厚壁圆筒最佳自紧压力的有限元分析

考虑厚壁圆筒在发生塑性变形后材料的强化及鲍辛格效应,建立与实际材料一致的数学模型来求解自紧压力与弹塑性分界半径的关系,以确定自紧压力的取值范围.并提出了最佳自紧压力的评定方法及求解过程,然后使用Chabeche循环塑性本构模型,模拟材料循环硬化及鲍辛格效应对残余应力的影响,并通过Marc有限元软件对厚壁圆筒的自紧及工作过程进行仿真,分析残余应力及工作过程中的最大应力与自紧压力的关系,通过比较,找出厚壁圆筒最大等效应力(包括平时及工作状态)与自紧压力的关系曲线,最后求出最佳自紧压力.     

基于三剪统一强度准则的厚壁圆筒自增强分析

基于三剪统一强度准则,考虑材料应变强化效应、包辛格效应、拉压异性及中间主应力的影响,采用双线性强化材料模型对厚壁圆筒进行自增强分析,得到了厚壁圆筒加载应力、残余应力和工作应力的解析解,提出了最佳自增强压力的计算方法,探讨了拉压比、强度准则变化参数的影响,比较了自增强处理和非自增强处理及双线性强化模型和理想弹塑性模型厚壁圆筒的应力分布差异。研究结果表明：厚壁圆筒的最佳自增强压力随半径比和强度准则参数的增大而增大;工作时的最大等效应力随半径比和强度理论参数的增大而减小,随拉压比的增大而增大;自增强等效应力的最大值在弹塑性分界面处,且应力沿壁厚的分布较均匀;与理想弹塑性模型相比,双线性强化模型所对应的弹塑性分界面半径和残余应力较小,且随着自增强压力的增大,两种模型的差值越来越大;等效应力随半径比的变化规律可为厚壁圆筒选择合理的壁厚提供一定的参考;自增强技术可改善厚壁圆筒工作时的实际应力分布,提高其极限承载能力。     

厚壁圆筒自增强理论与数值模拟对比分析

自增强处理技术能有效提高设备承载能力,在高压和超高压设备中具有广泛应用。在第三强度理论的基础上提出厚壁圆筒最佳自增强处理内压的简便计算公式,有助于设计人员快速确定最佳自增强处理内压。并利用有限元软件,建立了厚壁圆筒力学模型,对比自增强处理前后厚壁圆筒的应力分布,从分析结果可以看出,对于提高圆筒承载能力,自增强处理技术具有明显优势。同时,对厚壁圆筒有限元模型施加不同自增强处理内压,得到相同工作压力作用下不同自增强处理内压与厚壁圆筒最大应力值的关系曲线,从而确定厚壁圆筒的最佳自增强处理内压值。对比所推导的理论公式计算值,误差仅为6%,符合工程设计计算要求,可以在机械加工工程领域应用推广。     

含均布多轴向表面裂纹厚壁圆筒结构安全性评价

轴向表面裂纹对受内压厚壁圆筒结果的安全具有很大的影响.在分析含均布多轴向表面裂纹厚壁圆筒裂纹数目对尖端应力强度因子影响规律的基础上,对外径相同、含均布多轴向表面裂纹厚壁圆筒及以裂纹尖端到厚壁圆筒中心距离为内径厚壁圆筒在受相同内压情况下的最大周向应力进行了对比分析,结果表明:厚壁圆筒裂纹尖端应力强度因子随裂纹数目的增加而逐渐减小并趋于一恒定值,应力强度因子随裂纹数目的减小只是裂纹扩展速度或扩展可能性的减小,含裂纹厚壁圆筒的最大周向应力在N=2时最大,且当N≥2时随着裂纹数目的增加而减小,但仍大于等效减薄厚壁圆筒的最大周向应力,厚壁圆筒的安全性仍小于以等效减薄后的光滑厚壁圆筒.     

