裂纹检出概率对飞机结构维修间隔影响的研究

针对飞机结构裂纹检测的不完备性,考虑到疲劳裂纹具有时间延迟的特性,对Goranson模型进行改进,提出了基于时间的裂纹检出概率模型。并在此基础上建立了以复检间隔和首检间隔系数为变量,单位时间维修成本最小为目标函数的飞机结构维修间隔优化模型。通过裂纹检出概率模型中参数的变化对优化模型进行仿真计算,分析了裂纹检查概率对飞机结构维修间隔优化结果的影响情况,结果显示裂纹检出概率对维修间隔有显著的影响,其变化趋势与实际情况相符,表明提出的裂纹检出概率模型能够有效地应用于飞机结构维修间隔的优化与确定。     

飞机结构外R区的在役原位检测方法

针对某飞机结构外R(半径)区的损伤特征,在分析常规无损检测方法的优势和局限性的基础上,选择了涡流检测法对R区进行在役原位检测,并对该检测方法的检出能力及可靠性进行了研究和试验验证,最后制定了可靠的检测工艺,为飞机结构疲劳裂纹的无损检测工作提供了参考。     

无损检测技术可靠性的贝叶斯评估

针对无损检测数据具有的不确定性和样本采集的局限性,提出可靠性评估指标——损伤检出概率(POD)函数形式选取及参数估计带来的困难,首先提出基于贝叶斯公式和最优POD函数选取方法。其次针对贝叶斯后验概率难于求解的问题,将基于因子简化的贝叶斯信息准则(BIC)作为评判最优POD函数的准则。最后,通过算例分析表明基于贝叶斯方法选取的.POD函数适用于无损检测技术的可靠性评估。     

不同透照工艺对焊缝中缺陷的射线检验可靠性的影响

采用不同射线透照工艺,对带人工模拟缺陷(裂纹和未熔合)的异种金属焊缝试块进行了射线检验,得到了各缺陷的检验结果,并与解剖测量的缺陷尺寸进行了比较分析。通过检出/漏检数据,获得检验概率函数;通过信号响应数据,获得检验概率函数的分析方法。探讨了异种金属焊缝中缺陷的射线检验可靠性,分析了影响射线检验可靠性的主要因素。给出了缺陷的检出概率和检测概率曲线。     

粉末涡轮盘夹杂缺陷的超声检出概率

缺陷的检出概率是零件损伤容限设计和寿命预测的重要基础数据。针对发动机中的关键转动件——粉末涡轮盘中的夹杂缺陷,进行了超声检出概率研究。制作了不同埋深不同孔径的平底孔人工缺陷试样,模拟粉末盘中的非金属夹杂缺陷。采用6组探头的超声水浸分区聚焦检测工艺对上述人工缺陷试样进行检测,获得了不同缺陷的超声检出概率数据,并绘制出缺陷检出概率(POD)曲线。结果表明,采用特定的检测工艺,在95%的置信水平下,以90%概率检出的缺陷当量尺寸为0.167mm。     

焊接结构焊缝中缺陷参数不确定性处理方法

提出了含缺陷焊接结构中缺陷参数不确定性的工程处理方法.对于不同板厚、不同形状容器焊缝中的缺陷参数,可分别采用直接法、间接法以及考虑无损检测检出概率(POD)时缺陷参数不确定性的处理方法.同时对缺陷尺寸参数的分布规律与POD的定量关系进行了推论.     

焊接结构焊缝中缺陷参数不确定性处理方法

本文提出了含缺陷焊接结构中缺陷参数不确定性的工程处理方法。对于不同板厚、不同形状容器焊缝中的缺陷参数，可分别采用直接法、间接法以及考虑无损检测检出概率（POD）时缺陷参数不确定性的处理方法。同时对缺陷尺寸参数的分布规律与POD的定量管线进行了推论。     

飞机用铝合金抗疲劳性能的改进

近期发展的铝合金和处理状态提供了强度、韧性、抗应力腐蚀和抗剥落腐蚀等良好的综合性能.这些合金已正用在或准备用在一些飞机上.然而,飞机的可靠性和结构性能的提高,仍然取决于周期载荷裂纹扩展抗力.为了探讨合金成分和最佳抗疲劳裂纹扩展性能的关系,制定了一个测定显微组织和成分对这一性能影响的研究方案.美国空军材料试验室(AFML)报告中提出的全部试验程序、试验前后显微组织的检验、机械性能的测定(抗拉强度、撕裂强度和缺口韧性)以及由2到20兆帕、米~(1/2)的da/dn与ΔK的全部关系曲线,都是适用的.本文的目的是研究中等ΔK值时显微组织与疲劳裂纹的关系.     

