Micromechanical study on the influence of scale effect in the first stage of damage in composites

The variation in the apparent strength of a lamina in a laminate depending on the stacking sequence and thicknesses of the laminas of the laminate has been a matter of interest since the initiation of the extension of the applicability of composites. This fact led to the concept of in-situ strength, the problem itself being covered as a scale effect. In this paper this question is revisited moving towards the level where the damage appears, that is the micromechanical level. As the origin of the effect under consideration, the variation of thickness, takes place at a different level (mesomechanical), a multi-scale model is developed. It is possible in this model to vary the thickness of the lamina under consideration and to observe its effect on the damage. In this paper, only the first stage of damage, which appears in form of debondings between fibres and matrix, is taken into consideration. The analysis carried out shows that there is no scale effect at this first stage of the damage, which is corroborated by experimental evidences.