[±θ/902]碳/环氧层板横向裂缝与分层的测试及分析

本工作对[±θ/90₂]_S和[0_n/90₂]_S两系列碳/环氧层板在拉仲载荷下的横向裂缝与分层损伤,进行了实验研究和有限元分析.采用声发射技术跟踪配合显微观测多向层板损伤过程,分析了θ角变化与力学性能、初始损伤、累积等的关系.表明实测横向开裂与分层结果和采用能量判据有限元计算预测比较,符合良好.同时在扫描电镜内进行各类层板压缩试验,动态观测破坏形貌,讨论了不同θ铺层角的微观破坏机理.     

复合材料层板损伤过程的刚度分析

本文对典型铺设的[0₂/±45₂/90₂]_s碳/环氧复合材料层板中的典型损伤状态进行了实验观察,测定出损伤对层板刚度引起的下降率.建立了横向裂纹扩展、分层伴以横向裂纹扩展的三维有限元分析模型,计算出对层板刚度引起的下降率,并与实验值进行了比较.结果表明,横向裂纹和分层是层板的主要损伤型式,分层损伤扩展是一个主导性的稳定的损伤扩展过程,是导致刚度下降的主要因素.     

复合材料层板+θ/-θ层间断裂韧性研究

本文讨论了纤维增强复合材料层板沿+θ/-θ层间断裂韧性的研究方法;提出在满足一定力学条件时,可沿用机械载荷实验方法测得G_C中“纯机械部分”G_m;结合数值方法计算得出“纯温度部分”G_T,从而得到G_C.给出一个针对DCB试验的充分条件,据此设计铺层并对T300/648和T300/QY8911进行试验和分析(θ=0～30°)、讨论了大变形的影响并提出一个新的修正系数.结合θ对G_C的影响及断口微观形貌作了进一步讨论.     

碳-铝正交层板疲劳行为研究

本研究用真空热压法制备了两种铺层的C/AI正交层板(0/90/0)_s及(90/0/90)_s.在MTS NEW810上进行了一系列疲劳损伤及破坏试验.疲劳损伤的行为研究工作包括:以刚度下降为损伤参数对C/AI正交层板进行了降级应力分析,并由此来预计在△S_h以下,正交层板不会发生疲劳损伤累积.研究了C/Al正交层板在同一应力水平而不同应力范围作用下的疲劳响应,发现试样在疲劳损伤时其刚度下降值相近似,即疲劳破坏的门槛值依赖于所施加的应力水平.依据MMC对各种循环载荷的不同响应,基体的疲劳损伤状态在S-N平面上可分为三种不同的区域:无损伤区,损伤累积区和断裂区.利用扫描电镜及金相显微镜分别对其疲劳断口形貌、基体裂纹进行观察,对该正交层板的疲劳破坏行为进行分析及讨论.结果表明:C/Al正交层板的疲劳断口呈脆断型,其中主承力层(0°铺层)断口平齐,偏轴层(90°铺层)断口平齐最差,层间损伤形式有局部分层、界面连续开裂及复合丝之间基体开裂等三种形式;其疲劳破坏主导因素是层间局部严重损伤及主承力层中复合丝大量断裂由于其疲劳裂纹沿垂直于载荷方向迅速扩展,寻找适中的界面结合强度对改善C/Al层板的疲劳性能有很大影响.     

PP/PET原位成纤复合材料的增强效应

用挤出-拉伸-注塑法制得了PP/PET原位成纤增强复合材料,以不拉伸的普通共混材料作对照,研究了PET质量含量(C_m)对PET成纤性和材料拉伸强度(σ_t)及模量(E)的影响及其作用机制。结果表明,C_m由0增至20%时,PET纤维数量增多,纤维直径及其分散性以C_m=15%为界先减少后增大;材料的σ_t、E在C_m=15%时有最大值,分别比纯PP提高约20%和70%。熔体拉伸时分散相液滴的聚结-形变成纤对PET相形态随C_m的变化起关键作用,分散相对基体增强效应与两相界面缺陷效应的相互竞争,纤维对基体增刚作用受纤维数量和细度的双重控制,分别是决定材料σ_t~C_m、E~C_m关系的支配因素。     

