共查询到19条相似文献,搜索用时 218 毫秒
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柴油机的气缸盖、主轴承盖及连杆大头盖等部位,连接螺栓的轴向预紧力决定了螺栓连接牢度、密封性及可靠性。 用扳手拧紧螺栓使其产生轴向拉力时,螺栓同时承受拉应力和扭应力,当拉应力达到材料屈服强度的80%时,螺栓就会产生塑性变形,因此,紧固螺栓通常是在其弹性变形区域内进行的。 为了充分发挥螺栓的工作能力,螺栓的预紧应力可达材料屈服强度的 50%~70%,预紧力矩约为预紧力与螺纹公称直径之积的0.2倍。约50%的预紧力矩是由其螺旋面的摩擦力决定的,另50%则是由螺栓头螺母支承面的摩擦力决定的。用扭力扳手按要… 相似文献
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针对螺栓拉应力仅能测量螺栓连接零件受到的拉力,而无法测量压力的局限,在螺栓连接的两零件之间引入了高刚度弹性元件,并利用无线应变测试系统,通过测量螺栓因弹性变形产生拉力F的变化,实现了复杂工况下螺栓连接零件受拉压外力Fe的无线测量。设计、制造了测力螺栓和弹性元件;采用ANSYS软件分析了弹性元件的压应力及变形量,通过正交设计法优化了弹性元件的结构。建立了测量方法的计算模型,得到了测力螺栓受拉力F与螺栓连接零件所受的拉压外力Fe的关系,进行了不同预紧力下螺栓连接零件受拉压外力Fe的实验验证。研究结果表明,凹槽深度和单侧凹槽数量是影响弹性元件性能的关键因素。螺栓连接零件受拉压外力可以实时、准确地得到测量,零件受拉压外力与测力螺栓处受力为线性关系。 相似文献
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本文在对超声波测厚计测量螺栓栽荷的基础试验工作中,通过对试件螺栓的标定试验求取螺栓系数K,进而在模拟管法兰连接的试验装置上对螺栓的实际预紧载荷进行测量和调整试验,同时与应变计复测的结果作了比较。结果表明,经过改设声速微调器的超声波测厚计和探头耦合器用于监控法兰连接螺栓的预紧载荷能满足工程要求,螺栓载荷的平均值偏差为2%。用于调整残余螺栓力时,螺栓裁荷与平均值的偏差在士10~15%范围内。 相似文献
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《仪表技术与传感器》2019,(12)
针对传统螺栓应力测量方法的局限性,基于声弹性效应建立了超声螺栓轴向应力测量系统。测量系统由以FPGA为核心的下位机与基于LabVIEW的上位机两部分组成。研制了基于FPGA的超声激励、采集和传输控制模块,能灵活产生不同频率、不同周期数的高电压超声激励脉冲信号,以适应不同频率探头和不同类型螺栓对激励信号的要求。针对应力测量中超声回波信号周期重复的特征,系统结合等效时间采样法、三次样条插值法和平均值法,提高了螺栓轴向应力测量精度。试验结果表明,所建立的系统成功实现了螺栓轴向应力的精确测量,应力测量不确定度约为1.2 MPa。 相似文献
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对扭矩法控制螺栓预紧力进行理论分析,建立了螺栓三维模型.通过前处理软件将网格模型导入ABAQUS软件,运用面面接触分析螺栓预紧状态,计算出不同参数对接触面应力大小及分布影响;就预紧力矩的精确控制提出几点建议. 相似文献
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螺栓轴向应力的非线性超声检测技术研究 总被引:1,自引:0,他引:1
在工作过程中,螺栓常受到轴向应力的作用,作为最常见的紧固件之一,螺栓的服役质量对于安全生产至关重要。非线性超声技术对材料内部微结构的变化敏感,在检测螺栓轴向应力方面有极大的潜力。根据超声波在各向同性材料内部的传播规律,分析了非线性系数与基波幅值以及高次谐波幅值之间的关系,搭建了非线性超声检测系统。以45钢和304不锈钢材质的螺栓为研究对象,对不同轴向应力下的螺栓进行非线性超声检测,得到非线性系数与螺栓轴向应力之间的关系曲线。结果表明,螺栓的超声非线性系数随轴向应力的增大而单调增加,当轴向应力超过一定值时,非线性系数显著增大,说明非线性系数对应力变化敏感,可以用来表征螺栓的轴向应力。通过对相对非线性系数进行归一化和多项式拟合,得到螺栓轴向应力与归一化相对非线性系数之间的函数关系,然后采用非线性超声和线性体波检测两种方法对电子拉伸试验机施加的螺栓轴向应力进行检测验证试验,200 MPa以上的轴向应力采用非线性超声检测误差在6%以下,明显优于线性超声体波检测,研究结果为服役状况下螺栓的轴向应力检测提供了有效支撑。 相似文献
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基于金属杆件中高频超声导波的传播特性,提出使用柱面导波高阶不同模态群速度比值的单探头螺栓轴向应力测量方法。使用数值方法求解考虑晶粒散射衰减的Pochhammer-Chree方程,得到了导波群速度衰减系数频散曲线,并分析了其在高频区的传播规律。结合非线性声学以及弹性力学理论,推出基于群速度比值的螺栓轴向应力测量方法。搭建超声应力测量平台,讨论了脉冲超声激励下的实测导波信号特点并提出使用经验小波算法对信号进行模态分解,有效获取了信号中特定模态的群速度。使用该方法以及传统的纵横波声时比法进行了螺栓轴向应力对比标定和测量实验,结果表明前者平均测量误差约为4%,其精度明显高于传统方法(平均测量误差6%)且具有更简便的测量流程。 相似文献
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探讨了组合结构法在弹性接触问题中的应用,并以螺栓联接为例,建立了用弹性力学有限元的组合结构法解决繁杂弹性接触问题的力学模型。该模型综合考虑了设计精度、制造误差、装配情况及载荷工况等因素对螺栓受力的影响,能够精确给出螺纹载荷和根部应力分布规律以及螺栓联接的变形情况。 相似文献
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《机械工程学报(英文版)》2020,33(1):34-49
