开孔CFRP复合材料层合板的损伤解析和实验探究

采用解析计算和拉伸试验相结合的方法,对开孔CFRP复合材料板的孔边应力和损伤进行了研究。基于复变函数方法并结合Tsai-Hill失效准则,计算得到了层合板各单层的主应力分布和首次损伤载荷系数。为了测定层合板面内拉伸性能并对解析结果进行验证,基于ASTM D5766-07试验标准对CFRP层合板进行了拉伸试验。研究结果表明:当开孔CFRP层合板承受沿长轴方向拉伸载荷时,0°和±45°铺层为主承力层,且主应力σ1最大值出现在与孔中心成65°～115°和245°～295°范围内;各层最小首次损伤载荷系数出现在65°～115°范围内,其中,45°层和-45°层的损伤载荷系数最小;当载荷达到初始损伤载荷时,层合板开始出现内部损伤和参数退化;拉伸试验后CFRP复合材料板试件损伤的形式主要为基体开裂和纤维断裂,损伤的区域在孔周边61°～90°和241°～270°范围内,试验结果与解析计算结果基本一致。     

(±45°/90°/0°)_s准各向同性层合板的拉伸强度

根据经典层合板理论,层合板(±45°/90°/0°)s是准各向同性层合板,其拉伸刚度在板面内各个方向上都相同,而拉伸强度是随偏轴角θ改变而变化,即强度方面不具有各向同性的特点。本文首先研究(±45°/90°/0°)s这种准各向同性层合板拉伸强度在偏轴角θ从0°至45°之间的变化情况,然后通过分别改变单层板强度参数和弹性常数来研究该层合板的拉伸强度的变化情况,并分析其破坏形式。最后与NCF材料的试验结果进行了比较。     

铺层结构对EP/GF复合材料沉头螺栓连接失效的影响

以环氧树脂(EP)为基体,单层玻璃纤维(GF)布为增强体,利用真空辅助树脂传递模塑工艺制备了具有[0°]_(_(6s)),[45°/–45°]_(_(3s)),[0°/90°]_(_(3s)),[90°]_(_(6s))铺层结构的EP/GF复合材料层合板,通过拉伸失效实验研究了铺层结构对复合材料层合板沉头螺栓连接承载能力的影响,并进一步分析了4种铺层结构的沉头螺栓连接层合板在拉伸时的失效行为。结果表明,[45°/–45°]_(_(3s))与[0°/90°]_(_(3s))铺层结构的层合板均发生了承载失效,具有较高的螺栓连接承载能力,其中[0°/90°]_(3s)铺层结构的层合板最大拉伸载荷最高,为6.7 k N,[45°/–45°]_(3s)铺层结构的层合板具有最大的失效位移,为14.17 mm;[0°]_(6s)铺层结构的层合板发生了剪切开裂失效,其螺栓连接承载能力低于上述两种铺层结构;[90°]_(6s)铺层结构的层合板发生了净张力失效,其螺栓连接承载能力最低。     

T700／3234层合板力学性能的研究

研究了T700／3234层合板力学性能,T700／3234层合板铺层45°／-45°／0°／90°／0°／0°／90°／0°／-45°／45°.T700／3234中温固化环氧碳纤维单向预浸料适应于热压罐成型工艺方法.测试了23℃、60℃、80℃、100％下,T700／3234层合板拉伸性能、压缩性能、弯曲性能、层间剪切强度及层合板的拉伸剪切强度,得出不同温度下层合板各项力学性能的保持率,表明：T700／3234复合材料使用温度不大于80℃.     

Study on Testing Methods for In-plane Shear Properties of Composite Materials

对常用的剪切实验方法进行了简单介绍,并采用典型的±45°偏轴拉伸法和V形开口轨道剪切法对双轴向玻璃纤维布制成的层合板的常温和低温剪切性能进行了研究。实验结果表明,V形开口轨道剪切法测得的剪切强度和模量高于±45°偏轴拉伸法,玻璃纤维增强环氧树脂基复合材料在低温状态下的剪切性能与常温相比有所提高。     

复合材料面内剪切性能测试方法的研究

对常用的剪切实验方法进行了简单介绍,并采用典型的±45°偏轴拉伸法和V形开口轨道剪切法对双轴向玻璃纤维布制成的层合板的常温和低温剪切性能进行了研究。实验结果表明,V形开口轨道剪切法测得的剪切强度和模量高于±45°偏轴拉伸法,玻璃纤维增强环氧树脂基复合材料在低温状态下的剪切性能与常温相比有所提高。     

