Gradual failure in fibre/polymer laminates

In composites basically Fibre Failure (FF) and Inter Fibre Failure (IFF) of the individual layers of a laminate have to be distinguished. Whereas FF inevitably leads to total failure of the laminate certain IFF-modes are tolerable for many applications like for example pressure vessels. In these pressure vessels the damage process is gradual. When IFF has occurred in a layer the stiffness of this layer is lowered and part of its load transferred to other layers of the laminate leading there to higher stresses and potentially to further failure. This so called gradual failure process has so far not been considered in stress and strength analysis of FRP-components based on the Classical Laminate Theory (CLT). In order to change this unsatisfying situation comprehensive experimental data for the calibration of degradation models – which quantify the loss of stiffness – has been generated for the first time. With this data and the newly developed analytical program Subu the gradual failure process in Fibre/polymer-laminates can now be calculated more realistically.