Introduktion til glasfibre og kompositter

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1 Introduktion til glasfibre og kompositter
Bo Madsen Sektion for Kompositter og Materialemekanik Institut for Vindenergi Danmarks Tekniske Universitet IDA Seminar, København – D. 28. marts 2017

2 Lancaster bomber, World War II
1943, 2. Verdenskrig En af de første anvendelser af glasfiberkompositter til strukturelle komponenter British Air Marshal: ”GLASS! I won’t have you putting glass on any of my bloody aeroplanes, blast you!”

3 Molekylær opbygning af glas
Glas er opbygget af siliciumdioxid, hovedbestanddel i sand Glas har en amorf (ikke krystallinsk) molekylær struktur Glas på massiv form er følsom overfor defekter/revner  Lav styrke + stor spredning Glas på massiv form har en styrke på omkring 175 MPa

4 Styrke af glasfibre – Griffith’s eksperiment, 1921
Glass fibres with a diameter of about 15 m, and strength of about 1200 MPa Tyndere fibre fører til mindre sandsynlighed for defekter  Højere styrke Generelt vil et materiale på fiber form typisk have større styrke end samme materiale på massiv form

5 Fremstilling af glasfibre
Molten glass Glass fibres

6 Massiv form Fiber form Materialer på fiber form er mindre følsom over for defekter/revner, og udviser større styrke MEN fiber form har lav modstand overfor belastninger i andre retninger end træk, f.eks. tryk og tværgående belastninger Løsningen er at indstøbe fibrene i en matrix som kan overføre de ydre belastninger til fibrene, dvs. dannelse af et kompositmateriale

7 Wind turbine blades made of glass/polyester composites
Fibres: Glass fibres Carbon fibres Cellulose fibres and more …. Matrix: Polymers Metals Ceramics Composite material + = Glass fibres Polyester matrix Wind turbine blades made of glass/polyester composites

8 Loading along fibre direction
Unidirectional composite (lamina or ply) Properties and behaviour of composites Micromechanical models for stiffness and strength Shear lag models for transfer of external load from matrix to fibres Crack stopping mechanisms ......

9 Weight-based stiffness of composites
Carbon fibre composites Wood Glass fibre composites Aluminium Steel Composites show an exceptional combination of good mechanical properties and low weight, which is better than for most other construction materials

10 Loading along fibre direction
Unidirectional composite (lamina or ply) Properties and behaviour of composites Micromechanical models for stiffness and strength Shear lag models for transfer of external load from matrix to fibres Crack stopping mechanisms ......

11 Shear lag model – Transfer of external load from matrix to fibres
Fibre stress Position along fibre Fibre Model of a single fibre embedded in a block of matrix Matrix

12 Shear lag model – Transfer of external load from matrix to fibres
Fibre stress Position along fibre Fibre Model of a single fibre embedded in a block of matrix Matrix

13 Shear lag model – Transfer of external load from matrix to fibres
Fibre stress Position along fibre Fibre Model of a single fibre embedded in a block of matrix Matrix

14 Shear lag model – Transfer of external load from matrix to fibres
Fibre stress Position along fibre Fibre Matrix

15 Shear lag model – Transfer of external load from matrix to fibres
Fibre stress Position along fibre Fibre Fibre failure Matrix

16 Shear lag model – Transfer of external load from matrix to fibres
Fibre stress Position along fibre Fibre Fibre failure Matrix

17 Shear lag model – Transfer of external load from matrix to fibres
Loading of a composite may lead to failure of fibres, due spread of fibre strength Fibre failure does not necessarily lead to failure of the composite Fibre segments can carry full load after failure (except at their ends), and thereby they still contribute to the load-carrying ability of the composite

18 Materials anisotropy Loading along fibre direction (0°) Loading across fibre direction (90°) Composites are anisotropic (i.e. their properties depend on the loading direction) This is different from most other construction materials, which are isotropic The anisotropic properties of composites must be taking into account in the design of structural components

19 Stiffness of a composite as a function of loading direction

20 DEMONSTRATION Materials anisotropy Loading along fibre direction (0°)
Loading across fibre direction (90°) DEMONSTRATION

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22 Composite materials – Why
Composite materials show an exceptional combination of good mechanical properties and low weight, which makes their weight based (or specific) mechanical properties better than for other construction materials. 1 Composite materials provide opportunity for design of materials properties (mechanical, thermal, optical, electrical). 2 Components of composite materials are manufactured by an integrated process going directly from the fibre and matrix preforms to the finished component. 3

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