hw05
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University of California, Los Angeles *
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183A
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Aerospace Engineering
Date
Dec 6, 2023
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5
Uploaded by GrandLemurMaster943
MAE 183A: Spring Quarter 2023 Last Name First Name Page 1 of 1 Homework Assignment #05: Due Tuesday, May 09, 2023 Multiple Choice: MC13.1: A polymer melt has which of the following properties and characteristics? (a) becomes less resistant to flow as temperature increases, (b) becomes less resistant to flow at high shear rates, (c) becomes more resistant to flow as temperature increases, (d) becomes more resistant to flow at high shear rates, (e) high viscosity, (f) low viscosity, (g) Newtonian fluid, (h) viscoelasticity MC13.2: What are common sections of a conventional extruder barrel for thermoplastics? (a) compression section, (b) die section, (c) feed section, (d) heating section, (e) metering section, (f) shaping section MC13.3: The drag flow of polymer melt in the extruder barrel increases as which of the following parameters is increased? (a) diameter of the barrel, (b) head pressure, (c) rotational speed of screw, (d) temperature of polymer melt, (e) viscosity of polymer melt MC13.4: Which factors will reduce the amount of shrinkage during solidification and cooling in thermoplastic molding? (a) higher injection pressure, (b) higher molding temperature, (c) higher proportion of filler in the plastic, (d) lower injection pressure, (e) lower molding temperature, (f) lower proportion of filler in the plastic MC14.1: Rubber products can be described by which of the following? (a) elastomer reinforced with carbon black, (b) fiber reinforced composite, (c) particle reinforced composite, (d) polymer matrix composite, (e) pure elastomer, (f) pure polymer MC14.2: Relative to hand lay-up methods, what are some advantages of using prepregs prepared outside the mold and then laid onto the mold surface in successive layers? (a) closer control over fiber-resin mixture, (b) better surface finish, (c) easier for small parts, (d) more efficient method of adding laminations, (e) stronger moldings MC14.3: What is the tooling in filament winding that determines the shape of the filament-wound part called? (a) collet, (b) core, (c) fixture, (d) mandrel, (e) mold, (f) pattern MC14.4: Which of the following are not normally used in the processing of thermoplastic elastomers? (a) blow molding, (b) compression molding, (c) extrusion, (d) injection molding, (e) vulcanization Review Questions: Chapter 13: 13.3, 13.5, 13.19, 13.25 Chapter 14: 14.1, 14.9, 14.10, 14.19 Problems: Chapter 13: 13.2, 13.11, 13.21
HW 5 Review Questions 13.3 Viscosity is an important property of a polymer melt in plastics-shaping processes. Upon what parameters does viscosity depend? Viscosity depends on the shear rate and temperature. 13.5 Define die swell in extrusion. Die swell in extrusion is when the hot plastic expands as it exits the die opening. 13.19 Discuss some of the defects that can occur in plastic injection molding. Some of the defects that can occur in plastic injection molding are shrinkage, short shots, flashing, sink marks and voids, and wet lines. Shrinkage is usually the reduction in linear size that occurs during cooling from the molding temperature to room temperature. Short shots are a molding that has solidified before completely filling the cavity. Flashing typically occurs when the polymer melt is squeezed into the parting surface between mold plates or around ejection pins. Sink marks occur when the outer surface on the molding solidifies, but contraction of the internal material causes the skin to be depressed below the intended profile. Voids are caused by a similar process. But, the surface material retains its form, and the shrinkage is an internal void because of high tensile stresses on the still molten polymer. Weld lines occur when polymer melt flows around a core or other convex detail in the mold cavity and meets from opposite directions. 13.25 Why are the molds generally more costly in mechanical thermoforming than in pressure or vacuum thermoforming? The molds cost more in mechanical thermoforming because two halves are needed 14.1 What is a polymer matrix composite? Provide a definition. A polymer matrix composite (PMC) is a composite material that has a polymer embedded with a reinforcing phase like fibers or powders. 14.9 What is the difference between the wet lay-up approach and the prepreg approach in hand lay-up? The difference between the wet lay-up approach and the prepeg approach is that the wet lay-up approach does the impregnation of the resin into the fiber mat inside the mold, whereas the prepped approach prepares the impregnated layers of fiber reinforcement outside of the mold and are laid onto the mold surface afterwards. 14.10 Why are laminated FRP products made by the spray-up method not as strong as similar products made by hand lay-up?
Laminated FRP products made by the spray-up method are not as strong as similar products made by hand lay-up because they have randomly oriented short fibers, as opposed to the continuous and directed fibers in the hand lay-up method. 14.19 Name the four basic categories of processes used to shape rubber. The four basic categories of processes used to shape rubber are extrusion, calendering, coating, and molding and casting.
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