A simple multi-specimen apparatus for fixed stress fatigue testing

To cope with the time-consuming characteristics of fatigue tests, a multi-specimen fatigue testing apparatus, which could test 10 specimens at a time, was designed, constructed, and tested. The specimens are fixed around a rotating axis, and the required stresses are applied by weights attached on the other end of each specimen. The test mode can be categorized as a stress-controlled flexural fatigue test. Its performance was tested by comparing it with a commercial three-point bending fatigue testing apparatus. The stress versus number of cycles to failure curves of poly(methylmethacrylate) (PMMA), which were obtained from both fatigue testing equipment, showed results that were similar to each other. The fatigue test results of acrylic bone cement in a fixed-stress mode also showed good agreement between the data obtained from the new apparatus and the commercial apparatus. The test results seem quite reliable and show feasibility of significantly reducing the overall test periods. It may be valuable, especially for the fatigue tests, which must be done with a low frequency and a low applied stress level such as a fatigue test of bone cements.