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Slide 2 Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 1 Lecture 9 & 10 Processing Routes Hot-melt Impregnation system Step 1 Preparation of product form from resin and fiber Fiber is preimpregnated with a low molecular weight. Uncured resin to give a product form (prepreg) suitable for use in the lay-up and autoclave cure of advanced composites. Applicable to variety of resins, fiber and fiber forms. Unidirectional, continuous, collimated tape basic building block of advanced composites Slide 3 Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 2 Prepreg Preparation A major requirement-resin must penetrate/wet fibers-dictates process in use- From Solution- High viscosity resins are dissolved in solvents to form low viscosity solutions Reinforcement is passed through solution for impregnation. Major applicability to fabrics Slide 4 Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 3 Prepreg Preparation Hot-Melt Pure resin is heated to give low viscosity state Low viscosity resin flows/melts into reinforcement. Major applicability to continuous, unidirectional, collimated fibers. Slide 5 Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 4 Prepreg Characteristics Single layer (0.006-0.010 in thick) of fibers impregnated with resin on backing/release paper Width of 0.25- 60 in, length of hundreds of feet Resin content of 32- 42 % by weight Tack (self-adhesion of plies) Drapeability (ability to conform to shapes) Self-life Out-time Gel time Slide 6 Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 5 Advantages of Prepreg More uniform impregnation of reinforcement Higher fiber volumes Improved quality control (vs. In-house formulation) Easier Handling and fabrication (vs. wet lay-up) Adaptable to automation (cutting, forming) Wide variety of resins/fiber forms Major Concern reproducibility/ consistency Compositionally Behaviorally Slide 7 Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 6 Step 2 Preparation of composite from product form using an autoclave/ vacuum Bag cure: Plies-up prepreg mass is transformed by heat and pressure into a void free, densified, cured part. Plies/layers are compacted with pressure. Uncured/low molecular weight/weak resin is converted (cured) by heat to high molecular weight, cross-linked, structural resin. Slide 8 Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 7 Autoclave/Vacuum Bag Cure Process steps Lay-up Bagging Autoclave Cure Cycle Lay-Up Laying down of prepreg on a tool, ply by ply, in specific orientations. Performed manually or by machine Shape of tool, ply geometries dictated by design Tooling The vehicle on which the cure is performed Provides the shape to the part Provides the finish to the surface Locates indexing points Slide 9 Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 8 Autoclave/Vacuum Bag Cure Process steps Tooling is made from Metal (steel, Aluminum, Kirksite) Reinforced plastic Plaster Castable Ceramic Bagging Composite Lay-up on tool is incorporated into a vacuum bag with appropriate bagging materials. Bag applies compaction pressure to part Bagging materials control resin flow, gas evolution, and lateral movement of prepreg Slide 10 Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 9 Typical Autoclave Bag Lay-up Slide 11 Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 10 Autoclave Cure Cycle Consolidation/ densification/ cure of composite under a vacuum bag, in an autoclave, using a time/ temperature/ pressure profile. Slide 12 Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 11 Typical Time/ Temperature/ Pressure Cure Profile Slide 13 Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 12 Autoclave/ Vacuum Bag Vs Press Advantages of Autoclave Cures Reduced tooling cost Excellent for large area, complex contour parts More uniform pressure Efficient- Multiple componentsper load Slide 14 Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 13 Constituent Behavior During Processing Fiber- no changes Resin- Important physical changes General TackyNon-flowable FlowableHard SoftStrong Slide 15 Mechanical Engineering Department Advanced Composites Dr. Talal Mandourah 14 Major End Objectives of Composite Processing Wetting of fibers by resin Acceptable degree of cure Acceptable void content Acceptable fiber volume fraction