Strength Predictions for Lap Joints, Especially with Composite Adherends. A Review

Classical linear solutions (such as Volkersen, Goland and Reissner) of the lap joint problem are discussed, together with more advanced versions of the same type. Finite element techniques are shown to be the best way of treating the non-linear mechanics and material behaviour in real joints. Finally, when applied to composite adherends, the principles given here show how the strength can be increased by up to 500%.     

Influence of hybridization of glass fiber and talc on the mechanical performance of polypropylene composites

The effect of the hybridization of short glass fibers (GFs) and talc mineral filler on the tensile mechanical performance of injection‐molded propylene‐ethylene copolymer composites (PP_cop) with and without weld lines (WLs) was studied in this work. The fibrous reinforcement imparts high‐tensile stiffness and strength to the molding but originates a highly anisotropic composite. The negative effect of this anisotropy is even worse when WLs occur in the molding, as the high aspect ratio GFs tend to be oriented on the weak plane of the WL. Through hybridization of GF and talc, combined in different proportions, it is possible to obtain improved mechanical properties in comparison to the standard GF reinforced PP_cop composites. The combination of GF with talc was shown to be beneficial for the WL strength of PP_cop composites, once a synergism effect was achieved with the expected optimization of the fibers/particles packing efficiency of the hybrid reinforcement. At a given constant total reinforcement concentration, the experimental data of both tensile modulus and strength properties of the hybrid composites without WL were above the predictions derived from the estimated rule of mixtures. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Development of a Computer Program for the Design of Adhesive Joints

Adhesive joints are increasingly being used due to their improved mechanical performance and a better understanding of the mechanics of failure. To predict the joint strength, one must have the stress distribution and a suitable failure criterion. The literature contains many closed-form solutions for the stress distribution. However, the models are sometimes difficult to implement and use. The objective of the present work was to compile existing models of increasing complexity into user friendly software. Three main situations were considered: elastic adherends and adhesive, elastic adherends with nonlinear adhesive and nonlinear analyses for both adherends and adhesive. The adherends were both isotropic (metals) and anisotropic (composites). The joints considered are the single and double lap joints for most of the models. However, a sandwich model initially proposed by Crocombe can be used for any type of joint provided the boundary conditions are known. For each model proposed the compatible failure criteria are included to enable the user not only to have the stress distribution but also the failure load for a given joint/load scenario. Experimental tests corresponding to the three cases described above were carried out to validate the models implemented.     

环氧树脂/玻璃布/BN导热复合材料的制备与性能研究

采用高温模压成型法制备环氧树脂(EP)/玻璃布/氮化硼(BN)导热复合材料。探讨了BN用量和偶联剂处理对复合材料力学性能、导热性能和介电性能等影响。结果表明:当w(BN)=15%时,复合材料的冲击强度较高;导热性能随着BN用量的增加而增大;当w(BN)=25%时,改性复合材料的热导率为0.901 2 W/(m.K),此时复合材料仍保持较低的介电常数和介电损耗。当BN用量相同时,偶联剂表面处理可有效改善复合材料的力学性能和导热性能。     

Modeling the Influence of Orientation Texture on the Strength of WC–Co Composites

Two-dimensional finite element simulations were used to study the effects of orientation texture on the transverse rupture strengths of WC–Co composites. The model incorporates observed microstructural geometries, anisotropic thermal and elastic properties, and a fracture criterion that reproduces the strengths of known specimens. The results show that the greatest potential for increasing the strength occurs when the [001] axes of the carbide grains are orientated perpendicular to the sample loading direction. Furthermore, the strength increases in proportion to the degree of texture, and the texture-derived strength enhancement is greater in microstructures with a larger contiguity.     

