The authors would like to acknowledge the support of the DFG priority program 1599 &#34;Caloric effects in ferroic materials: New concepts for cooling&#34;&#160;(Projects: EG101/23-1, SCHU2217/2-1, SE704/2-1, EG101/29-2, SCH2217/3-2, SE704/2-2).&#160;

1. Sample Preparation

<ol>
	<li>Measure the SMA ribbon with calipers and determine the&#160;cross section of the sample.</li>
	<li>Prepare the sample for IR measurements by coating the ribbon with a thin layer of high emissivity (&#949;=0.96) paint. 
	Caution: The paint is classified as an irritant. Gloves, safety glasses and mouth protection must be worn during the processing of the paint.</li>
</ol>
2. Material Stabilization (Training)
Note: Initial mecha...

<ol>
	<li>F&#228;hler, S., R&#246;&#223;ler, U. K., 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=Caloric+effects+in+ferroic+materials:+New+concepts+for+cooling.">Caloric effects in ferroic materials: New concepts for cooling.</a> Adv. Eng. Mater. 14 (1-2), 10-19 (2012).</li><li>Moya, X., Defay, E., Heine, V., Mathur, N. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Too+cool+to+work.">Too cool to work.</a> Nat. Phys. 11 (3), 202-205 (2015).</li><li>Starkov, I. A., Starkov, A. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On+the+thermodynamic+foundations+of+solid-state+cooler+based+on+multiferroic+materials.">On the thermodynamic foundations of solid-state cooler based on multiferroic materials.</a> Int. J. Refrig. 37, 249-256 (2014).</li><li>Moya, X., Kar-Narayan, S., Mathur, N. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Caloric+materials+near+ferroic+phase+transitions.">Caloric materials near ferroic phase transitions.</a> Nat. Mater. 13 (5), 439-450 (2014).</li><li>Shaw, J. A., Kyriakides, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On+the+nucleation+and+propagation+of+phase+transformation+fronts+in+a+NiTi+alloy.">On the nucleation and propagation of phase transformation fronts in a NiTi alloy.</a> Acta Mater. 45 (2), 683-700 (1997).</li><li>Chang, B. -. C., Ja Shaw, ., Iadicola, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thermodynamics+of+Shape+Memory+Alloy+Wire:+Modeling+Experiments,+and+Application.">Thermodynamics of Shape Memory Alloy Wire: Modeling Experiments, and Application.</a> Contin. Mech. Thermodyn. 18 (1-2), 83-118 (2006).</li><li>Cui, J., Wu, Y. M., 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=Demonstration+of+high+efficiency+elastocaloric+cooling+with+large+Delta+T+using+NiTi+wires.">Demonstration of high efficiency elastocaloric cooling with large Delta T using NiTi wires.</a> Appl. Phys. Lett. 101 (7), 073904 (2012).</li><li>Ossmer, H., Lambrecht, F., G&#252;ltig, M., Chluba, C., Quandt, E., Kohl, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evolution+of+temperature+profiles+in+TiNi+films+for+elastocaloric+cooling.">Evolution of temperature profiles in TiNi films for elastocaloric cooling.</a> Acta Mater. 81, 9-20 (2014).</li><li>Ossmer, H., Chluba, C., Krevet, B., Quandt, E., Rohde, M., Kohl, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Elastocaloric+cooling+using+shape+memory+alloy+films.">Elastocaloric cooling using shape memory alloy films.</a> J. Phys. Conf. 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Mater. 30 (2), 141-150 (1998).</li><li>Miyazaki, S., Mizukoshi, K., Ueki, T., Sakuma, T., Liu, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fatigue+life+of+Ti-50+at.%+Ni+and+Ti-40Ni-10Cu+(at.%)+shape+memory+alloy.">Fatigue life of Ti-50 at.% Ni and Ti-40Ni-10Cu (at.%) shape memory alloy.</a> Mater. Sci. Eng. A. 273-275, 658-663 (1999).