by Ayatollahi, M.R.; Pavier, M.J.; Smith, D.J.

The elastic T-stress has been recognised as a measure of constraint around the tip of a crack in contained yielding problems. A review of the literature indicates that most methods for obtaining T are confined to simple geometry and loading configurations. This paper explores direct use of finite element analysis for calculating T. It is shown that for mode I more reliable results with less mesh refinement can be achieved if crack flank nodal displacements are used. Methods are also suggested for calculating T for any mixed mode I/II loading without having to calculate stress intensity factors. There is good agreement between the results from the proposed methods and analytical results. T-stress is determined for a test configuration designed to investigate brittle and ductile fracture in mixed mode loading. It is shown that in shear loading of a cracked specimen T vanishes only when a truly antisymmetric field of deformation is provided. However this rarely happens in practice and the presence of T in shear is often inevitable. It is shown that for some cases the magnitude of T in shear is much more than that for tension. The effect of crack length is also investigated.

DOI: 10.1023/A:1007581125618
Print publication date: 6/1/1998
View article on SpringerLink

by Lazzarin, P.; Tovo, R.; Filippi, S.

In fatigue crack growth analysis it is essential to know the stress distributions in the neighbourhood of stress raisers. If such distributions ahead of the uncracked notch are known, stress intensity factors may be obtained via the weight function or other methods. The procedure described in the present paper reconsiders the principal elastic stress expressions already reported by the authors for infinite plates with semi-infinite symmetric V-shaped notches and adapts them to some practical cases, in which the mutual influence of the notches as well as that of the plate finite size play an important role in stress distributions. The aim is therefore to give an approximate close-form solution for the longitudinal stress, valid for the entire ligament length, namely from notch tip to notch tip. Theoretical and numerical stress values are compared on this line, examining plates with semicircular, V and U-shaped notches subjected to remote uniaxial tension.

DOI: 10.1023/A:1007577629523
Print publication date: 6/1/1998
View article on SpringerLink

by Hurtado, J.A.

A complete solution is presented for the problem of a mode III crack in an infinite elastic perfectly-plastic solid under internal shear stress. This problem is the anti-plane strain equivalent of a mode I crack with internal pressure. The problem is transformed into a boundary value problem for a potential function. The particular case when the applied stress σA is equal to the yield stress σ0 is solved analytically, and the distance to the elastic-plastic boundary is obtained in closed form. The general case when σA σ0 is solved numerically by using the Boundary Element Method for potential problems. Numerical results are given for the distance to the elastic-plastic boundary and the crack tip opening displacement. The extent of the plastic zone ahead of the crack tip is shown to vary linearly with the ratio σA/σ0) when 0.5 ≤ (σA/σ0) ≤ 1.

DOI: 10.1023/A:1007422431415
Print publication date: 6/1/1998
View article on SpringerLink

by Balkan, H.; Madenci, E.

By using techniques appropriate to mixed boundary value problems, this study addresses the determination of stress intensity factors for a circular interface debonding between a thin layer and a substrate subjected to nearly uniform temperature change. The solution method involves three-dimensional equilibrium equations of thermo-elasticity under axisymmetry conditions. The stress intensity factors are obtained by solving the resulting pair of coupled singular integral equations numerically.

DOI: 10.1023/A:1007441514577
Print publication date: 6/1/1998
View article on SpringerLink

by Liu, Jin; Sutton, Michael; Lyons, Jed; Deng, Xiaomin

Using a novel, noncontacting experimental method, the values for creep fracture parameters C(t) and C* have been experimentally quantified from full field, time-dependent surface deformation measurements in the crack-tip region for the first time. Near-tip experimental deformation results were obtained for a stationary crack in alloy IN800 at 650^C and compared to predictions based on both far-field measurement and finite element analyses. Results indicate that (a) for short times, the C(t)- integral is time and path dependent; (b) for long times, the C(t)-integral approached a constant for all paths which is agreement with C* values obtained from far-field experimental data. Comparisons of experimental results with FEM solutions were illustrated by means of radial and angular variations, full-field contour plots, as well as line integration form. Results from these comparisons indicate that (c) the experimental strain data portrays trends similar to those observed in the FEM solutions; (d) experimental, near-tip strain values were different in magnitude from the predicted values for all angles, and (e) the transition time obtained from the tests was about 10 times longer than that calculated from a formula proposed by Riedel and Rice (1980), indicating that primary creep cannot be neglected for this material.

