Presentation on theme: "Teaching of Composites Brent Strong Brigham Young University."— Presentation transcript:
Teaching of Composites Brent Strong Brigham Young University
Course Details TitleComposites: Materials and Processes LevelBeginning graduate/advanced undergraduate Credit3 hours (2 lectures and 1 lab/week) PrerequisitesGeneral Engineering Materials (no organic chemistry) TextFundamentals of Composites Manufacturing, 2 nd Edition by A. Brent Strong
Curriculum Issues Required: Manufacturing students Option: Mechanical, chemical, civil engineering and occasionally others Gateway course: Engineering Materials or equivalent Focus – This course: Manufacturing methods including the chemistry (simplified) of crosslinking – Typical ME course: Laminate design
Basic Composite Concepts Concept 1: Composite components – Composites are made of two materials a continuous phase (matrix) and a discontinuous phase (reinforcement) – In the most common composites, the matrix is a polymeric resin and the reinforcements are fibers – The resin must bond to the fibers – The properties of the components are synergistic
Basic Composite Concepts Concept 2: Advantages and Disadvantages – Composites are not super materials without some drawbacks
Composites: Advantages and Disadvantages Advantages Lightweight High specific modulus Tailored properties Easily moldable Part consolidation Easily bondable Good fatigue resistance Good damping Crash worthiness Internal energy storage/release Low thermal expansion Low electrical conductivity Stealth Thermal transport (carbon fibers only) Disadvantages Cost of materials Lack of well-proven rules Metal and composite designs are seldom interchangeable Long development time Manufacturing difficulties Fasteners Low ductility Solvent/moisture attack Temperature limits Damage susceptibility Hidden damage EMI shielding sometimes required
Basic Composite Concepts Concept 3: Advanced and Engineering – Advanced composites optimize the relationship of mechanical properties and weight, or optimize thermal performance and weight Usually made from long, high performance fibers (carbon and aramid) and advanced resins Specific properties (accounting for density) are important – Engineering composites have good properties with a focus on cost Usually made from fiberglass, often chopped, and engineering resins Sometimes termed Fiberglass reinforced plastics (FRP)
Steel Al Composites Steel Al Composites Weight Thermal Expansion Al Steel Composites Specific Stiffness Al Steel Composites Specific Strength Steel Al Composites Fatigue Resistance Properties comparisons of metals and composites
Source: CFA (June 2000) Est. 3.9 Billion Lbs of Shipments Corrosion 11% Aircraft 1% Construction 20% Consumer 7% Electrical 10% Marine 11% Appliance 5% Other 3% Transport 32% U.S. Composites Shipments
Basic Composite Concepts Concept 4: Stealth – Stealth properties come from controlling radiation detection
Stealth Radiation Considerations Radar Infra-red Visual from ground Visual from above (satellite) Visual from other aircraft Sound Con-trail Radio transmissions Ultraviolet X-ray
B-2/B-52 Size Comparison
Radar Cross Section of Typical Airborne Objects Object Jumbo Jet B-17 (WWII) B-47 (Korean War) B-52 (Cold War) B-1B (First stealth) Large jet fighter Small jet fighter Small single engine plane Man Small bird Insect F-117A (stealth fighter) B-2 (stealth bomber) Radar Cross Section (m 2 )
Basic Composite Concepts PropertyMolecular Cause or Association Thermal ResistanceChemical components and bonding Resistance to Solvents or WaterPolarity PermeabilityCrystallinity Fire ResistanceAromaticity or halogen content Electrical PropertiesPolarity and filler content Weather resistanceAliphatic content, additives and fillers ToughnessAliphatic content, rubber tougheners Wet-out of fibersMolecular weight, backbone stiffness Concept 5: Matrix-dominated properties
Resin Choices (Most common) Unsaturated polyesters – Advantages: low cost, room or elevated temperature cure – Disadvantages: water absorption, low thermal stability, relatively poor mechanical properties Epoxies – Advantages: good adhesion, good thermal stability, good mechanical properties – Disadvantages: requires heat curing to develop properties, cost
Resin Choices (Common) Phenolics – Advantages: Excellent flame retardance and low smoke emission, good adhesive, good thermal and electrical insulation – Disadvantages: Brittle, difficult to cure Vinyl esters – Advantages: Easy to cure, good resistance to water absorption – Disadvantages: More expensive than polyesters, fewer choices in types of resins available
Metal, Ceramic and Polymeric Composites Metal and ceramic composites are for high temperatures
Metal, Ceramic and Polymeric Composites
Basic Composite Concepts Concept 6: Reinforcement-dominated properties – In advanced composites, the reinforcements typically carry over 90% of the load – Composites are non-isotropic materials (that is, they have directionality) – Many composites are layered and are called composite laminates
Resin Rules These rules allow for easy understanding of resin properties These rules require no previous knowledge of organic chemistry or plastics The rules allow prediction of trends in matrix- dominated properties
Resin Rules Resin Rule 1: Thermal Properties Thermal properties depend upon the difficulty with which polymer molecules separate from each other. – The separation of molecules the atoms remain bonded together in long chains. – The separation of atoms occurs at a much higher temperature than the temperatures at which molecules separate.