</li><li>Olbricht, J., Yawny, A., Cond&#242;, A. M., Lovey, F. C., Eggeler, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+influence+of+temperature+on+the+evolution+of+functional+properties+during+pseudoelastic+cycling+of+ultra+fine+grained+NiTi.">The influence of temperature on the evolution of functional properties during pseudoelastic cycling of ultra fine grained NiTi.</a> Mater. Sci. Eng. A. 481-482, 142-145 (2008).</li><li>Tu&#353;ek, J., Engelbrecht, K., Mikkelsen, L. P., Pryds, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Elastocaloric+effect+of+Ni-Ti+wire+for+application+in+a+cooling+device.">Elastocaloric effect of Ni-Ti wire for application in a cooling device.</a> J. Appl. Phys. 117 (12), 124901 (2015).</li><li>Zarnetta, R., Takahashi, R., 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=Identification+of+Quaternary+Shape+Memory+Alloys+with+Near-Zero+Thermal+Hysteresis+and+Unprecedented+Functional+Stability.">Identification of Quaternary Shape Memory Alloys with Near-Zero Thermal Hysteresis and Unprecedented Functional Stability.</a> Adv. Funct. Mater. 20 (12), 1917-1923 (2010).</li><li>Schmidt, M., Ullrich, J., 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=Thermal+Stabilization+of+NiTiCuV+Shape+Memory+Alloys:+Observations+During+Elastocaloric+Training.">Thermal Stabilization of NiTiCuV Shape Memory Alloys: Observations During Elastocaloric Training.</a> Shape Mem. Superelasticity. , (2015).</li><li>H&#246;hne, G., Hemminger, W., Flammersheim, H. -. 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> Differential Scanning Calorimetry. , (2003).</li><li>Heintze, O., Seelecke, 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+coupled+thermomechanical+model+for+shape+memory+alloys-From+single+crystal+to+polycrystal.">A coupled thermomechanical model for shape memory alloys-From single crystal to polycrystal.</a> Mater. Sci. Eng. A. 481-482, 389-394 (2008).</li><li>Furst, S. J., Crews, J. H., Seelecke, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Numerical+and+experimental+analysis+of+inhomogeneities+in+SMA+wires+induced+by+thermal+boundary+conditions.">Numerical and experimental analysis of inhomogeneities in SMA wires induced by thermal boundary conditions.</a> Contin. Mech. Thermodyn. 24 (4-6), 485-504 (2012).</li><li>Shaw, J., Kyriakides, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thermomechanical+aspects+of+NiTi.">Thermomechanical aspects of NiTi.</a> J. Mech. Phys. Solids. 43 (8), 1243-1281 (1995).</li><li>Schmidt, M., Sch&#252;tze, A., Seelecke, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cooling+Efficiencies+of+a+NiTi-Based+Cooling+Process.">Cooling Efficiencies of a NiTi-Based Cooling Process.</a> , (2013).</li><li>Achenbach, M., M&#252;ller, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+MODEL+FOR+SHAPE+MEMORY.">A MODEL FOR SHAPE MEMORY.</a> . Le J. Phys. Colloq. 43 (C4), 163-167 (1982).</li><li>M&#252;ller, I., Seelecke, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thermodynamic+aspects+of+shape+memory+alloys.">Thermodynamic aspects of shape memory alloys.</a> Math. Comput. Model. 34 (12-13), 1307-1355 (2001).</li><li>Ullrich, J., Schmidt, M., 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=Experimental+Investigation+and+Numerical+Simulation+of+the+Mechanical+and+Thermal+Behavior+of+a+Superelastic+Shape+Memory+Alloy+Beam+During+Bending.">Experimental Investigation and Numerical Simulation of the Mechanical and Thermal Behavior of a Superelastic Shape Memory Alloy Beam During Bending.</a> , (2014).</li><li>Bechtold, C., Chluba, C., Lima de Miranda, R., Quandt, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+cyclic+stability+of+the+elastocaloric+effect+in+sputtered+TiNiCu+shape+memory+films.">High cyclic stability of the elastocaloric effect in sputtered TiNiCu shape memory films.</a> Appl. Phys. Lett. 101 (9), 091903 (2012).</li></ol>

The authors have nothing to disclose.

