皇冠梨静压力学特性及模拟研究

目的 建立皇冠梨生理特性与力学损伤关系模型,实现果实静压过程的模拟研究。方法 通过材料松弛试验和静态压缩试验,研究果实材料力学特性。使用三维扫描方法辅助建立果实有限元模型,并对果实静载损伤过程进行模拟。结果 使用Maxwell黏弹性材料本构模型,成功模拟了果实流变特性。通过静压试验将所建立的梨果实黏弹性材料模型与传统弹塑性材料模型进行对比,误差降低了7%,从而验证了模拟的准确性。根据von Mises等效应力分布结果进行预测,发现在静载力为161.21 N时梨果实会出现明显损伤。结论 以上研究使用2种材料对静态压缩试验进行仿真模拟,进一步验证了使用数值模拟方法对水果静力学过程模拟的可靠性。为皇冠梨果实机械化采摘、储存包装及加工搬运过程提供了理论依据。     

船用高分子材料压缩蠕变特性研究

研究了四种船用高分子材料的蠕变特性,分析了其压缩蠕变曲线特点,以及试验中弹性变形、粘弹性变形及粘性变形在总变形中所占比例,最后建立材料压缩蠕变的Burgers模型,得到了试验数据的拟合方程和拟合曲线。由实测曲线和拟合曲线可知,利用Burgers模型可以准确分析试验期间材料的蠕变性能,并能较好地预测材料后期的蠕变行为。     

织物纤维干湿态压缩成型特性

对干态和湿态两种工况下的碳纤维和玻璃纤维织物进行了压缩成型特性实验,利用黏弹性理论模型,分析了上述两种工况下压缩、应力松弛和回弹阶段的黏弹性曲线和黏弹性模型参数。通过分析两种工况下织物纱线压缩成型3个阶段的变形机制,阐述了产生上述差异的原因。结果表明,对于织物压缩阶段,当达到相同的最大成型压力时,湿态织物的成型厚度比干态的成型厚度略大。湿态织物的压缩时间比干态的压缩时间短,且织物规格越小,相差时间越少。湿态织物压缩阶段的时间常数小于干态织物对应值。对于织物应力松弛和回弹阶段,介质较少渗入织物间隙,织物变形过程基本相同,织物在两种工况下的成型厚度差值与回弹厚度差值十分接近。因此,湿态下织物的回弹厚度比干态下的回弹厚度略大。应力松弛和回弹阶段的时间常数基本相同。上述研究结果对纤维增强树脂基复合材料的成型工艺具有了一定的指导意义。      

复合材料螺栓连接预紧力松弛的温度-时间依存行为

针对碳纤维增强环氧基复合材料机械连接结构耐久性设计中的2个关键问题:黏弹性预紧力松弛的温度-时间依赖行为及其长期性能预测方法进行研究。建立了以蠕变全应变理论为基础的预紧力松弛预测模型。36 h的恒温耐久试验表明:初始预紧力越大,温度越高,连接件预紧力松弛速率越快;复合材料连接件的松弛速率远大于金属连接件;预紧力松弛主要表现为材料蠕变过程。对比短期试验结果表明:本模型能较好地实现对不同温度、预紧力和连接材料的松弛预测,为确立试验数据的外推方法提供了依据。      

92负刚度蜂窝结构压缩性能分析

为准确开展以黏弹性材料为载体的负刚度蜂窝结构数值模拟研究,提出一种基于黏弹性广义Maxwell模型的负刚度蜂窝结构压缩性能数值模拟法。进行了尼龙12的动态机械分析(DMA)测试,基于广义Maxwell模型拟合实测动态模量数据,得到反映尼龙12动态黏弹性的无量纲模量g_i和松弛时间τ_i。建立了负刚度蜂窝结构的有限元模型,基于实测的动态黏弹性参数,进行压缩性能的数值模拟研究,并同压缩试验结果进行比较,验证了数值模拟的准确性,利用数值模拟研究几何参数对结构压缩性能的影响规律。结果表明,基于黏弹性广义Maxwell模型的负刚度蜂窝结构数值模拟分析法可较准确模拟结构的压缩性能,为预测负刚度蜂窝结构的力学性能提供帮助。     

深水静压环境中夹芯结构PUEPM芯材蠕变特性实验研究

通过弹性力学分析,将深水静压环境中夹芯结构芯材力学状态与加套筒静压实验中芯材的力学状态进行对比,提出研究深水静压环境中夹芯结构黏弹性芯材蠕变特性的套筒实验方法;针对三种不同配方的聚氨酯改性环氧基微珠增强吸声体(Polyurethane Modified Epoxy Resin Sound Absorption Materials,PUEPM)芯材开展准静态套筒压缩实验和加套筒蠕变实验,得到了芯材的蠕变性能。结果表明:玻璃微珠含量较低,短切纤维含量较高的分层PUEPM芯材具备较好的蠕变性能;玻璃微珠含量越大,芯材变形回弹性能越好;B型PUEPM芯材具备较好的综合力学性能。     

