首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 156 毫秒
1.
为分析充气压力对空气衬垫缓冲防护性能的影响,综合空气垫薄膜材料的拉伸变形和气室的压缩变形,建立了空气垫的冲击压缩力学模型。分析表明增大充气压力的总体效果是将使气垫的动刚度、承受的冲击载荷下降。原因是增大充气压力将使气垫薄膜在冲击过程的拉伸变形增大,气垫的体积比V0/Vt减小,而体积比在动刚度模型中是比充气压力更高阶的项。结合空气垫的弹性变形吸能机理分析,表明气垫薄膜的弹性变形可延长冲击载荷作用时间和吸能时间,从而提高空气垫的缓冲防护性能。对不同充气压力和气室宽度的空气垫,用7.5 kg的重锤进行冲击试验,结果表明:在不超过薄膜弹性限值的前提下,增大气垫的充气压力可降低气垫承受的冲击载荷峰值,提高气垫的缓冲防护性能,充气压力每增加20 k Pa,冲击载荷峰值降低10%以上。  相似文献   

2.
柱状塑膜空气垫承载与缓冲性能的试验研究   总被引:6,自引:6,他引:0  
针对不同规格的柱状塑膜空气垫进行准静态压缩实验,测定其承栽力-变形特性,分析充气压力、结构尺寸对空气垫的承载、缓冲性能影响.结果表明:随着充气压力的增大,空气垫承载力有所提高,对小规格空气垫,充气压力对承载力影响较为显著,但随着规格尺寸增大,其影响显著性降低;空气垫材料有良好的缓冲性能;当承载应力较小时,空气垫缓冲系数变化幅度很大;而当承载应力到达一定值时,空气垫表现出较稳定的缓冲性能.  相似文献   

3.
为了研究一种弹芯用聚碳酸酯材料在冲击作用下的动态力学响应,利用材料试验机和SHPB装置对该材料在不同应变率条件下动静态压缩性能进行测试分析,获得了该聚碳酸酯材料不同应变率下的应力应变曲线,试验结果表明:聚碳酸酯材料的压缩过程呈现明显的黏弹性现象,其动静态屈服强度和模量随着应变率的增加而变大,塑性阶段表现为应变软化与应变硬化相互作用的结果,且不同应变率下塑性阶段的应力应变曲线切向模量近似相等;基于试验结果建立了描述聚碳酸酯材料大变形力学行为的黏弹塑性本构模型,并得到了该材料的本构方程。对比分析显示,该模型可以较准确地描述聚碳酸酯材料动静态压缩行为。  相似文献   

4.
基于OpenSees中的BeamwithHingesElement单元,采用直接在截面层次上定义线弹性剪切恢复力模型,引入零长度单元利用粘结滑移材料模拟构件末端粘结滑移,考虑P-D效应引起的几何非线性,钢筋材料采用能精确模拟钢筋低周疲劳损伤与开裂现象的Mohle-Kunnath本构模型,分析构件在不同加载历史条件下的力学特性。研究构件在单调加载、非对称循环加载、对称循环加载条件下构件的力学特性,并进一步分析构件在不同循环周数条件下对称、非对称加载时构件的力学特性及钢筋材料应变随位移加载历史的变化特点,分析结果表明,钢筋混凝土框架柱在循环加载条件下的构件刚度退化、强度退化现象明显,构件的损伤程度随着剪跨比的降低和轴压比的增大逐渐加剧,构件随着循环周数的增加损伤程度更明显,钢筋材料应变随着循环周数的增加变化明显,随着轴压比增加和剪跨比的降低,构件刚度退化与强度退化随循环周数的增加更显著,钢筋应变同样有一定程度增加。  相似文献   

5.
弹性应变工程是指通过改变材料弹性应变的大小来调控和优化其物化性能的技术。人们早在1950年左右就发现弹性应变可以大幅提高单晶硅中载流子的迁移率,并在20世纪90年代后期将其应用在CMOS工业中,产生了数百亿美金的效益。但由于当时大弹性应变很难在其它材料体系内实现,弹性应变工程并没有引起人们的普遍关注。近年来,随着纳米材料制备技术的蓬勃发展,人们发现纳米材料能承受比其块体母材高达10~100倍的超大弹性变形。这重新燃起了人们对弹性应变工程的研究兴趣,并取得了很多富有应用前景的成果。例如,理论计算和初步的实验结果表明,拉应变能使锗从间接带隙半导体转变为直接带隙的半导体,从而显著改变其光学特性;应变梯度不仅能增加二硫化钼单分子层材料吸收太阳光的谱宽,而且能降低激子的束缚能,并使其沿应变增加方向定向移动;通过弹性应变调控可大幅提升光催化分解水制氢等。综述了弹性应变工程的发展历史和研究现状,并对其未来的发展方向进行了剖析和展望,期望为本领域的研究人员提供参考!  相似文献   

