304奥氏体不锈钢压力容器棘轮安定效应研究

发布时间：2018-03-01 04:45

本文关键词： 棘轮塑性安定混合强化非循环方法局部应变控制方法应变强化　出处：《华东理工大学》2014年博士论文　论文类型：学位论文

【摘要】：压力容器结构在循环载荷作用下的安全性越来越受到关注,为了保障设备安全,需要进行安定分析和疲劳分析。传统的安定分析方法在分析复杂结构时存在计算量大或计算结果过于保守等方面的不足,尤其对于304这类屈强比较低的奥氏体不锈钢材料,需要发展更加适应于工程应用的安定分析方法。本文以304不锈钢材料为研究对象,针对材料的棘轮安定机理、结构塑性安定载荷非循环计算方法、复杂结构塑性安定载荷的局部应变控制方法以及棘轮安定效应在结构应变强化技术中的应用等方面进行了理论、数值和试验研究。主要研究工作和结论如下： (1)304不锈钢棘轮安定机理的试验研究。根据Bauschinger效应,通过室温下的单轴棘轮试验获得了材料的弹性空间和塑性应变之间的关系,并在此基础上分别对等向强化、随动强化和混合强化模型下的材料棘轮安定性进行了分析,发现在混合强化模型下必然存在棘轮应变累积的问题。建立了单轴棘轮安定机理的数学迭代计算式,由此得到饱和棘轮应变是由弹性空间和循环载荷范围决定的。另根据Perzyna和Peirce粘塑性应变率方程,粘塑性应变率和弹性空间有关,试验结果表明,随着塑性应变的累积,弹性空间增大,粘塑性应变率会减小到零,因此最终饱和粘塑性应变由弹性空间和峰值应力决定。考虑材料的棘轮应变和粘塑性应变的交互作用,对弹性空间、饱和应变和加载工况三者之间的关系进行了分析,发现当应力比R≥0时,饱和应变只与峰值应力有关,与幅值应力大小无关,而当应力比R0的情况时,饱和应变是峰值应力和幅值应力的二次函数。基于上述分析,通过试验方法可以获得饱和应变和峰值应力的数据点,最后通过对这些数据点进行拟合,就可以建立应力比R≥0的塑性安定本构曲线。 (2)典型压力容器结构塑性安定载荷的非循环计算方法的研究。实际工程中,很大一部分压力容器承受的循环载荷为应力比R≥0的工况,依据Mises等效应力-等效应变关系,以塑性安定本构曲线作为有限元的材料模型,利用一次弹塑性有限元分析就可以直接获得结构的塑性安定载荷和相对应的累积应变,避免了逐循环计算过程,并通过循环内压作用下的实物容器的对比试验验证了该方法的准确性。与传统的安定计算方法相比,这种非循环方法可以有效的获得结构的真实承载能力,大大减少了计算时间,有利于工程应用。 (3)局部安定载荷的应变控制方法的研究。对于复杂压力容器结构,在采用非循环方法进行塑性安定载荷计算时,需同时考虑结构应力状态对计算结果的影响。本文采用应力三轴度TF作为应力状态的表征量,从损伤的角度发展了结构塑性安定载荷的局部应变控制方法,可有效的获得复杂结构的局部塑性安定载荷。利用该方法,对典型压力容器结构(比如筒体接管结构)的塑性安定载荷进行了统计计算,通过数学拟合,获得了其工程计算公式。 (4)棘轮安定效应在压力容器应变强化技术中的应用研究。在压力容器结构的应变强化技术中考虑棘轮安定效应,使用塑性安定本构曲线替代单向拉伸本构曲线,来预测结构大变形情况,这填补了该技术中的一项空白。在此基础上,提出了一种新的循环加载应变强化方式,与传统的恒压保载强化方式相比较,在达到相同的应变强化量时,应变强化后结构马氏体增量比恒压保载方式减少约50%,采用循环加载方式进行应变强化后,产品材料塑性消耗更少。 (5)应变强化压力容器结构的疲劳评定方法研究。通过预应变材料的疲劳试验,获得了应变强化条件下304不锈钢材料的应变控制疲劳寿命设计曲线,并从弹性空间的角度解释了低周疲劳平均应力松弛的机理。根据预应变强化条件下的疲劳设计曲线进行疲劳寿命评定,可以提高结构的疲劳设计寿命。
[Abstract]:Security and structure of pressure vessel under cyclic load is more attention, in order to protect the safety of equipment, the need for analysis of stability analysis and stability analysis of fatigue. The deficiencies of traditional methods of large amount of calculation or the result is too conservative in the aspects of complex structures, especially for the 304 yield of austenitic stainless steel materials the development of more suitable for engineering application of shakedown analysis. In this paper 304 stainless steel as the research object, aiming at the stability of ratchet mechanism of material, the structure of the plastic shakedown load of non cyclic calculation method of complex structure plastic shakedown load local strain control method and the ratchet effect in structural strain strengthening stability and application etc. in the theoretical, numerical and experimental research. The main research work and conclusions are as follows:
(1) experimental study on 304 stainless steel ratchet mechanism. According to the stability of the Bauschinger effect, the uniaxial ratcheting tests at room temperature to obtain the relationship between elastic material and plastic strain, and respectively based on the isotropic hardening, kinematic hardening and mixed hardening materials under the ratchet stability model are analyzed. Found in the mixed hardening model under the inevitable ratcheting strain problem. The mathematical formula of iterative uniaxial ratcheting shakedown mechanism is established, the saturated ratchetting strain is determined by elastic space and cyclic loading range. According to the Perzyna Peirce and the viscoplastic strain rate equation, the viscoplastic strain rate and the elastic space the test results show that, with the accumulated plastic strain, elastic space increases, the viscoplastic strain rate will be reduced to zero, so the final saturation by elastic viscoplastic strain space and peak stress will . considering the material viscosity interaction of