超支化聚合物对聚丙烯/剑麻纤维复合材料性能影响

为改善剑麻纤维(SF)与聚丙烯(PP)之间的相容性,在PP/SF复合材料中添加超支化聚酯(H101)、超支化环氧树脂(E102),研究了两种超支化聚合物(HBP)的热稳定性及对PP/SF复合材力学性能、熔体流动性和微观形貌的影响。热重分析表明,所使用的HBP均具有较好的热稳定性;扫描电子显微镜分析发现,HBP的加入使基体与纤维结合得更加紧密;力学性能测试表明,H101可不同程度地提高复合材料的拉伸、弯曲及冲击强度;E102可提高复合材料的拉伸及冲击强度,当E102含量为10%时,与PP/SF复合材料相比,冲击强度提高了72.24%。尽管HBP含量较高时复合材料的力学性能提高,但HBP会降低复合材料的熔体流动速率,选择HBP含量时需要综合考虑。     

晶须状碳酸钙填充聚合物材料性能的研究

研究了晶须状碳酸钙的填充量及表面处理状况对填充ＰＶＣ材料和ＰＰ材料性能的影响。力学性能和流变性能的测试结果表明，碳酸钙晶须作为填充材料，在相同的填充量下加工 交小、拉伸强度和冲击强度较高，对晶须进行适当的表面处理后，体系的性能可以得到进一步提高，这是因为晶须具有特殊的针状外形，在加工应力的作用下可以迅速地在聚合物熔体中定向排列，对体系起到良好的增强和增韧作用。     

Mechanical properties of poly(ether-ether-ketone) for engineering applications

An outline of the characteristics of PEEK and the versatility of its compositional forms (micro and macro composites) are given to illustrate its wide potential for success in engineering applications. Although it is necessary to have particular tabulations of mechanical properties for engineering design, these are seldom available and consequently it is argued that an understanding of stiffness, toughness and strength properties are required to fully exploit available manufacturer's data and thus develop the full potential of PEEK and its composites. Stiffness characteristics are considered in terms of a modulus function which is dependent on time under load and temperature. In its composite forms, whether reinforced with short or continuous fibres, stiffness anistropy can be both considerable and complex, but some empirical ground-rules are apparent. For continuous fibre composites even in the form of complex lay-ups, it is also possible to attempt some stiffness prediction from certain pseudo-elastic constants. Toughness of PEEK and its composites is described in terms of both comparative and intrinsic properties. Instrumented falling weight impact data, particularly as a function of temperature enable some insight into ductile-brittle transitions for the unreinforced material, but crack initiation and crack propagation processes for the various fibre reinforced forms. Intrinsic toughness is described in terms of linear elastic fracture mechanics theory. Strength properties are described for static and dynamic loading configurations. In particular, PEEK and its composites are evaluated for increasing test severities for strength characteristics; stress concentration, loading form and test temperature are considered.     

Voraussage der verformungs- und festigkeitseigenschaften von beton unter dauerlast

Using existing experimental data and statistical methods, the influence of different factors on the creep development and ultimate creep strain is analysed. Both linear and non-linear creep are investigated. It is shown that the creep behaviour of normal weight concrete can be reliably predicted for design when instead of traditional parameters of concrete mix proportion the standard concrete strength and the water content in concrete mix are used. The decrease of strength of concrete under high sustained load can also be predicted using fracture mechanics methods and statistical estimation of linear creep strain.     

热致性液晶聚芳酯纤维表面的化学修饰

采用环氧氯丙烷作为处理试剂,通过傅-克化学反应来修饰热致性液晶聚芳酯(TLCP)纤维的表面,并通过傅里叶变换红外光谱仪(FTIR)、万能电子强力仪、单丝拔出试验(SFP)与扫描电子显微镜(SEM)系统研究了化学修饰对纤维表面的化学结构、纤维力学性能、复合材料的界面剪切强度及纤维的表面形态的影响。研究结果表明:通过傅-克化学反应修饰TLCP纤维的表面,可以有效地提高TLCP单纤维-环氧树脂复合材料的界面剪切强度,相对于未修饰的纤维约提高了52%,表面化学修饰的最佳反应时间为40 min。此外,经修饰的TLCP单纤维表面没有明显的刻蚀或受损现象,且纤维的力学性能不会受到明显影响。傅-克化学反应修饰TLCP纤维可有效提高TLCP纤维-环氧树脂复合材料的界面性能。     

界面相容剂对生物质复合材料性能的影响

采用芥酸酰胺、十二苯磺酸和HY-3308三种界面相容剂制备了稻壳粉/低密度聚乙烯(LDPE)生物质复合材料,通过转矩流变仪、扫描电镜(SEM)和力学性能测试,探讨了不同种类界面相容剂对生物质复合材料性能的影响。结果显示:添加了十二苯磺酸的材料力学性能最好,拉伸强度、断裂伸长率与冲击强度达到9.83 MPa、407.3%、21.191 kJ/m^2,分别提高22.4%、331.0%、39.5%。实验结果表明,芥酸酰胺可提高加工流变性能。     

