Engineering Applications and Devices: Session 2
Program Organizers: Alan Pelton, G.RAU Inc.
Wednesday 11:35 AM
July 12, 2017
Location: Hyatt Regency Chicago
Experimental Determination of Crack Growth Rates during Thermo-Mechanical Cycling of NiTi and NiTiHf Shape Memory Alloys: Ceylan Hayrettin1; Theocharis Baxevanis1; Ibrahim Karaman1; Benjamin Young1; Serdar Ozguc1; Dmitris Lagoudas1; 1Texas A&M University
There is a pressing need in aerospace and automotive industries for lightweight and compact actuators that can generate high force and stroke. Shape memory alloys (SMAs) are promising candidates for these actuators due to their much higher actuation energy density than existing solutions. Because potential applications require reliable actuation under thermo-mechanical cycles, understanding crack growth in the presence of global phase transformation is important. Ni50Ti50 and Ni50.3Ti29.7Hf20 SMAs have been investigated in this study. Crack growth from mechanical cycling was determined for both phases. Although SMAs exhibit non-linear stress-strain response, they obey the Paris-Erdogan law. Thermal cycling produces significantly faster, but still stable, crack growth compared to mechanical cycling. The strain field during transformation was mapped with digital image correlation (DIC), and crack growth was investigated with Finite Element Analysis (FEA). It is hypothesized that global phase transformation causes an increase in the stress intensity factor at the crack tip.
Influence of Contact Friction on Force-deflection of Orthodontic NiTi Archwire: A Computational Study: Muhammad Fauzinizam Razali1; Abdus Samad Mahmud1; 1Universiti Sains Malaysia
The force response of NiTi archwire with respect to tooth movement in orthodontic leveling treatment depends largely on the sliding resistance of a bracket system. This study investigated the influence of contact friction between the wire and the bracket towards the force-deflection behavior of superelastic NiTi wire. A finite-element model of three brackets bending configuration was developed and a user material subroutines was employed to predict the force response. The archwire was bent to a certain displacement representing the curvature of the wire when installed at patient and the coefficient of contact friction with the brackets was defined at a range of 0.1 to 0.5. This investigation revealed that the force plateau of NiTi archwire occurred at positive slope, with steeper gradient recorded on the model with a higher friction coefficient. This implies that lower contact friction is preferable in a bracket system to preserve the force plateau characteristic.