The interrupted static fatigue (ISF) test can be used to evaluate the threshold for sub-critical crack growth, Kth. A critical theoretical analysis of this technique is presented in order to elucidate its advantages and limitations and to furnish some suggestions for a more definitive procedure for evaluating Kth. It was concluded that a critical parameter in the ISF procedure is the duration of the static hold time. In particular, one should demonstrate that the calculated value of Kth does not change when this holding time is increased. Moreover, the applied stress must be chosen such that a significant fraction of samples fail in the hold period. Two different approaches are suggested for calculating the value of Kth from experimental data. The first approach is considered preferable for materials with larger Weibull moduli and the threshold is determined from the applied stress intensity factor at which 50% of samples fails during the stress hold. In the second approach, the stress intensity factor applied to the weakest specimen during the stress hold is calculated for various hold times. Once this value becomes independent of hold time, it is equivalent to the threshold. © 1995.
The Interrupted Static Fatigue Test for Evaluating Threshold Stress Intensity Factor in Ceramic Materials: A Numerical Analysis
Sglavo, Vincenzo Maria;
1995-01-01
Abstract
The interrupted static fatigue (ISF) test can be used to evaluate the threshold for sub-critical crack growth, Kth. A critical theoretical analysis of this technique is presented in order to elucidate its advantages and limitations and to furnish some suggestions for a more definitive procedure for evaluating Kth. It was concluded that a critical parameter in the ISF procedure is the duration of the static hold time. In particular, one should demonstrate that the calculated value of Kth does not change when this holding time is increased. Moreover, the applied stress must be chosen such that a significant fraction of samples fail in the hold period. Two different approaches are suggested for calculating the value of Kth from experimental data. The first approach is considered preferable for materials with larger Weibull moduli and the threshold is determined from the applied stress intensity factor at which 50% of samples fails during the stress hold. In the second approach, the stress intensity factor applied to the weakest specimen during the stress hold is calculated for various hold times. Once this value becomes independent of hold time, it is equivalent to the threshold. © 1995.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione
