1.1
What are are the four categor categories ies of engineerin engineering g materials materials used used in manufacturin manufacturing? g? Answer. The four categories of engineering materials are (1) metals, (2) ceramics, (3) polymers, and () composite materials, which consist of non!homogeneous mi"tures of the other three types.
1.2 #dentify #dentify the four types types of permanent permanent $oining $oining process processes es used in assem%ly assem%ly.. Answer. The four types are welding, %ra&ing, soldering, and adhesi'e %onding.
1.3 A company company in'ests in'ests *+,+++ *+,+++ in a piece of production production euipme euipment. nt. The cost to install install the euipmen euipmentt in the plant - 2*,+++. The anticipated life of the machine - 12 years. The machine will %e used eight hours per shift, fi'e shifts per wee, *+ wees per year. Applica%le Applica%le o'erhead rate - 1/0. Assume a'aila%ility - 1++0. etermine the euipment cost rate if (a) the plant operates one shift per day and (%) the plant operates three shifts per day. olution (a) 4or a one!shift operation, hours of operation per year 5 - *+(1)(*)(/) - 2+++ hr6yr. 7sing 8. (1./), 9e - (*+,+++ : 2*,+++)(1.1/)6(;+ × 12 × 2+++) - +.;3*6min - 3/.1+6hr (%) 4or a three!shift operation, hours of operation per year 5 - *+(3)(*)(/) - ;+++ hr6yr. 9e - (*+,+++ : 2*,+++)(1.1/)6(;+ × 12 × ;+++) - +.2126min - 12.+6hr a%or cost rate 9 > - 1*.++(1.2)6;+ - +.3**6min This la%or cost should %e ad$usted for the fact that although the press operates .* hr6day, the operator is paid for / hr. 9> - +.3**(/6.*) - +.3 4inally, cost per stamping 9 pc - +.23 : (+.3 : +.*)(1.23*) : +.2+ - 1.*;6pc
1.* #n a long!running long!running high!produ high!production ction operatio operation, n, the starting starting wor part part cost - +.* each, each, and cycle cycle time - +.* min. 8uipment cost rate - 2/.++6hr, and la%or cost rate - 21.++6hr. @oth rates include o'erhead costs. Tooling cost - +.+*6pc. A'aila%ility of the production machine - ;0, and the scrap rate - 30. etermine (a) production rate and (%) finished part cost. olution (a) roduction rate, including effect of a'aila%ility (;+6+.*)(+.;) - ;./ pc6hr 5owe'er, %ecause of the 30 scrap rate, the production rate of accepta%le parts is = p - ;./(1 − +.+3) - .* pc6hr (%) 4actoring in a'aila%ility and scrap rate, part cost is 9 pc - +.*6+. : ((21 : 2/)6;+)(+.*6(+. × +.;)) : +.+* - 1.126pc
2.1
What What is the diff differe erence nce %etwe %etween en primary primary and and second secondary ary %ondin %onding g in the struc structure ture of of materia materials? ls?
Answer. rimary %onding is strong %onding %etween atoms in a material, for e"ample to form a moleculeB while secondary %onding is not as strong and is associated with attraction %etween molecules in the material. 2.2
What are some common point defects in a crystal lattice structure? Answer. The common point defects are (1) 'acancy ! a missing atom in the lattice structureB (2) ion!pair 'acancy (chotty defect) ! a missing pair of ions of opposite charge in a compoundB (3) interstitialcy ! a distortion in the lattice caused %y an e"tra atom presentB and () 4renel defect ! an ion is remo'ed from a regular position in the lattice and inserted into an interstitial position not normally occupied %y such an ion.
2.3
efine the difference %etween elastic and plastic deformation in terms of the effect on the crystal lattice structure. Answer. 8lastic deformation in'ol'es a temporary distortion of the lattice structure that is proportional to the applied stress. lastic deformation in'ol'es a stress of sufficient magnitude to cause a permanent shift in the relati'e positions of ad$acent atoms in the lattice. lastic deformation generally in'ol'es the mechanism of slip ! relati'e mo'ement of atoms on opposite sides of a plane in the lattice.
2.
5ow do grain %oundaries contri%ute to the strain hardening phenomenon in metals? Answer. Crain %oundaries %loc the continued mo'ement of dislocations in the metal during straining. As more dislocations %ecome %loced, the metal %ecomes more difficult to deformB in effect it %ecomes stronger.
2.*
What is the difference %etween crystalline and noncrystalline structures in materials? Answer. The atoms in a crystalline structure are located at regular and repeating lattice positions in three dimensionsB thus, the crystal structure possesses a long!range order which allows a high pacing density. The atoms in a noncrystalline structure are randomly positioned in the material, not possessing any repeating, regular pattern.
1.
tate 5ooeDs law. Answer. 5ooeDs >aw defines the stress!strain relationship for an elastic material - a constant of proportionality called the modulus of elasticity.
2.
σ -
8ε, where 8
efine the recrystalli&ation temperature for a metal. Answer. The recrystalli&ation temperature is the temperature at which a metal recrystalli&es (forms new grains) rather than wor hardens when deformed.
3.