6.
用Ritz法分析复合材料夹杂黏弹性阻尼材料的应变能   总被引:2,自引:0,他引:2       下载免费PDF全文
分析了复合材料夹杂黏弹性阻尼材料组成的对称层合板的线性弯曲,其中夹杂的黏弹性阻尼材料作为各向同性材料处理,既考虑面内应变能又考虑横向切应力应变能,用Ritz法研究各应力分量的应变能。以四边夹紧为边界条件的方形板为例,计算并分析了复合材料层和黏弹性层的应变能以及复合结构的损耗因子。结果表明,复合材料层的面内应变能占主要地位,而黏弹性层中xz方向和yz方向的切应力应变能占主要地位。黏弹性层与复合材料层的弹性模量之间的差异对复合结构的损耗因子有重要影响。  相似文献   

7.
针对组分材料体积分数任意分布的聚合物功能梯度材料,研究其在蠕变加载条件下Ⅰ型裂纹应力强度因子(SIFs)和应变能释放率的时间相依特征。由Mori-Tanaka方法预测等效松弛模量,在Laplace变换域中采用梯度有限元法和虚拟裂纹闭合方法计算断裂参数,由数值逆变换得到物理空间的对应量。分析边裂纹平行于梯度方向的聚合物功能梯度板条,分别考虑均匀拉伸和三点弯曲蠕变加载。结果表明,聚合物梯度材料应变能释放率随时间增加,其增大的程度与黏弹性组分材料体积分数正相关;材料的非均匀黏弹性性质产生应力重新分布,导致裂纹尖端应力场强度随时间变化,当裂纹位于黏弹性材料含量较低的一边时,应力强度因子随时间增加,反之,随时间减小。而且,材料的应力强度因子与时间相依的变化范围和体积分数分布以及加载方式有关,当体积分数接近线性分布时,变化最明显,三点弯曲比均匀拉伸的变化大。SIFs随时间的延长增加或减小、加剧或减轻裂纹尖端部位的“衰坏”,表明黏弹性功能梯度裂纹体的延迟失稳需要联合采用应力强度因子与应变能释放率作为双控制参数。  相似文献   

8.
目的 以聚丙烯材料为研究对象,研究密度对其动态冲击性能的影响。方法 对4种不同密度的聚丙烯材料进行动态压缩试验,分析接触力、位移和应变以及吸收能、比吸能的变化,从而研究动态条件下不同密度的聚丙烯材料的动态冲击性能。结果 当密度一定时,最大接触力、最大位移、最大应变、比吸能随冲击能的增大而增大。当冲击能一定时,最大接触力随密度的增大而增大,最大位移、最大应变、比吸能随密度的增大而减小。结论 考虑到轻量化以及成本因素,在安全范围内,选择缓冲材料时可以选择密度较小的聚丙烯材料。  相似文献   

9.
目的采用有限元数值模拟方法研究空气垫在静态压缩时的力学性能,以便更直观、系统地了解空气垫的静态压缩力学行为。方法以柱状空气垫为对象,建立空气垫的静态压缩物理模型和力学模型,并基于该有限元模型模拟该结构的静态压缩过程,分析结构尺寸和充气压力对其静态缓冲性能的影响,得到空气垫在不同压缩量下的应力分布规律和变形特点。同时,将试验结果与模拟结果进行对比。结果空气垫的变形是从接触钢板的地方开始的,上下位置同时被压缩,有限元分析结果与试验结果吻合良好。结论所建立的有限元模型和数值模拟方法结果准确、合理。  相似文献   

10.
正空气垫是一种应用广泛的缓冲包装材料,集经济环保效益于一体。承载性,是其缓冲效果重要决定因素,通过静态压缩试验和动态压缩试验能实现该性能的数据化表征。通过分析发现,空气垫缓冲包装的诸多工艺参数和流通环境,如薄膜材料的拉伸性、包装整体的密封质量、充气压力等,都会在一定程度上影响其承载性  相似文献   

