ACP_Intro_14.5 _S01_Composite_Introduction.pdf
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ANSYS Composite PrepPost Modeling Composites the Simple Way
Composite Introduction
1. Composite Introduction Agenda •
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General Introduction Composites Classification of Composites Matrix and Fiber Materials Reinforcement Forms Manufacturing Methods Draping Ply Drop Offs Positive and Negative Features of Composites
1. Composite Introduction Agenda •
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Raw Materials Numerical Approaches Single Plies Rules of Mixture Anisotropic, orthotropic, transversal isotropic From three dimensional stress state to plane stress Measurung Ply Properties Failure Indicator
1. Composite Introduction
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Composite materials are made of multiple layers of different materials.
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They are light weight and high in strength.
1. Composite Introduction Application Areas •
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Aerospace Wind Energy Sports & Recreation Motorsport Construction Automotive Marine Defense … and more
1. Composite Introduction Terms Fibers- Bonded or embedded reinforcing fibers that are usually responsible for the anisotropy of the composite.
Matrix- A homogeneous base material that forms the bulk of a composite material layer.
T
L Lamina- A composite material in sheet form usually referred to as a layer or ply. The material properties of a layer is usually determined through an equivalent homogenization (smearing) process.
Laminate- A stack of lamina joined together in arbitrary directions, referred to as a composite lay-up or stacking-sequence.
1. Composite Introduction
1. Composite Introduction Classification of Composites Based on Reinforcement Composite Materials can be classified by the type of
reinforcements used for the matrix material. A. Parti articl cle e Reinf einforce orced d Compo Composi site tess B. Fibe Fiberr Rei Reinf nfor orce ced d Com Compo posi sittes •
Short Fiber Fiber Reinforced
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Long Fiber Reinforced Reinforced
1. Composite Introduction A. Pa Particle rticle Reinf Reinforce orced d Composites Composites •
Particle reinforced reinforced composites consist of particles of one material dispersed in a matrix of a second material. Particles may have any shape or size, but are generally spherical, ellipsoidal, polyhedral, or irregular in shape.
Ceramic - Aluminum
1. Composite Introduction B. Fiber Fiber Rein Reinfo forc rced ed Compos Composit ites es •
Fiber reinforced composites (FRC) are composites where one material component (fiber) is used as a reinforcing reinforcing material for the matrix.
Carbon Fiber - Epoxy
Glass Fiber - Epoxy
1. Composite Introduction B. Fiber Fiber Rein Reinfo forc rced ed Composi Composites tes Short Fiber Reinforced Reinforced
Long Fiber Reinforced Reinforced
1. Composite Introduction
Random and oriented short fiber reinforced reinforced composites
Random and oriented long fiber reinforced composites
1. Composite Introduction Materials •
Matrix Materials Thermosets Thermoplastics Metals Ceramics •
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Fiber Materials Materials Glass Carbon Aramid (Kevlar) Boron Ceramics •
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1. Composite Introduction Gel Coats Gel coats are specialized polyester
resins formulated to provide a cosmetic outer surface on a composite product.
They provide the high quality finish for composite products and increase the durability and resistance of the
outer surface.
