高密度聚乙烯材料的注塑自增强工艺研究

本工作研究了在注塑机上进行体型聚乙烯试样的自增强成型工艺,探讨了自增强效果与注塑工艺之间的关系。 试验材料的自增强效果强烈地依赖于熔体的流动条件。在一个低熔体温度的范围内,发现有一个对应最大自增强效果的注塑温度。自增强效果随注塑压力的升高而增强。注塑速度和模具温度对自增强效果的影响很小。在其他可以类比的工艺条件下,试样的力学性能依试样形状的不同,表现出极不同的结果。  

Investigation of the Young's modulus of TiB needles in situ produced in titanium matrix composite

In situ Ti/TiB composites with different volume fractions of discontinuous TiB reinforcements were produced by powder metallurgy. After compacting Ti+TiB₂ powders by hot unidirectional pressure, heat treatments led to the in situ formation of distinctive needles of TiB, randomly distributed in the titanium matrix. The Young's modulus of TiB was evaluated using the ASW computation method and experimental Vickers micro-indentation. Three point bend tests were performed on Ti/TiB composites as a function of the TiB volume fraction in order to extract the Young's modulus of TiB from the elastic properties of the composite. The different values obtained according to these three methods were discussed and compared with the literature.  

Mechanical properties of carbon nanotube by molecular dynamics simulation

The mechanical properties of single-walled carbon nanotube (SWCNT) are computed and simulated by using molecular dynamics (MD) in this paper. From the MD simulation for an armchair SWCNT whose diameter is 1.2 nm and length is 4.7 nm, we get that its Young modulus is 3.62 TPa, and tensile strength is 9.6 GPa. It is shown that the Young modulus and tensile strength of armchair SWCNTs are 12 order higher than those of ordinary metal materials. Therefore we can draw a conclusion that carbon nanotubes (CNT) belong to a particular material with excellent mechanical properties.  

火灾场冲击波荷载作用下简支钢梁动力响应

根据火灾场不同时刻温度的变化,考虑火灾高温对结构钢弹性模量、屈服强度和钢梁塑性弯矩的影响,分析了火灾场中冲击波荷载作用下简支钢梁各个阶段不同时刻的动力响应,通过具体算例计算了火灾场工字形简支钢梁在冲击波荷载作用下弹性阶段和塑性阶段的变形,分析表明在计算火灾场冲击波荷载作用下简支钢梁的动力响应时,火灾高温对结构钢的弹性模量、屈服强度以及梁的塑性弯矩和动力响应有显著的影响。  

轻微界面反应对SiCP/6061Al复合材料弹性模量的影响

本文首次提出控制压铸SiC_P/6061Al 复合材料中轻微界面反应的方法, 并就反应的机理及其对材料弹性模量的影响规律和机制进行了研究。结果表明: 界面反应物为离散分布的小颗粒状MgAl₂O₄, 反应中氧的主要来源为原始态SiC 颗粒表面残留的SiO₂薄层; 该种反应物的存在有利于材料弹性模量的提高。  

研究单壁碳纳米管杨氏模量的一种能量方法

本文利用能量方法研究了单壁碳纳米管(single-walled carbon nanotubes, SWCNT)的杨氏模量.文中,首先采用分子力学理论得出了受轴向载荷作用下单壁碳纳米管的总势能;然后通过总势能与相应薄圆柱壳的应变能比较,推导出了单壁碳纳米管杨氏模量的计算公式.另外,从一系列碳纳米管杨氏模量的计算发现,本文研究结果与现有研究结果比较一致.  

Nanoindentation mapping of mechanical properties of cement paste and natural rocks

This paper reports a study to assess nanoindentation mapping of mechanical properties of cement paste and natural rocks. Initial work seems to show that mechanical property mapping by nanoindentation is feasible and can be related to microscopic information. Further work is however required on the effect of indent size and spacing. Such a testing technique can be very useful for materials with different phases to study the intrinsic properties of each component, and also the interaction and properties of the interfacial regions of different phases. The values of Young's modulus and hardness of the individual mineral phases were also determined by statistically analysing a large number of experimental data.  

Mechanical spectroscopy of polymer-magnetite composites

Mechanical properties of magnetite (Fe₃O₄) filled polypropylene (PP) prepared in an extrusion and injection molding process were investigated. Various grades of magnetite were used. Mechanical spectroscopy was performed in a temperature range from 173 to 428 K with frequencies from 10⁻¹ to 10² Hz, and the crystallinity of test samples was estimated. Damping spectra show an peak of the principal relaxation (285 K) at the glass transition temperature, a relaxation β-peak (220 K) attributed to local motions in the amorphous phase and an ′-peak (365 K) attributed to the relaxation in crystalline parts of the polymer. These peaks correspond to drops of the storage modulus.

The -peak is decreased by the extrusion process while the ′-peak is increased compared to not extruded PP. At high temperatures a drastic increase of the loss factor superposes the ′-peak for higher filler loadings. The crystallinity of the polymer matrices varies between 25 and 37%. At low temperatures the storage modulus increases with an increase in the magnetite fraction. The used particle size distributions show no significant influences on the storage moduli for temperatures from 173 to 285 K, whereas for temperatures above 285 K smaller mean particle sizes lead to higher storage moduli and lower loss factors.  

小直径环状试样静态杨氏模量测试仪的研制

介绍了微小试样材料弹性模量测试仪的组成概况(硬件及软件)。对测试仪做了标定、校核工作。利用该仪器实测了高温气冷堆包覆燃料颗粒SiC层(直径<1mm)的弹性模量。测试仪精度为:力:0-0.2N,+0.005N 位移:0.60μm,±0.5μm