(# 7nits) A tensile test pro'ides the following flow cur'e parameters strain!hardening e"ponent +.2* and strength coefficient - *++ Ea. etermine (a) flow stress at a true strain - 1.+ and (%) true strain at a flow stress - *++ Ea. olution (a) Ff - *++(1.+).2* - *++ Ea (%) ε - (*++6*++)16.2* - (1.+).+ - 1.++
.
(A) (# 7nits) A tensile test specimen has a gage length - *+ mm and its cross!sectional area - 1++ mm2. The specimen yields at /,+++ <, and the corresponding gage length - *+.23 mm. This is the +.2 percent yield point. The ma"imum load of /,+++ < is reached at a gage length - ;.2 mm. etermine (a) yield strength, (%) modulus of elasticity, and (c) tensile strength. (d) #f fracture occurs at a gage length of ;.3 mm, determine the percent elongation. (e) #f the specimen neced to an area - *3 mm 2, determine the percent reduction in area. olution (a) F - /,+++61++ - /+ Ea (%) s - 8 e. u%tracting the +.20 offset, e - (*+.23 ! *+.+)6*+.+ ! +.++2 - +.++2; 8 - s6e - /+6+.++2; - 1/.; " 1+ 3 Ea (c) T - /,+++61++ - /+ Ea (d) 8> - (;.3 ! *+)6*+ - 1.36*+ - +.3; - 3.;0 (e) A= - (1++ ! *3)61++ - +. - 0
*.
(79 7nits) A ceramic specimen is tested in a %ending test. #ts width - +.*+ in and thicness +.2* in. The length of the specimen %etween supports - 3.+ in. etermine the trans'erse rupture strength if failure occurs at a load - 12*+ l%.
olution T= - 1.*4>6%t2 - 1.*(12*+)(3.+)6(+.* " +.2* 2) - 1/+,+++ l%6in2 .1.
5ow does solidification of alloys differ from solidification of pure metals? Answer. ure metals solidify at a single temperature eual to the melting point. Eost alloys (e"ceptions are eutectic alloys) start to solidify at the liuidus and complete solidification occurs at the solidus, where the liuidus is a higher temperature than the solidus.
.2. What are some of the factors that affect the fluidity of a molten metal during pouring into a mold ca'ity? Answer. The factors include (1) pouring temperature a%o'e the melting point, (2) metal alloy composition, (3) 'iscosity of the liuid metal, and () heat transfer to the surroundings. .3. ure copper is heated to cast a large rectangular plate in an open mold. The plateGs length - 2+ in, width - 1+ in, and thicness - 2 in. 9ompute the amount of heat that must %e added to the metal to heat it from am%ient temperature (* °4) to a pouring temperature of 21++°4. The amount of metal heated will %e 1+0 more than what is needed to fill the mold ca'ity. ensity, melting point, and specific heat of the solid metal can %e found in Ta%les .1 and .2. The specific heat of copper in the molten state - +.++ @tu6l%m!4, and its heat of fusion - /+ @tu6l%m
U mp= c s ( T m −T 0 ) + hf + cl ( T p−T m ) olution Holume of rectangular plate H - (2+ " 1+ " 2) - ++.+ in 3 Holume of copper to %e heated - ++(1 : 1+0) - +.+ in 3 Assuming To - * °4 and using 8. (1+.1), 5 - +.32 " +I+.+2(1/1 ! *) : /+ : +.++(21++ ! 1/1)J - 12.3*I1*.3* : /+ : 1+.1J 5 - 3,3+ @tu
.. The flow rate of liuid metal into the downsprue of a mold - +./ >6sec. The cross!sectional area at the top of the sprue - *+ mm 2, and its length - 1* mm. What area should %e used at the %ase of the sprue to a'oid aspiration of the molten metal?
ν = √ 2 gh olution 4low rate K - +./ >6s - /++,+++ mm 36s Helocity ' - (2 " /1+ " 1*) +.* - 1/*3 mm6s Assuming 'olumetric continuity, area at %ase A - /++,+++61/*3 - 32 mm 2 .*. A riser in the shape of a sphere is to %e designed for a sand casting mold. The casting is a rectangular plate, with length - 2++ mm, width - 1++ mm, and thicness - 1/ mm. #f the total solidification time of the casting itself is nown to %e 3.* min, determine the diameter of the riser so that it will tae 2*0 longer for the riser to solidify.
( )
V T =C m A
2
olution 9asting 'olume H - >Wt - 2++(1++)(1/) - 3;+,+++ mm3 9asting area A - 2(2++ " 1++ : 2++ " 1/ : 1++ " 1/) - *+,/++ mm 2 H6A - 3;+,+++6*+,/++ - .+/;; 9asting TT - 9m(.+/;;)2 - 3.*+ min 9m - 3.*6(.+/;;)2 - +.+; min6mm2 =iser 'olume H - π36; - +.*23;3 =iser area A - π2 - 3.11;2 H6A - +.*23;363.11;2 - +.1;; TT - 1.2*(3.*) - .3* min - +.+;(+.1;;) 2 - +.++13;2 2 - .3*6+.++13; - 22*. mm 2 - .* mm
