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A rapid 3D stress analysis of sandwich structures made from composite face sheets and a lightweight core is needed for an efficient simulation of impact damage tolerance and resistance. For that reason, two finite shell element formulations based on layer-wise theories are developed using pure displacement approaches. The number of layers is confined to three, one for each skin laminate and one for the core, accounting for the very different stiffness of skin and core material. In order to obtain reasonable transverse shear stiffness properties and also improved transverse shear and normal stresses the equilibrium approach by Rolfes and Rohwer [1] is extended to a three-layered sandwich structure.

This paper presents an approach to facilitate comparison and optimization of sandwich material combinations. Equivalent homogenised sandwich material properties (bending stiffness, density and cost) are presented graphically in materials selection charts to enable an efficient performance per cost evaluation. The effects of core shear deformations and panel production costs can be included in those sandwich materials selection charts.

This paper presents discrete optimization of laminated sandwich panels with simply supported edges, under out-of-plane load that include honeycomb and extended cores. Because of problem complexity and discontinuity of variables, evolutionary algorithm (GA) is preferred for this optimization

In the present paper the structural optimization approach Discrete Material Optimization (DMO) is introduced and applied to stiffness maximization of locally reinforced sandwich structures. The aim of the optimization is for each element to choose the material from the set of candidate materials that minimizes the objective the most. A design study of a sandwich panel in three-point bending shows that the DMO method is successful in providing valuable clues to efficient design of such structures.

This paper introduces a Nonlinear Finite Element Analysis on damage propagation behavior of composite panels under in-plane uniaxial quasi-static compression after a low-velocity impact. The major damage modes due to the impact were incorporated into the model. A consequential core crushing mechanism was incorporated into the analysis. The critical far field stress corresponding to the onset of damage propagation near the damage zone was captured successfully with a good correlation with experimental data. These values can be used to predict the residual compressive strength of low-velocity impacted composite sandwich panels.

Bending behaviour of composite-skinned sandwich panels with both aluminium and nomex honeycombs have been investigated under a quasi-static loading with both HS and FE indenters. Damage mechanisms were identified as core crush, top-skin delamination and skin failure. A combination of skin thickness and indenter nose shape dictates not only the nature of these damage mechanisms but also their energy-absorbing capacity.

The authors developed new techniques to detect inside damages in honeycomb sandwich structures using small-diameter optical fiber sensors. We embedded sensors in the adhesive layer between the core and the facesheet. From a decrease in the transmitted optical power and the change in the form of the reflection spectra from fiber Bragg grating (FBG) sensors, the debonding and the impact damage could be detected sensitively in real-time.

Wrinkle defects may reduce the compressive strength of a face laminate for in-plane loading applied perpendicularly to the line of the wrinkle. To be able to decide whether a repair is needed it is necessary to know the magnitude of the strength reduction for a given wrinkle geometry. In the studies reported here, the influence of wrinkle defects on the in-plane compressive strength of quasi-isotropic CFRP laminates used in PVC foam-cored sandwich panels has been investigated by three approaches: testing of sandwich beam specimens in four-point bending, testing of sandwich panels with in-plane compression, and finite element simulation. Wrinkles involving different numbers of plies have been considered. Two different sandwich lay-ups typical of deck and hull bottom panels in a naval ship have been included.

Sandwiches are analyzed by the application of linear elastic fracture mechanics. An expression for the energy release rate is found by analytical evaluation of the J-integral. Also, a method for determining the mode mixity is described and applied. The theory presented is applied to a test method and the fracture toughness of two sandwiches are measured as function of the mode mixity.

Fatigue crack growth of foam core sandwich beams loaded in flexure has been investigated numerically. Extensive fatigue data from foam core sandwich composites under flexural loading were analyzed. A first core-skin debond parallel to the beam axis is considered. A static non-linear elastic two-dimensional finite element analysis of the sandwich beam is performed to evaluate the stress intensity factors at the crack tips.