1. Composite Introduction Reinforcement Forms Unidirectional Woven Mat Knit Stitched Braid •
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Roving
1. Composite Introduction Reinforcement Forms
Unidirectional
Woven
Mat
Knits
Stitched
Braiding
1. Composite Introduction Manufacturing Methods There are two general methods of manufacturing
composites. Open molding describes processes with materials being exposed to the atmosphere during the manufacturing process while closed molding processes
use two-sided mold sets or vacuum bags. •
Open Molding
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Closed Molding
1. Composite Introduction Manufacturing Methods •
Open Molding •
Hand Lay-Up
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Spray-up
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Filament Winding
1. Composite Introduction Manufacturing Methods •
Closed Molding Vacuum Bag Bag Molding Vacuum Infusion Processing Compression molding Pultrusion Resin Transfer Molding (RTM) Reinforced Reinforced Reaction Injection Molding (RRIM) Centrifugal Casting Continuous Lamination •
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1. Composite Introduction Manufacturing Methods •
Hand Lay-Up •
Composite layer are placed manually on a mold
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Resin is applied by pouring, pouring , brushing or spraying
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Layers Layers are added to build laminate thickness Low tooling costs and minimum investments in equipment Simple processing Wide range of part sizes Skilled operators allow good production rates rates and consistent quality Low volume and labor intensive intensive
Hand Laying Carbon Fiber
1. Composite Introduction Manufacturing Methods •
Using PrePreg Materials •
Fibers or fabrics with a pre-catalysed resin system impregnated by a machine
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Resin system reacts slowly at room temperature and is usually cured by heating at cure temperature temperature Higher fiber contents achievable Allows strong resins with high viscosity
1. Composite Introduction Manufacturing Methods •
Autoclave Curing •
Curing of thermoset composites uses mechanical and chemical processes
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Pressure is applied to remove remove trapped air and volatiles
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Plies and fiber are consolidated by pressure pressure
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Crosslink reaction, usually initiated by heating, is necessary to cure material
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Autoclave controls temperature and pressure Allows high strength to weight ratios
Construction of a composite fuselage section (Boeing 787)
1. Composite Introduction Manufacturing Methods •
Spray Up •
Chopped fiber reinforcements reinforcements and catalyzed catalyzed resin is placed onto a mold surface using a chopper/spray chopper/spray gun
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Laminate is rolled to compact chop
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Woven or knitted fabrics can be added Simple processing Low-cost tooling Portable equipment No part size limitations Chopped fibers Sealine spray layup from Motor Boat & Yachting
1. Composite Introduction Manufacturing Methods •
Filament Winding •
Resin impregnated fibers or laminates are
Filament winding of a subsea sphere by Windtec.no
wound around a mandrel in predefined pattern pattern •
Fibers and laminates can be pre-impregnated pre-impregnated or running through a resin bath before wound
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Composite is usually cured using autoclaves or ovens High strength to weight ratios Good control over uniformity and fiber orientation orientation Allows highly engineered products and strict tolerances Automatic process Limited designs (although new developments developments allow non cylindrical and non spherical designs)
1. Composite Introduction Manufacturing Methods •
Vacuum Bag Molding •
Improves Improves mechanical properties of open mold processes
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A release film is placed over the laminate
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Followed by a bleeder ply of fiberglass cloth, non-woven nylon, nylon, polyester polyester cloth, or other material that t hat absorbs excess resin from the laminate
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A breather ply of a non-woven fabric fabric is placed over the bleeder ply
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A vacuum bag is mounted over the entire assembly
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Vacuum is applied and the atmospheric pressure eliminates eliminates voids and excess resin
1. Composite Introduction Manufacturing Methods •
Vacuum Bag Molding More uniform consolidation Removing entrapped air Avoids hand layups being resin rich
How-To Use a Vacuum Bag
Improved core-bonding •
Vacuum Infusion •
The resin is introduced into the mold after the vacuum has pulled the bag down and compacted the laminate
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Resin completely saturates the reinforcements No resin excess offers substantial emission reductions
1. Composite Introduction Manufacturing Methods •
Compression Molding •
A mechanical or hydraulic hydraulic press with heated molds forms composite parts using sheet molding compound, bulk molding compound or liquid composite molding
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Sheet Molding Compound (SMC); Fiber reinforced reinforced polyester material using long strands of chopped fibers (> 1 inch)
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Bulk Molding Compound (BMC); Highly filled resin paste combined with short fibers (0.125- 0.5 inch)
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Liquid Composite Molding (LMC); Uses preforms preforms matching the finished design or mats (in case of plane shapes). s hapes). Resin is added into the open dies. High strength to weight ratios
1. Composite Introduction Manufacturing Methods •
Compression Molding Fast molding cycles High part uniformity Good surfaces available Automatic process Chopped fibers or preforming preforming necessary
1. Composite Introduction Manufacturing Methods •
Pultrusion •
Continuous method to manufacture composite parts having a uniform cross section
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Rovings or fiber mats are pulled through resin bath and then formed and cured in a heated die
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Cured parts are cut into desired lengths
The Pultrusion Process
Continuous process High strengths Limited to uniform cross sections Pultrusion
1. Composite Introduction Manufacturing Methods •
Combining Braiding & Pultrusion •
combines the braiding performing technique and composite pultrusion process to fabricate fabricate constant cross-section products
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Fiber angles can be oriented in the braiding process to achieve a specific angle along to the beam axis Continuous process High strengths Orientation Orientation of fiber angles Limited to uniform cross sections
Braid-Trusion of an L-shaped Braid-Trusion thermoplastic composite beam 30
© 2011 ANSYS, Inc.
