G-control fatigue testing for cyclic crack propagation in composite structures

This paper presents a computer controlled testing methodology called “The G-control Method” which allows cyclic crack growth testing using real-time control of the cyclic energy release rate. The advantages of using this approach are described and compared with traditional fatigue testing methods (displacement or load control). The compliance based analytical formulation for G-control is explained for the DCB specimen and then applied to experimental testing of the sandwich MMB specimen. Experimental results are presented for sandwich MMB specimens with fiberglass face sheets and PVC foam core, showing that the G-control method allows fatigue testing at a constant range of energy release rates leading to a constant crack propagation rate.