The determination of tearing energy, i.e. the energy available for crack growth, is an essential prerequisite for the estimation of the fatigue life of rubber components. Three methods of determining tearing energy are considered: from changes in total energy, from crack surface displacements, and by comparison with known values for the same crack growth rates. It is shown by applying experimental and numerical techniques to plane-stress testpieces, not necessarily of uniform stress or thickness, that the methods are satisfactory.
Abstract
Shattered rim defects are the result of large fatigue cracks that propagate roughly parallel to the wheel tread surface. They form and grow 12 to 20 millimeters (1/2 to 3/4 in.) below the tread surface. A typical shattered rim is shown in Figure 1. The clamshell pattern of the fracture surface is also typical of shattered rims. The clamshell pattern is formed because fatigue cracks at this depth in wheels have a shear component and, when the rolling direction is opposite, the cracks grow in a different direction forming a series of ridges and valleys. Miezoso, et alia have presented a mixed mode fracture mechanics analysis of the process of forming a clam-shell fatigue crack surface in wheels.
In this work we evaluate the application of the contour method to fatigue and fracture surfaces. Residual stress measurements were made on quenched and aged AA2124-SiCp composite using neutron diffraction, the contour method with wire EDM, and the contour method on a fatigue crack surface including brittle failure. The contour method successfully measured residual stresses from a wire electro-discharge cut surface, but the fracture method results suggest that residual stress information is lost due to plasticity during fatigue crack growth.
The tests of fatigue crack overload retardation were performed to gain a some what deeper understanding of overload retardation. We present an experimental investigation of fatigue crack retardation behavior caused by intermediate single peak tensile overload under constant amplitude cyclic loading. The compact tension (CT) specimens of API grade X80 pipeline steel were used in fatigue test. The results show there was an instant crack extension during overloading for the tested overload ratios. As soon as the overload cycle was removed, instant delay in crack growth occurred. The results should be of interest for fracture mechanics prediction models on fatigue crack growth under variable amplitude loading and overloading effect for oil and gas pipelines.
Residual Stress Measurements on a Metal Matrix Composite Using the Contour Method with Brittle Fracture