共查询到20条相似文献,搜索用时 906 毫秒
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文中以P92钢与Ni基焊材焊接热影响区为研究对象,通过采集紧凑拉伸试验过程中异种钢接头热影响区启裂及裂纹扩展的声发射特性信号,分析裂纹扩展的声发射信号幅值、频率分布、能量及振铃计数等特征参数,同时分析声发射特征信号与断口形貌之间的对应关系。结果表明:裂纹扩展声发射信号均为突发型信号,频率主要集中在50~200 kHz;裂纹稳定扩展的声发射信号具有平均幅值较低、总能量和振铃计数率参数变化平缓的特点;裂纹失稳扩展的声发射信号具有平均幅值较高、总能量和振铃计数率参数呈瞬时增加的特点;裂纹稳定扩展阶段的声发射特征信号与韧性断口特征相对应;裂纹失稳扩展阶段的声发射特征信号与准解理断裂或解理断裂特征相对应。 相似文献
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由声发射信号特征分析爆破试验过程中16MnR乙炔瓶预制裂纹的活动。一种以范性形变松弛应力,由于形变引起壁厚的减薄和材料的加工硬化,爆破时发生快速撕裂;另一种是预制裂纹前沿多次发生低能量撕裂,最后的爆破也比较“平稳”。 相似文献
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齿轮表层疲劳裂纹扩展的声发射模型 总被引:1,自引:0,他引:1
齿轮表面的疲劳磨损是齿轮故障的主要形式之一。从弹性力学的能量理论角度,推导出了齿轮齿表疲劳裂纹在扩展时的能量关系,并根据声发射信号的特征,构造出齿表疲劳裂纹在扩展时产生的声发射信号的理论模型,说明了影响声发射信号能量强度的主要因素为裂纹扩展时间、形变体积及载荷和弹性模量的变化率,从理论上证明了声发射技术用于检测疲劳磨损的可行性。 相似文献
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采用声发射(acoustic emission,AE)技术对7N01铝合金单边缺口三点弯曲试样不同应力比、不同峰值载荷下疲劳裂纹扩展过程中声发射信号进行了监测,建立了裂纹扩展速率、声发射计数(count)与应力强度因子之间的关系.结果表明,大部分的声发射信号主要产生于疲劳循环载荷的低应力阶段,这主要是低应力阶段的声发射活动主要与裂纹尖端的塑性变形和裂纹闭合现象有关,声发射计数与应力强度因子之间呈指数增长的关系.基于所建立的声发射计数率与裂纹扩展速率的关系,可以预测疲劳损伤结构的剩余寿命. 相似文献
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用超音速等离子喷涂设备在45钢基体上制备了铁基合金涂层。以球盘式疲劳试验机为平台,研究了涂层的接触疲劳损伤行为,探测并分析了涂层在不同应力水平下疲劳损伤的声发射反馈信号。结果表明,涂层的接触疲劳损伤过程主要包括弹塑性变形、裂纹萌生和缓慢扩展、裂纹亚临界扩展、裂纹失稳扩展4个阶段。裂纹萌生和缓慢扩展阶段是决定疲劳寿命长短的主要阶段。接触应力越大,裂纹亚临界扩展时间和失稳扩展时间越短。涂层的最终失效模式可以根据裂纹失稳扩展阶段声发射幅值的最大值来判断,发生点蚀失效时幅值最大值约为82.4 dB,剥落失效时幅值最大值约为90.2 dB,分层失效时幅值最大值约为91.3 dB。 相似文献
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Ki-Woo Nam Chang-Yong Kang Jae-Yoon Do Seok-Hwan Ahn Sang-Kee Lee 《Metals and Materials International》2001,7(3):227-231
The fatigue crack propagation of super duplex stainless steel was investigated for the effect of various volume fractions
of the austenite phase by changing the heat treatment temperature. We also analyzed acoustic emission signals obtained during
the fatigue crack propagation by the time-frequency analysis method. As the temperature of the heat treatment increased, the
volume fraction of austenite decreased and coarse grain was obtained. The specimen treated at 1200 had a longer fatigue life
and slower rate of crack growth. Results of time-frequency analysis of acoustic emission signals during the fatigue test showed
the main frequency of 200-300 kHz to have no correlation with heat treatment and crack length, and the 500 kHz signal to be
due to dimples and separation of inclusion. 相似文献
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飞机主承力构件疲劳裂纹萌生和扩展的声发射评价 总被引:2,自引:1,他引:1
讨论了利用声发射(AE)监测飞机关键部位疲劳裂纹形成和扩展的意义、可行性以及应当注意的问题.提出利用多参数识别和相关技术从高背景噪声中获取裂纹扩展所产生的声发射信号,并曾在疲劳试验过程中多次成功预报了飞机一些主承力构件的疲劳裂纹萌生和扩展. 相似文献
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Wolfgang Tillmann Frank Walther Weifeng Luo Matthias Haack Jens Nellesen Marina Knyazeva 《Journal of Thermal Spray Technology》2018,27(1-2):50-58
In order to guarantee their protective function, thermal spray coatings must be free from cracks, which expose the substrate surface to, e.g., corrosive media. Cracks in thermal spray coatings are usually formed because of tensile residual stresses. Most commonly, the crack occurrence is determined after the thermal spraying process by examination of metallographic cross sections of the coating. Recent efforts focus on in situ monitoring of crack formation by means of acoustic emission analysis. However, the acoustic signals related to crack propagation can be absorbed by the noise of the thermal spraying process. In this work, a high-frequency impulse measurement technique was applied