Search results for "Fracture Mechanics"
showing 10 items of 102 documents
Boundary elements analysis of adhesively bonded piezoelectric active repair
2009
Abstract This paper presents the analysis of active piezoelectric patches for cracked structures by the boundary element method. A two-dimensional boundary integral formulation based on the multidomain technique is used to model cracks and to assemble the multi-layered piezoelectric patches to the host damaged structures. The fracture mechanics behavior of the repaired structures is analyzed for both perfect and imperfect interface between patches and host beams. The imperfect interface, representing the adhesive between two different layers, is modeled by using a “spring model” that involves linear relationships between the interface tractions, in normal and tangential directions, and the …
Molecular Dynamics Study of Copper and Aluminum under Mechanical Strain
1998
AbstractMechanical properties of copper and aluminum have been studied using finite temperature molecular dynamics simulations. Atomic interactions have been described by a many-atom effective medium potential, which takes into account interactions up to third neighbors. The computed elastic constants showed good agreement with experimental data. Encouraged by these results the model was applied to study fracture in copper. Systems with a grain boundary and an initial cut serving as a crack seed have been studied. In the first case, crack nucleation and propagation took place exclusively at the grain boundary. In the second case, dislocation propagation was observed in one of the <110>…
Molecular-dynamics study of copper with defects under strain
1998
Mechanical properties of copper with various types of defects have been studied with the molecular-dynamics method and the effective-medium theory potential both at room temperature and near zero temperature. The loading has been introduced as constant rate straining and the dynamics of the process region of fracture is purely Newtonian. With the model three types of defects were studied: point defects, grain boundary, and an initial void serving as a crack seed. Point defects were seen to decrease the system strength in terms of fracture stress, fracture strain, and elastic modulus. Due to random microstructure, highly disordered systems turned out to be isotropic, which on the other hand …
Crack bifurcations in a strained lattice
1996
Dynamic crack propagation in a strained, granular, and brittle material is investigated by modeling the material as a lattice network of elastic beams. By tuning the strain and the ratio of axial to bending stiffness of the beams, a crack propagates either straight, or it branches, or it bifurcates. The crack tip velocity is calculated approximately for cracks that propagate straight. In a bifurcated crack the number of broken beams follows a scaling law. The shape of the branches is found to be the same as in recent experiments.
Nonsmooth Mechanics. Convex and Nonconvex Problems
1999
Nonlinear, multivalued and possibly nonmonotone relations arise in several areas of mechanics. A multivalued or complete relation is a relation with complete vertical branches. Boundary laws of this kind connect boundary (or interface) quantities. A contact relation or a locking mechanism between boundary displacements and boundary tractions in elasticity is a representative example. Material constitutive relations with complete branches connect stress and strain tensors, or, in simplified theories, equivalent stress and strain quantities. A locking material or a perfectly plastic one is represented by such a relation. The question of nonmonotonicity is more complicated. One aspect concerns…
Adaptive Planning in-Service Inspections of Fatigued Structures in Damage Tolerance Situations via Observations of Crack Growth Process
2017
From an engineering standpoint the fatigue life of a fatigued structure consists of two periods: (i) crack initiation period, which starts with the first load cycle and ends when a technically detectable crack is presented, and (ii) crack propagation period, which starts with a technically detectable crack and ends when the remaining cross section can no longer withstand the loads applied and fails statically. The main aim of this paper is to present more accurate innovative stochastic fatigue model for adaptive planning inspections of fatigued structures in damage tolerance situations via observations of crack growth process during a crack propagation period. A new crack growth equation is…
Numerical simulation of fatigue-driven delamination using interface elements
2005
This paper presents a computational technique for the prediction of fatigue-driven delamination growth in composite materials. The interface element, which has been extensively applied to predict delamination growth due to static loading, has been modified to incorporate the effects of cyclic loading. Using a damage mechanics formulation, the constitutive law for the interface element has been extended by incorporating a modified version of a continuum fatigue damage model. The paper presents details of the fatigue degradation strategy and examples of the predicted fatigue delamination growth in mode I, mode II and mixed mode I/II are presented to demonstrate that the numerical model mimics…
Digital image correlation analysis of interfacial debonding properties and fracture behavior in concrete
2007
The use of digital image correlation (DIC) as a fracture mechanics tool is described, for two projects currently underway. The goal of the first project is to examine the bond between carbon fiber reinforced polymers (CFRP) and concrete substrates. The second project involves the interfacial transition zone (ITZ) of plain concrete, and the softening and fracture behavior of this region. For both projects, DIC allows for precise measurement of the surface displacements of the deforming materials. The resulting strain data are higher in resolution than is possible with other experimental techniques. For both projects, the DIC results are being used to determine bond constitutive laws, which w…
Mooring Line Components With Semi-Brittle Behavior: Verification of Fitness for Purpose
2011
Low impact energy for Charpy V Notch (CVN) specimens and associated low Crack Tip Opening Displacement (CTOD) values have occurred on several occasions in high strength steel offshore mooring components. In the present work an Engineering Critical Assessment (ECA) for shackles has been carried out to demonstrate fitness for purpose. Typical values for CVN and CTOD are 17 Joules and 0.01 mm respectively at design temperature. The purpose of the present work is to demonstrate that even in the case where normal quality requirements are not met, the shackles may still have enough structural integrity and fatigue durability to withstand the load spectrum in the field during the planned target se…
Numerical Analysis of Piezoelectric Active Repair in the Presence of Frictional Contact Conditions
2013
The increasing development of smart materials, such as piezoelectric and shape memory alloys, has opened new opportunities for improving repair techniques. Particularly, active repairs, based on the converse piezoelectric effect, can increase the life of a structure by reducing the crack opening. A deep characterization of the electromechanical behavior of delaminated composite structures, actively repaired by piezoelectric patches, can be achieved by considering the adhesive layer between the host structure and the repair and by taking into account the frictional contact between the crack surfaces. In this paper, Boundary Element (BE) analyses performed on delaminated composite structures …