复合材料层合板单搭胶接力学性能检测技术与分析

胶接工艺缺陷对单搭胶接接头的拉伸剪切性能有着重要的影响。为了研究不同单搭接胶接层厚度对不同材质复合材料层合板胶接性能的影响规律,通过喷水穿透法超声C扫描对试样的剪切区域进行无损检测,并分别采用1mm、2mm、4mm的胶层厚度,以碳纤维/玻璃纤维复合材料层合板为被粘物,进行单搭胶接拉伸剪切性能试验。检测及试验结果表明:当胶层厚度h1mm时,对于相同材料的被粘物,胶层厚度越大,试件胶接接头剪切强度越小;相同的粘接剂厚度,以碳纤维增强复合材料板为被粘物的试件胶接接头剪切强度大于以玻纤增强复合材料板为被粘物的试件胶接接头强度;胶粘剂与碳纤维被粘物表面的润湿效果要优于胶粘剂与玻纤被粘物表面的润湿效果。     

周期激励下单搭接接头强度与振动特性研究

主要研究汽车轻量化粘接结构在周期性振动载荷激励下强度与振动属性的改变。首先,利用实验手段,研究了振动载荷对单搭接接头疲劳特性的影响,分析了疲劳后接头的强度及模态频率的变化;其次,通过仿真分析方法,建立了基于经典双线性内聚力模型(Cohesive Zone Model)的单搭接接头静态及动态仿真模型,对胶接接头的模态频率、振型及加载开裂过程中胶层单元失效扩展进行模拟,与此同时,探讨了疲劳载荷对胶层内聚力模型的弱化效应。最后,利用SEM电镜分析手段,从微观上分析了粘接接头疲劳损伤及断裂机理。     

单搭接胶接接头弹性应力的二维分析方法

提出一种能得到单搭接胶接接头二维弹性应力解析解的的一般分析方法.该方法从纵向正应力沿厚度线性分布的理论假设出发,用完整的几何方程与本构方程,在考虑了被粘物与胶层的剪应力和剥离正应力沿厚度的变化,而且严格满足包括搭接区端头胶层剪应力为零的所有边界条件下,能够准确地预测接头任意点的应力状态,并适用于被粘物/胶层几何和材料属性的任何组合.通过与以往的解析解和有限元分析结果对比表明:不仅胶层平均剪应力最大值发生在距胶层端头很近的位置处,而且平均剥离正应力最大值位置也距离接头端头很近.这与以往绝大多数理论解预测"胶层剪应力和剥离正应力最大值都发生在端头处"的结论不同;该解析解有很好的精度和较广的适用范围.     

胶层吸湿对单搭接接头影响的数值模拟

在建立胶桔剂吸涅本构模型的基础上,用弹塑性有限元法研究了聚丙烯酸酯胶层吸涅程度对单搭接接头上胶层中应力分布的影响.结果表明:随着胶层吸湿程度增加,单搭接接头上胶瘤处的峰值应力显著降低.对水分从搭接区两侧渗入胶层的总宽度变化时胶层中的应力分布作了研究,发现随渗入总宽度的增加,胶层中的等效应力Seqv峰值下降.因水分渗入后引起胶层溶胀,在胶瘤过渡到中间胶层的拐角处会产生严重变形,可能导致该处发生脱粘.     

奇异性法预测粘接厚度对单搭粘接接头失效的影响

通过应力奇异性模型预测了铝5052-铝5052单搭粘接接头初始失效位置的受力情况.与Bogy理论公式相比,应力奇异性有限元模型不但可以很好的确定奇异应力场的形状(应力奇异性指数),且还可以确定奇异应力场的大小(应力强度因子),实现了对单搭粘接接头强度的准确分析和预测.研究结果表明:粘接剂厚度的变化不会影响奇异点应力奇异性指数,但会影响该处应力强度因子,应力强度因子随着粘接剂厚度的增加而增大,应力强度因子越大,粘接界面强度越低,该变化趋势与试验结果相吻合.     

