Presentation is loading. Please wait.

Presentation is loading. Please wait.

Teaching of Composites

Similar presentations


Presentation on theme: "Teaching of Composites"— Presentation transcript:

1 Teaching of Composites
Brent Strong Brigham Young University

2 Course Details Title―Composites: Materials and Processes
Level―Beginning graduate/advanced undergraduate Credit―3 hours (2 lectures and 1 lab/week) Prerequisites―General Engineering Materials (no organic chemistry) Text―Fundamentals of Composites Manufacturing, 2nd Edition by A. Brent Strong

3 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

4 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

5 Basic Composite Concepts
Concept 2: Advantages and Disadvantages Composites are not “super” materials without some drawbacks

6 Composites: Advantages and Disadvantages
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) 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

7 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)”

8 Properties comparisons of metals and composites
Steel Composites Thermal Expansion Steel Al Composites Al Steel Composites Specific Strength Weight Al Steel Composites Specific Stiffness Steel Al Composites Fatigue Resistance

9 U.S. Composites Shipments
Transport Other 3% 32% Aircraft 1% Appliance 5% Marine 11% Construction 20% Electrical Consumer 10% Corrosion 7% 11% Est. 3.9 Billion Lbs of Shipments Source: CFA (June 2000)

10 Basic Composite Concepts
Concept 4: Stealth Stealth properties come from controlling radiation detection

11 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

12 B-2/B-52 Size Comparison

13 Radar Cross Section of Typical Airborne Objects
Radar Cross Section (m2) 100 80 40 10 1.0 5-6 2-3 0.01 0.1 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)

14 Basic Composite Concepts
Concept 5: Matrix-dominated properties Property Molecular Cause or Association Thermal Resistance Chemical components and bonding Resistance to Solvents or Water Polarity Permeability Crystallinity Fire Resistance Aromaticity or halogen content Electrical Properties Polarity and filler content Weather resistance Aliphatic content, additives and fillers Toughness Aliphatic content, rubber tougheners Wet-out of fibers Molecular weight, backbone stiffness

15 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

16 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

17 Metal, Ceramic and Polymeric Composites
Metal and ceramic composites are for high temperatures

18 Metal, Ceramic and Polymeric Composites

19 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”

20 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

21 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.

22 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

23 Resin Rules { Typical Polymer Temperature Heat Deflection
Flexibility Tm Tg Temperature Typical Polymer Heat Deflection Glass Transition Decomposition { Melting Temperature

24 Resin Rules Resin Rule 2: Mechanical Properties ― Mechanical properties depend upon the difficulty with which polymer molecules separate from each other.

25 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

26 Measuring factors related to chain length
As chain length increases, viscosity increases Consider pouring liquids from a cup Low viscosity fluid High viscosity fluid

27 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

28 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

29 Resin Rules Impediment 2: Crosslinks Formed during curing

30 Covalent bond (shared electrons)
Polymeric molecules Covalent bond (shared electrons) Crosslink bonds

31 { Thermal Properties X Typical Thermoplastic Typical Thermoset
Heat Deflection Glass Transition Decomposition { Melting Typical Thermoset Heat Deflection Glass Transition Melt Decomposition X Temperature

32 Viscosity curves for typical thermoplastic and thermosets
Gel Point Solids Liquid-Solid Line Viscosity Region A Region B Liquids Thermoset thinning due to temperature Thermoplastic Thermoset crosslinking Time/Temperature Thermoset combination (What is seen)

33 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)

34 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

35 Polyester polymerization
Monomers Acids A (di-acids) -Two types: unsaturated and saturated -(In polyesters crosslinking occurs at unsaturation sites) A G A Glycols G (di-alcohols) G A G A Polyester polymer G A

36 Polyesters − specific molecules
Acid Acid Acid Acid Acid Acid Acid Crosslinking occurs at the carbon-carbon double bonds the number of which can be increased when the polymer is made

37 Epoxies Crosslinking occurs only at the epoxy rings
CH3 CH2―CH―CH2 ―O― ( ―CH2―C―CH2― ―O― )n CH2―CH―CH2 CH3 O O Crosslinking occurs only at the epoxy rings CH3 H2C―CH―CH2―CH2 CH2―CH2―CH―CH2 N― ―CH2―C―CH2― ―N O O H2C―CH―CH2―CH2 CH2―CH2―CH―CH2 CH3 O O The tetra-functional epoxy has much greater crosslinking

38 Thermoplastics and Thermosets
Melting vs. decomposition Melted Decomposed

39 Resin Rules Impediment 3: Crystallinity
Formed when polymers pack tightly together

40 Covalent Bond (shared electrons)
Polymeric Molecules Covalent Bond (shared electrons) Amorphous Region Crystalline Region

41 Amorphous and Crystalline
Regions Amorphous (random entanglement) Semi-Crystalline or Crystalline (regular packing)

42 Three-dimensional representation of a crystalline polymer
Amorphous region Crystalline region

43 Liquid Crystal Polymer
Solid state Liquid state

44 Comparison of advanced and engineering thermoplastics and thermosets
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 Low cost Excellent fiber wet-out Moderate strength Standard TP mfg Short fibers Good toughness

