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physics
thermodynamics

Questions and Answers of Thermodynamics

Write an essay on polymeric materials that are used in the packaging of food products and drinks. Include a list of the general requisite characteristics of materials that are used for these
Write an essay on the replacement of metallic automobile components by polymers and composite materials. Address the following issues: (1) Which automotive components (e.g., crankshaft) now use
From the stress-strain data for poly(methyl methacrylate), determine the modulus of elasticity and tensile strength at room temperature [20°C (68°F)], and compare these values with those given in
Make two schematic plots of the logarithm of relaxation modulus versus temperature for an amorphous polymer (curve C in Figure 15.8).(a) On one of these plots demonstrate how the behavior changes
For thermoplastic polymers, cite five factors that favor brittle fracture.
(a) Compare the fatigue limits for polystyrene and the cast iron for which fatigue data are given in Problem 8.20. (b) Compare the fatigue strengths at 106 cycles for poly(ethylene terephthalate)
In your own words, describe the mechanisms by which semi crystalline polymers (a) elastically deform and (b) plastically deform, and (c) by which elastomers elastically deform.
Briefly explain how each of the following influences the tensile modulus of a semi crystalline polymer and why: (a) Molecular weight (b) Degree of crystallinity (c) Deformation by drawing (d)
Briefly explain how each of the following influences the tensile or yield strength of a semi crystalline polymer and why: (a) Molecular weight (b) Degree of crystallinity (c) Deformation by
Normal butane and isobutane have boiling temperatures of -0.5 and -12.3°C (31.1 and 9.9°F), respectively. Briefly explain this behavior on the basis of their molecular structures, as presented in
The tensile strength and number-average molecular weight for two poly(methyl methacrylate) materials are as follows:Estimate the tensile strength at a number-average molecular weight of 30,000 g/mol.
The tensile strength and number-average molecular weight for two polyethylene materials are as follows:Estimate the number-average molecular weight that is required to give a tensile strength of 195
For each of the following pairs of polymers, do the following: (1) state whether or not it is possible to decide whether one polymer has a higher tensile modulus than the other; (2) if this is
Compute the elastic moduli for the following polymers, whose stress-strain behaviors may be observed in the "Tensile Tests" module of Virtual Materials Science and Engineering (VMSE): (a)
For each of the following pairs of polymers, do the following: (1) state whether or not it is possible to decide whether one polymer has a higher tensile strength than the other; (2) if this is
Would you expect the tensile strength of polychlorotrifluoroethylene to be greater than, the same as, or less than that of a polytetrafluoroethylene specimen having the same molecular weight and
For each of the following pairs of polymers, plot and label schematic stress-strain curves on the same graph [i.e., make separate plots for parts (a), (b), and (c)].(a) Isotactic and linear
List the two molecular characteristics that are essential for elastomers.
Which of the following would you expect to be elastomers and which thermosetting polymers at room temperature? Justify each choice. (a) Epoxy having a network structure (b) Lightly cross linked
Ten kilogram of polybutadiene is vulcanized with 4.8 kg sulfur. What fraction of the possible crosslink sites is bonded to sulfur cross links, assuming that, on the average, 4.5 sulfur atoms
Compute the weight percent sulfur that must be added to completely crosslink an alternating chloroprene-acrylonitrile copolymer, assuming that five sulfur atoms participate in each crosslink.
The vulcanization of polyisoprene is accomplished with sulfur atoms according to Equation 15.4. If 57 wt% sulfur is combined with polyisoprene, how many cross links will be associated with each
For the vulcanization of polyisoprene, compute the weight percent of sulfur that must be added to ensure that 8% of possible sites will be cross linked; assume that, on the average, three sulfur
Demonstrate, in a manner similar to Equation 15.4, how vulcanization may occur in a butadiene rubber.
For the nylon polymer, whose stress strain behavior may be observed in the "Tensile Tests" module of Virtual Materials Science and Engineering (VMSE), determine the following: (a) The yield strength,
Determine values for the constants n and k (Equation 10.17) for the crystallization of polypropylene (Figure 15.17) at 160°C.
Name the following polymer(s) that would be suitable for the fabrication of cups to contain hot coffee: polyethylene, polypropylene, poly(vinyl chloride), PET polyester, and polycarbonate. Why?
Of those polymers listed in Table 15.2, which polymer(s) would be best suited for use as ice cube trays? Why?
For each of the following pairs of polymers, plot and label schematic specific volume versus temperature curves on the same graph [i.e., make separate plots for parts (a), (b), and (c)]. (a)
For each of the following pairs of polymers, do the following: (1) state whether or not it is possible to determine whether one polymer has a higher melting temperature than the other; (2) if it is
Make a schematic plot showing how the modulus of elasticity of an amorphous polymer depends on the glass transition temperature. Assume that molecular weight is held constant.
Briefly explain the difference in molecular chemistry between silicone polymers and other polymeric materials.
List two important characteristics for polymers that are to be used in fiber applications.
