热探针法测量超声场强度分布

采用热探针法测量了探头式超声设备在纯水中的一维和二维声场强度分布,探究超声强化化工过程的机理.声场强度随着轴向和径向距离的增加而衰减,并满足声场的衰减方程.由于器壁的反射,在轴向和径向产生了驻波.通过构建二维声场强度分布图,考察了超声频率、超声电功率对声场强度分布的影响,并观测了超声探头下方形成的气泡云.结果表明,不同频率下,40kHz下的声场强度高于30 kHz;同一频率下,超声电功率对声场强度的影响较小,探头下方气泡云的屏蔽作用是电功率影响较小的原因.     

沥青混凝土路面可靠性水平评价研究

基于材料的性能衰变机理,对材料的抗剪切、抗温裂、抗疲劳、抗水损强度衰减规律进行了研究,建立了强度性能衰减与保有系数分布密度函数的关系模型,并通过材料内部损伤可靠性水平和表观破损状况对该模型进行修正,实现了通过表征强度性能衰减分布规律的可靠性水平对路面状况进行评价.研究表明:当抗剪切、抗温裂可靠性水平均低于0.85,或者抗疲劳、抗水损可靠性水平均低于0.75时路面将发生剪切变形、温裂、疲劳、水损害等病害;而总可靠性水平低于0.65时,需要实施预防性养护;抗水损可靠性水平不低于0.65时进行防水处治,使得对路面进行大中修的开始时间推迟30%以上.     

循环噪声作用下周期调制双稳系统的驻留时间分布函数

提出了一种计算循环噪声作用下周期调制双稳系统驻留时间分布函数的理论方法。基于具有分段逃逸速率的两态模型理论,建立粒子逃逸的瞬时速率方程,推导得出驻留时间分布函数的递归表达式。基于此,分别计算信号振幅与循环噪声强度比值较大和较小2种不同情形下驻留时间分布函数的解析表达式。并且,从理论和数值模拟两方面分别阐明了循环噪声对驻留时间分布函数结构的影响。研究结果表明：驻留时间分布函数呈现指数衰减且在循环滞后时间处出现骤然下降趋势,且随着噪声强度和相关强度的增大驻留时间分布函数衰减速度变快,说明循环噪声能够加速粒子在势阱间的跃迁。此外,在周期信号的调制下,驻留时间分布函数在信号半周期的奇数倍处出现一系列峰值,这预示着系统发生了随机共振现象。     

再生混凝土抗压疲劳剩余强度试验研究

混凝土构件在承受循环荷载的过程中其强度不断降低,当疲劳加载至一定次数,构件此时的静载强度称为混凝土疲劳剩余强度,疲劳过程中混凝土剩余强度的衰减是结构破坏的主要原因.本文进行了普通混凝土和再生粗骨料取代率为100％的再生混凝土抗压疲劳剩余强度试验,对比分析了这两种混凝土的疲劳剩余强度衰减规律,建立了再生混凝土抗压剩余强度...     

煤体内部爆炸作用的模拟试验研究

在煤体中实施爆破作业是煤矿生产常用的技术手段,但煤体中爆炸作用机理目前尚不清楚.为研究煤体中爆炸作用情况,采用不同配比的相似材料模拟不同强度的煤体,在实验室完成了相似煤体内部的爆炸试验.利用USB超动态应变测试仪和DasView2软件测试分析了模拟煤体试件内部的动态应变波、爆炸应力波在不同强度的相似煤体中的衰减规律,通过对模拟试件切割,宏观描述了试件内部爆破产生的裂缝形成情况及其分布规律.     

浅海近程混响衰减

海底混响是主动声纳的重要背景干扰。研究混响的主要目的之一是得到混响干扰背景下主动声纳方程中的混响强度参数。应用射线声学理论研究了收发合置和分置两种情况下，倾斜海底的近程混响平均强度衰减特性；并且结合湖上实验数据的处理及分析，讨论了海水中声速分布、海底散射特性、海底倾斜角和海水中声速跃变层等因素对混响平均强度衰减特性的影响。数值计算以及实验结果表明：对浅海近程混响强度衰减规律影响最大的是海底散射特性；影响较小的是海底倾斜角。     

OCT系统中皮肤组织对光的漫反射和光能量吸收研究

针对光在高散射介质中的传播特性,研究了皮肤组织中径向漫反射强度R(r)和纵向能量吸收强度A(z).利用Matlab对高散射随机皮肤组织中光子的随机运行进行蒙特卡罗模拟计算,依次改变肌肉层参数,得到三类典型参数在不同取值时的R(r)与A(z).模拟结果表明,在其余参数不变,当吸收系数μα越大时,肌肉层中的能量衰减梯度越大,能量吸收强度的初值也越大,同时漫反射强度越小;当散射系数μs越大时,能量吸收强度的初值越大,衰减梯度也越大,漫反射强度的衰减梯度几乎相同;当各项异性因子g越大时,能量吸收强度的初值越小,即发生吸收的概率就越少,同时漫反射强度也越小;三类光学参数对R(r)影响程度相近并且较小,在半径为0.05cm范围内,漫反射强度均呈现出相类似的大梯度衰减.     

