MEEG 655/855: Principles of Composites Manufacturing

Assignment no:1

Due Date:  Lecture6(Sept. 13th)

I: Please select a composite manufacturing process to fabricate the following components. Choose the materials, i.e fibers (will it be glass, kevlar or carbon, will it be chopped fibers, continuous strands or woven) and resin (thermoset or thermoplastic). State your reasons for selection of the process and the materials. .

1. Turbine Housing for Jet Engines

2.Fuselage for Boeing Dreamliner

3.High Pressure tanks for Hydrogen Storage under 10, 000 Psi

4. Carbon Composite Car Chassis

5.Rocket Motor Casing

II. Composite materials are replacing traditional materials in many applications. List at least 5 examples of polymer composite material being used in different applications since 2000. Also state the reasons for the replacement. Can you think of a component or an application that is currently not being made of composite materials but will benefit greatly if it was ? State the benefits
 

III.   Consider a converging pultrusion die as shown below. As you pull the fibers through it does the resin pressure increase or decrease along the axial direction inside the die ? State you reason. Is it advisable to pull in the direction of converging or would it be more useful to pull in the opposite direction ?

IV. 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.
 
 


 
 

MEEG 655/855: Principles of Composites Manufacturing

Assignment no:2

Due Date: Sept. 27th

 
 

     I Squeeze flow between two circular disks:

Consider a thermoplastic containing fibers (GMT) material being squeezed between two circular platens. The radius of the disks is R and is much larger that the initial thickness hi. The material GMT is highly viscous and may be assumed to behave like a Newtonian fluid. If you continue to move the two disks   towards each other at the speed of  , how will the force required change with the thickness, radius of the disks and the material properties of GMT? Assume that the material sticks on the platen walls and does not slip along them. Will the force, F required also depend on the initial thickness hi of the material? Justify your answer

     II: Circulating slow flow of a viscous resin

 A thin plate (thickness 2kH) moves with constant velocity V through a wide and long container (thickness 2H, where H<< length (L) and the width (W)) filled with an incompressible viscous liquid. The fluid circulates in the container, moving to the right along the central core and moving to the left close to the fixed wall of the container.
     a. It is desired to find the velocity distribution in the container, away from the end disturbances. k is just slightly less than unity.
     b. Also calculate the force, required to move the plate if we ignore the end disturbances in terms of the V, L,W,k,H and viscosity, h  of the viscous fluid.
     c. If you modify this set-up such that the plate was a circular fiber tow and the container was cylindrical, would any fluid impregate inside the fiber tow?
         Do you expect the most impregnation downstream or upstream ? Why ?


 

III   Permeability Measurement Experiment

The goal is to find the permeability of a glass fabric and the possible variation in such a measurement. The permeability characterization experiment will be performed for a selected fiber volume fraction with the fluid being injected under constant injection pressure.  A video camera will record the visible flow front progression through the transparent mold lid. A scale may be placed along the mold length to later extract the information of location of the flow front as a function of time.
Steps in the procedure that should be followed are as follows:
1. Partially assemble the mold
2. Carefully cut the fabric layers (sufficient for two experiments)
3. Stack the fabric layer in the mold cavity
4. Close the mold
5. Prepare the corn syrup and water mixture and measure its viscosity (should be in the range of 50 to 500 cp) ( one cp is the viscosity of water)
6. Place the fluid in the container and pressurize it.
7. Inject the fluid into the mold with constant pressure at the inlet
8. Record the motion of the flow front with the camera
9. Stop the experiment when the fluid reaches the vent
10. Dismantle the setup
11. Clean up the mold and the area
12. Process the data to find the permeability

