Development of an Optical Device for Magneto-Mechanical Experiments

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Dr. Peter Mullner


Current magneto-mechanical experiments measure the macroscopic magnetic-field-induced strain (MFIS) of magnetic shape-memory alloys (MSMA) by measuring the deformation of a sample in one direction. The macroscopic strain is the result of reorientation of the lattice of the MSMA due to an applied magnetic field or mechanical deformation. The lattice is reoriented by moving twin boundaries (TB). To study the motion of individual twin boundaries, an optical magneto-mechanical device (OMMD) was built. Optics, lighting, and a high resolution camera (21 Mega pixels) were put into a custom built apparatus that allows the entire setup to be rotated. While the sample is aligned with the optics and camera, the apparatus is put between the pole pieces of a strong electro magnet with a magnetic field strength up to 2 T. Using the image analysis software “Machine Vision” of National Instruments, the live footage can be analyzed in real time to calculate strain values in two dimensions. Furthermore, the individual TB movements can be recorded and paired with positional data of the sample relative to the magnetic field using a rotational encoder connected in line with the OMMD. By using a modular design, the OMMD can easily be put onto a heating/cooling stage where the phase transformation, especially the martensite-austenite interface, can be studied without an applied magnetic field. Future modifications include combining the heating/cooling stage with the rotating OMMD apparatus for in situ phase transformation experiments in a magnetic field as well as the addition of optical filters and a quarter wave plate to enhance optical contrast.

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