Numerical Study On Delaminating-response Characteristics And Contact Force Measurement Of Composite Laminate Subjected To Small-Mass Impact

A model of delamination threshold load(DTL) of the T-joint of the wing beam and skin is proposed, based on the strain release energy rate of mode ? crack(G?) and inter laminar shear strength(ILSS). A set of low velocity impact tests were carried out on a co-cured composite wing box with areas of different thickness. Two types of impact sites are concerned, one at the middle of two wing beams(type A) and the other at the beam-skin T-joint(type B). With the delamination threshold load of a specified area, the G? and ILSS of it are obtained, which are then employed as references to compute the DTL under other cases. The DTL of type B is computed based on type A matches well with the test data. The liner function of the model is constructed and solved with linear fitting. The prediction accuracy is generally improved based on multiple sets of data.The finite element method(FEM) is used to establish a 3D model of composite laminates and a deformable impactor. The cohesive element is employed to simulate the delamination onset and growth. Firstly, the falling weight impact is simulated. Both of the delamination size and delamination threshold load from finite element simulation are in good agreement with the test data. A sudden drop of load occurs when the delamination initiation. The contact force calculated from strain of impactor match well with that output by the FEM software. The simulation of small mass impact show that the slope of contact force decreases when the delamination occurred. Based on the characteristics of contact force time histories, a program is developed to compute the DTL under impact.For the impact caused by small mass impactor, the strain of impactor is utilized to calculate the contact force, which is interfered by the longitudinal vibration of the impactor. The filtered contact force time history match with the real one, and a spike is observed from it at the time of delamination occurring. The velocity of the opposite site of impact also shows fluctuations corresponding to the delamination occurring, while the strain and displacement responses do not have this feature. Characteristics of impact response features are helpful to obtain and delamination threshold of contact force and energy in the test on impact resistance of composites.