基于SPH耦合FEM算法的喷丸残余应力和以裂纹扩展方向为判据的疲劳特性数值仿真研究

In the field of numerical simulations on residual stress induced by shot peening, most existing models are so-called micro models, which only include single or a few shots using Finite Element Method(FEM), therefore there are distinct differences from practical cases.In our researchies, Smooth Particle Hydrodynamics (SPH) coupled Finite Element Method (FEM) will be adopted to establish an innovative macro models involving a great deal of shots,which can deal with more relative parameters about shot peening process, and produce more useful results.Using SPH coupled FEM algorithm, a new micro model will also be formed to simulate a ball-shaped or angular particle impacting workpiece, in which the particle's rotation effect due to interaction between the particle and workpiece will be consided firstly, and the effect factors to surface morphologies and characteristic values of roughness will be investigated. Another important part in our researchies is to put forward a new viewpoint that the crack growth direction is a critical factor to influence the fatigue life due to crack growth happened on the surface of workpiece treated by shot peening. It comes from the fact that the effect layer of residual presure stress induced by shot peening is very thin,and in the condition of crack growth along to surface,the restrain effect to crack growth caused by residual presure stress should be significant, but it should become faint in the conditon of crack growth toward inside.An innovative numerical simulation model of crack growth will be put forward based on the viewpoint. Meanwhile the effect factors to crack growth direction are investigated, some new criteria to evaluate the fatigue life related crack growth treated by shot peening will be found.Some experiments related to verify those simulation models and results will also be carried out.

在数值仿真喷丸诱导残余应力场方面，现有基于有限元法的模型均为微观模型，即仅针对单/多丸粒建模，与实际工况存在显著差异。本研究拟采用光滑粒子流体动力学法(SPH)耦合有限元法(FEM)，建立含大量丸粒的新型宏观模型，将涉及更多喷丸影响参数，得到更丰富的仿真结果。此外还利用SPH耦合FEM法建立球形或锐边弹丸撞击靶材的微观模型，首次计及撞击时的弹丸翻转效应，分析喷丸参数对弹坑形貌和粗糙度特征值的影响。本研究的另一重要内容是首次提出裂纹扩展方向是影响喷丸工件表面裂纹扩展疲劳寿命的重要因素的新理念，其出发点是基于喷丸表面残余压应力影响层极薄，当裂纹沿表面扩展时，其残余压应力对裂纹扩展的抑制作用明显，而沿深度扩展则较差。为此提出一个新型裂纹扩展数值仿真模型，以期在分析裂纹扩展方向影响因素的同时，得到喷丸强化对裂纹扩展疲劳寿命影响程度的新判据。本研究还拟开展针对各仿真模型及结果的实验验证工作。

本项目以提高喷丸改善工件抗疲劳性能的功效为总研究目标，开展了一系列数值仿真和实验研究。首次提出一基于SPH耦合FEM法研究喷丸残余应力场的创新性数值模型，得到较传统模型更丰富而准确的仿真结果；基于喷丸残余应力加裂尖塑性导致裂纹闭合效应的研究，提出预测喷丸疲劳寿命数值分析新算法，揭示了喷丸强化提高疲劳性能的机理，修正了原计划拟以裂纹扩展方向为判据预测喷丸疲劳寿命的研究方向；增加了用实验和仿真的方法研究在交变载荷或裂纹扩展条件下，喷丸残余应力发生松弛和重分布的规律，为形成计及残余应力松弛的喷丸疲劳寿命预测新模型或算法奠定基础；首次通过实验和仿真手段，研究喷丸残余应力和表面粗糙度对喷丸疲劳寿命的综合影响，其中涉及影响喷丸强化作用和弱化作用的正、反两方面，通过两者综合作用下的喷丸疲劳寿命实验研究和两者相关性的仿真分析，得到了更具实际指导意义的喷丸优选参数，弥补了现有研究中仅研究喷丸残余应力或表面粗糙度对疲劳寿命单方面影响的不足，使其研究结果和结论更加全面、更具说服力。上述研究成果的取得标志着本项目研究圆满完成了各项规定研究内容，实现了预期研究目标。