Determination of Dynamic Tensile Properties for Low Strength Brittle Solids

We propose an indirect tensile testing method to measure the full dynamic tensile stress-strain curve of low strength brittle solids. In this method, we use the flattened-Brazilian disc (FBD) sample and apply the dynamic load with a modified split Hopkinson pressure bar (SHPB) system. Low amplitude dynamic loading forces are measured by a piezoelectric force transducer that is embedded in the transmitted bar. The evolution of the tensile stress at the center of the disc sample is determined via finite element analyses with the measured stress in SHPB as inputs. In a traditional Brazilian method, a strain gauge is mounted at the center of the specimen to measure the tensile strain, which is difficult to apply for low strength brittle materials. Therefore, a laser gap gauge (LGG) is used to monitor the expansion of the disc perpendicular to the loading axis, from which the average tensile strain is deduced. The numerical simulation reveals a linear relationship between the tensile strain at the center of the specimen and the average tensile strain and the relating factor is not sensitive to the material elastic parameters. The feasibility of this methodology is demonstrated with the SHPB-FBD experiments on a polymer bonded explosive (PBX).