无损检测技术检出概率统计分析方法

给出了结构件裂纹检测技术的检出概率统计分析方法，并提出了新的设想。     

基于ACFM的自升式海洋平台局部损伤检测

介绍了交流电磁场(ACFM)技术的检测原理,利用实验室加工的不同梯度裂纹尺寸的试板,对比分析了ACFM方法与磁粉检测(MT)方法的裂纹检出概率。根据海洋平台的结构特点及所处环境的特殊性,开发出基于ACFM技术的局部损伤检测过程实时音视频与检测结果远程同步显示的软、硬件系统;同时,借助于Bayes理论,得到基于无先验信息的点估计和置信下限,从而可以近乎准确地进行裂纹存在的概率评价;将该系统应用于某自升式海洋平台上,取得良好的现场检测效果,具有较好的实际工程应用价值。     

在役轧辊表面波检测裂纹深度的判定

超声表面波能有效检测出轧辊的表面裂纹,但由于其裂纹很浅且目前的超声波仪器无法对裂纹深度进行直接读数,因此轧辊表面裂纹深度的判定一直是困扰检测工作者的难题。通过计算得出了表面波检测中裂纹深度当量d与回波分贝差△的关系曲线,并将其应用于马钢各种型号的在役轧辊检测中,取得了良好效果。同时比对抛关系曲线并通过实践证明得出,GB／T23904--2009标准中的检测灵敏度调整方法不造用于磨削量最小为0．2mm的在役工作辊的表面波检测。该抛关系曲线使轧辊表面裂纹深度的判定更加简单准确,对在役工作辊的表面波检测具有一定的指导意义。     

Forced vibration behaviour and crack detection of cracked beams using instantaneous frequency

In this paper, a new method for crack detection in beams based on instantaneous frequency and empirical mode decomposition is proposed. The dynamic behaviour of a cantilever beam with a breathing crack under harmonic excitation is investigated both theoretically and experimentally. A simple single-degree-of-freedom system with varying stiffness is employed to simulate the dynamic behaviour of the beam. The time-varying stiffness is modelled using a simple periodic function. Both simulated and experimental response data are analysed by applying empirical mode decomposition and Hilbert transform and the instantaneous frequency of each oscillatory mode is obtained. It is shown that the instantaneous frequency oscillates between frequencies corresponding to the open and closed states revealing the breathing of the crack. The variation of the instantaneous frequency increases with increasing crack depth following a polynomial law and consequently can be used for estimation of crack size. Using the intrinsic modes of the system, the harmonic distortion of the distorted sinusoidal response is calculated. It follows that the harmonic distortion increases with crack depth following definite trends and can be also used as an effective indicator for crack size. The proposed time–frequency approach is superior compared to Fourier analysis and can be used to improve the effectiveness of vibration-based crack detection techniques.     

利用电位法监测疲劳裂纹的可行性研究

鉴于常规裂纹检测技术的不足,提出应用电位法对结构疲劳裂纹进行监测的方法。介绍了电位法检测裂纹的基本原理,通过基于铝箔纸的模拟试验研究,对应用电位法监测结构疲劳裂纹的可行性进行了论证。试验得到一组可反映监测电压值与裂纹的出现位置、长度及扩展关系的曲线,从而证明了应用电位法监测结构疲劳裂纹的可行性。     

Quantifying the vibrothermographic effect

Vibrothermography, also known as Sonic IR and thermosonics, is a method for finding cracks through thermal imaging of vibration-induced crack heating. Due to large experimental variability and equipment which has, up to now, yielded mostly qualitative results, little data has been available to help quantify the vibrothermographic effect. This paper quantitatively evaluates the relationship between vibrothermographic crack heating, crack size, and vibrational stress in a series of tests on 63 specimens each of Ti-6-4 titanium and Inconel 718 at three different sites with different equipments. Test specimens are excited in a resonant mode. Infrared cameras record the crack heating, and vibrational stress is evaluated from the known vibrational mode shape combined with vibrational velocities measured using a laser vibrometer. Crack heating increases both with crack length and dynamic vibrational stress level. Data from all three sites gives similar probability of detection (POD) curves. The relationship of crack heating to crack size and vibrational stress will provide a means in the future to predict crack detectability based on vibration measurements.     

基于参数降阶模态的分层贝叶斯在线裂纹检测

为了保证检测的稳定性和准确性,并且有效处理参数的关联性与强非线性,提出一种基于参数降阶模态的分层贝叶斯在线裂纹检测方法。提出一种用于递归输入、状态和参数估计的分层贝叶斯滤波器,它通过使用空间不完整和噪声可以仅输出测量振动。将所寻求的参数视为具有有限个更新状态的随机变量,参数状态的动力学由改进估计策略控制,该策略能够探索参数空间并识别目标值。进一步利用参数降阶模型对所提出的方法进行裂纹识别。最后通过航空航天应用中的真实组件对提出方法进行仿真,结果显示提出方法检测准确性和稳定性较高,证明了提出方法的有效性。     