Bolts are important fasteners indispensable in the manufacturing field for their advantages, which include convenient assembly and disassembly, easy maintenance, refastenability to prevent looseness, and the avoidance of a phase change in the connected material composition. The precise control of the tightening force in bolts is closely related to the safety and reliability of the connected equipment or structure. Although there are many methods for estimating the tightening force applied to a bolt during assembly, poor accuracy in controlling the preload during the tightening process and a lack of monitoring to determine the residual axial force in service remain issues in evaluating the safety of bolted assemblies. As a nondestructive testing technology, ultrasonic measurement can be applied to successfully address these issues. In order to help researchers understand the theoretical basis and technological development in this field and to equip them to conduct further in-depth research, in this review, the basic knowledge describing the state of stress and deformation of bolts, as well as conventional testing methods are summarized and analyzed. Then, through a review of recent research of the ultrasonic measurement of the axial stress in bolts, the influence of the e ective stressed length and temperature are analyzed and proposed methods of calibration and compensation are reviewed. In order to avoid coupling errors caused by traditional piezoelectric transducers, two newly proposed ultrasonic coupling technologies, the electromagnetic acoustic transducer(EMAT) and the permanent mounted transducer system(PMTS), are reviewed. Finally, the new direction of research of the detection of residual axial stress in in-service bolts that have been assembled to yield is discussed. 相似文献
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Measurement of material elastic constants for limited-size samples by ultrasonic method is described and validated. Based on acoustic microscope technology, the material elastic constants are determined by longitudinal wave and leak surface wave velocities simultaneously measured by developed ultrasonic system with a line-focus PVDF transducer. In this paper, the elastic constants of limited-size Cr2O3 doping on 0.2 PZN–0.8 PZT piezoelectric ceramic wafer sample are determined and the measurement errors are analyzed. The experimental results show this ultrasonic system can be used for measurement of material elastic constants for limited-size samples with high measurement precision, and the relative errors for Poisson’s ratio and Young’s module measurements are, respectively, less than 1% and 3%. It can satisfy the requirement of engineering and science research. Furthermore, it is suitable to measure elastic constants of both isotropic and anisotropic materials by ultrasonic method with help of developed ultrasonic system. 相似文献
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