Fabrication and Properties of Ti3SiC2/SiC Composites

Ti3SiC2/SiC composites were fabricated by reactive hot pressing method. Effects of hot pressing temperature, the content and particle size of SiC on phase composition, densification, mechanical properties and behavior of stress-strain of the composites were investigated. The results showed that ： （ 1 ） Hot-pressing temperature influenced the phase composition of Ti3SiC2/SiC composites. The flexural strength and fracture toughness of composites increased with hot pressing temperature. （2） It became more difficult for the composites to densify when the content of SiC in composites increased. It need be sintered at higher temperature to get denser composite. The flexural strength and fracture toughness of composites increased when the content of SiC added in composites increased. However, when the content of SiC reached 50 wt%, the flexural strength and fracture toughness of composites decreased due to high content of pore in composites. （3） When the content of SiC was same, Ti3SiC2/SiC composites were denser while the particle size of SiC added in composites is 12. 8 μm compared with the composites that the particle size of SiC added is 3 μm. The flexural strength and fracture toughness of composites increased with the increase of particle size of SiC added in composites. （4） Ti3SiC2/SiC composites were non-brittle fracture at room temperature.     

MECHANICAL AND THERMAL PROPERTIES OF NANO-AL2O3/NYLON 6 COMPOSITES

Nano-Al₂O₃-reinforced monomer casting nylon (NA/MCN) composites were prepared by using in situ polymerization. The average molecular weight of the matrix nylon was measured using gel permeation chromatography. The thermal-mechanical properties of the NA/MCN composites were characterized by thermo-dynamic mechanical analysis, and the results were compared with micro-Al₂O₃-reinforced nylon (MA/MCN) composites. A tensile property test was conducted to investigate the mechanical properties of neat nylon and composites. Experimental results showed that the average molecular weight of the matrix nylon filled with nano-alumina had little change and was higher than that with micro-alumina. The glass transition temperature (T_g) and storage moduli of NA/MCN composites were higher than that of neat nylon. During the experiment, it was also found that the tensile strength increased up to 52% when 3 wt.% of nano-Al₂O₃ particles were added. The thermal and tensile properties of NA/MCN composites were better than those of the MA/MCN composites when the same weight percentage of Al₂O₃ particles was used.     

Mechanical properties of functionally graded carbon black–styrene butadiene rubber composites: Effect of modifying gradation and average filler loading

The mechanical properties of functionally graded polymeric composites (FGPCs) with varying carbon black loading and the effect of stacking sequence in styrene butadiene rubber (SBR) matrix were studied. For a given average amount of nanofiller, the modulus of FGPCs for any given stacking sequence of layers is higher when compared with its uniformly dispersed polymeric composites (UDPCs) counterpart. Tensile strength, elongation at break, and tear strength either increase or decrease depending on the stacking sequence and average loading of the filler in FGPCs. In addition, the smoother gradation (i.e., lesser difference in the amounts of CB content in adjacent layers) and a wide gap of difference in CB content in a stack has a profound effect on the modulus and tensile strength of FGPCs. Dynamic mechanical analysis shows lesser damping in FGPCs than UDPCs. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

桦木纤维/不饱和聚酯复合材料制备与性能研究

采用硅烷偶联剂、乙醇和水等分别对桦木纤维(BF)和回收纸浆纤维进行表面处理,并分别将改性纤维作为不饱和聚酯树脂(UPR)的增强材料,制备相应的BF/UPR复合材料。研究了不同改性方法对复合材料界面性能的影响。结果表明:不同纤维种类、不同纤维表面处理方法和不同纤维用量对复合材料的界面性能、力学性能等影响较大;经硅烷偶联剂处理后的BF,可有效改善BF与UPR之间的界面相容性;当w(偶联剂处理BF)=16%时,相应复合材料的拉伸强度和冲击强度比纯UPR体系分别提高了31.0%和28.5%;在制备回收纤维/UPR复合材料之前应先对回收材料进行筛选,并且应优先选择对UPR基体树脂具有明显增强作用的回收纤维。     

