Neural Network Burst Pressure Prediction in Composite Overwrapped Pressure Vessels Using Mathematically Modeled Acoustic Emission Failure Mechanism Data

The purpose of this research was to predict burst pressures in composite overwrapped pressure vessels (COPVs) by using mathematically modeled acoustic emission (AE) data. Both backpropagation neural network (BPNN) and multiple linear regression (MLR) analyses were performed on various subsets of the low proof pressure AE data to predict burst pressures and to determine if the two methods were comparable. AE data were collected during hydrostatic burst testing on the 15-inch diameter COPVs. Once collected, the AE data were filtered to eliminate noise then classified into AE failure mechanism data using a MATLAB Kohonen self-organizing map (SOM). The matrix cracking only amplitude distribution data were mathematically modeled using bounded Johnson distributions with the four Johnson distribution parameters – ?, λ, γ, and η – employed as inputs to make both the BPNN and MLR predictions. The burst pressure predictions generated using a MATLAB BPNN resulted in a worst case error of 1.997% as compared to ?1.666% for the MLR analysis, suggesting comparability. However, the MLR analysis required the data from all nine COPVs to get approximately the same results as the BPNN training on just five COPVs; plus, MLR analyses are intolerant to noise, whereas BPNNs are not.     

复合材料高压气瓶声发射检测研究

芳纶纤维缠绕气瓶水压及爆破过程声发射特性表明，费利西蒂比是评价气瓶内部损伤的重要参数，它直接影响爆破强度，高的幅度分布值是气瓶爆破的先兆。     

压力容器声发射检测技术概述

阐述了声发射检测的基本原理,介绍了国内外压力容器声发射检测技术的发展历程和现状,给出了压力容器声发射检测方法的优点和压力容器用钢的声发射特性,最后指出了目前声发射检测需解决的问题和发展趋势。     

Burst Pressure Prediction and Structure Reliability Analysis of Composite Overwrapped Cylinder

Based on strength design for thin-walled isotropic cylinders and mechanical properties for the composite material, the equation to predict burst pressure of the composite overwrapped cylinder is established. Based on the equation, a structure reliability model is proposed to estimate the reliability of composite overwrapped cylinder by the advanced first order and second moment (AFOSM) method. The layer thicknesses, spiral winding layer angles, and the internal pressure are treated as random variables which obey normal distribution. Results shows that, the reliability of composite cylinders is reduced with the thickness of winding layers decreasing, and the thickness of loop winding layers plays the leading role on the reliability analysis. When the composite cylinder is operated in a low-level pressure, the reliability is not sensitive to the variation of the angle of spiral winding layers. And there will be a superior reliability, when the angle of spiral winding layers is within a certain range. Reducing variance of random variables is feasible to improve the structure reliability. The research also employs a reliability-based optimal design in the perspective of thickness and angles of composite winding layers. The strength of the optimized cylinder has been raised by 0.7% on the premise of cost saving and weight loss.     

Acoustic Emission in Composite Laminates

The response of a laminated plate to internal acoustic emission events is examined in detail. The plate consists of four layers of a unidirectional fiber composite material arranged in a cross-ply configuration. The sources considered include a vertical line couple, a horizontal line couple and a line double couple without moment. The latter is produced by the combination of two equal and opposite line couples and may be associated with a shear dislocation in the plane of the laminate. The particular response presented here is that of the normal upper surface displacement. Four different orientations of the line sources relative to the core fiber direction are considered. The sources may be located at any depth within the plate and results are shown for three locations, namely, the upper interface, the midplane and the lower interface. The receiver is positioned on the upper surface at a known distance from the line of action of the source. When this distance is small relative to the depth of the plate, it is possible to associate some of the peaks and troughs present in the response with the arrival of individual rays. At larger distances, the disturbance arises from the propagating Rayleigh Lamb modes.     

Damage Classification of Sandwich Composites Using Acoustic Emission Technique and k-means Genetic Algorithm

In this study acoustic emission (AE) technique was used for monitoring mode I delamination test of sandwich composites. Since, during mode I delamination test various damage mechanisms appear, their classification is of major importance. Hence, integration of \(k\) -means algorithm and genetic algorithm was applied as an efficient clustering method to discriminate different failure modes. Performing primary experiments to find the relationship between AE parameters and damage mechanisms, the AE signals of obtained clusters were assigned to distinct damage mechanisms. Also, the dominance of damage mechanisms was determined based on the distribution of AE signals in different clusters. Finally SEM observation was employed to verify obtained results. The results indicate the efficiency of the proposed method in damage classification of sandwich composites.     

基于声发射检测技术的PE/PE自增强复合材料破损机理分析

用声发射(AE)技术研究了聚乙烯自增强复合材料的拉伸损伤与断裂行为.宽带传感器记录了不同角度纤维铺层的复合材料试样在拉伸破坏过程中的声发射信号,用扫描电子显微镜(SEM)观察了试样的几种典型的损伤破坏断面,对比分析了不同类型的损伤机制.实验分析表明,拉伸过程中破坏机制对声发射信号的特征具有显著影响,不同损伤模式的信号频谱特征存在明显的差异.声发射检测能有效提取热塑性复合材料损伤破坏信息,在材料的结构损伤主动监测中有良好的应用潜力.     

