Research On Fracture Mechanism And Crack Propagation Form In Brittle PMMA Plates

Further research was conducted on the problem of dynamic crack propagations in brittle PMMA plates. The main research work and results were summarized below:(1)The high speed propagation and curving behavior of a crack in a pre-tensile loaded brittle PMMA plate were studied experimentally. The crack was initiated off-axially in the edge of the plate. Once initiated, the crack propagated and curved toward the center line of the plate. The curved path of the crack was strongly dependent on the initiation site, the farther the initiation site was, the more obvious curving behavior was, and it seemed uninfluenced by the preloading level unless the load was very high causing crack to branch. If two edge cracks were initiated simultaneously, only one would propagate to cause specimen break into two pieces.(2) A rate-dependent cohesive fracture model was developed and it was implemented into the commercial software ABAQUS explicit analysis modulus. The software was then used to simulate fast crack propagation problem. The numerical simulations provided results that fundamentally agree with the experimental results, and the velocity of crack calculated was the same as actual measurements.(3) A groove was opened in the middle of the PMMA plate, forming a weakened zone, the high-speed transmission behavior of the crack to be studied in the weakened zone, and high-speed photography and broken wire method were used respectively to record the crack propagation speed. It was found cracks bifurcation phenomenon did not occur under high preload, the velocity calculated was nearly 1000 m/s, while the limit of Rayleigh wave velocity of PMMA plate materials which measured through the experiment and calculation was 915 m/s. This was the first time in the PMMA plate that the crack speed reached to the limit of Rayleigh velocity in the test. Through the observation to the weaken the internal crack section of tank, as the velocity of crack propagation increased slowly, the crack surface developed mirror- sparse parabolic- dense groove parabolic- cycle model, and then with the increase of velocity to 1000 m/s, it could be observed the phenomenon of the highly fragmentation on the surface of crystals.