Catálogo de publicaciones - libros

Corrugated cardboard is very sensitive to atmospheric conditions. The aim of this work is to study the effects of these parameters, especialy the relative humidity (RH), on the mechanical behavior of corrugated cardboard sandwich structure. Tensile and three-point bending tests were used under various rates of relative humidity. An analytical model based on the classical laminate plate theory is used to predict the elastic behavior of the corrugated cardboard under different atmosphere conditions. The model is then extended to predict the inelastic behavior of the corrugated cardboard from the behavior of its components.

This paper summarizes a number of presumably new concepts within the general area of sandwich structures. The concepts have been analyzed numerically and/or analytically, manufactured, and tested. The concepts include strip or grid skin sandwich for light weight structures; graded or laminated sandwich cores; “artificial” balsa cores with higher strength and stiffness than conventional end grain balsa; and steel truss / sandwich skin hybrid ship hulls.

Structural foams or integral foams are monolithic components with a solid skin and a cellular core. We developed a new method to produce metallic integral foam with conventional casting machines. The advantages of the material are a low density, a high energy absorption capacity, a high weight specific bending stiffness and a remarkable damping capacity.

Closed moulding processes put new requirements on the core materials for sandwich structures. Two new foam core material grades have been developed to meet these requirements. The first will replace the existing standard grades but with improved strength, ductility and thermal properties while maintaining the excellent stiffness of today’s product. This grade is oriented towards closed manufacturing processes with processing at lower temperatures like infusion, RTM and VARTM and post cure up to 90°C. The second grade will provide full compatibility with low and medium temperature pre-preg and RFI systems for processing up to 160°C.

In addition, for the DIAB core infusion process with a grooved core material, the making up has been improved for weight sensitive applications by using an optimized finer groove pattern in the core surface to minimize resin uptake while still providing an even distribution and wet-out of the fibers.

Sandwich beams reinforced with K-Cor™ are characterized in terms of stiffness, strength and fracture by means of static tests, and compared to traditional sandwich materials. Stiffness is evaluated with a series of three flexure tests applied to each sample. Strength tests show different failure mechanisms for the two architectures. Mode I fracture properties are measured and a significant increase in the core toughness of reinforced samples is revealed.

In this paper, the out-of-plane compressive properties of thermoplastic hexagonal honeycombs are investigated by finite element analysis (FEA). Both linear (eigenvalue problem) and nonlinear buckling analyses are performed correspondingly on honeycomb perfect models and a hexagonal imperfect unit-cell model to determine actual honeycomb compressive properties. The numerical FEA results show much better agreement with the experimental results than other conventional theories.

This paper deals with experimental and analytical analysis of the mechanical behaviour of crushed foam cores. Three rigid cellular core materials are tested in uniaxial compression-tension-compression. An analytical model is proposed describing the stress-strain curve in tension and secondary compression. A special emphasis is laid on the relaxation behaviour of a crushed foam core in tension.

This paper presents first results from a project which aims to generate foam core properties under loading rates representative of those encountered during wave impact of racing yachts. First, special instrumentation enabled shear strain rates to be measured in-situ. Then a symmetrical shear test was designed to allow shear stress-strain behaviour to be determined at rates corresponding to those measured at sea. Image analysis was used to validate the test set-up. First results for high density foams indicate that quasi-static data may suffice for design.

A speckle full field interferometric technique is used for characterizing the Coefficient of Thermal Expansion of a PVC foam core through the thickness. A significant gradient is highlighted and is correlated to a gradient in density. A simulation shows the effect of taking such gradient into account on stress level in the core of a sandwich submitted to a temperature variation.

A full set of elastic constants was determined/estimated for two sandwich composite skin laminates. Out-of-plane compression and shear specimens were cut from skin laminates bonded together to avoid making thick laminates. The approach gives relatively low scatter for the elastic constants and little influence from the bonds as judged from finite element analysis.