加速预腐蚀与疲劳试验估算飞机结构日历寿命的新方法

提出估算日历寿命的一种新方法—线性累积破坏率准则法，其物理意义明确，简单明了.飞机机体的损伤模式描述为疲劳损伤和预腐蚀疲劳损伤，并将飞机结构的日历寿命定义为地面停放日历寿命和飞行日历寿命之和.选取破坏率为损伤参量，在环境腐蚀当量关系加速预腐蚀疲劳试验的基础上，通过疲劳寿命分布形式和概率密度函数求出破坏率来估算预腐蚀环境下的日历寿命.利用一组预腐蚀与疲劳试验数据对该方法进行了验证.     

腐蚀疲劳过程中载荷间交互作用的研究

介绍了近年来进行了Ａ５３７钢在３．５％ＮａＣｌ水溶液中阴极溶解与阴极充氢条件 下腐蚀疲劳裂纺扩展中载荷交互作用方面的一些研究结果。其中包括恒△Ｋ控制下的单周超载延迟作用, 裂纹扩展率的波型响应以及小幅载荷的幅度与相对主载荷的位置对裂纹扩展的影响规律等。     

环境腐蚀对Q345角钢疲劳性能的影响研究

目的研究Q345角钢构件的疲劳性能随腐蚀损伤发展的变化规律,为分析"腐蚀-疲劳"交替循环工况下试件疲劳性能变化情况奠定基础。方法首先通过连续疲劳振动和间隔疲劳振动两种疲劳试验,测试分析了疲劳荷载施加方式对试件疲劳性能的影响,其中,试件间隔振动分三次完成,每次振动次数为连续疲劳振动次数的1/3。然后,根据不同"浸泡-晾置"次数,给出了三种腐蚀方式,并在p H值为2的酸性溶液中对试件进行加速腐蚀损伤试验。采取"腐蚀-疲劳"交替循环加载方式对3组39根Q345角钢构件进行腐蚀疲劳试验,由试件腐蚀疲劳破坏的试验现象及测试结果,分析试件疲劳性能随腐蚀疲劳损伤的变化规律,并研究Q345角钢试件的风致振动疲劳性能因大气环境中腐蚀损伤发生及发展的退化规律。结果疲劳荷载为221.43 MPa时,三种"腐蚀-疲劳"工况下,CF1、CF2与CF3相比,试件的疲劳寿命分别退化了5.1%和2.7%。疲劳荷载为308 MPa和221.43 MPa时,单点试验结果未随腐蚀方式变化而发生明显变化,但是当疲劳荷载减小到156.22 MPa时,CF1、CF2与CF3相比,试件的疲劳寿命分别退化了6.3%和4.5%。结论腐蚀损伤试验中"浸泡-晾置"交替循环次数越多,损伤越大,试件疲劳寿命退化,反映Q345角钢构件的疲劳性能受大气环境干湿交替腐蚀损伤影响明显。同一腐蚀方式中,疲劳荷载越小,腐蚀的影响越显著,脆性破坏特征越明显。     

不同介质中Si3N4陶瓷的静疲劳与循环疲劳

系统研究了Si3N4陶瓷在空气、水、煤油3种介质中的静疲劳及循环疲劳特性。结果发现，在不同介质条件下，循环疲劳的应力腐蚀指数(n)相差不大，且远远低于相同介质条件下静疲劳的应力腐蚀指数。经分析发现，循环载荷部分或全部消除了显微组织屏蔽作用，对材料造成附加损伤，导致其疲劳寿命远远低于静疲劳寿命。     

变幅载荷下铝合金的腐蚀疲劳裂纹起始寿命

试验测定了铝合金切口件在变幅块谱下于３．５％ＮａＣｌ溶解中的腐蚀疲劳裂纹起始（ＣＦＣｌ）寿命,结果表明,变幅载荷谱中的大超载会显著延长ＣＦＣＩ寿命,并用超载方式和加载顺序具有明显的影响,根据反映大小载荷交互作用和腐蚀效应的超载ＣＦＣＩ寿命曲线,探讨了应用Ｍｉｎｅｒ累积损伤定则建立变幅载荷下切口件ＣＦＣＩ寿命估算模型的可行性,并应用平均秩对变幅块谱下ＣＦＣＩ寿命的分布进行了统计分析,讨论了变幅载荷谱     

