Title page for ETD etd-10222009-125105

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
  • Laminated materials.
Date of Defense 1991-09-05
Availability unrestricted
The 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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