Development of Fatigue Machine to Accommodate the Application of Overloads During Fatigue Crack Propagation Tests of Polymeric Materials

Different engineering components may be subjected to fatigue loading with sudden overloads which result in unexpected catastrophic failure. Polymeric pipes used in water and gas conveying networks may be subjected to this type of loading. The preparation of specimens for fatigue crack propagation tests from pipes as well as the application of overloads during such tests is a cumbersome issue. The present work introduces a technique for preparing and testing of single edge notch bending specimens made of polymeric pipes to conform with standards of fatigue test. Experiments were carried out on specimens made of High-Density Polyethylene (Grade 100) used in high pressure pipe applications. The proposed preparation sequences succeeded to minimize the effect of preparation process on the test results. Also, the developed fatigue machine is supplied by a special developed software which ensures a very smooth application of overloads during the fatigue crack propagation tests without any test disturbance. Crack retardation is observed in the tested specimens due to the overload effect.