机翼壁板斜搭接结构DFR值试验测定及理论计算

该文针对某型飞机机翼壁板斜搭接结构,采用试验测定和理论分析两种方法,对该结构DFR值进行分析,分别给出了试验测定的DFR值和理论计算的DFR值。分析结果表明:理论分析能够较好的模拟斜搭接试件的几何特征与受载情况,验证了该DFR理论分析方法的工程适用性,为机翼壁板斜搭接结构的DFR测定提供了参考依据。     

加筋沥青路面APA试验及其非线性疲劳损伤分析

应用沥青路面分析仪(APA)对沥青路面结构模拟试件进行多种荷载下的往返轮载疲劳试验,对比研究土工布、玻璃纤维格栅对沥青路面疲劳性能的加筋效果.在此基础上,提出沥青混合料非线性疲劳损伤演化模型,应用基于疲劳损伤力学的非线性有限元方法模拟APA 试验过程,分析了试件应力、变形、疲劳寿命等,并与试验结果对比,论证了所提疲劳损伤演化模型的合理性,指出因加筋材料的桥联效应显著地改善了裂缝穿过筋材后路面的受力变形状况,有效地延长路面的疲劳寿命.同时,基于疲劳损伤分析,进一步验证了Paris 公式可用于描述路面结构的疲劳裂缝稳定发展过程,并获得了有关的参数.     

基于超声导波的复合材料结构疲劳损伤监测实验研究

为快速评估复合材料结构的疲劳损伤状况,采用超声导波和时-频分析相结合的方法,对疲劳状态下的复合材料结构进行在线连续监测。对玻璃纤维增强复合材料试件进行拉伸疲劳试验,使用激光引伸计获取试件纵向刚度的变化,探究试件内部疲劳损伤的累积情况。利用小波变换对由压电传感元件激励和接收的超声导波信号在时频域进行分析,提取与疲劳损伤有关的信号特征;最后,通过多元偏值分析引入马氏平方距离,融合多个信号特征,确定复合材料试件中疲劳损伤的存在性以及表征其演变过程。实验结果表明所提出方法在复合材料结构疲劳损伤连续监测方面的有效性。     

一种多轴向耦合随机激励下缺口试件振动疲劳寿命预测方法EI北大核心CSCD

提出了一种多轴向耦合随机激励下缺口结构振动疲劳寿命预测的频域分析方法。实施了缺口试件的双轴向随机振动疲劳试验,研究了两个振动轴向上载荷谱之间的相干性和相位差对缺口试件疲劳损伤的影响规律;通过随机振动分析计算得到试件缺口根部各节点的应力功率谱密度矩阵,并假设缺口试件裂纹萌生点为历经von Mises应力最大均方根值的节点;缺口试件疲劳临界点可由疲劳裂纹初始点和修正临界距离理论确定;在疲劳临界点处通过Carpinteri-Spagnoli频域准则计算缺口试件的振动疲劳寿命,并与试验结果进行了对比。结果表明:该多轴缺口疲劳预测方法具有较高的预测精度,绝大部分预测结果都在3倍误差带内。     

钢桥钢梁整体节点疲劳试验研究

本文研究了钢桥钢梁中棱角焊缝构造细节的疲劳问题。依据钢桥设计中所采用的钢梁棱角焊缝构造细节形式,模拟设计制备了该细节的疲劳试件。通过疲劳试验研究和有限元分析,确定了该细节的疲劳抗力曲线和有关的统计参数,并建立了棱角焊缝构造细节疲劳破坏模型。该模型对于工程设计、桥梁检修等方面具有重要意义。     

钢轨各部位的弯曲疲劳性能

针对实物疲劳试验不能得到钢轨各截面上的疲劳性能参数,采用材料疲劳试验方法测钢轨不同部位的疲劳性能。按GB/T 4337-1984的方法在钢轨截面上取不同部位的试样进行旋转弯曲疲劳试验,在给定的1 000×104次循环基数上来测定弯曲疲劳极限。结果表明,轨底中心部位的弯曲疲劳性能最好,而轨头中心部位的弯曲疲劳性能最低。     

基于循环孔洞扩张模型的Q355钢超低周疲劳断裂数值模拟

基于微观断裂力学的循环孔洞扩张模型是进行钢材超低周疲劳断裂分析的有效手段。通过光滑圆棒循环加载试验,确定了Q355钢混合强化模型材料参数;进行了不同加载方式下Q355钢单边缺口试件的超低周疲劳试验,确定了试件的超低周疲劳寿命及其断裂发展过程;建立了单边缺口试件有限元模型,基于有限元分析结果,采用循环孔洞扩张模型对试件的超低周疲劳寿命进行了预测,并通过编写用户子程序,删除断裂单元以模拟试件的断裂扩展过程,对试件的超低周疲劳断裂全过程进行了数值模拟。数值模拟结果与试验结果基本吻合,验证了循环孔洞扩张模型对钢材超低周疲劳断裂全过程数值模拟的适用性。     

