Industrial Engineering Chapter 10 Some Examples Are Chanical Properties With Appropriate Ductility Pearson Education Inc Upper

Chapter 10

Properties and Processing of

Polymers and Reinforced Plastics;

Rapid Prototyping and Rapid Tooling

Questions

10.1 Summarize the most important mechanical and

physical properties of plastics in engineering ap-

maries of mechanical properties, make compar-

10.2 What are the major differences between the

properties of plastics and of metals?

There are several major differences that can be

enumerated, as described throughout the chap-

ter. Some examples are:

(a) Plastics are much less stiff than metals.

(b) They have lower strength than metals and

are lighter.

(c) The thermal and electrical conductivities

of metals are much higher than those for

10.3 What properties are influenced by the degree of

polymerization?

polymerization will lead to higher strength and

10.4 Give applications for which flammability of

plastics would be a major concern.

By the student. There are several applica-

tions where flammability of plastics is a major

concern. These include aircraft, home insula-

tion (thermal and electrical), cookware, cloth-

ing, and components for ovens and stoves (in-

cluding components such as handles and dials).

Students should be encouraged to describe ad-

ditional applications.

10.5 What properties do elastomers have that ther-

moplastics, in general, do not have?

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10.6 Is it possible for a material to have a hystere-

sis behavior that is the opposite of that shown

in Fig. 10.14, whereby the arrows are counter-

clockwise? Explain.

10.7 Observe the behavior of the tension-test spec-

Recall that the mvalue indicates the strain

Fig. 10.13 on p. 598 elongates extensively by

orientation of the polymer molecules, thus it

10.8 Why would we want to synthesize a polymer

with a high degree of crystallinity?

swered in several ways. Students may rely upon

Fig. 10.4, and note that a high degree of crys-

(b) Functional and decorative: electrical out-

By the student. The glass-transition tempera-

ture is the temperature where a thermoplastic

behaves in a manner that is hard, brittle and

glassy below this temperature, and rubbery or

sition temperature higher than the maximum

10.11 Why does cross-linking improve the strength of

polymers?

Cross-linked polymers have additional bonds

linking adjacent chains together (see Fig. 10.3

resent additional bonds that must be broken

10.12 Describe the methods by which optical proper-

which can alter the color or translucence of

oped. Based on the contents of this chapter, are

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10.14 Give several examples of plastic products or

components for which creep and stress relax-

important. As an example of the importance

of creep, consider polymers as pot handles in

cookware. As an example of stress relaxation,

10.15 Describe your opinions regarding recycling of

plastics versus developing plastics that are

in the intended time frame, and they may have

more failures in service. They can be signifi-

10.16 Explain how you would go about determining

the hardness of the plastics described in this

tion 2.6 (see also Fig. 2.22 on p. 52) are not

10.17 Distinguish between composites and alloys.

Give several examples.

By the student. Consider the following:

•With composites, the reinforcement is

10.18 Describe the functions of the matrix and the

reinforcing fibers in reinforced plastics. What

fundamental differences are there in the char-

acteristics of the two materials?

fibers are generally stronger and/or stiffer than

the polymer matrix. The function of the rein-

are made of reinforced plastics? How can you

tell that they are reinforced?

tion and students can develop a wide variety of

answers. Some suggestions are tennis rackets,

fiber reinforcements can be seen directly on the

By the student. See Table 16.1 on p. 956. A

typical comparison is given below:

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10.21 Compare the relative advantages and limita-

tions of metal-matrix composites, reinforced

10.22 This chapter has described the many advan-

tages of composite materials. What limita-

tions or disadvantages do these materials have?

What suggestions would you make to overcome

these limitations?

By the student. Consider, for example, two dis-

advantages as anisotropic properties and pos-

sible environmental attack of the fibers (espe-

cially water adsorption). Anisotropy, though

not always undesirable, can be reduced by hav-

ing a random orientation of reinforcing ma-

terials. Environmental attack of the fibers

would cause loss of fiber strength and possibly

10.23 A hybrid composite is defined as a material con-

taining two or more different types of reinforc-

ing fibers. What advantages would such a com-

posite have over other composites?

level could be obtained at a lower cost by using

a combination of fibers, rather than just one

load.

10.25 Assume that you are manufacturing a product

in which all the gears are made of metal. A

salesperson visits you and asks you to consider

(a) Will the plastic gear retain its required

strength, stiffness, and tolerances if the

temperature changes during its use?