The presented scientific test rig enables comprehensive investigation of elastocaloric materials and cooling processes by performing the experiments described in the protocol section. Precise alignment of the sample before clamping is crucial for all the experiments. Bad alignment can potentially lead to early material failure. Furthermore, the maximum applied strain has significant influence on the material lifetime, whereas the required strain to reach a complete phase transformation depends on the alloy composition. T...

Solid state cooling processes based on ferroic materials have potential to be environmentally friendly alternatives to the conventional vapor compression based process. Ferroic materials may exhibit magnetocaloric, electrocaloric and elastocaloric effects 1,2, as well as combinations of these effects, which are described as multicaloric material behavior 3. The different caloric effects in ferroic materials are currently being investigated as part of the German Science Foundation (DFG) Priority program SPP 1599 &#34;Caloric Effects in Ferroic Materials: New Concepts for Cooling&#34; 4. Shape Memory Alloys (SMA) which are investigated within this program show large elastocaloric effects, in particular Ni-Ti based alloys due to their large latent heats 5. The strain-induced phase transformation at high strain rates leads to significant temperature changes of the SMA, as shown in Figure 1. The adiabatic, exothermic phase transformation from austenite to martensite increases the SMA temperature. The endothermic transformation from martensite to austenite leads to a significant temperature decrease. These elastocaloric material properties can be used for solid-state cooling processes by applying a suitable mechanical loading and unloading cycle. Figure 2 shows a typical elastocaloric cooling cycle, following the Brayton cycle. The heat transfer between the heat source and the cold, unloaded SMA take place at low temperature levels. In the next phase, the SMA is in a contact-free state and the fast, adiabatic loading leads to a significant temperature increase of the SMA. The subsequent heat transfer between the hot SMA and the heat sink take place at constant strain of the SMA. Upon completion of the heat transfer, fast, adiabatic unloading leads to a significant temperature drop of the SMA below the temperature of the heat source, whereupon the next cooling cycle and the heat transfer with the heat source can start. The efficiency of the elastocaloric cooling process depends on the required mechanical work and the absorbed heat.
First, experiments monitoring the temperature field during tensile tests were performed by Shaw et al. 6,7, with the objective to investigate the formation of local temperature peaks during tensile tests of SMA strips and wires at different rates. The applied experimental method combined the measurement of the mechanical parameters (stress, strain and strain rate) with simultaneous acquisition of temperature fields by means of thermographic measurements. During loading and unloading of a SMA specimen with a tensile testing machine, an infrared (IR) camera was used to acquire IR images of the SMA sample. This technique enables the investigation of the strain rate dependent formation of temperature peaks. The measurement of the temperature distribution on the sample is very important for the investigation of the elastocaloric effects and the determination of the cooling properties of the material. A local temperature measurement &#8212; by applying a contacting temperature measurement &#8212; is not sufficient in order to characterize the cooling properties of the material. A measurement of the temperature field was also used by Cui et al. 8 for the study of elastocaloric effects in Ni-Ti wires. Furthermore, Ossmer et al. 9,10 showed that thermographic temperature measurements are also suitable for the investigation of elastocaloric effects in Ni-Ti based thin films, which required high frame rates of the IR camera for the investigation of adiabatic phase transformations at high strain rates. This technique allows for the investigation of elastocaloric quantities and the homogeneity of the temperature profile, which has a significant influence on the solid-state based heat transfer and the efficiency of elastocaloric processes.
The cooling efficiency of the material can be determined by calculating the required work based on the stress/strain measurements as well as the heat (which can be determined taking into account the temperature change and the heat capacity of the material). However, the experimental method does not enable the investigation of the elastocaloric material under process condition. This includes a heat transfer between the SMA and a heat source, which has a significant influence on the efficiency of the cooling effect.
The material characterization of cooling process conditions and the investigation of elastocaloric cooling processes require a test rig enabling solid-state based heat transfer, which cannot be investigated by any existing commercial system. To this end, a novel testing platform has been developed. The test rig is set up in two levels as shown in Figure 3. The upper level allows for basic elastocaloric material characterization and initial training procedures, similar to the previously described method (see Figure 4). The setup is equipped with a linear direct drive capable of loading and unloading the SMA at strain rates up to 1 sec-1 (see Figure 5). The linear direct drive enables the investigation of samples with a cross section of up to 1.8 mm2, while the typical sample length is 90 mm. The advantage of a linear direct drive is the high velocity and the high acceleration &#8212; in contrast to ball screw drives which are typically used for tensile tests. Furthermore, a load cell, as well as the integrated position measurement system of the linear drive, provides mechanical measurement data. A high-resolution IR camera (1,280 x 1,024 pixels) is used to measure the temperature profile of the SMA with up to 400 Hz (in the required temperature range). The use of a microscope lens with a resolution of 15 &#181;m/pixel enables the investigation of local temperature effects. The lower level of the test rig contains a mechanism that allows for alternating conductive heat transfer between the SMA and the heat source/heat sink (see Figures 6 and 7). The linear direct drive in the lower level switches between the heat source to the SMA and from the SMA to the heat sink, whereas a pneumatic cylinder lifts and lowers the heat source/sink (see Figure 8). Each actuator can be controlled independently allowing for investigation of different cooling process variations. The comprehensive measurement system enables measurements of mechanical parameters: actuator position, actuator velocity, SMA loading force, contact force between SMA and heat source/sink during heat transfer as well as thermal parameters (i.e., temperatures inside the heat source/sink, temperature distribution on the surface of the SMA and the heat source/sink). A more detailed description of the scientific testing platform is given in Schmidt et al. 11.