环氧玻璃钢层合板冲击破坏及其断口微观特征的研究

S-GF/Ep648复合材料层合板[0₉°/θ]_s冲击抗力试验的结果表明其冲击抗力值与铺层角θ无关,只受浸水时间的影响;而另一种铺层形式[+θ₈/-θ₈]的复合材料层合板,在落重冲击试验中却发现:在相同的冲击能量下,θ越大,分层破坏越严重,损伤区面积也越大。利用SEM-505扫描电子显微镜对发生穿透性断裂、层间分层断裂或仅出现冲击损伤等破坏形式的断口表面进行了观察和分析,讨论了影响该复合材料冲击断裂和冲击损伤性能的因素。     

各向异性损伤理论与复合材料层板损伤测量的实验研究(二)-复合材料层板损伤测量的实验研究

鉴于传统的断裂力学无法用于受损复合材料层板,本文探索了损伤力学在复合材料层板中的应用.文内介绍了复合材料层板损伤试验的概况及损伤测试方法,文中三种层板单向拉伸损伤试验结果的分析表明在单向拉伸载荷下基于J.Lemaitre应变等效性假设的损伤能释放率Y₂可用于描述受损复合材料层板的力学状态,它的演变方程通常可用Y₂=α(σ/σ_c)β的简单函数形式来描述.对特定的层板,α、β是与初始缺陷无关的常数,可由层板损伤试验确定.试验数据表明在单向拉伸载荷下,临界损伤能释放率对特定的层板也是与初始缺陷无关的常数,反应了材料抗损伤扩展的能力.所有这些结论都为进一步建立完整损伤破坏判据奠定了基础.     

500kV变电站厂界低频噪声控制指标适用性调查分析

随着电网设施的发展,变电站的低频噪声问题越来越受到关注。为分析500 kV变电站厂界低频噪声控制指标的适用性,基于实测数据对9座变电站厂界低频噪声进行了分析,并选取2座变电站分别对其实体围墙上下方和主变附近采取降噪措施前后的厂界噪声进行了比较。结果表明,变电站厂界低频噪声在中心频率为100 Hz的1/3倍频带上的峰值最为明显。厂界低频噪声样本低频段声能量比例θ_low和L_Ceq-L_Aeq平均值分别为87.2%和11.0 dB,并且呈现出L_Aeq较低的声样本的θ_low和L_Ceq-L_Aeq却较大的规律。围墙下方的厂界噪声L_Aeq和L_{100 Hz}通常小于围墙上方,但θ_low和L_Ceq-L_Aeq却可能更大。通过主变附近采取降噪措施使厂界噪声L_Aeq和L_{100 Hz}得到有效控制的情况下,θ_low和L_Ceq-L_Aeq也可能比原来更大。可见,直接引入θ_low和L_Ceq-L_Aeq指标来评价变电站厂界低频噪声存在一定缺陷。分析结果可为变电站厂界低频噪声排放控制指标选取和限值确定提供参考。     

SiC fibre by chemical vapour deposition on tungsten filament

A CVD system for the production of continuous SiC fibre was set up. The process of SiC coating on 19 μ m diameter tungsten substrate was studied. Methyl trichloro silane (CH₃SiCl₃) and hydrogen reactants were used. Effect of substrate temperature (1300–1500°C) and concentration of reactants on the formation of SiC coating were studied. SiC coatings of negligible thickness were formed at very low flow rates of hydrogen (5 × 10⁻⁵ m³/min) and CH₃SiCl₃ (1.0 × 10⁻⁴ m³/min of Ar). Uneven coatings and brittle fibres were formed atvery high concentrations of CH₃SiCl₃ (6 × 10⁻⁴ m³/min of Ar). The flow rates of CH₃SiCl₃ and hydrogen were adjusted to get SiC fibre with smooth surface. The structure and morphology of SiC fibres were evaluated.     

