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Glass/Vinylester composite laminates are comprehensively characterised to assess its impact response behaviour under moisture exposure in marine structures. An instrumented drop weight impact machine is utilised to determine the impact responses of dry and immersed specimens in normal, salted and sea water. The specimens, which had three different thicknesses, were subjected to water exposure for a very long period of over 20 months before tested in a low-velocity impact experiment. Water uptake was measured primarily to study the degradation profiles of GRP laminates after being permeated by water. Matrix dissolution and interfacial damage observed on the laminates after prolonged moisture exposure while the absorption behaviour was found typically non-Fickian. The weight of the composite plates firstly increased because of water diffusion up to month 15 and then decreased due to matrix degradation. The specimens with 3, 6 and 9 mm thickness exhibited maximum water absorption corresponding to 2.6%, 0.7% and 0.5% weight gain, respectively. In general, the results indicated that water uptake and impact properties were affected by thickness and less by water type. Impact properties of prolonged immersed specimens reduced remarkably, and intense failure modes detected almost in all cases. The least sensitive to impact damage were wet specimens with 9 mm thickness as they indicated similar maximum load and absorbed energy for different impact energies.

The behaviour of a hybrid bonded butt-joint, comprised of a double lap steel-GFRP and a GFRP sandwich composite part under three-point bending load is analysed through both numerical and experimental studies. The geometry of the joint is typical for marine applications and two possibilities of steel–to-composite connection are investigated: non-bolted and bolted. Deflection under the load point and strains at various locations of the joint were monitored and also numerically calculated. The tests revealed that the bolts used to connect the skin to steel do not have a remarkable effect on the joint's capacity and stiffness in bending conditions. The numerical models can contribute to predict the structural response of the joint up to the loading at which debonding initiates and also the failure location.

The deflection of the composite laminates and their maximum tensile strain in bending conditions are investigated in this study. For this purpose, different equivalent single layer and layerwise theories based on polynomial shape functions are used. Then Rayleigh–Ritz approximation technique and principle of minimum potential energy are applied to obtain the unknown coefficients of the displacement fields. The results are compared with the three dimensional finite element analysis and the experimental investigation. Also the process of obtaining material properties in tensile condition is explained completely. Regarding to the computational costs and agreement of the analytical and numerical results with the experimental ones, for both CCFF and SSFF boundary conditions the deflection prediction by layerwise HSDT is in a good consistency with the experimental results than the other plate theories and FEM method in this study. Although for obtaining strains in SSFF boundary conditions precisely FEM is more applicable.

To obtain the flexural response and the load-carrying capacity of composite plates with delamination, an efficient closed-form analytical solution is presented. Layerwise Higher-order Shear Deformation Theory and Rayleigh-Ritz approximation technique are applied. Fracture analysis is used to obtain the load-carrying capacity and primary steps of delamination propagation. The results include continuous functions. Furthermore, a considerable experimental study has been performed with specimens of various geometries and delamination types. The experimental investigation includes the fabrication procedure, tension experiments to obtain material properties and three-point bending tests of the delaminated plates.

A model of a composite-to-steel hybrid balcony overhang is tested to find its strength and stiffness under imposed shear and bending loads. The configuration tested is representative of a solution being considered for the balconies of cruise ships, where the substitution of steel by composites aims at weight saving. The steel component is a channel type of structure made of two plates that serve as external supports of the sandwich plate. A finite element model is used to compare with the experimental results and to predict the critical regions of stress concentration. The results include load-deflection and load-strain curves with the maximum value of the shear and bending loads. The critical locations and failure loads have been investigated too.

A composite-to-steel joint under bending and torsional loads is experimentally studied to determine their strength and stiffness and to calibrate numerical models with respect to the experimental measurements. The steel component is a channel type of structure made of two plates that serve as external supports of an inserted sandwich plate made of composite materials. The attachment of the steel joint to the structure is supported by a bracket. The results include load–deflection and load–strain curves, critical locations and failure loads, with the maximum value of the pure bending and combined torsion-bending moments. The good agreement between the numerical results obtained by finite element method and the experimental ones demonstrate that this kind of numerical analysis can estimate appropriately the behaviour of the structure.

