复合材料复习题库.doc

复合材料复习题库9.The transverse tensile strength of an aligned continuous fibre composite(A)is obtained when testing normal to(垂直于) the fibre axis,(B)is obtained when testing parallel to（平行于） the fibre axis,(C)is the lowest tensile stength,(D)is the highest tensile strength,(E)depends mainly on the properties of the matrix and of the fibre- matrix interface,(G) depends mainly on the properties of the fibres.Each of the sentences in questions 11 to 14 consists of an assertion followed bya reason. Answer:(A)if both assertion and reason are true statements and the reason is a correct explanation of the assertion,(B)if both assertion and reason are true statements but the reason is not a true explanation of the assertion,(C)if the assertion is true but the reason is a false statement,(D)if the assertion is false but the reason is a true statement,(E)if both the assertion and reason are false statements.11.The coefficient of thermal expansion of an MMC with a ceramic reinforcement is less than that of the matrix because the coefficient of thermal expansion of a ceramic is usually less than that of a metal. 12.Generally reinforcing a metal degrades both ductility and toughness because there is an increase in Youngs modulus. 13.Unfortunately reinforcement of a metal markedly reduces the fatigue resistance because cracks are readily formed within the reinforcement. 14.The specific strength and modulus of a silicon carbide particle(碳化硅 粒子) reinforced aluminium alloy are superior to those of the matrix because silicon carbide is more dense than the common aluminium alloys. 9. A,C,E; 11. A; 12. B; 13. E; 14. B; 9.Reinforcing alumina with SiC whiskers ABE(A)enhances the thermal shock resistance,(B)lowers the coefficient of thermal expansion,(C)decreases the thermal conductivity,(D)increases the density(E)improves the toughness.10.The room temperature tensile stress-strain curves in Figure 4.35 are for LAS-SiC fibre composites. The break-down of linearity in the curves at the point marked M is due to C（A）plastic deformation associated with dislocation motion, (B)fracture of the fibres,(C)matrix microcracking,(D)viscous flow of a glassy phase, (E)fibre pull-out.11.Chemical vapour deposition of a carbon matrix BE(A)is also commonly known as gas carbonization,(B)is also commonly known as chemical vapour infiltration,(C)produces a brittle composite with a glassy matrix,(D)is independent of deposition pressure,(E)is dependent on deposition temperature.9.ABE;10.C;11.BEIndicate whether statements 1 to 7 are true or false.1. Polyester(聚酯) and epoxy（环氧） are examples of thermosets(A) true(B) false2. Phenolic resins known as resoles or one-stage resins require the addition ofa curing agent prior to fabrication.(A) true(B) false3. Polycarbonate（聚碳酸酯） is an accepted generic term for synthetic polyamides（聚酰胺）(A) true(B) false4. Hand lay-up（手糊成型） requires little capital equipment but is labour intensive(A) true(B) false5. Figure 5.24 is a diagram of matched-die moulding（对模成型）(A) true(B) false6. It has been estimated that over three-quarters of all matrices of PMCs are thermosets and of these the majority is polyester.