基于ANSYS的复合材料层合板的拉伸失效模拟

基于ANSYS的APDL语言开发复合材料层合板的拉伸失效模块,实现有限元分析的参数化建模和累积失效分析.采用Solid64宴体单元建立复合材料层合板的三维模型,依据改进的三维Haisin失效准则对结构单元进行失效判断,并对失效单元进行刚度退化.当失效单元贯穿所有单层时,复合材料层合板结构彻底失效.通过对铺层方式为[0/45/-45/90]s复合材料层合板结构拉伸模拟,探讨其拉伸破坏形式,得到层合结构的最终拉伸强度,并把其拉伸强度与文献实验结果进行对比,得到的结果与实验一致.该方法简便直观,便于工程运用.     

复合材料层合板面内剪切的检测与分析

本文介绍了复合材料层合板的面内剪切试验方法,以ASTM美国标准ASTM D 7078/D7078M-05为方法指导,讨论了方法的优势、劣势以及使用过程中的经验,并对试验中出现的不连续现象作了归纳和假设。     

不同铺层复合材料螺栓连接的研究

实验研究了在E/D=4(边距/孔径),W/D=5(宽度/孔径)的3种铺层[90/+45/-45/0]s,[90/0/+45/-45]s,[+45/-45/90/0]s的玻璃纤维/环氧复合材料试样在不同的扭矩和垫片尺寸(外径(Dw)/内径(D))下的静态破坏强度。实验结果表明,试样破坏强度随夹持力增大而增大,但增加趋势不断减弱,在5Nm扭矩下三种铺层的强度分别比其销钉连接增大175%,196%,141%;在销钉连接下,[90/+45/-45/0]s铺层强度比[90/0/+45/-45]s铺层高12.7%,[+45/-45/90/0]s铺层强度比[90/+45/-45/0]s铺层高10.8%;在手动拧紧下[90/+45/-45/0]s铺层强度比[90/0/+45/-45]s铺层高3.5%,而[+45/-45/90/0]s铺层强度比[90/+45/-45/0]s铺层高0.37%;垫圈的外内径比在2～3范围内,试样强度伴随外内径比的增大而增大,在3～4时,强度变化很小。     

铝合金与碳纤维复合材料自冲铆接强度影响因素研究

分别采用厚度为2. 5 mm不同轴向碳纤维复合材料板和2. 5 mm 5052铝合金板进行自冲铆接实验,分析其接头的成形质量;利用万能拉伸试验机对其进行拉伸试验,并分析接头的失效形式。结果表明,相同轴向碳纤维复合材料板,7 mm铆钉接头质量和拉伸强度均优于6 mm铆钉接头质量和拉伸强度。7 mm铆钉的连接件拉伸强度比使用6 mm铆钉的拉伸强度,在[0/90]4铺层时增加了25. 45%,[0/180]_4铺层时进增加了13. 77%,[-45/45]_4铺层时增加了21. 12%;相同铆钉高度不同轴向时,接头质量并无明显差异,但最大载荷不同。高度6 mm铆钉时连接强度,[0/90]_4铺层比[0/180]_4铺层增加了29. 34%,[-45/45]_4铺层比[0/90]4铺层增加了16. 20%;高度7 mm铆钉时连接强度,[0/90]_4铺层比[0/180]_4铺层增加了42. 63%,[-45/45]_4铺层比[0/90]_4铺层增加了12. 18%。铆接件失效形式主要是铆钉从复合材料板处拉脱。在相同轴向下失效位移大致相同。     

Synthesis and characterization of some polyazomethine conducting polymers and oligomers

Polyazomethine polymers were prepared from the polycondensation of terephthaldehyde with different diamines, namely, benzidine, 2,3-diaminopyridine, 1,4-diaminoanthraquinone and 3,5-diamino-1,2,4-triazole. The electrical conductivities of the polymers were studied with doping with H₂SO₄ and 5% I₂ together with the undoped polymers. The crystallinity and morphology of the polymers were studied using XRD and scanning electron microscopy. A comparative study of the electrical conductivities of oligomers of polyazomethines and those of their corresponding polymers was performed. Received: 8 January 1997/Accepted: 10 May 1997     

Effect of contact at the interface on the compressive properties of fly ash-epoxy composites

Particulate composites based on polymer matrices generally contain fillers, especially those that are abundantly available and are cheaper. The inclusion of these, besides improving the properties, makes the system costwise viable. In the present study, fly ash was tried as a filler in epoxy. The filler particle surfaces were modified using three chemical surface treatment techniques in order to elicit the effect of adhesion at the interface on the mechanical properties of these composites. The compatibilizing of the filler with the use of a silane coupling agent yielded the best compression strength values. Scanning Electron Microscopy (SEM) has been used to characterize and supplement the mechanical test data.     

