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Development of a Magneto-Mechanical Actuator for the Measurement of Strain in Magnetic Shape Memory Alloys

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Technical Report

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Defence R and D Canada - Atlantic Dartmouth, NS Canada

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The Emerging Materials Section at DRDC Atlantic is involved in the development of magnetic shape memory alloys. As part of this research effort on the design, fabrication and characterization of magnetic shape memory alloys, the development of a device to measure the magneto-mechanical behaviour of these materials is required. This requires the redesign of the magneto-mechanical actuator device previously developed at DRDC Atlantic. This report describes the work by Martec Limited to redesign the magneto-mechanical actuator, during September to November 2003. The device measures strain in small 5-30 mm in length specimens as a function of applied magnetic field, compressive stress and temperature. The design allows for load up to 500 lb to be applied while displacement is monitored using a LVDT. Magnetic fields of up to 1 Tesla can be applied to the specimen. Load is applied using a manual machine screw. The magneto-mechanical actuator was redesigned to correct problems with the existing device and facilitate the addition of new components. This included rearrangement of the load train to eliminate movement of the specimen, other than from specimen deformation, during loading reducing friction due to misalignment and simplifying the mounting location of sensors, cooling devices, etc. Compressive loads are applied using a series of springs and measured with a load cell, with provisions for future introduction of a mechanical actuator. Strain is measured using the existing LVDT, but the design also include a access for non-contact strain measurement to measure both the longitudinal and transverse strains in the material and to allow the use of irregularly shaped specimens. An improved user interface for the data acquisition system to allow real-time plotting of test variables was developed. The device was demonstrated by obtaining the stress strain behaviour of a brass specimen.


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