双周疲劳载荷作用下焊接接头线性累计损伤分析

采用自制的超声频分量双周疲劳(CCF)试验装置,对16Mn的焊接接头试件进行低频疲劳载荷与超声频分量(高频)载荷复合加载,采用线性累计损伤理论来估算双周疲劳载荷作用下16Mn对接接头的疲劳寿命,并计算两个疲劳载荷分量各自造成的累计损伤比例.结果表明,使用Miner法则计算双周疲劳试件的疲劳累积损伤时,如果高低周疲劳载荷只是简单按照比例计算,会严重低估两个分量疲劳载荷之间的耦合作用;而低周疲劳载荷按外包络线计算的方法则能够很好的考虑到高低周疲劳载荷间的耦合作用.     

A damage-coupled multi-axial time-dependent low cycle fatigue failure model for SS304 stainless steel at high temperature

Based on the time-dependent strain cyclic characteristics and fatigue behaviors of SS304 stainless steel under multi-axial cyclic loading at 700 ? C, and in the frame of unified visoco-plastic cyclic constitutive model and continuum damage mechanics theory, the damage-coupled multi-axial time-dependent constitutive model and fatigue failure model were proposed. In the model, the evolution equation of damage was introduced in and the time-dependent effects, e.g. holding time, loading rate, were taken into account. The model was applied to the simulation of whole-life cyclic deformation behaviors and prediction of LCF life for SS304 stainless steel in multiaxial time-dependent low cycle fatigue tests. It is shown that the simulated results agree well with experimental ones.     

TC4钛合金的多轴高周疲劳损伤及强度退化研究

不同工况下TC4(Ti-6Al-4V)钛合金疲劳累积损伤及强度退化存在较大差别。为了充分表征载荷参数的影响,基于Chaboche损伤模型以及改进的多轴疲劳损伤准则,提出新的强度退化模型,开展了TC4钛合金的多轴高周疲劳(HCF)寿命预测和强度退化评估。首先,开展TC4合金在一系列加载路径下的多轴比例和非比例疲劳试验。将Chaboche非线性损伤准则和临界平面法与提出的损伤控制参数相结合,描述了TC4合金的非线性疲劳损伤计算和寿命预测。其次,进一步建立了基于累积损伤的非线性强度退化模型,并证明了该模型在不同载荷工况下均可以获得更高的精度。实验结果表明,由于考虑载荷参数的影响,提出的TC4钛合金疲劳寿命与强度退化预测结果精度远高于其他的预测模型。     

ST12汽车钢板拉剪点焊接头的疲劳强度

针对车身使用的ST12低碳钢板,利用生产线上焊接设备制备了电阻点焊接头拉剪疲劳试件.对点焊接头区域进行了金相组织观测,测量了焊点附近的维氏硬度值分布.在MTS材料疲劳试验机上进行了恒幅疲劳加载,得到了ST12低碳钢板的电阻点焊接头的S-N曲线.基于所得的S-N曲线进行了两级疲劳加载试验,对两级加载下的线性累积疲劳损伤进行了分析.累积损伤结果分析表明,ST12低碳钢板电阻点焊件在两级加载下存在加载次序效应,高-低加载次序下加载次序效应更为明显.     

