The response and the damage of graphite/epoxy composite laminates subjected to low-velocity impact are analytically and experimentally investigated. First, impact response is analyzed using the finite element method based on various theories including a higher order shear deformation plate theory and three dimensional theory. Also, the von-Karman plate theory is applied to consider large deflection of the laminate.
For an experimental research, a drop weight type impact test system is set up. Using this test system, the velocity of the impactor and the impact force history are measured. An error due to a difference in measuring position of sensor is corrected by counting friction effects. Experimental schemes to fix boundary edges of laminate specimens in impact testing are investigated. Impact tests on specimens fixed by using those schemes are carried out.
A new method for simple prediction of the impact force history is proposed. Frequency characteristics of the numerical impact force history from the finite element analysis using a contact law are investigated by modal analysis. The frequencies of that numerical impact force history are well agreed with natural frequencies of the system which the mass of an impactor is lumped with the laminate. Predicted impact force histories from this method are well agreed with the numerical ones from the finite element analysis using the contact law.
Also, in order to estimate in-situ strengths on matrix failure of each inner ply in composite laminates, the transverse matrix crack onset strain of cross-ply laminates subjected to tensile loading is analyzed using the finite element method. The matrix crack onset stress computed by this analytical method is applied as in-situ strengths on tensile matrix failure.
Finally, the damaged areas of the laminates due to the low-velocity impact are effectively estimated. The nonlinear static analysis of the laminate subjected to the maximum impact force predicted using the present simple method on the impact force history is performed. A failure criterion on delamination is used, in which the in-situ strengths analyzed by the present method on matrix failure are applied. Ply by ply delamination areas estimated from the present analysis are compared with the experimental ones by the deply technique.
