Crack-Path Effect on Material Toughness

1990 ◽  
Vol 57 (1) ◽  
pp. 97-103 ◽  
Author(s):  
Asher A. Rubinstein
Keyword(s):  
Crack Path ◽  
Numerical Procedure ◽  
Crack Tip ◽  
Elastic Solid ◽  
Singular Integral Equations ◽  
Length Change ◽  
Curvilinear Crack ◽  
Linear Elastic ◽  
System Of Cracks ◽  
Remote Stress

The material-toughening mechanism based on the crack-path deflection is studied. This investigation is based on a model which consists of a macrocrack (semi-infinite crack), with a curvilinear segment at the crack tip, situated in a brittle solid. The effect of material toughening is evaluated by comparison of the remote stress field parameters, such as the stress intensity factors (controlled by a loading on a macroscale), to effective values of these parameters acting in the vicinity of a crack tip (microscale). The effects of the curvilinear crack path are separated into three groups: crack-tip direction, crack-tip geometry pattern-shielding, and crack-path length change. These effects are analyzed by investigation of selected curvilinear crack patterns such as a macrocrack with simple crack-tip kink in the form of a circular arc and a macrocrack with a segment at the crack tip in the form of a sinusoidal wave. In conjunction with this investigation, a numerical procedure has been developed for the analysis of curvilinear cracks (or a system of cracks) in a two-dimensional linear elastic solid. The formulation is based on the solution of a system of singular integral equations. This numerical scheme was applied to the cases of finite and semi-infinite cracks.

Fracture characteristics of solids containing doubly-periodic arrays of cracks

1978 ◽  
Vol 360 (1702) ◽  
pp. 373-387 ◽  
Keyword(s):  
Closed Form Solution ◽  
Crack Tip ◽  
Elastic Solid ◽  
Singular Integral Equations ◽  
Form Solution ◽  
Stress Concentrations ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Fracture Characteristics ◽  
Crack Tip Opening

The stress relaxation process from the tips of doubly-periodic (rectangular and diamond-shaped) arrays of slit-like cracks contained in an infinite elastic solid is studied under both plane and anti-plane strain conditions. The displacement discontinuities due to slit-like cracks are represented by distributions of suitable dislocations. The latter are determined from singular integral equations resulting from the satisfaction of the traction-free conditions at the crack faces. In the absence of a closed form solution, these equations are solved numerically after expanding the non-singular part of the kernel in a series of Chebyshev polynomials. Results are presented for the extent of spread of plasticity from each of the cracks and for the crack-tip opening displacement as functions of the horizontal and vertical crack spacings and the externally applied stress and discussed from the point of fracture initiation from an array of stress concentrations. It is shown that an array of cracks can have a detrimental or beneficial effect on the fracture characteristics of the solid depending on the far-field state of stress. Moreover, the crack-tip opening displacement is practically independent of the horizontal separation of cracks for small values of the distance of vertical separation and depends only on the latter.

Investigation on Stress and Strain Singularity in LEFM

2006 ◽  
Vol 306-308 ◽  
pp. 31-36
Author(s):  
Zheng Yang ◽  
Wanlin Guo ◽  
Quan Liang Liu
Keyword(s):  
High Stress ◽  
Crack Tip ◽  
Plane Stress State ◽  
Stress And Strain ◽  
Linear Elastic ◽  
Geometrical Nonlinear ◽  
Maximum Crack ◽  
Elastic Fracture ◽  
Plain Strain ◽  
Strain Singularity

Stress and strain singularity at crack-tip is the characteristic of Linear Elastic Fracture Mechanics (LEFM). However, the stress, strain and strain energy at crack-tip may be infinite promoting conflicts with linear elastic hypothesis. It is indicated that the geometrical nonlinear near the crack-tip should not be neglected for linear elastic materials. In fact, the crack-tip blunts under high stress and strain, and the singularity vanishes due to the deformation of crack surface when loading. The stress at crack-tip may still be very high even though the singularity vanishes. The low bound of maximum crack-tip stress is the modulus of elastic in plane stress state, while in plain strain state, it is greater than the modulus of elastic, and will increase with the Poisson’s ratio.