February 7, 2013
1. Composite Introduction Manufacturing Methods •
Resin Transfer Molding (RTM) •
Reinforcement Reinforcement material (can be continuous fibers, mats, preforms, preforms, or woven fabrics) is placed between two matching mold surfaces
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Resin is injected into the mold and wets out all surfaces of the reinforcing materials
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Curing at room temperature or by heated molds (cycle ( cycle time)
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Vacuum can be applied to increase resin flow High quality finish Fast production Allows complex surface designs High tooling costs Limited part sizes
Resin
1. Composite Introduction Manufacturing Methods •
Reinforced Reinforced Reaction Injection Molding (RRIM) •
Reinforcement material and resin are mixed and injected into a closed mold
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Short fibers or flakes are usually used to create a more isotropic material behavior
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Structural Reaction Injection Molding (SRIM) •
This process uses two resin components which are combined and mixed together, then injected into a mold cavity containing reinforcement. In the mold cavity, the resin rapidly reacts and cures to form the composite part
1. Composite Introduction Manufacturing Methods •
Centrifugal Casting •
Used for making cylindrical, hollow shapes such as tanks, pipes and poles
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Chopped strand mat is placed into a hollow, hollow, cylindrical mold, or continuous roving is chopped and directed onto the inside walls of the mold
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The resin is applied to the inside of the rotating mold
1. Composite Introduction Manufacturing Methods •
Continuous Lamination •
Creates Creates composites in sheet form such as composite glazing, corrugated corrugated or flat construction panels, and electrical insulating materials
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Reinforcement Reinforcement is combined with resin and sandwiched between two plastic carrier films
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Sheet takes shape under forming rollers, rollers, and the resin is cured to form the composite
1. Composite Introduction Hand Layup
Automated Prepreg
Winding
RTM
Geometry
Complex
Complex
Near to rotational
Complex
Holes/Inserts
Possible
Possible
Difficult
Possible
Stiffeners
Possible
Possible
Difficult
Possible
Back Tapering
Possible
Possible
Not possible
Difficult
Moderate – Good1
Good1
Moderate1
Good2
Fiber Architecture
Any
Any
Limited
Any
Typ. Fiber Volume Content
40%
65%
50%
50%
Middle
High
Middle
Middle
Quality
Moderate
Very good
Middle
Good
Reproducability
Moderate
Very good
Good
Good
Low
Very High
High
High
Surface
Mechanical Properties
Tooling Costs Co sts According to Ermanni, ETH Zürich
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only one side
1. Composite Introduction From Fibers to Finished Composite Components
By SGL Group The Carbon Company
1. Composite Introduction Draping •
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The ability to drape describes the formability of textile preforms preforms and how they adapt themselves to the contour of 3D surfaces Draping is simulated to avoid wrinkles or other undesired effects effects and to consider changes of the fiber orientation
1. Composite Introduction Draping of a Ply Inside a Ply
In a Laminate
„Trellis“-Effect:
change of angle between fiber directions due to shearing
Fiber Stretching: curvature of woven fibers changes due to tensile loading
Fiber Straining: due to elasticity of fibers
Fiber Translation: due to slipping, especially at edges and corners
Translation: translation of plies with respect to each other
According to Ermanni, ETH Zürich
1. Composite Introduction Draping •
High ability to drape and low deformation resistance allow draping of complex geometries
h g i h
e p a r D o t y t i l i b A
2DKnitted Fabrics Mats
2D-Wovens
3D-Wovens w o l
UD-Clutch
high
low Deformation Resistance Plank, Wiesbaden 1992
1. Composite Introduction Ply Drop Offs •
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Achieve gradual thickness changes and tapering in composite laminates Introduces resin pockets, which may lead to delamination failure terminated plies
resin pocket
1. Composite Introduction Positive Features of Composite Designs •
Oriented stiffness and strength properties
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Material properties adjustable by engineers (material design)
