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engineering
mechanical engineering
Questions and Answers of
Mechanical Engineering
Is it possible for a material to have a hysteresis behavior that is the opposite of that shown in Fig. 10.14, whereby the arrows are counterclockwise? Explain.
Explain why thermoplastics are easier to recycle than thermosets?
Describe the principle of shrink-wrap?
List the characteristics required of a polymer for the following applications: (a) A total hip replacement insert, (b) A golf ball, (c) An automotive dashboard, (d) Clothing, and (e) A child's doll.
How can you tell whether a part is made of a thermoplastic or a thermoset? Explain.
Describe the features of an extruder screw and comment on their specific functions?
An injection-molded nylon gear is found to contain small pores. It is recommended that the material be dried before molding it. Explain why drying will solve this problem?
What determines the cycle time for (a) Injection molding, (b) Thermoforming, and (c) Compression molding? Explain.
Does the pull-in defect (sink marks) shown in Fig. 10.57 also occur in metal-forming and casting processes? Explain.
List the differences between the barrel section of an extruder and that on an injection-molding machine?
Identify processes that are suitable for making small production runs of plastic parts, such as quantities of 100 or fewer. Explain?
Observe the behavior of the tension-test specimen shown in Fig. 10.13 and state whether the material has a high or low m value? Explain.
Review the Case Study at the end of this chapter and explain why aligners cannot be made directly by rapid prototyping operations?
Explain why rapid prototyping approaches are not suitable for large production runs?
List and explain methods for quickly manufacturing tooling for injection molding?
Careful analysis of a rapid-prototyped part indicates that it is made up of layers, with a white filament outline visible on each layer. Is the material a thermoset or a thermoplastic? Explain.
What are the similarities and differences between stereolithography and cyberjet?
Explain how color can be incorporated into rapid-prototyped components?
Calculate the areas under the stress-strain curve (toughness) for the material in Fig. 10.9. Plot them as a function of temperature and describe your observations?
In Fig. 10.9 that, as expected, the elastic-modulus of the polymer decreases as temperature increases. Using the stress-strain curves given in the figure, make a plot of the modulus of elasticity
Calculate the percentage increase in the mechanical properties of reinforced nylon from the data given in Fig. 10.19?
Why would we want to synthesize a polymer with a high degree of crystallinity? Explain.
A rectangular cantilever beam 75 mm high, 25 mm wide, and 1 m long is subjected to a concentrated force of 100 N at its end. Select two different unreinforced and reinforced materials from Table 10.1
Sections 10.5 and 10.6 described several plastics and their applications. Rearrange this information by making a table of products and the type of plastics that can be used to make the products?
Determine the dimensions of a tubular steel drive shaft for a typical automobile. If you now replace this shaft with shafts made of unreinforced and reinforced plastic, respectively, what should be
Calculate the average increase in the properties of the plastics listed in Table 10.1 as a result of their reinforcement, and describe your observations?
In Example 10.4, what would be the percentage of the load supported by the fibers if their strength is 1250 MPa and the matrix strength is 240 MPa? What if the strength is unaffected but the elastic
Estimate the die clamping force required for injection molding 10 identical 1.5-in.-diameter disks in one die. Include the runners of appropriate length and diameter?
A 2-liter plastic beverage bottle is made from a parison which has the same diameter as the threaded neck of the bottle and has a length of 5 in. Assuming uniform deformation during blow molding,
Estimate the consistency index and power-law index for the polymers in Fig. 10.12?
An extruder has a barrel diameter of 100 mm. The screw rotates at 100 rpm, has a channel depth of 6 mm, and a flight angle of 17.5°. What is the highest flow rate of polypropylene that can be
The extruder in Problem 10.88 has a pumping section that is 2.5 m long and is used to extrude round polyethylene solid rod. The die has a land of 1 mm and a diameter of 5 mm. If the polyethylene is
Add more items to the applications column in Table 10.3?
