I: Answer in one to two sentences
1.Why do thermoplastics have shorter processing times than thermosets?
2.Why is it easier to process with thermosets than with thermoplastics?
3.Compare the percentage of elongation at break for glass, graphite,
and aramid fibers with aluminum and steel in the table below. What material properties
are improved with increase in percentage elongation at break?
How is specific strength calculated for these materials?

4.What are the commonly used fibers and resins in the thermoset
composites industry?
5.Which thermoset and thermoplastic resins are used for high temperature
composite applications?
6.What are the differences between woven and non-woven fabrics?
Write the pros and cons of these fabrics?
7.What is a prepreg ? List types of prepregs and write down the composite manufacturing techniques that use prepregs.
 

II: Injection Molding

1. What is ``fountain flow'' in injection molding? What process and material parameters determine its significance? What is the result of this flow?
2. What are ``skin'' and ``core'' layers in injection molding?
3. Does the length of the fibers change during the flow of suspension in injection molding? Explain why.
4. Give some examples of common products that are injection molded.
 

III: Extrusion
1. What are the two phenomena that help to soften and then melt the solid polymer pellets in an extrusion machine before it is pushed by the screw? Which one creates more heat?
2. What is ``die swelling?'' What causes it?
3. What are the similarities and differences between the extrusion and injection molding processes?
4. Give some examples of common products that are manufactured with the extrusion process.

IIIc: Compression Molding

1. What is ``initial charge'' in the compression molding process? Why is it crucial to properly place it inside the mold?
2. The tensile strength and elastic modulus of compression molded parts might exhibit significant variations from one molding to another. What are the two main reasons?

IV: Advanced Thermoplastic Manufacturing

List the advanced composite thermoplastic manufacturing methods. What are the advantages and disadvantages of these manufacturing processes?

V: Advanced Thermoset Composites

List important transport issues in thermoset filament winding, autoclave processing and liquid composite molding. Name at least two issues that are common to all the thermoset processes listed above, and name two issues that are specific to each individual process.

VI: Process Selection

You have been chosen to select a composite manufacturing process due to your familiarity with the processes as a result of the course you took at the University of Delaware. Your company is looking at making the following components and would like you to recommend which process should be considered with a single sentence explanation as to why you selected that process.
1.) Short fiber reinforced dashboards for the new Acura car.
2.) Telephone poles for the city of Newark
3.) I-beams for Ford Passenger Vans
4.) Axi-symmetric casing for the rocket motor
5.) Recycleable door panels for the Mercedes Benz
6.) A composite spring for a helicopter.
7) Tail of Airbus 330

VII: Manufacturing Process and Part Geometry

I.  Consider unidirectional stretching of a cylinder as shown in the figure below. At any time, t, assume that R(t) is independent of z.

(a) Using only the conservation of mass show that the velocity field is given by
   uz  =  U *z/L(t)        and ur = - U *r/2*L(t)

b)   find the components of the strain rate tensor

c) Neglecting surface tension and inertia, calculate the force F required to pull the Newtonian Viscous cylinder.

II. Flow through a Circular pipe

Resin of viscosity 1 Poise is made to flow through a tube of radius R from a bucket at atmospheric pressure by applying a perfect vacuum. The length of the tube is L.
(a) Calculate the steady state flow rate of the resin through the tube if R= 6 mm and L= 30 cm.
(b) Now if you attach a second tube of R= 3mm and L= 30cm at the end of the first tube through an air tight fitting, by what percentage will the flow rate reduce by as compared to the flow rate in part (a) ?

 III. A layer of fluid with thickness d (delta)  flow down  a vertical wall as shown below. Gravity acts to pull the fluid down the wall.

 a.Find and sketch the velocity distribution for a Viscous Newtonian fluid of viscosity m (mu).
b. If you can measure the flow rate, what will be its thickness d (delta) in terms of viscosity and the flow rate Q
 
 

 1.Heating of a composite between two aluminum plates

Consider a glass-polypropylene composite 0.3 cm  thick  at room temperature of 25C to be heated by conduction by  aluminum platens  held at 150C.

   1. How long will it take for the midplane of the glass-polypropylene composite containing 50% glass fibers to reach 125C?.
   2.If the composite contained 50% carbon fibers instead of glass fibers, how long would you wait until the center reaches 125C?.
   3.If these composites were placed in an oven at 200C, estimate the time  it would take to heat the composite to 175C. Assume the heat
     transfer coefficient between the air and the composite is 5 W/mK
 

2. Viscosity Measurements:
Below you are given some of the measurements made using a cone and plate viscometer of the torque and angular velocities. The radius of the plate is 1 cm and the angle of the cone is 9 degrees (pi/20)

         Torque (N-m)             angular Speed (rad/s)
         2.08E-05 0                    .015707963
         2.08E-04                        0.157079633
         6.53E-04                         1.570796327
         2.12E-03                         15.70796327
         6.47E-03                         157.0796327
 

   a.Find the two parameters if one were to use a two parameter power-law model
  b.Using the power-law model determine the pressure drop required to pump this material at a flow rate of 100 cc/s through a circular tube of radius 1 cm that is one meter long.
c. What would be your calculation for the pressure drop if you had assumed the fluid to be Newtonian?
 
