应力应变转换的TBM刀座焊缝三维裂纹扩展模型
发布时间：2018-08-04 13:58
【摘要】：在运用TBM进行隧道开挖的工程中,刀盘上的刀座是最常发生疲劳破坏的结构,破坏形式多表现为沿焊缝的疲劳裂纹和刀座的过载变形,并最终导致刀座性能失效。刀座的失效会对滚刀的安装精度和工作状态造成影响,改变滚刀的受力特性,并加速滚刀的破坏,最终影响掘进效率。因此,针对刀座焊接疲劳寿命预测及其焊接结构的改进具有重要的工程实际意义。本文围绕TBM刀座焊接疲劳寿命预测和焊接结构改进的问题,进行了一系列研究。(1)根据TBM刀盘板厚超厚特点,基于平面应力条件的小时间裂纹扩展模型不再适用,故引入塑性约束因子α来改变材料屈服应力值,将内部裂纹和沿板厚方向扩展的裂纹尖端平面应力/应变状态的转变进行等效。根据不同板厚试样的裂纹扩展疲劳试验,得到α与板厚t的关系方程：α=0.73t-0.943,提出了适用于大板厚的应力/应变转换的小时间尺度三维约束裂纹扩展模型。另外,将焊接残余应力对焊缝区应力特征的影响考虑在内,对小时间裂纹扩展模型进一步改进,使其适用于焊缝裂纹扩展寿命的预测。(2)采用C(T)焊接试样进行焊缝疲劳裂纹扩展寿命试验,记录了裂纹扩展长度α0与载荷循环次数N的关系数据,并运用修正后的寿命预测模型对C(T)试样的焊缝疲劳裂纹扩展寿命进行预测,理论预测结果与疲劳试验数据对比结果显示,疲劳试验结果处于理论预测寿命的0.5-2倍范围内,在工程中是可接受的,证明了寿命预测模型和方法的有效性。(3)根据工程实例中TBM刀座的结构和载荷特点,以及刀座正面焊缝常出现疲劳裂纹的情况,对刀座正面焊缝形式进行改进,将角焊缝改为对接焊缝,为节省仿真计算成本,设计缩尺简化模型代替现役刀座和新型刀座的结构特点,对刀座缩尺简化结构的残余应力场进行仿真分析,对比两种结构的残余应力场,得出新型结构的残余应力场对提高疲劳性能更有利。(4)运用提出的寿命预测模型对刀座缩尺结构的焊缝裂纹扩展寿命进行了预测。根据相似理论,反推得到工程实例刀座的焊缝裂纹扩展寿命,得到现役刀座焊接结构的寿命为6.04km,新型刀座焊接结构的寿命为7.74km,与现役结构相比,新型结构的焊缝疲劳裂纹扩展寿命预测提高了28%,设计的新型刀座焊接结构比现役刀座焊接结构有更好的疲劳性能。
[Abstract]:In the engineering of tunnel excavation with TBM, the tool holder on the cutter head is the most common structure with fatigue failure. The failure forms are mostly the fatigue crack along the weld seam and the overload deformation of the tool holder, and finally lead to the failure of the tool holder performance. The failure of the tool holder will affect the installation accuracy and working state of the hob, change the mechanical characteristics of the hob, accelerate the destruction of the hob, and ultimately affect the tunneling efficiency. Therefore, the prediction of welding fatigue life of tool holder and the improvement of welding structure have important engineering significance. This paper focuses on the prediction of fatigue life of TBM tool holder and the improvement of welding structure. (1) according to the characteristics of TBM cutter plate thickness and super-thickness, the small time crack propagation model based on plane stress condition is no longer applicable. Therefore, the plastic constraint factor 伪 is introduced to change the yield stress value of the material, and the transformation of the plane stress / strain state of the crack tip along the plate thickness is equivalent to that of the inner crack. According to the fatigue test of crack propagation of specimen with different thickness of plate, the equation of 伪 and thickness t is obtained: 伪 0.73t-0.943. A small time scale confined crack propagation model is proposed for the stress / strain conversion of large plate thickness. In addition, the influence of welding residual stress on the stress characteristics of weld zone is taken into account, and the small time crack propagation model is further improved. It is suitable for the prediction of weld crack growth life. (2) the fatigue crack growth life test of weld seam is carried out with C (T) welding specimen, and the relation data between crack propagation length 伪 0 and load cycle number N are recorded. The modified life prediction model is used to predict the fatigue crack propagation life of weld seam of C (T) specimen. The results of theoretical prediction and fatigue test show that the fatigue test results are within the range of 0.5-2 times of the theoretical predicted life. It is acceptable in engineering, which proves the validity of life prediction model and method. (3) according to the structure and load characteristics of TBM tool holder in engineering example, fatigue crack often appears in the front weld of tool holder. In order to save the cost of simulation, a simplified model was designed to replace the active tool holder and the new type tool holder in order to save the cost of simulation. The residual stress field of the simplified structure is simulated and analyzed, and the residual stress field of the two structures is compared. It is concluded that the residual stress field of the new structure is more favorable to improve the fatigue performance. (4) the life prediction model is used to predict the crack propagation life of the weld seam of the tool holder scale structure. According to the similarity theory, the weld crack propagation life of the tool holder in engineering example is obtained. The service life of the welding structure is 6.04km, and the life of the new type welding structure is 7.74km, which is compared with the active structure. The prediction of fatigue crack propagation life of the new type structure has been improved by 28%. The designed new type of tool holder welding structure has better fatigue performance than the existing tool holder welding structure.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：U455.3
