Experimental study of the appearance of the damage in composite laminates

Abstract

The scale effect in Composite Materials, consisting in the delay in the first damage appearance as ply thickness decreases, is, at present, a phenomenon under study due to the use of ultrathin plies (whose thickness may reach 20 microns) in the most leading industries. Based on this, the appearance of the first damage is experimentally analysed in this work for [04,90n,04] conventional laminates where n=1,2,4,8,16,32. The objectives are to study damage mechanisms occurrence as the thickness of the weakest layer varies when subjecting the laminate to uniaxial tension and to check if the scale effect is present. Acustical techniques have been employed for damage detection and optical and electronical microscopy have been used for its observation. The conclusions lead to well-diferenced mechanisms of damage for the different thicknesses analysed: high thicknesses show unstable damage resulting in an explosive failure of the whole laminate, whereas low thicknesses show a more stable damage, it being less significant for the laminate integrity. In addition, an scale effect is detected, since the load at which the failure is generated decreases as the thickness increases. In future works the same analysis will be presented for ultrathin plies.