钨表面形貌控制及其在循环热载荷作用下的热疲劳性能

钨作为聚变装置中的壁材料在各种循环热载荷作用下的热疲劳行为是一个重要的问题。采用电子回旋共振(ECR)等离子体系统在多晶钨表面进行形貌控制实验,然后采用电子束对抛光和具有一定表面形貌的样品开展循环热载荷实验。结果表明,表面形貌对在循环热载荷下发生的循环塑性变形造成的损伤特征影响很小,在300次循环热载荷下某些晶粒中形成了微裂纹及挤出片结构,它们在不同晶粒中按着某一特定的方向平行排列。此外,在不同条件下通过等离子体刻蚀在钨表面制备了不同的三棱锥状和均匀的纳米结构。对损伤区域的截面进行了分析并给出了在循环热载荷下这种结构形成过程的示意图。     

加载方式对Si3N4陶瓷疲劳特性的影响

系统研究了加载方式(静载荷、循环载荷、动载荷)对Si3N4陶瓷疲劳特性的影响。结果发现，加载方式不同，材料的应力腐蚀指数n亦不相同，其中，静载下n最大，动载荷次之，循环载荷下n最小，并分析了循环载荷及动载荷对材料造成的附加损伤。     

Effect of Phosphate-Buffered Solution Corrosion on the Ratcheting Fatigue Behavior of a Duplex Mg-Li-Al Alloy

This work reports the uniaxial ratcheting and fatigue behavior of a duplex Mg-Li-Al alloy under the influence of phosphate-buffered solution corrosion. Microstructural observations reveal pitting and filament corrosion defects, which impair the load-bearing capacity of the alloy and cause stress concentration, thus leading to an accelerated accumulation of ratcheting strain and shortened fatigue life under the same nominal loading conditions. Comparing Smith model, Smith-Watson-Topper model, and Paul-Sivaprasad-Dhar model, a ratcheting fatigue life prediction model based on the Broberg damage rule and the Paul-Sivaprasad-Dhar model was proposed, and the model yielded a superior prediction for the studied magnesium alloy.     

GH30和GH34合金的蠕变－疲劳交互作用

研究了ＧＨ３０和ＧＨ３４合金的蠕变－疲劳交互作用，观察到两种负交互作用：ＧＨ３０合金在先蠕变后疲劳的条件下的负交互作用和ＧＨ３４合金在连续循环蠕变的条件下的负交互作用。前者的交互作用项中疲劳损伤指数远大于蠕变损伤指数。因而负交互作用主要是由于预蠕变部分地抑制了后续疲劳的损伤。后者的交互作用项中的蠕变损伤指数远大于疲劳损伤指数。因而负交互作用主要是由于疲劳部分地消除了蠕变损份。还用微观观察的结果分析了这两种负交互作用的微观本质。     

奥-贝球铁疲劳损伤过程的在线跟踪分析

应用系统分析的方法，通过三点弯曲疲劳试验，跟踪监测了奥-贝球铁试样的疲劳损伤过程。实验结果表明，在循环加载过程中，奥-贝球铁中石墨球与基体组织间的界面首先发生疲劳损伤开裂，在多数情况下疲劳裂纹并不在界面开裂处萌生，进一步的疲劳损伤是由于界面的开裂不同程度影响了基体组织内的滑移等塑性变形，并在基体内萌生疲劳裂纹。试验表明奥-贝球铁中石墨球与基体组织间的界面具有一定的疲劳强度。     

EFFECTS OF STRAIN RATIO ON THERMAL-MECHANICAL CYCLIC STRESS-STRAIN RESPONSE AND FATIGUE LIFE IN DS SUPERALLOY DZ125

The effects of strain ratio on thermal-mechanical cyclic stress-strain response and fatigue life in DS superaUoy DZ125 have been studied by performing tests at various strain ratio experiments, under strain-controlled and temperature cycling from 550 to 1000℃. It is shown that thermal-mechanical cyclic stress-strain response behavior not only depend on magnitude of strain, and temperature-loading phase angle, but also strain ratio. Fatigue life at strain ratio Rε=-0.3 is longer than that of strain ratio Rε=-1.0, under in-phase thermal-mechanical loading. However, Fatigue life at strain ratio Rε=-0. 3 is shorter than that of strain ratio Rε=-1. 0, under out-of-phasethe rmal-mechanical loading. The thermal-mechanical fatigue (TMF) damage model was discussed. Results of fractography show that fatigue, creep and oxidation damage always occur during TMF. The main damage mode depends on loading wave, strain ratio and magnitude of strain.     

