in order to find mode-locking conditions.

When a laser is mode-locked, it emits a train of ultra-short pulses at a repetition rate determined by the laser cavity length. This article outlines a ...

Characterization of Anisotropic Leaky Mode Modulators for Holovideo

Holovideo displays are based on light-bending spatial light modulators. One such spatial light modulator is the anisotropic leaky mode modulator. This modulator is particularly well suited for holographic video experimentation as it is relatively simple and inexpensive to fabricate1-3. Some additional advantages of leaky mode devices include: large aggregate bandwidth, polarization separation of signal light from noise, large angular deflection and frequency control of color1. In order to realize these advantages, it is necessary to be able to adequately characterize these devices as their operation is strongly dependent on waveguide and transducer parameters4. To characterize the modulators, the authors use a commercial prism coupler as well as a custom characterization apparatus to identify guided modes, calculate waveguide thickness and finally to map the device's frequency input and angular output of leaky mode modulators. This work gives a detailed description of the measurement and characterization of leaky mode modulators suitable for full-color holographic video.

This work describes fabrication and characterization of anisotropic leaky mode modulators for holographic video.

Holovideo displays are based on light-bending spatial light modulators.  One such spatial light modulator is the anisotropic leaky mode modulator.  This ...

Stimulated Stokes and Antistokes Raman Scattering in Microspherical Whispering Gallery Mode Resonators

Dielectric microspheres can confine light and sound for a length of time through high quality factor whispering gallery modes (WGM). Glass microspheres can be thought as a store of energy with a huge variety of applications: compact laser sources, highly sensitive biochemical sensors and nonlinear phenomena. A protocol for the fabrication of both the microspheres and coupling system is given. The couplers described here are tapered fibers. Efficient generation of nonlinear phenomena related to third order optical non-linear susceptibility &#935;(3) interactions in triply resonant silica microspheres is presented in this paper. The interactions here reported are: Stimulated Raman Scattering (SRS), and four wave mixing processes comprising Stimulated Anti-stokes Raman Scattering (SARS). A proof of the cavity-enhanced phenomenon is given by the lack of correlation among the pump, signal and idler: a resonant mode has to exist in order to obtain the pair of signal and idler. In the case of hyperparametric oscillations (four wave mixing and stimulated anti-stokes Raman scattering), the modes must fulfill the energy and momentum conservation and, last but not least, have a good spatial overlap.

Efficient generation of nonlinear phenomena related to third order optical non-linear susceptibility &#935;(3) interactions in triply resonant silica microspheres is presented in this paper. The interactions here reported are: Stimulated Raman Scattering (SRS), and four wave mixing processes comprising Stimulated Anti-stokes Raman Scattering (SARS).

Dielectric microspheres can confine light and sound for a length of time through high quality factor whispering gallery modes (WGM). Glass microspheres ...

Subsurface Defect Localization by Structured Heating Using Laser Projected Photothermal Thermography

The presented method is used to locate subsurface defects oriented perpendicularly to the surface. To achieve this, we create destructively interfering thermal wave fields that are disturbed by the defect. This effect is measured and used to locate the defect. We form the destructively interfering wave fields by using a modified projector. The original light engine of the projector is replaced with a fiber-coupled high-power diode laser. Its beam is shaped and aligned to the projector&#39;s spatial light modulator and optimized for optimal optical throughput and homogeneous projection by first characterizing the beam profile, and, second, correcting it mechanically and numerically. A high-performance infrared (IR) camera is set up according to the tight geometrical situation (including corrections of the geometrical image distortions) and the requirement to detect weak temperature oscillations at the sample surface. Data acquisition can be performed once a synchronization between the individual thermal wave field sources, the scanning stage, and the IR camera is established by using a dedicated experimental setup which needs to be tuned to the specific material being investigated. During data post-processing, the relevant information on the presence of a defect below the surface of the sample is extracted. It is retrieved from the oscillating part of the acquired thermal radiation coming from the so-called depletion line of the sample surface. The exact location of the defect is deduced from the analysis of the spatial-temporal shape of these oscillations in a final step. The method is reference-free and very sensitive to changes within the thermal wave field. So far, the method has been tested with steel samples but is applicable to different materials as well, in particular to temperature sensitive materials.

This method aims at locating vertical subsurface defects. Here, we couple a laser with a spatial light modulator and trigger its video input to heat a sample surface deterministically with two anti-phased modulated lines while acquiring highly resolved thermal images. The defect position is retrieved from evaluating thermal wave interference minima.

The presented method is used to locate subsurface defects oriented perpendicularly to the surface. To achieve this, we create destructively interfering ...

In Situ High Pressure Hydrogen Tribological Testing of Common Polymer Materials Used in the Hydrogen Delivery Infrastructure

High pressure hydrogen gas is known to adversely affect metallic components of compressors, valves, hoses, and actuators. However, relatively little is known about the effects of high pressure hydrogen on the polymer sealing and barrier materials also found within these components. More study is required in order to determine the compatibility of common polymer materials found in the components of the hydrogen fuel delivery infrastructure with high pressure hydrogen. As a result, it is important to consider the changes in physical properties such as friction and wear in situ while the polymer is exposed to high pressure hydrogen. In this protocol, we present a method for testing the friction and wear properties of ethylene propylene diene monomer (EPDM) elastomer samples in a 28 MPa high pressure hydrogen environment using a custom-built in situ pin-on-flat linear reciprocating tribometer. Representative results from this testing are presented which indicate that the coefficient of friction between the EPDM sample coupon and steel counter surface is increased in high pressure hydrogen as compared to the coefficient of friction similarly measured in ambient air.

In Situ High Pressure Hydrogen Tribological Testing of Common Polymer Materials Used in the Hydrogen Delivery Infrastructure

A test methodology for quantifying tribological properties of polymers used in hydrogen infrastructure service is demonstrated and characteristic results for a common elastomer are discussed.

High pressure hydrogen gas is known to adversely affect metallic components of compressors, valves, hoses, and actuators. However, relatively little is ...