基于微观胞元的镍基单晶合金应力松弛数值模拟

Simulation on Stress Relaxation of DD3 Nickel-Based Single Crystal Superalloy Based on Micro Cell Model

对DD3镍基单晶高温合金薄壁圆筒试样在680℃进行了拉/扭低周疲劳试验,基于单晶合金的微观结构特性,建立了γ/γ′双相微观多胞元力学模型,采用双线性随动Hill硬化模型,对试样进行拉/扭循环位移加载有限元数值模拟。研究结果表明:高温非对称循环载荷下,试样轴向表现出应力松弛行为和非弹性形变累积,其中基体相最先出现塑性累积变形,导致低周疲劳破坏。数值模拟研究发现,使用单个胞元模型进行拉/扭多轴位移加载,会出现边界应力畸变现象,与试验结果不相吻合,而采用多个胞元力学模型则可以避免发生边界应力畸变现象,能够更好地模拟高温非对称循环载荷下的应力松弛行为和对单晶合金进行应力弱化损伤研究。

The tension-torsion experiments at 680 ℃ on DD3 nickel-based single crystal superalloy thin-wall tube samples were conducted. Based on the microstructure characteristics of nickel-based single crystal alloy, two-phase multi- cell microscopic scale mechanical model were established. Using the bilinear follow Hill hardening model, made finite element numerical simulation of tension / torsion cyclic displacement loading on the samples. It is indicated that the sample axis showed stress relaxing behavior and inelastic deformation accumulation under high temperature asymmetric cyclic loading. The matrix phase appeared plastic deformation accumulation at first and led to low cycle fatigue damage. The numerical simulation found that the boundary stress distortion phenomenon appeared with a single cell for tension-torsion displacement loading, it is not consistent with experimental results. While using multi-cell model could avoid this phenomenon, it can better simulate stress relaxation behavior under asymmetric cyclic loading at high temperature and study stress weaken damage for single crystal alloy.