(b) How acceptable is the wear resistance and

fatigue life of the plastic gears?

(c) Is it compatible with meshing metal gears

and other components in the gear train?

(d) Are there any backlash problems?

(e) What are its frictional characteristics?

(f) Is the lighter weight of the plastic gear sig-

nificant?

(g) Is noise a problem?

bricants present?

(i) Will the supplier be able to meet the quan-

tity demanded?

(j) How much cost savings are involved? (See

10.26 Review the three curves in Fig. 10.8, and de-

scribe some applications for each type of be-

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Fig. 10.10.

food containers with impact strength at

low temperatures, such as in freezers.

will not crack at a wide range of tempera-

or impact resistant, it must be limited to

be used in passenger cars? If so, which compo-

nents? Explain.

tions concerning automobiles: (1) Radiators

with copper honeycomb structure to improve

10.29 Other than those described in this chapter,

what materials can you think of that can be

regarded as composite materials?

•Walls: consists of a plaster matrix with

wood stud or metal reinforcements.

10.30 What applications for composite materials can

you think of in which high thermal conductivity

would be desirable? Explain.

and.3.9.5. Composite materials with high ther-

ment, and identify the components that are

weight of these materials, combined with high

stiffness and strength, thus resulting in superior

10.32 We have described several material combina-

tions and structures in this chapter. In relative

sponses with appropriate rationale. For exam-

ple, very low temperature applications require

(1) considerations of the polymer or matrix me-

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10.33 Explain how you would go about determin-

ing the hardness of the reinforced plastics and

composite materials described in this chapter.

What type of tests would you use? Are hard-

ness measurements for these types of materials

meaningful? Does the size of the indentation

make a difference in your answer? Explain.

By the student. The important consideration

here is the fact that the smaller the indentation,

the more localized the hardness measurement

will be (see Section 2.6). Consequently, one

can then distinguish the hardness of the ma-

trix and the reinforcements separately by using

small indentations. A large indentation, such

metalworking techniques to the forming and

shaping of plastics.

uous extrusion process. Injection molding of

composites is difficult because the fluidity of

the material is essential to ensure proper filling

of the die, but characteristics and presence of

the fibers interferes with this process. Plastics

which are produced through reaction molding

are difficult to produce through other means,

and other processes are not readily adaptable

to allow sufficient mixing of the two ingredi-

ents. These difficulties should, however, be re-

garded as challenges and thus novel approaches

are encouraged. The students are encouraged

to develop additional answers.

10.37 Would you use thermosetting plastics in injec-

tion molding? Explain.

cross-linking of the material. The major draw-

back associated with this change is that, be-

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10.39 Give examples of several parts that are suitable

for insert molding. How would you manufacture

these parts if insert molding were not available?

Fig. 10.30 on p. 628. Some common parts are

screw drivers with polymer handles, electrical

volved in making a metal beverage container

versus a plastic one?

beverage can must have sufficient strength to

prevent from rupturing under internal pressure

10.41 Inspect several electrical components, such as

light switches, outlets, and circuit breakers, and

describe the process or processes used in mak-

electrical components may be potted.

10.42 Inspect several similar products that are made

of metals and plastics, such as a metal bucket

explain the reasons for their differences, if any.

much lower elastic modulus, as well as in-

volve designs with higher section modulus.

forced plastics. Identify which of the following

fiber orientation and arrangement capabilities

Sheet-molding compound X

Tape lay-up X X

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10.44 As you may have observed, some plastic prod-

ucts have lids with integral hinges; that is, no

other material or part is used at the junction

section, which can bend easily, thus acting like

a hinge. It should be noted that there are signif-

10.45 Explain why operations such as blow molding

and film-bag making are done vertically and

why buildings that house equipment for these

10.46 Consider the case of a coffee mug being pro-

duced by rapid prototyping. Describe how the

top of the handle can be manufactured, since

Fig. 10.49b on p. 649 would have to be used.

