Abstract

Abstract

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.

Abstract

Numerous studies on the use of laminates manufactured with ultra-thin composite laminates have shown the existence of a significant delay in the appearance of damage, a phenomenon known as the Scale Effect. To study the effect that layer thickness may have on the damage mechanisms that appear at higher values of the load, this work analyses whether the use of ultra-thin laminates exhibits a better behaviour in the instants prior to failure and laminate rupture. For this purpose, different laminates have been manufactured with ultrathin thickness material formed by the same number of laminae oriented at 0 and 90 degrees, but with different stacking sequences, distributing the laminae such that the thicknesses of the resulting layers are different. The laminates have been subjected to uniaxial tension up to values close to the ultimate load in order to observe and compare the different damage morphologies that appear in the 90 and 0 degrees layers, using optical microscopy techniques for the observation of the damage. On the other hand, the loads for which the failure of the selected laminates happens have also been compared. The results obtained from this study show different behaviour of the laminates depending on the thickness of their 0 and 90 degrees layers in the moments prior to failure and at the instant when failure occurs.