本文编号：2164104
[Abstract]:In the engineering of tunnel excavation with TBM, the tool holder on the cutter head is the most common structure with fatigue failure. The failure forms are mostly the fatigue crack along the weld seam and the overload deformation of the tool holder, and finally lead to the failure of the tool holder performance. The failure of the tool holder will affect the installation accuracy and working state of the hob, change the mechanical characteristics of the hob, accelerate the destruction of the hob, and ultimately affect the tunneling efficiency. Therefore, the prediction of welding fatigue life of tool holder and the improvement of welding structure have important engineering significance. This paper focuses on the prediction of fatigue life of TBM tool holder and the improvement of welding structure. (1) according to the characteristics of TBM cutter plate thickness and super-thickness, the small time crack propagation model based on plane stress condition is no longer applicable. Therefore, the plastic constraint factor 伪 is introduced to change the yield stress value of the material, and the transformation of the plane stress / strain state of the crack tip along the plate thickness is equivalent to that of the inner crack. According to the fatigue test of crack propagation of specimen with different thickness of plate, the equation of 伪 and thickness t is obtained: 伪 0.73t-0.943. A small time scale confined crack propagation model is proposed for the stress / strain conversion of large plate thickness. In addition, the influence of welding residual stress on the stress characteristics of weld zone is taken into account, and the small time crack propagation model is further improved. It is suitable for the prediction of weld crack growth life. (2) the fatigue crack growth life test of weld seam is carried out with C (T) welding specimen, and the relation data between crack propagation length 伪 0 and load cycle number N are recorded. The modified life prediction model is used to predict the fatigue crack propagation life of weld seam of C (T) specimen. The results of theoretical prediction and fatigue test show that the fatigue test results are within the range of 0.5-2 times of the theoretical predicted life. It is acceptable in engineering, which proves the validity of life prediction model and method. (3) according to the structure and load characteristics of TBM tool holder in engineering example, fatigue crack often appears in the front weld of tool holder. In order to save the cost of simulation, a simplified model was designed to replace the active tool holder and the new type tool holder in order to save the cost of simulation. The residual stress field of the simplified structure is simulated and analyzed, and the residual stress field of the two structures is compared. It is concluded that the residual stress field of the new structure is more favorable to improve the fatigue performance. (4) the life prediction model is used to predict the crack propagation life of the weld seam of the tool holder scale structure. According to the similarity theory, the weld crack propagation life of the tool holder in engineering example is obtained. The service life of the welding structure is 6.04km, and the life of the new type welding structure is 7.74km, which is compared with the active structure. The prediction of fatigue crack propagation life of the new type structure has been improved by 28%. The designed new type of tool holder welding structure has better fatigue performance than the existing tool holder welding structure.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：U455.3
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