An extruder has a barrel diameter of 4 in., a channel depth of 0.25 in., a flight angle of 18°, and a pumping zone that is 6 ft long. It is used to pump a plastic with a viscosity of 100 × 10-4
What flight angle should be used on a screw so that a flight translates a distance equal to the barrel diameter with each revolution?
For a laser providing 10 kj of energy to a spot with diameter of 0.25 mm, determine the cure depth and the cured line width in stereolithography. Let Ec = 6.36 × 1010 J/m2 and Dp = 100 (m?
For the stereolithography system described in Problem 10.92, estimate the time required to cure a layer defined by a 40-mm circle if adjacent lines overlap each other by 10% and the power available
The extruder head in a fused-deposition-modeling setup has a diameter of 1 mm and produces layers that are 0.25 mm thick. If the velocities of the extruder head and polymer extrudate are both 50
The extruder head in a fused-deposition-modeling setup has a diameter of 1 mm and produces layers that are 0.25 mm thick. If the velocities of the extruder head and polymer extrudate are both 50
Referring to Fig. 10.7, plot the relaxation curves (i.e., the stress as a function of time) if a unit strain is applied at time t = ta?
Derive a general expression for the coefficient of thermal expansion in the fiber direction for a continuous fiber-reinforced composite?
Estimate the number of molecules in a typical automobile tire. Estimate the number of atoms?
Which properties of glasses allow them to be shaped into bottles by blowing? Are there any similarities to some of the sheet-metal forming operations, described in Chapter 7? Explain.
What properties should a plastic sheet possess when used in laminated glass, as in automotive windshields? Explain.
Consider some ceramic products that you are familiar with and outline a sequence of processes involved in manufacturing each of them?
Explain the difference between physical and chemical tempering of glass?
What do you think is the purpose of the operation shown in Fig. 11.27d? Explain.
Injection molding is a process that is used for plastics, powder metals, and ceramics. Why is it suitable for all these different types of materials?
Are there any similarities between the strengthening mechanisms for glass and those for other metallic and nonmetallic materials described throughout this text? Explain, giving specific examples.
Describe and explain the differences in the manner in which each of the following flat surfaces would fracture when struck with a large piece of rock: (a) Ordinary window glass, (b) Tempered glass,
What is mechanical alloying and what are its advantages over conventional alloying of metals, described in Section 5.2?
Describe the similarities and the differences between the processes described in this chapter and those in Chapters 5 through 10?
What is the doctor-blade process? Why was it developed?
Describe the methods by which glass sheet is manufactured?
Describe the differences and similarities in producing metal and ceramic powders. Which of these processes would be suitable for producing glass powder? Explain.
How are glass fibers made? List and explain the various applications of these fibers.
Would you consider diamond a ceramic? Explain.
What are the similarities and differences between injection molding, metal injection molding, and ceramic injection molding?
Aluminum oxide and partially stabilized zirco-nia are normally white in appearance. Can they be colored? If so, how?
It was stated that ceramics have a wider range of strengths in tension than do metals. List the reasons why this is so?
Estimate the number of particles in a 500-g sample of iron powder, if the particle size is 50 /μm?
It is possible to infiltrate P/M parts with various resins, as can be done with metals. What possible benefits would result from infiltration? Give some examples.
Assume that the surface of a copper particle is covered with a 0.1-μm-thick oxide layer. What is the, volume occupied by this layer if the copper particle itself is 75 μm in diameter? What could be
Determine the shape factor for a flakelike particle with a ratio of surface area to thickness of 12 × 12 × 1, for a cylinder with dimensional ratios 1:1:1, and for an ellipsoid with an axial ratio
It was stated in Section 3.3 that the energy in brittle fracture is dissipated as surface energy. It is also noted that the comminution process for powder preparation generally involves brittle
Referring to Fig. 11.6a, what should be the volume of loose, fine iron powder in order to make a solid cylindrical compact 25 mm in diameter and 15 mm high?
In Fig. 11.7e note that the pressure is not uniform across the diameter of the compact. Explain the reasons for this variation?
Plot the family of pressure-ratio px / po curves as a function of x for the following ranges of process parameters: μ = 0 to 1, k = 0 to 1, and D = 5 to 50 mm?
