Premium
The need to re‐evaluate laminate design criteria
Author(s) -
Piggott Michael R.
Publication year - 2000
Publication title -
polymer composites
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.577
H-Index - 82
eISSN - 1548-0569
pISSN - 0272-8397
DOI - 10.1002/pc.10205
Subject(s) - stiffness , aerospace , epoxy , materials science , enhanced data rates for gsm evolution , payload (computing) , composite material , structural engineering , work (physics) , softening , computer science , mechanical engineering , engineering , telecommunications , computer network , network packet , aerospace engineering
Abstract The aerospace industry uses carbon‐fiber epoxy laminates for structures to reduce weight and increase payload. The “standard” design criterion for strength is that proposed by Tsai‐Wu. For stiffness, which is generally more critical than strength, classical laminated plate theory (LPT) is used. The normal lay‐ups considered for commercial aircraft are made up from 0°, 90° and ± 45° orientations. Angle ply laminates, [± ϕ] ns , with ϕ fixed to some angle such as 20°, are not normally used (although this type of structure is employed with great success in the pressure vessel industry). According to the Tsai‐Wu criterion, such a structure should be extremely weak, which probably accounts for the absence of simple angle ply structures in aerospace designs. However if short and wide samples (aspect. ratio 0.5 or less) are tested, higher values are obtained for modulus and much higher values for strength than the long narrow samples used to develop the Tsai‐Wu criterion. The short and wide sample test results are in agreement with results from tests on tubes. These observations show that there is an “edge softening” effect: long narrow samples have a relatively large amount of this soft edge. Since design software normally uses Tsai‐Wu and LPT, large errors in strength and significant errors in stiffness are possible at this stage, and better lay‐up designs may be totally missed. The experimental work leading to these conclusions is described and innovative designs are discussed.