变宽截面箱梁剪力滞效应研究

将变宽度截面箱梁的剪力滞翘曲位移函数定义为三次抛物线形式,用能量变分原理建立了分析变宽截面箱梁剪力滞效应的控制微分方程,并用差分法求解此方程。分别计算了简支箱梁在集中荷载和均布荷载作用下的正应力,并用有限元法作了验证。将计算结果与等截面箱梁的应力进行对比,总结变宽箱梁剪力滞效应的分布规律。结果表明,均布荷载作用下,相对于等截面梁,变宽箱梁的顶板应力变化幅度更大,峰值更高,箱梁的顶板宽度变化对剪力滞效应影响较大;在集中荷载作用下,等截面与变宽度箱梁跨中截面的应力相近,应力分布曲线吻合较好,说明顶板宽度变化对剪力滞效应影响较小;分别在集中和均布荷载作用下,箱梁跨中截面应力均为正剪力滞分布状态。当箱梁顶板、底板和悬臂板宽度相等时,剪力滞效应控制微分方程也适用于等截面箱梁。     

Nonlinear Finite Element Analysis of γ-Graphyne Structures under Shearing

In this study, a nonlinear, spring-based finite element approach is employed in order to predict the nonlinear mechanical response of graphyne structures under shear loading. Based on Morse potential functions, suitable nonlinear spring finite elements are formulated simulating the interatomic interactions of different graphyne types. Specifically, the four well-known types of γ-graphyne, i.e., graphyne-1 also known as graphyne, graphyne-2 also known as graphdiyne, graphyne-3, and graphyne-4 rectangular sheets are numerically investigated applying appropriate boundary conditions representing shear load. The obtained finite element analysis results are employed to calculate the in-plane shear stress–strain behaviour, as well as the corresponding mechanical properties as shear modulus and shear strength. Comparisons of the present graphyne shearing response predictions with other corresponding estimations are performed to validate the present research results.     

自由剪切流动中颗粒扩散的自相似特性

为了研究自由剪切流动中颗粒扩散的统计特性,对空间发展模式的三维气固两相射流和时间发展模式的三维气固两相混合层进行了直接数值模拟.其中对气相不可压缩Navier-Stokes方程的求解分别采用有限容积方法和拟谱方法,对离散惯性颗粒的跟踪采用单向耦合的拉格朗日方法.统计结果显示,当流场进入自相似状态后,以流场速度梯度二阶不变量Q为自变量的颗粒数的概率分布函数也呈现出与颗粒尺寸和时间发展无关的自相似特性.     

某支板式超音速剪切流燃烧的数值研究

针对某支板火焰稳定结构数值研究了二维超音速流动和燃烧规律,提出不同燃料供给方案,比较了采用全氢气、全甲烷和不同比例的混合燃气等情况下的燃烧性能.结果表明:单一燃料时,氢气超燃性能很好,但会出现热量雍塞,而甲烷无法燃烧,两种混合燃料方案均在燃烧室内出现了稳定的火焰,但氧气消耗率不理想,基于上述结论给出了一些提高超燃性能的改进措施.     

X状Z向碳pin增强泡沫夹层结构剪切刚度预报

综合考虑了面板对横向增强Z-pin的不同约束情况,结合空间网架结构和等效夹杂方法,提出了X状Z-pins增强泡沫夹层结构剪切刚度的预报模型,经实际计算后与已有的实验值和有限元模拟值比较,证明该方法具有足够的工程精度.计算表明,X状Z-pins能大幅度地提高泡沫夹层结构的剪切刚度,并具有良好的可设计性,可以通过改变Z-pin材料,Z-pin的体积分数、角度、直径等参数改变其力学性能.其中,Z-pin体积分数越大、拉伸模量越高、直径越大,Z-pins增强泡沫夹层结构的剪切刚度越高.     