厚壁圆筒自增强处理的数值模拟

弹塑性理论的自增强技术可以提高厚壁圆筒的承载能力,推导了厚壁圆筒在内压作用下的自增强压力,并基于ANSYS分析结果对解析值进行验证。采用三个载荷步加载,对厚壁圆筒的自增强处理过程进行了弹塑性有限元模拟分析,得出了不同阶段应力的分布规律。在弹性状态下,分析值与解析值误差小于0.4%,从而验证了模拟分析的可靠性。在分析过程中得到的一些值得注意的规律及图形可供工程设计时参考,也使得弹塑性理论公式中参数间的关系和变化规律更清晰。     

热预应力自增强厚壁圆筒研究

厚壁圆筒自增强处理技术的关键在于预应力。传统的自增强处理技术采用的是机械预应力方法,即在圆筒投入使用前,对其施加超过操作压力的自增强压力,使之获得残余预应力。考虑到厚壁圆筒内、外壁存在温差时,筒壁中有热应力产生,因此针对厚壁圆筒自增强问题,提出了以热应力作为预应力的自增强技术。具体研究了圆筒壁厚、温差等对热应力与总应力(热应力与操作应力的叠加)的影响、热应力与总应力的变化趋势、各种参数间的约束条件;在分析热应力与总应力特性的基础上,得出最佳设计条件,提出了基于第四强度理论的热预应力自增强厚壁圆筒的设计方法。结果表明,热预应力能有效地降低和均化厚壁圆筒的操作应力;按照所提出的设计方法,在确保圆筒安全的前提下,可使圆筒获得最大的承载能力和最小的壁厚。     

热-机载荷下厚壁圆筒自增强压力与安全性分析

推导厚壁圆筒在内压及热梯度载荷作用下的最佳自增强压力,并基于ANSYS优化分析结果对理论解进行验证.同时进一步探讨循环热机载荷下自增强对厚壁圆筒安定行为的影响.结果表明,不考虑热载荷时自增强处理会增大工作状态下圆筒内外壁应力差,从而降低结构的疲劳强度;当量纲一温度tn(0.75时,最佳自增强压力的理论解与数值解一致,最大误差不超过1%,而当0.75相似文献   

热-机械载荷下厚壁圆筒自增强压力优化分析

理论上推导了厚壁圆筒在内压及热载荷共同作用下的最佳自增强压力,并基于ANSYS的优化分析结果对理论解进行了验证。结果表明最佳自增强压力的理论解与数值解一致,最大误差不超过1%;另外,不考虑热载荷进行自增强后,会增大工作状态下厚壁圆筒内外壁应力差,降低结构的疲劳强度;工程上可根据本文解析解进行自增强处理,以提高厚壁圆筒的承载能力。     

关于厚壁圆筒自增强容器的理论研究

基于第四强度理论的观点，推导出了确定厚壁圆筒自增强处理时最佳弹塑性界面半径的计算公式；并进一步推导出了经过自增强处理的压力容器的最大允许工作内压的公式，最后为工程实际提出了自增强厚壁圆筒最大工作压力的控制条件。其理论及公式具有一定的理论与实用价值。     

基于双线性强化模型的挤压凹模自增强技术研究

为了进一步提高单层冷挤压凹模的弹性承载能力,可对其进行自增强处理.建立考虑材料应变硬化和包辛格效应的双线性强化自增强理论模型,得到自增强凹模三个加载过程的应力情况,并确定自增强压力的范围.采用ANSYS有限元软件对自增强挤压凹模的应力分布规律及内壁的位移做了数值模拟分析,模拟结果和理论计算相吻合.将采用双线性强化模型和理想弹塑性模型的结果进行比较,得到应变硬化和包辛格效应对自增强效果的影响规律.在凹模工作压力一定的情况下,通过优化分析,得到满足凹模尺寸精度和强度要求的最佳自增强压力,数值优化结果和理论解析值吻合较好,可为工程应用提供理论依据.     