聚乙烯/ 石墨纳米复合材料的制备、结构和导电性

用溶液插层(SI ) 和母料熔体混合(MMM ) 方法制备了聚乙烯(PE ) / 马来酸酐接枝聚乙烯(gPE ) / 膨胀石墨(EG) 导电纳米复合材料, 以直接熔体混合(DMM ) 法制备的PE/ gPE/ EG、PE/ EG复合材料作对照, 通过电导率(σ) 测试, TEM、SEM、OM 观察和DSC 分析, 研究了制备方法、EG体积或质量分数( ? 或f_m ) 和gPE质量含量( C_g ) 对复合材料结构和σ的影响。结果表明, SI、MMM、DMM 法制备的C_g/ f_m = 115 复合材料和PE/ EG对照材料的逾渗阈值?_c 分别为2.19 %、3.81 %、4.68 %和5.35 %;当C_g/ f_m 由1 增至4 时, MMM、DMM 法制备的f_m = 9 %复合材料的σ分别跃升12 和8 个数量级;产生这些差异和现象的原因, 可根据复合材料中EG分散相形态和内部微结构随制备方法、?和C_g/ f_m 的变化, 按逾渗理论来解释。     

Stiffness of reinforced concrete slabs subjected to torsion

The study of torsion in reinforced concrete members began in the early twentieth century but it has become more widespread in the past 60 years. Even today, this topic has not been deeply researched with respect to slabs. This work reports a study on the behavior of reinforced concrete slabs subjected to torsion, with particular attention to the stiffness in state I and state II (uncracked and cracked phase) and to the relation T–θ (torsional moment-twist). It is known that torsional forces lead to a much larger loss of stiffness in state II, due to the strong cracking, than the loss of flexural stiffness. When the member is predominantly subjected to bending moments the K _I/K _II ≈ 3–5 is usually admitted, but when torsion has a preponderant role this relationship is not valid. This study may alert the scientific community to a seemingly unknown relation: torsional stiffness of reinforced concrete slabs, in the cracked phase, is about 1/17–1/15 of the stiffness in the elastic phase. For the analysis of slab deformation, particularly under service conditions, accurate knowledge of the slab stiffness in state II is important. The knowledge of T–θ relation is also important to perform a numerical nonlinear analysis. An experimental program was designed and carried out in which 9 slabs were tested until failure. To submit the slabs predominantly to torsional moments, vertical movement at 3 corners was restricted and the action was applied to the fourth corner. Based on the results obtained, the following relations were defined: load–displacement (P–d), torsional moment-twist (T–θ) and K _T,I/K _T,II.     

高速铁路桥上有砟-无砟轨道过渡段动力学研究

基于京沪高速铁路特大桥上的有砟轨道与CRTS II型板式无砟轨道之间的过渡段实例,建立了车辆-轨道耦合动力学有限元计算模型,通过不同结构处理措施对有砟-无砟轨道过渡段动力学特性的影响研究,研究表明：当有砟轨道轨下胶垫刚度为55～75MN/m,无砟轨道轨下胶垫刚度为20～30MN/m时,有砟轨道的整体刚度大于无砟轨道;当有砟轨道轨下胶垫刚度为55～75MN/m,无砟轨道轨下胶垫刚度为40～50MN/m时,无砟轨道整体刚度与有砟轨道大体相当;过渡段枕、宽枕等不宜在有砟轨道刚度大于无砟轨道时使用;采用道砟胶结后提高了道床的整体性及过渡段轨道结构的稳定性,但增加了轨道刚度,应同时降低轨下胶垫刚度,以减小轮轨力;辅助轨只是增加了轨道结构的稳定性,对轨道刚度影响较小。     

Stiffness and fracture analysis of laminated composites with off-axis ply matrix cracking

