Fracture Behavior and Crack Growth Resistance Curve

Load-point displacement must be used, since the strain energy for the body is defined as one-half the applied load times this displacement. 

Instrumentation - load cell, linearly variable differential transformer (LVDT), clip gage, etc. 

Must have sufficient number of data points to ensure accuracy particularly for crack length near zero. 

Accuracy and precision important must be free from systematic errors and must minimize variability because of the double differentiation involved in going from A versus P, to C(= A/P) versus a, and then to dCjda versus a. 

Two types of nonlinearities must be recognized and corrected (i) unavoidable misalignment in the system, and (ii) crack closure. A third type, associated with significant plastic deformation at the crack tip, is not permitted (use of too high a load in calibration). 

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Fracture Behavior and Crack Growth Resistance Curve... 

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