Fracture Mechanics of Periodic Multilayers With Different Microstructural Scales and Moduli Contrast

2008 ◽  
Vol 75 (5) ◽  
Author(s):  
Linfeng Chen ◽  
Marek-Jerzy Pindera
Keyword(s):  
Fracture Mechanics ◽  
Crack Opening ◽  
Strain Energy Release ◽  
Computational Effort ◽  
Mode I ◽  
Preliminary Calculation ◽  
Opening Displacement ◽  
Microstructural Refinement ◽  
Loading Mode ◽  
Microstructural Effects

In a recent investigation of microstructural effects in finite periodic multilayers, we have shown that under Mode I loading, the crack-opening displacement approaches that of the same crack in an equivalent homogenized material as the microstructure comprised of alternating stiff and soft layers becomes increasingly finer. In contrast, Mode I stress intensity factor asymptotically converges to values that depend on the stiffness of the cracked layer. Preliminary calculation of Mode I strain energy release rate as a function of the microstructural refinement suggested that this may be a better fracture mechanics parameter for assessing fracture toughness of periodic layered media. Herein, we extend the above investigation by considering both Mode I and II loading to study the effect of layer modulus ratio on fracture mechanics parameters as a function of microstructural refinement. The previously introduced concept of partial homogenization of the microstructure sufficiently far from the crack is also pursued in order to gauge its efficiency in correctly capturing fracture mechanics parameters with a minimum of computational effort. The fracture mechanics parameters are shown to be influenced by the local microstructure to an extent that depends on the layer modulus mismatch. An accurate calculation of these parameters requires the retention of several layers adjacent to the affected cracked layer whose number depends on the modulus mismatch and loading mode.

Determination of cohesive laws in wood bonded joints under mode I loading using the DCB test

Holzforschung ◽  
2013 ◽  
Vol 67 (8) ◽  
pp. 913-922 ◽  
Author(s):  
Filipe G.A. Silva ◽  
Jose Xavier ◽  
Fábio A.M. Pereira ◽  
José J.L. Morais ◽  
Nuno Dourado ◽  
...  
Keyword(s):  
Strain Energy ◽  
Inverse Method ◽  
Strain Energy Release Rate ◽  
Direct Method ◽  
Crack Opening ◽  
Strain Energy Release ◽  
Mode I ◽  
Bonded Joints ◽  
Opening Displacement ◽  
Cohesive Laws

Abstract The cohesive laws (CLs) have been investigated by means of direct and inverse methods concerning wood bonded joints under pure mode I. The experimental results were obtained by tests with double cantilever beam. The direct method is based on the differentiation of the relation between strain energy release rate and crack opening displacement at the crack tip. An equivalent crack method was used to evaluate the strain energy release rate in the course of the test without monitoring the crack length, which is difficult to observe exactly. The crack opening displacement was determined by postprocessing local displacements measured by digital image correlation. The inverse method requires a previous assumption of the CL shape, and as such, a trilinear law with bilinear softening relationship was selected. The cohesive parameters were identified by an optimization procedure involving a developed genetic algorithm. The idea is to minimize an objective function that quantifies the difference between the experimental and the numerical load-displacement curves resulting from the application of a given law. A validation procedure was performed based on a numerical analysis with finite elements. Both methods in focus provided good agreement with the experimental data. It was observed that CLs adopted by the inverse method are consistent with the ones obtained with the direct method.

A mode I crack with multiple islands of ideal contact between the crack faces: An asymptotic model

2021 ◽  
pp. 108128652110214
Author(s):  
Ivan Argatov
Keyword(s):  
Crack Opening ◽  
Reduction Factor ◽  
Mode I ◽  
Asymptotic Model ◽  
Mode I Crack ◽  
Opening Displacement ◽  
Multiple Contacts ◽  
Scaling Hypothesis ◽  
Penny Shaped Crack ◽  
Crack Faces

The problem of a mode I crack having multiple contacts between the crack faces is considered. In the case of small contact islands of arbitrary shapes, which are arbitrarily located inside the crack, the first-order asymptotic model for the crack opening displacement is constructed using the method of matched asymptotic expansions. The case of a penny-shaped crack has been studied in detail. A scaling hypothesis for the compliance reduction factor is formulated.

Crack Opening Area for an Isolated Crack Subjected to a Symmetric Mode I Stress Distribution

2004 ◽  
Author(s):  
E. Smith
Keyword(s):  
Stress Distribution ◽  
Crack Opening ◽  
Operating Conditions ◽  
Mode I ◽  
Stress Distributions ◽  
Simple Derivation ◽  
Opening Displacement ◽  
System A ◽  
Simplified Procedure ◽  
Leak Before Break

In developing a leak-before-break case for a component in a pressurized system, a key element is an estimation of the size of through-thickness crack that will give a measurable leakage under normal operating conditions, and this requires a knowledge of the crack opening area. In this context, the paper presents a simple derivation of an expression for the crack opening area associated with an isolated crack that is subjected to a general Mode I symmetric tensile stress distribution which could arise from a combination of applied and residual stresses. The paper also presents a simple derivation of an expression for the crack opening displacement at the crack centre which, coupled with the assumption that the crack opening profile conforms to an elliptical shape, has been used as the basis for a simplified procedure for estimating the crack opening area. The resulting expressions are validated by comparing them with known results for specific stress distributions. They are also used to give new results for a cosine stress distribution.