Characterization of Crack Tip Damage Zone Formation on Alloy 625 During Fatigue Crack Growth at 750°C by Transmission EBSD Method

2017 ◽  
Author(s):  
Yuji Ozawa ◽  
Tatsuya Ishikawa ◽  
Yoichi Takeda
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Power Plants ◽  
Crack Path ◽  
Damage Zone ◽  
Crack Tip ◽  
Loading Frequency ◽  
Zone Formation ◽  
Alloy 625

In order to clarify the mechanism of fatigue crack growth in alloy 625, which is a candidate material for use in advanced ultra supercritical power plants, the crack tip damage zone formation after a crack growth test conducted in high temperature steam was investigated. It was observed that the oxide thickness at the crack tip tended to increase with decreasing cyclic loading frequency. The crack path was a mix of transgranular and intergranular fractures. According to the grain reference orientation deviation (GROD) maps, it was revealed that the density of geometrically necessary dislocations (GNDs) in the matrix along the crack path and ahead of crack tip increased with an increase in the fatigue crack growth rate (FCGR) due to environmental effects. It was observed that (1) mobile dislocations at the crack surface were blocked due to the thick oxide layer, resulting in an increase in the density of GNDs, and (2) an increase in the density of GNDs might induce stress concentration at the crack tip, deformation twinning, and the acceleration of FCGRs.

scholarly journals Dynamic Mixed Mode I-II Crack Kinking Under Oblique Stress Wave Loading in Brittle Solids

1990 ◽  
Vol 57 (1) ◽  
pp. 117-127 ◽  
Author(s):  
Chien-Ching Ma
Keyword(s):  
Stress Intensity ◽  
Stress Wave ◽  
Stress Intensity Factors ◽  
Crack Tip ◽  
Elastic Solid ◽  
Perturbation Parameter ◽  
Intensity Factors ◽  
Linear Superposition ◽  
Dynamic Stress Intensity Factors ◽  
Brittle Solids

The dynamic stress intensity factors of an initially stationary semi-infinite crack in an unbounded linear elastic solid which kinks at some time tf after the arrival of a stress wave is obtained as a function of kinking crack tip velocity v, kinking angle δ, incident stress wave angle α, time t, and the delay time tf. A perturbation method, using the kinking angle δ as the perturbation parameter, is used. The method relies on solving simple problems which can be used with linear superposition to solve the problem of a kinked crack. The solutions can be compared with numerical results and other approximate results for the case of tf = 0 and give excellent agreement for a large range of kinking angles. The elastodynamic stress intensity factors of the kinking crack tip are used to compute the corresponding fluxes of energy into the propagating crack-tip, and these results are discussed in terms of an assumed fracture criterion.

scholarly journals The influence of elastic deformations in high-strength structural materials on the hydrogen transport

2021 ◽  
Vol 225 ◽  
pp. 01010
Author(s):  
Polina Grigoreva ◽  
Elena Vilchevskaya ◽  
Vladimir Polyanskiy
Keyword(s):  
Chemical Potential ◽  
Potential Gradient ◽  
Elastic Solid ◽  
High Strength ◽  
Ideal Gas ◽  
Linear Elastic ◽  
Coupled Diffusion ◽  
Elastic Boundary ◽  
Linear Effects ◽  
Solid System

In this work, the diffusion equation for the gas-solid system is revised to describe the non-uniform distribution of hydrogen in steels. The first attempt to build a theoretical and general model and to describe the diffusion process as driven by a chemical potential gradient is made. A linear elastic solid body and ideal gas, diffusing into it, are considered. At this stage, we neglect any traps and non-linear effects. The coupled diffusion-elastic boundary problem is solved for the case of the cylinder under the tensile loads. The obtained results correspond to the experimental ones. Based on them, the assumptions about the correctness of the model and its further improvement are suggested.

