by Yang, Jiashi; Guo, Shaohua

This note discusses inconsistencies arising in connection with using strain gradient theories in the analysis of cracks.

DOI: 10.1007/s10704-005-7120-8
Print publication date: 5/1/2005
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by Yang, Jiashi; Guo, Shaohua

This note calls attention to an old error in the theories for extensional motions of plates, which still persists today; in particular, it often appears in analyses of cracks in plates.

DOI: 10.1007/s10704-005-7119-1
Print publication date: 5/1/2005
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by Wallbrink, C. D.; Peng, D.; Jones, R.

This paper presents a new method for predicting the stress intensity factors around a partly circumferential elliptical surface crack in a pipe. The solution is applicable to structures with both double and single curvature. The technique involves a conformal transform in conjunction with a semi-analytical approach that uses a finite element model to obtain the stress distribution in the undamaged structure. By using an indirect methodology, the model development is simplified and the analysis time is minimised. As such a coarse mesh can be used to obtain solutions for multiple crack geometries. Three examples are presented to verify this methodology. They include a partly circumferential elliptical crack under uniform tension, a pipe subject to a residual stress field, and a problem involving double curvature. For simple loading the solution compares with other published solutions to within 5% for an external crack, and to within 15% for an internal crack. For more complex loading conditions the majority of the solutions were within 5% of other published results at the deepest point, and most solutions at the surface agreed to within 15%. For the problem involving double curvature, the solutions agreed to within 4% for an internal crack, and 15% for an external crack.

DOI: 10.1007/s10704-005-0628-0
Print publication date: 5/1/2005
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by Yang, Qingda; Cox, Brian

A trend in the last decade towards models in which nonlinear crack tip processes are represented explicitly, rather than being assigned to a point process at the crack tip (as in linear elastic fracture mechanics), is reviewed by a survey of the literature. A good compromise between computational efficiency and physical reality seems to be the cohesive zone formulation, which collapses the effect of the nonlinear crack process zone onto a surface of displacement discontinuity (generalized crack). Damage mechanisms that can be represented by cohesive models include delamination of plies, large splitting (shear) cracks within plies, multiple matrix cracking within plies, fiber rupture or microbuckling (kink band formation), friction acting between delaminated plies, process zones at crack tips representing crazing or other nonlinearity, and large scale bridging by through-thickness reinforcement or oblique crack-bridging fibers. The power of the technique is illustrated here for delamination and splitting cracks in laminates. A cohesive element is presented for simulating three-dimensional, mode-dependent process zones. An essential feature of the formulation is that the delamination crack shape can follow its natural evolution, according to the evolving mode conditions calculated within the simulation. But in numerical work, care must be taken that element sizes are defined consistently with the characteristic lengths of cohesive zones that are implied by the chosen cohesive laws. Qualitatively successful applications are reported to some practical problems in composite engineering, which cannot be adequately analyzed by conventional tools such as linear elastic fracture mechanics and the virtual crack closure technique. The simulations successfully reproduce experimentally measured crack shapes that have been reported in the literature over a decade ago, but have not been reproduced by prior models.

DOI: 10.1007/s10704-005-4729-6
Print publication date: 5/1/2005
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by Hasanyan, D. J.; Piliposian, G. T.

This paper considers the stress–strain state of a body consisting of two bonded uniform ferromagnetic half-spaces, with an interfacial penny-shaped crack. The body is assumed to be acted on by a uniform magnetic field in a direction normal to the crack and interface. The problem is reduced to the solution of singular integral equations with respect to two unknown functions on a finite interval. These functions are defined analytically, allowing us to obtain formulae for the magnetoelastic stresses and coefficient of stress intensity. From these formulae, the influence of various physico-mechanical parameters and the magnetic field on the stress strain state of the body in the vicinity of crack is studied.

DOI: 10.1007/s10704-005-3062-4
Print publication date: 5/1/2005
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by Gaffard, V.; Besson, J.; Gourgues-Lorenzon, A. F.

A new model considering both deformation and damage evolution under multiple viscoplastic mechanisms is used to represent high temperature creep deformation and damage of a martensitic stainless steel in a wide range of load levels. First, an experimental database is built to characterise both creep flow and damage behaviour using tests on various kinds of specimens. The parameters of the model are fitted to the results and to literature data for long term creep exposure. An attempt is made to use the model to predict creep time to failure up to 105 h.

DOI: 10.1007/s10704-005-2528-8
Print publication date: 5/1/2005
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by Zalounina, Alina; Andreasen, Jens

A surface crack penetrating the interface between a presstressd hard coating and a substrate is analysed in terms of linear fracture mechanics in order to assess the fatigue properties of such a composite. Assuming Paris’ law, fatigue crack growth rate allows the determination of “safe” regimes, where a crack always experiences closure.

DOI: 10.1007/s10704-005-7193-4
Print publication date: 5/1/2005
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