声发射技术在纤维增强复合材料损伤检测和破坏过程分析中的应用研究进展

声发射作为一种无损检测技术,具有主动性、几何形状不敏感性、即时性和特征性等优点。声发射技术通过建立复合材料损伤和破坏特征与声发射信号间的关联,分辨复合材料随加载过程的各种失效模式,结合加载过程中的应力应变曲线,从而获得失效机制。本文对声发射检测技术在纤维增强复合材料研究中的应用和分析方法进行了综述,并对其在复合材料领域的应用趋势进行了展望。     

声发射检测复合材料飞轮损伤与断裂的结构模拟试验

对复合材料飞轮的受力与损伤情况进行了分析,设计了静态加载结构模拟复合材料飞轮的断裂与损伤,并对此结构进行了试验。用声发射方法检测了复合材料损伤与断裂的全过程,证明了该结构的合理性与可行性。     

Early Diagnostics of Damage and Fracture Zones in Composite Materials Using Brittle Strain Gauges and Acoustic Emission

The integrated use of the acoustic emission technique and brittle oxide strain gauges for testing the deformation of damage and fracture zones in samples of polymer composite materials (PCM) at the early phases is considered. For the realization of the proposed technique, integrated parameters were used and software including the cluster analysis and the classification of registered AE pulses was developed, which made it possible to differentiate crack formation signals in the brittle layer of a strain gauge from all the other signals that occur at the early phase of the deformation of PCM samples in the online mode. The use of acoustic emission testing and control video recording for the registration of cracks in a brittle oxide strain gauge with the threshold deformation value of 1000 μm/m provided the precise diagnostics of the forthcoming fracture zone in a sample at the early loading phase under the load level of 10–15% of the limiting one long before the beginning of the active PCM structural degradation phase and made it possible to determine the distribution fields of the highest main deformations in the region of a strain gauge and to perform their quantitative evaluation.     

Fatigue Failure Process Characterization for Carbon Fiber Sheet Reinforced Steel Rods Using the Acoustic Emission Technique

Acoustic emission (AE) technique is a widely used CM technique. In this paper, AE technique was used to characterize the fatigue failure process for carbon fiber sheet (CFS) reinforced steel rod. The AE signals at the frequency band of 50–400 kHz are detected by using AE sensors mounted on the steel rod and analyzed by both parameter analysis and spectrum analysis in order to investigate the feasibility of using the AE technique to identify various failure modes during fatigue failure process for CFS reinforced steel rods. Tension-tension fatigue experiments were carried out on both CFS reinforced and unreinforced steel rods. Based on AE energy parameter analysis using wavelet decomposition method, failure process was initially divided into three stages for unreinforced specimen and seven stages for CFS reinforced specimen. The frequency contents within the frequency band of 50–400 kHz for various failure modes in each stage including crack initiation, developing, final rupture in steel rod and matrix crack, debonding in CFS were revealed by fast Fourier transform (FFT) method. Further wavelet transform (WT) analysis was performed to illustrate the sequences of the failure modes and main failure mode in each stage by the occurrence time and longest duration time, respectively. This work indicates that the proposed method is promising for distinguishing failure stages qualitatively and identifying failure modes quantitatively in CFS reinforced steel rods.     

压力容器声发射检验中信号去噪研究

压力容器作为工业系统中的重要设备,其安全运行直接影响工业生产的安全性.通过定期对压力容器进行声发射信号检测,可及早发现设备缺陷,保障安全生产.由于压力容器检验现场各种噪声普遍存在,导致采集的声发射信号严重失真甚至淹没在噪声信号中.通过研究小波阈值去噪,自适应滤波原理,采用小波-自适应联合滤波,进行含噪信号去噪处理.     