Derive an expression, similar to Eq. (11.2), for compaction in a square die with dimensions a by a?
For the ceramic material described in Example 11.7, calculate (a) The porosity of the dried part if the porosity of the fired part is to be 9% and (b) The initial length, L", of the part if the
What would be the answers to Problem 11.67 if the quantities given were halved?
Plot the UTS, E, and k values for ceramics as a function of porosity, P, and describe and explain the trends that you observe in their behavior?
What concerns would you have when electroplating P/M parts? Explain.
Plot the total surface area of a 1-g sample of aluminum powder as a function of the natural log of particle size?
Conduct a literature search and determine the largest size of metal powders that can be produced in atomization chambers?
Coarse copper powder is compacted in a mechanical press at a pressure of 20 tons / in2. During subsequent sintering, the green part shrinks an additional 8%. What is the final density of the part?
A gear is to be manufactured from iron powder, with a final density that is 90% of that of cast iron. It is known that the shrinkage in sintering will be approximately 5%. For a gear 2.5 in. in
What volume of powder is needed to make the gear in Problem 11.73 if its thickness is to be 0.5 in.?
The axisymmetric part shown in the accompanying figure is to be produced from fine copper powder and is to have a tensile strength of 200 MPa. Determine the compacting pressure and the initial mass
What techniques, other than the powder tube process, could be used to produce super conducting monofilaments? Explain.
Describe other methods that can be u manufacture the parts shown in Fig. 11.1a. Comment on the advantages and limitations of each of methods over P/M?
If a fully-dense ceramic has the properties of UTSo = 180 MPa and Eo = 300 GPa, what are these properties at 20% porosity for values of n = 4, and 7, respectively?
Calculate the thermal conductivities for ceramics at porosities of 1%, 5%, 10%, 20%, and 30% k" = 0.7 W / m-K?
Describe the effects of different shapes and sizes of metal powders in P/M processing, commenting on the magnitude and significance of the shape factor of the particles?
A ceramic has ko = 0.65 W / m-K. If this ceramic is shaped into a cylinder with a porosity distribution of P = 0.1(x / L) (l - x / L), where x is the distance from one end of the cylinder and L is
Assume that you are asked to give a quiz to students on the contents of this chapter. Prepare three quantitative problems and three qualitative questions, and supply the answers?
Make sketches of several P/M products in which density variations would be desirable. Explain why, in terms of the function of these parts?
Compare the design considerations for P / M products with those for products made by (a) Casting and (b) Forging. Describe your observations?
It is known that in the design of P/M gears, the distance between the outside diameter of the hub and the gear root should be as large as possible. Explain the reasons for this design consideration?
How are the design considerations for ceramics different, if at all, than those for the other materials described in this chapter? Explain.
Are there any shapes or design features that are not suitable for production by powder metallurgy? By ceramics processing? Explain.
What design modifications would you recommend for the part shown in Problem 11.75? Explain your reasoning.
The axisymmetric parts shown in the accompanying figure are to be produced through P/M. Describe the design changes that you would recommend?
Assume that in a particular design, a metal beam is to be replaced with one made of ceramics. Discuss the differences in the behavior of the two beams, such as with respect to its strength,
Comment on the shapes of the curves and their relative positions shown in Fig. 11.6?
Describe your thoughts regarding designs of internal combustion engines that have ceramic pistons?
Assume that you are employed in technical sales in powder-metallurgy products. What applications currently using non-P/M parts would you try to develop? What would you advise your potential customers
Pyrex cookware displays a unique phenomenon: It functions well for a large number of cycles and may then shatter into many pieces. Investigate this phenomenon, list the probable causes, and discuss
It has been noted that the strength of brittle materials, such as ceramics and glasses, is very sensitive to surface defects such as scratches (notch sensitivity)? Obtain some pieces of these
Make a survey of the technical literature and describe the differences, if any, between the quality of glass fibers made for use in reinforced plastics and those made for use in fiber-optic
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