Thermal Properties Thermal transitions and thermal stability are linked – Thermal stability is the temperature at which a polymer can be used and still have acceptable properties – Failure to perform is usually associated with molecular motion and so the same concepts associated with thermal transitions apply to thermal stability
Resin Rules Resin Rule 2: Mechanical Properties Mechanical properties depend upon the difficulty with which polymer molecules separate from each other.
Resin Rules Impediment 1: Entanglement (molecular weight) – Increases in molecular weight (length of the polymer chain) result in increases in thermal and most mechanical properties – Analogy: spaghetti
Measuring factors related to chain length As chain length increases, viscosity increases – Consider pouring liquids from a cup Low viscosity fluid High viscosity fluid
The Great Dilemma in Polymers Polymers must have good properties – Good properties are favored by high molecular weight Polymers must have good processing – Good processing is favored by low molecular weight
The Great Dilemma In Polymers Thermoplastics meet the dilemma by compromise – High enough molecular weight to get adequate properties – Low enough molecular weight to process OK Thermosets meet the dilemma by crosslinking – Low molecular weight initially (for wetout and processing) followed by curing to increase molecular weight – No compromise is required
Resin Rules Impediment 2: Crosslinks – Formed during curing
Crosslink bonds Covalent bond (shared electrons) Polymeric molecules
Viscosity Time/Temperature Liquid - Solid Line Solids Liquids Region A Region B Thermoset thinning due to temperature Thermoset crosslinking Thermoset combination (What is seen) Gel Point Thermoplastic Viscosity curves for typical thermoplastic and thermosets
Thermoplastics Thermoplastics are not crosslinked and so they melt Thermoplastics are molded as molten liquids Thermoplastics are cooled to solidify Thermoplastics can be re-melted repeatedly Kitchen example: candy Thermoplastics are tough rather than brittle Examples of thermoplastics: polyethylene, polystyrene, nylon, polycarbonate, acrylic, Teflon®, PET (thermoplastic polyester)
Thermosets Thermosets are crosslinked and do not melt Crosslinking is sometimes called curing Thermosets are processed as room temperature liquids Thermosets are heated to solidify Kitchen example: cake Thermosets are often brittle Examples of thermosets: polyesters, vinyl esters, epoxies, phenolics, polyimides
Polyester polymerization Monomers Glycols G (di-alcohols) Acids A (di-acids) -Two types: unsaturated and saturated -(In polyesters crosslinking occurs at unsaturation sites) G G G G A A A A A Polyester polymer
Polyesters specific molecules Crosslinking occurs at the carbon-carbon double bonds the number of which can be increased when the polymer is made Acid
CH 2 CH 2 CHCH 2 O O H 2 CCHCH 2 CH 2 O O CH 2 CCH 2 CH 3 N N CH 2 CCH 2 CH 3 O O CH 2 CHCH 2 O O ( )n)n Epoxies Crosslinking occurs only at the epoxy rings The tetra-functional epoxy has much greater crosslinking
Thermoplastics and Thermosets Melting vs. decomposition Melted Decomposed
Resin Rules Impediment 3: Crystallinity – Formed when polymers pack tightly together
Crystalline Region Amorphous Region Covalent Bond (shared electrons) Polymeric Molecules
Amorphous and Crystalline Amorphous (random entanglement) Semi-Crystalline or Crystalline (regular packing) Crystalline Regions
Three-dimensional representation of a crystalline polymer Crystalline region Amorphous region
Liquid Crystal Polymer Liquid state Solid state
Advanced Thermoset Advanced Thermoplastics Engineering Thermoset Engineering Thermoplastic High temperature capabilities High Cost High strength High modulus Good fiber wet-out Brittle High cost Solvent resistance High toughness Poor wet-out High strength Low cost Excellent fiber wet-out Moderate strength Brittle Low cost Standard TP mfg Short fibers Moderate strength Good toughness Comparison of advanced and engineering thermoplastics and thermosets
Resin Rules Impediment 4: Polarity – Occurs when F, O, N, and Cl are present
Polarity NSNSSNSN SNSN SNSN Attacked by water molecules Polyester
Bonding between fiberglass and resin Fiberglass Sizing (alkylsilane) Nonpolar regions (weak attraction) - - A highly polar molecule Largely non-polar region Polyester Mixed polar/non-polar
Weight gain (%) Exposure time (hours) Vinyl ester resin Polyester resin Weight gain in water of polyester and vinyl ester resins
Resin Rules Impediment 5: Aromaticity – Presence of aromatic groups (containing benzene molecule or similar group) – Aromatic rings are hard, flat objects – Aromatic objects increase stiffness of the polymer, especially as they are integrated into the backbone or into a network
a) Aromatic group (benzene) b) Polystyrene (pendant aromatic) c) Epoxy (aromatic backbone) d) Phenolic (aromatic network) H H H H H H Aromatic molecules
An imide-based epoxy CH 3 CO C C C N C O O C O CCC O O O C C C N C O O OC C O O CCCO Super high thermal stability
Aromaticity Aromatic content increases the flame resistance of the polymer Aromatic content decreases the weathering resistance of the polymer Materials with little aromatic character are called aliphatic
Vinyl Ester Epoxy FR Polyester Phenolic (ASTM E-162 for thermoset composites) Vinyl Ester Epoxy FR Polyester Phenolic (ASTM E-662 for thermoset composites) 100 Specific Optical Density Flame Spread Index Flammability
NBS Smoke Chamber (Smoldering) Epoxy Polyester Phenolic Optical Density Time (min)
Resin Rules Resin rule 3: Materials containing halogen atoms (F, Cl, Br, I) have good flame retardance properties. – Smoke evolution is increased with halogens
Reinforcement Rules Reinforcement rule 1: Fiberglass is the least expensive of the major types of reinforcement and is often about the same strength as other major reinforcement types. – Fiberglass composites are often called FRP (for fiberglass reinforced plastics) – Fiberglass is used in most composite applications
%10%20%30%40%50% Coefficient of Thermal Expansion, ppm/ o F (ppm/ oC ) Flex Modulus (ksi) Izod Impact, ft-lb/in (J/mm ) Elongation (%) Tensile Strength (ksi) CTE Flex Modulus Izod Impact Elongation Tensile Strength Scales for each property Effects of fiber content on properties of nylon
Reinforcement Rules Reinforcement rule 2: Carbon/graphite is the stiffest of the common fiber reinforcements and generally has the best specific strength and specific stiffness.
