Cyclic stretch-bending: mechanics, stability and formability

Cyclic stretch-bending has been studied using the so-called Continuous-Bending-under-Tension (CBT) test. This is a modified tensile test where the specimen is subjected to repetitive bending at the same time. A wide variety of materials have been tested this way. A simple mechanical model is presented incorporating non-constant bending radius and cyclic material behaviour that is verified experimentally. The increased stability allowing high levels of uniform straining is discussed, a stability parameter is presented. The mechanisms of failure are discussed as are the different types of fracture that are observed. The overall conclusion is that many observed results are determined by the test method, and are as such independent of the material tested.