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On the Recovery Stress of a Ni50.3Ti29.7Hf20 High Temperature Shape Memory AlloyRecovery stress in shape memory alloys (SMAs), also known as blocking stress, is an important property generally obtained during heating under a dimensional constraint as the material undergoes the martensitic phase transformation. This property has been instinctively utilized in most SMA shape-setting procedures, and has been used in numerous applications such as fastening and joining, rock splitting, safety release mechanisms, reinforced composites, medical devices, and many other applications. The stress generation is also relevant to actuator applications where jamming loads (e.g., in case the actuator gets stuck and is impeded from moving) need to be determined for proper hardware sizing. Recovery stresses in many SMA systems have been shown to reach stresses in the order of 800 MPa, achieved via thermo-mechanical training such as pre-straining, heat treatments or other factors. With the advent of high strength, high temperature SMAs, recovery stress data has been rarely probed, and there is no information pertinent to the magnitudes of these stresses. Thus, the purpose of this work is to investigate the recovery stress capability of a precipitation strengthened, Ni50.3Ti29.7Hf20 (at.) high temperature SMA in uniaxial tension and compression. This material has been shown to exhibit outstanding strength and stability during constant-stress, thermal cycling, but no data exists on constant-strain thermal cycling. Several training routines were implemented as part of this work including isothermal pre-straining, isobaric thermal cycling, and isothermal cyclic training routines. Regardless of the training method used, the recovery stress was characterized using constant-strain (strain-controlled condition) thermal cycling between the upper and lower cycle temperatures. Preliminary results indicate recovery stresses in excess of 1.5 GPa were obtained after a specific training routine. This stress magnitude is significantly higher than conventional NiTi stress generation capability.
Document ID
20150023061
Document Type
Presentation
Authors
Benafan, O. (NASA Glenn Research Center Cleveland, OH United States)
Noebe, R. D. (NASA Glenn Research Center Cleveland, OH United States)
Padula, S. A., II (NASA Glenn Research Center Cleveland, OH United States)
Bigelow, G. S. (NASA Glenn Research Center Cleveland, OH United States)
Gaydosh, D. J. (Ohio Aerospace Inst. Cleveland, OH, United States)
Garg, A. (Toledo Univ. OH, United States)
Halsmer, T. J. (Jacobs Technology, Inc. Cleveland, OH, United States)
Date Acquired
December 15, 2015
Publication Date
September 21, 2015
Subject Category
Mechanical Engineering
Metals and Metallic Materials
Report/Patent Number
GRC-E-DAA-TN26891
Meeting Information
ASME 2015 Conference on Smart Materials, Adaptive Structures and Intelligent Systems (SMASIS 2015)(Colorado Springs, CO)
Funding Number(s)
WBS: WBS 081876.02.03.50.04.01
Distribution Limits
Public
Copyright
Public Use Permitted.
Keywords
Recovery Stress
High Temperature Shape Memory Alloy
NiTiHf

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