(A) true(B) false7. Although many benefits accrue from reinforcing PEEK（聚醚醚铜）, unfortunately the creep properties are significantly degraded with the result that PEEK matrix composites cannot be used at temperatures in excess of 40 .(A) true(B) falseFor each of the statements of questions 8 to 14, one or more of the completions given are correct. Mark the correct completions.8. Thermosetting polymers(A) are also known as thermoplastic polymers,(B) are also known as rubbers,(C) readily cross-link during curing,(D) cannot be cured,(E) cannot be reheated and reshaped9. Thermoplastics(A) are cross-linked polymers,(B) are linear polymers,(C) may have branched chains,(D) readily flow at elevated temperatures,(E) cannot be reheated and shapedI0.Polyetheretherketone(聚醚醚铜)(A) is also known as PEEK,(B) is a type of nylon,(C) is a thermoplastic,(D) is a semi-crystalline polymer,(E) has a high glass-transition temperature of 143 11 Spray-up(A) is faster than hand lay-up,(B) involves spraying a non-viscous resin at a preform,(C) involves spraying chopped fibres and resin on to a mould,(D) composites have to be rolled to give a smooth surface finish,(E) composites have to be rolled to remove entrapped air, (F)composites have to be vacuum degassed to remove entrapped air12. Pultrusion(A) is a slow labour intensive production method,(B) is particularly suited to the production of large, complex, planar shapes,(C) is used for the production of rods of uniform cross-section,(D) involves pushing fibres into a closed mould containing resin,(E) involves pulling resin impregnated fibres through a heated die.13. The mechanical properties of glass-reinforced epoxies are affected by moisture because(A) the epoxy matrix becomes more brittle,(B) the water acts as a plasticizer(C) the glass transition temperature is reduced,(D) the epoxy transforms to a weaker polyester,(E) the glass fibres can be degraded.14. Fatigue crack growth rate in PEEK matrix composites(A) is slower than in monolithic PEEK for the same test conditions,(B) is faster than in monolithic PEEK for the same test conditions,(C) obeys the law of mixtures,(D) obeys the Paris-Erdogan equation,(E) is proportional to the stress intensity factor range raised to a power,(F) is proportional to the square root of the creep modulus.Each of the sentences in questions 15 to 20 consists of an assertion followed by a reason. Answer:(A) if both assertion and reason are true statements and the reason is a correct explanation of the assertion,(B) if both assertion and reason are true statements but the reason is nota true explanation of the assertion,(C) if the assertion is true but the reason is a false statement,(D) if the assertion is false but the reason is a true statement,(E) if both the assertion and reason are false statements.15. Thermosets are usually stiffer than thermoplastics