11.
复式空心钢管混凝土组合轴压弹性模量分析   总被引:1,自引:0,他引:1  
将复式空心钢管混凝土柱分成混凝土、内钢管和外钢管三部分,作为拟平面轴对称问题进行分析。应用弹性力学中的势能驻值原理进行弹性理论分析,描述复式空心钢管混凝土柱在小变形下的弹性行为及套箍机理。导出了钢管混凝土柱在轴向压力作用下的套箍系数、组合轴压弹性模量的理论计算公式。分析结果表明:复式空心钢管混凝土的组合轴压弹性模量与钢管的泊松比、混凝土的泊松比有着必然的联系,同时钢管与混凝土之间的"套箍作用"对组合弹性模量也有一定的影响。组合轴压弹性模量随着含钢率的增大基本成线性增长,并得到了复式空心钢管混凝土柱在轴力作用下的应力分配比不是简单地按单轴弹性模量比分配的结论。  相似文献   

12.
研究了硬质合金内衬的多层组合超高压筒体的强度优化设计。以等强度理论为设计原则,建立了以各外层径比(外径与内径的比值)为变量,容器总径比为约束,弹性承压能力最大为目标的优化设计数学模型。应用Lagrange乘子法进行优化,得到了各层最优径比公式及最大内压公式。在此基础上,从叠加原理出发,推导了不同材料多层容器的层间缩套压力及过盈量的最优精确解。最后通过实际算例与分析表明,硬质合金内衬的组合容器需要更大的缩套压力,对于三层容器,中间层和内衬主要承担径向压应力,而外层主要承担周向拉应力。  相似文献   

13.
The dependence of X-ray intensity on the pressure and type of ambient gas was investigated for LiNbO3 single crystals polarized in the c-axis direction at pressures of approximately 1 to 30 Pa. Ionization of surrounding gas molecules by the electric field generated by the crystal led to the production of both positive ions and free electrons. The electrons were accelerated toward a Cu target, radiating both white X-rays and X-rays specific to the crystal or target material by bremsstrahlung. The integrated X-ray intensity per cycle in the energy range 1 to 20 keV showed a local maximum value at a pressure Pmax. The logarithm of Pmax was proportional to the Boltzmann factor using the first ionization energy of each ambient gas molecule. The value of Pmax was found to be independent of the electrical surface area of the crystal. The integrated X-ray intensity was approximated qualitatively by a quadratic function with pressure, which was upwardly convex. It was found that one of the causes of the reduction in X-ray intensity at pressures P > Pmax is the adsorption of positive ions generated by the ionization of gas molecules on the negative electric surface. It was also discovered that the lifetime of the X-ray radiation device could be improved when the X-ray radiation case was covered with another hermetically sealed decompression case. The gas with the smallest first ionization energy, with a partial pressure of Pmax, was enclosed inside the X-ray radiation case (inner case) and the gas with the largest first ionization energy was enclosed at a suitable pressure between the inner and outer cases.  相似文献   

14.
Subject of this analytical investigation is a rotating two-layered hollow cylinder under generalized plane strain subject to an elevated temperature at the inner surface or to internal pressure. It is presupposed that the inner cylindrical layer consists of the heavier material, whereas the outer layer is made of a material with lower density, like for example in a steel/aluminum tube. Criterion for the maximum permissible stress is the yield criterion by von Mises, and the device is optimized with respect to its weight. It is found that plasticization may start at different radii, and the study provides not only a comprehensive overview of the elastic limits of composite tubes of the above type but also a straightforward procedure for determining the optimum composition.  相似文献   

15.
This work uses a 3-D discrete element simulation to calculate the elastic and kinetic energy for a nonuniform granular shear flow to determine whether the ratio of these energies is sufficient to identify specific flow regimes of granular materials in a fashion to other dimensionless parameters such as inertial number and dimensionless stiffness. We first obtain the critical packing fraction under isostatic compression, then analyze the mean and fluctuating parts of the elastic and kinetic energy as the granular flow reaches a steady state. External work performed on a system during granular flow partially dissipates into heat, while the remaining work is stored in particles as elastic and kinetic energy; thus processes occurring at a particle level not only control the energy transformation, but also affect the bulk behavior of a granular flow. The effective frictions are correlated with the mean elastic energy to mean kinetic energy ratio and it is interesting to find a power law function with an index of $-0.16$ for the systems used in this work. Analysis of this ratio’s ability to classify flow shows that its determination is quite sufficient to identify specific flow regimes of granular materials, even though energy has a scalar expression. Therefore, these energetics studies can provide a theoretical basis for unifying the mechanics of granular flows over the entire range of regimes.  相似文献   