Effect of inhomogeneous distribution of non-metallic inclusions on crack path deflection in G42CrMo4 steel at different loading rates

2015 ◽  
Author(s):  
S. Henschel ◽  
L. Krüger
Keyword(s):  
Fracture Mechanics ◽  
Crack Growth ◽  
Crack Path ◽  
Testing Machine ◽  
Crack Tip ◽  
Crack Growth Resistance ◽  
Impact Testing ◽  
Inhomogeneous Distribution ◽  
Metallic Inclusions ◽  
Crack Tip Blunting

An inhomogeneous distribution of non-metallic inclusions can result from the steel casting process. The aim of the present study was to investigate the damaging effect of an inhomogeneous distribution of nonmetallic inclusions on the crack extension behavior. To this end, the fracture toughness behavior in terms of quasi-static J-?a curves was determined at room temperature. Additionally, dynamic fracture mechanics tests in an instrumented Charpy impact-testing machine were performed. The fracture surface of fracture mechanics specimens was analyzed by means of scanning electron microscopy. It was shown that an inhomogeneous distribution significantly affected the path and, therefore, the plane of crack growth. Especially clusters of non-metallic inclusions with a size of up to 200 ?m exhibited a very low crack growth resistance. Due to the damaging effect of the clusters, the growing crack was strongly deflected towards the cluster. Furthermore, crack tip blunting was completely inhibited when inclusions were located at the fatigue precrack tip. Due to the large size of the non-metallic inclusion clusters, the height difference introduced by crack path deflection was significantly larger than the stretch zone height due to the crack tip blunting. However, the crack path deflection introduced by a cluster was not associated with a toughness increasing mechanism. The dynamic loading ( 1 0.5 5 s MPam 10 ? ? K? ) did not result in a transition from ductile fracture to brittle fracture. However, the crack growth resistance decreased with increased loading rate. This was attributed to the higher portion of relatively flat regions where the dimples were less distinct.

Study on the Relationship Between Interaction Factors and Stress Intensity Factor for Elliptical Flaws

2017 ◽  
Author(s):  
Kisaburo Azuma ◽  
Yinsheng Li ◽  
Kunio Hasegawa
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Front ◽  
Elastic Solid ◽  
Element Analysis ◽  
Linear Elastic ◽  
Close Proximity ◽  
Interaction Factors ◽  
The Relationship

The interaction of multiple flaws in close proximity to one another may increase the stress intensity factor of the flaw in structures and components. This interaction effect is not distributed uniformly along the crack front. For instance, the strongest interaction is generally observed at the point closest to a neighboring flaw. For this reason, the closest point could show a higher value of the stress intensity factor than all other points in some cases, even if the original value at the point of the single flaw is relatively low. To clarify the condition when the closest point shows the maximum stress intensity factor, we investigated the interaction of two similar elliptical flaws in an infinite model subjected to remote tension loading. The stress intensity factor of the elliptical flaws was obtained by performing finite element analysis of a linear elastic solid. The results indicated that the interaction factors along the crack front can be expressed by a simple empirical formula. Finally, we show the relationship between geometrical features of the flaw and the stress intensity factor at the closest point to a neighboring flaw.

The Neumann problem in plane deformations of a micropolar elastic solid with micropolar surface effects

2020 ◽  
Vol 26 (1) ◽  
pp. 30-44
Author(s):  
Alireza Gharahi ◽  
Peter Schiavone
Keyword(s):  
Neumann Problem ◽  
Existence Theorems ◽  
Surface Elasticity ◽  
Elastic Solid ◽  
Singular Integral Equations ◽  
Surface Effects ◽  
Integral Representations ◽  
Matrix Functions ◽  
Micropolar Elasticity ◽  
The Neumann Problem

We consider the Neumann problem in a theory of plane micropolar elasticity incorporating micropolar surface effects. The incorporation of surface elasticity utilizes the Eremeyev–Lebedev–Altenbach shell model, leading to a set of second-order boundary conditions describing the separate micropolar elasticity of the surface. The Neumann problem is of particular interest, since the question of solvability is complicated by the fact that the corresponding systems of homogeneous singular integral equations admit nontrivial solutions that affect the solvability of both the interior and exterior Neumann boundary value problems. We overcome this difficulty by constructing integral representations of the solutions based on specifically constructed auxiliary matrix functions leading to uniqueness and existence theorems in appropriate classes of smooth matrix functions.

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