Thermal fracture is prevalent in many engineering problems and is one of the most devastating defects in metal additive manufacturing. Due to the interactive underlying physics involved, the computational simulation of such a process is challenging. In this work, we propose a thermo-mechanical phase-field fracture model, which is based on a thermodynamically consistent derivation. The influence of different coupling terms such as damage-informed thermomechanics and heat conduction and temperature-dependent fracture properties, as well as different phase-field fracture formulations, are discussed. The model is numerically implemented with the finite element method. Finally, the model is applied to simulate the hot cracking in additive manufacturing. Thereby not only the thermal strain but also the solidification shrinkage is considered. As for the thermal profile, both analytical temperature solution and numerical thermal field around the melting pool are taken into account. Based on the latter approach, the influence of different process parameters is further studied. The study reveals that the solidification shrinkage strain takes a dominant role in the formation of the circumferential crack, while the temperature gradient is mostly responsible for the central crack. Process parameter study demonstrates further that a higher laser power and slower scanning speed are favorable for keyhole mode hot cracking while a lower laser power and quicker scanning speed tend to form the conduction mode cracking. The numerical predictions of the hot cracking patterns are in good agreement with similar experimental observations, showing the capability of the model for further studies. 

/pdf/a-thermo-mechanical-phase-field-fracture-model-application-2p5e62yn.pdf

A thermo-mechanical phase-field fracture model: Application to hot cracking simulations in additive manufacturing

We present a phase field-based framework for modelling fatigue damage in Shape Memory Alloys (SMAs). The model combines, for the first time: (i) a generalized phase field description of fracture, incorporating multiple phase field formulations, (ii) a constitutive model for SMAs, based on a Drucker–Prager form of the transformation surface, and (iii) a fatigue degradation function, with damage driven by both elastic and transformation strains. The theoretical framework is numerically implemented, and the resulting linearized system is solved using a robust monolithic scheme, based on quasi-Newton methods. Several paradigmatic boundary value problems are addressed to gain insight into the role of transformation stresses, stress-strain hysteresis, and temperature. Namely, we compute Δε − N curves, quantify Paris law parameters, and predict fatigue crack growth rates in several geometries. In addition, the potential of the model for solving large-scale problems is demonstrated by simulating the fatigue failure of a 3D lattice structure. 

Modelling fatigue crack growth in shape memory alloys

/pdf/probabilistic-failure-mechanisms-via-monte-carlo-simulations-1knilhmd.pdf

Probabilistic failure mechanisms via Monte Carlo simulations of complex microstructures

Nonlinear thermo-elastic phase-field fracture of thin-walled structures relying on solid shell concepts

https://doi.org/10.1016/j.engfracmech.2022.108693

A stress-based poro-damage phase field model for hydrofracturing of creeping glaciers and ice shelves

A generalised phase field model for fatigue crack growth in elastic–plastic solids with an efficient monolithic solver

/pdf/a-generalised-phase-field-model-for-fatigue-crack-growth-in-2m8rs89n.pdf

/pdf/a-coupled-phase-field-formulation-for-modelling-fatigue-2fkqyalu.pdf

A coupled phase field formulation for modelling fatigue cracking in lithium-ion battery electrode particles

We present a novel micromechanics-based phase field approach to model crack initiation and propagation in carbon nanotube (CNT) based composites. The constitutive mechanical and fracture properties of the nanocomposites are first estimated by a mean-field homogenisation approach. Inhomogeneous dispersion of CNTs is accounted for by means of equivalent inclusions representing agglomerated CNTs. Detailed parametric analyses are presented to assess the effect of the main micromechanical properties upon the fracture behaviour of CNT-based composites. The second step of the proposed approach incorporates the previously estimated constitutive properties into a phase field fracture model to simulate crack initiation and growth in CNT-based composites. The modelling capabilities of the framework presented is demonstrated through three paradigmatic case studies involving mode I and mixed mode fracture conditions. 

Micromechanics-based phase field fracture modelling of CNT composites

We present a phase field-based electro-chemo-mechanical formulation for modelling mechanics-enhanced corrosion and hydrogen-assisted cracking in elastic–plastic solids. A multi-phase-field approach is used to present, for the first time, a general framework for stress corrosion cracking, incorporating both anodic dissolution and hydrogen embrittlement mechanisms. We numerically implement our theory using the finite element method and defining as primary fields the displacement components, the phase field corrosion order parameter, the metal ion concentration, the phase field fracture order parameter and the hydrogen concentration. Representative case studies are addressed to showcase the predictive capabilities of the model in various materials and environments, attaining a promising agreement with benchmark tests and experimental observations. We show that the generalised formulation presented can capture, as a function of the environment, the interplay between anodic dissolution- and hydrogen-driven failure mechanisms; including the transition from one to the other, their synergistic action and their individual occurrence. Such a generalised framework can bring new insight into environment–material interactions and the understanding of stress corrosion cracking, as demonstrated here by providing the first simulation results for Gruhl’s seminal experiments. 

MT. Niknejad

Papers

A generalised phase field model for fatigue crack growth in elastic–plastic solids with an efficient monolithic solver

A generalised phase field model for fatigue crack growth in elastic–plastic solids with an efficient monolithic solver

A coupled phase field formulation for modelling fatigue cracking in lithium-ion battery electrode particles

Micromechanics-based phase field fracture modelling of CNT composites

A generalised, multi-phase-field theory for dissolution-driven stress corrosion cracking and hydrogen embrittlement