Mechanical property measurement brittle failure

In the present study we analyze the results of HDPE pipe sustain pressure test at elevated temperature and various hoop stress level (80 C 4.7 5.5 MPa). Some material properties are shown in Table 1. The failure time for each stress level is recorded, when the leak is observed. After the specimen failure, the fracture surface was inspected by optical and SEM microscopy to observe and characterize the fracture mechanism. All brittle fractures observed resulted from through cracks. A number of various size small cracks have also been developed at the time, when the largest crack(s) caused the le. In many cases, multiple through cracks were detected. It offers for analysis a set of cracks grown under the same controlled tenqierature and stress level. All the observed cracks have been originatod from inclusions. The size and location of an inclusion play an important role in failure time. A combination of random size and location of the inclusions results in a large scatter in failure time at the same applied stress, commonly reported for pipe failures [9]. A summary of plied stresses, failure time, inclusion size and location observed on the fracture surface is presented Table 2. The size of the inclusion is reported in wall thickness direction. The normalized apparent depth of inclusion location indicated in the Table 2, was measured as the ratio between the distance from the inclusion center to outer surface and... 

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