In this work a theoretical/analytical, computational and experimental study of unidirectional glass-fiber reinforced epoxy composites is carried out. The concept of boundary interphase is used in order to determine the elastic constants of the composite. A finite element analysis is adopted in order to correlate with the derived theoretical values of the elastic constants. Finally, these results are compared with experimental findings obtained from tensile experiments performed on composites of the material used in order to predict the fracture of composites.
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Themes: Failure Mechanisms in Advanced Materials and Structures
USING ANALYTICAL APPROACH FOR CALCULATING LOCALIZED STRESS FIELD NEAR CENTRAL SLIT CRACK IN AMORPHOUS MATERIAL AT ATOMISTIC SCALE
The localized stress field helps in predicting the crack initiation and its growth in fracture mechanics. At an atomistic scale, a localized stress field has been calculated by virial theorem for anisotropic materials. However, there is still confusion regarding its validation and comparison, as its origin differs from continuum stress. Moreover, finding the localized stress field at the atomic site for amorphous materials are complicated and tedious by the virial approach due to the presence of different elements at disordered positions. Therefore, there is a need to develop a method which does not have there drawbacks. The present work has developed an analytical approach to calculate localized stress fields at an atomistic scale. First, the stress field calculated with this method has been validated in crystalline materials like silicon with virial and finite element (FEM) results. As this method validates linear elasticity near the crack tip. The same localized approach has been used in silica to validate stress field with FEM result. The proposed method in the present work can be used under mixed-mode conditions to study crack initiation and its growth in amorphous solids.
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MECHANICS OF INTERACTION OF GROWING CRACK WITH GRAIN BOUNDARY IN BICRYSTAL SOLIDS
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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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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