共查询到16条相似文献,搜索用时 156 毫秒
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基于声弹性原理,研究板材厚度方向、螺栓轴向方向(以下简称z轴方向)宏观残余应力分布的超声无损检测方法。针对被测构件厚度不均匀对应力检测精度的影响非常大、检测原理繁杂不适合工程应用、拉伸实验中拉伸形变对应力系数测量精度的影响很大等问题,采取超声横波、纵波相结合的方法重新推导检测公式,并提出采用一发一收模式进行拉伸实验,通过对实验数据进行拟合,由公式计算出声弹性系数代替应力系数。然后结合插值、互相关等算法,采用VC++编制z轴方向残余应力超声检测软件并搭建检测系统。分别对性能为A2-70,4.8,8.8,长度依次为135 mm,100 mm,100mm的M20的螺栓进行拉伸实验,比对计算拉伸应力与检测拉伸应力,结果表明,该测量系统的绝对误差限为20 MPa,相对误差小于25%,且应力值较大时,相对误差有所减小,当应力值大于100 MPa时,相对误差小于5%,非常实用。 相似文献
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针对不同厚度的病变组织,改变声焦域轴向长度能提高高强度聚焦超声在临床治疗过程中的安全性和有效性。基于多频超声波叠加原理,该文提出了变厚度(多频)聚焦换能器,并设计了两种类型变厚度聚焦换能器。根据瑞利积分法推导了变厚度聚焦换能器声场,计算和分析了变厚度聚焦换能器的声焦域轴向长度,并与等厚度(单频)聚焦换能器声焦域轴向长度进行对比。结果显示,变厚度聚焦换能器中心到边缘的厚度变化趋势与声焦域轴向长度变化相关,中间薄两边厚换能器声焦域轴向长度缩短,中间厚两边薄换能器声焦域轴向长度变长,且实验验证了理论的正确性。研究结果可为变厚度聚焦换能器声场研究和高强度聚焦超声的临床治疗提供参考。 相似文献
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用单摆测定当地的重力加速度的实验中,为了减小误差.常采用增加全振动次数和加大摆长的方法.但学生在测量时,常出现相差半个周期或数错全振动的次数,以及由于摆长长度是直尺长度的几倍,使摆长不易测准.为此,笔者根据实验室现有条件,自己动手作了改进,从而减少了... 相似文献
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4 mm腔长高功率单管半导体激光器封装应力的研究 总被引:1,自引:0,他引:1
为了减小长腔长高功率单管半导体激光器在封装过程中引入的热应力,根据应力改变禁带宽度的原理,理论上推导了应力与波长漂移的关系,提出了一种通过测量激光器脉冲条件下的光谱来定量计算激光器应力的方法。利用这种方法得到的研究结果表明,焊接质量直接决定着应力的大小,由焊接质量的不同引起的应力差值超过了300 MPa,提出了优化焊接回流曲线的方法,使激光器的应力由原来129.7 MPa降低到53.4 MPa,该方法还有效的解决了封装应力随储存时间变化的问题。实验表明,激光器光谱图的测量分析是研究高功率单管半导体激光器封装应力的有效方法,也是检测分析烧结工艺的有效手段。 相似文献
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将快速傅里叶变换(FFT)与线性调频Z变换(CZT)联合变换的方法应用到法布里-珀罗(F-P)腔传感器的解调中,从理论上分析了该方法的解调原理及误差.模拟计算得出,该联合算法解调出的腔长的相对误差达到0.01%,腔长的最大绝对误差小于0.05 μm.在对测量范围为O~3 MPa的F-P腔微机电系统(MEMS)压力传感器进行的解调试验中,该算法可以辨别0.01 MPa的压力,腔长与压力数据的拟合度为0.99316,测量压力与实际压力的标准偏差小于0.005 MPa.实验结果表明,FFT与CZT联合解调的方法可以在较少计算量的基础上达到较高的精度,满足实际需求. 相似文献
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Estimation of clamping force in high-tension bolts through ultrasonic velocity measurement 总被引:1,自引:0,他引:1
The estimation of clamping force has been regarded as the main issue in the maintenance of high-tension bolts. This paper proposes a method which uses the dependency of ultrasonic velocity on stress based on the nonlinear elastic effect. The variation of ultrasonic velocity in the range of actual stress acting in the bolt is very small so that the precise measurement of ultrasonic velocity is needed. In this paper, we adopt a method to measure ultrasonic velocity, where the TOF (time of flight) of a tone-burst ultrasonic wave is precisely measured by using the phase detection technique. In order to verify the usefulness of the proposed method, two kinds of experiments are carried out. The first one measures ultrasonic velocity when the bolt is stressed by the tension tester, and from this, the exact axial force acting in the bolt can be determined. The results show good agreement with the expected linear relationship between ultrasonic velocity and axial stress. The second experiment measures ultrasonic velocity when the bolt is stressed by the torque wrench. The results show that ultrasonic velocity decreased as the torque increased, which is identical to the theoretically expected tendency. From these results, it can be said that the proposed method is adequate in evaluating clamping force in high-tension bolts. 相似文献
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S. A. Pulnev V. I. Nikolaev A. A. Priadko A. V. Rogov A. V. Chikiryaka S. P. Nikanorov 《Bulletin of the Russian Academy of Sciences: Physics》2009,73(10):1398-1401
Recovery stress generation under thermal cycling has been experimentally studied in clamped shape memory Cu-Al-Ni single crystals
up to 9% reversible strain. It is shown that such crystals are capable of repeated force generation upon heating up to 600
K and single actuation when heated to 700 K with a maximal stress of 350 MPa. The main principles of designing cyclic linear
actuators are considered and a technique for calculating their force characteristics is proposed. The calculation is based
on the mathematical model of linear actuator. 相似文献
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A method is proposed to measure the stress on a tightened bolt using an electromagnetic acoustic transducer (EMAT). A shear wave is generated by the EMAT, and a longitudinal wave is obtained from the reflection of the shear wave due to the mode conversion. The ray paths of the longitudinal and the shear wave are analyzed, and the relationship between the bolt axial stress and the ratio of time of flight between two mode waves is then formulated. Based on the above outcomes, an EMAT is developed to measure the bolt axial stress without loosening the bolt, which is required in the conventional EMAT test method. The experimental results from the measurement of the bolt tension show that the shear and the mode-converted longitudinal waves can be received successfully, and the ratio of the times of flight of the shear and the mode-converted longitudinal waves is linearly proportional to the bolt axial tension. The non-contact characteristic of EMAT eliminates the effect of the couplant and also makes the measurement more convenient than the measurement performed using the piezoelectric transducer. This method provides a promising way to measure the stress on tightened bolts. 相似文献