桩底灌浆在桩端周围土体中引起的应力分析

为研究桩底灌浆在桩端周围土体中引起的应力 ,基于桩底灌浆分析求得压力头梯度分布 ,采用有限元法分析了由灌浆产生的渗透力在桩端周围土体中引起的应力及其分布 .分析结果表明 ,灌浆在周围土体中引起的应力沿径向迅速衰减 ,主要作用范围集中在浆球内 .由于水泥砂或水泥砾石的刚度与强度很高 ,在研究灌浆桩的整体性能时 ,可将凝结后的浆球作为桩身的延伸部分予以考虑     

低弗汝德数水跃特性的实验研究

本文以实测资料为基础,对中低弗汝德数水跃下游的时均流速分布,紊动强度分布和沿程衰减,以及它们与河床冲刷之间的关系进行研究分析,同时对水跃的基本方程,紊动流速的测量和信号处理进行了探讨。     

等离子体对电磁波反射与吸收的统计分析

为降低反射电磁波能量和雷达的目标有效截面,用统计分析方法研究了雷达波在均匀非磁化等离子体中传播时所发生的反射、吸收与衰减;模拟了在厚度为10cm、密度在1016～1019m 3、碰撞频率在0.1～10GHz范围内的均匀等离子体中,电磁波频率在1～20GHz、服从均匀和正态2种分布情况时的反射、吸收与衰减.结果表明：对于不同电磁波频率概率分布,等离子体频率和碰撞频率对电磁波反射、吸收与衰减的影响本质相同,只是定量的差别;当电磁波频率服从不同分布时,反射系数、吸收系数与衰减量的分布不同.     

Microstructure and mechanical properties of Al-Zn-Cu-Mg-Sc-Zr alloy after retrogression and re-aging treatments

The mechanical properties and stress corrosion cracking (SCC) resistance of an Al-Zn-Cu-Mg-Sc-Zr alloy under different aging conditions were investigated. The dependence of microstructure and mechanical properties on aging parameters was evaluated by tensile test, hardness test and conductivity measurement. The results show that for the alloys with retrogression and re-aging treatment (RRA), the conductivity increases with the retrogression time and temperature, while the tensile strength decreases. The transmission electron microscopy (TEM) results show that the precipitates η(MgZn₂) at grain boundary aggregate apparently with retrogression time and the precipitates inside the matrix exhibit the similar distribution to T6 temper, which comprises fine GP zones, large η′(MgZn₂) and η(MgZn₂) phases. According to the mechanical properties and microstructure observations, the optimal RRA regime is recommended to be 120 °C, 24 h + 180 °C, 30 min + 120 °C, 24 h. The strength level of the alloy after the optimum RRA treatment is similar to that in T6 condition and the SCC resistance is improved obviously in contrast to T6 condition.     

Preliminary Investigation of Copper Joints Soldered with Sn58Bi

In recent years, intensive studies have been carried out to find an alternative for Tin (Sn)-Lead (Pb) solder alloys with increasing demand over lower temperature solder alloys in current electronic packaging industry. High temperature operational solder alloys seem to produce drawback to other components on the printed circuit board (PCB). Low melting temperature Sn58Bi substrate as a potential replacement was investigated in this paper based on the melting properties, wettability, and shear strength. The Sn58Bi was soldered at a temperature below 200 ℃ on the Cu substrate, and the shear strength and contact angle were calculated. A peak temperature (melting temperature, TM) of 144.83 ℃ was identified. Single lap joint method was performed at a strain rate of 0.1 mm/min and an average shear strength of 23.4 MPa was found from three samples. The contact angle (wettability) was calculated to study the solder joint behaviour at reflow temperature of 170 ℃. The contact angle of the Sn58Bi was found to be 32.4 ° and considered to be desired value since the angle is less than 50 °. The low temperature soldering provides a preliminary result to allow further application on the real PCB.     

Structure and properties of an ultra-high strength 7xxx aluminum alloy contained Sc and Zr

An ultra-high strength aluminum alloy was produced by casting and then extruded to rods.The effect of heat treatment on the microstructure and mechanical properties of the alloy was investigated.After single ageing(120℃,24 h),the tensile strength was 812.4 MPa and the elongation was 6.2%.After retrogression reaging(RRA),the tensile strength was 751.2 MPa and the elongation was 6.4%.The strengthening mechanism is considered as fine grain strengthening,substructure strengthening and dispersion strengthening by Al_3(Sc,Zr).     

