An integral is developed for calculating opening mode stress intensity factor at any point on the front of an irregular planar crack embedded in an infinite solid and subjected to an arbitrary normal stress field. No other solutions are available for irregular cracks, therefore the integral is first used to analyze three-dimensional regular cracks for which there are solutions. An embedded square crack is used to illustrate the integral procedure for an irregular shape. The integral is also used to explain qualitatively how irregular fatigue cracks will grow.

Thermoplastic components subjected to cyclic loading may distort because of localized rises in temperature and/or fracture because of incremental (fatigue) crack propagation from microscopic cracks or defects produced during the manufacturing process or by service conditions. The object of the present paper is to show quantitatively how the first mode of failure, which is referred to as cyclic thermal softening, can be related to loss compliance, specimen geometry and the frequency and magnitude of the cyclic load. The results of cyclic bending tests on polymethylmethacrylate (p.m.m.a.) and Polyvinylchloride (p.v.c.) beams of rectangular and circular cross-section are analysed. For the service conditions considered the p.m.m.a. specimens showed both failure modes whereas the p.v.c. specimens failed as a result of incremental (fatigue) crack propagation.

This paper describes a computationally efficient weight function technique which can be used to estimate the opening-mode stress intensity factor around the perimeter of planar surface or embedded cracks. The accuracy of the weight function itself and of the numerical quadrature schemes adopted are verified for elliptical cracks with a wide range of aspect ratios. The technique is then applied to longitudinal-radial cracks at the inner surface, including crossbores, of thick-walled pressure vessels. The results obtained for a wide range of crack depths, aspect ratios and vessel diameter ratios agree well with the predictions obtained by others using finite element, boundary element and modified mapping collocation methods, as well as with previously unpublished experimental data. The paper also considers the applicability of the ASME Boiler and Pressure Vessel Code procedures for estimating K1 for these defects.

An analytical method is presented for calculating real contact ratios for plastic/plastic or plastic/steel spur gear pairs. A comparison is made with published experimental data and the method is used to explain the importance of load sharing in thermoplastic gearing.