反对称矩阵的外在美和内在美的教学呈示

关于对称矩阵的美韵,笔者已经撰文做过研究,而反对称矩阵的美韵并不亚于对称矩阵。本文对反对称矩阵之美亦从“内”与“外”进行分析和探索。     

Fatigue crack growth resistance of SiC<Subscript>p</Subscript> reinforced Al alloys: Effects of particle size,particle volume fraction,and matrix strength

The main aim of this work was to study the effects of particle size, particle volume fraction, and matrix strength on the long fatigue crack growth resistance of two different grades of Al alloys (Al2124-T1 and Al6061-T1) reinforced with SiC particles. Basically, it was found that an increase in particle volume fraction and particle size increases the fatigue crack growth resistance at near threshold and Paris regimen, with matrix strength having a smaller effect. Near final failure, the stronger and more brittle composites are affected more by static modes of failure as the applied maximum stress intensity factor (K _max) approaches mode I plane strain fracture toughness (K _IC).     

Thixoforging of continuous fiber-reinforced AlSi/AlMg-alloys

High strength in combination with low density is the key features for lightweight constructions in automotive and aerospace applications. Tailor-made fiber reinforcements in light-metal matrices could help to achieve this goal. However, the integration of fibers with conventional casting-route manufacturing techniques like squeeze casting or diffusion bonding restricts the component geometry and results in elevated process cost due to long cycle times and the need of additional fiber coatings. In the center of competence for casting and thixoforging Stuttgart (CCT), new processes for manufacturing metal matrix composites are developed. Long-fiber reinforced Al–Si alloys and components are produced by thixoforging of laminates made of alternating metal matrix layers and carbon fiber fabrics. This paper illustrates the manufacturing technology and first experimental results with special focus on fiber penetration and infiltration behavior and also on the formation of fiber-matrix interface to analyze fiber damage by mechanical or chemical attack.     

一种新型针状合金-金刚石复合钻头胎体配方的试验研究

本文首先介绍一种用于卵砾石地层钻进的新型针状硬质合金钻头的设计原理，而后简要说明其胎体配方组成机理。在分析胎体性能要求的基础上，选择了六组配方，对其进行抗弯强度、抗剪强度，硬度性能、冲击韧性、SEM照片等试验，优选了四号配方，试制了钻头。生产试验结果表明，这种新型复合型钻头钻进萝日砾石地层的平均时效1．89m／h、平均每回次进尺为2．3m，平均钻头寿命19．81m，具有实用和推广价值。     

复合材料凝固过程中的颗粒/界面行为数学模型

根据颗粒增强金属基复合材料凝固过程中的颗粒 /界面作用微观机理 ,导出颗粒附近温度场 ,液 /固界面形状 ,颗粒受力情况及颗粒吞并 /推移临界条件数学模型。分析了热导率、颗粒尺寸和凝固速度不同对颗粒 /界面行为的影响。     

粉末冶金法制备SiC晶须增强MB15镁基复合材料

采用粉末冶金法制备了SiC晶须增强镁基复合材料(SiCW／MB15)试样。通过检测基体显微硬度探讨了SiCW对镁合金时效规律的影响，并借助扫描电镜(SEM)、透射电镜(TEM)和拉伸试验，研究了混粉方式对复合材料室温力学性能、SiCW分布及显微结构的影响。结果表明，MB15及其复合材料的时效硬化曲线上均存在双峰现象；SiCW的加入既提高了MB5的硬度，又加快了其时效速度：混粉方式对晶须分布及SiCW／MB15复合材料的室温力学性能影响很大。     

原位生成Al2O3、TiB2和Al3Ti/Al复合材料的热循环行为

本文研究了Al-TiO2-B系原位生成Al2O3、TiB2和Al3Ti/Al颗粒增强铝基复合材料的热循环行为，研究结果表明了纯铝及B／TiO2摩尔比分别为0、1和2的颗粒增强铝基复合材料的热循环行为具有以下结果，纯铝和复合材料热循环后均产生了残余应变和滞后环；Al-TiO2-B系列复合材料热循环应变的各项指标均比纯铝基体大大降低，且具有较小的内耗功和较好的热稳定性，可以预测其具有较高的热疲劳寿命，热循环曲线能很好的评估复合材料在温度循环变化的环境中工作时的热稳定性和热疲劳。     

Influence of the composition of the binder and the carbonation on the zeta potential values of hardened cementitious materials

Electroosmotic experiments have been carried out on eight different mixes of hardened cementitious matrixes including concrete, mortar and pastes, different types of binders, carbonated and non-carbonated specimens and different test conditions. From these trials, the zeta potential values have been determined and the optimum experimental parameters and devices have been established. In addition, the influence of the composition of the binder on the zeta potential has been quantified indicating that higher amounts of Al₂O₃ in the binder lead to higher positive values of zeta potential, while the SiO₂ acts just on the opposite side. This has been explained in terms of the different i.e.p. (isoelectric point) for both oxides. Concerning the influence of carbonation, it increases the absolute value of the zeta potential toward more negative values; this behaviour has been attributed to the influence of the specifically adsorbed Ca²⁺ in the negative sites of the surface in the non-carbonated samples.     

催化无基体法制备碳纳米管

用一种新的催化裂解法 ,制备出了直径在 2 0～ 30nm ,长度为 2 0 0 μm的碳纳米管。在此方法中 ,繁琐的催化剂制备工艺被省略 ,催化剂前驱体在载气带动下直接进入反应器。另外还发现两类结构独特的碳纳米管。     

用弯曲模型推导二组元复合材料杨氏模量新公式

用弯曲模型推导了适用于悬丝耦合弯曲共振法检测金属第二组元的杨氏模量的理论公式。通过实验数据计算。结果表明在两组元h2/h1≈1时与文献[2]的计算结果几乎接近，为用悬丝耦合弯曲共振法检测各种减振材料，陶瓷材料杨氏模量提供了理论公式；同时用改进后的弯曲模型推导出了适用于纤维复合材料横向杨氏模量的预测公式。