基于声发射技术的热障涂层损伤行为

热障涂层以优异的隔热、耐磨和耐蚀性而被广泛应用于航空涡轮发动机中。由于热障涂层体系内部结构复杂,服役环境苛刻,导致其失效不可预测。热障涂层系统内的表面开裂和界面分层是限制热障涂层长时间使用的瓶颈问题,且热障涂层的过早剥落失效会导致合金基体暴露在高温燃气中,这可能引起灾难性的后果。针对涂层的裂纹扩展行为,最重要也最直接的研究方法就是对热障涂层的整个失效过程进行实时无损检测,为寿命预测提供最直接的证据。声发射技术是一种实时动态的无损检测方法,可直接检测热障涂层失效过程中的裂纹扩展行为,因此在热障涂层失效检测领域得到了广泛的应用。然而,造成热障涂层损伤失效的因素较多,如失效机理复杂、失效形式多样,以及声发射信号本身的随机性和不可逆性,使得利用声发射技术检测热障涂层失效整个过程的研究还不够全面。目前,已通过声发射技术的参数分析和波形分析实现了对热障涂层损伤失效的定性、定量和定位分析,并对涂层寿命进行了预测。参数分析是以多个简化的波形特征参数来表示声发射信号的特征,即对一些特征量进行统计的过程,如能量、频率、幅度等。采用声发射特征参数法可定量评估热障涂层的损伤程度并对涂层的寿命进行预测。目前人们从连续损伤累计、某一特定参量变化等多个角度预测热障涂层的寿命,但是各种寿命预测模型主要是根据实验结果的经验或半经验公式,随着热障涂层的发展以及对热障涂层失效机理认识的不断加深,寿命预测模型也在不断发展与完善。波形分析是通过对声发射信号的时域波形或频谱特征分析来获取缺陷信息的一种信号处理方法。从理论上讲,波形分析应当能给出任何所需的信息,因而波形也是表达声发射源特征最精确的方法,目前主要通过小波变换把声发射波形信号从时域变换到频域,进而识别其损伤模式并实现声发射源的定位。本文对声发射技术进行了简要的介绍,总结了声发射技术参数分析和波形分析在热障涂层损伤模式识别、损伤位置的定位、损伤程度的定量评估和剩余寿命预测方面的研究进展,指出了当前研究中存在的问题并对其下一步的发展进行了展望。     

蜂窝夹层复合材料压缩损伤声发射特征研究

应用声发射技术对蜂窝夹层复合材料压缩损伤过程进行了实验研究。分析载荷与声发射信号经历图,依据其损伤过程和声发射特征,发现随着加载载荷的增加,复合材料的损伤逐步增大。在加载初始阶段,仅有少量声发射信号,各种表征信号量小幅度增加;在加载中期,声发射信号增多,各种表征信号量不断增大;在加载后期,声发射信号明显突增,各种表征信号量急剧增加。复合材料压缩损伤破坏与声发射的幅值、能量、撞击、上升时间、持续时间和计数等参量相关。蜂窝夹层复合材料试件的应力-应变曲线近似为直线,应变速率与声发射信号特征相互对应。     

Predicting Failure Strength of Randomly Oriented Short Glass Fiber-Epoxy Composite Specimen by Artificial Neural Network Using Acoustic Emission Parameters

Acoustic emission (AE) peak amplitude and cumulative energy emitted during 50% of failure of composite specimen was collected, analyzed, and utilized to predict the ultimate tensile strength (UTS) using artificial neural network (ANN) and the performance of various training algorithm on prediction was analyzed. AE data have been collected from finite numbers of randomly oriented short glass fiber-epoxy tensile specimens, while loading up to failure in a tensile testing machine. AE response from each of the specimen was classified and segregated by understanding the failure mechanism. A feed forward back-propagation type ANN was designed and the segregated data of amplitude hits and cumulative energy was processed using two separate networks to predict the UTS of corresponding specimens using it with appropriate parameters and the results were analyzed.     

复合微穿孔板吸声结构声学性能预测

本文旨在将微穿孔板吸音结构与多孔材料复合,得到中低频吸音性能较好的复合层声学结构。以微穿孔板多边形穿孔截面、穿孔率、空腔厚度和多孔材料类型为变量,设计复合层声学结构,给出复合层声学结构吸声系数的理论计算方法和声学有限元仿真预测模型。利用3D打印技术制备精度较高的微穿孔板实验样本,利用阻抗管法对复合层声学结构的吸声系数进行实验室测量。对比预测结果和实验数据,发现两者具备很好的一致性。研究表明：复合层声学结构具有很好的中低频吸声系数,通过调整微穿孔板穿孔截面形状和穿孔率可以对中低频段（50-1600Hz）噪音进行有效控制。     

基于声发射技术监测疲劳磨损失效的研究进展

现代工业的一些重要零部件在变载荷的作用下易发生疲劳磨损失效.声发射技术作为一种新型的无损监测技术,可以实现早期的安全预警,被广泛应用在机械零件、工程构件及涂层的失效监测上.参数分析法是最常用的声发射信号处理方法.典型的声发射特征参数包括能量、计数、幅值等.对声发射信号参数法分析轴类零件及涂层的失效模式的研究现状进行了较为全面的综述,最后总结了目前存在的问题,简述了解决思路,以期为声发射技术监测疲劳磨损失效奠定良好的基础.     

Damage Monitoring of an Historical Masonry Building by the Acoustic Emission Technique

Acoustic Emission (AE) of the materials that are subject to stress and strain states is a methodology for non-destructive investigation, originally applied to industrial steel structures. Here it is proposed by the authors for identifying the damage in masonry buildings. This experimental method was used to monitor the masonry structure of an historical building, “Casa Capello”, located in the centre of the Rivoli Municipality (near Turin, Italy). This house, built on pre-existing 14th century foundations, was thoroughly restructured at the end of the 18th century and has recently undergone restoration and enlargement works. Non-destructive AE tests were carried out on a few masonry portions of the building in order to evaluate and define the development of the cracking phenomena which had been observed in a number of structural parts after the collapse of a breast wall on the down hill side of the building. With the measurement system adopted, entailing no loading or invasive procedures, it proved possible to predict the arrest of crack growth and the concomitant onset of a new stability condition.