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Parameters Parameters to modify e.g. type of fibers and matrix, fiber volume fraction, fiber orientation, stacking sequence, layer thickness, fabrication method
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Significant reduced weight compared to metals
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High stiffness and strength properties with respect to weight
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High fatigue resistance
1. Composite Introduction Positive Features of Composite Designs •
Specific material characteristics possible (e.g. thermal stability due to negative coefficient coefficient of thermal expansion of carbon fibers)
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Reduced corrosion tendency
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Low moisture absorption
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Damping of vibrations
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Less sensitive for imperfections (geometrical and physical) physical)
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Electrical conductivity or non-conductivity (depending on the materials m aterials used)
1. Composite Introduction Negative Features of Composite Designs •
Low stiffness and strength perpendicular to fiber direction
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Large thermal strains perpendicular to fiber direction
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Low interlaminar shear stiffness and strength strength
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Long time durability (especially concerning environmental UV, aging …) influence, e.g . heat, moisture, chemical, UV,
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Heat resistance (e.g. fire resistance of matrix material)
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Undesirable brittle failure behavior (safety concepts)
1. Composite Introduction Negative Features of Composite Designs •
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Open questions concerning recycling Difficulties in damage detection (x-rays, (x-rays, ultra sonic, thermo graphic, non-destructive methods)
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Open questions concerning reparability
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Relatively high material costs
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Problems with conventional joints (bolts, rivet, adhesive)
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Sensitive with respect to the fabrication process process (flaws, bubbles, dust)
1. Composite Introduction Raw Materials •
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Composite materials are made of at least two distinct materials One component (fiber) is used as a reinforcing reinforcing material for the matrix
Carbon Fiber - Epoxy
The matrix holds fibers The matrix will guarantee a load transfer transfer in between the fibers as well as external loadings into the fibers
Matrix takes forces in between fibers
Fibers take forces in fiber direction
1. Composite Introduction Relative Importance of Fibers and Matrix Fiber
Matrix
Mechanical Properties Stiffness Strength Fatigue Damage tolerance Impact behavior Thermo-mechanical properties Fiber-matrix bonding Ermanni, ETH Zürich
No Importance
High Importance
1. Composite Introduction Relative Importance of Fibers and Matrix Fiber
Matrix
Physical Properties Corrosion Behavior Thermal Stability Chemical Stability Electrical properties Ermanni, ETH Zürich
No Importance
High Importance
1. Composite Introduction Glass Fibers •
Basically silica(SiO2)
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Isotropic properties
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E-glass („electrical“ glass) Most common fiber Moderate stiffness, high strength Relatively Relatively heavy Good chemical, environmental conditions and fire resistance inexpensive •
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Glass Fiber Roving
1. Composite Introduction Glass Fibers •
R-, S-glass („strength“ glass, other chemical mixture) higher stiffness (+20%) and strength strength compared to E-glass expensive •
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Glass Fiber Roving
1. Composite Introduction Carbon Fibers •
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Orthotropic properties Many different types available Expensive to extremely expensive Low density Low ductility in impact Coefficient of thermal expansion nearly zero Electrically conductive
Carbon Fiber Sandwich
1. Composite Introduction Carbon Fibers •
PAN (polyacrylnitrile)-fiber Low stiffness Very high tensile & compressive strength (HT-, HS-, HM-fibers) Pitch-fiber High to ultra high stiffness (HM-, UHM-fiber) High tensile and low compressive strength Large scatter scatter in material properties •
