The Study On The Experiment Of The Dynamic Fracture Toughness Of Rate-dependent And Elastic-plastic Materials

As the basic branch of the dynamic fracture theory,the study on the characterization and measure method of the dynamic fracture toughness of elastic-plastic materials is very challenging.Yet,due to the restriction of experimental instruments and measure technology,and the coupling effect of instruments and specimens,the study progresses slowly.There are still many problems unsovled since 1860's.Currently,the study on dynamic fracture toughness of elastic-plastic materials under high loading rates is seldom.Since the rate-dependent material is used widely,it is necessry to study the influence of loading rates on the fracture touchiness of the material.It is of great benefit to the design of preventing dynamic fracture and safe assessing.A test for dynamic plane-strain crack initiation is carried out on a bar-bar tensile impact apparatus by using short and columned specimens with circumferential notches of 45 steel at room temperature.Dynamic J-intergral is calculated by extending the J-integral formula of Rice and using the load-displacement curve on ligament plane.The time of crack initiation is determined by the compliance changing method and corresponding dynamic crack initiation toughness J_IDis obtained.The results show that the dynamic fracture toughness of 45steel is reduced while raising the loading rate.The dynamicstress-strain behaviors under diferent strain rates and dynamic fracture behaviors under diferent loading rates are obtained.In order to research the mechanism of dynamic fracture,the fractured surface of dynamic tensile and dynamic fracture is investigated by microscope-analysis technique.