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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