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由焊缝组织引起的声波衰减及散射严重影响奥氏体不锈钢焊缝的超声TOFD检测效果,这在无损检测方面是亟待解决的难题.文中分析焊缝中各角度检测声束形成的缺陷衍射波幅度及检测信号信噪比特征,揭示声波传播特性的影响因素.结果表明,不锈钢焊缝中的超声波传播具有明显的各向异性特征,柱状晶生长方向与声束入射方向的夹角对检测波衰减及散射具有显著影响;文中结合金相结构图建立焊缝组织模型进一步解释了声波传播各向异性的形成机理;并以此为基础提出一次波检测方法和二次波检测方法,获得了较好的检测效果. 相似文献
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为研究油气悬架系统振动衰减规律,得出振动衰减特性,根据油气悬架系统结构特征,在考虑等温平衡过程和快速加载过程的基础上,建立油气悬架系统弹性力数学公式和阻尼力数学公式,利用能量守恒原理推导出油气悬架系统振动数学模型。通过数值计算仿真及试验研究,得出油气悬架系统自身振动衰减规律及有关结构参数对衰减规律的影响情况。结果表明:仿真结果与试验结果基本一致,油气悬架系统对振动的衰减幅度呈现出周期性递减趋势,大部分振动能量在激励后的前两个振动周期被消耗掉;悬架结构参数的改变不仅影响振幅衰减程度,而且影响振动衰减周期。 相似文献
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利用有限元软件ABAQUS,建立了7A52铝合金焊后超声冲击的有限元模型,预测不同超声冲击工艺参数对7A52铝合金残余应力大小和分布的影响. 分析了超声冲击振幅、频率、静压力对焊接残余应力的影响规律. 旨在探讨超声冲击工艺参数对7A52铝合金焊接残余应力改善的影响因素. 计算结果表明,超声冲击振幅对残余应力场影响显著,频率次之,静压力对残余应力场影响最小;增大冲击振幅能够显著提高焊缝接头处的残余压应力值,且会增大压应力产生区域;增大超声冲击频率,会增加接头处残余压应力值,但增加的幅度有限;静压力对残余压力影响不明显. 用所建模型计算得到的数值结果规律与实测的残余应力值基本一致. 相似文献
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The development of attenuation tomography for concrete is discussed. Fundamental ultrasonic measurements of cubic specimens and numerical simulations of wave motion were conducted to examine the decay in amplitude of ultrasound when impinged by defect, and compare its sensitivity to the delay in travel time. An algorithm was then developed to facilitate simultaneous tracing and distribution of amplitude factor in a three-dimensional model by iterative computation. The algorithm was used for reconstruction of attenuation tomographic for visualizing concrete interior. Experimental results indicated successful identification for the location of a defect that was embedded in concrete, thus implying the potential of attenuation tomography as a complementary method to the travel time tomography to enhance soundness evaluation of concrete. 相似文献
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Ultrasonic detection of defects in strongly attenuating structures using the Hilbert–Huang transform
Non-destructive testing of polymer materials meets specific problems caused by a high attenuation of ultrasonic signals. When the expected flaws are close to the interfaces, the signals reflected by the flaws may be hidden in the tail of much stronger signals caused by front reflection from the sample and by interfaces between the adjacent layers. For improved detection of defects in plastic pipes, a new approach based on a combined application of non-linear deconvolution and the Hilbert–Huang transform is proposed.The first step of the algorithm is the elimination of strong ultrasonic echo signals reflected by interfaces. The second step is processing of ultrasonic signals using the Hilbert–Huang method. In order to improve visualization of defects we have proposed a new presentation of the Hilbert–Huang spectrum based on calculation of the product of the amplitude and the instantaneous frequency of analytic signal and displaying this product in a three-dimensional plot. The experimental investigations demonstrated a good performance of the proposed technique in the case of highly attenuating plastic pipes. 相似文献
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工程车辆油气悬架建模存在诸多非线性影响因素,根据其结构特点和工作原理,基于气体状态方程和油液孔口出流方程建立其非线性数学模型;并以此为基础搭建Simulink数学模型和ADAMS油气悬架试验台多体动力学模型;为验证模型准确性,搭建油气悬架试验台,进行油气悬架动态特性试验,获得激励频率变化对油气悬架动态特性的影响规律。对比分析联合仿真和试验结果验证了非线性数学模型和联合仿真模型的准确性与可靠性,为工程车辆油气悬架系统的特性研究及整车动力学特性研究提供了参考。 相似文献
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The objective of this paper is to introduce a newly developed nondestructive test technique called the normalized impact-echo spectrum and its application to monitoring the stiffening process of mortar. The impact-echo method is an effective and nondestructive technique for locating flaws in concrete. The depth of an air–concrete interface is determined by identifying the large amplitude peak in the spectrum at the dominant frequency corresponding to multiple wave reflections from the interface. However, the measure of the peak amplitude does not make sense because it changes with different impact forces. To make the peak amplitude meaningful, there is a need to normalize the spectrum on impact force. After normalization, the amplitudes in impact-echo spectra can provide useful information on the intensity of wave reflections at the interface. In this paper, the normalized impact-echo spectra were used to monitor the setting process of mortar. Experimental results demonstrate that the normalization of the impact-echo spectra can make the peak amplitude steady for various impacts and the coefficient of variation is less than 1.5%. The variation in the amplitude of the normalized impact-echo spectrum with the mortar age can indeed reflect the stiffening process of mortar. The results show that the proposed technique is suitable to monitor the setting process of mortar. 相似文献
