共查询到17条相似文献,搜索用时 187 毫秒
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借助超声相控阵技术对耐候钢对接接头开展疲劳失效过程动态监测. 基于超声波探头的信号特征,研究其扇形扫描反射过程,建立实时扫查方案, 并对10 mm厚的耐候钢对接接头实施实时监测.结果表明,当疲劳寿命为5 × 104次时,相控阵检测到多个裂纹从对接接头焊趾部位萌生,并沿着板厚扩展,当疲劳寿命超过3.5 × 105次时,裂纹开始快速扩展. 与疲劳试验断口对比发现,基于相控阵检测得到的裂纹尺寸与试验结果基本一致,验证了相控阵裂纹动态检测的准确性. 根据裂纹深度a、裂纹长度2c与循环次数N关系,明确了裂纹动态演化行为,并获得中厚板耐候钢对接接头表面裂纹的扩展演化规律. 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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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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This study demonstrates that eddy current testing can be an effective method for monitoring the growth of surface breaking cracks with the aid of computational inversion techniques. A uniform eddy current probe with 23 arrayed detectors was designed, and pseudo monitoring tests were carried out to measure signals due to six mechanical fatigue cracks introduced into type 316L austenitic stainless steel plates. In the test the position of the probe was fixed to simulate monitoring. The depths of the cracks were evaluated using a computational inversion method developed on the basis of k-nearest neighbor algorithm. The depths of the mechanical fatigue cracks whose actual depths were 1.1, 2.1, 3.1, 5.5, 6.7, and 8.5 mm were evaluated to be 0.9, 1.9, 3.8, 4.3, 7.0, and 5.7 mm, respectively. Additional simulations were conducted to demonstrate the stability of the method. 相似文献
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During the last decade many techniques were developed to detect fatigue cracks, and estimate their location and size. Unfortunately, most of the currently available nondestructive testing methods are off-line: the operational (or fatigue) loading and the inspection are considered as two distinct stages. Mostly, the loading should be released before inspection can take place, and sometimes the device under test even has to be disassembled. In this article, an experimental methodology based on ultrasonic surface waves will be developed to continuously inspect a structure during its operation. The proposed method uses spectral information of transmitted surface waves at several working points of the operational load. Simple statistical indicators of the transmitted wave energy during loading are introduced in order to be able to monitor the structural health on-line. As a validation experiment, a propagating fatigue crack in a sinusoidally loaded beam will be considered. In addition, a comparison with an off-line method is made, showing that the on-line method is also much more sensitive. 相似文献
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Cold hole expansion effect on the fatigue crack growth in welds of a 6061-T6 aluminum alloy 总被引:1,自引:0,他引:1
K.C. Viveros R.R. Ambriz A. Amrouche A. Talha C. García D. Jaramillo 《Journal of Materials Processing Technology》2014,214(11):2606-2616
Compact test specimens were extracted from a 6061-T6 aluminum alloy welded plate with a thickness of 9 mm to analyze the cold hole expansion effect on fatigue crack growth tests conducted in mode I cyclic loading. At R = 0.1, a sharp crack in base metal, weld metal and heat affected zone was propagated from 17 to 24 mm. The fatigue crack growth at 24 mm (α = a/W = 0.3) was delayed by drilling a hole at the crack tip and applying a cold hole expansion of 4.1%. The residual stress fields due to cold hole expansion were determined with the finite element method. The fatigue crack growth testing was continued up to a crack length of 35 mm (α ∼ 0.43) at the same R, and crack opening displacements of the post-expansion crack were also determined with the finite element method. The results were expressed in terms of crack length versus number of cycles, as well as, fatigue crack growth rate as a function of applied and effective stress intensity factor range. The cold hole expansion contributed to delay the fatigue crack growth in base metal, and to a lesser extent in the weld metal and heat affected zone. A crack closure effect was determined by means of load versus crack opening displacement curves of the post-expansion crack, which was, completely or partially closed, in welded zones with compressive residual stress fields. The fracture surfaces of each welded zone were analyzed to elucidate the crack nucleation zone and its relation with the residual stress field. In all cases the crack was initiated at the surface of the specimen where the residual stresses were positive. 相似文献
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采用对比疲劳试验方法,研究了相对挤压量、终铰参量、衬套开缝放置角度等工艺参数和特征对开缝衬套挤压TA15钛合金连接孔疲劳增益的影响。结果表明,开缝衬套挤压技术可有效提高TA15钛合金孔结构疲劳强度,延长其疲劳寿命;相对挤压量越大,孔挤压疲劳增益越大,但是TA15钛合金对挤压量非常敏感,微小的相对挤压量波动会导致显著的疲劳增益波动;在完全去除开缝衬套在孔壁遗留的材料凸脊前提下,0.190 mm和0.065 mm两种单边终铰参量对TA15孔结构挤压疲劳增益有明显影响,0.190 mm单边铰削量时挤压疲劳增益更大,而非终铰参量越小越好;在smax=400 MPa,R=0.1疲劳载荷条件下,衬套开缝与试样最窄截面平行放置,仍能够获得明显的疲劳增益,但相对于与试样与最窄截面呈90°放置,疲劳增益会略有下降,建议在实际孔挤压操作中,衬套开缝尽量避开最窄截面放置。 相似文献
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P. Cavaliere G. Campanile F. Panella A. Squillace 《Journal of Materials Processing Technology》2006,180(1-3):263-270
The effect of processing parameters on mechanical and microstructural properties of AA6056 joints produced by Friction Stir Welding was analysed in the present study. Different samples obtained by employing rotating speeds of 500, 800 and 1000 rpm and welding speeds of 40, 56 and 80 mm/min were produced. The mechanical properties of the joints were evaluated by means of microhardness (HV) and tensile tests at room temperature. Fatigue tests on the welds were carried out by using a resonant electro-mechanical testing machine under constant loading control up to 250 Hz sine wave loading. The low cycle (LCF) and high cycle (HCF) fatigue tests were conducted in the axial total stress-amplitude control mode with R = σmin/σmax = 0.1, for all the welding and rotating speeds used in the present study. It was observed that the specimens welded at 56 mm/min showed the best behaviour in the low cycle regime. The microstructural evolution of the material was analysed by optical observations of the welds cross sections. 相似文献