Cone-and-Plate Shear Stress Adhesive Test

A test geometry is described which will produce a state of essentially pure constant shear stress in an adhesive bond. The adherends are fabricated from two cylindrical elements, one with a convex conical end section and the other with a flat plate end section. The axes of these two cylinders are aligned and the two end sections are bonded together with the test adhesive. The adhesive test volume is a disk with conical indentation. An analysis of the state of stress in the adhesive, with torsional loading of the adherends, shows that a single component of shear stress is present and this shear stress is essentially constant throughout the adhesive volume for small values of the cone angular opening. The advantages of a constant shear stress adhesive test are many and one of the most significant is the ability to accurately measure in-situ material properties. Preliminary test results are reported.     

The role of Glu87 and Trp89 in the lid of Humicola lanuginosa lipase

The importance of Glu87 and Trp89 in the lid of Humicola lanuginosalipase for the hydrolytic activity at the water/lipid interfacewas investigated by site-directed mutagenesis. It was foundthat the effect on the hydrolytic activity upon the replacementof Trp89 with Phe, Leu, Gly or Glu was substrate dependent TheTrp89 mutants displayed an altered chain length specificitytowards triglycerides, with a higher relative activity towardstriacetin and trioctanoin compared with tributyrin. Trp89 wasshown to be lessimportant in the hydrolysis of vinyl esterscompared with ethylesters and triglycerides. An exclusive effecton the acylation reaction rate by the mutation of Trp89 wasconsistent with the data. It is suggested that Trp89 is importantin the process of binding the acyl chain of thesubstrate intothe activesite for optimal acylation reaction rate. The Trp89Phemutation resulted in an increased hydrolytic activity towards2-alkylalkanoic acid esters. This is suggested to be due toreduction of unfavourable van der Waals contacts between Trp89and the 2-substituent of the substrate. Thus, in contrast tonatural substrates, Trp89 has a negative impact on the catalyticefficiencywhen substrates with bulky acyl chains are used. Incontrast to the Trp89 mutations, the effect on the hydrolyticactivity of the Glu87Ala mutation was almost substrate independent,35–70% activity of wild-type lipase. Areduction of boththe acylation and deacylation reaction was consistent with thedata.     

格栅剪力键的FRP板与混凝土粘结性能试验研究

针对不同界面连接形式的FRP板与混凝土进行单剪试验,重点研究破坏形式、极限承载力及破坏机理等内容,研究表明:布置单向剪力连接件时,增加连接件数量、减小连接件间距可以提高界面抗剪承载力,也可改善构件弹性阶段整体刚度;提出的双向格栅剪力连接件可明显提高界面整体抗剪承载力,并可增强弹性阶段构件整体刚度。     

β-Apo-8′-Carotenoic acid and its esters in sunflower oil oxidation

The oxidation kinetics of sunflower oil (SO) and pure triacylglycerols of sunflower oil (TGSO) in the presence of different concentrations (0.0008–0.02%, 1.9–32.7×10⁻⁵ M) of β-apo-8′-carotenoic acid (CA), ethyl β-apo-8′-carotenoate (EC), and β-apo-8′-carotenoylglycerol (CG) were studied. The process was performed at high (kinetic regime) and low (diffusion regime) oxygen concentrations at room temperature and at 100°C and in the dark and in daylight. CA, EC, and CG were not antioxidants in TGSO systems. However, the carotenoid derivatives, especially CA, increased the stability of tocopherol-containing SO at room temperature and in daylight. The stabilization effect was more evident in a kinetic regime of oxidation. The synergism between the carotenoids and tocopherols was characterized by the increase of the stabilization factor F and activity A. F and A were highest for CA (F=1.2–5.5, A=2.4–78.6), followed by EC (F=1.2–3.5, A=1.7–14.6) and CG (F=1.1–2.1, A=1.6–5.5) in the kinetic regime for SO exposed to daylight at room temperature. Presented at the 91st AOCS Annual Meeting & Expo, April 25–28, 2000, San Diego, California.     