A composite-to-steel butt-joint applied to joining large composite sandwich panels to steel ships is studied and its design is improved based on numerical simulations combined with test results. A cohesive zone model is adopted to simulate interfacial debonding of the joint. Cohesive property parameters of the interfaces are obtained by multiple calculations and comparisons with experimental results. Three schemes for improving the design of the joint are proposed. The numerical simulation results of the improvement schemes based on the cohesive parameters obtained before indicate that these three schemes can effectively relieve the shear stress concentration and improve the stress field on the critical region, thus delaying the interfacial debonding and the core strength failure, thus increasing the bearing capacity of the joint.

A Layerwise Higher Order Shear Deformation Theory is developed for plates containing rectangular embedded delaminations undergoing non negligible lateral deflections. The effects of different parameters of the composite laminate and delaminated area are investigated analytically under buckling load and the results are compared with the three dimensional finite element analysis. The results demonstrate the effects of different geometrical parameters of the delaminated area and thickness on the deflection of a composite laminate. Also the initiation of debonding in opening and sliding fracture modes is predicted using the developed formulation.

The effects of different parameters of the composite laminate and delaminated area are investigated analytically under buckling load based on a developed Layerwise Higher Order Shear Deformation Theory and the results are compared with the three dimensional Finite Element Analysis. The results demonstrate the consequences of different geometrical parameters of the delaminated area, lay-up sequences and thickness of the laminate on the deflection of a composite plate containing through-the-width delamination.

The effects of different boundary conditions on the composite laminate containing embedded and through-the-width delamination under bending load are investigated analytically based on a developed Layerwise Higher Order Shear Deformation Theory (LHSDT) and the results are compared with the three-dimensional Finite Element Method (FEM). Contact energy has been calculated. The results demonstrate the ability of the presented method of predicting the displacement fields of a composite laminate containing delamination and obtaining stress-strain curves in bending condition. Moreover, strain energy release rate can be achieved using the obtained displacements to evaluate the initiation of delamination propagation around the boundaries of the considered delaminated region. Furthermore, the failure of the laminate will be predicted using conventional theories such as Tsai-Wu.

The deflection of composite laminates and their maximum compressive and tensile strains under in-plane compression, buckling and post-buckling conditions are investigated in this study. For this purpose, different equivalent single layer and layer wise theories based on polynomial and trigonometric shape functions are used. Then the Rayleigh–Ritz approximation technique and the principle of minimum potential energy are applied to obtain the unknown coefficients of the displacement fields. The results are compared with a three-dimensional finite element analysis and an experimental program is conducted to produce data for validation of theoretical and numerical methods. Mesh independency is also studied to evaluate the accuracy of the finite element results. Regarding to the computational costs and agreement of the analytical and numerical results with the experimental ones, the layer wise higher order shear deformation theory (LHSDT) based on polynomial shape functions is the most efficient and flexible theory in calculation of the deflection and strains for the very thin to thick laminates in the buckling and post-buckling conditions.

The mechanical properties of a sandwich panel and its skin, which are the main components of a steel-composite balcony overhang, are compared before and after the failure of the large-scale hybrid joint specimen subjected to imposed shear and bending loads. For this purpose, unidirectional tensile and three-point bending tests are performed on the extracted specimens from the failed balconies. The results include load-deflection and stress-strain curves and tables containing the strength and elasticity modulus for all extracted specimens. Repeating the tensile and flexural tests regarding to ASTM standards and comparing the results with the initial values of properties, contributed to find that the core shear modulus and the flexural strength of the skin reduce remarkably.

An improved and efficient analytical solution is proposed to predict the behaviour and the ultimate strength of composite laminates containing delamination. For this purpose, a Layerwise Higher order Shear Deformation Theory based on polynomial shape functions using Rayleigh–Ritz approximation technique are utilized. The ultimate strength and initial stages of propagation of the delaminated zone are determined using fracture analysis. The results demonstrate continuous functions to calculate in-plane and out-of-plane displacements, rotations, strains, stresses, energy and load carrying capacity under in-plane compressive loading. Moreover, a significant experimental investigation has been carried out for specimens with cross-ply stacking sequence and various material properties, geometries, delamination type and boundary conditions. The experimental study includes fabrication process, tensile tests to determine material properties and buckling test of the defected specimens.