Structural testing of large notched composite specimens under combined shear and pressure
Résumé
The VIRTUOSE project aims at reducing the number of experiments from the test
pyramid that is necessary to certify aeronautical composite structures. Thanks to the
VERTEX test rig [1, 2], a combined loading of tension/compression-shear-pressure
can be applied on large specimens (400*400mm2 area of interest). Around the world,
only few test rigs allow testing of structural specimens under multiaxial loadings. At a
component level, between the coupon level and the assembly level, representative
loadings are enforced on a large notched specimen representative of a composite
fuselage section. The specimens are manufactured with 13 plies of unidirectional
carbon/epoxy prepreg. Three notched panels with various stacking sequences are
submitted to shear until failure. Three matching specimens are tested under shear up
to failure with an additional initial internal pressure. Based on previous studies [1-3],
methods of measurement have been developed to characterize global strains and
loads fluxes undergone by the structure. Digital image stereo-correlation on the upper
skin of the specimen is used to get full displacements fields. Once the curvature has
been computed, the laminate theory allows the assessment of the fields of membrane
stresses, in-plane loads and moment fluxes. Fluxes characterization on the specimen
ends is of the utmost importance for industrial partners because the load cases used
to size such panels are based on maximal allowable fluxes. The influence of the
additional internal pressure on the failure scenario of the three different stacking
sequences has been thoroughly analysed. Infrared thermography helped to clarify the
failure chronology