Other processes such as selective laser sintering

10.47 Make a list of the advantages and disadvantages

By the student. As examples, the students

could investigate (a) cost (where FDM, 3DP,

STL have advantages over SLS of metals, for ex-

10.48 Explain why finishing operations generally are

needed for rapid-prototyping operations. If you

the part has to be cured in order to fully de-

velop its mechanical properties (the laser does

10.49 A current topic of research involves producing

parts from rapid-prototyping operations and

then using them in experimental stress analysis,

ally manufactured parts, especially, for exam-

10.50 Because of relief of residual stresses during cur-

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10.51 One of the major advantages of stereolithog-

raphy and cyberjet is that semi- and fully-

transparent polymers can be used, so that in-

ship-in-the-bottle type of part; d (d) market-

ing models to explain the internal features of a

10.52 Based on the processes used to make fibers

as described in this chapter, explain how you

would produce carbon foam. How would you

make a metal foam?

erature search. One approach is to produce a

polymer foam followed by a carburization pro-

10.53 Die swell in extrusion is radially uniform for cir-

cular cross-sections, but is not uniform for other

cross-sections. Recognizing this fact, make

a qualitative sketch of a die profile that will

produce (a) square and (b) triangular cross-

sections of extruded polymer, respectively.

10.54 What are the advantages of using whiskers as

a reinforcing material? Are there any limita-

tions?

than other fibers because of their small size

and lack of defects (see pp. 105 and 463).

Whiskers will yield composite materials with

10.55 By incorporating small amounts of blowing

agent, it is possible to produce polymer fibers

with gas cores. List some applications for such

10.56 With injection-molding operations, it is com-

mon practice to remove the part from its run-

ner and then to place the runner into a shredder

and recycle into pellets. List the concerns you

would have in using such recycled pellets as op-

posed to so-called virgin pellets.

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10.57 What characteristics make polymers attractive

for applications such as gears? What character-

10.58 Can polymers be used to conduct electricity?

If a polymer’s chemistry can be identified, then

a polymer product can be cut into small pieces

preferred orientation, similar to the effect of

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or warp in the presence of bodily fluids;

support the loads developed during nor-

mal walking, sitting, and standing; not

portant, as well as impact strength and

toughness. The polymer needs to have a

stiffness consistent with typical golf balls,

demanding) shapes. It also has to be

available in a range of desired colors,

cloth and withstand normal wear and tear.

The polymer must have low elastic modu-

cleanable.

10.63 How can you tell whether a part is made of a

thermoplastic or a thermoset? Explain.

10.64 Describe the features of an extruder screw and

comment on their specific functions.

and depth is larger than elsewhere on the

screw.

the pressure and flow rate needed for the

extrusion operation.

10.65 An injection-molded nylon gear is found to con-

tain small pores. It is recommended that the

10.66 What determines the cycle time for (a) injection

molding, (b) thermoforming, and (c) compres-

sion molding?

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ing processes? Explain.

The type of defect shown in Fig. 10.57 also oc-

casting, and on p. 5.64 the same features are

10.68 List the differences between the barrel section

of an extruder and that on an injection-molding

heating elements and less from friction,

so there will be more (or larger capacity)

10.69 Identify processes that are suitable for making

10.70 Review the Case Study to this chapter and ex-

plain why aligners cannot be made directly by

rapid prototyping operations.

10.71 Explain why rapid prototyping approaches are

for producing parts (2 hours or so for a small

part is rapid when only one part is required.

10.72 List and explain methods for quickly manufac-

turing tooling for injection molding.

•An RTV molding/urethane casting opera-

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used, using an RTV mold, filled with pow-

10.73 Careful analysis of a rapid-prototyped part in-

dicates that it is made up of layers with a white

filament outline visible on each layer. Is the ma-

terial a thermoset or a thermoplastic? Explain.

process requires adjacent layers to fuse after

10.74 List the advantages of using a room-

temperature vulcanized (RTV) rubber mold

in injection molding.

10.75 What are the similarities and differences be-

tween stereolithography and cyberjet?

both processes rely on the same layer-creation

technique, namely liquid-layer curing, (b) both

use a principle of using a photopolymer to cre-

10.76 Explain how color can be incorporated into

•The ZCorp (see Fig. 10.52 on p. 651)

versions of three-dimensional printing ma-

curve (toughness) for the material in Fig. 10.9,

plot them as a function of temperature, and de-

(◦C) (MJ/m3)

-25 140

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Temperature (°C)

-50 0 50 100

800

600

10.78 Note in Fig. 10.9 that, as expected, the elastic

modulus of the polymer decreases as temper-

strain. The following table can be constructed:

-25 70 1.75

0 60 1.5

10.79 Calculate the percentage increase in mechani-

cal properties of reinforced nylon from the data

p. 585 as 1.4 GPa.

(J/m) 295b321

80c14

10.80 A rectangular cantilever beam 75-mm high, 25-

mm wide, and 1-m long is subjected to a con-

and steel, and for the same beam dimensions,

calculate the maximum deflection. Compare

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