Name: intermediate strain rate material characterization with digital image correlation
Uploaded: 2019-03-01T14:00:00
Description: Watch this Scientific Journal Video about Intermediate Strain Rate Material Characterization with Digital Image Correlation at JoVE.com

The authors acknowledge the great assistance from Dmitrii Klishch, Michel Delannoy, Tyler Musclow, Fraser Kirby, Joshua Ilse and Alex Naftel. Financial support by the National Research Council Canada (NRC) through the Security Materials Technology (SMT) Program is also appreciated.

1. Specimen preparation
<ol>
	<li>Prepare dog bone shaped tensile specimens according to ISO standard6 in advance. 
	NOTE: Similar specimens are also used4.</li>
	<li>Install strain gauges on the tab section (mandatory for load measurement) and on the gauge section (optional for strain measurement) of the tensile specimen.
	<ol>
		<li>Select the proper model of strain gauge based on the size, maximum extension, testing temperature, electrical resistance, etc.<sup cla...

<ol>
	<li>Xiao, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dynamic+tensile+testing+of+plastic+materials.">Dynamic tensile testing of plastic materials.</a> Polymer Testing. 27 (2), 164-178 (2008).</li><li>Nemat-Nasser, S., Isaacs, J. B., Starrett, J. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hopkinson+techniques+for+dynamic+recovery+experiments.">Hopkinson techniques for dynamic recovery experiments.</a> Proceedings of Royal Society of London A Mathematical Physical and Engineering Sciences. 435 (1894), 371-391 (1991).</li><li>Bruce, D., Matlock, D., Speer, J., De, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Assessment+of+the+strain-rate+dependent+tensile+properties+of+automotive+sheet+steels.">Assessment of the strain-rate dependent tensile properties of automotive sheet steels.</a> SAE World Congress. , (2004).</li><li>Rahmat, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dynamic+mechanical+characterization+of+aluminum:+analysis+of+strain-rate-dependent+behavior.">Dynamic mechanical characterization of aluminum: analysis of strain-rate-dependent behavior.</a> Mechanics Time-Dependent Materials. , (2018).</li><li>Gray, G., Blumenthal, W. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Split-Hopkinson pressure bar testing of soft materials. 8, 1093-1114 (2000).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> ISO 26203-2:2011; Metallic materials-Tensile testing at high strain rates-Part 2: Servo-hydraulic and other test systems. , 15 (2011).</li><li>Rahmat, M., Naftel, A., Ashrafi, B., Jakubinek, M. 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J., Simunovic, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+high-strain+rate+mechanical+behavior+of+AZ31+magnesium+alloy+using+3D+digital+image+correlation.">Characterization of high-strain rate mechanical behavior of AZ31 magnesium alloy using 3D digital image correlation.</a> Advanced Engineering Materials. 13 (10), 943-948 (2011).</li><li>Mansilla, R. A., Garc&#237;a, D., Negro, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dynamic+tensile+testing+for+determining+the+stress-strain+curve+at+different+strain+rate.">Dynamic tensile testing for determining the stress-strain curve at different strain rate.</a> 6th International Conference on Mechanical and Physical Behaviour of Materials Under Dynamic Loading. 10 (9), 695-700 (2000).</li><li>Zhu, D., Mobasher, B., Rajan, S. D., Peralta, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+Dynamic+Tensile+Testing+Using+Aluminum+Alloy+6061-T6+at+Intermediate+Strain+Rates.">Characterization of Dynamic Tensile Testing Using Aluminum Alloy 6061-T6 at Intermediate Strain Rates.</a> Journal of Engineering Mechanics. 137 (10), 669-679 (2011).</li><li>Schossig, M., Bieroegel, C., Grellmann, W., Bardenheier, R., Mecklenburg, T. <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+strain+rate+on+mechanical+properties+of+reinforced+polyolefins.">Effect of strain rate on mechanical properties of reinforced polyolefins.</a> 16th European Conference of Fracture. , 507-508 (2006).</li><li>Xia, Y., Zhu, J., Wang, K., Zhou, Q. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Design+and+verification+of+a+strain+gauge-based+load+sensor+for+medium-speed+dynamic+tests+with+a+hydraulic+test+machine.">Design and verification of a strain gauge-based load sensor for medium-speed dynamic tests with a hydraulic test machine.</a> International Journal of Impact Engineering. 88, 139-152 (2016).</li><li>Yang, X., Hector, L. G., Wang, 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+Combined+Theoretical/Experimental+Approach+for+Reducing+Ringing+Artifacts+in+Low+Dynamic+Testing+with+Servo-hydraulic+Load+Frames.">A Combined Theoretical/Experimental Approach for Reducing Ringing Artifacts in Low Dynamic Testing with Servo-hydraulic Load Frames.</a> Experimental Mechanics. 54 (5), 775-789 (2014).</li><li>Xia, Y., Zhu, J., Zhou, Q. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Verification+of+a+multiple-machine+program+for+material+testing+from+quasi-static+to+high+strain-rate.">Verification of a multiple-machine program for material testing from quasi-static to high strain-rate.</a> International Journal of Impact Engineering. 86, 284-294 (2015).</li><li>Yan, B., Kuriyama, Y., Uenishi, A., Cornette, D., Borsutzki, M., Wong, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Recommended+Practice+for+Dynamic+Testing+for+Sheet+Steels+-+Development+and+Round+Robin+Tests.">Recommended Practice for Dynamic Testing for Sheet Steels - Development and Round Robin Tests.</a> SAE International. , (2006).</li><li>Borsutzki, M., Cornette, D., Kuriyama, Y., Uenishi, A., Yan, B., Opbroek, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Recommendations+for+Dynamic+Tensile+Testing+of+Sheet+Steels.">Recommendations for Dynamic Tensile Testing of Sheet Steels.</a> International Iron and Steel Institute. , (2005).</li><li>Rusinek, A., Cheriguene, R., B&#228;umer, A., Klepaczko, J. R., Larour, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dynamic+behaviour+of+high-strength+sheet+steel+in+dynamic+tension:+Experimental+and+numerical+analyses.">Dynamic behaviour of high-strength sheet steel in dynamic tension: Experimental and numerical analyses.</a> The Journal of Strain Analysis for Engineering Design. 43 (1), 37-53 (2008).</li><li>Diot, S., Guines, D., Gavrus, A., Ragneau, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Two-step+procedure+for+identification+of+metal+behavior+from+dynamic+compression+tests.">Two-step procedure for identification of metal behavior from dynamic compression tests.</a> International Journal of Impact Engineering. 34 (7), 1163-1184 (2007).</li><li>LeBlanc, M. M., Lassila, D. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+hybrid+Technique+for+compression+testing+at+intermediate+strain+rates.">A hybrid Technique for compression testing at intermediate strain rates.</a> Experimental Techniques. 20 (5), 21-24 (1996).</li><li>Xiao, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+dynamic+tensile+testing.">Analysis of dynamic tensile testing.</a> 11th International Congress and Exhibition on Experimental and Applied Mechanics. , (2008).</li><li>Othman, R., Gu&#233;gan, P., Challita, G., Pasco, F., LeBreton, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+modified+servo-hydraulic+machine+for+testing+at+intermediate+strain+rates.">A modified servo-hydraulic machine for testing at intermediate strain rates.</a> International Journal of Impact Engineering. 36 (3), 460-467 (2009).</li><li>Kwon, J. B., Huh, H., Ahn, C. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+improved+technique+for+reducing+the+load+ringing+phenomenon+in+tensile+tests+at+high+strain+rates.">An improved technique for reducing the load ringing phenomenon in tensile tests at high strain rates.</a> Annual Conference and Exposition on Experimental and Applied Mechanics. Costa Mesa, United States. , (2016).</li><li>Pan, W., Schmidt, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Strain+rate+effect+in+material+testing+of+bulk+adhesive.">Strain rate effect in material testing of bulk adhesive.</a> 9th International Conference on Structures Under Shock and Impact. 87, 107-116 (2006).</li><li>Zhang, D. N., Shangguan, Q. Q., Xie, C. 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The raw data obtained from the experiment is influenced by the specimen geometry and strain gauges location on the specimen. The load data in low strain rate dynamic tests acquired by a piezo-electric load washer incorporated into the load frame at higher strain rates (Bruce et al.3 suggested &#62; 10/s, while for Wang et al.9 reported this limit to be 100/s) typically suffer from large amplitude oscillations due to dynamic waves associated with the loadin...

