The Expanding Fracture Behavior Of Cylinder Shell On The Impact Loading

The metal cylinder shells expanded to fracture loading by internal shock was applied very extensive in engineering applications. In this paper, the recent progresses in the law of fraction, the criterion of fraction, the material constitution and the experimental technique in the expanding fraction of metal cylinder shell were critically reviewed firstly. An experimental technique based on the SHPB experiment device was established by numerical simulation and experimental studies on45steel for the absence of an experimental technique which could recover the freezing sample after loading and research the fracture process. This experimental technique could research the dynamic expanding fraction of the metal cylinder shell between102s-1～104s-1strain rate, radial strain, radial strain-rate, internal pressure loading and circumferential tensile stress could been monitored in real time at the process of expansion deformation until to fraction, and the time of fraction, the radial fracture strain, the radial fracture strain-rate, the circumferential tensile fracture stress could also be accurately determine. The whole process of the crack of45steel cylinder shell from initiation to the expansion could be observed by controlling the experimental pulse width of loading to recover the freezing sample, and the fracture mechanism of metal cylinder shell was fully researched, which could give some theoretical basis and guidance for the research of the fracture criterion and the engineering applicationsThe fracture behavior of two kinds of thickness (inner, outer diameter, respectively7mm/8mm and7mm/7.5mm) of45steel cylinder shell was researched in different strain-rates on the experimental technique based on the SHPB device, the fracture characteristic of45steel cylinder shell was obtained. Firstly, the fracture strain of the45steel cylinder shell was increased and the fracture time would be reduced for the increasing of loading strength or the reducing cylinder shell’s wall. Secondly, the crack of the45steel cylinder shell by the internal shock loading in this experimental strain-rate (102s-1～104s-1) was generated at the outer wall by experimental research, and the form of crack would been changed from tensile to shear by the increasing of loading strength; the analysis of stress state by numerical simulation interpreted this phenomena. The shear crack would expand along the shear direction and the tensile crack would expand some distance along the radial direction and then expand along the shear direction in this experimental strain-rate. Thirdly, the form of fraction of the45steel cylinder shell would been changed from mixed fraction to pure shear fraction by increasing loading strain-rate, the critical loading strain-rate was1.8×103s-1for the cylinder shell of out diameter7.5mm, and1.5×103s-1for out diameter8mm. Finally, the multiple cracks on the45 steel cylinder shell would been observed by increasing loading strain-rate, the critical loading strain-rate of multiple cracks was2.4×103s-1for cylinder shell of out diameter7.5mm, and1.6×103s-1for cylinder shell of out diameter8mm.A new experimental phenomena-layered groove was observed in this experiment, there were many parallel grooves along axial separated the fractured section of the45steel cylinder shell into many layered. There were some characteristics of layered groove. Firstly, the layered grooves were generated by tensile stress, and all of them were lie on the fracture surface symmetrically. The layered grooves were the branch of crack tip when the crack reducing it’s propagation velocity or even stopping, the fracture part on cross-section would contract (the outer part contracted more seriously than the inner part) by the unloading wave from the fracture surface, this non-uniform distributed residual stress field make the radial crack tip to branch, but the shear crack could not been branch. The depth of the layered groove(the depth of the branch of crack tip) was not deep, just about5μm, because of the low stress intensity of the residual stress field, and the layered groove could also change the propagation direction of the crack from one plane to anther which two were parallel Secondly, the number of the layered groove would reduce and the location of the layered groove would be much closer to the outer wall for the same size cylinder shell by increasing the loading strain-rate, the layered groove would disappear when the loading strain-rate reached a critical value because of the propagating speed of crack would not reduce obviously, not even stop. The layered groove on the cylinder shell at the most serious raised position would be disappeared when the loading strain-rate rised at1.6×103s-1for the cylinder shell of out diameter8mm, and2.2×103s-1for the cylinder shell of out diameter7.5mm.