强震下的钢结构焊缝疲劳性能研究

发布时间：2018-06-17 08:21

本文选题：焊缝 + 高应变低周疲劳　；参考：《东南大学》2016年硕士论文

【摘要】：在强震作用下,高耸高层钢结构焊接节点焊缝极易产生疲劳损伤累积,造成焊接节点的破坏甚至整个结构的倒塌,但国内外对焊缝在强震作用下的低周疲劳性能仍缺乏系统的研究。本文围绕强震作用下高耸高层钢结构焊缝疲劳劣化机理与寿命预测这一主题,针对高应变低周疲劳问题,通过一系列焊缝轴向等幅高应变低周疲劳试验,系统研究了焊缝在高应变循环过程中表现的疲劳性能,获得了焊缝在高应变低周疲劳中的循环应力应变响应特征和循环应力应变关系,提取了相关性能参数,揭示了焊缝在循环加载过程中应力应变变化规律及其机械性能、循环韧度和Masing特性等性能特征量的循环相关性,并在其疲劳性能的基础上提出了基于裂纹尖端塑性应变能的寿命预测模型,结合试验S-N曲线对模型进行了对比验证。试验研究表明,对接焊缝在高应变低周疲劳过程中,表现出一定程度的循环软化特征,但是很快就进入稳态循环直至破坏。循环过程中,焊缝呈现出明显的拉压塑性应变不对称性。在塑性变形过程中,正向受拉加载引起塑性应变强化,反向受压加载时出现塑性应变软化,具有强烈的包辛格效应。通过X射线衍射分析了循环过程中焊缝残余应力的变化,发现残余应力在循环前期即释放,对焊缝低周应变疲劳性能影响不大。通过不同应变幅下稳态应力应变响应的对比,发现随着总应变幅的增加,弹性应变幅数值变化很小,塑性应变幅在总应变幅中的比例逐渐增大。高应变幅下,焊缝主要发生塑性变形。随着总应变幅的增大,塑性应变幅相应增大,焊缝的循环韧度增大,焊缝能够吸收的过载能量增加。根据Hollmom方程拟合得到焊缝高应变低周稳态循环应力应变关系式,对比母材钢循环应力应变曲线关系结果可知,焊缝的循环强度系数和循环硬化指数均低于母材。通过比较焊缝单调拉伸试验和不同循环次数拉伸阶段的循环应力应变曲线可知,循环作用下焊缝金属循环强度系数小于单调拉伸弹性模量,屈服强度下降,塑性性能下降。同时焊缝金属材料稳态滞回曲线的上半段不能完全重合,因而焊缝金属Masing特性不明显。通过积分计算滞回环包络面积求解焊缝的循环滞回能,看出在循环过程中,随着循环次数的增加,焊缝的塑性应变能基本保持不变,变化区间小于1%。大量塑性应变造成的塑性应变能的累积,进而产生的不可逆损伤是产生疲劳破坏的根本原因。伴随着裂纹的扩展,裂纹尖端总是存在一个变化的塑性区,而循环过程中塑性应变能具备循环稳定性,所以裂纹尖端塑性应变能是一个描述高应变低周疲劳损伤的重要参量,可以用来预测低周疲劳寿命。本文按照Irwin塑性区模型,运用Mises准则,重新推导了裂纹尖端塑性应变能与应力幅的关系,取单向拉伸的极限塑性应变幅对应的应力计算了临界状态塑性应变能。假设临界塑性应变能与疲劳寿命之间为幂函数关系,考虑断裂前最后—次弹性应变能积累的影响,参考Manson-Coffin公式的形式,得到了基于尖端塑性应变能的疲劳寿命预测公式,试验表明该模型适合焊缝高应变低周疲劳。
[Abstract]:Under the action of strong earthquake, the weld joint weld of high rise steel structure is very easy to produce fatigue damage accumulation, cause the damage of welding node and even the collapse of the whole structure, but the low cycle fatigue performance of weld under strong earthquake is still lack of systematic research at home and abroad. For high strain and low cycle fatigue, the fatigue performance of weld in high strain cycle is studied systematically, and the cyclic stress-strain relationship and cyclic stress-strain relationship in high strain and low cycle fatigue are obtained by a series of high strain low cycle fatigue tests. The related performance parameters were extracted, and the cyclic correlation of the stress and strain changes and the mechanical properties, the cyclic toughness and the Masing characteristics were revealed. The life prediction model based on the plastic strain energy of the crack tip was put forward on the basis of the fatigue performance, and the model of the test S-N curve was combined with the model. The experimental study shows that the butt weld exhibits a certain degree of cyclic softening in the process of high strain and low cycle fatigue, but it quickly enters the steady state cycle until it is destroyed. In the process of circulation, the weld exhibits obvious tension and plastic strain asymmetry. In the process of plastic deformation, it is induced by tensile loading. Plastic strain intensification and plastic strain softening have a strong Basinger effect. The change of residual stress in the welding seam is analyzed by X ray diffraction. It is found that the residual stress is released at the early stage of circulation and has little effect on the low cycle strain fatigue properties of the weld. With the increase of the total strain amplitude, it is found that the change of elastic strain amplitude is very small, and the proportion of plastic strain amplitude in the total amplitude increases gradually. Under high strain amplitude, the plastic deformation is mainly formed. With the increase of the total strain amplitude, the plastic strain amplitude increases correspondingly, the cyclic toughness of the weld increases and the weld can absorb the overload. Energy increases. According to the Hollmom equation, the stress-strain relationship of high strain and low cycle steady state cycle is obtained. Compared to the results of the relationship between the cyclic stress and strain curves of the base metal steel, the cyclic strength coefficient and the cyclic hardening exponent of the weld are lower than that of the parent material. The stress strain curve shows that the cyclic strength coefficient of the weld metal is less than that of the monotone tensile modulus, the yield strength decreases, and the plastic properties decrease. At the same time, the first half section of the steady-state hysteresis curve of the weld metal material can not be completely overlapped, so the Masing characteristic of the weld metal is not obvious. The calculation of the envelope area of the hysteresis loop is solved by integral calculation. In the cyclic hysteresis energy of the weld, it is found that the plastic strain energy of the weld is basically kept unchanged with the increase of the number of cycles in the cycle process. The variation interval is less than the accumulation of plastic strain energy caused by the plastic strain of 1%., and the irreversible damage is the fundamental cause of the fatigue failure. There is always a changing plastic zone, and the plastic strain can have the cyclic stability during the cycle process, so the plastic strain energy at the crack tip is an important parameter to describe the high strain and low cycle fatigue damage. It can be used to predict the low cycle fatigue life. In this paper, the crack tip is rededuced by the Mises criterion in accordance with the model of the Irwin plastic zone. The plastic strain energy is related to the stress amplitude, and the critical state plastic strain energy is calculated by the stress corresponding to the ultimate plastic strain amplitude. Assuming that the critical plastic strain energy is a power function relationship with the fatigue life, the impact of the last elastic strain energy accumulation before the fracture is taken into consideration, and a reference to the form of the Manson-Coffin formula is obtained. The fatigue life prediction formula based on tip plastic strain energy shows that the model is suitable for high strain low cycle fatigue of weld.
【学位授予单位】：东南大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TU973.13

【参考文献】