INDENTATION AND PENETRATION LAW FOR GFRP LAMINATES UNDER IMPACT CONDITIONS

摘要

Static and low velocity impact tests were carried out on carbon fibre reinforced plastic plates of various thickness, lay up and architecture [1, 2], which where loaded at the centre by hemispherical steel indentors. The tests were performed up to complete penetration, using different impact conditions. The tests were, then, carried out at growing energy levels in order to characterise the damage initiation and propagation. Because of the big number of the parameters involved in the phenomenon, in order to predict the behaviour of the material, semi empirical models were developed [3, 4, 5] on the base of the data collected. In particular, a law to predict the indentation depth, I, as a function of the absorbed energy indicating that the constants appearing in the model are negligibly influenced by the laminate type and thickness, and constraint conditions adopted was developed. The importance of this study was related, especially in aeronautical field, to the BVID concept and the necessity to know the impact energy and, so, the residual strength of the structure, from a simple visual analysis. In general, the dent depth is strongly dependent on many parameters like the particular laminate, its thickness, the constrain conditions, tup geometry and impact speed. The availability of analytical tools for the prediction of indentation under known impact conditions would simplify the problem. It was shown that, if the ratio of the impact energy to the penetration energy is adopted as the independent parameter, the relationship proposed is negligibly affected by the laminate type and thickness. On the other hand, the necessity to know the penetration energy, U{sub}p, conducted to a calculation of a model [4], accounting only for the reinforcement volume and tup diameter. Thanks to this study, it should be possible to have information about the performance of CFRP laminates in terms of impact energy and residual properties through an indentation measurement, knowing the indentor diameter.