Figure 2. Mechanical coupling between magnetostrictive coating and substrate that is exposed to a magnetic field. 1. Introduction/Background The use of composite materials in high performance applications are becoming more common. One of the main concerns though, is that detection of highly stressed areas such as defect and crack locations are difficult. By utilizing thermal stress analysis (TSA), almost any section under stress can be examined. TSA takes advantage thermal imaging camera that detects the temperature change when a material is being stressed. These temperature gradients can be directly correlated with stress. Terfenol-D is a magnetostrictive material that exhibits high deformation when exposed to a magnetic field. By imbedding Terfenol D in an epoxy and applying it as a coating to a surface of a part, the part can become stressed by applying a magnetic field. Coupling both the TSA system and Terfenol-D coating can allow for the testing of many types of structures with one test system. In this The use of thermoelastic stress analysis in composite materials induced by magnetostrictive effects Peng Yang, Rani Elhajjar, Chiu T. Law Aluminum Substrate Terfenol-D Epoxy Bar Figure 1. Cantilever beam that consits of a Terfenol-D Epoxy bar mounted onto an aluminum substrate. 2. Theory Figure 4. Temperature gradient along bottom side of cantilever sample with an applied load. Scale units is in Kelvins Figure 5. Von Mises Stress distribution along cantilever sample as a result of mechancial loading using FEA. Units are in Psi. (Top) Isometric view. (Middle) Bottom view. (Bottom) Side view. Figure 6. Predicted Von Mises Stress distribution along cantilever sample as a result of the magnetostrictive effect. Units are in Psi. (Top) Isometric view. (Middle) Bottom view. (Bottom) Side view. TSA Camera Slider Crank Clamped Sample Rubberband Connection Power-drill Power TSA Camera Rubberband Connection Clamped Sample Figure 3. Experimental setup to test mechanical stress of the cantilever beam using TSA camera. A Terfenol-D/epoxy bar is mounted onto an aluminum substrate to form a cantilever beam shown in Figure 1. When a magnetic field is applied, the Terfenol-D elongates causing deformation in the substrate. As the bottom side of the substrate compresses, it releases heat that is capture by the TSA system (Figure 2). The setup uses a slider crank powered by a hand drill Figure 3. The slider crank induces a cyclic load to the cantilever sample. A rubber band connection is used to limit the displacement of the cantilever beam. The sample is mounted sideways with the bottom facing the camera. The bottom of sample is painted black to increase emissivity of substrate. The load is applied at a rate of 7.6Hz for 200 cycles. 3. Test Setup TSA is able to detect stress gradients in substrate (Figure 4) in terms of temperature from the mechanical loading FEA results shows close correlation with the TSA system (Figure 5) in terms of stressed locations from mechanical loading A model was generated predicting the effect that the Terfenol D epoxy bar will have on the substrate when it is exposed to a magnetic field by replacing the magnetic strain with an equivalent thermo-induced strain (Figure 6). 4. Results/Conclusion Reduce noise in TSA detection system. Run the test using a magnetic field to see how the FEA model compares. Replace aluminum substrate with carbon fiber composite. Experiment with different volume fractions of Terfenol-D in the epoxy Experiment with different thickness of the Terfenol-D epoxy composite. 5. Future Work The authors would like to acknowledge the support from the UWM Research Growth Initiative (RGI) for the project. Acknowledgements [1] Liu, Xin’en and Zheng, Xiaojing. A nonlinear constitutive model for magnetostrictive materials. Acta Mech Sinica (2005). Vol 21, p [2] Kobayashi, Albert S. (1993) “Handbook on Experimental Mechanics, Second Edition.” Society of Experimental Mechanics. P References1. Introduction/Definitions Research Goal: Utilize a coating made from Terfenol-D to induce stress in a composite structure that can be detected using Thermoelastic Stress Analysis (TSA) Definition TSA - Thermal imaging technique which detects principal stress in a material by correlating it to temperature change Terfenol-D - A giant magnetostrictive material that will deform its shape producing strain when exposed to a magnetic field. Project Scope: Detecting the mechanical stresses on an aluminum cantilever beam using TSA and predict its behavior with an applied magnetic field. Test Specimen: Terfenol-D particles embedded in epoxy mounted on an aluminum substrate (Figure 1). Magnetic Test: A magnetic field is applied to the specimen causing the Terfenol-D embedded in epoxy to elongate and compressing the substrate releasing heat that should be detectable to the thermo- imaging camera (Figure 2). No mechanical load will be applied. Mechanical Test: A power drill spins a slider crank mechanism at 7.6hz to induce stress in the specimen. A rubber band connection limits the displacement and the bottom of the specimen is painted black to increase emissivity of the thermo-response for the TSA camera (Figure 3). No magnetic field is applied. 3. Test Setup