 



Assignment no:4
Due Date:  Lecture 18(October 28th)

Ia. Composite Manufacturing in a Mold: How Filling time changes with variations along the edges? (25 points)

Start with Darcy’s Law and the definition of the Darcy averaged velocity (xff is the distance from the inlet to the flow front):


Derive the time to fill the entire mold for a one-dimensional, constant pressure injection.  The final formula should be in the form:


Where,
m fluid viscosity
L length of mold
f porisity of preform
Kxx permability of preform in flow direction
Pinj injection pressure
 

We will explore the following geometry:



Use the above derived analytical solution to calculate the time to fill for the one-dimensional, constant pressure injection.

Ib: Numerical simulation to quantify effect of racetracking (50 points)

Using LIMS, simulate the above case and get the time to fill and see how it compares to the analytical solution.  Next, apply race tracking along the top edge of varying amounts.  Simulate the flow using LIMS and note the fill time for each case.  Plot the normalized race tracking strength (Krace/Kbulk) versus the normalized time to fill (t to fill / time to fill w/ no race tracking).  Preform 10 different simulations varying Krace/Kbulk from 1-150.
 

II. Dimensionless Analysis (25 points)

Isothermal Newtonian Flow into a Cavity

Consider flow in a disk mold as shown in the figure below. Write down conservation of mass and momentum equations along with BC. State plausible assumptions to simplify them. Select characteristic values to derive the non-dimensional form of the equations and eliminate terms that will be insignificant. Find the time it will take to fill the mold if the resin is injected into the mold under constant pressure of Po.


 
 




Assignment no:5
Due Date:  Lecture 22(Nov. 11th)

I. EXTRUSION

A screw extruder is 50 mm in diameter, 1 m long, has a 50mm lead, a channel 5 mm deep and a flight 3 mm wide. It is used to pump a fluid with viscosity of 50,000  poise and operates at a screw speed of 50 rpm.

a. What is the maximum possible flow rate of the extruder under the circumstances ? What is the maximum possible pressure drop ?

b. A die is attached to the end of the extruder, for which flow rate, is given as

where K=8.5 x 10^-5 cm³. What are the resulting flow rate and pressure drop ?

c. Does the  flow rate and pressure  in Part  (b) change if the viscosity increases ?

II. INJECTION MOLDING

2. Consider injection molding of a plaque 1 meter long, 50 centimeters wide and  0.25 centimeters thick. The injection is at one end of the plaque all along the width as shown in the figure below.

 
 

Two different plaques are to be manufactured. First one will contain polypropylene with 25% glass fibers which has an effective viscosity of 100 Poise and the second one contains nylon with 30% carbon fibers which has an effective viscosity of 1000 Poise. The mold wall is held at 25C. The polypropylene melt temperature is 175C and that of Nylon is 250C. The effective thermal conductivity of polypropylene with 25% glass is k= 1W/mC and that of Nylon with 30% carbon fibers is 10 W/mK. The injection rate is held constant at 100 cc/sec.
a. Find the approximate frozen layer thickness assuming fully developed flow away from the injection gate and the flow front for both, polypropylene and nylon
b. Find the maximum pressure that will be required approximately to fill the both the polypropylene and the nylon plaque.
c. If your marketing dept. wants to reduce the thickness of the plaque by half, how much pressure will the injection molding machine have to generate to fill the plaque under the same flow rate conditions?

III. FINAL PROJECT SELECTION AND PLAN

Submit:
A. The title of your project
B. Project Proposal

The project proposal should be about 300 words and should
State the issue and the process that will be addressed, the approach that will be followed to solve the problem and an outline of the work to be performed.

The final project presentation and report should describe
a. The process
b. The issues that will gain from scientific analysis
c. The specific issue you want to address
d. Governing Equations and Constitutive Laws used
e. Choice and explanation of Boundary Conditions
f. Identification of material, geometric and process parameters
g. Assumptions and their justification
h. Non-Dimensionalization of the equations and boundary conditions
i. Solution method and Parametric studies
j. Comment on Results
k. How the model can be revised to improve the representation of the issue that you addressed
 

 

 

Assignment no:6
Due Date:  Lecture28(Dec. 7th)

. a) What process would you use to make a solid circular fishing rod using carbon fibers and vinyl ester resin ?
b) What are the important geometric, material and process parameters that will impact the final properties and performance of the rods?
c) Assume that the process you used does not completely cure the resin, so you have to place the rod in an oven at temperature Toven to post cure the rod. The initial temperature of the rod is Tint when you place it in the oven and the convective heat transfer coefficient is h between the oven and the outside surface of the rod.
(i) Write the energy equation that will govern the heat transfer process and the temperature variation in the rod along with the boundary conditions.
(ii) Identify the important parameters and non-dimensionalize the energy equation and boundary conditions using characteristic values
(iii) Eliminate terms that are not important assuming that L>>>R
(iv) A long time after the curing reaction is complete, what will be the final temperature profile inside the fishing rod?