A stress-continuous laminate theory for composites and sandwich structures

This paper proposes a new Equivalent Single Layer (ESL) theory, termed the Higher-order Laminate Theory with A-Priori Stress Continuity (HLT-APSC). Starting from an assumed transverse stress field, HLT-APSC inherently ensures that the derived displacement functions satisfy the C° continuity conditions for transverse displacements and stresses. This approach yields higher accuracy than traditional ESL theories in predicting both the bending deformations of thick plates and higher-order vibration modes. The governing equations and boundary conditions for free vibration are derived within the HLT-APSC framework. The accuracy of HLT-APSC is evaluated through four laminated / sandwich beam case studies. Validated against reference solutions, the proposed HLT-APSC yields natural frequency errors of 3.125%, 12.85%, and 10.00% for the first three cases, respectively. In comparison, the traditional Third-order Shear Deformation Theory (TSDT) results in errors of 3.125%, 14.02%, and 54.98%. For the fourth example, the predicted error is merely 1.182%. Furthermore, HLT-APSC is capable of capturing the C° continuity of transverse shear and normal stresses. The proposed HLT-APSC offers a new perspective for enhancing the predictive accuracy of ESL theories. Despite its current limitations, the HLT-APSC is expected to contribute to more efficient and accurate modeling of relatively thick composite laminates and sandwich structures with soft cores.