胶接体系的胶接强度、粘结能及损伤破坏研究

胶接是指一种用粘合剂实现连接和固持的方法,胶接形式的金属薄板在汽车工业,建筑业以及航空航天领域有着广泛的应用.论文采用有限元模拟方法,研究了该胶接体系在受载状态下的滑剪破坏行为,重点关注了胶层粘结能,搭接长度,胶层厚度对胶接接头承载能力的影响,同时初步探讨了胶层的界面损伤情况.胶层粘结能的提高能够显著提高接头的承载能力.此承载能力受搭接长度和胶层粘结能的共同影响,较大的粘结能情况下,提高搭接长度能够显著提高接头的承载能力.胶层厚度对接头的承载能力也存在影响,在论文考虑的厚度范围内,提高厚度能够增强接头的承载能力.最后初步考虑了接头在达到载荷峰值时刻的胶层损伤情况.     

单搭拉剪胶焊接头的应力和刚度分析

胶焊复合连接技术兼具胶接和点焊的优点,它因提高结构强度和刚度而使车辆轻量化成为可能.以胶接理论为基础,考虑了被粘体剪切应变,将焊点视为大剪切弹性模量胶粘剂,胶层和焊点沿其厚度方向的剪应力不变,建立了胶焊单搭拉剪接头的线弹性应力解析模型.在应力模型基础上,将接头各组成部分看作是独立承载的拉伸和剪切弹簧单元,得到了其刚度解析模型.应力模型中的正应力和剪应力与有限元解吻合得较好,证明理论模型正确,参数研究中确定了影响胶焊单搭接头应力分布特征的关键耦合参数.     

钛合金异质自冲铆接头力学性能及失效机理分析

对钛合金异质单搭及T型自冲铆接头进行拉伸-剪切实验和剥离实验,对比接头的静力学性能,用扫描电子显微镜对接头典型断口进行研究,分析其微观失效机理。结果表明:TA1-Q215接头的最大失效载荷大于相同搭接类型的TA1-AA5052接头;TA1-AA5052单搭接头因下板断裂失效,为韧性断裂特征;TA1-Q215单搭接头上板铆钉孔撕裂处为韧窝形貌,铆钉与下板分离过程中,下板发生塑性变形并与铆钉产生严重刮擦现象;TA1-AA5052T型接头因铆钉与下板分离失效,下板出现明显的撕裂棱;当TA1-Q215T型接头失效形式为铆钉与上板分离时,上板撕裂处为准解理断裂机制;当铆钉与下板分离时下板撕裂处为韧性断裂,铆钉从下板剥离过程中产生刮痕。     

OPTIMAL SPECIMEN DESIGN FOR LAP SHEAR TEST

在采用搭接剪切试件进行的剪切强度实验中,试件失效往往是由于试件两端的剥离应力过大,而不是切应力造成的,这往往造成错误的实验结果. 通过有限元和光弹实验相结合的方法研究在搭接结构中引入凹槽以使试件所受的切应力均匀分布并减少两端的剥离应力,从而提高实验精度的可行性. 研究表明,只要凹槽的形状和位置合适,完全可以达到上述效果,从而实现了搭接剪切试件的优化设计.     

胶补加筋板应力强度因子及胶层剪应力计算

 在铆钉力法的基础上，提出计算胶接修补加筋板结构应力强度因子及胶层剪应力的解析法, 对分析胶接修补的加筋板强度具有现实意义. 利用影响系数，可以得到筋条、补片及蒙皮位 移的表达式，根据位移协调条件，建立联立方程，从而得到胶层剪应力及铆钉力. 通过解析 式，计算裂纹尖端的应力强度因子，分析补片对结构修补的效果，综合考虑了筋条及补片对 应力强度因子的影响.     

Stagnation-point flow of couple stress fluid with melting heat transfer

Melting heat transfer in the boundary layer flow of a couple stress fluid over a stretching surface is investigated. The developed differential equations are solved for homotopic solutions. It is observed that the velocity and the boundary layer thickness are decreasing functions of the couple stress fluid parameter. However, the temperature and surface heat transfer increase when the values of the couple stress fluid parameter increase. The velocity and temperature fields increase with an increase in the melting process of the stretching sheet.     

