高强铝合金十字接头疲劳寿命特性研究
发布时间：2019-05-29 16:35
【摘要】：铝合金十字接头被广泛应用于高铁列车的转向架的焊接中,由于长时间承受循环载荷的作用,所以容易发生疲劳断裂问题,本文针对7N01铝合金材料十字接头为研究对象,分别针对疲劳萌生和扩展两个阶段进行研究,通过实验和有限元相结合的方法计算疲劳裂纹萌生和疲劳裂纹扩展寿命。通过对7N01母材和焊缝材料进行低周疲劳实验,拟合母材和焊缝的循环应变幅-寿命曲线,通过对实验结果的分析发现,在载荷水平较低,寿命较长的情况下,弹性应变对试件的疲劳过程的影响大,塑性应变影响很小,随着载荷的增加,塑性应变所占的比重会快速增加,当载荷水平在较高时,此时塑性应变起处于主要的地位,对疲劳过程起到了主要推进过程;通过有限元的方法模拟十字接头的应力分布状态,发现应力集中位置和实际疲劳过程中的开裂位置吻合,并计算获得疲劳失效位置的应力集中系数。考虑到焊接过程是一个快速加热又快速冷却的过程,分析了焊接接头残余应力在循环过程中的松弛情况,同时考虑到不对称载荷的影响,对循环应力幅-寿命关系式加以修正;求解以循环应力-应变方程和Neuber双曲线方程构成的方程组的解求出局部应变,在将其代入修正后的循环应变-寿命公式,求得试件在焊趾处和焊缝处的疲劳裂纹萌生寿命。引入了权函数的思想,推导出板边裂纹应力强度因子的表达式;分别利用有限元计算法,膜应力、弯曲应力法和节点力法,对十字接头焊趾处进行应力场分布求解,结合权函数导出的应力强度因子公式,计算出试件的应力场强度因子,通过对结果的分析发现,节点力法所求的应力场强度因子随裂纹长度的分布变化更符合真实的结果;将所求的应力场强度因子带入Pairs公式求解试件的疲劳扩展寿命;介绍了结构应力法的原理,并利用结构应力法求解十字接头的疲劳总寿命;将结构应力法求得的疲劳总受寿命,分阶段求得的疲劳萌生寿命和和扩展寿命相加的疲劳总寿命以及实验中记录的试件疲劳寿命,三者分析比较,发现三者基本上能较好的吻合,从而验证了所用的计算方法的合理性。
[Abstract]:The aluminum alloy cross joint is widely used in the welding of the bogie of the high-speed rail train, and the fatigue fracture is easy to occur due to the long-time bearing of the cyclic load. The cross joint of the 7N01 aluminum alloy material is the research object, The fatigue crack initiation and fatigue crack propagation life were calculated by the combination of experiment and finite element method. By carrying out low-cycle fatigue experiment on the 7N01 base material and the welding seam material, the cycle of the base material and the welding line should be fitted with an amplitude-life curve, and the influence of the elastic strain on the fatigue process of the test piece is large under the condition that the load level is lower and the service life is long by the analysis of the experimental result, The influence of plastic strain is very small, with the increase of load, the specific gravity of plastic strain will increase rapidly, and when the load level is higher, the plastic strain is in the main position at this time, and the fatigue process plays a major advance. The stress distribution state of the cross joint is simulated by the finite element method, and the stress concentration position and the crack position in the actual fatigue process are found to coincide with each other, and the stress concentration coefficient of the fatigue failure position is calculated. Considering that the welding process is a rapid heating and rapid cooling process, the relaxation of the residual stress of the welded joint during the cycle is analyzed, and the influence of the asymmetric load is taken into account, and the cyclic stress amplitude-life relation is corrected. The local strain is obtained by solving the solution of the equations of the cyclic stress-strain equation and the Neuber hyperbolic equation, and the fatigue crack initiation life of the test piece at the toe and the weld is obtained after the modified cyclic strain-life formula is substituted into the modified cyclic strain-life formula. The method of weight function is introduced, and the expression of the stress intensity factor of the crack stress of the plate edge is derived. The stress field distribution and the stress intensity factor formula derived from the weight function are calculated by using the finite element method, the film stress, the bending stress method and the node force method. The stress field intensity factor of the test piece is calculated. Through the analysis of the result, the stress field strength factor obtained by the node force method is more consistent with the real result with the distribution change of the crack length, and the obtained stress field strength factor is taken into the Pairs formula to solve the fatigue extension life of the test piece; The principle of the structural stress method is introduced, and the fatigue life of the cross joint is solved by the structural stress method. The fatigue life, the fatigue life and the fatigue life of the fatigue life and the fatigue life of the test piece recorded in the experiment are calculated by the structural stress method. The analysis and comparison show that the three are basically good agreement, thus the rationality of the calculation method used is verified.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG407
本文编号：2488061
[Abstract]:The aluminum alloy cross joint is widely used in the welding of the bogie of the high-speed rail train, and the fatigue fracture is easy to occur due to the long-time bearing of the cyclic load. The cross joint of the 7N01 aluminum alloy material is the research object, The fatigue crack initiation and fatigue crack propagation life were calculated by the combination of experiment and finite element method. By carrying out low-cycle fatigue experiment on the 7N01 base material and the welding seam material, the cycle of the base material and the welding line should be fitted with an amplitude-life curve, and the influence of the elastic strain on the fatigue process of the test piece is large under the condition that the load level is lower and the service life is long by the analysis of the experimental result, The influence of plastic strain is very small, with the increase of load, the specific gravity of plastic strain will increase rapidly, and when the load level is higher, the plastic strain is in the main position at this time, and the fatigue process plays a major advance. The stress distribution state of the cross joint is simulated by the finite element method, and the stress concentration position and the crack position in the actual fatigue process are found to coincide with each other, and the stress concentration coefficient of the fatigue failure position is calculated. Considering that the welding process is a rapid heating and rapid cooling process, the relaxation of the residual stress of the welded joint during the cycle is analyzed, and the influence of the asymmetric load is taken into account, and the cyclic stress amplitude-life relation is corrected. The local strain is obtained by solving the solution of the equations of the cyclic stress-strain equation and the Neuber hyperbolic equation, and the fatigue crack initiation life of the test piece at the toe and the weld is obtained after the modified cyclic strain-life formula is substituted into the modified cyclic strain-life formula. The method of weight function is introduced, and the expression of the stress intensity factor of the crack stress of the plate edge is derived. The stress field distribution and the stress intensity factor formula derived from the weight function are calculated by using the finite element method, the film stress, the bending stress method and the node force method. The stress field intensity factor of the test piece is calculated. Through the analysis of the result, the stress field strength factor obtained by the node force method is more consistent with the real result with the distribution change of the crack length, and the obtained stress field strength factor is taken into the Pairs formula to solve the fatigue extension life of the test piece; The principle of the structural stress method is introduced, and the fatigue life of the cross joint is solved by the structural stress method. The fatigue life, the fatigue life and the fatigue life of the fatigue life and the fatigue life of the test piece recorded in the experiment are calculated by the structural stress method. The analysis and comparison show that the three are basically good agreement, thus the rationality of the calculation method used is verified.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG407
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