Influence of reverse yielding on residual stresses induced by autofrettage

The paper investigates the influence of reverse yielding on residual stresses induced by autofrettage. On the basis of reverse loading tests, a material model is developed and implemented into analytical procedures capable of treating the elasto-plastic deformation behaviour of thick-walled tubes during both loading and unloading phases. The results show that residual hoop stresses are drastically reduced near the tube bore as compared with residual stresses obtained from conventional isotropic hardening analysis. Pure kinematic hardening analysis is also shown to overestimate residual hoop stress induced by autofrettage.     

超高压压缩机填料盘润滑油孔自增强的研究

超高压压缩机填料盘结构复杂并承受很高的压力脉动,填料盘润滑油孔附近会产生明显的应力集中,需要自增强处理来得到良好的预应力状态。本文通过建立填料盘三维有限元模型,利用ANSYS双线性随动强化模型模拟自增强处理过程,分析自增强前后润滑油孔对填料盘等效应力分布、等效对称循环载荷、周向应力分布的影响,定量分析对润滑油孔施加自增强的必要性,得到自增强压力推荐范围。     

Residual stress analysis of an external grooved thick-walled pressure vessel

Residual stress analysis of an autofrettaged thick-walled pressure vessel containing an external groove was described in order to calculate the stress concentration at the external groove. The autofrettage residual stress distributions of the external grooved thick-walled pressure vessel were simulated using an equivalent thermal loading from the analogy of thermal and autofrettage residual stress fields. Thermal stresses due to the simulated thermal loadings for various degrees of autofrettage overstrain level were computed using finite element methods. Very high stress concentration factors due to autofrettage loadings were obtained at the external groove root that contained a sharp root radius. Experimental measurement of residual stresses for a fully autofrettaged smooth thick-walled pressure vessel using an equivalent saw cut method resulted in very close agreement with the theoretical autofrettage residual stress distributions. The stress analysis results implied that the autofrettage residual stress concentration might cause a cracking problem at the external groove root of the thick-walled pressure vessel, indicating that lower autofrettage overstrain and a groove geometry change were desirable for enhanced durability.     

Autofrettage of thick-walled pipe bends

The bending of a thick-walled cylinder to a given radius involves an elastic–plastic deformation that results in a residual, axial stress distribution. The latter alternates from maximum tension to maximum compression between top and bottom halves of the cross-section. The residual stress levels depend upon the depth of plastic penetration and may be determined as a closed solution when they arise from a bending moment applied to either a non-hardening or linearly-hardening material. When the bent pipe receives an autofrettage treatment without an intermediate heat treatment, this produces a further residual, triaxial stress state. The interaction between the residual states from bending and autofrettage has an important effect upon the net axial stress and the equivalent stress. It is shown that large plastic penetrations arising from bending and autofrettage can residually stress the section beyond its yield point: in tension and in compression across both its halves. With the unloading from each process, a Bauschinger effect reduces the yield point to assist with the onset of reversed plasticity. The latter is far less beneficial than when unloading is elastic. It is shown how a nonlinear kinematic hardening model can be employed to avoid unloading plasticity at the inner and outer diameters. The consequence of interacting residual stresses is that axial stress can play as important a role as hoop stress when designing for safe service loadings. In general, an enhanced residual stress state is beneficial when compressive but detrimental when tensile. Pre-compression is often employed in practice to reduce tensile stress arising from internal pressure, axial force and self-weight. Here, the compressive residuals arising from an autofrettage treatment have long been exploited to enhance the fatigue life of process piping and weaponry.     

