On the Energy Release Rate During Global Thermo-Mechanically-Induced Phase Transformation in Shape Memory Alloys

2013 ◽  
Author(s):  
Antonino Parrinello ◽  
Theocharis Baxevanis ◽  
Dimitris Lagoudas
Keyword(s):  
Phase Transformation ◽  
Shape Memory Alloys ◽  
Energy Release Rate ◽  
Shape Memory ◽  
Energy Release ◽  
Release Rate ◽  
Crack Tip ◽  
Crack Driving Force ◽  
Order Of Magnitude ◽  
Specific Material

In this work, the effect of thermo-mechanically-induced global phase transformation (actuation) on the crack driving force in Shape Memory Alloys (SMAs) is investigated by means of the finite element method. The prototype problem of an infinite center-cracked SMA plate is analyzed during a thermal cycle in isobaric, plane strain loading conditions. The temperature variation is sufficient to induce global phase transformation. The Virtual Crack Closure Technique (VCCT) is employed to measure the crack tip energy release rate during the entire actuation cycle. Results show that the energy release rate can increase drastically during actuation, an order of magnitude for specific material systems. This in turn implies that crack growth may be triggered as a result of thermo-mechanically-induced phase transformation. The sensitivity of the crack tip energy release rate during actuation on key thermo-mechanical parameters is studied.

On the Fracture Toughness of Pseudoelastic Shape Memory Alloys

2013 ◽  
Vol 81 (4) ◽  
Author(s):  
Theocharis Baxevanis ◽  
Chad M. Landis ◽  
Dimitris C. Lagoudas
Keyword(s):  
Fracture Toughness ◽  
Phase Transformation ◽  
Shape Memory Alloys ◽  
Energy Release Rate ◽  
Shape Memory ◽  
Energy Release ◽  
Release Rate ◽  
Crack Tip ◽  
Reverse Phase ◽  
Element Analysis

A finite element analysis of quasi-static, steady-state crack growth in pseudoelastic shape memory alloys is carried out for plane strain, mode I loading. The crack is assumed to propagate at a critical level of the crack-tip energy release rate. Results pertaining to the influence of forward and reverse phase transformation on the near-tip mechanical fields and fracture toughness are presented for a range of thermomechanical parameters and temperature. The fracture toughness is obtained as the ratio of the far-field applied energy release rate to the crack-tip energy release rate. A substantial fracture toughening is observed, in accordance with experimental observations, associated with the energy dissipated by the transformed material in the wake of the growing crack. Reverse phase transformation, being a dissipative process itself, is found to increase the levels of toughness enhancement. However, higher nominal temperatures tend to reduce the toughening of an SMA alloy—although the material's tendency to reverse transform in the wake of the advancing crack tip increases—due to the higher stress levels required for initiation of forward transformation.

On the Effect of Latent Heat on the Fracture Toughness of Pseudoelastic Shape Memory Alloys

2014 ◽  
Vol 81 (10) ◽  
Author(s):  
Theocharis Baxevanis ◽  
Chad M. Landis ◽  
Dimitris C. Lagoudas
Keyword(s):  
Fracture Toughness ◽  
Shape Memory Alloys ◽  
Energy Release Rate ◽  
Shape Memory ◽  
Energy Release ◽  
Latent Heat ◽  
Release Rate ◽  
Crack Tip ◽  
Thermomechanical Coupling ◽  
Adiabatic Conditions

A finite element analysis of steady-state crack growth in pseudoelastic shape memory alloys under the assumption of adiabatic conditions is carried out for plane strain, mode I loading. The crack is assumed to propagate at a critical level of the crack-tip energy release rate and the fracture toughness is obtained as the ratio of the far-field applied energy release rate to the crack-tip critical value. Results related to the influence of latent heat on the near-tip stress field and fracture toughness are presented for a range of parameters related to thermomechanical coupling. The levels of fracture toughness enhancement, associated with the energy dissipated by the transformed material in the wake of the growing crack, are found to be lower under adiabatic conditions than under isothermal conditions [Baxevanis et al., 2014, J. Appl. Mech., 81, 041005]. Given that in real applications of shape memory alloy (SMA) components the processes are usually not adiabatic, which is the case with the lowest energy dissipation during a cyclic loading–unloading process (hysteresis), it is expected that the actual level of transformation toughening would be higher than the one corresponding to the adiabatic case.

Mode I Steady Crack-Growth in Superelastic Shape Memory Alloys

2012 ◽  
Author(s):  
Theocharis Baxevanis ◽  
Dimitris Lagoudas ◽  
Chad Landis
Keyword(s):  
Shape Memory Alloys ◽  
Energy Release Rate ◽  
Shape Memory ◽  
Energy Release ◽  
Crack Growth ◽  
Release Rate ◽  
Crack Tip ◽  
Scale Transformation ◽  
Small Scale ◽  
Mode I

A numerical analysis of quasi-static, steady state crack growth in superelastic Shape Memory Alloys (SMAs) under small-scale transformation conditions is carried out for plane strain, mode I loading. Crack growth is assumed to proceed at a critical level of the crack-tip energy release rate. Finite-element results concerning the mechanical fields near the advancing crack tip are presented and the ratio of the far-field applied energy release rate to the crack-tip energy release rate is obtained for a range of thermomechanical parameters. A substantial fracture toughening is observed associated with closure stresses placed on the crack tip by the transformed material left behind in the wake of the advancing crack tip.

scholarly journals Crack Growth and Energy Release Rate for an Angled Crack under Mixed Mode Loading