<img alt="Figure 5" src="/files/ftp_upload/53626/53626fig5.jpg" /> 
Figure 5. Scheme of the upper level of the test rig. A linear direct drive for loading and unloading of the SMA sample with integrated position measurement system; a load cell for measuring of tensile forces, as well as a high-resolution IR camera (1,280 x 1,024 pixels) for temperature profile acquisitions.
<img alt="Figure 7" src="/files/ftp_upload/53626/53626fig7.jpg" /> 
Figure 7. Scheme of the lower level of the test rig. A linear direct drive for switching between heat sink and heat source; a pneumatic cylinder to make contact between the SMA sample and the heat source/sink; temperature sensors have been integrated in the heat sink/source to measure the core temperature of the blocks. A compression load cell for measuring the contact force between the SMA and the heat source/sink is integrated in the heat transfer mechanism and not visible in this scheme.
The test rig allows for the investigation of different alloy compositions and sample sizes as well as geometries (ribbons, wires). Furthermore, the setup enables comprehensive investigations of elastocaloric materials and cooling processes. The previously described experiments can be performed and the execution will be described step-by-step in the protocol section of this manuscript.
Material stabilization:
Stable material behavior is important for the use of elastocaloric materials in cooling systems. To this end, a mechanical stabilization procedure is applied. During this procedure the material passes mechanical loading and unloading cycles and performs a phase transformation from austenite to martensite. The material stabilization shows a strong rate dependency. High loading rates lead to a temperature change of the material, which is caused by the latent heat of the phase transformation. This temperature change has a similar influence on the material stabilization, as do mechanical training cycles at various temperatures 12-15. In addition to the well-known mechanical 13 and caloric 16 stabilization, a thermal material stabilization can be observed with the designed setup by applying thermography 17.
Material characterization:
After an initial mechanical training procedure, the material shows stable mechanical, thermal and caloric behavior allowing the elastocaloric material properties to be characterized. Therefore, mechanical cycling at different rates is performed whereas, in contrast to the training procedure, the elastocaloric characterization includes a holding phase after loading and unloading. For the duration of the holding phase the SMA strain is kept constant until an ambient temperature level is reached again. This type of experiment is required in order to determine the lowest achievable temperature after unloading, starting from ambient temperature levels, as well as the material efficiency. Rate dependent formation of local temperature peaks can be observed, with higher rates leading to an increasingly homogeneous temperature distribution. Furthermore, by increasing the strain rate the temperature change equally increases until adiabatic conditions are achieved. The material efficiency can be determined by calculating the required mechanical work, based on a force-displacement diagram of an adiabatic experiment, as well as the absorbable heat, based on the mean temperature change of the material during unloading and the heat capacity of the sample.
Elastocaloric cooling process:
The investigation of the cooling efficiency of SMAs under process conditions requires the heat transfer between the SMA cooling medium and a heat source, as well as a heat sink. For this purpose, the SMA is in contact with a solid-state heat source (following adiabatic unloading) and a heat sink (following adiabatic loading). The efficiency of the process strongly depends on the process control and the thermal boundary conditions. The comprehensive investigation of the cooling process requires a variation of the control parameters in order to determine the most efficient process control. The individual influence of the parameters (contact time, SMA strain, SMA strain rate, contact phase (contact during the loading/unloading phase or following) and contact force) on the process performance has to be investigated. Furthermore, the influence of the changing thermal boundary condition by increasing number of cooling cycles has to be taken into account.
Model validation:
The development of a thermomechanically coupled material model, capable of reproducing the mechanical and thermal material behavior during cooling cycle, is crucial for the development of a novel cooling technology. The model allows for material and process optimization by reduced experimental and material development effort. The validation requires an initial isothermal tensile test of a stabilized material to generate the required mechanical material input data (elastic modulus of the austenite and the martensite phase, the width of the mechanical hysteresis as well as the transformation strain). The validation of the model takes place on the basis of tensile tests at different rates. The required caloric input data for the model can be determined by differential scanning calorimetry (DSC) following the mechanical experiments. The DSC measurements have to be performed after the mechanical test in order to measure the caloric material properties of a stabilized sample.