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1. Composite Introduction Aramid Fibers (also known as Kevlar, Twaron) •
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Orthotropic properties Lowest density of all fibers Higher stiffness compared to glass fiber High tensile strength Low compressive strength Highly ductile in impact Woven Aramid Negative Negative coefficient of thermal ther mal expansion Moisture absorption decreases material properties Available with low stiffness (life vests, robes, etc.) Moderately Moderately expensive
1. Composite Introduction Other Fiber Materials Materials •
For special application, e.g. embedded in ceramic or metal matrix Boron Silicon Carbide (SiC) Silicon Oxide (SiO 2) Aluminum Oxide (Al 2O3) others •
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1. Composite Introduction Thermosets as Matrix Material •
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Isotropic properties Polyester (unsaturated) Most common resin Good resistance against chemicals and UV-light Catalytic reaction, short curing time, emits styrene Large shrinkage during curing Inexpensive •
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1. Composite Introduction Thermosets as Matrix Material •
Epoxy Most often used resin for high quality composite materials Very good strength properties, good gluing properties Curing with hardener through polyaddition is critical in view of health Low shrinkage Expensive •
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Epoxy Resin and Hardener
1. Composite Introduction Thermosets as Matrix Material •
Vinyl ester Properties in between Polyester Polyester and Epoxy Very good chemical resistance Low shrinkage Moderate price •
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1. Composite Introduction Thermoplastics as Matrix Material •
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Different Different production process necessary (valid for mass production) Needs heat to be formed and solidified Creeps at larger temperatures Larger ductility then thermosetting
Press for Thermoplastics, University Kaiserslautern
1. Composite Introduction Thermoplastics as Matrix Material •
PP (Polypropylene), PE (Polyethylene), PA (Polyamide), PEEK (Polyether ether ketone) High ductile resistance Good mechanical properties Temperature resistance (up to max. 250 °C) Expensive Polyamide Less thermal resistance but less expensive PTFE (Teflon) (Teflon) Temperature resistant •
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1. Composite Introduction Non-Polymer Matrix Materials •
Metal-Matrix-Composites (MMC) Aluminum Titanium Copper Magnesium Ceramics-Matrix-Composites (CMC) Aluminum oxide Mullite Carbon Silicon carbide Concrete •
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Ceramic Particles in Aluminum
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Steel Fiber Reinfo Reinforced rced
Bor Fibers in Aluminum
1. Composite Introduction Core Materials •
Foam Polyurethane Polyurethane PU Polyvinylchloride PVC Polystyrene PS Honeycombs Aluminum Plastic (Nomex) Glass / Penol Nomex Paper Honeycomb Wood Balsa Prestressed wooden cores •
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Foam
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Balsa
1. Composite Introduction Numerical Approaches Get a feeling for size.
5.000.000 : 1 Scale relation geometry to fiber diameter Rotor Diameter 82m Hub Height up to 100m (Figure Coutesy by REpower Systems SE )
1. Composite Introduction Numerical Approaches
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Micro-Scale Approach
Meso-Scale (Laminate Level) Approach Macro-Scale Approach
1. Composite Introduction Numerical Approaches •
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The most detailed approach describes the micro-structure of the composite. This includes fiber shape, fiber location and material properties of reinforcement reinforcement and matrix. If only displacements, buckling loads, or vibration frequencies and modes are required, the laminate can be analyzed as a homogeneous shell using a macro-scale approach. In this case the stress distribution can not be obtained.
1. Composite Introduction Numerical Approaches •
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Analyzing strains, stresses stresses and failure criteria of the composite laminate requires requires to model the single layers a composite design is built up by. by. This method is called meso-scale approach. It requires material properties and thicknesses for each layer of the design. ANSYS Composite PrepPost PrepPost is mainly used to prepare and evaluate evaluate composite specific results of a design using the meso-scale approach.