软体沙发产品质量安全知识

软体沙发是指适用于会客、休息等室内用途的沙发，不适用于木制的沙发椅。软体沙发（以下简称沙发）是指使用软质材料、木质材料或金属材料制成，具有弹性、有靠背的座具。沙发产品主要按座面弹性材料、包覆面料和使用功能进行分类。按照座面弹性材料可分为：中凹型弹簧和包布弹簧沙发、蛇簧沙发、弹性绷带沙发、海绵沙发、棕纤维沙发、混合型弹簧沙发；按照包覆面料可分为：皮革沙发、再生革沙发、人造节沙发、布艺沙发、布革沙发；按照使用功能可分为：单人沙发、双人沙发、二人沙发、组合沙发、多用沙发等。     

空心玻璃微珠填充环氧树脂复合材料力学性能

对不同填充质量比的改性空心玻璃微珠(HGB)/环氧树脂复合材料进行了拉伸、压缩准静态实验。研究了改性空心玻璃微珠不同填充量对复合材料密度、弹性模量、拉伸强度和压缩强度的影响, 并分析其应力松弛。实验发现, 材料的各项数据随填充比增加均有所降低。空心玻璃微珠的填入使材料表现出脆性破坏, 但破坏前有较大的变形, 破坏后回弹率大, 说明玻璃微珠的填充增强了材料的弹性。HGB/环氧树脂复合材料具有明显的应力松弛现象, 且填充比越高, 应力松弛速率越大, 可见HGB/环氧树脂复合材料具有明显的黏弹性。      

纸基摩擦材料纤维、树脂含量和孔隙率对压缩回弹性能的影响

纸基摩擦材料属多孔材料，其摩擦磨损性能与压缩回弹性能密切相关。研究了纸基摩擦材料纤维的含量及类型、树脂的含量，以及材料的孔隙率对其压缩回弹性能的影响。结果表明，材料配方及孔隙率会显著改变材料的压缩率和回弹率。纤维和树脂含量的增加都会造成纸基摩擦材料压缩率的降低和回弹率的升高。其中，树脂含量对材料压缩率的影响较大，纤维含量对材料回弹率的影响较大。加入混杂纤维的材料比较单纯采用芳纶纤维浆粕的材料具有更低的压缩率和更高的回弹率，其中混杂有纸浆纤维的材料压缩回弹性能最好。纸基材料的孔隙率越大，材料压缩率越大，回弹率越低。     

结晶高聚物硬弹性材料的研究进展──Ⅰ．硬弹性材料的力学性能

硬弹性材料是近年发展起来的一种新型弹性体，它是一类结晶或非晶的高聚物在特定的条件下加工而成的材料。硬弹性材料的力学性能和形态结构明显不同于普通的弹性体，具有高弹性、高模量、突出的低温弹性和拉伸时能形成微孔等特性。本文主要介绍了这种材料的力学性能的各个方面，包括力学特征、拉伸特性，应力松弛和蠕变行为，力学损耗和滞后现象，溶剂浸润的影响以及断裂行为等。     

沙发海绵座垫性能对坐姿舒适性的影响

本文采用主观评价与体压分布测试相结合的方法,分析海绵座垫下陷硬度、各层海绵搭配形式与坐姿舒适性的关系,为从人体工程学的角度优化沙发座垫设计提供科学理论依据。研究结果表明:海绵座垫下陷硬度和各层海绵的搭配形式均对坐姿舒适有较大的影响,座垫下陷硬度应从表层至底层逐渐增大。     

静态载荷下丝瓜络的能量吸收性能研究

为了深入了解丝瓜络的力学性能、能量吸收特性及其规律,对丝瓜络进行了轴向静态压缩试验,再通过拟合试验数据得到丝瓜络的单位体积的吸能量与密度的关系式。试验结果表明:丝瓜络的应力-应变曲线有3个阶段,即弹性阶段、屈服平台阶段和密实化阶段,屈服平台阶段的平台应力在0.15~0.50 MPa之间,密实化应变在70%左右,且其平台区较长,是一种理想的吸能材料;丝瓜络是一种对密度敏感的材料,其屈服强度、平台应力和单位体积的吸能量均随密度的增加而增加,密实化应变随密度增加而减小;丝瓜络单位质量的吸能量可以与泡沫铝材料相媲美。研究结果可作为设计基于丝瓜络结构的新型超轻仿生材料结构的基础数据     

Numerical investigation of compressive behaviour of luffa-filled tubes

The behaviour of luffa and luffa-filled tubes under uniaxial compression was investigated numerically using finite element analysis (FEA) and analytically by theoretical models. The FEA models were validated against experimental data. Parametric study was carried out using the validated FEA models to examine the effects of the density of luffa, the thickness to diameter ratio of tube and the cross-sectional topology of luffa core. It was found that the optimal density of the luffa as filler for the luffa-filled tubes was closely related to the optimal density of the luffa sponge. It increased with the increase of the thickness to diameter ratio of the tube. The cross-sectional topology of the filler material had a negligible effect on the specific energy absorption per unit mass even when the deformation pattern of the luffa-filled tube was changed from the diamond mode to the concertina one.     

