3 , respectively.

8.53 In terms of molecular structure, explain why phenol-formaldehyde (Bakelite)

will not be an elastomer.

10.50 Compute the mass fractions of αferrite and cementite in pearlite. assuming

that pressure is held constant.

10.52 (a) What is the distinction between hypoeutectoid and hypereutectoid steels?

(b) In a hypoeutectoid steel, both eutectoid and proeutectoid ferrite exist. Explain the difference between them. What will be the carbon concentration in each? 10.56 Consider 1.0 kg of austenite containing 1.15 wt% C, cooled to below 727_C

(a) What is the proeutectoid phase?

(b) How many kilograms each of total ferrite and cementite form?

(c) How many kilograms each of pearlite and the proeutectoid phase form? (d) Schematically sketch and label the resulting microstructure.

10.60 The mass fractions of total ferrite and total cementite in an iron–carbon alloy

are 0.88 and 0.12, respectively. Is this a hypoeutectoid or hypereutectoid alloy? Why?

10.64 Is it possible to have an iron–carbon alloy for which the mass fractions of total

ferrite and proeutectoid cementite are 0.846 and 0.049, respectively? Why or why not?

第四章习题和思考题

7.3 A specimen of aluminum having a rectangular cross section 10 mm _ 12.7 mm

is pulled in tension with 35,500 N force, producing only elastic deformation. 7.5 A steel bar 100 mm long and having a square cross section 20 mm on an edge is

pulled in tension with a load of 89,000 N , and experiences an elongation of 0.10 mm . Assuming that the deformation is entirely elastic, calculate the elastic modulus of the steel.

7.7 For a bronze alloy, the stress at which plastic deformation begins is 275 MPa ,

and the modulus of elasticity is 115 Gpa .

(a) What is the maximum load that may be applied to a specimen with a cross-sectional area of 325mm, without plastic deformation?

(b) If the original specimen length is 115 mm , what is the maximum length to which it may be stretched without causing plastic deformation?

7.8 A cylindrical rod of copper (E _ 110 GPa, Stress (MPa) ) having a yield strength

of 240Mpa is to be subjected to a load of 6660 N. If the length of the rod is 380 mm, what must be the diameter to allow an elongation of 0.50 mm?

7.9 Consider a cylindrical specimen of a steel alloy (Figure 7.33) 10mm in diameter

and 75 mm long that is pulled in tension. Determine its elongation when a load of 23,500 N is applied.

7.16 A cylindrical specimen of some alloy 8 mm in diameter is stressed elastically

in tension. A force of 15,700 N produces a reduction in specimen diameter of 5 _ 10_3 mm. Compute Poisson’s ratio for this material if its modulus of elasticity is 140 GPa .

7.17 A cylindrical specimen of a hypothetical metal alloy is stressed in compression.

If its original and final diameters are 20.000 and 20.025 mm, respectively, and its final length is 74.96 mm, compute its original length if the deformation is totally elastic. The elastic and shear moduli for this alloy are 105 Gpa and 39.7 GPa, respectively.

7.19 A brass alloy is known to have a yield strength of 275 MPa, a tensile strength of

380 MPa, and an elastic modulus of 103 GPa . A cylindrical specimen of this alloy 12.7 mm in diameter and 250 mm long is stressed in tension and found to elongate 7.6 mm . On the basis of the information given, is it possible to

compute the magnitude of the load that is necessary to produce this change in length? If so, calculate the load. If not, explain why.

7.20 A cylindrical metal specimen 15.0mmin diameter and 150mm long is to be

subjected to a tensile stress of 50 Mpa; at this stress level the resulting deformation will be totally elastic.

(a) If the elongation must be less than 0.072mm,which of the metals in Tabla7.1 are suitable candidates? Why ?

(b) If, in addition, the maximum permissible diameter decrease is 2.3×10-3mm,which of the metals in Table 7.1may be used ? Why?

7.22 Cite the primary differences between elastic, anelastic, and plastic deformation

behaviors.

7.23 diameter of 10.0 mm is to be deformed using a tensile load of 27,500 N. It must

not experience either plastic deformation or a diameter reduction of more than 7.5×10-3 mm. Of the materials listed as follows, which are possible candidates? Justify your choice(s).

7.24 A cylindrical rod 380 mm long, having a diameter of 10.0 mm, is to be

subjected to a tensile load. If the rod is to experience neither plastic deformation

nor an elongation of more than 0.9 mm when the applied load is 24,500 N, which of the four metals or alloys listed below are possible candidates?

7.25 Figure 7.33 shows the tensile engineering stress–strain behavior for a steel alloy.

(a) What is the modulus of elasticity? (b) What is the proportional limit?

(c) What is the yield strength at a strain offset of 0.002? (d) What is the tensile strength?

