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Many crack propagation equations have been proposed over the years to improve prediction accuracy and incorporate a variety of effects. The works of Head, [6] Frost and Dugdale, [7] McEvily and Illg, [8] and Liu [9] on fatigue crack-growth behaviour laid the foundation in this topic. The general form of these crack propagation equations may be ...
Fracture mechanics is the field of mechanics concerned with the study of the propagation of cracks in materials. It uses methods of analytical solid mechanics to calculate the driving force on a crack and those of experimental solid mechanics to characterize the material's resistance to fracture.
In a 1961 paper, P. C. Paris introduced the idea that the rate of crack growth may depend on the stress intensity factor. [4] Then in their 1963 paper, Paris and Erdogan indirectly suggested the equation with the aside remark "The authors are hesitant but cannot resist the temptation to draw the straight line slope 1/4 through the data" after reviewing data on a log-log plot of crack growth ...
In materials science, fracture toughness is the critical stress intensity factor of a sharp crack where propagation of the crack suddenly becomes rapid and unlimited. A component's thickness affects the constraint conditions at the tip of a crack with thin components having plane stress conditions and thick components having plane strain ...
Note that the equations above are derived using the crack closure integral. If the energy release rate exceeds a critical value, the crack will grow. In this case, a new FEA simulation is performed (for the next time step) where the node at the crack tip is released.
Microscopic material failure is defined in terms of crack initiation and propagation. Such methodologies are useful for gaining insight in the cracking of specimens and simple structures under well defined global load distributions. Microscopic failure considers the initiation and propagation of a crack.
Fastran is a computer program for calculating the rate of fatigue crack growth by combining crack growth equations and a simulation of the plasticity at the crack tip. Fastran models accelerations and retardation and other variable amplitude loading effects in crack growth using a crack closure model.
In a falling R-curve regime, as a crack propagates, the resistance to further crack propagation drops, and it requires less and less applied in order to achieve each subsequent increment of crack extension . Materials experiencing these conditions would exhibit highly unstable crack growth as soon as any initial crack began to propagate.