Harshad Paranjape

Recent advances in the Data Science methods for acquiring and analyzing large amounts of materials deformation data have the potential to tremendously benefit Nitinol (Nickel–Titanium shape memory alloy) implant design and simulation. We review some of these data-driven methodologies and provide a perspective on adapting these techniques to Nitinol...

Digital image correlation data and Bayesian inference used together facilitate rigorous quantification of the uncertainty in material input parameters for finite element simulations of superelastic deformation.

We implement an approach using Bayesian inference and machine learning to calibrate the material parameters of a constitutive model for the superelastic deformation of NiTi shape memory alloy. We use a diamond-shaped specimen geometry that is suited to calibrate both tensile and compressive material parameters from a single test. We adopt the Bayes...

Computational modeling and simulation are commonly used during the development of cardiovascular implants to predict peak strains and strain amplitudes and to estimate the associated durability and fatigue life of these devices. However, simulation validation has historically relied on comparison with surrogate quantities like force and displacemen...

Background: Implantable medical devices manufactured from superelastic Nickel-Titanium (NiTi) shape memory alloy are subjected to cyclic deformation during their life. During the design of such devices, their durability is assessed using simulations of fatigue indicator parameters. This simulation-based approach is limited by the assumptions made i...

The low symmetry martensite phase in Nickel-Titanium (NiTi) shape memory alloy (SMA) has a hierarchical microstructure with micro-scale crystallites, which themselves consist of nano-laminates with an internal twin structure. The martensite phase deforms inelastically though reorientation of the twin structure. Furthermore, structural features in t...

We describe a novel endovascular technique in which three 0.014” guidewires are placed in parallel through a 0.035” lumen catheter, in order to create a stiff platform to allow for delivery of 0.035” profile devices through challenging anatomy. Three illustrative cases are presented: a difficult aortic bifurcation during lower extremity interventio...

Computational modeling and simulation are commonly used during the development of cardiovascular implants to predict peak strains and strain amplitudes and to estimate the associated durability and fatigue life of these devices. However, simulation validation has historically relied on comparison with surrogate quantities like force and displacemen...

Transformation-induced plasticity due to the motion of martensite fronts is a key mechanism for damage accumulation during cyclic loading of NiTi shape memory alloys (SMAs). Intuitively, a larger motion of martensite fronts should result in a larger accumulation of defects, and lead to a shorter low-cycle fatigue life. We validate this hypothesis t...

Superelastic Nitinol is a widely used material to manufacture implantable medical devices. Simulations are extensively used in the design, optimization, and durability assessment of Nitinol implants. The constitutive response of superelastic materials is non-linear, anisotropic, and asymmetric in tension vs. compression. The existing methods to det...

Deformation characterization of low-symmetry phases such as martensite in SMAs is challenging due to a fine-scale hierarchical microstructure. Using X-ray microLaue diffraction, in-situ deformation of martensite is examined in a notched NiTi specimen. The local deformation is influenced by the notch stress field, initial martensite microstructure,...

Three types of fatigue testing are performed to elucidate the effects of prestraining superelastic Nitinol on its subsequent fatigue lifetime: rotary bending and tension-tension testing of wire, and beam bending using diamond-shaped specimens fabricated from tubing. Results show that local plastic deformation during prestraining induces residual st...

Porous NiTi shape memory alloys have applications in the biomedical and aerospace fields. Recent developments in metal additive manufacturing have made fabrication of near-net-shape porous products with complicated geometries feasible. There have also been developments in tailoring site-specific microstructures in metals using additive manufacturin...

We present a strain-based formulation of macroscopic plastic deformation that accounts for anisotropy in both the initial yielding and subsequent hardening. Both isotropic and kinematic hardening are considered. Thus the model captures the evolution in the deformation response on cyclic loading including the Bauschinger effect, and the accumulation...

Microstructural elements in NiTi shape memory alloys (SMAs) – precipitates, phase boundaries, inclusions, grain boundaries – can be viewed as sources of multiscale constraint that influence their deformation response. We characterized in situ, and in 3D, the deformation and the evolution of microstructure during a tension test in a superelastic NiT...

This study demonstrates a transition from a structure-dominated response to a microstructure-dominated response around machined features in a polycrystalline NiTi shape memory alloy (SMA), as the size of the features relative to the mean grain size is varied. The specific structural features considered are a pair of holes of varying separation and...

Compression of a single crystal, superelastic NiTi shape memory alloy (SMA) micro-pillar and the stress-field around an ellipsoidal twinned martensite (M) plate embedded in an austenite (A) matrix were simulated using a coupled phase transformation and crystal plasticity model. Post-mortem transmission electron microscopy (TEM) analysis of the disl...