DOI: 10.1023/A:1007485813696
Print publication date: 6/1/1998
View article on SpringerLink

by Lorriot, T.; Martin, E.; Quenisset, J.M.; Rebière, J.P.

A new experimental procedure is proposed which allows the determination of parameters of mass-spring models used to analyse the CHARPY impact test. It is based on the measurement of the tup load and the specimen deflection during the impact test. The contact stiffness between the tup and the specimen is derived from the ratio of the specimen deflection over the tup displacement. The model predictions are compared with experimental results obtained from impact tests performed on PMMA specimens.

DOI: 10.1023/A:1007583731072
Print publication date: 6/1/1998
View article on SpringerLink

by Meguid, S. A.; Wang, X. D.

In this article, we examine the dynamic interaction between two cracks in a piezoelectric medium under incident antiplane shear wave loading. The theoretical formulations governing the steady-state problem are based upon the use of integral transform techniques and a self-consistent iterative method. The resulting dynamic stress intensity factors at the interacting cracks are obtained by solving the appropriate singular integral equations using Chebyshev Polynomials at different loading frequencies. Numerical examples are provided to show the effect of the geometry of the cracks, the piezoelectric constants of the material and the frequency of the incident wave upon the dynamic stress intensity factor of the cracks.

DOI: 10.1023/A:1007521018293
Print publication date: 6/1/1998
View article on SpringerLink

by Wang, Wei-Chung; Hwang, Chi-Hung

In this paper, the amplitude fluctuation (AF) electronic speckle pattern interferometry (ESPI) method was adopted to investigate the vibration characteristics of a composite plate containing an edge crack. The change of the modal shapes was discussed. In addition, the stress intensity factors (SIFs) induced by the resonant vibration were evaluated.

DOI: 10.1023/A:1017161511565
Print publication date: 6/1/1998
View article on SpringerLink

by Qin, Qing-Hua; Mai, Yiu-Wing; Yu, Shou-Wen

Dilute, Self-Consistent (SC), Mori-Tanaka (MT) and differential micromechanics methods are developed for microcrack- weakened thermopiezoelectric solids. These methods are capable of determination of effective properties such as the conductivity, electroelastic moduli, thermal expansion and pyroelectric coefficients. The above material constants affected by the microcracks are derived by way of Stroh’s formulation and some recently developed explicit solutions of a crack in an infinite piezoelectric solid subjected to remote thermal, electrical and elastic loads. In common with the corresponding uncoupled thermal, electric and elastical behavior, the dilute and Mori-Tanaka techniques give explicit estimates of the effective thermoelectroelastic moduli. The SC and differential schemes, however, give only implicit estimates, with nonlinear algebraic matrix equations, of the effective thermoelectroelastic moduli. Numerical results are given for a particular cracked material to examine the behavior of each of the four micromechanics models.

DOI: 10.1023/A:1007423508650
Print publication date: 6/1/1998
View article on SpringerLink

by Shi, Yaowu; Han, Zhunxiang; Fu, Jianqin

In the present work the effects of weld strength undermatch on fracture toughness of heat affected zone (HAZ) have been studied. In the investigation a high strength low alloyed steel (HSLA) with 800 MPa strength class was used, and the undermatched welded joints were made with two weld strength mismatch levels. Three-point bending test specimens with crack depth to specimen width ratio a/W ranging from 0.05 to 0.5 were extracted from the welded joints. The test results show that strength mismatching gives an obvious influence on the fracture toughness of coarse grained HAZ for the undermatched joints. The lower the weld strength mismatching, the higher the fracture toughness of the HAZ. In addition the tendency of fracture toughness change with crack depths is much the same as in previous studies on base metals or weld metals, that is, fracture toughness of the HAZ is increased with reduction of crack depths. From the measured results it shows that the macroscopically mechanical heterogeneity of the welds may have more important influence on the fracture toughness of the HAZ than the meso-heterogeneity in the reheated coarse grained HAZ. Furthermore, numerical verification indicates that the stress triaxiality at crack tip may be the essential reason for the change of fracture toughness of HAZ. It is also shown that the yield strength of HAZ determined by the limit load in the three-point bend test represents the combinative effects of HAZ and its surrounding materials.

DOI: 10.1023/A:1007411221854
Print publication date: 6/1/1998
View article on SpringerLink