Experimental and numerical investigations of the shear behavior of binary particle blends

In this study, a Schulze ring shear tester and the discrete element method (DEM) are employed to investigate the effect of polydispersity on the binary shear flows. Both experimental results and DEM simulations show that the preshear stresses are greater for binary blends than for monodispersed particles. The flowability of these mixtures is strongly affected by the solid fraction, with minimal flow function values correlating to maximum packing fraction. However, minimum flow function values are not observed at the same packing fractions where the maximum preshear stress occurs. Using DEM, it is demonstrated that the decrease of angular velocity of larger particles due to the addition of small adhesive particles reduces and the fraction of large-small particle contact both make contributions to shear stress difference. A mechanism is proposed to quantify the effects of these two factors.     

Expression of immunoglobulin and scavenger receptor superfamily domains as chimeric proteins with domains 3 and 4 of CD4 for ligand analysis

One approach to the analysis of leucocyte cell surface proteinsis to express their domains with part of another protein asa carrier. We report the use of two immunoglobulin superfamily(IgSF) domains from rat CD4 (CD4d3+4) in producing domains fromvarious superfamilies as chimeric proteins in Chinese hamsterovary cell lines. Four types of construct were successfullyexpressed containing: (i) the two IgSF domains of CD48; (ii)the IgSF domain of mb-1 which is part of the B cell antigenrecognition complex; (iii) a T cell receptor V domain; and (iv)the N-terminal domain of CD5 which belongs to the scavengerreceptor superfamily. This CD5 chimeric protein was antigenkfor a panel of CD5 mAbs showing that mAbs with functional effectsreacted with the N-terminal domain of CD5. The CD48 chimericprotein has been used both as multivalent complexes producedby crosslinking with mAbs recognizing CD4 and in a monomericform to analyse the kinetics of the interaction between CD48and CD2 [van der Merwe et al. (1993) EMBO J., 12, 4945–4954].     

Single antibody domains as small recognition units: design and in vitro antigen selection of camelized, human VH domains with improved protein stability

Folding stabilities of camelized human antibody VH domains werestudied through the determination of their melting points inthermodenaturation experiments. The melting point of a VH domainoriginating from a synthetic library of human VHs, which hadbeen optimized for the use as small recognition units throughthe mimicking of camelid antibody heavy chains occurring naturallywithout light chain, was 56.6C compared with 71.2C of theoriginal human VH. Its stability was improved (melting point61.6C) through three mutations to mimic camelid VHs even further:Va137 was replaced by phenylalanine and two cysteines were introducedat positions 33 and 100b. The resulting VH folded properly andformed a second intradomain disulphide between the extra cysteines.The new mutations were then built constitutively into a phage-displayVH library, from which antigen-specific VHs were selected. Twowere analysed for stability with melting points of 72.6 and75.3C. Thus secondary camelization enabled the isolation ofVHs with improved folding stabilities exceeding even that ofthe original human VH. This indicates an effect on folding stabilityfor some mutations specific in the light chain lacking camelidheavy chains.     

Analysis of the catalyic mechanism of a fungal lipase using computer-aided design and structural mutants

Both an active enzyme conformation and stabilization of tetrahedraltransition states are essential for the catalysis of ester bondhydrolysis by lipases. X-ray structural data and results fromsite-directed mutagenesis experiments with proteases have beenused as a basis for predictions of amino acid residues likelyto have key functions in lipases. The gene encoding a lipasefrom Rhizopus oryzae was cloned and expressed in Escherichiacoli. Site-directed mutagenesis of this gene was used to testthe validity of computer-aided predictions of the functionalroles of specific amino acids in this enzyme. Examination ofthe kinetic constants of the Rhizopus oryzae lipase variantsallowed us to identify amino acid residues which are directlyinvolved in the catalytic reaction or which stabilize the activegeometry of the enzyme. The combination of these results withmolecular mechanics simulations, based on a homology-derivedstructural model, provided new information about structure-functionrelationships. The interpretation of the data is consistentwith results obtained with other hydrolases, such as proteases.