composites 3 Flashcards
what are some pros of polymeric fibres?
high stiffness comparable with lower stiffness carbon fibres. low density. high toughness.
what are some cons of polymeric fibres?
low compression strength (instability of relatively kinked molecular structure). severe degradation in UV from sunlight
why are ceramic fibres used?
great elevated temperature and chemical stability. high stiffness but low strength (except for using whiskers)
what type of fibres do not increase stiffness?
glasses and ceramics. for carbon and polymer, stiffness many times higher than bulk products
what type of fibres do not show anisotropy?
glasses and ceramics usually isotropic, while carbon and polymers more anisotropic (the ones with high stiffness are anisotropic)
why are polymeric fibres weak in compression?
inherentlly unstable kinked molecular structure
why are carbon fibres weak in compression?
longitudinal modulus increases with strain so they become stiff when extended but less stiff when compressed
what is good about the fibre making processes’ tendency to eliminate flaws?
high strength even with glass fibres, this is only reason why glass fibres better than bulk
what is the relationship between strength and length of fibres?
shorter lengths are generally stronger than longer lengths - Weibull distribution
