13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- relies on the direct measurement of the strain field near the crack tip by means of a strain gauge. KI (t) = εy(t)E 2πr Cos θ 2 1+Sin θ 2 Sin3θ 2 − ν(1−Sin θ 2 Sin3θ 2 ) " #$ % &' , (5) where r is the radial distance from the crack tip to the strain gauge and θ is the angle from the crack path, [6]. 4. Results & Discussion 4.1. PMMA Tests All tests were performed at ambient temperature. The static fracture toughness has also been determined for comparison. Fig. 3(a) shows a typical incident and reflected strain trace from a fracture test. The striker velocity leaving the muzzle was approximately 8.5 m/s determined using a high-speed camera, which results in a particle velocity of 6 m/s at the load point of the apparatus from Eq. (2). Using Eq. (1) the load applied to the specimen was determined and is illustrated in Fig. 3(b). For this test the value of (a/W) was 0.33 and using Eq. (4) the temporal SIF was found as shown in Fig. 4. Figure 3(a). Superposition of incident and reflected strain trace, (b) Variation of applied load with time Figure 4. Stress intensity evolution for PMMA at 6m/s Time to fracture
RkJQdWJsaXNoZXIy MjM0NDE=