课程名称︰材料科学 课程性质︰必修 课程教师︰宋家骥 开课学院：工学院 开课系所︰工程科学与海洋工程学系 考试日期（年月日）︰2008/6/18 考试时限（分钟）：120 是否需发放奖励金：是 （如未明确表示，则不予发放） 试题 : Give as much written explanation as possible of your reasoning, and write clearly and legibly. 1.Multiple choice:(23pt) (a)single-choice questions:(3pt each) *I.the room temperature stress-strain responses are shown in the figure. which type of polymer is most likely to have plastic response? a.aligned, cross linked case b.network case c.semi-crystalline case d.crystalline ceramics II.increasing the amount of cemetite in a steel will: e.result in a less brittle steel f.decreace the eutecoid temperature g.increace the eutectoid composition h.result in a harder steel III.the fracture surface from a ductile failure in metal is not characterized by: i.little necking j.grainy or faceted surface k.cup-and-cone fracture surface l.final shear at 45度 angle relative to the tensile direction IV.the electrical conductivity of a piece of metal generally decreace with m.increasing deformation n.increasing impurity content o.increasing temperature p.all of the above V.which of the following statements is true regarding electical properties? q.copper-beryllium alloys are precipitation hardened and have better conductivity than high-purity copper. r.some polymeric materials have been synthesized to have twice of the conductivity of copper on a weight basis. s.an impurity of N-type semiconductor is called an acceptor. t.piezoelectricity exhibits spontaneous polarization. (b)multiple-choice questions:(choice two answers for each question,4pt each) VI.concerning hot working versus cold working of metals, a.hot working requires less energy to deform the material b.cold working produces materials with higher strength c.hot working produce a better surface finish d.cold working producee relatively ductile materials VII.the electrical conductivity of a semiconductor such as silicon e.increases with temperature f.drceases with temperature g.increases with doping h.decreases with soping 2.describe four major mechanisms of strengthening in metal and briefly explain them:(8pt) 3.compare and contrast these two forms of failure: fatigue and creep.(7pt) 4.sometimes cosψcosλin the resolved shear stress equation is termed the Schmid factor. For an FCC single crystal oriented with its [100] direction parallel to the loading axis.(10pt) a)determine the magnitude of the schmid factor. b)compute the resolved shear stress along a (111)plane and in a [100] direction when a tensile stress of 60Mpa is applied. 5.a relatively large plate of a glass is subjected to a tensile stress of 45MPa. if the specific surface energy and modulus of elasticity for this glass is 0.3J/m^2 and 69GP,respectively. (a)determine the maximum length of a surface flaw that is possible without fracture.(10pt) (b)determine the plane strain fracture toughness.Assume that the calue of Y is 1.5.(5pt) *6.for a 45 wt% Sn-55 wt% Pb alloy at 150度C, calculate the relative amount of each phase present in terms of volume fraction. At 150度C take the densities of Pb and Sn to be 11.23 and 7.24 g/cm^3,respectively.(10pt) *7.for 0.35 wt% C austenite, cooled to below 727度C, determine the following: (a) what is the proeutectoid phase? (b) the fractions of the proeutectoid phase ferrite and pearlite. (c) the fraction of eutectoid ferrite.(12pt) 8.(a) using the data in table 12.1, compute the resistance of a copper wire 3 mm in diameter and 2m long. (b) what would be the current density if the potential drop across the ends of the wire is 0.05V?(10pt) 9.what is the minimum diameter of the wire so that ΔV<1.5V? using the data in table12.1.(5pt)Cu wire with 100m and I=2.5A Table 12.1 electrical conductivity silver 6.8*10^7 copper 6.0*10^7 gold 4.3*10^7 10.polymers for enginerring use can be classified as:(a)thermoplastic,(b) thermosetting,and (c)elastomeric. Fill in the type ID for each polymer listed in the following.(3pt) I.natural rubber__________ II.polyethylene(PE)__________ III.polyester(PET)__________ 11.A sheet of BCC iron 1mm thick eas exposed to a carburizing gas atmosphere on one side and a decarburizing atmosphere on the other side at 725度C of steady-state diffusion. after having reached steady state, the iron was quickly cooled to room temperature. the carbon concerntrations at two surfaces of the sheet were determined to be 0.012 and 0.0075wt%. compute the diffusion coefficient if the diffusion flux is 1.4*10^-8 kg/m^2-s. the density of carbon and iron is 2.25g/cm^3. and 7.87g/cm^3 (12pt) -- 题号前面打*的题目是代表有附图 --

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