Type of Document Master's Thesis Author Peel, Larry D. URN etd-10222009-125105 Title Compression failure of angle-ply laminates Degree Master of Science Department Engineering Mechanics Advisory Committee
Advisor Name Title Hyer, M. W. Committee Chair Johnson, E. R. Committee Member Morris, D. H. Committee Member Keywords
- Laminated materials.
Date of Defense 1991-09-05 Availability unrestricted AbstractThe present work deals with modes and mechanisms of failure in compression of angleply
laminates. Experimental results were obtained from 42 angle-ply IM7/8551-7a specimens
with a lay-up of [ (±9) I (=t=9)]6s where 9, the off-axis angle, ranged from 0° to 90°.
The results showed four failure modes, these modes being a function of off-axis angle. Failure
modes include fiber compression, inplane transverse tension, inplane shear, and in plane
transverse compression. Excessive interlaminar shear strain was also considered as an important
mode of failure. At low off-axis angles, experimentally observed values were considerably
lower than published strengths. It was detennined that laminate imperfections in
the form of layer waviness could be a major factor in reducing compression strength. Previously
developed linear buckling and geometrically nonlinear theories were used, with
modifications and enhancements, to examine the influence of layer waviness on compression
response. The wavy layer is described by a wave amplitude and a wave length. Linear
elastic stress-strain response is assumed. The geometrically nonlinear theory, in conjunction
with the maximum stress failure criterion, was used to predict compression failure
loads and failure modes for the angle-ply laminates. A range of wave lengths and amplitudes
were used. It was found that for 0° s 9 s 15° failure was most likely due to fiber compression.
For 15° < 9 .s 35° failure was most likely due to inplane transverse tension. For 35° < 0 ~ 70° failure was most likely due to inplane shear. For 0 > 70° failure was most
likely due to inplane transverse compression. The fiber compression and transverse tension
failure modes depended more heavily on wave length than on wave amplitude. Thus using
a single parameter, such as a ratio of wave amplitude to wave length, to describe waviness
in a laminate would be inaccurate. Throughout, results for AS4/3502, studied previously,
are included for comparison. At low off-axis angles, the AS4/3502 material system was
found to be less sensitive to layer waviness than IM7 /8551-7 a. Analytical predictions were
also obtained for laminates with waviness in only some of the layers. For this type of waviness,
laminate compressive strength could also be considered a function of which layers in
the laminate were wavy, and where those wavy layers were. Overall, the geometrically nonlinear
model correlates well with experimental results.
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