Characterization And Measurement Of Metals Dynamic Fracture Toughness

The investigation on dynamic fracture toughness in metal materials is a leading topic of fracture dynamics, concerning with the combination and interaction of solid mechanics, material science and solid physics and etc. However, because of the limitation of testing equipments and experimenting techniques, only a few progresses have been achieved in researches on describing and testing on fracture commencing toughness, stable developing resistance and fracture ceasing toughness in materials, especially elasto-plastic materials, under dynamic loading. Furthermore, some projects have not been in progress or reported. Defects, even errors, exist in the methods regarding description and test mentioned above to some extent. Consequently, a standard can not be established for material performance study and engineering application. Therefore, it is urgent to probe and investigate in order to obtain effective description and test methods of material dynamic fracture properties. Its value not only exists in engineering significance, but also lies in the important academic values of fracture movement study under impactive load.As to description and test on fracture toughness, by analysis and investigation, there are several aspects of the main task in the present paper as follows.1. The influence on load, namely, the corresponding fracture toughness, by the transformation of flare head has been discussed during the fracture toughness testing of three-point buckling test sample on Hopkinson compression bar device. It provides preferable references to the testing of fracture toughness by three-point bucking method on hopkinson compression bar device which has been often discussed.2. The Hopkinson compression bar device has been altered to shoot bullets with different caliber in experiments.3. A clamp device has been designed to satisfy impactive tension experiment on Hopkinson compression device. It provides Hopkinson compression device notonly with realization of impactive tension for different types of test pieces, but only with realization of dynamic impact experiment for standard test pieces by loading on plane strain test pieces under compact tension during static fracture experiment, which offers an new way of fracture toughness testing in dynamic impactive tension and dynamic fracture mechanics.4. An equivalent spring mass model has been established for test pieces under compact tension. The equivalent mass has been given and the expression of dynamic stress intensity factor has been obtained, which provides a theoretic model for dynamic fracture toughness testing of real compact tension test pieces in standard test pieces and a new description method for equivalent spring mass of stress intensity factor response curves of compact tension test pieces.5. An FEM analysis has proceeded on compact tension test pieces. Through calculations on the two typical loads, we have obtained the result which accords to the established equivalent spring mass theoretic model.6. Based on the established equivalent spring mass theoretic model, a new method has been given for dynamic fracture toughness testing on compact tension test pieces and effective results have been gained. Furthermore, the rationality has been verified on description and test of K_Id and the effectiveness of the device and the method has been proved.Generally speaking, fracture toughness of materials is always related to loading velocity. The change of loading velocity can cause variation of fracture propagating mechanism. All above will make it difficult for the description and test of dynamic fracture toughness, especially, the dynamic fracture toughness of elasto-plastic materials. In the recent decades, investigation on the description and test of dynamic fracture toughness has not achieved significant progresses and breakthroughs. Frankly, by far, there has been no recognized and reliable criterion for fracture propagating, including propagating resistance curve and fractureceasing criterion. Until now, No country has publicized a formal standard for dynamic fracture toughness testing. In the present paper, the extending work done for the study on dynamic fracture toughness is only in primary stage. It offers a new helpful research to improvement and consummation of dynamic fracture toughness testing and provides theoretic and experimental references to further investigation in this field.