Laminated Composite Plate Model Considering Interfacial Imperfection Based on Quasi-Conforming Element Technique

Laminated composite plates widely used in industries are prone to various defects at the interfaces between layers in complex usage environments and manufacturing processes, also known as the interfacial imperfection. Therefore, based on the third-order zigzag displacement field and a layer-spring model, a four-node quadrilateral quasi-conforming plate element (QCQ4) is proposed to calculate the free vibration of the composite laminates with interfacial imperfection. In addition, combined with the numerical results from other literature, it is verified that the proposed plate element (QCQ4) can effectively obtain the stress and deflection of the composite laminates with interfacial imperfection, and accurately calculate the free vibration of laminates with different geometries, thicknesses and fiber directions. Furthermore, numerical results show that when the dimensionless interface parameter R characterizing the interfacial imperfection increases from 0.0 to 1.0 and 5.0, respectively, the maximum reduction in the natural frequency of the laminated thick and thin plates in the first six modes exceeds 33% and 37%. This means that R=1.0 and R=5.0 seem to be two critical values for evaluating whether thick and thin laminates will experience a significant decrease in stiffness due to interfacial imperfection. Besides, it is also found that as the increase of the dimensionless interface parameter R, the 4th and 5th mode shapes of the square and circular laminate, and the 5th and 6th mode shapes of the triangular laminate will change compared with the mode shapes of laminates without interfacial imperfection.