16.
The elastic solution for one to four radial cracks emanating from either the inner or outer surface of a circular ring is considered. For cracks emanating from the outer surface, internal pressure is considered, while for cracks emanating from the inner surface, the loading is uniform external tension. The technique used for the solution is the modified mapping-collocation approach. Data is presented for two wall ratios for each geometry.  相似文献   

17.
Weight‐adjusted inner products are easily invertible approximations to weighted L2 inner products. These approximations can be paired with a discontinuous Galerkin (DG) discretization to produce a time‐domain method for wave propagation which is low storage, energy stable, and high‐order accurate for arbitrary heterogeneous media and curvilinear meshes. In this work, we extend weight‐adjusted DG methods to the case of matrix‐valued weights, with the linear elastic wave equation as an application. We present a DG formulation of the symmetric form of the linear elastic wave equation, with upwind‐like dissipation incorporated through simple penalty fluxes. A semidiscrete convergence analysis is given, and numerical results confirm the stability and high‐order accuracy of weight‐adjusted DG for several problems in elastic wave propagation.  相似文献   

18.
Porous strategies based on nanoengineering successfully mitigate several problems related to volume expansion of alloying anodes. However, practical application of porous alloying anodes is challenging because of limitations such as calendering incompatibility, low mass loading, and excessive usage of nonactive materials, all of which cause a lower volumetric energy density in comparison with conventional graphite anodes. In particular, during calendering, porous structures in alloying-based composites easily collapse under high pressure, attenuating the porous characteristics. Herein, this work proposes a calendering-compatible macroporous architecture for a Si–graphite anode to maximize the volumetric energy density. The anode is composed of an elastic outermost carbon covering, a nonfilling porous structure, and a graphite core. Owing to the lubricative properties of the elastic carbon covering, the macroporous structure coated by the brittle Si nanolayer can withstand high pressure and maintain its porous architecture during electrode calendering. Scalable methods using mechanical agitation and chemical vapor deposition are adopted. The as-prepared composite exhibits excellent electrochemical stability of > 3.6 mAh cm−2, with mitigated electrode expansion. Furthermore, full-cell evaluation shows that the composite achieves higher energy density (932 Wh L−1) and higher specific energy (333 Wh kg−1) with stable cycling than has been reported in previous studies.  相似文献   

19.
根据粘弹性材料有限变形的应变能密度函数、Maxwell模型的松弛函数及气泡的变形梯度张量,推导出蛋白质气泡有限变形的应力方程.并结合气泡的动力学方程,得到气泡在内外压力差、弹性有限变形应力及粘性耗散应力共同作用下内径的非线性振动方程.利用该方程,通过数值模拟方法,对蛋白质气泡有限变形时的振动特性进行了分析,研究了气泡内外压力差、膜的厚度、膜的粘性以及气泡大小对气泡振动特性的影响.结果表明,蛋白质气泡的振动具有非线性特性,当初始压力差不同时,气泡的振动频率、振幅、速度的变化是不同的,停止振动时的大小也不相同;增加膜的厚度和膜的粘性会抑制气泡的振动,增强气泡承受载荷的能力;对于大小不同的气泡,尺寸较小的气泡振动频率高,速度衰减慢.  相似文献   

20.
The compression characteristics of two particle size fractions (< 90 microm, 105-210 microm) of paracetamol were examined. Each fraction produced extremely weak tablets and displayed a high tendency to cap. Low correlation coefficients of the initial parts of the Heckel plots, a low strain rate sensitivity, and an increase in mean yield pressure (from 34.2 to 45.5 MPa) with decrease in particle size all confirmed that the main mechanism during the compaction of paracetamol was fragmentation. The 105-210-microm particles underwent more fragmentation than the less than 90-microm powder. Heckel analysis confirmed that the larger size fraction of paracetamol produced denser compacts than the smaller fraction. The 105-210-microm fraction resulted in tablets with lower elastic recoveries and elastic energies. The elastic, plastic energy ratios indicated that the majority of energy involved during the compaction of paracetamol was utilized as elastic energy, indicative of massive elastic deformation of paracetamol particles under pressure.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号