Failure simulation of four point bending CFRP laminate specimen including wrinkles
Résumé
The influence of manufacturing defects in laminated composites is an major field of research according to their detrimental effects on the residual strength of the structure [1]. Among the different types of defects, wrinkling and waviness are perhaps one of the most common and detrimental, especially under compression. Here the term
“waviness” is used to describe in-plane misalignment of fibers and the term “wrinkling” refers to out-of-plane misalignment of fibers. In the literature, wrinkling in a planar part is massively studied [2-3] but to our knowledge, less interest was paid to the influence of wrinkling present in the radius of a curved part. In this paper, a numerical study the
influence of wrinkles contained in the radius of L-shape specimen tested under four-point bending tests is done.
The used model called ‘Discrete Ply Model’ (DPM) and developed at Institut Clement Ader [4–6] a decade ago [4–6], which has already demonstrated its capability to give a good agreement between experimental results and simulation of four points bending tests without wrinkles [7]. Several specimens with different severities of wrinkling were manufactured. Concave moulds were used with two strategies of stacking. The first one consists classically to lay in the concave mould the different plies to obtain the stacking desired without defect. The second method permits to introduce wrinkling of plies and consists in realizing the staking on a table and afterwards introducing the
package in the mould. Depending on the number of plies previously stacked on the table, the wrinkles observed are more or less significant. By combining these two methods, the intensity of wrinkling created can be adjusted and regulated. This strategy produced good results when the number of plies initially stacked on a flat surface is low. When too much plies are used to insert wrinkling under the radius of curvature of the part, the defects created are too serious and many voids emerge caused by wrinkling of plies.
Four points bending tests on the different specimens produced were carried out. Digital images correlation and infrared thermographic imaging were used simultaneously to follow the damage of specimens. This instrumentation has enabled to capture the scenario of failure of L-angle shapes with presence of wrinkling under the radius of
curvature. Finally, the DPM was used to numerically simulate the tests previously mentioned taking into consideration the ply wrinkling experimentally observed. For that, a range of points corresponding to the interface of the different plies was measured and used to create a mesh, which perfectly corresponds to the specimen