1. Composite Introduction Single Plies •
The Ply Coordinate System System •
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1-Direction: Parallel Parallel to fiber direction (also II-direction, L-direction or x-direction) 2-Direction: Perpendicular Perpendicular to fiber direction (also direction, T-direction or y-direction) 3-Direction: Normal to ply (also „out of plane“ or z-direction)
1. Composite Introduction Unidirectional Plies •
Fiber Volume Fraction Fiber Volume
F •
Fiber Fiber Weight
A A A F
F
tot
M
Total Weight
G G
F
tot
A A A F
F
F
F
M
M
Matrix Weight Fraction M
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F
Fibers
Fiber Weight Fraction F
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Total Volume
V V
Matrix Matrix Weight Total Weight
Conversion
G G
M
tot
A
M
M
A A F
F
M
M
1
F
1
1 F
M
M
1
Matrix
1. Composite Introduction Unidirectional Plies •
Fiber volume fraction, fiber mass and the ply thickness are dependent values
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Wovens and Fabrics: •
Fiber volume fraction for specific ply thickness
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Ply thickness for a specific fiber volume fraction
F
M t
F
F
t
t arg et
2
t arg et
M F
F
kg M F m
F
1. Composite Introduction Rules of Mixture •
Rules of mixture mixt ure are used to estimate material properties (Young's (Young's modulus in the 1 and 2 direction) of a composite based on the fiber and matrix material properties
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Multiple different different rules of mixture exist in literature, all of them are an estimation
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Using the rules of mixture m ixture we simplify the mechanics of the composites layers layers
1. Composite Introduction Rules of Mixture, Halpin-Tsai Equations •
Semi-empirical model
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Contiguity factor usually defined empirical by curve fitting. See recommended values on next slide. E 1
1 1 E F 1
E M 1 E F 1 E M 1
E M 1
E 2
1 1 E F 2
1
1
E M 2 E F 2 E M 2
E M 2
G12
1 1
G F 12
1
1
G M 12
G M 12 G F 12 G M 12
1
1
1. Composite Introduction Rules of Mixture, Halpin-Tsai Equations Contiguity factor E1 for perfectly aligned continuous fibers
=
E1 for imperfectly (or wavy) aligned continuous fibers
< (often in range of 100-1000)
E1 for aligned discontinuous fibers
= 2 fiber aspect ratio
E2 for aligned continuous or discontinuous fibers
= 2
G12 for aligned continuous or discontinuous fibers
= 1
(Source: Fire properties of polymer composite materials by A. P. P. Mouritz,A. G. Gibson)
1. Composite Introduction Rules of Mixture, Jones E 1
E F 1
G12
12 21
(1 ) E M
G M G F 12 G M
(1 ) G F 12
F 12 (1 ) M 12
E 2 E 1
E 2
E M E F 2
E M
(1 ) E F 2
1. Composite Introduction Rules of Mixture, Puck •
Empirical modification with respect to experimental values using a nonlinear approach according to Puck E 1
(1 ) E M
E F 1
E 2
E M
*
(1 0.85 2 )
E M
*
E F 2
1.25
(1 )
E M
*
E M 2
1 M
0.5)
G12
G M (1 0.6
12
G M G F 12
(1 )1.25
F 12 (1 ) M
21 12
E 2 E 1
1. Composite Introduction Homogeneous and Heterogeneous Materials •
Heterogeneous materials have have varying properties at different different locations within the material
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In contrast, properties for homogeneous materials (e.g steel) are the same at every location within the material
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Composite laminate material is considered predominantly as a homogenous material for simulations on a laminate level.
1. Composite Introduction Anisotropic Material Material •
Isotropic material (e.g. steel) has the same properties in any direction.
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Anisotropic material has properties (mechanical, etc.) that vary with the orientation.