<table border="0" cellpadding="0" cellspacing="0" width="1134">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:273px;">Linear direct drives</td>
			<td style="width:116px;">ESR-Pollmeier</td>
			<td style="width:179px;">ML 1418-U5-W1</td>
			<td style="width:567px;">SMA loading/unloading; heat transfer</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Pneumatic cylinder&#160;</td>
			<td>Festo</td>
			<td>ADNGF-40 574031</td>
			<td>Contact between heat source/sink and SMA</td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;">Inductive position measurement system&#160;</td>
			<td>AMO</td>
			<td>LMKA-1101.1NN-1.0-0</td>
			<td></td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;width:273px;">Tension and compression load cell</td>
			<td style="width:116px;">Futek</td>
			<td>LCF451; FSH02241</td>
			<td>SMA force</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:273px;">Compression load cell</td>
			<td style="width:116px;">Futek</td>
			<td>LTH300; FSH00297</td>
			<td>Contact force</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:273px;">IR camera</td>
			<td style="width:116px;">Infra Tec</td>
			<td>Image IR 9360; M91129</td>
			<td>1280x1024 pixels; Maximum frame rate 3200 Hz&#160;</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:273px;">Real-Time Controller&#160;</td>
			<td style="width:116px;">National Instruments</td>
			<td style="width:179px;">NI CompactRIO-9074</td>
			<td>Data acquisiton and control system</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:273px;">Camera varnish</td>
			<td style="width:116px;">Tetenal</td>
			<td align="right" style="width:179px;">105202</td>
			<td></td>
		</tr>
	</tbody>
</table>

experimental methods for investigation of shape memory based elastocaloric cooling processes and model validation

Shape Memory Alloys (SMA) using elastocaloric cooling processes have the potential to be an environmentally friendly alternative to the conventional vapor compression based cooling process. Nickel-Titanium (Ni-Ti) based alloy systems, especially, show large elastocaloric effects. Furthermore, exhibit large latent heats which is a necessary material property for the development of an efficient solid-state based cooling process. A scientific test rig has been designed to investigate these processes and the elastocaloric effects in SMAs. The realized test rig enables independent control of an SMA&#39;s mechanical loading and unloading cycles, as well as conductive heat transfer between SMA cooling elements and a heat source/sink. The test rig is equipped with a comprehensive monitoring system capable of synchronized measurements of mechanical and thermal parameters. In addition to determining the process-dependent mechanical work, the system also enables measurement of thermal caloric aspects of the elastocaloric cooling effect through use of a high-performance infrared camera. This combination is of particular interest, because it allows illustrations of localization and rate effects &#8212; both important for efficient heat transfer from the medium to be cooled.
The work presented describes an experimental method to identify elastocaloric material properties in different materials and sample geometries. Furthermore, the test rig is used to investigate different cooling process variations. The introduced analysis methods enable a differentiated consideration of material, process and related boundary condition influences on the process efficiency. The comparison of the experimental data with the simulation results (of a thermomechanically coupled finite element model) allows for better understanding of the underlying physics of the elastocaloric effect. In addition, the experimental results, as well as the findings based on the simulation results, are used to improve the material properties.

