Experimental and computational investigation of the effect of phase transformation on fracture parameters of an SMA

Abstract

A comprehensive, multi-method experimental characterization of fracture is conducted on shape memory alloy NiTi that exhibits superelasticity due to austenite-to-martensite stress induced phase transformation. This characterization includes (i) load-based measurement of critical stress intensity factor (K max ) using ASTM standard E399, (ii) measurement of crack tip opening displacement (CTOD) per ASTM standard E1290, (iii) the digital image correlation (DIC) characterization of the transformation zone as well as the displacement-field based measurement of K max from the DIC data. Samples have also been tested at T=100 °C to suppress the martensitic transformation to investigate transformation toughening. The experimental investigation is complemented with finite element (FE) analysis that uses Auricchio-Taylor-Lubliner constitutive model. A direct observation with DIC revealed a small scale transformation (K-dominance). K max of the transforming material is higher than that of the transformationsuppressed material tested at 100 °C, suggesting transformation toughening. At 100 °C, the material becomes quite brittle with a very small crack-tip plastic zone when the transformation mechanism is blocked. By measures of critical CTOD, the gap widens even more between the superelastic and transformation-suppressed cases, particularly because of the side effect that, in this very interesting material, material modulus increases with temperature. Evaluating the transformation zone from the DIC strains with reference to the uniaxial stress-strain curve, an equivalent strain form is proposed in conjunction with the plane stress FE prediction.

Crack Growth Behavior in NiTi Shape Memory Alloys Under Mode-I Isothermal Loading: Effect of Stress State

“…Implementing various constitutive models [7][8][9][10][11], fracture of SMAs has been studied numerically in the presence of stationary cracks [12][13][14][15][16][17][18][19]. It is shown that stress concentration at the crack tip causes forward transformation (i.e.…”

Electromigration Response of Microjoints in 3DIC Packaging Systems

“…It is important to develop, and combine the existing model, with failure prediction models [23][24][25][26] to study the microstructural effects upon ductile failure in the LVI solder joints to effectively retain good strength and ductility during accelerated EM conditions in 3DIC systems.…”

A three-dimensional constitutive model for the martensitic transformation in polycrystalline shape memory alloys under large deformation

“…However, it has been reported that SMAs can reversibly deform to a relatively large strain regime up to 8% [35,36]. Also for specific boundary value problem such as fracture in SMAs, the strain levels close to the crack tip are well beyond 10% [37,38] within the finite strain regime. In addition to such relatively large strain, SMA-based actuators (e.g., spring, beam, torque tube) may also undergo large rotation during their deployment.…”