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The stiffness of an isotropic material is described by two properties, the modulus of elasticity E and Poisson’s ratio ν,
whereas anisotropic material requires up to 21 properties
1. Composite Introduction Anisotropic Material Material •
Material definition requires the full 6 ×6 elastic coefficient matrix [D]
xx D D yy zz D xy D yz D xz D
11
21
D22
31
D32
D33
41
D42
D43
51
D52
D53
61
D62
D63
D
xx symmetry yy zz D xy yz D D D D D xz 44
54
55
64
65
66
1. Composite Introduction Orthotropic Material Material •
An orthotropic material has three planes of material symmetry symmetry
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A unidirectional unidirectional fiber-reinforced fiber-reinforced composite composite may may be considered to be orthotropic
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One plane of symmetry is perpendicular to the fiber direction, and the other two can be any pair of plane orthogonal to the fiber direction Fibers
Z Matrix
Y X
1. Composite Introduction Orthotropic Material Material
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Fibers
Matrix
Nine constants are required to describe an orthotropic material E x E y E z xy ,
,
,
yz xz
,
,
,
G xy G yz G xz ,
,
xx D D yy zz D xy yz
11
D12
D13
21
D22
D23
31
D32
D33 D44 D55
xx yy zz xy yz D
1. Composite Introduction Orthotropic Material Material
•
Fibers
Matrix
The compliance matrix S S D
1
E xx E yy zz E xy yz xz 1
x
yx
E
y
xy
1
x
E y
xz x
is defined as
E
zx z
zy
E
z
yz
E
y
1
E z 1
G xy 1
G yz 1
G
xx yy zz xy yz xz
1. Composite Introduction Transversal Isotropic Material •
Transversal isotropic materials are orthotropic materials characterized characterized by isotropic material material behavior behavior in one material material symmetry plane
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A unidirectional layer has transversal isotropic material behavior with the fiber direction as symmetry axis
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A woven fabric has transversal transversal isotropic material behavior with the out of plane normal direction as symmetry axis
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The number of constants constants to define is reduced to 5
1. Composite Introduction Transversal Isotropic Material •
Unidirectional Layer E y
G xy
•
E z
G xz
xy xz
G yz
E y
2 1 yz
Unidirectional
Woven Fabrics E x
G yz
E y
G xz
yz xz G xy
E x
2 1 xy
Woven
1. Composite Introduction Isotropic Material Material •
Most common materials of industrial use are isotropic (aluminum, steel, etc.)
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Isotropic materials have have an infinite number of planes of symmetry, symmetry, meaning that the properties are independent of the orientation
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Two constants (Young modulus and Poisson’s Ratio) are necessary to represent the elastic properties of isotropic material
1. Composite Introduction From Three Dimensional to Plane Stress State •
Composite materials are often used in form of plates and shells, which have two dimensions (length and width) much larger than the third dimension (thickness). When the thickness of a plate is small compared to the other dimension, it is reasonable to assume that the transverse transverse stress is zero (σ Z =σ 3=0).
1. Composite Introduction From Three Dimensional to
x S 11 y S 12 xy
Plane Stress State z
0,
yz
xx S S yy zz S xy yz xz
11
0,
xz
S 12
Compliance Matrix
0
S 13
21
S 22
S 23
31
S 32
S 33 S 44 S 55
xx yy zz xy yz S xz
1
S 11
S 12
E 1 S 21
S 12 S 22
1
, S 22
E 2
S
x y S 66 xy
, S 66
1
G12
12
E 1
Stiffness Matrix
D
x D11 D12 x y D12 D22 y D66 xy xy
66
D11
E 1
, D22
S 12 S 21 1
E 2 E
E 2
12 E 2
12
2
, D66
G12
1. Composite Introduction Transformation to the Global Coordinate System •
Layers are defined with different specific fiber angles
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In order to build a stiffness matrix for the complete layup the stiffness matrixes for each layer are transformed from the layers x,y,z or 1,2,3 coordinate system into the global coordinate system using a transformation matrix
cos 2 T sin 2 sin cos
2
sin 2
cos sin cos
2 sin cos 2 2 cos sin 2 sin cos
X x
y 2 cos 2 sin 2 cos T 1 sin 2 sin cos sin cos
2 sin cos 2 sin cos 2 2 cos sin
z
Y
Z
1. Composite Introduction Transformation to the Global Coordinate System x X y T Y XY xy
X Y T XY
1
x y xy
X x
y
x X y T Y XY xy
X Y T XY
1
x y xy
Y
Z
Compliance Matrix X S 11 Y S 12 XY
S 12 S 22
Stiffness Matrix D11 D12 D12 D22 X Y
XY
X Y S 66 XY D66
X Y
XY
S
z
1
T S T
D
1
T D T
1. Composite Introduction Layered Shell-Elements in ANSYS
4-Node Structural Shell •
8-Node Structural Shell
Structural shell elements require the definition of the following following mechanical material properties per layer •
Young's Modulus in X, Y and Z direction
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Shear Modulus in the XY, YZ and XZ plane
