Two levels of fidelity are used for minimum weight design of a composite bladestiffened panel subject to crack propagation constraints. The low fidelity approach makes use of an equivalent strain constraint calculated by a closed form solution for the stress intensity factor. The high fidelity approach uses the stress intensity factor directly as the constraint and computes it from the stress d...

MATCHED asymptotic expansions are used to examine the stress and pore pressure fields near the tip of a plane strain shear (mode II) crack propagating on an impermeable plane in a linear elastic diffusive solid. For propagation speeds V that are large compared with c/I, where c is the diffusivity and I is the cracklength, boundary layers are required at the crack-tip and on the line ahead of th...

Objectives To determine the incidence of crack formation and propagation in apical root dentin after retreatment procedures performed using ProTaper Universal Retreatment (PTR), Mtwo-R, ProTaper Next (PTN), and Twisted File Adaptive (TFA) systems. Materials and Methods The study consisted of 120 extracted mandibular premolars. One millimeter from the apex of each tooth was ground perpendicula...

This experimental study investigated the effects of quenching and tempering heat treatment on fatigue behavior and also tempering temperature and time holding of AISI 1060 steel. At first, the specimens were austenitized at 800˚C for 1 hour, and then were quenched in the water bath of 25˚C temperature. After that, tempering process was done at the temperature of 250˚C, 450˚C and 650˚C for 1 and...

Various theories in the past have addressed the correlation of material properties and the respective acoustic emission release during fracture. Whilst these theories yield good predictions for fundamental relationships, they neglect the dynamic displacements during crack formation. This paper presents first results for a new acoustic emission crack source model based on a finite element modell...

Water molecules play a fundamental role in the physics of slow crack propagation in glasses. It is commonly understood that, during stress-corrosion, water molecules that move in the crack cavity effectively reduce the bond strength at the strained crack tip and, thus, support crack propagation. Yet the details of the environmental condition at the crack tip in moist air are not well determined...

The presented work introduces a numerical parametric study on the crack propagation direction under mixed-mode conditions (mode I + II). It is conducted for the geometry of an eccentric asymmetric fourpoint bending of a single edge notched beam specimen; various levels of mode-mixity are ensured by modifications in the crack length and crack eccentricity. The direction of crack propagation is e...

To perform crack propagation in a solid model, a high computational power is required, mainly at three-dimensional mesh generation and structural analysis steps. At each crack propagation step, the mesh is rebuilt and a new structural analysis is performed. If a large scale cracked model is being analyzed, time consumed by mesh generation and analysis may be extremely large or even prohibitive ...

A two-dimensional numerical model of microstructural e ects in brittle fracture is presented, with an aim towards the understanding of toughening mechanisms in polycrystalline materials such as ceramics. Quasi-static crack propagation is modelled using the extended nite element method (X-FEM) and microstructures are simulated within the framework of the Potts model for grain growth. In the X-FE...

This study evaluated the tradeoffs amongst fatigue crack propagation resistance, wear resistance, and oxidative stability in a wide variety of clinically-relevant cross-linked ultra-high molecular weight polyethylene. Highly cross-linked re-melted materials showed good oxidation and wear performance, but diminished fatigue crack propagation resistance. Highly cross-linked annealed materials sho...