Damage and Fracture Mechanics of Advanced Materials Overview

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Songyun Ma

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+49 241 80 98286

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Overview

In many high-performance engineering and biomedical materials, damage and fracture processes under operating conditions are coupled with phase transformation, electrochemical reaction, wear, diffusion and fluid transport, such as degradation and ageing of silicon electrodes in lithium-ion batteries, corrosion fatigue of biodegradable implants and thermomechanical fatigue of high-temperature alloys. In the research field of damage and fracture mechanics, we focus on experimental and numerical methods for predicting the damage and fracture behaviour of novel high-performance materials, which plays an essential role in assessing the mechanical integrity of highly stressed components under complex loads. Based on innovative material testing and numerical approaches, we develop multiscale methods for modelling complex material damage and component failure in multiphysics environments.

 

Multiscale modelling of corrosion-fatigue behaviours of magnesium alloys

As revolutionary biomedical materials, biodegradable magnesium alloys have a broad application prospect in orthopaedic implants. Recently, various surface modification technologies have been developed to control their rapid corrosion rates in physiological environments and overcome the related clinical problems. However, corrosion-fatigue damage under long-term complex loadings can result in the failure of coated magnesium implants during the healing process. The accurate evaluation of the degradation of structural integrity required a deep understanding of corrosion-fatigue mechanisms of magnesium alloys across different scales.

To this end, we develop multi-physics and multiscale computational methods to study the corrosion-fatigue behaviour of magnesium alloys in physiological environments. Artificial intelligence is utilised to establish the structure-property relationship for coated magnesium alloys. Furthermore, in vitro biological tests are used to validate the computational results.

 

Fracture and fatigue of fibre-reinforced hydrogel composites

Time-dependent fracture in fibre-reinforced hydrogel composites Copyright: © IAM Time-dependent fracture in fibre-reinforced hydrogel composites

Hydrogels are highly hydrated polymer networks swollen by water molecules. Due to their biocompatibility and biodegradability, hydrogels have been extensively used in biomedical and bioengineering applications. Recently, novel hydrogel composites have been developed by introducing reversible physical bonds and reinforced with nano- or microfibres to improve fracture toughness. The hydrogel composites generally exhibit time-dependent deformation behaviours, which are mainly attributed to chain rearrangements, breaking/reforming of physical chains and fluid transport. These coupled time-dependent processes and the anisotropy significantly influence the fracture and fatigue of hydrogel composites. In this context, we aim to develop advanced constitutive models within a thermodynamically consistent frame of continuum mechanics to describe the nonlinear deformations, fluid transport and damage of hydrogel composites. According to the mechanisms of fracture and fatigue, efficient computational methods are developed to predict the fatigue behaviour of hydrogel composites. These research results for understanding and quantifying the time-dependent fatigue behaviours will facilitate the development of the next generation of tough hydrogel materials or devices.

 

3D-printed metallic glasses: microstructural characterization, mechanical properties and modeling

Bulk metallic glass (BMG), a novel class of metallic alloys, exhibits mechanical properties due to amorphous structures. Selective laser melting (SLM), a recently developed additive manufacturing technique, enables the production of BMG components with intricate geometries. The present research focuses on addressing the structure-property relationships of Zr-based SLM-processed BMGs, including the characterization of microstructures, the influence of printing defects on the mechanical properties and the related modelling and simulations.

For characterising the microstructures of Zr-based BMGs processed under different SLM conditions, we utilise non-destructive X-ray micro-CT and scanning electron microscopy to evaluate the morphology of irregular lack-of-fusion pores and gas-induced pores. Nanoindentation tests with various loads are carried out to determine the mechanical properties of Zr-based SLM-processed BMGs. Moreover, 3D micromechanical simulations of defect-free and defect-containing samples are used to study the structure-property relationship by correlating the structural defects to the mechanical performance. At the macroscopic level, we develop a thermodynamically-consistent nonlocal damage model to describe the unique deformation and damage behaviours of BMGs. The proposed anisotropic damage model accounts for large inelastic deformations, damage-induced anisotropy and tension-compression asymmetry (TCA). The gradient-type enhancement of the Helmholtz-free-energy function is adopted to overcome the mesh dependency of finite element computations. Both unnotched and notched micro-cantilever beam experiments are used to validate the computational simulations of shear band formations and damage patterns in BMG samples under different loading conditions.