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油气悬架以其良好的非线性特性而被广泛应用。以单气室油气悬架系统为研究对象,考虑气体在油液中的溶解和掺混、油液可压缩性及内部密封摩擦等的影响,基于气体状态方程、油液孔口出流方程,建立其非线性数学模型,通过数学模型找出影响油气悬架输出特性的主要结构参数和工作参数;设计并搭建油气悬架试验台,在ADAMS中搭建试验台虚拟样机模型,在AEMSim中搭建油气悬架系统的液压模型,在Simulink中设计频率加权函数滤波器,通过ADAMS/AMESim/Simulink三者联合搭建分析模型;通过试验与仿真结果对比验证了模型的准确性;分析主要参数对其动态特性的影响规律,为实际设计提供了参考。 相似文献
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在总结分析国内外有关PDC切削齿性能测试方法的基础上,采用常规检测方法对不同生产厂家的5种PDC产品的磨耗比、冲击韧性和热稳定性进行测试、评价和优选,并对优选出的2种PDC在微钻试验平台上进行实钻性能测试。结果表明:用微钻试验的钻进效率衰减系数和钻进效率均峰值来评价PDC实钻性能,方法科学,数据准确,结果实用,可作为煤矿用PDC钻头切削齿选型的参考依据。 相似文献
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定量研究了Marx法测量低内耗试样内耗及模量亏损时各种粘结剂引起的所谓操作效应。对于水杨酸苯酯,水玻璃混合剂之类弱粘结剂所造成的背景内耗既不能忽略也不是常数,它与粘结层温度、热应力、时间、干燥程度和应变振幅等因素有关。经过高温热循环,粘结剂中出现徽裂缝时呈现双共振峰。在稍高频率的反常共振峰所测得的内耗,随应变振幅或大振幅激发时间的增加而减小,并且在小振幅时效中增大。当反常共振峰频率与正常共振峰靠近时,在内耗-振幅或内耗-时间图上呈现峰值效应。观察到各种共振振幅-频率滞后回线,在一定非线性回线和时效场合下观察到可重复的试样振幅的概周期跳动。 采用高温高强度粘结剂后,上述现象均消失,但是热应力使石英传递棒开裂或试样范性变形。 分析了Marx法的适用范围及改进途径。 相似文献
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《International Journal of Machine Tool Design and Research》1984,24(1):45-69
A non-linear theory of machine tool chatter is presented. It is shown that even when the machine tool structure is linear or only slightly non-linear (as appears to be the case), large non-linearity is introduced by two causes. Firstly, by the chatter amplitudes exceeding a certain value, dependent on the mean chip thickness and the vibrating tool leaving the workpiece. Secondly, by a non-linearity of the cutting force characteristics.By combining these non-linear effects with the linear operative receptance of the machine tool structure, non-linear stability conditions are derived which describe a surface in the three-dimensional space defined by rotational speed, depth of cut and chatter amplitude. Sections through this surface provide the traditional (linear) stability chart relating depth of cut and rotational speed, as well as non-linear charts relating chatter amplitude with depth of cut. The latter are used for discussing the mechanism of stabilisation of chatter amplitudes and the phenomenon of finite amplitude instability. It is shown that the physical cause of finite amplitude instability lies in the non-linearity of the cutting force characteristic.The theory presented leads to conclusions of practical significance. The most important of these is that when the cutting force characteristic is non-linear the cutting process may be stabilised by a large increase of the mean chip thickness.Theoretical work is supported by experiments and good correlation between these is noted. 相似文献
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功率超声振动珩磨颤振是影响零件加工表面质量的主要因素之一,其稳定性研究具有重要意义.利用解析法和作图法对建立的轴向超声振动珩磨非线性动力学模型分别从轴向和径向进行了稳定性分析,得出刚度非线性因素对轴向稳定性影响不明显,超声激振频率对轴向响应幅值有较大影响,推导出径向系统稳定性方程,得出加工参数与响应幅值的关系,对抑制颤振方法提供了理论基础. 相似文献
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Z.M. Zhang C.J. Xu J.C. Wang H.Z. Liu School of Materials Science & Engineering Xi''''an University of Technology Xi''''an China ) State Key Laboratory of Solidification Processing Northwestern Polytechnical University Xi''''an China 《金属学报(英文版)》2006,19(3):223-227
Ultrafine-grained pure aluminum L2 with a mean grain size of 1.0μm was produced by equal channel angular pressing (ECAP) and annealing at 150℃ for 2h. Damping behavior of the alloy was measured using a dynamic mechanical thermal analyzer. The alloy had an excellent damping capacity Q-1 with the ambient value being 9.8×10-3 at 1.0Hz when the strain amplitude was 2.0×10-3. The damping behavior of the alloy showed a non-linear damping variation tendency, that is, with an increase in temperature and a decrease of frequency, the damping capacity of the alloy increased. The damping capacity increased with the strain amplitude when the strain amplitude was less than 4.6×10-5. When the strain amplitude was higher than 4.6×10-5, the damping capacity became a constant and independent of strain amplitude. The high damping capacity was attributed to dislocation unpinning and a drag of dislocation on pinning points. 相似文献