2020 ◽  
Vol 10 (12) ◽  
pp. 4227
Author(s):  
Yali Yang ◽  
Seok Jae Chu ◽  
Wei song Huang ◽  
Hao Chen
Keyword(s):  
Energy Release Rate ◽  
Numerical Method ◽  
Energy Release ◽  
Release Rate ◽  
Mixed Mode ◽  
Crack Tip ◽  
Theoretical Expression ◽  
Propagation Mechanism ◽  
Mode I ◽  
Theoretical Derivation

The evaluation of energy release rate with angle is still a challenging task in metal crack propagation analysis, especially for the mixed Mode I-II-III loading situation. In this paper, the energy release rate associated with stress intensity factors at an arbitrary angle under mixed mode loadings has been investigated using both a numerical method and theoretical derivation. A relatively simple and precise numerical method was established through a series of spatial-inclined ellipses in Mode I-II and ellipsoids in Mode I-II-III, with different propagation angles computed from simulation. Meanwhile, a theoretical expression of the energy release rate with angle for a crack tip under a I-II-III mixed mode crack was deduced based on the propagation mechanism of the crack tip under the influence of a stress field. It is confirmed that the theoretical expression deduced could provide results as accurately as the present numerical method. The present results were confirmed to be effective and accurate by comparison with experimental data and other literature.

On Conservative CTOD Estimation Using Far Crack Deformation Field

2013 ◽  
Author(s):  
Piotr Bednarz ◽  
Jaroslaw Szwedowicz
Keyword(s):  
Energy Release Rate ◽  
Energy Release ◽  
Release Rate ◽  
Crack Tip ◽  
Material Behavior ◽  
Deformation Field ◽  
Nonlinear Material ◽  
Small Scale ◽  
Engineering Practice ◽  
Nonlinear Energy

In general engineering practice, crack tip opening displacement (CTOD) is very convenient approach for prediction of the components fracture mechanics (FM) lifetime. FM lifetime calculations are defined very well in industry and the lifetime prediction methods based on the CTOD resolve linear and nonlinear material behavior for monotonic and cyclic responses. The experiments confirm that under plasticity conditions the crack tip blunts for small scale or large scale yielding while, crack flanks open against each other only under elastic conditions. However, the CTOD application requires a very fine mesh in order to predict a crack tip deformation in reliable manner. Therefore, much more engineering work have to be involved in fine FE modeling. The crack tip flank deformation is crucial parameter responsible for reliable prediction of the nonlinear energy release rate, which is obtained from Hutchinson-Rice-Rosengren solution and the Shih rule. In accordance with design guidelines, the nonlinear energy release rate obtained from the CTOD must be evaluated conservatively to meet demands of RAM (Reliability, Availability and Maintainability). By using far crack deformation field, the paper proposes an engineering approach, which predicts the CTOD in a conservative manner under elastic-plastic conditions. This novel method is validated numerically by applying the well-known J-integral approach.

Effect of Solvent Diffusion on Crack-Tip Fields and Driving Force for Fracture of Hydrogels

2015 ◽  
Vol 82 (8) ◽  
Author(s):  
Nikolaos Bouklas ◽  
Chad M. Landis ◽  
Rui Huang
Keyword(s):  
Boundary Conditions ◽  
Energy Release Rate ◽  
Energy Release ◽  
Crack Growth ◽  
Release Rate ◽  
Crack Tip ◽  
Far Field ◽  
Solvent Diffusion ◽  
Effect Of Solvent ◽  
Transient Energy

Hydrogels are used in a variety of applications ranging from tissue engineering to soft robotics. They often undergo large deformation coupled with solvent diffusion, and structural integrity is important when they are used as structural components. This paper presents a thermodynamically consistent method for calculating the transient energy release rate for crack growth in hydrogels based on a modified path-independent J-integral. The transient energy release rate takes into account the effect of solvent diffusion, separating the energy lost in diffusion from the energy available to drive crack growth. Numerical simulations are performed using a nonlinear transient finite element method for center-cracked hydrogel specimens, subject to remote tension under generalized plane strain conditions. The hydrogel specimen is assumed to be either immersed in a solvent or not immersed by imposing different chemical boundary conditions. Sharp crack and rounded notch models are used for small and large far-field strains, respectively. Comparisons to linear elastic fracture mechanics (LEFM) are presented for the crack-tip fields and crack opening profiles in the instantaneous and equilibrium limits. It is found that the stress singularity at the crack tip depends on both the far-field strain and the local solvent diffusion, and the latter evolves with time and depends on the chemical boundary conditions. The transient energy release rate is predicted as a function of time for the two types of boundary conditions with distinct behaviors due to solvent diffusion. Possible scenarios of delayed fracture are discussed based on evolution of the transient energy release rate.

Experimental and FEM Analysis of the Fracture Behavior in NiTi Shape Memory Alloys

2006 ◽  
Vol 324-325 ◽  
pp. 919-922 ◽  
Author(s):  
Xin Mei Wang ◽  
Zhu Feng Yue
Keyword(s):  
Fracture Toughness ◽  
Phase Transformation ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Fracture Behavior ◽  
Micromechanical Model ◽  
Crack Tip ◽  
Fem Analysis ◽  
Transformation Behavior ◽  
Niti Shape Memory Alloys

In the present work, the fracture toughness of a NiTi pseudoelastic alloy has been obtained by experiments on CT specimens, which is KIC =39.38MPa·m1/2. Then the stress induced phase transformation behavior in front of the crack tip of the CT specimen is simulated by a micromechanical model considering the different elastic properties between martensite and austenite. The results show that the pre-crack promotes phase transformation at the crack tip. And the phase transformation is localised near the crack tip. It is also shown that phase transformation reduces the Mises stress around the crack tip.

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