because of the strong covalent bonding of the cross-links in the thermosets.16. Many thermoplastics are partially crystalline because thermoplastics cross-link to form a rigid network17. Acrylonitrile-butadiene-styrene (ABS) is a terpolymer(三元共聚物) because it is a multi-phase material.18. The moulds used in resin transfer moulding may be complex, large and made from relatively inexpensive materials such as glass reinforced plastics because only low pressures are employed in the process.19. Vacuum forming requires matched-dies because, as in vacuum-assisted resin injection, extremely high pressures are involved.20. The longitudinal stiffness of continuous fibre reinforced epoxy is about 100 GPa irrespective of whether the reinforcement is glass, carbon or aramid because the glass-fibre reinforced epoxy has the highest density.Self-assessment1. A; 2. B; 3. B, 4. A; 5. B; 6. A; 7.B; 8. C,E; 9. B,C,D; 10. A,C,D,E; 11. A,C,D,E; 12. C,E; 13. B,C,E; 14. A,D,E; 15. A; 16. C;17. B; 18. A; 19. E; 20. D; 1.为什么玻璃纤维的拉伸强度比同成分的块状玻璃高？微裂纹假说：玻璃纤维高温成型时减少了玻璃溶液的不均匀性，使微裂纹产生的机会减少。此外，玻璃纤维断面较小，随断面积的减少，微裂纹存在的几率也减少，从而使纤维强度提高。玻璃纤维由于表面微裂纹尺寸与数量减少，从而减少了应力集中，使纤维具有较高的强度。分子取向假说：在玻璃纤维成型过程中，由于拉丝机的牵引力作用，使玻璃纤维分子产生定向排列，从而提高了玻璃纤维的强度。2.影响玻璃纤维强度的因素有哪些？如何影响？解释原因?1、纤维直径和长度对拉伸强度的影响一般情况，玻璃纤维的直径愈细，抗拉强度越高，但在不同的拉丝温度下拉制的同一直径的纤维强度，也可能有区别。玻璃纤维的拉伸强度和长度有关，随着纤维长度的增加，拉伸强度显著下降直径和长度对玻璃纤维拉伸强度的影响，可以用微裂纹假说来解释。因为随着纤维直径和长度的减小，纤维中微裂纹会相应减少，从而提高了纤维强度。2、化学组成对强度的影响 一般是含碱量越高、强度越低。无碱纤维比有碱纤维的拉伸强度高20%研究证明，高强和无碱纤维，由于成型温度高，硬化速度快，结构链能大等原因，因此具有很高的抗拉强度。含K2O和PbO 成分多的玻璃纤维强度较低。3、玻璃液质量对玻璃纤维强度的影响 A）结晶杂质的影响：当玻璃成分波动或漏板温度波动或降低时，可能导致纤维中结晶的出现。实践证明，有结晶的纤维比无结晶的纤维强度要低。B）玻璃液中的小气泡也会降低纤维的强度。曾试验用含小气泡的玻璃液拉直径为5.7um,的玻璃纤维其强度比用纯净玻璃液拉制的纤维强度降低20%。4、成型条件对玻璃纤维的影响实践证明，用漏板拉制的玻璃纤维强度高于用玻璃棒法拉制的纤维。在玻璃棒法中，用煤气加热生产的纤维又比用电热丝加热生产的纤维强度为高。如用漏板法拉制10um，玻璃纤维的强度为1700MPa，而用棒法拉制相同直径的玻璃纤维强度仅为1100MPa。这是因为玻璃棒只加热到软化，粘度仍然很大，拉丝时纤维受到很大的应力；此外玻璃棒法是在较低温度下拉丝成型，其冷却速度要比漏板法为低。用各种不同成型方法生产的玻璃纤维的强度各不相同。用漏板法拉制的纤维强度最高，气流吹拉长棉次之，玻璃棒法再次之。然后是蒸汽立吹短棉，强度最低是蒸汽喷吹矿棉。在采用漏板拉丝的方法中，采用较高的成型温度，较小的漏孔直径，可以提高纤维强度。5、表面处理对强度的影响 在连续拉丝时，必须在单根纤维或纤维束上敷以浸润剂，它在纤维表面上形成一层保护膜，防止在纺织加工过程中，纤维间发生相互摩擦，而损伤纤维降低强度。玻璃布经热处理除去浸润剂后，强度下降很多，但在用中间粘结剂处理后，强度一般都可回升，这是因为中间粘结剂涂层一方面对纤维起到保护作用，另一方面对纤维表面缺陷有所弥补。6、存放时间对强度的影响 玻璃纤维存放一段时间后其强度会降低，这种现象称为纤维的老化。主要是空气中的水分对纤维侵蚀的结果。此，化学稳定性高的纤维强度降低小，如同样存放233年的有碱纤维强度降低33%，而无碱纤维降低很少。7、施加负荷时间对强度的影响 玻璃纤维强度随着施加负荷时间的增长而降低。当环境温度较高时，尤其明显。可能是吸附在微裂纹中的水分，在外力作用下，使微裂纹扩展速度加快的缘故。3.复合材料的界面定义是什么？包括哪些部分？复合材料的界面是指基体与增强物之间化学成分有显著变化的、构成彼此结合的、能起载荷传递作用的微小区域。界面通常包含以下几个部分：基体和增强物的部分原始接触面；基体与增强物相互作用生成的反应产物，此产物与基体及增强物的接触面；界面的效应(1)传递效应界面能传递力，即将外力传递给增强物，起到基体和增强物之间的桥梁作用。(2)阻断效应结合适当的界面有阻止裂纹扩展、中断材料破坏、减缓应力集中的作用。(3)不连续效应在界面上产生物理性能的不连续性和界面摩擦出现的现象，如抗电性、电感应性、磁性、耐热性、尺寸稳定性等。(4)散射和吸收效应光波、声波、热弹性波、冲击波等在界面产生散射和吸收，如透光性、隔热性、隔音性、耐机械冲击及耐热冲击性等。(5)诱导效应一种物质(通常是增强物)的表面结构使另一种(通常是聚合物基体)与之接触的物质的结构由于诱导作用而发生改变，由此产生一些现象，如强的弹性、低的膨胀性、耐冲击性和耐热性等界面效应是任何一种单一材料所没有的特性，它对复合材料具有重要的作用。界面效应既与界面结合状态、形态和物理-化学性质有关，也与复合材料各组分的浸润性、相容性、扩散性等密切相关。4.复合材料界面具有哪些效应？复合材料界面效应有：1、传递效应：界面可将复合材料体系中基体承受的外力传递给增强相，起到基体和增强相之间的桥梁作用。2、阻断效应：基体和增强相之间结合力适当的界面有阻止裂纹扩展、减缓应力集中的作用。3、不连续效应：在界面上产生物理性能的不连续性和