The Journal of Strain Analysis for Engineering Design

A generalized experimental method for measuring mixed-mode stress intensity factors is described for use in orthotropic materials. Moiré interferometry has been used to record the whole field surface displacements of double-edge cracked specimens made from unidirectional laminated composites. The moiré patterns were subsequently used to determine mode I and mode II stress intensity factors (K_I and K_II) by utilizing the displacement fields around the crack tip. The equations expressing K_I and K_II as functions of the displacement fields were reformulated to encompass the orthotropic material constants. A method for deriving these has been described. The accuracy of the results was found to depend on the precision in determining the location of the crack tip, as well as the measurement of the fringe spacing.

In this study, the stress and stiffness analyses of modified double-containment corner joints, in which plates are bonded at a right angle into slots of a corner support, were carried out using the finite element method. It was assumed that the adhesive and plates had linear-elastic properties. The presence of adhesive fillet at the adhesive free ends was taken into account. The corner joint was analysed for three loading conditions, two linear and one bending moment. It was found that the loading in the y direction is the most critical loading condition and that maximum stress concentrations occurred around the adhesive free ends. A detailed study of adhesive stresses showed that the peak adhesive stresses occurred at the lower free end of the left vertical adhesive layer-slot interface for the loading conditions P_y and M_b respectively and the lower free end of the right vertical adhesive layer-slot interface for the loading condition P_x. In addition, the effects of horizontal and vertical support lengths, slot depth and support thickness on the peak adhesive stresses and the overall joint stiffness were investigated. Dimensions of the corner support were given relative to the plate thickness.

In this paper, the effect of the variations of material combinations on the fracture behaviour of an arbitrarily inclined crack terminated at a bimaterial interface was investigated. By using the complex variable method, a comprehensive analysis of the state of stress and stress intensity factors (SIFs) was performed. The digital photoelastic technique was also employed to verify the analytical results. To ensure the accuracy in the process of determining SIFs, a visual check between experimentally obtained images and theoretically reconstructed images was performed. It was concluded that far-field effects usually found in the homogeneous case had to be included in the stress equations.

‘C’-shaped test specimens have been used to find the interlaminar strength of woven carbon/epoxy composite laminates in tension and in combined tension with minor transverse tractions. An analytical solution for the stress distribution within the “C” specimen, of arbitrary lay-up, is developed to permit a rigorous interpretation of the results, which confirm that the presence of relatively minor through-thickness stresses will have a profound influence on the strength of the component.

This paper reports a study on the determination of stress intensity factors in tubular joints in offshore jacket structures. Using finite elements, information on stress concentration factors and through-thickness stress distributions was first obtained from uncracked geometries. This was correlated with the stress intensity factors in joints containing semi-elliptical cracks which were modelled with line-spring elements. The validity of the numerical models was established, using a simple T-joint, by comparing the results with existing experimental data and results from three-dimensional finite element analyses. Various modelling assumptions used in previous numerical work were critically examined. The multi-planar effects in tubular joints were simulated by subjecting the out-of-plane braces to various loadings and restraints. It was found that a relationship exists between the stress concentration factor, the degree of bending and the stress intensity factor for the various loading and restraint cases considered, and that the stress intensity factors in multi-planar tubular joints can be estimated by suitably modifying an existing empirical equation for surface cracks in plain plates.

The closed-form equations given are based on the results of finite element analyses of double-edge-notched plates subject to tension or in-plane bending. The notch dimensions were varied in a parametric survey from shallow, part-circular forms to deep, sharp, slits with semi-circular ends, giving stress concentration factors varying from 1.2 to 13 (net stress basis).

The concept of a configuration factor for notches, similar to that used to calculate crack-tip stress field intensity factors, is introduced. It is shown in the first instance that the analogous crack configuration factor can be used directly to modify the elastic stress concentration factor for an elliptical hole, giving closed-form functions that do not involve empirical fitting constants and have acceptable practical accuracy. Reasons for the effectiveness of this form are given, together with an analysis of the points where the notch stress concentration factors diverge from the simple closed form. Further refinements that improve accuracy are given and comparisons are also made with stress concentration factors for hyperbolic edge notches.

The relative movements between the centre-lines of the strands of a wire rope during bending are analysed, as are the movements between the individual wires forming those strands. The formulae are applied to an example, and used to identify the position of greatest relative movement (slip). This position coincides with the most common location of wire failures in bend-over-sheave fatigue testing, suggesting that such slip calculations may form a valuable input to wire rope fatigue predictions.