Laminar and turbulent burning velocities of propane in spherical vessels

Laminar and turbulent burning velocities of C₃H₈/air mixtures under moderately elevated temperature and pressure conditions have been determined experimentally using spherical combustion bombs. The results are reported here and the effects of temperature, pressure, turbulence intensity and stoichiometric ratio are included. The results obtained are compared with those of other researchers. The laminar burning velocity obtained from the pressure-time curves without compensation for the reaction zone thickness is lower than those determined using burners. A reaction zone thickness correction which reduces the difference is suggested and this relies on an assessment based on the different histories found experimentally when different initial temperatures were used for the isentrope through the standard state. For mixtures with initially low turbulence levels, both the turbulent burning velocity and the burning velocity ratio, turbulent to laminar, increase as the combustion progresses. The rate of increase becomes larger with increase in the initial and instantaneous turbulence intensity, temperature and stoichiometric ratio. Deviation from the Damköhler relationship is noted.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.     

固液两相流体对直齿轮跑合热弹流润滑的影响

建立了含有固体颗粒的接触区弹流模型,修正了Reynolds方程,考虑了润滑油对颗粒拖曳力的影响,考虑了颗粒速度随颗粒运动位置的变化,还考虑了颗粒自旋和热效应的影响,分析了颗粒运动位置变化和自旋对压力、膜厚和温度的影响,最后对算例结果进行了比较验证.结果表明:颗粒速度随颗粒运动位置变化而变化,在接触区中心附近颗粒速度趋于稳定;颗粒位于接触区中心附近时,接触区最大温度升高明显,颗粒所在区域瞬态温升较大;当颗粒靠近两啮合轮齿表面时,最小膜厚和最大温度均有所减小;颗粒顺时针自旋对最小膜厚和最大温度影响显著,顺时针自旋和逆时针自旋对接触区瞬态温升均影响较大,颗粒所在区域温度升高明显;自旋角速度增大,最小膜厚减小,最大温度升高,颗粒所在区域瞬态温升增大.     

The coupling influence of airflow and temperature on the wall-wetted fuel film distribution

The coupling influence of airflow and temperature on the two-dimensional distribution of the film resulted from fuel spray impinging on a horizontal flat wall was studied with experiments. The horizontal airflow direction was perpendicular to the vertical axis of the injection spray. The results show that, as air velocity increases, the film shape turns from a circle to an oblong. As wall temperature increases, the film area shrinks. Film thickness decreases as wall temperature or air velocity increases. The boiling point of the fuel is an important temperature to affect the film area and the film thickness. Film center moves more far away in the downstream direction as air velocity increases. For a certain air velocity, film center moves less far away as wall temperature increases.     

Stratified magnetohydrodynamic flow of tangent hyperbolic nanofluid induced by inclined sheet

This paper studies stratified magnetohydrodynamic(MHD) flow of tangent hyperbolic nanofluid past an inclined exponentially stretching surface. The flow is subjected to velocity, thermal, and solutal boundary conditions. The partial differential systems are reduced to ordinary differential systems using appropriate transformations.The reduced systems are solved for convergent series solutions. The velocity, temperature,and concentration fields are discussed for different physical parameters. The results indicate that the temperature and the thermal boundary layer thickness increase noticeably for large values of Brownian motion and thermophoresis effects. It is also observed that the buoyancy parameter strengthens the velocity field, showing a decreasing behavior of temperature and nanoparticle volume fraction profiles.     

