MECHANICAL ASPECTS OF THE DYNAMIC TEAR TEST SPECIMEN.

The importance of dynamic fracture toughness as a controlling influence on the design and integrity of high performance structures is becoming more generally recognized. Since tear test procedures involve dynamic loading, a rigorous analysis of this test method can provide direct translation of test results into structural parameters such as fracture stress and stress intensity values of fracture mechanics in addition to tear energy values. This report concerns the development of a dynamic analysis for the two principal elements in the tear test, namely, the hammer and the specimen. Several methods of analysis for predicting the hammer force-time curves are discussed and an analysis based on simple bending theory which predicts the beam bending moments and stresses is presented. The calculated force-time relationship for the hammer was in good agreement with experimental results. The results indicate that the first peak in the hammer force-time curves is not directly related to fracture but is caused by inertia effects. For the specimen, the calculated stresses and bending moments predicted by the dynamic analysis agree fairly well with experimental values. Both calculated and experimental values of dynamic stresses and moments are lower than those calculated from a static analysis; and therefore, in the dynamic tear test a static analysis cannot be used to calculate fracture stresses or stress intensity factors. (Author)