涂层界面结合强度检测研究(Ⅰ):涂层结合界面应力的理论分析

利用激光划痕测试法和弯曲应力理论，建立了涂层结合界面应力的理论模型，推导出结合界面剪应力、正应力和剥离应力分布公式，分析了结合界面应力产生的机理.理论分析结果表明，界面正应力主要集中在界面中心区域内，而在界面边缘附近，正应力迅速下降，在界面边缘处其值降为0；剪应力和剥离应力主要集中在界面边缘区域内，在远离界面边缘区域，剪应力和剥离应力则迅速下降；涂层中正应力和涂层厚度、基体厚度以及杨氏模量无关，界面间剪应力以及剥离应力随涂层厚度增加而增加，并且由涂层与基体厚度以及杨氏模量所共同决定.     

冲击压缩下铝、铜、钨的剪切模量和屈服强度与压力和温度的相关性

对铝、铜和钨在冲击压缩状态下的剪切模量和屈服强度的实验数据进行了综合分析，并与St einberg-Cochran-Guinan(SCG)模型的计算结果进行了比较，结果表明，铝在50 GPa、铜在1 00 GPa、钨在200 GPa冲击压力以内，三种材料的剪切模量和屈服强度随温度和压力的变化 趋势基本相似，即SCG模型的假设Y′_pY₀=G′_pG ₀,Y′_TY₀=G′_TG₀对这三种材料在上述冲击压力范围内近似成立，利用该模型可以较好地描述材料在冲击压缩 下的本构行为. 关键词： 剪切模量 屈服强度 压力 温度     

液体喷射抛光材料去除机理的研究

从实验出发,研究了液体喷射抛光中抛光区的特征及材料的去除机理。得到了垂直喷射时在材料的去除区域呈W型的环状分布现象,并运用射流与冲击理论对这一现象做了详细地分析。实验结果表明,磨料粒子碰撞时的剪切作用对材料的去除来说占主导地位,而直接冲击作用占次要地位。     

Stress-Structure Relationship of the Reversible Associating Polymer Network under Start-up Shear Flow

We adopt Langevin dynamics to explore the stress-structure relationship of telechelic reversible associating polymer gel during startup shear flow, with shear strengths varying from Wi=12.6 to Wi=12640. At weak shear flow Wi=12.6, the shear stress proportionally increases with shear strain at short times, followed by a strain hardening behavior and then passes through a maximum(σmax, γmax) and finally decreases until it reaches the steady state. During the evolution of stress, the gel network is only slightly broken and essentially maintains its framework, and the strain hardening behavior originates from the excessive stretching of chains. On the other hand, the stress-strain curve at intermediate shear flow Wi=505.6 shows two differences from that at Wi=12.6, namely, the absence of strain hardening and a dramatic increase of stress at large strains,which is caused by the rupture of gel network at small strains and the network recovery at large strains, respectively. Finally, at very strong shear flow Wi=6319.7, the gel network is immediately broken by shear flow and the stress-strain curve exhibits similar behaviors to those of classical polymeric liquids.     

Effect of annealing temperature on interrelation between the microstructural evolution and plastic deformation in polymers

The mechanical loading induced flow of glassy polymers is triggered by the nucleation of shear transformation units, and strongly depends on the initial microstructural state of the material. Therefore, investigation of the possible relationship between the microstructural state variables and plastic deformation is required for a better understanding of the macroscopic response of this class of materials during large deformation. In this study, free volume content is considered as a state variable and thermal treatment is selected as a process through which the accelerated and forced evolution of the free volume can be imposed. For two well‐known glassy polymers, poly(methyl methacrylate) and polycarbonate, the free volume content alteration upon annealing is monitored via positron annihilation spectroscopy, and the changes of the micro‐ and macromechanical properties are also obtained by utilizing nanoindentation technique and employing the homogeneous amorphous flow theory. The correlation between the microstructural state variable, that is, free volume, and the micromechanical state variable, that is, shear activation volume, is then investigated. The results reveal opposite direction of alterations of free volume and shear activation volume with annealing temperature. Accordingly, the possibility of the existence of an interrelation between these two state variables is critically discussed. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1286–1297