Abstract
The total plastic strain energy which is consumed during fracture of a plain-sided CT specimen is separated into several components. These are the energies required for deforming the specimen until the point of fracture initiation, for forming the flat-fracture surfaces, for forming the shear-lip fracture surfaces, and for the lateral contraction and the blunting at the side-surfaces, W lat. Characteristic crack growth resistance terms, R flat and R slant, are determined describing the energies dissipated in a unit area of flat-fracture and slant-fracture surface, respectively. R flat is further subdivided into the term R surf, to form the micro-ductile fracture surface, and into the subsurface term, R sub, which produces the global crack opening angle. Two different approaches are used to determine the fracture energy components. The first approach is a single-specimen technique for recording the total crack growth resistance (also called energy dissipation rate). Plain-sided and side-grooved specimens are tested. The second approach rests on the fact that the local plastic deformation energy can be evaluated from the shape of the fracture surfaces. A digital image analysis system is used to generate height models from stereophotograms of corresponding fracture surface regions on the two specimen halves. Two materials are investigated: a solution annealed maraging steel V 720 and a nitrogen alloyed ferritic-austenitic duplex steel A 905. For the steel V 720 the following values are measured: J i=65 kJ/m2, R surf=20 kJ/m2, R flat=280 kJ/m2, R slant=1000 kJ/m2, W lat=30 J. For the steel A 905 which has no shear lips, the measured values are: J i=190 kJ/m2, R flat=1000 kJ/m2, and W lat=45 J. Apart from materials characterization, these values could be useful for predicting the influence of specimen geometry and size on the crack growth resistance curves.
Key words: Elastic-plastic fracture mechanics, fracture energy, energy dissipation rate, fracture surface analysis.
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Stampfl, J., Kolednik, O. The separation of the fracture energy in metallic materials. International Journal of Fracture 101, 321–345 (2000). https://doi.org/10.1023/A:1007500325074
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DOI: https://doi.org/10.1023/A:1007500325074