Effect of Aging on Fracture Toughness and Stress Corrosion Cracking Resistance of Forged 7475 Aluminum Alloy

The effects of two-stage aging and retrogression and reaging heat treatment on the fracture toughness and stress corrosion cracking resistance of 7475 alloy were studied. The fracture toughness, conductivity and strength of samples of nine groups under duplex aging conditions and three retrogression and reaging heat treatments were also measured. Incorporating the microstructure and property, we found that when the condition of the first order aging kept identical, the fracture toughness and stress corrosion cracking resistance increase with aging time and the second aging temperature. The optimal treatment conditions are （ 115℃×7h ＋ 185 ℃×13h） among all tested two-stage aging treatments. Although the 7475 alloy treated by RRA method shows the highest strength and its stress corrosion cracking resistance after twenty minutes retrogression can also reach the same level as those by the optimal treatment of （115℃×7h＋ 185℃×13h ）, the fracture toughness is even low.     

棉籽壳振动分离筛振动连板断裂事故分析

从振动力学和机械强度角度对棉籽壳振动分离筛连板断裂现象提出运动模型,并进行了分析计算,提出了相应的解决措施.     

独立职业监事制度初探

独立职业监事,是指和公司主要股东、董事会、经理层以及公司本身没有重大利害关系,依法律和合同独立履行公司监督职责的专业职业人员.在我国股份公司的监事会中引入独立职业监事,建立独立职业监事制度,是增进监事会独立性,提升监事会监控能力,适应股份公司尤其是上市公司资本社会化的需要.独立职业监事的选任应采取同业竞争的机制,由股东大会择优选择独立职业监事事务所,再由入选的独立职业监事事务所指派其成员出任该股份公司的监事.这样,独立职业监事的激励机制和约束机制都将十分有效.     

柱下钢筋砼独立基础的抗剪设计问题

本文论述了板式基本的三种破坏模式及抗剪设计方法,明确提出了板式基础的抗剪强度验算是设计中的一个不容忽视的问题。     

覆铜箔用高吸水性纸制造工艺的研究

研究了影响覆铜箔原纸吸水高度的主要因素以及原纸吸水高度与抗张强度、厚度、打浆度的关系及添加助剂对覆铜箔原纸性能的影响，由此确定出生产覆铜箔原纸最佳的纤维原料组成及制浆工艺和抄造条件。     

板级电子封装跌落／冲击中焊点应力分析

建立了板级BGA封装跌落/冲击问题的三维有限元模型,采用Input-G方法对PCB板的变形及焊锡接点应力等动力学响应进行了分析,探讨了约束条件对计算结果的影响,对焊点剥离应力产生的机理进行了讨论,提出了快速估算焊点应力的等效静力学模型并分析了误差.结果表明,模型中PCB板固定螺栓处的约束条件处理对结果有较大影响,合理的处理方法是在PCB板4个螺栓作用区的上下表面均施加水平方向位移约束.焊点应力最大值出现在冲击后0.4 ms,最大剥离应力发生在角部焊点与PCB板一侧的铜垫交界处.焊点应力与PCB板的弯曲变形密切相关,应力峰值和PCB板的变形峰值在时间上具有同步性.挠度等效静力学模型得到的焊点应力比动力学模型高23%左右.     

Hydration Characteristics and Humidity Control Performance of Calcium Silicate Board Prepared from Mine Tailing and Diatomite

The feasibility of utilizing molybdenum tailing and diatomite as siliceous materials to prepare calcium silicate board was explored. The influences of molybdenum tailing/diatomite proportion on hydration characteristics, thermal conductivity, water absorption, flexural strength and moisture adsorption-desorption property of calcium silicate board were investigated in detail. The experimental results reveal that molybdenum tailing is environmentally friendly to prepare building materials. The main hydration products in calcium silicate board under autoclaved condition are C-S-H with low crystallinity and tobermorite. Molybdenum tailing is favorable to the formation of tobermorite. The flexural strength and bulk density of the calcium silicate board gradually increase when the content of molybdenum tailing increases. Netlike C-S-H is formed with the increase of diatomite content during autoclaved curing process, resulting in the enhancement of moisture adsorptiondesorption performance and the reduction of thermal conductivity. The optimal content of molybdenum tailing is 20%, furthermore, the flexual strength and thermal conductivity of calcium silicate board at this content meet the Chinese standard JC/T564.1-2008.