摩擦片非线性损伤累积计算与寿命预测

摩擦片是车辆传动系统的重要部件,持续性的制动或者离合使得摩擦片承受较大范围的冲击载荷,需要对该工作环境摩擦片进行寿命预测.提出了一种基于冲击非线性损伤累积的摩擦片损伤计算方法,即:设定应力门槛值,对超过应力门槛值的冲击衰减应力曲线积分,进行非线性损伤计算.理论计算与试验结果对比表明:该方法可用于摩擦片损伤计算和寿命预测,效果良好.     

金属杆锚固系统中导波传播特性的试验研究

根据金属杆的尺寸特性，提出了把锚固金属杆作为波导介质来处理．应用导波方法对金属杆锚固质量进行评价的思想。通过试验时导波在金属杆中的传播特性进行了定性分析，得出了不同频率的纵向导波在同尺寸与不同尺寸金属杆中传播时，其波速改变与振幅衰减的一般规律。在相同的条件下，高频波比低频波的波速要高但其能量衰减较快；同一频率的纵向导波在自由金属杆中传播时，波速比在锚固金属杆中传播时的波速要高，但其能量的衰减幅度较低，根据振幅的衰减程度可定性地确定金属杆的锚固质量。     

奥氏体不锈钢焊缝超声TOFD检测中声波传播特性分析及其应用

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.     

油气悬架系统振动衰减特性分析

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。     

超声冲击工艺参数对装甲铝合金焊接应力影响的有限元分析

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.     

Tomographic reconstruction for concrete using attenuation of ultrasound

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.     

低频机械振动焊接振动工艺参数的优化

研究了在三种振动频率和两种振幅下振动焊接试板残余应力分布、焊缝金相组织、冲击性能、疲劳寿命相对常规焊接的变化情况.从上述指标测试结果来看.最佳参数组合为振动频率取于第一阶共振峰峰值左侧一半处对应的频率,而振幅取3档.从总体上看,振动频率对焊接质量的影响要比振幅显著,所以应优先对振动频率寻优.     

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.     

基于ADAMS与Simulink工程车辆油气悬架非线性建模分析

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。     

Use of the normalized impact-echo spectrum to monitor the setting process of mortar

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.     

激光冲击选区强化对2024铝合金叶片振动响应特性的影响

目的 探究激光冲击强化技术对2024铝合金叶片振动性能的影响,并探寻最理想的冲击参数.方法 运用Johnson-Cook动态塑性本构模型模拟激光冲击选区强化过程,对强化后的2024航空铝合金叶片的振动特性进行分析.将2024铝合金在激光冲击强化过程中产生的残余应力场和梯度密度分布导入模型,量化激光冲击强化对2024铝合...     

基于ADAMS/AMESim/Simulink油气悬架动态性能影响因素分析

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。     

PDC实钻性能的测试与评价

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。      

NON-LINEAR INTERNAL FRICTION PHENOMENA ASSOCIATED WITH FLOWING AND CRACKING OF ADHESIVE IN MARX METHOD

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。     

负载敏感液压系统的防冲击技术研究

针对负载敏感液压系统在快操作时出现压力冲击的问题,以汽车起重机卷扬系统为载体进行防冲击技术研究。采用AMESim软件建立负载敏感液压系统的仿真模型,结合实验数据对仿真模型进行优化。通过仿真分析,找出导致压力冲击的根源。在此基础上,对液压系统进行优化设计。仿真结果和整机测试数据均表明:采用三通流量阀原理的防冲击阀,能有效降低液压系统压力冲击幅值,防冲击效果显著。     

水浸探头对1Cr21Ni5Ti钢棒材底波监控的影响

分析了水浸探头对1Cr21Ni5Ti不锈钢棒材底波监控的影响因素,采用了不同频率和不同聚焦类型的水浸探头,设置了不同距离的水程,利用LS200B型设备对被检棒材进行超声检测,使用PROCESS图像评估软件对C扫描图像进行分析。结果表明,1Cr21Ni5Ti棒材在圆周方向底波波幅是变化的;探头频率、聚焦类型和水程距离都会影响被检棒材的底波波幅水平。     

轴向功率超声振动珩磨颤振的稳定性分析

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.     

超声冲击强度对焊接接头疲劳寿命的影响

采用超声冲击处理方法对Q345B钢十字接头进行处理,对比分析了两种振幅下焊接接头疲劳寿命的变化. 结果表明,在25 μm振幅下焊接接头的疲劳寿命相较18 μm振幅下焊接接头的疲劳寿命提高了4.3~7.6倍,从超声冲击处理后的宏观形貌、微观断口、冲击区域表层组织等方面比较分析了不同振幅下超声冲击疲劳延寿差异的原因,并建立有限元模型进行焊接温度场、应力场和超声冲击的数值模拟,将试验结果与有限元计算结果进行综合对比分析. 结果表明,同等冲击条件下振幅越大,压应力层更深,试件表面压应力值更大.     

DAMPING BEHAVIOR OF ULTRAFINE-GRAINED PURE ALUMINUM L2 AND THE DAMPING MECHANISM

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.     

Modeling and simulating of unloading welding transformer

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