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The debonding and falloff of ceramic tile systems are common failure modes for ceramic finishes of buildings and infrastructures due to the damage accumulation caused by application of mechanical load or changes in environmental conditions. To better understand the mechanism of the damage, a newly developed push-off test was conducted and a quantitative acoustic emission (AE) technique was developed to detect the damage processes during the loading history. The source locations of internal damage were determined by a new three-dimensional algorithm. Test results show that the growth of damage and the onset of failure can be monitored by AE technique. Also, the experimental results indicate that a probability density function of AE activity can be used to quantitatively describe the degree of damage of a material. It was found that the ceramic tile system with a lower strength adhesive displayed a higher AE rate than that with a higher strength adhesive at the same loading level prior to failure. 相似文献
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Experimental Mechanics - Recently, a technique for rapidly determining a material’s fatigue limit by measuring energy dissipation using infrared thermography has received increasing interest.... 相似文献
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Additive manufacturing (AM) is a novel and innovative production technology that can produce complex and lightweight engineering products. In AM components, as in all engineering materials, fatigue is considered as one of the principle causes of unexpected failure. In order to detect, localise and characterise cracks in various material components and metals, acoustic emission (AE) is used as a non-destructive monitoring technique. One of the main advantages of AE is that it can be also used for dynamic damage characterisation and specifically for crack propagation monitoring. In this research, we use AE to monitor the fatigue crack growth behaviour of Ti6Al4V components under four-point bending. The samples were produced by means of AM as well as conventional material. Notched and unnotched specimens were investigated with respect to the crack severity and crack detection using AE. The main AE signal parameters –such as cumulative events, hits, duration, average frequency and rise time– were evaluated and indicate sensitivity to damage propagation in order to lead to a warning against the final fracture occurrence. This is the first time that AE is applied in AM components under fatigue. 相似文献
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Marvin A. Hamstad 《Experimental Mechanics》1986,26(1):7-13
The technique of acoustic emission has two broad applications areas. The first is nondestructive evaluation. The second is
as a tool in studies or research which are not fundamentally directed towards acoustic emission. It is this second application
with which we are concerned here. Acoustic emission is a very useful tool in this role because of its high sensitivity, real-time
capability, volume-monitoring approach, and sensitivity to any process or mechanism which generates sound waves. This paper
presents a comprehensive review of areas where acoustic emission (AE) has been used for materials studies on composite materials.
The following fields, among others, will be covered: (1) time-dependent composite properties, (2) impact studies, (3) correlation
of AE with stress level, (4) application to matrix cure studies, (5) relationship of AE-detected damage to other measures
of damage, (6) studies of the effects of matrix material, (7) application to differences in second phase, (8) interface studies,
(9) AE and dimensional stability, (10) AE applied to orientation studies, and (11) environmental effects. This review will
emphasize the roles that AE can play as a tool for the materials scientist: (1) discovery of damage mechanisms, (2) characterization
of damage progression with increasing time or stress, (3) optimization of fabrication variables, and (4) reduction in the
numbers of test specimens required in various studies. 相似文献
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为了深入探究复合材料层合板结构的损伤机理和损伤演化,应用声发射技术和图像相关技术同步实时监测含孔碳纤维复合材料层合板试样在静拉伸过程中的损伤演化。实验结果表明,试样表面应变场呈现局部化特征。对应变集中带在加载方向的应变值进行了统计分析,获得了应变场的特征统计量(标准差)随加载的演化模型。层合板损伤时产生声发射信号的峰值频率大小能够有效区分复合材料的损伤模式,由此,建立了基于损伤模式累积声发射数的损伤演化模型。通过对应变场演化模型和声发射损伤演化模型的分析,可以将复合材料的损伤演化分为损伤初始阶段、损伤平稳扩展期、损伤严重阶段三个部分。统计分析结果表明:在损伤严重阶段,基于声发射事件数的各种损伤的损伤变量和局部应变场标准差快速增长,因此局部应变场统计标准差可以作为后期局部损伤严重程度的识别指标。 相似文献
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纤维增强复合材料的破坏机理 总被引:5,自引:0,他引:5
纤维增强复合材料本身是一个非均匀各向异性力学结构。复合材料的研制、设计和使用都与力学密切相关。复合材料的破坏机理比金属材料复杂,不同组分的构成使其在加工中存在和使用中带来的缺陷比金属多。它的破坏机理与纤维、基体组分的性能,粘结强度,纤维铺设方向和顺序,工作条件等有关。需要采用有效的试验和分析方法,研究复合材料在不同 相似文献
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The present study deals with the examination of the acoustic emission signatures of distinct fracture modes. Tensile and mixed mode cracking is excited in specimens of marble and cement mortar and the acoustic emission behavior is monitored. Tensile cracking incidents show a preference to higher frequencies and shorter waveforms unlike shear events. The results imply that adequate analysis of simple AE features enables the characterization of the current fracture condition of the material and consequently predictions on the remaining safe service life for monolithic, as well as microstructured materials. 相似文献
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疲劳过程中生热机理的实验探讨 总被引:1,自引:0,他引:1
传统的疲劳试验方法确定材料的疲劳极限时试验周期长、需要试件多,故高试验成本成为疲劳试验中一个难以解决的问题.文中利用具有准确、快速、便捷、低成本等优点的热像法测定了多种载荷工况下Q235钢的疲劳极限,并对不同的黏或/和塑性效应主导的生热机制进行了探讨.材料疲劳过程中,疲劳极限之下的载荷引起的温度波动来源于热弹性效应,温升来源于材料的非弹、塑性效应(如黏性效应);而疲劳极限之上的载荷引起塑性功累计,导致疲劳损伤产生,使得温升机制出现转折.通过对试验数据的分析,求出了材料的黏性系数,给出了利用塑性能耗的起点确定材料疲劳极限的方法. 相似文献
