It is shown that the J-integral can be directly evaluated from single load-displacement records for a series of crack toughness specimens having the common feature that their only significant length dimension is that of the uncracked ligament. For the special case of bending loads on the ligament of a deeply cracked bar, J is shown to be twice the work of deformation divided by the ligament area. This and like results are employed to discuss Charpy and “equivalent energy” toughness measures and also to evolve yet simpler estimating procedures for the J-integral.
An important fracture mechanics problem is the determination of fracture toughness values with small specimens that fail after yielding. The J Integral has an explicit meaning in terms of notch tip conditions in the plastic range and can be calculated from single specimen test data. In this paper, an improved J Integral analysis is developed for the Compact specimen by considering the combined loading that exists on the net section. The analysis agrees•with linear elastic fracture mechanics in the elastic range and gives a resvJLt close to that given by the Equivalent Energy Method in the plastic range.
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In nonlinear applications of computational fracture mechanics, energy release rate techniques are used increasingly for computing stress intensity parameters of crack configurations. Recently, deLorenzi used the virtual-crack-extension method to derive an analytical expression for the energy release rate that is better suited for three-dimensional calculations than the well-known J-integral. Certain studies of fracture phenomena, such as pressurized-thermal-shock of cracked structures, require that crack tip parameters be determined for combined thermal and mechanical loads. A method is proposed here that modifies the isothermal formulation of deLorenzi to account for thermal strains in cracked bodies. This combined thermo-mechanical formulation of the energy release rate is valid for general fracture, including nonplanar fracture, and applies to thermo-elastic as well as deformation plasticity material models. Two applications of the technique are described here. In the first, semi-elliptical surface cracks in an experimental test vessel are analyzed under elastic-plastic conditions using the finite element method. The second application is a thick-walled test vessel subjected to combined pressure and thermal shock loading.
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