FIBER REINFORCED COMPOSITES by linzhengnd

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									                     FIBER REINFORCED COMPOSITES
                                    Professor R. Bordia

This lab exercise is partially based on a lab from MSE 423 - Fiber Reinforced
Composites taught at the University of Washington. In this lab we will investigate the
manufacture and testing of composites. Today’s lab session is in three parts:

   1. Fabricate carbon-fiber/resin composites
   2. Conduct three-point bending tests on composite samples
   3. Observe Instron tensile testing of composite samples

At a later lab we will observe the microscopy of the composite samples.

To prepare composite samples in a lab we have two basic techniques:

      Fibers and resin by wet lay-up method
      Prepreg tape and fabric

In our lab we will use the wet lay-up method. Unidirectional carbon fibers will be
laminated using a standard polyester laminating resin. We will prepare laminate samples
with the fibers all in one direction (unidirectional) and with the fibers at 90 to each other
(cross-ply). After fabrication the laminates will be machined into test specimens and
used to obtain mechanical properties of the composites.

Fabrication of laminates using wet lay-up technique

Equipment Needed:      Cutting board and T-squares
                       Sharp carpet knifes
                       Heavy 'rolling pins' to assist with compaction
                       Two part resin
                       Glass and Carbon fibers (cut in 12" x 12" pieces)
                       Release film (14 mil Mylar)
                       Brushes, rubber squeegee, & plastic spreaders
                       Acetone (for cleanup)

Caution: The methyl ethyl keytone (MEK) catalyst is hazardous. Gloves must be worn at
all times when working with these materials.
The following are the fiber directions required for laminate preparation: (Note: angle
directions are important!)




Each group will construct one laminate using carbon fibers. You will be given the fiber
orientation in the lab.

Prepare the workspace by covering with a layer of Mylar or similar material. Prepare the
resin. Place a layer of fibers on the Mylar and coat with resin using a brush. Work the
resin between the fibers brushing along the fiber direction. This will ensure that the fibers
remain aligned. Once the first layer is coated with resin, place the second layer of fibers
on the first in the required orientation, then compact the layers with the rolling pin. Apply
resin again making sure to work the resin between the fibers. Repeat the above process
until the desired number of layers is reached. The laminate is then left to cure at room
temperature or may be cured at elevated temperatures depending on the resin used.

Note: Gloves must be worn at all times when working with these materials.

Three-Point Bending Test
We will use a three-point bending apparatus developed for lab in ENGR 170 -
Introduction to Materials Science. This apparatus uses a bathroom scale to determine the
applied force. See handout for information on this test.


Instron Tensile Testing
One of the main advantages of fiber reinforced composites is the ability to tailor the
mechanical properties. The mechanical properties are dictated by fiber orientation. In this
section of our composites lab we will observe the mechanical properties of different
materials. The effects of fiber orientation will be emphasized. If we had more time, the
effect of material aging on mechanical properties should also be investigated. Cross
sections of the laminates will be prepared and micrographs taken in a later lab.

Equipment needed:
    Testing Machine (Instron, MTS)
    Loading grips for testing machine
    Adhesive
    Saw to cut specimens to desired dimensions
Schematic of sample showing orientation of fibers

Initially the specimens will be cut from the panels
made in the previous labs. Unidirectional
specimens will be tested according to ASTM D
3039. Use of tabs is required for each specimen
and it is necessary to attach the tabs at least 24
hours before testing to allow the adhesive to cure.
Refer to ASTM D 3039 for calculations required
(Modulus of Elasticity and Tensile strength).

								
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