局部应力应变疲劳的能量方法

应用Neuber准则分析弹塑性材料缺口件时局部应力应变估计过高，因此预测初始寿命常给出过于保守的结论.由于当量应变能密度（Equivalent strain energy density, ESED）准则在Neuber准则的塑性变形项上增加了系数，局部应力应变估计结果更为准确.基于能量方法讨论了循环加载下材料的塑性应变能密度，发现ESED准则相比Neuber准则多考虑了塑性应变能密度，这是ESED准则局部应变场估计值远低于Neuber准则的估计值的能量理论基础.疲劳试验的结果验证了以上结论.     

Concurrent ratcheting and stress relaxation at the notch root of steel samples undergoing asymmetric tensile loading cycles

The current study intends to develop a framework model to assess ratcheting and stress relaxation at the notch root of 1045 steel samples over asymmetric loading cycles. The framework involves the Ahmadzadeh‐Varvani (A‐V) kinematic hardening rule to control ratcheting progress and Neuber rule to accommodate for local stress and strain components at the vicinity of notch root. Plastic strain at notch root was first coupled with its counterpart in the A‐V model to establish a relation between local stress and backstress components. Calculated local stress and strain values at turning points enabled the A‐V model to assess ratcheting strain over each loading cycle. The stepwise drop in stresses at peak‐valley tips of hysteresis loops at the notch root was associated to coupled framework of the A‐V model and Neuber rule through constancy in local strain while ratcheting progressed over each cycle. This relaxed out the local stresses at tips of hysteresis loops to position on Neuber hyperbolic curve. Predicted ratcheting values at notch root of various diameters closely agreed with those of measured in steel samples over stress cycles.     

Rethinking fatigue crack growth: Crack growth at constant R and strain energy

This paper is the first of a series attempting to apply my 57‐year experience with durability and damage tolerance of aerospace structures to answer the question; why, after 50 plus years, have we not reached agreement on the validity of current crack growth assumptions. To address this question, new concepts are introduced and interpreted in terms of strain energy. The tentative answer to the question is that when interpreted in terms these new concepts and strain energy, there are serious conceptual errors in the da/dn diagrams that make the data base very difficult to properly interpret. The materials presented raise new questions and provide possible answers to old ones.     

Neuber公式应用于对接接头焊趾应力分析的修正

在平面应力和平面应变状态下,根据不同理论应力集中系数的对接接头焊趾处的应力集中系数和应变集中系数的弹塑性有限元计算结果,分析了Neuber尖缺口公式、钝缺口公式和钝缺口Sonsino修正公式的适用性,并进一步对Neuber公式进行了修正,修正表达式为Kσ+Kt2·Kε+Kt2=K2t。     

局部应力应变疲劳的能量方法

应用Neuber准则分析弹塑性材料缺口件时局部应力应变估计过高，因此预测初始寿命常给出过于保守的结论．由于当量应变能密度（Equivalent strain energy density,ESED）准则在Neuber准则的塑性变形项上增加了系数，局部应力应变估计结果更为准确．基于能量方法讨论了循环加载下材料的塑性应变能密度，发现ESED准则相比Neuber准则多考虑了塑性应变能密度，这是ESED准则局部应变场估计值远低于Neuber准则的估计值的能量理论基础．疲劳试验的结果验证了以上结论，     

Neuber法则在汽轮机转子寿命估算中的应用

高温大容量汽轮机在启动、停机以及负荷波动时对机组的使用寿命有很大影响。正确分析机组在多种工况下转子的应力水平和寿命损耗是当前大型机组保证安全运行及加强寿命管理中亟待解决的关键问题之一。为此,应用Neuber法则对600MW超临界机组转子进行了寿命损耗计算。计算结果表明冷态启动对转子的寿命损耗最大。     

Multiaxial fatigue life prediction method in the ground vehicle industry

The extensive progress which has been made in the multiaxial fatigue area over the past 5 to 10 years has allowed wider application of the multiaxial fatigue method in component durability design in the ground vehicle industry. The method adopts the long established local strain–life approach and includes several new features. (1) A three-dimensional cyclic stress–strain model, used to simulate the elastic–plastic material behavior under complicated loadings. (2) The critical plane approach, which requires the fatigue analysis to be performed on various potential failure planes before determining the lowest fatigue life. (3) A biaxial damage criterion, to better quantify fatigue damage under various loading conditions. (4) A multiaxial Neuber equivalencing technique, used to estimate, from the elastic finite element stress results, the multiaxial stress and strain history of plastically deformed notch areas. This paper examines the application of the above features to the fatigue analyses of three generic service/test histories: a constant amplitude (baseline) test history, a history directly recorded by strain gages mounted on the critical location of a structural component, and a loading history recorded in multichannels for a complex structure.     

Local limit loads in components with competing failure locations

The plastic limit load is an important feature of the S‐N curve. The classical way of plastic limit load calculation using elastic‐ideal plastic material behaviour is restricted to one location of the component. Complex components normally have several fatigue critical locations, for all of them the local plastic limit loads has to be determined. By the classical way the plastic limit load can be evaluated only for one of them. A new method is presented. The local plastic notch factor K_p and the corresponding plastic limit loads are calculated applying Neuber's rule to FE calculations with plastic hardening material. The new method is validated on the basis of six different notched specimens. The need and capability is exemplarily shown on a specimen with two competing failure locations.     

关于Neuber方程的理论证明及在疲劳分析中的应用

根据弹性理论中保守系统的最小余能原理推导出任意应力状态下Ｎｅｕｂｅｒ方程的普遍形式。从理论上证明了当缺口体满足保守力系条件时Ｎｅｕｂｅｒ方程具有普遍适用性。同时还对Ｎｅｕｂｅｒ方程推广应用到循环加载时存在的问题进行了讨论，并给出了相应的修正方程。     

基于Neuber公式的焊接制造对运载火箭储箱承载力的影响

利用Neuber公式对大型运载火箭的2219铝合金储箱液压过程中能够承受的内压力进行估算. 其中,接头微区的力学性能通过微小力学试验得到,不同结构模型接头焊趾处的弹性理论应力集中系数通过线弹性有限元法得到. 最后将微区力学性能代入有限元模型进行弹塑性计算,验证Neuber公式计算贮箱承载力的精度. 对比发现,在承载力预测中,接头局部的力学性能以及几何缺陷引起的应力集中情况都会严重影响结构的承载力,极端危险条件下的应力集中系数可以达到5.156,而承载压力仅有1.21 MPa,为无焊缝时承载力的37.81%;Neuber公式的应力误差为8.5%,应变误差为2.3%,其估算结构承载力的精度比较高.