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An experimental study was conducted to determine the validity of a delta J criterion for fatigue crack growth. Fatigue crack growth rates up to 0.10 mm/cycle were measured on compact tension specimens. Tests were conducted under delta J control using a computerized test system. Fatigue crack growth rates under variable delta J, J-increasing, constant delta J, and sloping-line test conditions were measured on 304 stainless steel and HY100 material. Linear elastic fracture mechanics crack growth rates were measured for comparison.
The results show that there is an excellent correlation between the fatigue crack growth rate and the effective J-integral range. The effective J-integral range was calculated from the area under the load/load-line displacement curve that was above the crack closure load. Correlation between the fatigue crack growth rate and the effective crack-opening displacement was poor. Correlations between the fatigue crack growth rate and the effective stress-intensity factor were poor for the 304 stainless steel and good for the HY100 material.
The crack closure behavior was measured for both materials. The crack closure loads were always compressive and either increased or decreased with crack length, depending upon the test type.
nonlinear fracture mechanics, J, -integral, delta , J, effective stress-intensity factor, crack closure, automated testing, computer control, 304 stainless steel, HY100 alloy, fracture mechanics
Manager, Research Laboratory, Instron,