A non-equilibrium approach to processing Hopkinson Bar bending test data: Application to quasi-brittle materials

Abstract

International audienceThe aim of this paper was to describe a method of analysing the test data recorded during a Hopkinson Bar bending test. This three-point dynamic bending test was designed for testing the strength of materials under dynamic loads. It is carried out on a specimen consisting of a beam placed on two supports, which is subjected to an impact. The use of Hopkinson Bar as supports makes it possible to determine the forces and displacements at these points. An analytical solution for the transient response of a long beam subjected to a transverse impact was used to determine the impact force and the displacement. This procedure applies for the first few instants when the motions generated by the impact have not yet reached the supports, and the mechanical state of the specimen is identical to that of an unsupported beam. It is suitable for use with quasi-brittle materials for which failure occurs at the very beginning of the test. The material strength is determined at the time of failure, which is characterised by a sudden decrease in the bending moment. The results of a test in which a quasi-brittle material was loaded up to failure are presented and analysed as outlined above. The results obtained confirm the relevance of the present method

A Simple Methodology to Measure the Dynamic Flexural Strength of Brittle Materials

“…In other words, for the first 12 [μs] of the loading after the stress wave reaches the specimen, the specimens basically behave as infinite. A similar observation was also reported in Delvare et al [17] from much larger specimens.…”

“…In other instances, e.g. [17], the incident and reflected signals are quite different for a much larger specimen geometry.…”

“…At this stage, one should note the very recent work of Delvare et al [17], who developed a full dynamic bending test of brittle beams to assess their flexural strength. The idea is to use a model of the dynamic response of the beam to assess its strength on the one hand, while failure is identified from the experimental signals.…”

Measurement of dynamic fracture toughness by double torsion testing

“…The dynamic double torsion testing machine was developed by using a bending test on the basis of split Hopkinson pressure bar testing (Higashida and Ogawa, 1990), (Ogawa, et al, 1998), (Delvare, et al, 2010), (Pierron, et al, 2011), (Chen and Song, 2011), (Xia and Yao, 2015). The machine is illustrated in Fig.…”

“…First, the specimen shape, in particular the initial crack length, and the duration of the impact force applied to the specimen were experimentally and numerically analyzed in terms of the natural frequency of the specimen in order to measure the critical fracture toughness independently of the length. Second, a testing machine was designed for a bending test based on the split Hopkinson pressure bar test (Higashida and Ogawa, 1990), (Ogawa, et al, 1998), (Delvare, et al, 2010), (Pierron, et al, 2011), (Chen and Song, 2011), (Xia and Yao, 2015) to measure impact and reaction forces. The forces and specimen deflection calculated from strain histories of the input and output bars in the testing machine were formulated on the basis of onedimensional wave propagation theory.…”