纸木复合蜂窝材料蠕变性能研究

主要是利用四元件Burger模型对纸木复合蜂窝材料蠕变性能进行研究,其中蠕变实验采用三点弯曲的加载方式.研究结果表明:四元件模型可以用来模拟纸木复合蜂窝材料的短期蠕变行为;瞬间弹性变形和延迟弹性变形均随着应力水平的加大而加大;参数A和B、 C和D关联度大小依次为B＞D＞C,该材料的瞬时弹性变形和延迟弹性变形之间联系紧密.建议可通过单板与纸板直接胶合来提高纸木复合蜂窝复合材料的胶接性能.     

Experimental studies on ice shells in Asahikawa

An ice shell is thin, and its structural material is snow-ice. It may be an efficient form of instant shelter for snowy and cold regions. This paper describes two field studies on ice domes carried out in Asahikawa. The first one is an investigation on the creep collapse of a 5-m span model under a concentrated load acting on a circular area at the apex. Normal displacements and temperatures were measured up to the collapse. Experimental collapse time was examined, introducing the classical creep buckling value of a completely spherical shell under uniform external pressure. The second study deals with both the construction technique and the creep test of a 10-m span model. The construction technique consists of: (1) inflating a membrane bag covered with rope, (2) spraying it with snow and water, (3) solidifying the snow-ice sherbet on it, and (4) removing the bag and rope for reuse. Subsequently, a creep test was carried out under snow load, and its structural behaviour up to the collapse was examined. Based on the results of these studies, the production of 20–30-m span ice shells may be practicable.     

模压成型的杨木纤维/高密度聚乙烯复合材料蠕变性能和蠕变模型

采用长为850~2 000 μm的杨木纤维(PWF)增强高密度聚乙烯(HDPE), 利用模压成型法制备了PWF/HDPE复合材料, 对其进行了弯曲力学性能测试、无缺口简支梁冲击强度测试、24 h弯曲蠕变-24 h回复性能测试、1 000 h蠕变性能测试及蠕变后残余弯曲力学性能测试, 并利用两参数指数模型、Findley指数模型及四元件Burgers模型拟合蠕变曲线。结果表明: PWF/HDPE复合材料的弯曲强度为21.14 MPa, 弹性模量为2.31 GPa, 无缺口冲击强度为6.77 kJ/m2;24 h形变为0.803 mm, 24 h回复率为78.46%, 蠕变后弯曲强度下降了6.45%, 而弹性模量增加了8.95%;1 000 h形变为0.809 mm, 蠕变后弯曲强度保留了72.35%, 弹性模量增加了10.67%;3种模型中, 四元件Burgers模型拟合PWF/HDPE复合材料蠕变性能的效果较好。      

Elastic and plastic deformations of plaster units under uniaxial compressive stress

The suitability of plaster building units to structural application is determined not only by the strength behaviour but to a large degree also by the deformation behaviour. In plaster units under permanent load there occur elastic, retarded elastic, and plastic deformations, which primarily depend on the quality of the raw materials, on placing and hardening conditions, on the structure of the hardened material, on the stress applied, and on the moisture content. The interrelations between the deformation behaviour and the above mentioned effects were investigated and—as far as as possible—plotted and mathematically evaluated. For characterizing the building material specific values such as moduli of elasticity and creep values and the conditions for its application are given.     

Mechanical properties of functionally graded 2-D cellular structures: A finite element simulation

Functionally graded cellular structures such as bio-inspired functionally graded materials for manufacturing implants or bone replacement, are a class of materials with low densities and novel physical, mechanical, thermal, electrical and acoustic properties. A gradual increase in cell size distribution, can impart many improved properties which may not be achieved by having a uniform cellular structure.The material properties of functionally graded cellular structures as a function of density gradient have not been previously addressed within the literature. In this study, the finite element method is used to investigate the compressive uniaxial and biaxial behavior of functionally graded Voronoi structures. Furthermore, the effect of missing cell walls on its overall mechanical (elastic, plastic, and creep) properties is investigated.The finite element analysis showed that the overall effective elastic modulus and yield strength of structures increased by increasing the density gradient. However, the overall elastic modulus of functionally graded structures was more sensitive to density gradient than the overall yield strength. The study also showed that the functionally graded structures with different density gradient had similar sensitivity to random missing cell walls. Creep analysis suggested that the structures with higher density gradient had lower steady-state creep rate compared to that of structures with lower density gradient.     

Creep rupture of a phenolic-alumina particulate composite

The creep and creep rupture behaviour of a phenolic-alumina particulate composite was determined in an aqueous environment. Flexural creep tests were carried out in which the loading-point displacement was measured as a function of applied stress and time. The material exhibits power-law creep behaviour in which the steady-state creep rate is a power function of the initial applied elastic stress. The creep exponent was found to be 5.3. The creep rupture behaviour can be explained using a modified Monkman-Grant relationship which provides a failure criterion that is independent of applied stress and stress state.