Most materials demonstrate some degree of strain rate dependency in their mechanical behavior1 and, therefore, mechanical testing conducted only at quasistatic strain rates is not suitable to determine the material properties for dynamic applications. The strain rate dependency of materials is typically investigated using five types of mechanical testing systems: conventional screw drive load frames, servo-hydraulic systems, high-rate servo-hydraulic systems, impact testers, and Hopkinson bar systems1. Split Hopkinson bars have been a common facility for the dynamic characterization of materials for the past 50 years2. There have also been efforts to modify Hopkinson bars to test at intermediate and lower strain rates. However, these facilities are typically more suitable for the high strain rate characterizations of the material (i.e., usually greater than 200/s). There is a gap in the literature on the strain rate characterization of material properties at intermediate strain rates in the range of 10&#8722;200/s (i.e., between quasistatic and high strain rate results obtained from split Hopkinson bars3), which is due to the limited access to facilities and a lack of reliable procedures of intermediate strain rate material testing.
A high-speed servo-hydraulic load frame applies load to the specimen at a constant and predefined velocity. These load frames benefit from a slack adaptor, which, in tensile tests, allows the crosshead to reach the desired velocity before the loading starts. The slack adaptor allows the head to travel a certain distance (e.g., 0.1 m) to reach the target velocity and then starts applying the load to the specimen. High-speed servo-hydraulic load frames typically perform tests under displacement control mode and maintain a constant actuator velocity to produce constant engineering strain rates3.
Techniques for measuring specimen elongation are generally classified as either contact or noncontact techniques4. Contact techniques include the use of instruments such as clip-on extensometers, while laser extensometers are employed for noncontact measurements. Since contact extensometers are prone to inertia influences, they are not suitable for dynamic tests; noncontact extensometers do not suffer from this problem.
Digital image correlation (DIC) is an optical, non-contact, full-field strain measurement technique, which is an alternative approach to strain gauging to measure strain/load and overcome some of the challenges (e.g., the ringing phenomenon) associated with dynamic material characterization5. Resistance strain gauges can suffer from limitations such as a limited area of measurement, a limited range of elongation, and limited mounting methods, whereas DIC is always capable of providing a full-field strain measurement from the specimen surface during the experiment.
The presented procedure describes the use of a high-speed servo-hydraulic load frame along with DIC and can be used as a complementary document to the recently developed standard guidelines6 to clarify the details of the experimental procedure. The section on the servo-hydraulic load frame can be followed for a variety of test setups (e.g., tensile, compressive, and shear) and even with common quasistatic load frames as well, and, therefore, covers a vast range of facilities. Furthermore, the DIC section may be applied separately to any type of mechanical or thermal tests, with minor modifications.