Cite five important characteristics for polymers that are to be used in thin-film applications.
Cite the primary differences between addition and condensation polymerization techniques
For the phenol-formaldehyde (Bakelite) polymer, whose stress strain behavior may be observed in the "Tensile Tests" module of Virtual Materials Science and Engineering (VMSE), determine the
(a) How much ethylene glycol must be added to 47.3 kg of terephthalic acid to produce a linear chain structure of poly(ethylene terephthalate) according to Equation 15.9? (b) What is the mass of the
Nylon 6,6 may be formed by means of a condensation polymerization reACtion in which hexamethylene diamine [NH2-(CH2)6-NH2] and adipic ACid reACt with one another with the formation of water as a
What is the distinction between dye and pigment colorants?
Cite four factors that determine what fabrication technique is used to form polymeric materials.
Contrast compression, injection, and transfer molding techniques that are used to form plastic materials.
Why must fiber materials that are melt spun and then drawn be thermoplastic? Cite two reasons.
Which of the following polyethylene thin films would have the better mechanical characteristics: (1) formed by blowing, or (2) formed by extrusion and then rolled? Why?
In your own words, briefly describe the phenomenon of viscoelasticity.
For some viscoelastic polymers that are subjected to stress relaxation tests, the stress decays with time according towhere Ïƒ(t) and Ïƒ(0) represent the time-dependent and initial (i.e., time =
The logarithm of Er(t) versus the logarithm of time is plotted for polyisobutylene at a variety of temperatures. Make a plot of Er(10) versus temperature and then estimate its Tg.
(a) Contrast the manner in which stress relaxation and viscoelastic creep tests are conducted. (b) For each of these tests, cite the experimental parameter of interest and how it is determined.
Composite materials are now being utilized extensively in sports equipment. (a) List at least four different sports implements that are made of, or contain composites. (b) For one of these
It is desired to produce an aligned and continuous fiber-reinforced epoxy composite having a maximum of 50 vol% fibers. In addition, a minimum longitudinal modulus of elasticity of 50 GPa (7.3 × 106
It is desired to produce a continuous and oriented carbon fiber-reinforced epoxy having a modulus of elasticity of at least 83 GPa (12 Ã— 106 psi) in the direction of fiber alignment. The
It is desired to fabricate continuous and aligned glass fiber-reinforced polyester having a tensile strength of at least 1400 MPa (200,000 psi) in the longitudinal direction. The maximum possible
It is necessary to fabricate an aligned and discontinuous carbon fiber-epoxy matrix composite having a longitudinal tensile strength of 1900 MPa (275,000 psi) using 0.45 volume fraction of fibers.
A tubular shaft similar to that shown in Figure 16.11 is to be designed that has an outside diameter of 80 mm (3.15 in.) and a length of 0.75 m (2.46 ft). The mechanical characteristic of prime
The mechanical properties of aluminum may be improved by incorporating fine particles of aluminum oxide (Al2O3). Given that the moduli of elasticity of these materials are, respectively, 69 GPa (10
For a continuous and oriented fiber-reinforced composite, the moduli of elasticity in the longitudinal and transverse directions are 19.7 and 3.66 GPa (2.8 × 106 and 5.3 × 105 psi), respectively.
(a) Verify that Equation 16.11, the expression for the fiber load-matrix load ratio (Ff/Fm), is valid. (b) What is the Ff/Fc ratio in terms of Ef, Em, and Vf?
In an aligned and continuous glass fiber-reinforced nylon 6,6 composite, the fibers are to carry 94% of a load applied in the longitudinal direction.(a) Using the data provided, determine the volume
Assume that the composite described in Problem 16.8 has a cross-sectional area of 320 mm2 (0.50 in.2) and is subjected to a longitudinal load of 44,500 N (10,000 lbf).(a) Calculate the fiber-matrix
A continuous and aligned fiber-reinforced composite having a cross-sectional area of 1130 mm2 (1.75 in.2) is subjected to an external tensile load. If the stresses sustained by the fiber and matrix
Compute the longitudinal strength of an aligned carbon fiber-epoxy matrix composite having a 0.25 volume fraction of fibers, assuming the following: (1) an average fiber diameter of 10 × 10-3 mm
It is desired to produce an aligned carbon fiber-epoxy matrix composite having a longitudinal tensile strength of 750 MPa (109,000 psi). Calculate the volume fraction of fibers necessary if (1) the
Compute the longitudinal tensile strength of an aligned glass fiber-epoxy matrix composite in which the average fiber diameter and length are 0.010 mm (4 × 10-4 in.) and 2.5 mm (0.10 in.),
(a) From the moduli of elasticity data in Table 16.2 for glass fiber-reinforced polycarbonate composites, determine the value of the fiber efficiency parameter for each of 20, 30, and 40 vol%
For a polymer-matrix fiber-reinforced composite, (a) List three functions of the matrix phase. (b) Compare the desired mechanical characteristics of matrix and fiber phases. (c) Cite two reasons why
Estimate the maximum and minimum thermal conductivity values for a cermet that contains 85 vol% titanium carbide (TiC) particles in a cobalt matrix. Assume thermal conductivities of 27 and 69 W/m-K
(a) What is the distinction between matrix and dispersed phases in a composite material? (b) Contrast the mechanical characteristics of matrix and dispersed phases for fiber-reinforced composites.