Material stabilization (Training):
Figure 9 shows a stress/strain diagram of 50 training cycles. The investigated sample is a Ni-Ti ribbon with a cross section of A = 1.45 mm2. The applied strain rate of 1 x 10-3 sec-1 leads to a mean temperature increase of &#916;T = 12.2 K. The temperature increase has a significant influence on the stabilization effect 12...

Watch this Scientific Journal Video about Experimental Methods for Investigation of Shape Memory Based Elastocaloric Cooling Processes and Model Validation at JoVE.com

Experimental Methods for Investigation of Shape Memory Based Elastocaloric Cooling Processes and Model Validation

Experimental methods for investigation of solid state cooling processes and characterization of elastocaloric material properties of Shape Memory Alloys (SMA) are presented. A custom-built test rig has been designed for controlling and comprehensive monitoring of elastocaloric cooling processes. Furthermore, it provides a validation platform for thermomechanically coupled modeling approaches.

Shape Memory Alloys (SMA) using elastocaloric cooling processes have the potential to be an environmentally friendly alternative to the conventional vapor ...

The overall goal of this experiment is to investigate elastocaloric materials and elastocaloric cooling processes. To this end, a scientific test rig has been developed to perform basic material characterizations and advanced elastocaloric process controls. Our method describes the influence of material properties and process control on the cooling power and efficiency of the cooling process.The findings enable the development of optimized elastocaloric cooling processes, which are the basis for the design of efficient cooling devices. During fast adiabatic loading, the latent heats of the shape memory alloy lead to a temperature increase during loading, and a temperature decrease during subsequent unloading. The investigation of the elastocaloric cooling process is a collaboration between the material science group at Ruhr University in Bochum, and two groups from mechatronics engineering at Saarland University, Saarbrucken, Germany.It involves the optimization of the materials as well as the processes, and also the development of a simulation tool. The developed scientific test rig enables the study of the elastocaloric effect for solid state heat transfer between the shape memory alloy and a heat source and the shape memory alloy and a heat sink. The main advantage of this technique is to the independent investigation of the influence of each control parameter on process values like work and heat.Furthermore, this system is equipped into comprehensive system to measure mechanical and terminal quantities at every process step. To begin, use calipers to measure the shape memory alloy ribbon, and determine the cross section of the sample. Then, coat the sample with a thin layer of a high emissivity plate.Next, set the target position in the motor controller program to zero micrometers, and click on the operation enabled button. At this position, the distance between the clamps is 90 millimeters. Place the sample between clamps of the experimental setup, and use a special designed alignment tool to align the sample.Then, use a mounting aid to tighten the clamps, and a torque wrench to tighten the screws to a force of 20 newton-meters. The lineup of the semper is very critical. The pulley on semper will fail after just a few cycles.Start the IR camera software, and load the calibration for a 50 millimeter lens combined with a closeup lens. Choose an image size of 1, 280 by 100 pixels, and a temperature range of minus 20 to 50 degrees celsius, and then use the motor focus unit to position the camera. Open the control program for training and material characterization.Next, set the start position to zero micrometers and choose a target position of 4, 500 micrometers, so the material undergoes a complete phase transformation. Set the linear direct drive velocity to 45 microns per second, which is equivalent to a strain rate of five times 10 to the negative four per second. Next, set the holding time to zero seconds, the number of cycles to one, the IR camera acquisition rate to 50 milliseconds per frame, and then click on the start button to load the settings.Now, open the IR camera software, choose a file name, and allocate 5, 000 frames. Switch from an internal to an external trigger source, and start the data acquisition mode. Then, open the control program and press the start experiment button to run the experiment.To begin characterizing the material, open the control program for training and material. Then, set the start position so that the sample is under zero load to begin with, and set the target position equivalent to the target position of the training, which was 4, 500 micrometers. Next, set the strain rate as desired, and choose a linear direct drive velocity of 9, 000 micrometers per second, which leads to an adiabatic phase transformation for samples with a cross sectional area that is 0.75 millimeters by 1.4 millimeters or larger.Set the holding time to 180 seconds to