共查询到16条相似文献,搜索用时 281 毫秒
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对发动机壳体的钢/绝热层层间脱粘缺陷,采用常规超声检测技术检测这种高声阻抗材料下有多层低声阻抗材料的脱粘缺陷有相当大的困难。通过对兰姆波传播特性的分析,并以相应的试验方法,验证了兰姆波在发动机壳体层间脱粘缺陷检测中的有效性。 相似文献
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介绍一种将传统边界元法和兰姆波的本征模式函数相结合的混合边界元法,以此计算兰姆波在板材内部传播时遇到障碍物或不连续界面时所发生的反射(或透射)问题,得到了若干频率入射兰姆波与板中不同深度缺陷相互作用的关系。数值计算结果表明,兰姆波与板中不连续体相互作用后存在模式转换现象,此工作对板材兰姆波的快速无损检测有一定的借鉴作用。 相似文献
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航空金属薄板在加工时由于夹杂产生的气孔会随着使用过程中的拉伸和挤压而形成一种闭合型的分层缺陷。针对此类缺陷的检测,提出一种相控阵全聚焦成像算法与兰姆波检测结合的方法。首先从原理上分析并确定激励兰姆波的模态、频率及楔块的角度,其次对3 mm厚度不锈钢板中不同规格、形状的分层缺陷进行试验。结果表明:本研究方法能够对分层缺陷的轮廓成像;兰姆波易受缺陷上端面反射影响,导致缺陷下端面成像出现拖尾图像,且缺陷上端的定位定量精度要高于缺陷下端面;上端面缺陷的定位误差均在4%以内。 相似文献
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复合材料层板泄漏兰姆波检测技术研究 总被引:2,自引:0,他引:2
当一定频率的超声波以适当角度对置于浸液中的薄板材料斜入射时,在板中能激励产生兰姆波,同时在声束入射点附近产生泄漏波声场。采用泄漏兰母皮C扫描技术,可成功地检出复合材料层板中的分层及孔隙等缺陷。 相似文献
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小直径不锈钢薄壁管广泛应用于电站机组的冷凝器中,常规涡流检测方法难以发现纵向贯通的条状缺陷。在Ф25mm×1mm和Ф38mm×2mm不锈钢管壁上,沿轴向和周向加工深度分别为0.1mm、0.2mm和0.5mm的人工切槽,并进行检测试验研究,确定了兰姆波检测技术对小直径不锈钢薄壁管上人工缺陷的可检性,探讨了对不锈钢薄壁管材进行兰姆波检测的有效性和可靠性,提出以兰姆波检测技术对小直径不锈钢薄壁管进行检测的建议。 相似文献
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为了有效识别薄壁十字激光焊结构中未焊透缺陷,开展了超声Lamb波法检测研究. 采用有限元分析方法模拟了A0和S0模态Lamb波在薄壁中与缺陷的作用结果,对缺陷尺寸与回波反射系数的关系进行了预测. 在此基础上,进行仿真结合试验,确定了不同模态Lamb波的入射点、激励角度,探讨了A0和S0模态Lamb波用于识别1.9 mm厚薄板十字激光焊接结构未焊透缺陷的可行性,并获得了超声Lamb波反射系数与缺陷尺寸的关系. 结果表明,仿真研究和试验实测结果的趋势具有较好的一致性. 采用超声Lamb波检测时,A0模态波能够有效检测十字焊接结构中的未焊透缺陷,且可一定程度上表征缺陷的尺寸;而S0模态波对结构中的未焊透缺陷不易于识别. 相似文献
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Two-dimensional (2D) experimental models are often used to study wave propagation problems. The advantages of using 2D experimental models, as opposed to 3D models, is the reduction of both extraneous reflections and mathematical complexity. Further, many structural elements conform to this geometry. The following study examines Rayleigh wave motion in thin Plexiglas sheets. Source–receiver time domain measurements were made at different locations on the Plexiglas sheet. The time–distance space was 2D-Fourier transformed into the frequency–wavenumber space to facilitate the analysis of wave modes propagating in the Plexiglas sheet. Experimental results showed that fundamental symmetric (S0) and antisymmetric (A0) Lamb waves propagated through the plate. Along the thickness of the plate, a non-dispersive Rayleigh wave was generated. Lamb waves were found to interfere with the Rayleigh wave. The assumption of generalized plane stress is preserved if higher mode Lamb waves have low energy content. 相似文献
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Glass Fiber Reinforced Plastics (GFRP) are fast becoming a viable new construction material. They are being used for rehabilitating old concrete structures—columns, beams, slabs and walls—by gluing the composite plate to the concrete surface. Proper attachment between the GFRP plate and the concrete surface is necessary for efficient use of GFRP composites to increase the strength of the rehabilitated structures. Delamination between the rehabilitated structure and the GFRP plate significantly reduces the strength of the reinforced structure. Hence, delamination defects, if present at the interface, should be detected as soon as possible. In this paper, two ultrasonic techniques to detect delamination defects between the GFRP plate and the concrete surface are presented. One technique uses longitudinal waves or P-waves and the second technique uses Lamb waves. It is found that both techniques can detect the defect when used properly. However, Lamb waves give a better image quality of the defect than longitudinal waves. 相似文献