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In fracture mechanics, the energy release rate, , is the rate at which energy is transformed as a material undergoes fracture.Mathematically, the energy release rate is expressed as the decrease in total potential energy per increase in fracture surface area, [1] [2] and is thus expressed in terms of energy per unit area.
In physical terms, additional energy is needed for crack growth in ductile materials as compared to brittle materials. Irwin's strategy was to partition the energy into two parts: the stored elastic strain energy which is released as a crack grows. This is the thermodynamic driving force for fracture.
The crack is expected to propagate when the strain energy release rate exceeds a critical value - called the critical strain energy release rate. The fracture toughness and the critical strain energy release rate for plane stress are related by
For the situation where the plate is large compared to the size of the crack and the location of the force is relatively close to the crack, i.e., , , , , the plate can be considered infinite. In that case, for the stress intensity factors for F x {\displaystyle F_{x}} at crack tip B ( x = a {\displaystyle x=a} ) are [ 11 ] [ 12 ]
The J-integral represents a way to calculate the strain energy release rate, or work per unit fracture surface area, in a material. [1] The theoretical concept of J-integral was developed in 1967 by G. P. Cherepanov [2] and independently in 1968 by James R. Rice, [3] who showed that an energetic contour path integral (called J) was independent of the path around a crack.
In fracture mechanics, a crack growth resistance curve shows the energy required for crack extension as a function of crack length in a given material.For materials that can be modeled with linear elastic fracture mechanics (LEFM), crack extension occurs when the applied energy release rate exceeds the material's resistance to crack extension .
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The J-integral represents the energy that flows to the crack, hence, it is used to calculate the energy release rate, G. Additionally, it can be used as a fracture criterion. This integral is found to be path independent as long as the material is elastic and damages to the microstructure are not occurring.