MATERIAL AND PROCESS INFORMATION
Reinforcement material:             Fiberglass: Random Mat
Density: 2570 kg/m3
Aerial weight: to be measured
Number of layers: 2 (for each experiment)
Mold:  Cavity thickness: 3.2 mm and Width: 206.4 mm
Resin system:                             Mixture of corn syrup and water
Viscosity: to be measured
Injection pressure to be obtained during the experiment: 10-15 psi (Please DO NOT exceed)
OTHER INFORMATION
A.  Measure the aerial weight of the preform used and deduce its porosity value for the experiment using the dimensions of the mold
B.  Conduct the experiment in a group of 3 or 4 and save the data collection video of the experiment (bring a memory stick or a zip disk)
C.  Find the permeability of the preform for the fiber volume fraction you used for your experiment. Show all your calculations on how you obtained the permeability value.
D. List possible errors in your experiments and recommend how you would improve the experiment.

The group can share the experimental data but the report should be written individually.
Justin Alms (jbalms@udel.edu) will help you with the experiment. Groups will be assigned in class.
Please see Justin in room 007 and he will walk you over to CCM where you will be given the materials and
instruction for conducting the experiment.

MEEG 655/855: Principles of Composites Manufacturing

Assignment no:3

Due Date:  October 4th

  1. Consider flow of resin in a circular mold from a circular hole of three centimeter in diameter. Assume the permeability of the preform to be isotropic so the flow will be concentric.
    1. Analytic Solution: Formulate a relationship of how the radius of the flow front changes with time as a function of the fabric permeability, fiber volume fraction, inlet hole size, thickness of the mold and the viscosity of the resin. Assume the inlet pressure to be constant.
    2. Numerical Solution with LIMS: Four meshes representing a circular disk 50 cm in diameter similar to that shown on the right are provided to you in the MEEG655 folder. Two of the meshes were created using SolidWorks and the other two were created using LEGO. Each mesh was created with a different degree of refinement. Use LIMS UI to calculate the fill time for each mesh by injecting from the center. Perform this task twice for each mesh, once where you select only the center node located at position (0,0,0) as the injection gate. Then once again where you model the injection gate of a one centimeter in diameter injection tube. Use the LIMS UI  to select all the nodes near the central node that lie within the area of the tube to model the injection hole. 
    3. Compare the filling time of your 8 meshes with the analytic filling time. Use the following properties for your analysis:

Submit as a pdf file:

  1. Screen shots of each filling sequence, there should be eight total.
  2. Table describing the mesh name, number of nodes in mesh, fill time, relative error with analytical solution
  3. Explanation of results. Try to explain differences in the results you saw (if any).

II. Tracking Flow Fronts in VARTM using LIMS:

To model the VARTM process you will have to provide different permeabilities for the distribution media and the preform.The goal is to see how the flow in the distribution media leads the flow in the preform for the following geometry

This current type of tracking will require you to use the LIMS console and the results are viewable in the LIMS UI.Two meshes are provided that represent the same geometry except the degree of refinement is different for each case.The mold is half a meter long and is six millimeters thick.The mesh represents only the fabric, you will have to add one-dimensional element to model the presence of distribution media as shown during the class.Once all the properties of the mesh are properly set you can save the mesh for further analysis.The injection gate properties can be set during the execution of the simulation.All the nodes along the left boundary will be used as injection gates as shown in the picture above.After the simulation is complete, please plot the Lead length which is the difference between the movement of the flow front along the top in the distribution media and the movement of the resin along the bottom (tool surface) as a function of time for both cases.

Use the following properties for your analysis:

Submit as a pdf file:

  1. Screen shots of the two simulations results.
  2. Table describing mesh name, number of nodes, fill time.
  3. Explanation of results. Try to explain any differences in results (if any).
  4. One graph that shows the lead length v/s time for the coarse as well as fine mesh.