工业纯锆的低周疲劳特性及寿命预估

通过轴向对称应变控制法对工业纯锆的低周疲劳性能进行研究，讨论了工业纯锆的循环应力-应变响应、软硬化特性、累积滞后规律、疲劳寿命以及塑性应变能的影响。结果表明：在总应变幅大于0.5%时工业纯锆均表现出循环硬化；工业纯锆疲劳寿命满足Basquin-Coffin-Manson经验关系式，其过渡寿命为1548周；利用塑性应变能对疲劳损伤进行了有效评估，总应变幅度越低，滞回曲线面积越小，即塑性应变能越低，疲劳寿命越长；疲劳断口呈现明显的疲劳辉纹特征，随总应变幅的增加疲劳辉纹的数量减小宽度增加。     

结构有限寿命设计法——名义应力法

介绍了一种结构有限寿命设计方法——名义应力法。阐述了名义应力有限寿命设计法的一般步骤,并对设计方法中的几个关键问题如应力谱的简化处理、疲劳寿命的预测等做了详细的介绍。以线性累积损伤法则和应力-寿命曲线为依据,推导出适用于变幅载荷下的有限寿命设计公式。最后通过算例说明采用此方法的优越性。     

疲劳损伤过程的热能耗散分析

利用能量作疲劳损伤基本参量,建立了疲劳损伤的能耗结构,在试验的基础上,围绕着疲劳损伤过程中的不可逆能耗分析,系统地研究了循环过程及循环内的疲劳损伤热能耗散变化规律,并寻找出疲劳过程中循环滞回能与有效能耗(储能)之间联系。     

HEAT ENERGY DISSIPATION IN FATIGUE DAMAGE PROCESS

Using the dissipated energy as an essential parameter,the energy dissipative structure in pro-cess of fatigue damage of materials has been established.Through thermodynamic analysis forirreversible energy dissipation in fatigue damage process,the heat dissipative variations incyclic loading process as well as in a cycle have been systematically studied on the basis of lowcycle fatigue tests and infrared measurement of self-heating thermography.Meanwhile,thecyclic hysteresis energy and efficient energy dissipation (stored energy) have been proposedduring fatigue damage process.     

Corrosion fatigue behavior of a steel with sprayed coatings

This paper describes the corrosion fatigue behavior and fracture mechanisms of a steel with different sprayed coatings. Rotating bending fatigue tests were conducted in 3% NaCl solution using specimens of a medium carbon steel with sprayed coatings of a ceramic (Cr₂O₃), a cermet (WC-12%Co) and two metals (Ni-11 % P and Al-2% Zn). The corrosion fatigue process was basically the same for ceramic, cermet, and Ni-11 % P sprayed specimens. That is, the corrosive media could be supplied from the specimen surface to the substrate through cracks initiated during fatigue cycling and/or pores in the coatings, and thus corrosion pits were generated followed by subsequent crack initiation and growth in the substrate. The corrosion fatigue strength of ceramic sprayed specimens was slightly improved compared to that of the substrate steel because the under-coating (Ni-5%A1) could impede the penetration of the corrosive media although the ceramic coating had a poor resistance to cracking under cyclic loading. Cermet sprayed specimens also exhibited improved corrosion fatigue strength because of the high resistance to cracking and the low volume fraction of pores of the coating. In Ni-11 % Psprayed specimens, cracks were initiated in the coating even at low stress levels; thus the corrosion fatigue strength was the same as that of the substrate. Anodic dissolution took place in Al-2 % Zn coating because the coating was electrochemically poor, and thus the substrate was cathodically protected. Therefore, the corrosion fatigue strength of Al-2 % Zn sprayed specimens was enhanced to as high as the fatigue strength of the substrate in room air. Based on the experimental results, a dual-layer coating consisting of WC-12%Co and Al-2%Zn was fatigue tested. The coating was effective at low stress levels and exhibited long life under conditions where corrosion fatigue strength was critical.