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			<td height="21" style="height:21px;width:280px;">Camera Lens</td>
			<td style="width:183px;">Opto Engineering</td>
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			<td style="width:167px;">Telecentric lens 23-64</td>
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			<td height="21" style="height:21px;width:280px;">High Speed Camera&#160;</td>
			<td style="width:183px;">SAX Photron Fastcam&#160;</td>
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			<td height="21" style="height:21px;width:280px;">High Speed DAQ&#160;</td>
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			<td height="21" style="height:21px;width:280px;">High Speed Servo-Hydraulic Load Frame</td>
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			<td height="21" style="height:21px;width:280px;">Jab Bullet Light with diffuser&#160;</td>
			<td style="width:183px;">AADyn JAB BULLET&#160;</td>
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			<td style="width:167px;">&#160;15&#176; diffusers&#160;</td>
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			<td height="21" style="height:21px;width:280px;">Strain gauge</td>
			<td style="width:183px;">Micro-Measurements</td>
			<td style="width:175px;">Model EA-13-062AQ-350</td>
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intermediate strain rate material characterization with digital image correlation

The mechanical response of a material under dynamic load is typically different than its behavior under static conditions; therefore, the common quasistatic equipment and procedures used for material characterization are not applicable for materials under dynamic loads. The dynamic response of a material depends on its deformation rate and is broadly categorized into high (i.e., greater than 200/s), intermediate (i.e., 10&#8722;200/s) and low strain rate regimes (i.e., below 10/s). Each of these regimes calls for specific facilities and testing protocols to ensure the reliability of the acquired data. Due to the limited access to high-speed servo-hydraulic facilities and validated testing protocols, there is a noticeable gap in the results at the intermediate strain rate. The current manuscript presents a validated protocol for the characterization of different materials at these intermediate strain rates. Strain gauge instrumentation and digital image correlation protocols are also included as complimentary modules to extract the utmost level of detailed data from every single test. Examples of raw data, obtained from a variety of materials and test setups (e.g., tensile and shear) is presented and the analysis procedure used to process the output data is described. Finally, the challenges of dynamic characterization using the current protocol, along with the limitations of the facility and methods of overcoming potential problems are discussed.

The duration of a dynamic test is typically comparable to the time required for the stress waves to travel a round trip over the length of the load train (i.e. grips, specimen, and loading) system1. A dynamic test is valid if the number and amplitude of stress waves during a dynamic test is controlled so that a dynamic equilibrium is achieved, and the specimen experiences a homogeneous deformation at an almost constant strain rate. The Society of Automotive Enginee...

Watch this Scientific Journal Video about Intermediate Strain Rate Material Characterization with Digital Image Correlation at JoVE.com

Intermediate Strain Rate Material Characterization with Digital Image Correlation

Here we present a methodology for the dynamic characterization of tensile specimens at intermediate strain rates using a high-speed servo-hydraulic load frame. Procedures for strain gauge instrumentation and analysis, as well as for digital image correlation strain measurements on the specimens, are also defined.

The mechanical response of a material under dynamic load is typically different than its behavior under static conditions; therefore, the common ...

