纯钛带激光冲击成形实验及数值模拟

发布时间：2018-08-18 12:34

【摘要】：传统金属板料成形技术逐渐不能满足现今产品快速更新的需求,开发新的金属板料塑性成形技术意义重大。激光冲击成形(LSF)技术是一种集成形与强化于一体的新型塑性成形技术,具有高压、高速、精确成形的特点,用于小批量、多品种、形状复杂的新产品的生产有一定优势,具有长远的发展前景。纯钛因密度小、比强度高、耐腐蚀、良好的生物相容性等优点而被广泛应用于航空航天、汽车工业、医疗等领域,将激光冲击成形技术应用于纯钛的塑性成形,对于研究纯钛的新型塑性成形技术、促进纯钛的应用具有重要意义。本文以交叉轧制纯钛带TA1为研究对象,对其进行不同激光功率密度下多次冲击成形研究。通过实验与数值模拟技术相结合,研究了钛带成形性能,分析了钛带微观结构变化。主要工作与结论如下:钛带表面在激光冲击后形成圆形凹坑,冲击中心减薄量和成形深度最大,且减薄量和成形深度随激光功率密度和冲击次数的增加而增加。受激光热影响,表面发生不同程度烧蚀,表面粗糙度增加。多次激光冲击致使钛带表层硬度增加和强化。钛带经十多次连续冲击后发生破裂,其位于冲击中心处,断口内部分布有韧窝、撕裂棱和层裂,表现为韧性断裂。钛带激光冲击破裂机制为减薄机制和层裂机制,减薄引起缩颈,从而在断口处形成大量韧窝,层裂是激光以脉冲形式作用的结果。激光冲击钛带塑性变形是以滑移与孪生两种方式共同作用的结果,形成了大量平行形变孪晶、高密度位错以及滑移带,硬度提高是发生加工硬化的结果。冲击表面还发现了周期性波纹结构。数值模拟结果表明,激光冲击在钛带表面引入高幅值的残余压应力,呈“W”形分布,且残余压应力值随功率密度的增加而增加,随冲击次数增加而先增加后减小,冲击中心处在多次冲击后逐渐形成残余拉应力;成形深度与壁厚减薄量均随功率密度和冲击次数的增加而增加;钛带在6.11GW/cm2的功率密度下冲击15次后达到成形极限而破裂,破裂位置位于中心处;比较了实验与模拟结果中的最大成形深度、最大减薄率和破裂位置,模拟结果与实验结果基本一致。
[Abstract]:The traditional sheet metal forming technology can not meet the needs of rapid product renewal gradually. It is of great significance to develop new sheet metal plastic forming technology. Pure titanium is widely used in aerospace, automotive industry, medical and other fields because of its low density, high specific strength, corrosion resistance and good biocompatibility. Laser shock forming technology is applied to the plastic forming of pure titanium, which is helpful to the research of new pure titanium. In this paper, Cross-rolled pure titanium strip TA1 was studied by multiple impact forming under different laser power densities. The forming properties of titanium strip were studied by combining experimental and numerical simulation techniques, and the microstructure changes of titanium strip were analyzed. The conclusions are as follows: the surface of titanium strip forms circular pit after laser shock, the thinning of impact center and the forming depth are the biggest, and the thinning and forming depth increase with the increase of laser power density and impact times. Titanium band ruptures after more than ten consecutive shocks. There are dimples, tearing edges and spallation in the fracture surface, which are ductile fracture. The mechanism of laser shock rupture of titanium band is thinning mechanism and spallation mechanism. The necking is caused by thinning, and a large number of dimples are formed at the fracture surface. The plastic deformation of the laser-impacted titanium strip is the result of the interaction of slip and twin, resulting in a large number of parallel deformation twins, high density dislocations and slip bands. The hardness of the laser-impacted titanium strip is increased as a result of work hardening. The high amplitude residual compressive stress was introduced on the surface of the titanium strip, and the residual compressive stress increased with the increase of power density, first increased and then decreased with the increase of impact times. The residual tensile stress gradually formed at the impact center after repeated impact. At 6.11GW/cm2 power density, the titanium band reaches the forming limit and breaks after 15 times of impact, and the fracture location is located at the center. The maximum forming depth, the maximum thinning rate and the fracture location are compared between the experimental and simulation results, and the simulation results are basically consistent with the experimental results.
【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.23;TG665

【参考文献】