Effect of optimum plastic depth on stresses and load-bearing capacity of autofrettaged cylinder

Autofrettage is an effective measure to even distribution of stresses and raise load-bearing capacity for (ultra-)high pressure apparatus. Currently, the research on autofrettage has focused mostly on specific engineering problems, while general theoretical study is rarely done. To discover the general law contained in autofrettage theory, by the aid of the authors’ previous work and according to the third strength theory, theoretical problems about autofrettage are studied including residual stresses and their equivalent stress, total stresses and their equivalent stress, etc. Because of the equation of optimum depth of plastic zone which is presented in the authors’ previous work, the equations for the residual stresses and their equivalent stress as well as the total stress and their equivalent stress are simplified greatly. Thus the law of distribution of the residual stresses and their equivalent stress as well as the total stress and their equivalent stress and the varying tendency of these stresses are discovered. The relation among various parameters are revealed. The safe and optimum load-bearing conditions for cylinders are obtained. According to the results obtained by theoretical analysis, it is shown that if the two parameters, namely ratio of outside to inside radius, k, and depth of plastic zone, kj, meet the equation of optimum depth of plastic zone, when the pressure contained in an autofrettaged cylinder is lower than two times the initial yield pressure of the unautofrettaged cylinder, the equivalent residual stress and the equivalent total stress at the inside surface as well as the elastic-plastic juncture of a cylinder are lower than yield strength. When an autofrettaged cylinder is subjected to just two times the initial yield pressure of the unautofrettaged cylinder, the equivalent total stress within the whole plastic zone is just identically equal to the yield strength, or it is a constant. The proposed research theoretically depicts the stress state of ultra-)high pressure autofrettaged cylinder more accurately and more reasonably and provides the reference for design of (ultra-)high pressure apparatus.     

碳纤维缠绕储氢瓶的有限元自紧分析和爆破压力预测

根据高压储氢瓶的金属内胆和外部碳纤维缠绕层的结构特点进行各向同性金属和各向异性复合材料叠层的有限元建模。考虑自紧作用与气瓶的实际工况,对气瓶在不同内压下应力和变形的弹塑性响应进行了分析。参考DOT CFFC标准对气瓶进行了自紧设计和弹塑性加卸压模拟分析。基于渐进破坏理论,用Tsai-Wu失效准则判断复合材料失效模式,并据此修改单元刚度;利用单元生死技术,依据失效单元数目的急剧增大来预测气瓶的爆破压力,与文献试验结果相比误差很小,验证了该方法的可靠性。     

残余应力松弛和自增强处理压力对在役高压容器的安全影响

为了确定残余应力松弛和自增强处理压力对在役高压容器安全性能的影响,通过分析测试结果获得了残余应力的松弛规律,计算了在工作压力、残余应力作用下的当量等效应力沿壁厚分布情况,模拟计算出了不同的工作压力、自增强处理压力下的安全系数,推导出了最佳自增强处理压力。结果表明所研究的高压聚乙烯反应管在使用10年后,环向应力在近内壁区衰减最快,从-600MPa衰减到-333MPa,衰减率达45%;在弹性区衰减较小,残余应力峰值位置外移,但其峰值大小变化不大。对于自增强处理后的压力容器,在工作压力作用下,随着残余应力的松弛,内壁面当量等效应力增大,当量等效应力在弹塑性交界处最大,应该按此处的当量等效应力计算安全系数。依据示例聚乙烯反应管尺寸,模拟计算出在工作压力分别为180、280、380MPa时,经过自增强处理压力分别为606、677、743MPa的最佳自增强处理后,其安全系数比残余应力全部衰减为0时分别高16%、26%、37%。压力容器工作压力越大,经最佳自增强处理后安全系数增大得越多,但残余应力衰减对其安全影响越大。     

A comparative study of thermal and hydraulic autofrettage

Thermal autofrettage is a potential process to generate beneficial compressive residual stresses at and around the inner wall of a thickwalled cylinder for increasing its pressure carrying capacity. Due to its simplicity and inexpensive arrangement, it can compete with the conventional hydraulic autofrettage process. In this work, a comparative study of the thermal autofrettage and the hydraulic autofrettage is carried out. As the thermal autofrettage does not require hydraulic power pack, the process is more economical than the hydraulic autofrettage. The thermal autofrettage process is also studied for the thick-walled cylindrical vessels subjected to high thermal gradient with or without pressure and is compared with the hydraulic autofrettage. Comparison shows that for cylinders subjected to high thermal gradient without pressure, the thermal autofrettage is superior to the hydraulic autofrettage.