EFG Virtual Crack Closure Technique for the Determination of Stress Intensity Factor

2011 ◽  
Vol 250-253 ◽  
pp. 3752-3758 ◽  
Author(s):  
Xue Ping Chang ◽  
Jun Liu ◽  
Shi Rong Li
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Closure ◽  
Crack Opening ◽  
Crack Tip ◽  
Strain Energy Release ◽  
Virtual Crack Closure Technique ◽  
Opening Displacement ◽  
Closure Technique

The aim of this paper is to introduce a virtual crack closure technique based on EFG method for thread-shape crack. The cracked component is discretized and the displacement field is determined using a coupled FE/EFG method, by which EFG nodes are arranged in the vicinity of crack tip and FE elements in the remain part in order to improve computational efficiency. Two typical parameters, nodal force and crack opening displacement attached to crack tip are calculated by means of setting up an auxiliary FE zone around crack tip. Strain energy release rate (SERR), further stress intensity factor (SIF) are determined by the two parameters. The method to calculate SIF is named as virtual crack closure technique based on EFG method. It is showed by several numerical examples that using the method presented in this paper, SIF on the crack tip can be obtained accurately.

Mode Mixity in the Fracture Toughness Evaluation of Heat-Affected-Zone Material Using SEN(T) Experiment

2021 ◽  
Author(s):  
Sureshkumar Kalyanam ◽  
Yunior Hioe ◽  
Gery Wilkowski
Keyword(s):  
Fracture Toughness ◽  
Crack Growth ◽  
Heat Affected Zone ◽  
Crack Opening ◽  
Growth Direction ◽  
Mode I ◽  
Mode Ii ◽  
Mode Mixity ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement

Abstract SEN(T) specimens provide good similitude for surface cracks (SC) in pipes, where a SC structure has lower constraint condition than typically used fracture toughness specimens such as SEN(B) , and C(T). Additionally, the SENT specimen eliminates concern of material anisotropy since the crack growth direction in the SENT is the same as in a surface-cracked pipe. While the existing recommended and industrial practices for SEN(T) have been developed based on assumption of homogenous or mono-material across the crack, their applicability for the evaluation of fracture toughness of heat-affected-zone (HAZ) were evaluated in this investigation. When conducting tests on SEN(T) specimens with prescribed notch/crack in the HAZ, the asymmetric deformation around the crack causes the occurrence of a combination of Mode-I (crack opening) and Mode-II (crack in-plane shearing) behavior. This mode mixity affects the measurement of the crack-tip-opening-displacement (CTOD) and evaluation of elastic-plastic fracture mechanics parameter, J. The CTOD-R curve depicts the change in toughness with crack growth, in a manner similar to the J-R curve methodology. The experimental observations of Mode-I and Mode-II behavior seen in tests of SEN(T) specimens with notch/crack in the HAZ and as the crack propagates through the weld/HAZ thickness were investigated. The issues related to and the changes needed to account for such behavior for the development of recommended practices or standards for SEN(T) testing of weld/HAZ are addressed.

Fracture Mechanics

2012 ◽  
pp. 101-145
Keyword(s):  
Fracture Mechanics ◽  
Strain Energy ◽  
Subsequent Development ◽  
Strain Energy Release ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Linear Elastic ◽  
Energy Release Rates ◽  
Cracked Structures ◽  
Crack Tip Opening

Abstract Fracture mechanics is the science of predicting the load-carrying capabilities of cracked structures based on a mathematical description of the stress field surrounding the crack. The fundamental ideas stem from the work of Griffith, who demonstrated that the strain energy released upon crack extension is the driving force for fracture in a cracked material under load. This chapter provides a summary of Griffith’s work and the subsequent development of linear elastic and elastic-plastic fracture mechanics. It includes detailed illustrations and examples, familiarizing readers with the steps involved in determining strain energy release rates, stress intensity factors, J-integrals, R-curves, and crack tip opening displacement parameters. It also covers fracture toughness testing methods and the effect of measurement variables.

Fracture mechanics in design and service: ‘living with defects’ - Assessment of defects: the c.o.d. approach

1981 ◽  
Vol 299 (1446) ◽  
pp. 155-167 ◽  
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Crack Opening ◽  
Local Stress ◽  
Concentration Effects ◽  
Opening Displacement ◽  
Widespread Application ◽  
Linear Elastic ◽  
Applied Loading ◽  
Displacement Approach

In welded construction particular problems arise with the application of fracture mechanics for the assessment of the effect of defects on structural performance. In many practical cases the use of plane strain linear elastic fracture mechanics methods is invalidated by the actual material thicknesses of interest, by residual stresses or by local stress concentration effects, and by local yielding. The crack opening displacement approach was originally devised as a means of extending linear elastic methods to more widespread application to welded structures. This required the development of a means of assessing fracture toughness, and a means of relating this fracture toughness to the applied loading conditions, and to sizes and types of defects which might be present. The success of this method of assessing defects over a period of some 10-12 years will be illustrated, together with a discussion of the inherent limitations of the approach and possible improvements resulting from recent research into slow tearing and design curve relationships.

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