This dataset consists of grain structure information in terms of grain centroid and volume, crystal orientation of the grains, and the full lattice strain tensor averaged over each grain for a poly-crystalline NiTi shape memory alloy specimen that undergoes martensitic phase transformation on loading. These measurements are performed using far-fiel...

Deformation heterogeneities within microstructures of polycrystalline shape memory alloys (SMAs) during superelastic stressing are studied using both experiments and simulations. In situ X-ray diffraction, specifically the far-field high energy diffraction microscopy (ff-HEDM) technique was used to non-destructively measure the grain-averaged stati...

Two prevalent myths of Nitinol mechanics are examined: (1) Martensite is more compliant than austenite; (2) Texture-free Nitinol polycrystals do not exhibit tension–compression asymmetry. By reviewing existing literature, the following truths are revealed: (1) Martensite crystals may be more compliant, equally stiff, or stiffer than austenite cryst...

div class="title">Revealing Transformation and Deformation Mechanisms in NiTiHf and NiTiAu High Temperature Shape Memory Alloys Through Microstructural Investigations - Volume 22 Issue S3 - L. Casalena, J. M. Sosa, D. R. Coughlin, F. Yang, X. Chen, H. Paranjape, Y. Gao, R. D. Noebe, G. S. Bigelow, D. J. Gaydosh, S. A. Padula, Y. Wang, P. M. Anderso...

The coupling between phase transformations and plasticity in shape memory alloys (SMAs) is studied by developing a finite element framework in which the constitutive relation captures both phase transformations at the martensite correspondence variant (CV) scale and rate-dependent crystal plasticity in austenite. Load-free and load-biased thermal c...

div class="title">Transformation and Deformation Characterization of NiTiHf and NiTiAu High Temperature Shape Memory Alloys - Volume 21 Issue S3 - L. Casalena, D. R. Coughlin, F. Yang, X. Chen, H. Paranjape, Y. Gao, R. D. Noebe, G. S. Bigelow, D. J. Gaydosh, S. A. Padula, Y. Wang, P. M. Anderson, M. J. Mills

Superelastic Nitinol micromechanics are studied well into plastic deformation regimes using neutron diffraction. Insights are made into the nature of initial transformation, bulk transformation, plastic deformation, and unloading. Schmid factor predictions based on habit plane variants are found to best describe the very first grains that transform...

This work demonstrates how the statistical pseudoelastic performance of individual grains is affected by the local grain neighborhood in polycrystalline shape memory alloys (SMAs). This is achieved using a microstructural finite element (FE) model calibrated to homogenized Ti-50.9 at% Ni SMA. The results show a three-fold variation in the grain lev...

Combining novel experimental approaches with simulations of the underlying phenomena can be used to study a range of physical processes in shape memory alloys. Here, we study the connection between transformation and plasticity in near equiatomic NiTi shape memory alloys, the role of precipitates in promoting and/or suppressing transformation in Ni...

A microstructural finite element (FE) model for shape memory alloys (SMA) is developed in which the austenite phase can plastically deform and/or transform to crystallographic martensite correspondence variants (CVs). The thermal and stress-induced phase transformation and reorientation of martensite is modeled using the phase field (PF) method. Th...

An emerging class of Ni-based high temperature shape memory alloys (HTSMAs) display high reliability, light weight and increased capability while lowering space and power consumption for many energy and transportation applications. This research focuses on developing a fundamental understanding of the inherent microstructure-property relationship o...

Finite element models of tissue engineering scaffolds are powerful tools to understand scaffold function, including how external mechanical signals deform the scaffold at the meso- and microscales. Fiber geometry is needed to inform finite element models of fiber-based tissue engineering scaffolds; however, the accuracy and utility of these models...

Fully recrystallized commercial-purity aluminum sheets were deformed by limiting dome height tests, the following strain modes: uniaxial tension (US), near plane strain tension (PS), and equibiaxial tension (BS) were identified using standard procedure. The deformation texture developments differed significantly depending on the strain mode. Althou...

AA6022 samples were deformed at different temperatures and strain rates and to respective true strains of 1.0 and 2.0. Though the deformation was immediately followed by quenching, the as-deformed samples contained recrystallized grains. A convention was adopted, based on grain size and in-grain misorientation developments, to distinguish between t...

AA6022 samples were deformed at different temperatures and strain rates and to respective true strains of 1.0 and 2.0. Though the deformation was immediately followed by quenching, the as-deformed samples contained recrystallized grains. A convention was adopted, based on grain size and in-grain misorientation developments, to distinguish between t...