Study Of Impact Response Of TiNi Phase Transformation Cantilever

Phase transformation(PT) can greatly affect the mechanical response of material and structure. It is a basic problem and major research task of solid mechanics and material science. Because of the peculiar mechanical behavior phase transformation material has gained widespread application. The study of mechanical property is relatively mature, but it is very short of the study of the mechanical property of the phase transformation structures, especially the response under impact loading. In this paper, the impact response of pseudoelastic phase transformation cantilever(PPTC) is systematically investigated experimentally and numerically, and found some interesting phenomena and regularity, gained in-depth understanding about regularity of propagation of the phase transformation flexural wave(PTFW), formation and development of phase transformation hinge(PTH), and impact response of PPTC.Experimental investigation was conducted on two typical phase transformation materials-FeMnNi alloy and TiNi alloy using light gas gun and MTS. It is found that for FeMnNi alloy upon high velocity impacting the a-e PT can greatly change the shock wave profile and spall the sample into pieces, and addition of Mn and Ni may lower the transformation pressure strongly. Because of the different initial phases, TiNi alloy is in pseudoelastic(PE) or shape memory effect(SME) state. Martensite PT PE and R PT exhibits SME.Experimental investigation was conducted on PE and SME TiNi cantilever with rectangular section under transversal impact using a revised split Hopkinson pressure bar (SHPB) apparatus. It is found that PTH of the PTC is recoverable and its strain increases fluctantly upon impact, but the asymmetry between the tension and compression side is not remarkable. For PE cantilever, when impacting free end, PTH formed at the root, and the deformation of PTH increases and it forms earlier as the impact velocity increases; When the impact velocity is high a little PT maybe appear in the middle of the beam at first. When the impacting location is at the third of the beam length from free end PTFW may appear at first, several PTHs can form and deformation of the two hinges near the root displays such a trend that when one increases the other decreases, and the peak and valley of the two hinges is opposite. For SME beam R PTFW appears at first, and PTH can also form when martensite PT occurs. Occurrence of PT and existence of PTH can attenuate the vibration of beam greatly, and R PT attenuates the vibration faster. After impact, a PE beam will come back to its original shape, SME beam has some residual deformation which does not increase with increasing impact velocity and disappears upon heating.Using a simplified ideal PE constitutive model, the behavior of the beam section is theoretically analyzed. Regularity of development and evolvement of PT zone and of motion of phase boundaries is disclosed, and corresponding analytic expression is given. Then moment-curvature relationship of rectangular beam during the loading and unloading procedure is obtained, and the energy dissipation due to PT of rectangular beam during a complete loading-unloading cycle is given.Numerical simulation study is conducted on the propagation problem of PTFW in ideal PPTC using FEA software LS-DYNA, and the problem of initiation, propagation, reflection and unloading of PTFW is discussed. Results show that PTFW is initiated by development and enlargement of elastic flexural wave(EFW), and PTH may form at the center of the peak of PTFW; When beam section material enter the second phase the second phase EFW may occur and waveform will be distorted seriously. The reflected flexural waves and the incident waves at the fixed end of the beam are approximately symmetry, and the reflected elastic flexural waves could distinctively change the waveform of PTFW. Whether PT occurs at the fixed end or not and the time depends on the intensity of the elastic wave peak which arrives the fixed end and reflects. The effect of the unloading flexural wave, which is dispersive and developing, on the loading wave is depended on the phasic difference when they meet. When the unloading wave and reflected wave at the fixed end action at the same time, the spatio-temporal evolution map of the whole phase transformation zone is represented by many discrete and closed zone.Numerical simulation study is conducted on the dynamic response of PPTC under step or rectangular pulse load. Different pattern and the evolution procedure of PTH and the dynamic behavior of PPTC under high but short pulse load is analysed. Under step load different patterns such as hinge zone at the root, single, double hinge and continuous hinge zone in the middle may form. After unloading PTH recovers and moves, PT zones redistribute along the beam and different evolution patterns form. Under high but short pulse load response of PPTC may be divided into four phases: propagation of flexural waves and formation of PTH during loading procedure, complex evolution of PTH after unloading, intensive whipping of the beam during swinging toward the maximal deflection, and to-and-fro movement around the root of the beam; the first three phases occupy relatively short time but the majority of energy is dissipated.Simulation result of the experiment shows that several impacts occur between the bullet and the PPTC at the early stage where the bullet kinetic energy decreases greatly; The occurrence of PT near the free end is caused by the reflection of flexural wave at the free end; The energy dispersion due to PT mainly occurs before the cantilever swing back to the equilibrium position for the first time. When the hardening modulus is added into the model simulation result is more approaching to the experimental result.