Effect of electromagnetic bulging on fatigue behavior of 5052 aluminum alloy

The effect of electromagnetic bulging on the fatigue behavior of the 5052 aluminum alloy was investigated through tensile–tensile fatigue testing. The intriguing finding is that the bulged specimens exhibited enhanced fatigue strength as depicted by maximum stress vs the number of cycles until failure (S–N) curves, by comparison with these original aluminum alloys. Although the fatigue process of the original and budged alloys follows the same mechanism with three distinct steps, namely, crack initiation at a corner of the tested samples, stable crack propagation with typical fatigue striations and finally catastrophic fracture with dimple fractographic features. The typical crack propagation rate vs stress intensity factor range (da/dN–ΔK) curves derived from the spacing of striations reveal a lower crack propagation rate in the bulged specimens. The enhancement of fatigue strength in electromagnetically bulged aluminum alloy is further rationalized in-depth on the basis of strain hardening and dislocation shielding effect.     

FRACTURE RESISTANCE OF 3D-C／SiC COMPOSITES AT 1300℃

Based on the energy conservation, the elastic energy linked to the compliance change, non-elastic energy dissipated by irreversible deformation and the resistance for crack propagation were quantitatively characterized by evaluation the load/qoad point displacement curves tested by three points bend experiment with single notch beam at 1300℃. The cracks length was determined by compliance calibration curves. It is shown by experimental results that the compliance of 3D-C/SiC composites changes with the cracks can be described by third order polynomial. The variation of crack advancing resistance with non-dimensional equivalent crack length presents a convex curve. The crack advancing resistance increases firstly and then decreases with the non-dimensional equivalent crack length, finally is in comparatively low level. The maximum values of crack advancing resistance are 269.73k J/m^2 for nondimensional equivalent crack length of 0.318 and original notch length of 0.35mm, and 138.65kJ/m^2 for non-dimensional equivalent crack length of 0.381 and original notch length of 2.06mm, respectively.     

FRACTURE RESISTANCE OF 3D-C/SiC COMPOSITES AT 1300℃

Based on the energy conservation, the elastic energy linked to the compliance change,non-elastic energy dissipated by irreversible deformation and the resistance for crack propagation were quantitatively characterized by evaluation the load/load point displacement curves tested by three points bend experiment with single notch beam at 1300℃. The cracks length was determined by compliance calibration curves. It is shown by experimental results that the compliance of 3D-C/SiC composites changes with the cracks can be described by third order polynomial. The variation of crack advancing resistance with non-dimensional equivalent crack length presents a convex curve. The crack advancing resistance increases firstly and then decreases with the non-dimensional equivalent crack length, finally is in comparatively low level. The maximum values of crack advancing resistance are 269.73k J/m2 for nondimensional equivalent crack length of 0.318 and original notch length of 0.35mm,and 138.65k J/m2 for non-dimensional equivalent crack length of 0.381 and original notch length of 2.06mm, respectively.     

非线性超声脉冲反转法在铝合金焊缝疲劳寿命预测中的应用

以不同疲劳寿命的铝合金焊缝为例研究了疲劳过程中的超声波非线性效应,同时建立了非线性参数与疲劳寿命的关系曲线(S-N曲线).采用脉冲反转法对非线性超声信号进行处理.结果表明,经过脉冲反转法获得的S-N曲线与经过滤波模块获得的S-N曲线相比谐波幅值提高了一倍,所以脉冲反转法可以提高非线性超声检测法表征疲劳损伤程度能力,而S-N曲线在疲劳过程中呈先缓慢增长后快速增长,最后下降的趋势,此趋势对应了材料疲劳的3个阶段,而金相组织验证了曲线的准确性,所以通过非线性超声脉冲反转法来预测疲劳寿命是可行的.     

GH864合金蠕变/疲劳裂纹扩展速率及a-N曲线分析

研究了GH864合金不同保载时间下650℃蠕变/疲劳裂纹扩展行为,分析了裂纹扩展过程中蠕变和氧化的作用,以及a-N曲线的转折点含义。结果表明:保载5s时GH864合金以穿晶断裂为主,疲劳作用占主导;保载90s时GH864合金以沿晶断裂为主,蠕变作用占主导。利用Saxena模型可较好地表征本实验条件下650℃蠕变/疲劳交互作用的裂纹扩展速率曲线,可估算较高应力强度因子和较低应力强度因子的裂纹扩展速率。另外,用Saxena模型可求出蠕变和疲劳的表达式,对比分析高温蠕变/疲劳交互作用的裂纹扩展过程中蠕变和疲劳的作用及所占的比例。最后针对a-Ni/Nf、da/dN-a曲线及da/dN-N曲线变换中出现的拐点,结合断口形貌分析了转折点对应的含义。高温合金及其它材料的裂纹扩展速率曲线也适用于以上曲线分析方法。