Reinforcement Rules Reinforcement rule 3: Aramid is the toughest of the major types of composite reinforcements.
Reinforcement Rules Reinforcement rule 4: Reinforcement forms can be of several types depending on the type of manufacturing process that is used.
Reinforcement Forms Tow (or roving if fiberglass) Cloth fabric Preform Mat Prepreg
Manufacturing Rules Manufacturing rule 1: Put the fibers where the loads are going to be.
Manufacturing Methods Hand Lay-up (wet and prepreg) Prepreg Wet
Manufacturing Methods Spray-up – Fibers are chopped, coated with resin and sprayed onto the mold
Manufacturing Rules Manufacturing rule 2: Control the temperature, viscosity, and crosslinking reaction.
Curing Profile Temperature (°F) Time Begin heat after full pressurization of autoclave Vacuum ± minutes 1-5°F/minute (critical for precipitate) Autoclave
Manufacturing Rules Manufacturing rule 3: Compact the composite during cure to ensure that the layers are properly adhering and that the air bubbles are reduced.
Pump Hydraulic pressure Mold Heated platen Material charge Heated platen Ejector system Compression Molding
Vacuum Bagging Provides for increased part consolidation Reduces matched die mold costs
Thermoplastic Thermoforming Blanks Oven Clamp Clamping Pressing Press (in two modes) Finished Part
Manufacturing Rules Manufacturing rule 4: Composites are often part of assemblies and great care must be used to properly finish the structure.
Summary Composites have succeeded in current products from automobiles to bathtubs
Summary Composites have great promise for the future
Space Plane X Spaceport Circling radius for landing
Summary CategoryConcept/Rule Composites general 1 Composites are mixtures of two materials in which both materials retain some of their individual properties but also combine in such a way that the combined materials have some properties that are superior to either of the materials individually. Composites general 2 While composites are certainly unique among structural materials, they are not super materials that have no disadvantages. Composites general 3 Composites can be conveniently divided into two categoriesadvanced and engineering. Composites general 4Stealth properties come from controlling radiation detection. Composites general 5Some properties of the composite are dominated by the matrix. Composites general 6 Some properties of the composite are dominated by the reinforcement. Resin Thermal properties Thermal properties depend upon the difficulty with which polymer molecules separate from each other. Resin Mechanical Mechanical properties depend upon the difficulty with which polymer molecules separate from each other (impediments). Resin Mechanical Impediment 1Molecular weight increases entanglement Resin Mechanical Impediment 2Crosslinks inhibit molecular motions. Resin Mechanical Impediment 3Crystallinity restricts molecular movement. Resin Mechanical Impediment 4Polarity restricts molecular motion. Resin Mechanical Impediment 5Aromatic groups reduce molecular flexibility. Resin FlammabilityMaterials containing halogen atoms (F, Cl, Br, I) have good fire retardance properties.
Summary CategoryConcept/Rule Reinforcement 1 Fiberglass is the least expensive of the major types of reinforcement and is often about the same strength as other major reinforcement types. Reinforcement 2 Carbon/graphite is the stiffest of the common fiber reinforcements and generally has the best specific strength and specific stiffness. Reinforcement 3 Aramid is the toughest of the major types of composite reinforcements. Reinforcement 4 Reinforcement forms can be of several types depending on the type of manufacturing process that is used. Manufacturing 1Put the fibers where the loads are going to be. Manufacturing 2Control the temperature, viscosity, and crosslinking reaction. Manufacturing 3 Compact the composite during cure to ensure that the layers are properly adhering and that the air bubbles are reduced. Manufacturing 4Composites are often part of assemblies and great care must be used to properly finish the structure.