Matrix cracks parallel to the fibres in the off-axis plies is the first intralaminar damage mode observed in laminated composites subjected to static or fatigue in-plane tensile loading. They reduce laminate stiffness and strength and trigger development of other damage modes, such as delaminations. This paper is concerned with theoretical modelling of unbalanced symmetric laminates with off-axis ply cracks. Closed-form analytical expressions are derived for Mode I, Mode II and the total strain energy release rates associated with off-axis ply cracking in [0/θ]_s laminates. Stiffness reduction due to matrix cracking is also predicted analytically using the Equivalent Constraint Model (ECM) of the damaged laminate. Dependence of the degraded stiffness properties and strain energy release rates on the crack density and ply orientation angle is examined for glass/epoxy and carbon/epoxy laminates. Suitability of a mixed mode fracture criterion to predict the cracking onset strain is also discussed.     

双层轻板墙隔声量予计中对钢龙骨刚度的确定

钢龙骨双层轻板墙的墙体隔声量（R）比木龙骨的墙体有明显提高,其主要原因在于轻钢龙骨的侧向弹性减少了双层墙板之间的声耦合。作者在早年推导这类双层墙隔声量（R）预计公式时,引入了轻钢龙骨侧向等效刚度的参量,隔声量的预计结果与实验值相当符合。20多年来不断受到有关方面关注和引证,但无实质性进展。目前龙骨侧向等效刚度参量仍采用以隔声试验的结果来推算,尚不能直接由实验方法测定。近年有人尝试采用测试浮筑地板下面弹性材料的动态刚度的方法来测定弹性龙骨的动态刚度,结果偏差很大,显然不妥。提出在实验技术上能作进一步研究。     

再议钢龙骨刚度对薄板间壁隔声的影响

轻钢龙骨在双层薄板间壁隔声中起着固体声传递作用,它较之经由空腔的空气声传递复杂得多,对间壁的中频隔声更为重要。自上世纪80年代该文作者提出以轻钢龙骨侧向刚度作为预计间壁隔声的参量以来,许多研究工作者在这方面积累了不少理论分析和实验资料,使得龙骨刚度对间壁隔声的影响有了更多认识。文章对此作了评述,并指出双层间壁中间联系构件(钢龙骨)的力学特性这一关键性参量该如何确定,还需作进一步探索。     

Retention mechanisms in reversed-phase liquid chromatography. Stationary-phase bonding density and partitioning

The partitioning model of retention for reversed-phase liquid chromatography, described by mean-field statistical thermodynamic theory, asserts that one principal driving force for solute retention is the creation of a solute-sized cavity in the stationary phase. Beyond a critical stationary phase bonding density, increased grafted chain density should result in enhanced chain ordering, which will increase the energy necessary for solute cavity formation and result in decreased chromatographic partition coefficients. We have evaluated chromatographic partition coefficients over an octadecyl bonding density range of 1.6-4.1 mumol/m2 and have found a maximum in partition coefficient at approximately 3.1 mumol/m2. Retention, however, approximately plateaus due to compensating changes in the partition coefficient and stationary phase volume. This provides unequivocal evidence that partitioning is the dominant form of retention for small nonpolar solutes.     

地铁上盖层间隔震建筑设计研究

层间隔震技术是提升地铁上盖结构抗震性能的有效措施。为识别影响该类结构关键设计指标的控制因素,从而指导该类结构的精细设计,依托一大底盘-双塔楼地铁上盖层间隔震工程案例,考虑了3种塔楼方案和4种隔震层方案,设计了12个分析案例。基于精细模型分析了塔楼、隔震层和大底盘相对刚度比和隔震层屈重比对9个关键设计指标的影响规律,包括塔楼和大底盘的中震减震系数、大震最大层间位移角和楼面绝对加速度,以及隔震层的大震位移、极大面压和极小面压,识别了影响各设计指标的关键影响因素。结果表明:对于塔楼,减震系数和楼面最大绝对加速度的控制因素是隔震层刚度和屈重比,减小两者可以取得更好的控制效果,增大塔楼刚度也会存在一定的控制效果,但相对有限;增大塔楼刚度和减小隔震层刚度及屈重比可以一定程度控制塔楼最大层间位移角,当两者达到一定程度后控制效果均趋于稳定。对于大底盘,塔楼和隔震层对其设计指标影响相对较小。对于隔震层,隔震层刚度及屈重比是大震隔震层位移的主要控制因素,其减小会显著增大该位移;塔楼刚度是极大面压的控制性因素,刚度的增大会带来重力的增大,从而带来极大面压的增大;增大塔楼刚度和减小隔震层刚度均可显著控制支座中的拉应力,其中塔楼刚度的增大效果更为突出。该研究的相关成果可为地铁上盖层间隔震建筑的抗震性能控制和设计提供参考。     