The mechanical performance of materials depends on the rate of load application. Our protocol can be used to capture material behavior at intermediate strain rates. The main advantage of this technique is that the materials can be characterized while using a non-contact, full field strain measurement technique to capture surface strains with high-speed cameras.The intermediate strain rate characterization of materials often requires dealing with undesirable oscillation called ringing in the results, which should be avoided through proper specimen design, and test protocol. Before beginning the procedure, prepare dog bone-shaped tensile specimens, according to International Organization for Standardization parameters. Next, paint the surface of the specimen to exhibit high contrast features.Matching the contrast pattern to the camera image sensor size such as each dark contrast feature is composed of approximately three pixels or more, then, set the specimen aside, to let the paint dry. When the specimen is ready, turn on the power to the control console, and confirm that the isolation valve, from the pump to the high rate frame is open, before turning on the computer. From the desktop, start the controller application, selecting the high rate calculate displacement cfg configuration, and clicking reset, to clear interlock one.Start the hydraulic pump, and open the service manifolds to one at a time, waiting until the low indicator stops flashing, before pressing the high indicator for each manifold. Start the test design software, and confirm that the hydraulic pump, and high service manifold one, are on. Then click, file, new, test from template and custom templates, and select tension test.For strain gauge set up, set the switch of the load frame crosshead control, to the low rate, and match the wires of the specimen strain gauge, to the wires of the strain gauge box inside the test chamber according to the wire colors. Then, in the controller application, under auxiliary inputs, and strain one, select the maximum range of the strains. Next, activate the manual control, and enter the position of the head to the full extension at minus 125 millimeters.Turn off the enable manual command checkbox, and uncheck the exclusive control box. An elastic cord may be used to hold the slack adapter in a retracted position to make room for installing the coupon. Use the mounting fixture to align the coupon inside the grips.Press the key icon to active the handset and confirm that the exclusive control box in the software is unchecked. Make sure the top grip is loose to prevent an undesirable load application to the specimen, and remove the elastic cord. Press the wheel icon to activate the controller, and slowly roll the wheel to bring the head down until the bottom arm of the slack adapter is almost fully retracted.Press the key icon again, to deactivate the handset and check the exclusive control box using the manual control to bring the head to exactly minus 125 millimeters. Use a wrench and a key to rotate the slack adapter to tighten the top grips without twisting the coupon, and check the spiral washers between the slack adapter and the intermediate cross head to make sure that the washers are tight, and that there is no axial clearance along the load train. Then, return the frame to the high rate and make sure that the enclosure doors are tightly closed.To set the instrument up for digital image correlation, open the high speed imaging viewer software and click detect before saving the set up. Click camera option and select the input-output tab to set the external signals. To set the frame rate and frame resolution, click variable and set the camera frequency and the data acquisition box acquisition rate to the same number as the high speed data acquisition system in the load frame.Then, open the high speed data acquisition in the high speed imaging viewer, and select the required channels and samples per frame. To run the test, open the tension test and select new test run to enter a valid file name. Modify the fields as necessary and click okay.For the ramp rate, select the nominal desired head velocity and click okay. A series of prompts will appear reminding that the key hardware should be checked after which the test can be initiated by clicking on the run icon. On the control console, press and hold the arm charge accumulator switch to arm the system.Then, press fire to complete the test. The speed of the test should be calculated based on real life scenarios for example for a car crash simulation speed of around eight meters per second can be applied. For data analysis, export the raw data from the load frame computer into the post-processing software of choice and determine the location on the gauge section where the specimen failed.Restrict the strain field to a local area of the vicinity of the failure section and measure and record the strain in the local area. Then, draw a stress strain curve obtained from the measurements. Both of these test were performed properly but the load data directly extracted from the load frame force link could not be used in this test in an alternative load measurement technique such as tab section strain gauging, was necessary.In this test however, the raw load data from the load frame was in good agreement with the strain gauge loads. A typical example of digital image correlation results for a dog bone aluminum specimen with a strain field evolution with time on the entire gauge section is shown. The uniform strain within a given cross section of the specimen illustrates a proper loading and data analysis during the test.And the loss of digital image correlation in the last image was due to severe necking that resulting in paint flaking and was unavoidable immediately before the failure at the vicinity of the failure zone. These stress strain curves obtained from digital image correlation and from the load frame cross head displacement data, illustrate and average stress strain for the entire gauge section and demonstrate the validity of the technique and a good agreement between the results. A comprehensive evaluation of the results ensures that the protocol is carried out within the boundaries of valid assumptions.Such as the inertia dominant regime or non-slip conditions and grips. Following this procedure a range of different mechanical characterization tests such as sheer, bending, puncture, or compression tests can be performed on a variety of materials. This technique fills the gap, between quasi static tests and ultra high strain rate characterization techniques.Enabling us to fully characterize material behaviors as a function of strain rate.

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