南京长江第四大桥钢桥面铺装疲劳性能试验研究

结合南京长江第四大桥钢桥面铺装实体工程,开展铺装层混合料20℃疲劳性能试验。为了使试验结果能够更真实地反映主桥铺装的实际情况,直接采用主桥铺装使用的混合料成型试件,其中,带钢板复合梁试件为施工现场摊铺、碾压成型。室内试验对铺装结构单层采用劈裂疲劳试验,选择0.2、0.3、0.4、0.5、0.6这5个等级的应力水平,对组合结构采用带钢板复合梁疲劳试验,荷载水平为6 kN、7 kN、8 kN,并通过回归分析得到疲劳方程。     

混凝土受拉疲劳试件的有限元分析

以国家自然科学基金资助项目《混凝土多轴疲劳破坏准则》(50078010)的试验研究为背景,运用有限元分析软件ANSYS对混凝土多轴疲劳试验中采用的试件进行单轴静态受拉分析,指出了受拉疲劳试件在设计及试验中所存在的问题并给出合理建议。     

采用确定性裂纹增长方法对铝合金铆接结构寿命分析的研究

对一种典型的航空铝合金铆接结构模型试件进行了疲劳试验. 针对该模型分别采用确定性裂纹增长方法和等效SSF法进行了寿命评估, 并与试验结果进行了比较. 结果显示, 两种评估方法都具有良好的评估精度. 当采用确定性裂纹增长方法对结构寿命进行分析时, 必须通过试验对于结构原始疲劳质量进行准确的评估, 结构寿命的评估结果会敏感的随着结构细节初始缺陷尺寸上界的变化而变化.     

DFR based fatigue reliability assessment of riveted lap joint accounting for correlations

The objective of this paper is to analyse the effect of correlation on the fatigue reliability of a riveted lap joint with multiple rivets using a fast reliability assessment approach based on the detail fatigue rating method. The detail fatigue rating method, DFR method, is based on the nominal stress fatigue approach. The DFR represents the inherent characteristic of fatigue capacity of a structure independent from the applied fatigue load. The fatigue reliability assessment model of a structure is proposed based on the relations of fatigue loading, characteristic fatigue life and DFR. The upper and lower bounds of fatigue reliability of a riveted lap joint structure with multiple rivets subjected to fatigue loading is analysed using the DFR and Ditlevsen approaches accounting for the correlations between rivet holes failures.     

Fatigue life estimation of tubular joints – a comparative study

In fatigue analysis, the structural detail of tubular joint has taken great attention among engineers. The DNV/GL‐RP‐0005 is covering this topic quite well for simple and clear joint cases. For complex joint and geometry, where joint classification is not available and there is limitation on validity range of non‐dimensional geometric parameters, the challenges become a fact among engineers. The classification of joint is an important factor to consider in fatigue analysis. These joint configurations are identified by the connectivity and the load distribution of tubular joints. To overcome these problems to some extent, this paper compares the fatigue life of tubular joints in offshore jacket according to the stress concentration factors (SCF) in DNV/GL‐RP‐0005 and finite element method employed in Abaqus/CAE. The paper presents the geometric details, material properties and load history of the considered jacket structure. It then describes the global structural analysis and identification of critical tubular joints for fatigue life estimation. Hence, fatigue life is determined based on the guidelines provided in design codes. Fatigue analysis of tubular joints is conducted using the finite element employed in Abaqus/CAE as the next major step. Finally, predicted SCFs and fatigue lives are compared, and these observations tend to conclude that even though the fatigue life, which is calculated based on code given SCFs, provides more realistic prediction to the simple uniplanar joints, there is a doubt for complex joints and geometry, where joint classification is not available. Also, the study emphasized that it is very important to preciously investigate SCFs by considering accurate geometry of complex tubular joints for a good judgement of fatigue life.     

风速风向联合分布对结构风致疲劳寿命可靠性的影响

在进行结构风振疲劳寿命可靠性分析时,需要先求得建筑结构所在位置处的风速风向联合分布函数。本文首先对建筑结构附近两个气象站的气象资料进行统计分析,得到建筑结构位置处两个不同的风速风向联合分布函数,然后分析了不同的风速风向联合分布函数对一实际结构系统风振疲劳主要失效模式以及结构系统风振疲劳失效概率的影响。本文分析表明：用不同的风速风向联合分布函数计算风振疲劳寿命时会得到不同数目的主要失效模式,并且对结构系统的风振疲劳失效概率影响较大。     

辊压预应变对焊接接头组织性能的影响

采用辊压加载的方法在焊接接头处形成微量的塑性预应变,研究辊压变形后材料本身的疲劳性能和力学性能变化(不计表面效应)。利用 SEM 观察疲劳断口和 TEM 观察位错形貌。试验结果表明,虽然金属辊压变形后的强度和硬度有所提高,但疲劳极限明显降低,断口呈完全的脆性状态,位错大量增殖并表现为胞状亚结构。可以认为,辊压后材料中位错的特殊结构和材料内部所形成的损伤累积是疲劳性能下降的主要原因。     