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R.V. Prakash T. PravinT. Kathirvel Krishnan Balasubramaniam 《Theoretical and Applied Fracture Mechanics》2011,56(1):1-6
The surface temperature of stainless steel SS304 low cycle fatigue specimens subjected to cyclic loading was studied using infrared thermography technique. The thermal data mapped onto the various stages of cyclic stress-strain curve shows the ability of these measurements to identify the yield points in both the compression and tension loading. Based on the results of this study, it is possible to identify the state of stress for materials such as elastic tension, plastic tension, elastic compression, plastic compression during cyclic loading using infrared thermographic data. The thermo-elastic slope and thermo-plastic slope was observed to be dependent on the prior loading cycles. 相似文献
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为研究周期荷载应力水平对煤样声发射特征的影响,采用PFC数值软件开展了3种不同应力水平的等幅周期荷载数值模拟试验,分析了周期荷载应力水平对煤样破坏循环次数、声发射计数及损伤演化特征的影响。研究结果表明:周期荷载作用下,煤样破坏过程中的声发射活动呈现初始、相对平静和活跃三阶段演化规律,且在煤样破坏前的周期荷载卸载阶段及低应力水平阶段几乎没有声发射活动;周期荷载上限应力水平的微小提高会加快煤样的破坏过程。提出了声发射比率的概念,当声发射比率大于1时,表明煤样即将发生破坏。声发射比率可作为预测现场工程煤体失稳的重要指标。 相似文献
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This paper demonstrates the feasibility of infrared thermography to determine the so-called fretting fatigue limit. Fretting fatigue tests are performed on aluminum and steel specimens. The coupled fatigue and tangential loads are sequentially increased (block loading) whilst the normal load is kept constant for all blocks. The temperature data is processed and analyzed using a Fast Fourier Transform (FFT) algorithm implemented in the commercial software Matlab. It is demonstrated that the second harmonic of the temperature signal can be linked to the specific loading block below which no or negligible damage is generated in the specimen. The stress amplitude of this block is considered to be a best estimate of the fretting fatigue limit. A constant amplitude fretting fatigue test with this stress amplitude confirmed that the specimen remains intact at 107 cycles. 相似文献
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A series of experiments has been conducted to determine the effect of loading variables such as cyclic frequency, load ratio, and material on acoustic emission from fatigue-crack propagation. It is shown that the applied-stress intensity range (ΔK) is the controlling parameter for all materials studied while the other parameters have lesser effects. Two potential methods for engineering application of acoustic emission during fatigue loading are described. 相似文献
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Acoustic emission (AE) supplies information on the fracturing behavior of different materials. In this study, AE activity was recorded during fatigue experiments in metal coupons. The plates were characterized by a symmetric V-shape notch and were loaded in tension-tension fatigue until final failure with concurrent AE activity monitoring. The relatively broad bandwidth of the sensors enabled the recording of a wide range of frequencies up to 1 MHz. AE parameters like energy and duration exhibited a certain increase with the accumulation of damage although the hit rate was not significantly influenced. Furthermore the behavior of RA value (ratio of rise time to amplitude of the waveforms) which quantifies the shape of the first part of the AE signals and has been used for characterization of the cracking mode, showed a certain shift indicating the transition from tensile mode to shear which can be confirmed by the visual observation of the crack geometry after the experiment. The time history of RA is similar to the crack propagation rate (da/dN) curve but exhibits the rapid hyperbolic growth consistently about 1000 cycles earlier than final failure. Therefore, the use of acoustic emission parameters is discussed both in terms of characterization of the damage mechanisms, as well as a tool for the prediction of ultimate life of the material under fatigue. 相似文献
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An experimental technique is presented for measuring the heat dissipation and localization during cyclic loading of materials.
The temperature field is measured by a number of thermistors and an infrared camera, which scans the specimen surface continuously.
The specimen is mounted inside an isothermal chamber. The measured whole-field temperature can be used for detection of damage
propagation and localization. The resolution of the technique under various boundary conditions is discussed using a onedimensional
model for the heat loss under steady-state conditions. Applications of the technique are demonstrated for specimens made of
fiber-reinforced ceramic and polymer matrix composites (PMCs). A methodology is proposed for measuring changes in damping
and stiffness properties of viscoelastic polymer matrix composites using the temperature rise of a cyclic loaded specimen.
It is demonstrated that for a ceramic matrix composite, where interfacial frictional sliding gives rise to heat dissipation,
the temperature resolution can be used for detection of stress-strain hysteresis with an accuracy better than that of the
stress-strain data. 相似文献
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复合材料层压板在压缩破坏过程中包含了丰富的声发射信息.为了研究含冲击损伤的复合材料层压板的压缩破坏机制,采用声发射观察层压板的压缩破坏过程,通过分析声发射信号的特征规律,表征了在压缩载荷下材料损伤的形式及其演化过程.结果表明:通过对声发射参数(撞击计数、能量、幅值、事件位置)和载荷曲线进行综合分析,发现损伤的发展过程经过了初始阶段、平稳扩展期和断裂阶段,冲击造成的分层区域最先出现屈曲并最早破坏;在损伤初始阶段和平稳扩展期间,损伤是一种渐进式的增长,层压板具有一定的承载能力;在断裂阶段损伤快速扩展,层压板的承载能力迅速下降,在出现纤维密集断裂的现象后整体破坏. 相似文献