MEEG 655/855: Principles of Composites Manufacturing

Assignment no:4

                                                                                                                            Due Date:  November  1st, 2007

1a. Consider a thermoset composite being  heated from the two faces by raising their temperatures to initiate a curing reaction. Sketch the temperature profile through the thickness (i) at early stage (ii) at steady state

1b Heating of a a thermoplastic 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 (For glass and Carbon properties please check the web/library/text)

2a: PEEKresin is a engineering thermoplastic resin that is highly viscous and exhibits shear thinning behavior. This resin is placed between two circular disks and squeezed at a constant rate. When the distance between the two disks is 10 millimeters, the force required is 10,000 N and when the distance between the disks reduces to 5 mm, the force required is 40,000 N.  If you used power law model to describe the behavior of PEEK, what will be the power law index n for this material based on these two data points ?

2b: Epoxy resin can be shear thinning. You use cone and plate  viscometer at different  angular velocities and record the Torque. 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)


 

i..Find the two parameters if one were to use a two parameter power-law model. Note that this material does have a Newtonian Plateau at lower shear rates
ii..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.
iii.. What would be your calculation for the pressure drop if you had assumed the fluid to be Newtonian?
 

MEEG 655 PRINCIPLES OF COMPOSITE MANUFACTURING PROCESSES
ASSIGNMENT #5
Due: Nov 15th, 2007


I. The objective is to non-dimensionalize and simplify the following energy equation for the case of flow of a viscous thermoplastic Newtonian suspension in a cavity of length L, width W and thickness h by injection molding. The initial temperature of the melt coming into the mold is Ti and the wall temperature of the cavity is Tw. The injection of the material is done under a constant flow rate of Q cc/s. The thickness h << L and W. Assume that   is zero.

a. Identify independent and dependent parameters
b. Choose characteristic values to non-dimensionalize these parameters
c. Non-dimensionize the equation assuming that only shear stresses are important
d. Identify two important non-dimensional numbers (Brinkman number: measures the role of viscous dissipation compared to conduction, and Peclet number which measures the heat convected in the axial direction compared to the heat conducted in the transverse direction)
e. For small Pelcet number and uniform flow and heat transfer in the width direction, state the non-dimensional governing equation from part (d)
f. Find the steady state non-dimensional temperature solution for Brinkman number of  1, 10 and 100 and plot the temperature profile through the thickness.
 
 

II. 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% carbon fibers which has an effective viscosity of 100 Poise and the second one contains nylon with 30% glass 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% carbon is k= 10 W/mC and that of Nylon with 30% glass fibers is 0.1 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. 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 m = 5 x 105 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 ?

     b. A die is attached to the end of the extruder, for which flow rate, is given as
     Q = KDP/m,
     where K=8.5 x 10-5 cm3. What flow rate and pressure result ?

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

MEEG 655 PRINCIPLES OF COMPOSITE MANUFACTURING PROCESSES
ASSIGNMENT #6
Due: Nov 29th, 2007
1. Axisymmetric compression molding:

Consider the flow of an SMC charge in a radial mold. The Newtonian viscosity of the material is 1000 Poise. The initial radius of the charge is 5 cm and the initial thickness is 6 mm. The mold radius is 25 cm.

(a) How long will it take to squeeze the charge to half its thickness under a constant force of 1000 N. Assume no slip boundary conditions at the walls
(b) In this case, you will compress the charge at a constant rate of 0.1 mm/s. Under no slip boundary conditions, plot the Force w.r.t until the charge reaches half its initial thickness.
(c) Repeat (b) with slip BC with slip coefficient B=0.05

2. Derive the equation for rise of a resin in a bundle of fiber tow. Assume the fiber tow has a permeability of K, porosity of f. The height H is the final height the resin reaches and is related to the capillary pressure. Conduct an experiment to determine the permeability of the tow in the fiber direction in the laboratory and answer the following questions.
 

How would the stationary height H, permeability K, fill time Tf vary in the following cases:

A. If we put a circumferential tie around the tow
B. If we used a higher viscosity resin
C. If the fiber diameter was smaller but made from the same material with the same sizing. Assume that the porosity of the sample does not change.
D. If we used a liquid of same viscosity, but was much more wetting (higher capillary pressure)