to separate different acoustic sources by visualizing the characteristic signal of crack formation via quasi-real-time Fourier analysis. The investigations were carried out on a twin wire arc spraying process, utilizing FeCrBSi as a coating material. The impact of the process parameters on the acoustic emission spectrum was studied. Acoustic emission analysis enables to obtain global and integral information on the formed cracks. The coating morphology and coating defects were inspected using light microscopy on metallographic cross sections. Additionally, the resulting crack patterns were imaged in 3D by means of x-ray microtomography. 相似文献
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Specimens of sensitized type AISI 304 stainless steel were subjected to constant load and exposed to an aqueous sodium thiosulphate solution. Intergranular stress-corrosion cracking was monitored simultaneously for electrochemical noise, acoustic emission, and specimen elongation. A section of the gauge length was monitored optically with subsequent analysis by digital image correlation. Correlations between the results were observed and analysed. Electrochemical noise and elongation are associated with crack propagation from the early stages, whereas acoustic emission is associated with the final stages of fracture. Digital image correlation analysis is sensitive to crack development, and is used to measure crack length and crack openings. 相似文献
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通过声发声法及插销试验对高强钢的氢致裂缝的启裂、扩展以及断裂过程进行了试验研究,凭借第一个(或连续数个)A、E 信号成功地捕获了启裂点。实验结果表明:环形缺口插销试件中延迟裂缝的启裂位置是有规律的,常位于熔合线与缺口相交处附近.根据A.E 波形可将整个过程划分为启裂、延迟扩展、快速扩展、瞬时断裂四个时期,在断口上也可看到相应的分区,利用扫描电镜研究了各区的微观形貌。随着裂缝从延迟区→快速区→终断区扩展,裂缝前端的断裂强度因子K 逐渐加大,H_D 逐渐减少,断口形貌也有IG+QC_(HE)→QC+DR→DR 的变化。作者认为,延迟扩展期体现氢致延迟裂缝的本质。因此.启裂及延迟扩展区的断口是最有代表性的。此外,利用多试样法探讨了插销试件上裂缝的扩展途径。本文还讨论了,氢含量对延迟裂缝扩展区的断口微观形貌的影响,除氢处理后的试件中无IG(或很少),低氢时有较多的(IG)_(DR),高氢下则冰糖状IG 形貌增多,证实了氢对原奥氏体晶界有明显的脆化作用。 相似文献
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采用分子动力学方法研究了6H-SiC脆性切削的声发射响应。研究了原子尺度下6H-SiC的微变形和裂纹形核,同时对加工过程中的声发射源进行了识别,分析了其相应的声发射特征。结果表明,6H-SiC在77 nm切削深度下的脆性变形过程简单但不寻常;在6H-SiC切削过程中位错不会连续扩展,变形后的工件在刀具挤压作用下被分割成块,并由位错的快速扩展引发裂纹。对于影响声发射源特征的因素研究发现:初始压应力会导致声发射功率的下降;频率-能量分析中可见的3种声发射源分别是晶格振动、位错扩展和裂纹扩展。此外,在1 K温度下,2次明显的位错传播的声发射响应比晶格振动具有更高的频率特性,但总能量水平最低。相反地,裂纹扩展的声发射响应具有更为明显的频率分布特性和能量特性。 相似文献
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Fossil power plant high energy, high temperature steam headers have been found to be susceptible to thermal fatigue assisted creep degradation. These mechanisms initiate and grow cracks in chrome molybdenum headers, from the bore hole edges and stub tube-to-header welds. Linking up of multiple cracks can lead to explosive expulsion of tubes and severe shorting of the header life. In order to extend the header life and operate safely, a better understanding of crack growth that may occur during specific plant operating conditions is needed. With that understanding, harsh operating conditions that may be causing excessive crack propagation and header damage can be curtailed. Acoustic emission monitoring of headers was performed to assist in identifying operating conditions that lead to header damage. This Electric Power Research Institute (EPRI) sponsored program found acoustic emission activity levels correlated to identified crack growth and analytically calculated stresses. Utilizing these results, draft EPRI guidelines have been developed to aid electric utilities in performing acoustic emission monitoring on superheater headers. 相似文献