The interaction between corrosion management and structural integrity of aging aircraft

Aircraft joints feature prominently in aircraft structural degradation; fatigue cracking and corrosion damage are major issues, which can reduce joint strength and degrade service life. Protecting the structure against corrosion usually involves use of highly developed protective coatings – paints and sealants – and, increasingly, the application of corrosion inhibiting compounds (CICs) which retard corrosion principally by penetrating into crevices and cracks, and displacing water. A combination of coatings and CIC use can provide effective corrosion protection, but both interact – in different ways – with joint structural performance and overall system durability. This paper discusses the interaction between these two corrosion protection measures and fatigue performance of joints. The first issue relates to the extent to which application of CICs (or other lubricants) can cause a reduction in the fatigue life of mechanically fastened joints. The CICs are lubricants which will reduce the friction at the faying surface of the joint, and change the load transfer characteristics of the joint. This paper discusses results from a test program assessing the fatigue life and failure mode of simple riveted lap joints; the results show a distinct reduction in fatigue life for joints containing CICs, and the paper discusses the changes thought to be responsible for the reduction. The second issue discussed is the degradation of protective coatings in service. Joints are key locations for coating cracking and failure, because areas such as sheet ends and fastener heads, where displacements are concentrated, may produce concentrated strain in coatings. So far, however, the potential influence of aircraft loading on coating degradation prognostics has received little attention. This paper discusses the role of joint displacement in service as a factor contributing to degradation in aircraft coatings at joints, and argues that this local strain effect, and indeed structural loading history, needs to be considered in predicting and assessing rates of coating degradation. It describes analyses of displacements in aircraft joints, to identify the levels of strain and to identify the roles and relative contributions of the various deflections in the joints. The results indicate the potential for very large strains in coatings.     

The effect of adherent thickness on fatigue life of adhesively bonded joints

The effect of adherent thickness on the fatigue performance, fatigue limit, and failure mode of adhesively bonded thin aluminum single lap joint (SLJ) was experimentally and numerically investigated. High‐cycle fatigue tests were performed, and fatigue life was estimated using various fatigue criteria and finite element modeling. Based on the experimental results, increase in adherent thickness leads to increase in fatigue limit. In addition, failure location changes from adhesive to adherent by increasing the adherent thickness. It seems that in adherent failure, selecting a sheet with higher fatigue strength is required to achieve higher fatigue life. Also, based on the analysis of different fatigue criteria, Smith‐Watson‐Topper criterion could predict the joint fatigue life more accurately by considering the mean stress effect and the plastic strain. Finally, as an important result, an unsymmetrical SLJ specimen was evaluated as an industrial case study, and the empirical estimated life was consistent with the experimental results.     

飞机典型机械紧固连接件腐蚀疲劳性能的试验研究EI

本文研究了飞机机械紧固连接件在腐蚀环境下的疲劳性能。试验结果表明，腐蚀环境在大多数情况下降低紧固件的疲劳寿命，其中盐雾环境对双剪密封铆接件的疲劳寿命的影响最为严重。给出了机械紧固件在不同状态下的细节疲劳额定值（ＤＦＲ）和可靠性寿命（Ｎ＿（９５／９５））。     

非对称荷载下疲劳强度临界值的统一公式

本文对非对称荷载下的疲劳强度临界值预测公式和疲劳寿命预测公式进行了系统深 入的研究,分析了著名的Ｇｏｏｄｍａｎ公式,Ｓｏｄｅｒｂｅｒｇ公式和Ｇｅｒｂｅｒ公式的适用条件,建立了 一种新的疲劳强度临界值预测公式和疲劳寿命预测公式。新公式的最大优点是,对实际破坏 面的形状不做任何限制,并可使用任意疲劳寿命实验数据进行拟合。     

Fatigue strength assessment of laser stake‐welded web‐core steel sandwich panels

This paper investigates the fatigue strength assessment of web‐core steel sandwich panels. The production of these structures is made possible by laser stake welding. The investigation in this study considered two series of panels, one being an empty steel structure and the other filled with in situ polyurethane foam in order to increase the panel stiffness. Both series were tested under cyclic bending loading condition (R = 0) until one of the panel joints failed completely. A 3D panel bending response was analysed using finite element method. The J‐integral values at the panel joints were obtained by means of plane strain finite element analysis and by using displacements from 3D panel response. The influence of the weld geometry on the J‐integral value was investigated. It was found that the J‐integral value is similar in the cases of the average and critical geometry. The contact between the joint plates is possible in some cases, but its influence proved to be insignificant for the fatigue strength assessment. The study further shows that by using the average geometry, the J‐integral approach was able to identify the critical panel joints and present the fatigue strength results from both panel series in a narrow scatterband. The fatigue strength at two million cycles obtained for the panels within this study was in agreement with the laser stake welds and other steel joint types from previous studies. However, the slope of the panels fatigue resistance curve was found to be shallower than in the case of joints.