The Improvement And Application Of High Temperature Split Hopkinson Tensile Bar System Based On X-ray

We have designed a set of miniature high-speed impact tensile testing device(Split Hopkinson tension bar,SHTB)with heating system based on the principle of one-dimensional elastic stress wave.The X-ray phase contrast imaging,heating system and SHTB are used to study the mechanical properties and mesoscopic strain fields of AZ31 magnesium alloy at different temperatures.The launch tube of the tensile test device adopts a double-layer structure which is consisting of outer tube and inner tube.With the double-layer structure,the problem of pre-movement of the rod can be effectively solved.In order to solve the disalignment effect in the process of holding the specimen,we have designed a specimen jig with a square groove shape and a serrated surface to ensure the specimen under a coaxial state.In this way,the accuracy of the experiment has been improved.As most of the materials have temperature sensitive,we have designed a miniature heating system on the basis of SHTB.The heating system is suitable for X rays and easy to install and disassemble.The selection of power and heating element for the heating system are based on the experimental demand,economic cost,and SHTB size et al.The heating range of this heating system is from room temperature to 700 °C.With the X-ray phase contrast imaging,we have designed two groups of temperature experiment(room temperature and 150 °C),and the AZ31 magnesium alloy is selected as the experimental verification object.The macro and meso tensile deformations mechanisms of AZ31 magnesium alloys have been studied.We have found that the flow stress of AZ31 magnesium alloy under the room temperature is higher than the 150 °C situation.For the both temperature experiments,the average tensile strain of the sample is higher than the average shear strain.The inhomogeneity degree and strain concentration points of the tensile strain field rise as the bulk strain increases.Then the strain concentration points start to merge and result in tensile fracture occurs.Comparing the two temperature experiment,the inhomogeneity degree of the specimen strain filed under the 150 °C is lower than the room temperature situation.The probable reason is that the probability of homogeneous nucleation has been increased with the temperature improved.