ratcheting strain and plastic strain, the elastic space, the relationship between saturated strain and loading conditions of the three are analyzed, and found that when the stress ratio R = 0, saturated strain only with peak stress, stress amplitude and size, and when the stress R0 ratio, saturated peak strain is a quadratic function and amplitude of stress. Based on the above analysis, the test method can get saturated strain and peak stress data, by the end of the fitting, we can establish a stress ratio R = plastic constitutive stability 0 curve.
(2) study on the calculation method of typical pressure vessel structure plastic shakedown load of non circulation. In practical engineering, a large part of the pressure vessel subjected to cyclic loading stress ratio R = 0 for the condition, according to the Mises equivalent stress - strain relationship with plastic constitutive model for stability curve for the material the finite element method, using an elastic-plastic finite element analysis can directly get the structural plastic shakedown loads and the corresponding cumulative strain is avoided by cycle calculation process, and through the contrast test of real vessel circulation under internal pressure to verify the accuracy of the method. Compared with the traditional calculation method of stability and this non circulation method can effectively obtain the real bearing capacity of the structure, greatly reduces the calculation time for engineering application.
(3) to study the strain control method of local stability load. For the complex structure of pressure vessel, calculate the plastic shakedown load in the non circulation method, the structure must also consider the effect of stress state on the calculation results. The stress of three axis TF as representation of stress state and local strain the control method of the plastic shakedown load from the perspective of damage development, can effectively obtain the complex structure of local plastic shakedown loads. Using this method, the typical pressure vessel structure (such as cylinder nozzle structure) of the plastic shakedown load for statistical calculation, through mathematical simulation, calculation formula to obtain the project.
(4) application of the ratchet effect in pressure vessel stability and strain hardening. Strain in the structure of pressure vessels to strengthen stability in ratchet effect is considered, the use of plastic stability constitutive curves instead of uniaxial tensile constitutive curve to predict the structure of large deformation, which fills a gap in the technology in this. On the basis, puts forward a new way to strengthen the cyclic load strain, load strengthening method compared with the traditional constant pressure, the same amount of strain hardening, strain hardening martensite structure after the incremental ratio constant pressure holding mode is reduced by about 50%, the cyclic loading of strain hardening materials, plastic products consume less.
(5) study on the fatigue evaluation method of pressure vessel structure strain hardening. Through fatigue test of pre strain material, the strain hardening condition of strain controlled fatigue life design under the curve of 304 stainless steel materials, and explains the low cycle fatigue mechanism of stress relaxation from the average elastic space angle. According to the pre strain hardening fatigue design curve under the condition of fatigue life assessment, can improve the fatigue life of structure design.

【学位授予单位】：华东理工大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TH49

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