7050铝合金材料R曲线的三维效应与试验研究

裂纹扩展阻力曲线(R曲线)反映了疲劳裂纹扩展断裂的真实物理过程,但是现阶段测量材料R曲线的方法在计算试样阻抗应力强度因子时,未考虑厚度的影响,并且在计算裂纹扩展阻力R时,仅考虑了平面应力状态与平面应变状态两种极端情况,忽略了更为普遍的过渡状态。首先对中心孔裂纹板进行了三维弹塑性有限元分析,通过计算其三维应力强度因子表示式,建立了裂纹扩展阻力与试样厚度的关系模型。其次,依据三维状态下能量释放率与应力强度因子的关系式,结合裂纹扩展阻力与试样厚度的关系式,建立了不同厚度试样三维裂纹扩展阻力R值的计算模型。最后,基于该模型,通过试验测定了不同厚度7050铝合金板的R曲线,得到了R曲线与试样厚度的函数关系式。

The Three-dimensional Effect and Experimental Study on Material R Curves of 7050 Aluminium Alloy

Material R curves can reflect the true physical process of fatigue crack growth. But only the plane stress and plane strain situations are considered by using present methods to calculate the value of resistance stress intensity factor. While the effect of thickness is not considered when calculating the value of KR. Firstly, the present test method The 3-D stress intensity factor expression of center-cracked tension plate is calculated by using 3-D elastic-plastic finite element method, and then the relation model between crack propagation resistance and thickness of plate is established. Then, combining with the relationship between crack propagation resistance and thickness of plate, a new model for calculating crack growth resistance value R of specimen with different thickness is provided based on the relationship between the energy release rate and the stress intensity factor in 3-D state. Finally, based on this model, the R curves of 7050-T7451 aluminum alloy plates with different thickness are determined by test, and the function relationship between the R curve and sample thickness is obtained.