allow enough time for the sample to reach the desired initial temperature prior to the experiment. Then, set the number of cycles to one, the IR camera acquisition rate to 5 milliseconds per frame, and click on the start button to load the settings. Next, open the IR camera software, choose a file name, and allocate 80, 000 frames for the experiment.Switch from an internal to an external trigger source, and start the data acquisition mode. In the control program, press the start experiment button to start the experiment. In order to investigate local temperature peaks, first switch off the light.Then, remove all heat sources from the IR camera's field of view, and change the lens to a microscope lens. Next, change the camera calibration settings, load a microscope lens, and calibrate an image size of 500 by 250 pixels within the range of 20 to 50 degrees celsius. Use the motor focus unit to focus the sample.Then, perform a standard tensile test at a linear direct drive velocity of 900 microns per second, as previously described. With the sample still in place start the IR camera software and load the calibration for the 50 millimeter lens with closeup lens. Choose an image size of 1, 280 by 1, 024 pixels, and a temperature range of negative 20 to 50 degrees celsius.Open the control program and set the control parameters. Set the start position of the linear direct drive for the shape memory alloys so that the sample is under zero load. Also, set the target position equivalent to the target position of the training.Set the velocity of the linear direct drive for loading and unloading of the shape memory alloy to 9, 000 micrometers per second. Then, set the velocity of the linear direct drive in the lower level of the setup to 100 millimeters per second. Next, set the contact time to six seconds.Choose the contact after the loading and unloading mode and set the number of cycles to 40. Choose an IR camera acquisition rate of 20 milliseconds per frame, and then click on the start button to load the settings. In the IR camera software, choose a file name, and allocate 50, 000 frames for the experiment.Switch from an internal to an external trigger source and start the data acquisition mode. Finally, open the control program and press the start experiment button. This will begin the elastocaloric cooling cycle.In this movie clip, a nickel titanium ribbon is being strained during training. The controlled stretching leads to a mean temperature increase of 12.2 degrees Kelvin. The material follows a typical hysteresis curve and eventually settles into a response like that shown in red.Shown here with a nickel titanium copper vanadium ribbon, the hysteresis width increases with increased strain rates. This is a result of the temperature change during the phase transformation. The diagram shows that after a certain point, there is no further increase of the temperature change in response to increasing strain rate.This infrared video shows that by increasing the number of cooling cycles, the temperature differences between heat sink and heat source increase, and results in a decreasing minimum and maximum temperature change of the material. After the first cycle, an inhomogeneous temperature profile arises because the heat sink and heat source do not contact the entire ribbon. Here you can see the comparison between experiment and simulation of a tensile test.The underlying model of the simulation is a modification of the thermomechanically coupled Mueller Achenbach Selleck Model. This shows that the model is able to reproduce the mechanical as well as the thermal behavior of the material. So while attempting the procedure, it's important to remember that the design requirements are monitoring all the cooling steps, and also a straight forward control of the variation parameters.Thermal encapsulation will increase the efficiency of the process, however the observability would be greatly reduced. For the development of a real device afterwards, you would of course take it into consideration. Following this procedure, other process variations besides the adiabatic process control, like unadiabatic adiabatic combined processes can be performed in order to answer additional questions like the influence of the contact phase and on the process efficiency and cooling power.After watching this video, you should have a good understanding of the elastocaloric cooling effect, and how materials optimization and process control influence the cooling power and efficiency of the process.

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JoVE Journal

Engineering

10.9K Görüntüleme.  Saarland University. The overall goal of this experiment is to investigate elastocaloric materials and elastocaloric cooling processes. To this end, a scientific test rig has been developed to perform basic material characterizations and advanced elastocaloric process controls. Our method describes the influence of material properties and process control on the cooling power and efficiency of the cooling process.The findings enable the development of optimized elastocaloric cooling processes, which are the...