7.27 A load of 44,500 N is applied to a cylindrical specimen of steel (displaying the

stress–strain behavior shown in Figure 7.33) that has a cross-sectional diameter of 10 mm .

(a) Will the specimen experience elastic or plastic deformation? Why? (b) If the original specimen length is 500 mm), how much will it increase in

length when t his load is applied?

7.29 A cylindrical specimen of aluminum having a diameter of 12.8 mm and a gauge length of 50.800 mm is pulled in tension. Use the load–elongation characteristics tabulated below to complete problems a through f.

(a) Plot the data as engineering stress

versus

engineering strain.

(b) Compute the modulus of elasticity. (c) Determine the yield strength at a strain

offset of 0.002.

(d) Determine the tensile strength of this alloy.

(e) What is the approximate ductility, in percent elongation? (f ) Compute the modulus of resilience.

7.35 (a) Make a schematic plot showing the tensile true stress–strain behavior for a

typical metal alloy.

(b) Superimpose on this plot a schematic curve for the compressive true

stress–strain behavior for the same alloy. Explain any difference between this curve and the one in part a.

(c) Now superimpose a schematic curve for the compressive engineering

stress–strain behavior for this same alloy, and explain any difference between this curve and the one in part b.

7.39 A tensile test is performed on a metal specimen, and it is found that a true plastic

strain of 0.20 is produced when a true stress of 575 MPa is applied; for the same metal, the value of K in Equation 7.19 is 860 MPa. Calculate the true strain that results from the application of a true stress of 600 Mpa.

7.40 For some metal alloy, a true stress of 415 MPa produces a plastic true strain of

0.475. How much will a specimen of this material elongate when a true stress of 325 MPa is applied if the original length is 300 mm ? Assume a value of 0.25 for the strain-hardening exponent n.

7.43 Find the toughness (or energy to cause fracture) for a metal that experiences both

elastic and plastic deformation. Assume Equation 7.5 for elastic deformation, that the modulus of elasticity is 172 GPa , and that elastic deformation terminates at a strain of 0.01. For plastic deformation, assume that the relationship between stress and strain is described by Equation 7.19, in which the values for K and n are 6900 Mpa and 0.30, respectively. Furthermore, plastic deformation occurs between strain values of 0.01 and 0.75, at which point fracture occurs.

7.47 A steel specimen having a rectangular cross section of dimensions 19 mm×3.2

mm (0.75in×0.125in.) has the stress–strain behavior shown in Figure 7.33. If this specimen is subjected to a tensile force of 33,400 N (7,500lbf ), then (a) Determine the elastic and plastic strain values.

(b) If its original length is 460 mm (18 in.), what will be its final length after the load in part a is applied and then released?

7.50 A three-point bending test was performed on an aluminum oxide specimen

having a circular cross section of radius 3.5 mm; the specimen fractured at a load of 950 N when the distance between the support points was 50 mm . Another test is to be performed on a specimen of this same material, but one that has a square cross section of 12 mm length on each edge. At what load would you expect this specimen to fracture if the support point separation is 40 mm ?

7.51 (a) A three-point transverse bending test is conducted on a cylindrical specimen

of aluminum oxide having a reported flexural strength of 390 MPa . If the speci- men radius is 2.5 mm and the support point separation distance is 30 mm ,

predict whether or not you would expect the specimen to fracture when a load of 620 N is applied. Justify your prediction.

(b) Would you be 100% certain of the prediction in part a? Why or why not? 7.57 When citing the ductility as percent elongation for semicrystalline polymers, it is

not necessary to specify the specimen gauge length, as is the case with metals. Why is this so?

7.66 Using the data represented in Figure 7.31, specify equations relating tensile

strength and Brinell hardness for brass and nodular cast iron, similar to Equations 7.25a and 7.25b for steels.

8.4 For each of edge, screw, and mixed dislocations, cite the relationship between the

direction of the applied shear stress and the direction of dislocation line motion. 8.5 (a) Define a slip system.

(b) Do all metals have the same slip system? Why or why not?

8.7. One slip system for theBCCcrystal structure is _110__111_. In a manner similar

to Figure 8.6b sketch a _110_-type plane for the BCC structure, representing atom positions with circles. Now, using arrows, indicate two different _111_ slip directions within this plane.

8.15* List four major differences between deformation by twinning and deformation

by slip relative to mechanism, conditions of occurrence, and final result.

8.18 Describe in your own words the three strengthening mechanisms discussed in

this chapter (i.e., grain size reduction, solid solution strengthening, and strain hardening). Be sure to explain how dislocations are involved in each of the strengthening techniques.

8.19 (a) From the plot of yield strength versus (grain diameter)_1/2 for a 70 Cu–30 Zn