弱正交异性材料残余应力测量的声弹性方法

为了适应工程材料的残余应力无损测量的要求,本文将横波和纵波声弹性相结合,建立适用於弱正交异性材料的平面声弹性残余应力测量方法,并应用该方法及自行研制的横波换能器对焊接试件的二维残余应力进行了测试。     

车-桥系统耦合振动响应的简便计算

依据振动理论推导出了二自由度模型车辆与桥梁系统竖向耦合振动微分方程，采用模态分析的离散化方法，将复杂的偏微分方程问题转化为变系数常微分方程问题，并将微分方程数值积分的Runge-Kutta方法引入到该时变系统的振动响应计算中，使复杂的耦合响应问题得到简便的解决。通过算例验证了该方法的有效性和简便性。该方法只需要直接数值积分，具有公式简单，编程方便，计算速度快等优点，特别适合于工程实际问题的计算，并且不仅适用于匀速运动车辆，也适用于变速运动车辆。     

A novel technique for time-resolved detection and tracking of interfacial and matrix fracture in layered materials

A novel experimental technique is developed for time-resolved detection and tracking of damage in the forms of delamination and matrix cracking in layered materials such as composite laminates. The technique is non-contact in nature and uses dual or quadruple laser interferometers for high temporal resolution. Simultaneous measurements of differential displacement and velocity at individual locations are obtained to analyze the initiation and progression of interfacial fracture and/or matrix cracking/delamination in a polymer matrix composite laminate system reinforced by graphite fibers. The measurements at multiple locations allow the speeds at which interfacial crack front (mode-I) or matrix cracking/delamination front (mode-II dominated) propagates to be determined. Experiments carried out use three-point bend configurations. Impact loading is achieved using a modified Kolsky bar apparatus with a complete set of diagnostics for load, deformation, deformation rate, and input energy measurement. This technique is used to characterize the full process of damage initiation and growth. The experiments also focused on the quantification of the speed at which delamination or damage propagates under primarily mode-I and mode-II conditions. The results show that the speed of delamination (mode-I) or the speed of matrix cracking/delamination (primarily mode-II) increases linearly with impact velocity. Furthermore, speeds of matrix failure/delamination under primarily mode-II conditions are much higher than the speeds of mode-I crack induced delamination under mode-I conditions.     

Dynamic shearing resistance of molten metal films under high pressures and extremely high shearing rates

In the present study plate-impact pressureshear experiments have been conducted to study the dynamic shearing resistance of molten metal films at shearing rates of approximately 10⁷ s⁻¹. These molten films are generated by pressure-shear impact of relatively low melt-point metals such as 7075-T6 Al alloy with high hardness and high flow-strength tool-steel plates. By employing high impact speeds and relatively smooth impacting surfaces, normal interfacial pressures ranging from 1–3 GPa and slip speeds of over 100 m/s are generated during the pressure-shear loading. The resulting friction stress (∼100 to 400 MPa) combined with the high slip speeds generate conditions conductive to interfacial temperatures approaching the fully melt temperature regime of the lower melt-point metal (7075-T6 aluminum alloy) comprising the tribo-pair. During pressure-shear loading, laser interferometry is employed to measure normal and transverse motion at the rear surface of the target plate. The normal component of the particle velocity provides the interfacial normal traction while the transverse component provides the shearing resistance of the interface as it passes through melt. In order to extract the critical interfacial parameters, such as the interfacial slip-speed and interfacial temperatures, a Lagrangian finiteelement code is developed. The computational procedure accounts for dynamic effects, heat conduction, contact with friction, and full thermo-mechanical coupling. At temperatures below melt the flyer and target materials are described as an isotropic thermally softening elastic-viscoplastic solid. For material elements with temperatures in excess of the melt point, a purely Newtonian fluid constitutive model is employed. The results of this hybrid experimental-computational study provide insights into the dynamic shearing resistance of molten metal films at high pressures and extremely high shearing rates.     

JP-10裂解的激波管实验与动力学模拟

利用单脉冲激波管对碳氢燃料JP-10在1150~1300K条件下的高温热裂解特性进行了实验研究,采用气相色谱法分析热裂解产物并获得了热裂解速率系数.主要裂解产物有乙烯、乙炔、丙烯、丁烯、1,3-丁二烯、环戊二烯、环戊烯、苯、甲苯,以及少量的甲烷、乙烷、二甲苯和甲基环戊烯.将每次激波管实验后所有产物浓度累加, JP-10裂解速率系数由实验测定.为了消除激波运行中非理想性和边界层效应导致反应温度确定的误差,采用对比速率法确定裂解温度,即在反应物中加入少量热解速率已知的内标物,根据内标物在相同的激波管实验条件下的裂解程度确定反应温度.根据内标物裂解量确定的激波管裂解反应温度通常小于采用传统测量激波速度由激波关系计算的反射激波后5区温度.在1200~1300K之间两种方法得到的温度吻合得较好,差异在20K以内,随着温度升高,两者差异增大.在实验研究的基础上,依据San Diego Mechanism对JP-10高温裂解过程进行了动力学模拟.结果显示:主要裂解产物中乙烯、乙炔和1,3-丁二烯产量随温度变化的实验值与San Diego Mechanism的模拟结果有很好的一致性,但环戊烯产量的实验值比模拟值高很多,预示JP-10裂解中完全开环和部分开环反应都是重要的裂解通道.      

Studies of Mental “Noise”

Successive tests of subjects' performance in reaction time tasks were treated as time series and submitted to spectrum analysis. Rather than revealing the white noise expected by the view that variability is due to random error (equivalent power across frequency), the power spectra revealed colored noise. The slopes of the power spectra did not vary much for tasks differing in memory requirements. Spectrum analysis of time series from the logistic map also showed colored noise in regions on the edge of chaos, showing that the presence of colored noise in cognitive data need not oblige a theoretical account based on a complex, high-dimensional, system.     

LIF技术测量浓度场的影响因素分析

本文研究了作为示踪剂的荧光素钠的谱图，测定了荧光素钠在蒸馏水和普通自来水中的吸光系数，估算了荧光分子的平均寿命。最后，详细分析了浓度、激光功率、温度、ｐＨ值和截止滤光片对荧光强度的影响。     

大变位时物体变形测量的相关性恢复方法

本文提出根据白光散斑图像数据模拟刚体位移复位的相关性恢复方法，以解决物体大变位情况下的变形测量问题     

裂纹扩展速度对焦散线的影响和动态应力光学常数的测定

本文从焦散线形成原理的数学描述出发,用扩展裂纹尖端附近的应力分量表达式,在前人工作的基础上,作了详细的数值计算。特别分析了裂纹扩展速度对焦散斑和初始曲线的形状、大小的影响,为测量扩展裂纹尖端的动态应力强度因子K_1~d提供了依据,并通过拟合得到了以裂纹扩展速度为参量的修正因子表达式。本文还提出了一种测定透明材料动态应力光学常数的方法,并用这一方法测定了有机玻璃的动态应力光学常数。