Exoerimental And Numerical Study Of Transverse Impact Response Of TiNi Phase Transformation End Clamped Beam

TiNi alloy is one of shape memory alloys, which was explored and applied longbefore. Due to its unique shape memory effect (SME) and pseudoelastic (PE),excellent corrosion resistance and biocompatibility, the application of TiNi alloyspans a wide variety of industrial sectors such as aerospace, machinery, electronics,biomedical and so on. Although a lot of key works were concentrated on the materialproperties of TiNi alloy, the considerations of structural mechanisms was initial. Oneof worthy works is to develop the common characteristic of material and structuralresponse.This paper selects beam, the basis structural component, as object to investigatethe dynamic mechanical behavior of PE TiNi beam under transversal impact withexperimental and numerical methods. The formation and development of phasestransformation is exposed and the mechanism of energy dissipation is studied, whichprovide definitely basis for theory and applications.With the view of experiment, the experimental setup is developed many timesto make sure that fixed condition is realized and the influence of that is investigated.The experiment of TiNi end clamped beams in the PE state under transversal impactwas conducted with a modified Split Hopkinson Pressure Bar (SHPB) apparatus and ahigh speed CCD camera. For comparison, the impact response of A3 steel endclamped beam with the same geometry was also studied. It might draw the followingconclusions: 1, The entire impact response of the TiNi end clamped beams can bedivided into three stages, that is, the early wave motion stage, the dynamic structuralresponse stage and the free vibration stage. In early wave motion stage, thepropagation and reflection of the elastic flexural waves dominate the wave responsefor about 0.5ms, that is, the head of elastic flexural wave propagating back and forthin the beam for about 4-5 times. 2, Under the transversal impact at the midpoint, themartensitic phase transition will occur at both the impact position and fixed ends ofthe end clamped beam, which can make the strain concentration and even generate thephase transition hinges (THs) at these locations. The THs have great effects on thedynamic response of end clamped beams. They make further concentration of strainand energy dissipation and let the beam become a hinged beam structure. Theexperimental results show the TiNi end clamped beams and THs can recover without any residual deformation after impact due to the reverse phase transition, whichdiffers from the conventional elastic-plastic beams and plastic hinges. 3, Theexperimental strain signals indicate there is a significant axial tension stress in the endclamped specimens, which causes the asymmetry of tension and compression strainsof both sides at the same location of the beam. Due to the axial tension stress, a THformed at the impact position or the fixed end is probably a single side hinge at thetensile side. 4, The energy absorption coefficientηof TiNi end clamped beamsincreases considerably with the initial kinetic energy of the projectile E0, whileimpacting with the same E0, theηunder short projectile impact is higher than thatunder longer projectile impact. 5, Comparing the experimental results of TiNi endclamped beams with that of TiNi cantilever beams, the end clamped specimens havesmaller deflection and shorter interaction time with the projectile, but larger axialforce than that of cantilevers under impact of projectiles with the same length andspeed.In the numerical part, the impact experiment for TiNi clamped beam mentionedabove is simulated by the finite element software LS-DYNA. The numerical resultsreveal that: 1, The TH formed at the impact position or the fixed end is confirmeddefinitely a single side hinge at the tensile side. 2, Under the impact of projectile, theload-displacement curve of TiNi clamped beam could be divided into several stages,that is, impact fluctuation, load hardening,Ⅱphase elastic stage, unload linear,unload plateau and unload completed. 3, The regular evolution of martensiticpercentage correlates closely with the impact response of beam. 4, The dynamicresponse of TiNi clamped beam is decided by loading condition, geometry and so on.5, TiNi clamped beam dissipate energy via marstensitic transformation, however,when the input energy is up to some degree, the energy absorption is saturated.