A D V A N C E D M A T E R I A L S & P R O C E S S E S | M A R C H 2 0 2 3 3 8 SMJ HIGHLIGHTS damping. The impact tests were carried out using two test benches: high-speed impacts were carried out using a vertical firing pressure gun and low-velocity impacts were studied with a bullet drop test. In addition, an original approach of a dynamic mechanical analysis (DMA) is proposed in order to obtain more in-depth understanding of the relationship between microstructure, deformation mechanisms, and damping capacity. The specimens are studied at different microstructure states: single β, dualphase β + αʺ, and martensitic phase. A correlation is established between the evolution of the damping factor as function of the applied strain and the occurrence of the corresponding deformation mechanisms. The stress-induced martensite mechanism contributes to the improvement of the damping factor. The highest damping capacity is observed for the dual-phase specimen (β + αʺ). It is shown that the contribution of both the reorientation martensite variants and stress-induced martensitic transformation led to a damping capacity higher than a single deformation mechanism one (Fig. 2). December 2022 A FINITE-STRAIN PHASE-FIELD DESCRIPTION OF THERMOMECHANICALLY INDUCED FRACTURE IN SHAPE MEMORY ALLOYS M.M. Hasan, M. Zhang, and T. Baxevanis A finite-strain, phase-field model for thermomechanically induced fracture in shape memory alloys (SMAs), i.e., fracture under loading paths that may take advantage of either the superelastic response or the shape memory effect in SMAs, is presented based on the Eulerian logarithmic (Hencky) strain and the logarithmic objective rate. Based on experimental observations suggesting that SMAs fracture in a stress-controlled manner, damage is assumed to be driven by the elastic energy, i.e., phase transformation is assumed to contribute to crack formation and growth indirectly through stress redistribution. The model is restricted to quasistatic mechanical loading (no latent heat effects) and thermal loading sufficiently slow with respect to the time rate of heat transfer by conduction (no thermal gradients) and can describe phase transformation and orientation of martensite variants from a self-accommodated state. A single fracture toughness value is assumed—that of martensite—thus, the temperature range of interest is below Md, which is the temperature above which the austenite phase is stable. The numerical implementation of the model in an efficient scheme is described and its ability to reproduce experimental observations on the fracture response of SMAs and handle complex geometries and loading conditions is demonstrated (Fig. 3). December 2022 UNEQUALLY AND NON-LINEARLY WEIGHTED AVERAGING OPERATORS AS A GENERAL HOMOGENIZATION APPROACH FOR PHASE FIELD MODELING OF PHASE TRANSFORMING MATERIALS V. von Oertzen and B. Kiefer The phase field method has been shown to have tremendous potential to serve as a continuum modeling approach of microstructural evolution mechanisms in many contexts, such as alloy solidification, fracture, and chemo- mechanics. By replacing sharp interfaces between phases with a diffuse representation, additional degrees of freedom, namely order parameters, enter the continuum model, in order to describe the current phase state at each material point. Single-phase properties thus need to be interpolated carefully within diffuse interface regions by applying mixture rules subject to specific, microscopic constraints in an underlying homogenization framework. However, there exists a variety of well- established nonlinear interpolation schemes—especially incorporating symmetric or hyperspherical order parameters—which cannot consistently be described within conventional homogenization theories. To overcome this problem, an extension toward unequally, nonlinearly weighted averaging operators is presented, in which conventional, unweighted homogenization represents a special case. The embedding of Reuss–Sachs, Taylor–Voigt, and rank-one convexification models—extended by nonlinear interpolation—within the proposed framework is demonstrated by identifying necessary constraints on corresponding weighting functions. Since this concept Fig. 2 — Experimental set-up: (a)Pressure gun and (b) drop ball test. Fig. 3 — Stress–strain response under uniaxial isothermal loading (a) at T = 298 K and T = 353 K and (b) at T = 385 K. (b) (a) 1 2
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