Center notched sample

A center-notched panel of polystyrene at 25°C has a crack of 1.0 cm width see Figure 11.226. The critical stress intensity factor, K was determined by other experiments to be 6 MPa-m. Will the sample fail under a stress of 10 MPa ... 

A sample of poly(methyl methacrylate) at room temperature has a center notched crack of 2.0 cm in diameter. If is 0.80 MPa m, what is the critical stress to propagate the crack ... 

A center notched rubber-toughened epoxy sample has a crack of 0.015 m width. If a stress of 1 x 10 Pa is imposed, will the sample fail ... 

We test the impact resistance of polymer plaques using the configuration shown in Fig. 8.8. We subject circular injection molded plaques to the shock of a falling weight with a hemispherical impacter. This test is also known as the Dart Drop Test . Samples can fail in a brittle or a ductile manner. Brittle samples often shatter. Ductile samples can split or a small disk may be punched out of their center. This test provides results that are analogous to those obtained from un-notched impact beam testing. 

The experiments were performed on commercially available samples of HOPE, PP, PA 6, PA 66, PBT, POM, and PEEK. Their trade namra are listed in Table 1. The dimensions and shape of the test samples, as shown in Fig. 1, were chosen to maintain a state of plane strain. A round notch of 0.5 mm radius was introduced in the center of one edge of the sample by machining. The samples were loaded in the three-point bending test using an Instron-type testing machine. For microscopic observations. 

A related alternative to the Izod test is the Charpy test, preferred in ISO standards, in which a sample supported (not gripped) at each end is subject to an impact in the center. According to the test a notch may be present in the center of the sample on the face opposite to that subjected to impact. 

Shown in Figure 5.3, this test measures the extent to which the ends of a known length of tape will droop in a given period of time. In this test, a rectangular sample of tape with a length width ratio of at least 10 1 is centered lengthwise on a flat support. The support plate is notched... 

Small pieces from compression molded plaques were cut into thin strips of approximately 50mm x 8mm. A razor notch was placed on both edges along the center of the strips to help induce a straight fracture. The strip was held between the jaws of a pair of pliers and submerged into liquid nitrogen for approximately five minutes. A second set of pliers were cooled at the same time so that when the sample was removed, it could be quickly freeze fractured. A razor blade was used to... 

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