Effect of short polyethylene terephthalate fibers on properties of ethylene-propylene diene rubber composites

The alteration in some properties of electron beam (EB) cured ethylene-propylene diene rubber (EPDM) reinforced by polyethylene terephthalate (PET) fiber was investigated in this study. Bonding system Resorcinol/Hexamethylenetetramine/Silica (RHS) was used to enhance the fiber/EPDM adhesion and to maintain optimum composite strength properties. Mechanical properties of composites namely; tensile strength, hardness and modulus at 100 % elongation have been enhanced by adding PET fibers and increasing irradiation dose. Moreover, the effect of fiber loading and irradiation dose on the soluble fraction behavior of the composite in benzene was also investigated. The soluble fraction of the composites decreased with increasing the fiber loading and irradiation dose. The extent of fiber alignment and strength of fiber-rubber interface adhesion were analyzed from the anisotropic swelling measurements. In addition, thermal stability of the composites was increased. Besides, the mechanical properties like tensile strength and stiffness were improved by thermal ageing. Scanning electron microscopy (SEM) for the fractured surfaces and Wide- angle X- ray diffraction (WAXD) of the investigated samples confirmed that the adhesion occurred between fibers and EPDM.     

聚甲醛/弹性体/碳酸钙复合材料的研究

用弹性体和CaCO3复合改性POM。采用TPU为增韧剂，CaCO3为增强剂，研究了加工方法、组成比、填料用量、粒径及分散形态等因素对复合材料性能尤其是冲击韧性的影响。结果表明，两步法制备复合材料的冲击韧性大大高于一步法；且纳米级CaCO3填充复合材料的综合性能优于其它粒径大小的填料；适量的弹性体及无机纳米填料的加入利于获得较好的增韧效果，当弹性体用量约为10％，CaCO3用量为3％时，与纯POM相比，冲击强度提高了3倍，弯曲模量与纯POM接近。     

Calculation, Measurement, and Control of Interface Strength in Composites

Strength and energy criteria for interface delamination are given for composite systems involving anisotropic fibers. The tensile strength of planar interfaces is measured with a modified laser spallation experiment involving a laser Doppler displacement interferometer. The technique for achieving desired interface properties is demonstrated on an Nb/Al₂O₃, interface. In the as-deposited state, the strength is determined to be 0.28 GPa. The interface strength is controlled with sputter-deposited Cr and Sb interlayers. The strength of Nb/Al₂O₃ interfaces varies from 0.28 to 0.35 GPa when the Cr layer thickness varies from 1 to 50 Å. The strength is reduced to 0.16 GPa with Sb thickness of 70 Å.     

Gas-assisted Injection Molded Polypropylene/Glass Fiber Composite: Foaming Structure and Tensile Strength

Tensile strength of isotactic polypropylene (iPP)/glass fiber (GF) composites and neat iPP molded respectively by gas-assisted injection molding (GAIM) was examined. For comparison, tensile strength of the counterparts, which were molded by conventional injection molding (CIM) under the same processing conditions but without gas penetration, was also examined. Tensile strength of the CIM parts steadily increases with the increase of the GF content. For neat iPP molded by GAIM, as the gas pressure increases the tensile strength increases. However, for the iPP/GF composites, the tensile strength generally decreases when the gas pressure increases. And, at a given content of GF, tensile strength of the parts molded by GAIM is unexpectedly lower than that of the counterparts molded by CIM. At a given gas pressure, the higher the fiber content, the lower the tensile strength. In addition, scanning electron microscope (SEM) results show that foaming structure should be responsible for the poor tensile strength of the composites molded by GAIM. The poor adhesion between the glass fibers and the matrix and the unique properties of the gas used in GAIM process are the substantial factors in the formation of foaming structure.     

氧化锌晶须/聚丙烯复合材料性能的研究

制备了四针状氧化锌晶须(T—ZnOw)／聚丙烯复合材料,研究了不同偶联剂处理的T—ZnOw及其用量对复合材料力学性能的影响,并对偶联机理做了初步探讨。研究结果表明,当添加T-ZnOw质量分数为20％时,复合材料的力学性能最好;与处理前相比,处理后的T—ZnOw复合材料的拉伸强度和冲击强度有不同程度的提高;不同偶联剂处理的T—ZnOw对复合材料力学性能的影响不同。