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Poisson's Ratio in the XY, YZ and XZ plane
1. Composite Introduction Element Technology in ANSYS •
A layup can also be defined for solid elements (SOLID185, SOLID186) and solid like shell elements (SOLSH190) in ANSYS
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Furthermore discrete reinforcements (REINF264) are possible for shell and solid elements
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Please see the ANSYS Theory Theor y Reference Reference in the ANSYS Help (// Theory Reference) Reference) for more information on element technology in ANSYS
1. Composite Introduction Measuring Ply Properties •
Mechanical properties of composite materials depend on the production process and the specific material properties of the basic materials used as well as on the manufacturing process of the composite design
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General material databases are available (ESAComp has a comprehensive comprehensive material database) but the data provided are standard material data
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For individual material data ask your material manufacturer about data, recommended tests and/or recommended test laboratories
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Contact test laboratories offering offering standard test (ISO or ASTM) and non standard tests
1. Composite Introduction Measuring Ply Properties •
International Organization Organization for Standardization Standardization
“The International International Organization for Standardization is an international international standard-setting standard-setting body composed of representatives from various national standards organizations.”
Examples: •
ISO 14125:1998 fiber-reinforced fiber-reinforced plastic composites -- Determination of flexural properties
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ISO 527-5:2009 Plastics -- Determination Determination of tensile properties -- Part Part 5: Test conditions for unidirectional fiber-reinforced fiber-reinforced plastic composites
1. Composite Introduction Measuring Ply Properties •
American Society for Testing and Materials (ASTM)
“ASTM International is an international standards organization that develops and publishes voluntary consensus technical technical standards for a wide range of materials, products, systems, and services ser vices..”
Examples: •
Committee Committee D30 on Composite Materials
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ASTM D7205 / D7205M - 06 Standard Test Method for Tensile Properties of Fiber Reinforced Reinforced Polymer Matrix Composite Bars
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ASTM D7617 / D7617M - 11 Standard Test Method for Transverse Shear Strength of Fiber-reinforced Fiber-reinforced Polymer Matrix Composite Bars
1. Composite Introduction Tension Tests and Failure Mode
Unidirectional Composite Composit e Tensile Tensile Test
1. Composite Introduction Compression Tests and Failure Mode
1. Composite Introduction In-Plane Shear Tests and Failure Modes
1. Composite Introduction Failure Indicator FPF – First-Ply-Failure First-Ply-Failure Indicator •
Mathematical equations indicating first failure failure of any ply
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Indicates the occurring failure mode: fiber tension, fiber compression, matrix tension, matrix compression
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Determines reserve factor, inverse reserve factor, margin of safety
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Typical criteria: Max. Stress, Max. Strain, Tsai-Wu, Tsai-Hill, Hashin, Puck2D, Puck3D, Cuntze
1. Composite Introduction Failure Indicator LPF – Last-Ply-Failure (Progressive Damage) •
Further loading beyond FPF until ultimate failure of laminate.
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Post-failure Post-failure formulations needed (ply-discount method)
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May also include energy dissipating methods
1. Composite Introduction Delamination •
Interface Interface failure between two plies in normal norm al direction Interlaminar
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Failure Failure
Driven by normal stress in thickness direction
1. Composite Introduction Debonding •
Interface failure between face sheet and core of sandwich structures.
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Only predictable when core and sheet are separately modeled.
Compression Test
1. Composite Introduction Wrinkling •
Local buckling of a face sheet under compression
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Failure indicator available using shell modeling of sandwich
Core Failure •
Local failure of core in shear or tensile loading
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Failure indicator available using shell modeling of sandwich
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