Presentation on theme: "Composites: basics and terminology John Summerscales."— Presentation transcript:
Composites: basics and terminology John Summerscales
Structure of module MATS324 one lecturer o John Summerscales (JS) two themes o materials selection and characterisation o manufacturing processes assessed by one coursework report + one 3h examination Complemented by MATS320 lecturers Richard Cullen & John Summerscales for coursework assignment Stephen Grove (SMG) on stress analysis assessment by module MATS320 final report
Reading for a degree Each lecture has: PowerPoint slides on extranet o these need JS “soundtrack” (i.e. lectures) individual lecture webpages on extranet o also read these to reinforce your learning … and to really understand the topic follow up the references and/or review papers
Support materials for module Home page on Extranet o MATS231: o MATS324: Lecture schedule, notes and PowerPoint: o Home page also includes: o subject index o map of local composites companies o links to Library Reading Lists o and many other useful resources ;-) see MooDLE student portal for assessments
Support materials Lecture & practical schedule Review papers Free e-booksSubject index
Practical manufacture and test of a composite plate attendance at Health and Safety lecture is an essential prerequisite for coursework o list of attendees circulated for signature o if your name is not on the list, you will not be allowed to do the practical o if you do not do the practical you will fail the coursework element and hence the module.
Civil and structural engineering Bridges Rehabilitation o Enhanced carrying capacity of offshore rigs o Repairs to LUL tunnels, plus bridges & pipework Cladding o (~30 years) Mondial/Montedison House Buildings o (not so) temporary structures
Outline of this lecture Anisotropy Fibre volume fraction (V f ) Areal weight of fabric (W F ) Basic rule-of-mixtures Glass transition temperature (T g ) Crystalline melting point (T m ) Stacking sequence notation
Anisotropy Degree of anisotropy Principal axes PropertiesExample IsotropicOrthogonalConstant regardless of directionMetals Square symmetric OrthogonalTwo different principal axesUnidirectional fibres or woven cloth OrthotropicOrthogonalThree different principal axesUnidirectional weave with light weft AnisotropicAny angleConstant relative to axesFilament wound tube or many crystals AeolotropicAny angleMay change with positionTimber
Fibre volume fraction (Vf) n = the number of layers A F = the areal weight of the fabric ρ f = density of the fibre, and t = the thickness of the laminate.
Areal weight of fabric (A F ) For a balanced fabric, the parameters are: o N f = number of filaments per tow o N T = number of tows in unit width of fabric o r f = radius of the fibre cross-section o ρ f = density of the fibre Crimp increases areal weight by ~1% at 10˚, 3% at 20˚ or 6.5% at 30˚ maximum crimp angle.
Basic rule-of-mixtures 1 Elastic properties (e.g. density or modulus) of composite calculated by rule-of-mixtures E C = κ. η d. η L. η O. V f. E f + V m. E m if the first term of the equation is large, the second term can be neglected
Basic rule-of-mixtures 2a The parameters are: E C = modulus of composite V x = volume fraction of component x E x = modulus of component x subscripts f and m are fibre and matrix respectively
Basic rule-of-mixtures 2b κ = fibre area correction factor * η d = fibre “diameter” distribution factor * η L = fibre length distribution factor η O = fibre orientation distribution factor * these two factors are set to unity for man-made fibres (but see lecture A9 on natural fibres)
Basic rule-of-mixtures 3 η L = fibre length distribution factor 1 for continuous fibres fractional for long fibres 0 if fibre below a “critical length”
Basic rule-of-mixtures 4 η O = fibre orientation distribution factor a weighted function of fibre alignment, essentially cos 4 θ: o 1 for unidirectional o 1/2 for biaxial aligned with the stress o 3/8 for random in-plane o 1/4 for biaxial fabric on the bias angle
Basic rule-of-mixtures 5 V f = fibre volume fraction o for random o for fabrics o for unidirectional consolidation pressure: o no pressure gives the lower value o V f increases with pressure
Basic rule-of-mixtures 6 E f = elastic modulus of fibre o glass = ~70 GPa (equivalent to aluminium) o aramid = ~140 GPa o carbon = ~210 GPa (equivalent to steel) figures above are lowest values i.e. for standard fibres
Transition temperatures in ascending order T g = glass transition temperature T c = peak crystallisation temperature T m = crystalline melting point typically T m = T g ±50 °C nb: no melting point in amorphous materials T p = processing temperature typically T p = T m + ~30°C for “semi”-crystalline polymers T g follows cure temperature in thermosets T d = degradation/decomposition temperature may limit T p (especially for PVC)
Glass transition temperature (Tg) Temperature at which segmental motion of the chain is frozen out o below Tg polymer is elastic/brittle o above Tg polymer is viscoelastic/tough o more rigorous than heat distortion temperature T g for thermoplastics = T m - ~200°C T g for thermosets follows cure temp.
Crystalline melting point (Tm) all polymers have a T g only some polymers have a T m o they must be able to form crystals normally a regular repeating structure rarely 100% crystalline polymers may degrade before melting usually the case for thermoset
Composites How fibres can be arranged in order of increasing stiffness and strength: 3-D random o e.g. injection moulding grades. planar random o e.g. moulding compounds, chop strand mat, random swirl. quasi-isotropic (QI) o e.g. continuous fibres oriented at 0 ° /-45 ° /90 ° /+45 ° or 0 ° /60 ° /120 °. bidirectional o e.g. woven fabrics or cross-plied UD laminates at 0 ° /90 °. unidirectional (UD) o e.g. pultrusions and aligned monolithic fibre composites.
Four types of fibre-reinforced composite Monolithic (material) o all layers aligned parallel laminate (structure - see next slides) o orientation changes between layers hybrid (structure – MATS324 lecture A6) o more than one type of fibre (e.g. carbon/glass) Sandwich (structure – MATS320) o composite skins and lightweight core
Laminate stacking sequence notation typical laminate stacking sequence is: o [0º/+45º/-45º/90º] ns where the subscripts are: o n is the number of repeats of the sequence o Q indicates antisymmetric laminate o s means the laminate is symmetric o T is the total number of plies o overbar denotes that the laminate is symmetric about the mid-plane of the ply Thus for n = 2 above, the sequence will be: o 0º/+45º/-45º/90º/0º/+45º/-45º/90º * 90º/-45º/+45º/0º/90º/-45º/+45º/0º o with * denoting the line of symmetry.
I-beam vs stacking sequence Beam stiffness reduces from left to right: Equivalent beam: high EI vs low EI segments Laminated composite plate: 0° layer or 90° layer
Key points of this lecture resources on Student Portal and Extranet anisotropy fibre volume fraction (Vf) areal weight of fabric (A F … sometimes W F ) basic rule-of-mixtures glass transition temperature (Tg) crystalline melting point (Tm) stacking sequence notation