Composite Manufacturing Defects
Common composite manufacturing defects include void of different shapes
and sizes, different location of void (i.e. within the matrix or in between two adjacent plies).
Other forms of manufacturing defects in composite laminates result from hand-Layup and automated
fiber placement processes, which can cause intra-ply overlap resulting in fiber waviness and/or
resin rich pocket gap defects. The presence of gaps containing resin rich pockets and/or wavy
fibers affects the performance of laminate modulus and strength properties. It is important
to account for manufacturing defects and their variability on material and structural response.
Modeling manufacturing defects by means of finite element analysis (FEA) is impractical.
The modeling of voids and fiber waviness is very time consuming. Additionally, use of FEA will
introduce other challenges as some voids, when modeled, can cause stress concentration issues.
Micro-mechanics based approach is the most efficient approach to model and analyze effects from
composite manufacturing defects.
Not accounting for the deterministic and probabilistic nature of composite manufacturing
defects can increase the risk associated with the use of composite sin critical structures such
as those used in aerospace. For example, manufacturing defects can reduce the stability of composite
structures and reduce their impact resistance. To account for such defects, designers tend to
reduce the strength allowables used in design, resulting in increased weight and cost.
How we address it
AlphaSTAR devised a numerical approach combining multi-scale progressive failure
analysis to predict the in-situ degraded ply properties containing voids of different sizes
and shapes and gaps.
GENOA's PFA module allows the insertion of manufacturing defects in composite laminates for
use in progressive failure analysis.
Simplified practical approach for modeling of manufacturing defects
Determination of equivalent ply properties with defects for use in multi-scale progressive
Capture damage and fracture evolution in presence of manufacturing defects
Determine loss in strength and stiffness due to manufacturing defects
Reduce number of tests by validating coupons tests with defects then use approach to assess
effects at component level
AlphaSTAR assessed risks associated with composite manufacturing defects for aerospace
and automotive industries.
|J. Sawicki, P. J. Minguet, "The Effect of Interply Overlaps and Gaps upon the Compression Strength of Composite Laminates" 39th AIAA/SDM Conference Paper, AIAA-98-1786, Long Beach, CA, 1998|
|Damage marked in red in open hole laminate under compression with gap defects obtained from multi-scale PFA|