Deformation characteristics of composite laminates—part II: an experimental/numerical study on equivalent single-layer theories

The problem of defining a range of validity for the most commonly used equivalent single-layer theories for laminated composite plates is addressed in this study. The experimental method described in part I (Bosia F, Botsis J, Facchini M, Giaccari P. Deformation characteristics of composite laminates—part I: speckle interferometry and embedded Bragg grating sensor measurements. Composites Science and Technology [in press]) to determine surface and internal strains in laminates is used to reconstruct strain distributions through the thickness of laminated plates in various cases, from the thin- to the thick-plate range. Three- and four-point bending of simply supported specimens are considered. Additionally, electronic speckle pattern interferometry is employed to visualize the through-the-thickness displacement distribution on the lateral side of the specimens, and highlight the onset of a nonlinear behaviour. Experimental results are compared to finite element simulations using both laminated shell and solid elements. The effect of non-uniform contact between specimens and both loading and support members in the experimental configuration is discussed, and finite-element simulations are modified accordingly. A discrepancy between the predictions of the two considered equivalent-single-layer theories and experimental results is found in the thick-plate range.