45 Resin Rules Impediment 4: Polarity
Occurs when F, O, N, and Cl are present

46 Polarity N S S N S N S N Polyester d+ d- d+ d- d+ d- d+ d-
Attacked by water molecules

47 Bonding between fiberglass and resin
− A highly polar molecule d+ Sizing (alkylsilane) − Mixed polar/non-polar d- d+ Nonpolar regions (weak attraction) d- d+ Polyester − Largely non-polar region

48 Weight gain in water of polyester and vinyl ester resins
6 Polyester resin 5 4 Weight gain (%) 3 2 Vinyl ester resin 1 50 100 150 200 250 Exposure time (hours)

49 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

50 Aromatic molecules b) Polystyrene (pendant aromatic)
H b) Polystyrene (pendant aromatic) a) Aromatic group (benzene) c) Epoxy (aromatic backbone) Aromatic molecules d) Phenolic (aromatic network)

51 Super high thermal stability
An imide-based epoxy O CH3 O O―C C―O C C C C N N C C C C O O C―C―C―O― ―C C― ―O― C―C―C O O C―C―C―O O― C―C―C O O Super high thermal stability

52 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

53 Flammability Flame Spread Index Specific Optical Density Vinyl Ester
Epoxy Epoxy FR Polyester FR Polyester Phenolic Phenolic 10 20 30 40 100 200 300 400 500 600 (ASTM E-162 for thermoset composites) (ASTM E-662 for thermoset composites)

54 NBS Smoke Chamber (Smoldering)
700- 600- 500- 400- 300- 200- 100- Epoxy Polyester Optical Density Phenolic Time (min)

55 Resin Rules Resin rule 3: Materials containing halogen atoms (F, Cl, Br, I) have good flame retardance properties. Smoke evolution is increased with halogens

56 Halogenated polymers Polyvinyl chloride (PVC)
Polytetrafluoroethylene (PTFE) Brominated Epoxy

57 Reinforcements Ceramic whiskers Fiberglass Carbon/Graphite Aramid
Basalt UHMWPE Ceramic whiskers

58 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

59 Effects of fiber content on properties of nylon
Expansion, ppm/oF (ppm/oC) Coefficient of Thermal Izod Impact, ft-lb/in (J/mm ) Flex Modulus (ksi) Elongation (%) Strength (ksi) Tensile CTE Flex Modulus Izod Impact Elongation Tensile Strength Scales for each property 0% 10% 20% 30% 40% 50%

60 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.

61 Reinforcement Rules Reinforcement rule 3: Aramid is the toughest of the major types of composite reinforcements.

62 Reinforcement Rules Reinforcement rule 4: Reinforcement forms can be of several types depending on the type of manufacturing process that is used.

63 Reinforcement Forms Tow (or roving if Mat fiberglass) Prepreg
Cloth fabric Preform

64 Manufacturing Rules Manufacturing rule 1: Put the fibers where the loads are going to be.

65 Filament Winding

66 Pultrusion

67 Manufacturing Methods
Hand Lay-up (wet and prepreg) Wet Prepreg

68 Manufacturing Methods
Spray-up Fibers are chopped, coated with resin and sprayed onto the mold

69 Manufacturing Rules Manufacturing rule 2: Control the temperature, viscosity, and crosslinking reaction.

70 Curing Profile 355±10 400 120 minutes 300 Temperature (°F) 130 200
1-5°F/minute (critical for precipitate) 100 Begin heat after full pressurization of autoclave Time Vacuum Autoclave

71 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.

72 Compression Molding Heated platen Material charge Mold Heated platen
Pump Hydraulic pressure Heated platen Material charge Mold Heated platen Ejector system

73 Vacuum Bagging Provides for increased part consolidation
Reduces matched die mold costs

74 Autoclaves

75 Thermoplastic − Thermoforming
Press (in two modes) Blanks Clamp Finished Part Oven Clamping Pressing

76 Manufacturing Rules Manufacturing rule 4: Composites are often part of assemblies and great care must be used to properly finish the structure.

77 Sandwich Materials

78 Summary Composites have succeeded in current products from automobiles to bathtubs

79 Summary Composites have great promise for the future

80 Space Plane Circling radius for landing X Spaceport

81 Summary Category Concept/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 categories―advanced and engineering. Composites ― general 4 Stealth properties come from controlling radiation detection. Composites ― general 5 Some 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 1 Molecular weight increases entanglement Resin ― Mechanical ― Impediment 2 Crosslinks inhibit molecular motions. Resin ― Mechanical ― Impediment 3 Crystallinity restricts molecular movement. Resin ― Mechanical ― Impediment 4 Polarity restricts molecular motion. Resin ― Mechanical ― Impediment 5 Aromatic groups reduce molecular flexibility. Resin ― Flammability Materials containing halogen atoms (F, Cl, Br, I) have good fire retardance properties.

82 Summary Category Concept/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 1 Put the fibers where the loads are going to be. Manufacturing 2 Control 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 4 Composites are often part of assemblies and great care must be used to properly finish the structure.

83 Composites are dynamic!
Thank You Composites are dynamic!


Download ppt "Teaching of Composites"

Similar presentations


Ads by Google