高速碰撞下圆柱壳自由梁的穿孔特性

利用二级轻气炮加载,进行了球状2A12铝弹丸垂直撞击圆柱壳自由梁实验。并进行了弹丸速度、圆柱壳直径和壁厚等因素对穿孔直径影响的数值模拟,数值模拟结果和实验结果基本吻合。通过量纲分析和数值模拟结合,推导了穿孔直径与相关影响参数的经验关系式。研究结果表明:当圆柱壳直径和厚度不变时,高速撞击产生的穿孔直径在径向和轴向都随着弹丸速度增大而增大;当弹丸速度和圆柱壳厚度不变时,高速撞击产生的穿孔直径随着圆柱壳自由梁直径的增大而减小;当弹丸速度和圆柱壳直径不变时,穿孔直径随着圆柱壳厚度的增大而减小。     

Generation of the mean flow in the fluid layer with a nonuniformly heated wavy boundary

The problem of convection in the horizontal fluid layer with a wavy lower boundary is considered. It is shown that for the periodic temperature distribution with a certain phase shift given on the wavy boundary, in the fluid layer a unidirectional horizontal flow arises. The flow velocity linearly decreases with increase in attitude and depends on the relief distribution wavelength. There is an optimum wavelength (of the order of the layer thickness) at which the velocity reaches its maximum value.     

Heat transfer by laminar flow of an elastico-viscous fluid in posttreatment analysis of wire coating with linearly varying temperature along the coated wire

The present study focuses on the heat transfer by the laminar flow of an elastico-viscous fluid in posttreatment of wire coating analysis with linearly varying temperature on the surface of coated wire. The surface of wire (uncoated) and the surface of coated wire were subjected to two thermal boundary conditions. The constitutive equation of motion and equation of energy have been solved by using perturbation theory for velocity, pressure distribution along the radial direction and temperature distribution. The theoretical analysis of flow rate, average velocity, shear stress, thickness of coated wire, and force on the total wire were also derived. Moreover, the flow phenomenon has been studied under the influence of elastic number R _e velocity ratio U and the dimensionless number S in the ranges 0?≤?R _e ?≤?20, 0.2?≤?U?≤?1.4 and 0?≤?S?≤?20. We noticed that with the increase in elastic number R _e velocity decreases whereas thickness of the coated wire and force on the total wire increases. Also temperature profile decreases with the increase of non-dimensional parameter S.     

Flow of variable thermal conductivity fluid due to inclined stretching cylinder with viscous dissipation and thermal radiation

The aim of the present study is to investigate the flow of the Casson fluid by an inclined stretching cylinder. A heat transfer analysis is carried out in the presence of thermal radiation and viscous dissipation effects. The temperature dependent thermal conductivity of the Casson fluid is considered. The relevant equations are first simplified under usual boundary layer assumptions, and then transformed into ordinary differential equations by suitable transformations. The transformed ordinary differential equations are computed for the series solutions of velocity and temperature. A convergence analysis is shown explicitly. Velocity and temperature fields are discussed for different physical parameters by graphs and numerical values. It is found that the velocity decreases with the increase in the angle of inclination while increases with the increase in the mixed convection parameter. The enhancement in the thermal conductivity and radiation effects corresponds to a higher fluid temperature. It is also found that heat transfer is more pronounced in a cylinder when it is compared with a flat plate. The thermal boundary layer thickness increases with the increase in the Eckert number. The radiation and variable thermal conductivity decreases the heat transfer rate at the surface.     

不同迎爆面结构的泡沫金属对甲烷气体爆炸传播阻隔性能的实验研究

通过自行设计的爆炸管网设备进行实验,提出通过改变泡沫金属迎爆面的结构来增大与爆炸火焰的接触面积,结合爆炸超压、火焰传播速度和火焰温度等参数来评价不同迎爆面设计结构的泡沫金属的阻隔爆性能。结果表明,在相同厚度的前提下,在材料迎爆面增加一定的锯齿形波纹会使整体的阻隔爆性能有所提升,爆炸超压、火焰传播速度和火焰温度的衰减率随着迎爆面锯齿角度的减小而增大。当泡沫金属迎爆面锯齿角度为30°时,爆炸超压、火焰传播速度和火焰温度的衰减率分别为74.0%、76.18%和91.93%,爆炸超压下降速率为30.76 MPa/s,材料后端熄爆参数为17.68 MPa·℃,阻隔爆效果较好。