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Plot of Load vs. Displacement. The energy release rate is defined [3] as the instantaneous loss of total potential energy per unit crack growth area , , where the total potential energy is written in terms of the total strain energy , surface traction , displacement , and body force by
The fracture toughness and the critical strain energy release rate for plane stress are related by = where is the Young's modulus. If an initial crack size is known, then a critical stress can be determined using the strain energy release rate criterion.
the stored elastic strain energy which is released as a crack grows. This is the thermodynamic driving force for fracture. the dissipated energy which includes plastic dissipation and the surface energy (and any other dissipative forces that may be at work). The dissipated energy provides the thermodynamic resistance to fracture.
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.
It is denoted by critical stress intensity factor or critical strain energy release rate. [15] For unidirectional fiber reinforced polymer laminate composites , ASTM provides standards for determining mode I fracture toughness G I C {\displaystyle G_{IC}} and mode II fracture toughness G I I C {\displaystyle G_{IIC}} of the interlaminar matrix.
The critical parameter in fracture mechanics is the stress intensity factor (K), which is related to the strain energy release rate (G) and the fracture toughness (G c). When the stress intensity factor reaches the material's fracture toughness, crack propagation becomes unstable, leading to failure.
Strain energy release rate per unit fracture surface area is calculated by J-integral method which is a contour path integral around the crack tip where the path begins and ends on either crack surfaces. J-toughness value signifies the resistance of the material in terms of amount of stress energy required for a crack to grow.
The strain energy density is defined as the energy invested into the volume unit of polymeric material for deformation, also known as the elastic energy per unit volume in the solid. In crack nucleation approach, no crack is introduced into the sample initially, and crack initiation is observed under loadings. Crack Growth Approach