(a) Calculate and compare the specific longitudinal strengths of the glass-fiber, carbon-fiber, and aramid-fiber reinforced epoxy composites in Table 16.5 with the following alloys: tempered (315°C)
(a) List four reasons why glass fibers are most commonly used for reinforcement. (b) Why is the surface perfection of glass fibers so important? (c) What measures are taken to protect the surface of
(a) Cite several reasons why fiberglass-reinforced composites are utilized extensively. (b) Cite several limitations of this type of composite.
(a) What is a hybrid composite? (b) List two important advantages of hybrid composites over normal fiber composites.
(a) Write an expression for the modulus of elasticity for a hybrid composite in which all fibers of both types are oriented in the same direction. (b) Using this expression, compute the longitudinal
Derive a generalized expression analogous to Equation 16.16 for the transverse modulus of elasticity of an aligned hybrid composite consisting of two types of continuous fibers.
Briefly describe pultrusion, filament winding, and prepreg production fabrication processes; cite the advantages and disadvantages of each.
Briefly describe laminar composites. What is the prime reason for fabricating these materials?
A large-particle composite consisting of tungsten particles within a copper matrix is to be prepared. If the volume fractions of tungsten and copper are 0.60 and 0.40, respectively, estimate the
(a) Briefly describe sandwich panels. (b) What is the prime reason for fabricating these structural composites? (c) What are the functions of the faces and the core?
(a) What is the distinction between cement and concrete? (b) Cite three important limitations that restrict the use of concrete as a structural material. (c) Briefly explain three techniques that are
Cite one similarity and two differences between precipitation hardening and dispersion strengthening.
For some glass fiber-epoxy matrix combination, the critical fiber length-fiber diameter ratio is 50. Using the data in Table 16.4, determine the fiber-matrix bond strength.
(a) For a fiber-reinforced composite, the efficiency of reinforcement Î· is dependent on fiber length l according towhere x represents the length of the fiber at each end that does not
A continuous and aligned fiber-reinforced composite is to be produced consisting of 30 vol% aramid fibers and 70 vol% of a polycarbonate matrix; mechanical characteristics of these two materials are
Is it possible to produce a continuous and oriented aramid fiber-epoxy matrix composite having longitudinal and transverse moduli of elasticity of 57.1 GPa (8.28 × 106 psi) and 4.12 GPa (6 × 105
(a) Briefly explain the difference between oxidation and reduction electrochemical reactions.
Demonstrate that the constant K in Equation 17.23 will have values of 534 and 87.6 for the CPR in units of mpy and mm/yr, respectively.
A piece of corroded steel plate was found in a submerged ocean vessel. It was estimated that the original area of the plate was 10 in.2 and that approximately 2.6 kg had corroded away during the
A thick steel sheet of area 400 cm2 is exposed to air near the ocean. After a one-year period it was found to experience a weight loss of 375 g due to corrosion. To what rate of corrosion, in both
(a) Demonstrate that the CPR is related to the corrosion current density i (A/cm2) through the expression CPR = KAi/nρ (17.38) where K is a constant, A is the atomic weight of the metal
Using the results of Problem 17.13, compute the corrosion penetration rate, in mpy, for the corrosion of iron in citric acid (to form Fe2+ ions) if the corrosion current density is 1.15 × 10-5 A/cm2.
(a) Cite the major differences between activation and concentration polarizations. (b) Under what conditions is activation polarization rate controlling?
(a) Describe the phenomenon of dynamic equilibrium as it applies to oxidation and reduction electrochemical reactions.
Lead experiences corrosion in an acid solution according to the reaction Pb + 2H+ → Pb2+ + H2 The rates of both oxidation and reduction half-reactions are controlled by activation polarization. (a)
The corrosion rate is to be determined for some divalent metal M in a solution containing hydrogen ions. The following corrosion data are known about the metal and solution: (a) Assuming that
The influence of increasing solution velocity on the overvoltage-versus-log current density behavior for a solution that experiences combined activation-concentration polarization is indicated. On
(a) Write the possible oxidation and reduction half-reactions that occur when magnesium is immersed in each of the following solutions: (i) HCl, (ii) an HCl solution containing dissolved oxygen,
Why does chromium in stainless steels make them more corrosion resistant in many environments than plain carbon steels?
Briefly explain why cold-worked metals are more susceptible to corrosion than non cold-worked metals.
Briefly explain why, for a small anode-to-cathode area ratio, the corrosion rate will be higher than for a large ratio. Solution
For a concentration cell, briefly explain why corrosion occurs at that region having the lower concentration.
(a) What are inhibitors?
Briefly describe the two techniques that are used for galvanic protection.

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