Molecular Dynamics (MD) simulations have been carried out to understand the mechanics of crack
interaction with Grain Boundary (GB) under different scenarios. Specifically, different stages of a growing
crack, like crack growth initiation and arrest at GB have been studied. The study was done by evaluating
the Stress Intensity Factor (SIF) using near-tip stress field at each of these stages i.e. crack growth initiation
and arrest at GB. To perform this simulation, an understanding of rotation transformation has been applied
to form an aluminum bi-crystal.
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Themes: Failure Mechanisms in Advanced Materials and Structures
LONG-TERM PERFORMANCE OF POST-INSTALLED CONCRETE SCREWS
Concrete screws are a type of anchor used in structural and non-structural applications in uncracked and cracked concrete. The load transfer is based on mechanical interlock between the threads and concrete. Like all anchor products, they undergo rigorous testing during product assessment which at the moment does not cover the sustained load behavior. This investigation aims at studying the sustained-load behaviour of concrete screws by performing a series of tensile tests. Short-term tests were first performed from which the ultimate load capacity of the screws was determined. Long-term tests were then performed at different load levels, selected as a function of the short-term capacity. The time to failure and displacements were recorded throughout each test. The resulting experimental data was used to generate time-to-failure curves and fit the regression models that are currently used for the long-term assessment of chemically bonded anchors. Finally, the predicted long-term capacity for a 50-year lifetime is presented and compared to adhesive anchors.
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NON-FOURIER HEAT CONDUCTION AND NONLOCAL THEORY, RECENT PROGRESS AND APPLICATION IN THERMAL FRACTURE ANALYSIS [Keynote]
Non-Fourier heat conduction theories have recently been introduced to thermal stress analysis to account for the wave-like behavior of heat conduction under extreme thermal environments, such as high temperature gradient, extremely low temperature, or heat transport in heterogenous microstructures. When considering the highly localized heating process in laser manufacturing, nonlocal heat conduction needs to be included in the heat conduction equation. Combined non-Fourier, nonlocal thermoelastic theories revealed new phenomena in thermal stress analysis of cracked structures. This presentation summarizes some recent progress in thermal fracture analysis using nonlocal, non-Fourier thermoelastic theories.
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USING A HIERARCHY OF POROSITY TO IMPROVE THE FRACTURE TOUGHNESS OF METAMATERIALS
Mechanical metamaterials have been quickly growing in popularity based on their lightweight, multifunctional properties. One of the factors limiting their widespread adoption in weight baring applications, however, is their poor fracture toughness compared to bulk materials. Arrestor planes have been added to gyroid surface metamaterials and solid beams to manipulate the path of a propagating crack and improve the fracture toughness. The arrestor planes used a hierarchy of porosity interacting with the features inherent in the gyroid topology to direct propagating cracks into natural features that served to arrest the crack. This methodology was tested in both brittle polymer and stainless steel with toughening ranging from 22% to 300% depending on material.
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THE IMPACT OF MULTIAXIALITY ON THE STATIC AND FATIGUE FRACTURE OF CARBON/EPOXY POLYMER COMPOSITES
Polymer composites can be used in a plethora of applications, creating lightweight and durable structures. Their anisotropy together with the complexity of the laminate structure can lead to multiaxial stress states within the material, which can significantly affect the fracture process. In this work, carbon/epoxy laminates with different stacking sequences, and consequently different stress states, are tested under static and fatigue conditions. It is demonstrated that multiaxiality plays a crucial role in the fracture process and that shear stresses create severe damage conditions within the material.
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STRONG AND TOUGH FIBROUS HYDROGELS REINFORCED BY MULTISCALE HIERARCHICAL STRUCTURES WITH MULTIMECHANISMS [Keynote]
Tough natural materials such as nacre, bone, and silk exhibit multiscale hierarchical structures where distinct toughening mechanisms occur at each level of the hierarchy, ranging from molecular uncoiling to microscale fibrillar sliding to macroscale crack deflection. An open question is whether and how the multiscale design motifs of natural materials can be translated to the development of next-generation biomimetic hydrogels. Here, we will discuss a recent work [1] on fabricating strong and tough hydrogel with architected multiscale hierarchical structures using a freeze-casting–assisted solution substitution strategy. The underlying multiscale multimechanisms are attributed to the gel’s hierarchical structures; hydrogen bond–enhanced fibers with nanocrystalline domains; and cross-linked strong polyvinyl alcohol chains with chain-connecting ionic bonds. This study establishes a blueprint of structure-performance mechanisms in tough hierarchically structured hydrogels and can inspire advanced design strategies for other promising hierarchical materials.
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