Isotherm and kinetic behavior of adsorption of anion polyacrylamide (APAM) from aqueous solution using two kinds of PVDF UF membranes

To determine the isotherm parameters and kinetic parameters of adsorption of anion polyacrylamide (APAM) from aqueous solution on PVDF ultrafiltration membrane (PM) and modified PVDF ultrafiltration membrane (MPM) is important in understanding the adsorption mechanism of ultrafiltration processes. Effect of variables including adsorption time, initial solution concentration, and temperature were investigated. The Redlich-Peterson equation of the five different isotherm models we chose was the most fitted model, and the R(2) was 0.9487, 0.9765 for PM and MPM, respectively; while, the pseudo-first-order model was the best choice among all the four kinetic models to describe the adsorption behavior of APAM onto membranes, suggesting that the adsorption mechanism was a chemical and physical combined adsorption on heterogeneous surface. The thermodynamic parameters were also calculated from the temperature dependence (Δ(r)G(m)(θ), Δ(r)H(m)(θ), Δ(r)S(m)(θ)), which showed that the process of adsorption is not spontaneous but endothermic process and high temperature favors the adsorption.     

Interactions of vitamin K3 with herring-sperm DNA using spectroscopy and electrochemistry

By means of ultraviolet-visible (UV-Vis) and fluorescence spectra, the binding ratio between vitamin K(3) and herring-sperm DNA in a physiological pH environment (pH = 7.40) was determined as n(K3):n(DNA) = 2:1, and the binding constants of vitamin K(3) binding to DNA at different temperatures were determined as K(θ)(298K) = 1.28 × 10(5) L·mol(-1) and K(θ)(310K) = 7.19 × 10(4) L·mol(-1), which were confirmed using the double reciprocal method are Δ(r)H(m)(θ) = -3.57 × 10(4) J·mol(-1), Δ(r)G(m)(θ) = -2.92 × 10(4) J·mol(-1), and Δ(r)S(m)(θ) = 217.67 J·mol(-1)K(-1). The driving power of this process was enthalpy. An intercalation binding of the vitamin K(3) with DNA was supported by a competitive experiment using acridine orange (AO) as a spectral probe. By combination analysis of the Scatchard method and cyclic voltammetry, we suggested that the interaction mode between vitamin K(3) and herring-sperm DNA would be a mixed mode. The quinonoid, duality fused-ring of vitamin K(3) can intercalate into the base pairs of DNA, and there is an electrostatic binding along with intercalation binding.     

Features of the Nyström Method for the Sherman-Lauricella Equation on Piecewise Smooth Contours

The stability of the Nyström method for the Sherman-Lauricella equation on contours with corner points $c_j$ , $j = 0, 1,··· , m$ relies on the invertibility of certain operators $A_{c_j}$ belonging to an algebra of Toeplitz operators. The operators $A_{c_j}$ do not depend on the shape of the contour, but on the opening angle $θ_j$ of the corresponding corner $c_j$ and on parameters of the approximation method mentioned. They have a complicated structure and there is no analytic tool to verify their invertibility. To study this problem, the original Nyström method is applied to the Sherman-Lauricella equation on a special model contour that has only one corner point with varying opening angle $θ_j$ . In the interval ($0.1π$, $1.9π$), it is found that there are 8 values of $θ_j$ where the invertibility of the operator $A_{c_j}$ may fail, so the corresponding original Nyström method on any contour with corner points of such magnitude cannot be stable and requires modification.