| An experimental and numerical study was completed to evaluate the characteristics of the T*ϵ integral fracture criterion and to explore the possibility of using it to predict crack linkup and residual strength of aircraft structures containing MSD. The study included five different crack configurations, ranging from one to five cracks, for studying the basic characteristics of the T*ϵ integral in the single crack environment as well as in the multiple cracks environment with interactions between cracks.; Moiré interferometry was used to determine the orthogonal displacement fields surrounding stably growing cracks and a procedure was developed to evaluate T*ϵ directly from the displacement data. Elastic-plastic finite element analyses of the fracture specimens were evaluated by inputting the measured moiré displacement data along the width, 10 to 25mm away from the crackline, of the specimens.; Overall, the experimentally and the FE determined T*ϵ values were in excellent agreement with each other. Both experimentally and FE evaluated T*ϵ showed that T*ϵ is contour size dependent. However, for a constant integral contour size, T* ϵ is constant during steady state crack growth. Cracks on all five specimen configurations exhibited crack growth at similar T*ϵ values. Thus T*ϵ integral is a local fracture parameter and that it is independent of the specimen geometry or crack configurations.; Crack growth simulation based on the T*ϵ criterion to predict crack linkup and residual strengths correlated very well with test results. On the average, the predicted maximum loads were within 3% of the test results.; The CTOA criterion is a local fracture parameter and the angle is constant during steady state crack growth, similar to the T*ϵ integral. However, during the initial stage of crack growth where crack tunneling and shear lip formation exist, the measured CTOA was larger than the steady state CTOA and are scattered. For problems where fracture occurs immediately within crack growth, the CTOA criterion may not be very reliable since the CTOA criterion is usually assumed constant through out the fracture process.; The plastic zone criterion was also used to predict the crack linkup and residual strength. It was shown that the criterion worked well for some cases but poorly for others. |
