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Repair and strengthening of masonry and reinforced concrete structures is becoming a very important topic in the field of the Civil Engineering. At this aim, the use of Fibre Reinforced Plastic (FRP) for repair and/or retrofitting of concrete and masonry structures is becoming a successful and increasingly utilised technique. The success of retrofitting techniques depends on more extent on the bond performance between the FRP reinforcement and the substrate. In particular, when curved concrete members are strengthened with FRP sheets, a combination of shear and normal stresses is transferred at the interface, causing, in many cases, a premature failure. In the present paper the influence of curvature of FRP-strengthened masonry elements is investigated, both in terms of bond-slip laws and failure mechanisms. In detail, an experimental investigation, aimed to analyse the bond between FRP sheets and curved masonry elements, is reported. At this aim a bending test has been performed on curved masonry elements reinforced with CFS (Carbon Fiber Sheet). In particular the state of stress and strain at the interface is analyzed varying the curvature of the elements and the width of the bonded sheets. Finally a theoretical analysis is performed in order to interpret the obtained results.

This paper reports on the development and the optimization of a thermoforming process (compression molding) for thermoplastic sandwich panels. The skins of the panels are fabricated from polypropylene (PP)/continuous glass fibers dry prepregs in the form of a commingled fabric. The use of two different types of core material has been used, a PP foam and a PP honeycomb. Additionally, two alternative methods for the thermoforming process have been analyzed, using either a one-stage or a two-stage process. In the one-step process, skin molding and skin-core bonding are carried out simultaneously. In the two-stage process, the skins are first thermoformed and then bonded to the core as the second stage. The influence of the selected process parameters on the mechanical properties of the panels has been experimentally investigated, leading to the identification of the preferred processing conditions. Polym. Compos. 25:307–318, 2004. © 2004 Society of Plastics Engineers.

ABSTRACT: In this article, a procedure for recycling of polypropylene (PP)-based sandwich panels is presented. PP/glass laminates as the skins and PP foam as the core material are used. The waste panel is converted into short-fiber composite material. The panel is first ground by a mill and homogenized in a mixer or an extruder, then the pellets are re-ground and injection molded. The influence of mixer parameters and fiber content on the mechanical and physical properties of the recycled material is experimentally investigated. The orientation and length of the glass fibers are measured using an optical microscope; SEM analysis is used to characterize the morphology of injection-molded samples.

Sandwich panels are widely utilised for different engineering applications. They consist of two stiff and strong material skins and a low modulus material core; a favourable selection of face and core materials allows the sandwich system to develop the optimum structural characteristics, weight and cost for a specific application. The use of high performance materials allows for a considerable reduction in geometrical dimensions; as a consequence, instability issues become of importance and could cause failure of the structural elements before the ultimate material strength is reached. The objective of the work has been to study the buckling behaviour of flat simply supported sandwich panels with isotropic deformable core and laminated composite faces, the whole being subjected to compressive uniaxial or biaxial in-plane loads. In particular, the experimental evaluation of the critical buckling load of panels with different fibre arrays in the face units has been undertaken; the models were examined under both uniaxial and biaxial loading conditions. In addition, a numerical finite element model was developed and used to compare the results with those of the experimental solution. The face materials of the panels were made from a GFRP wet lay-up and the PVC foam was used as the core material. The paper will discuss the issues of the experimental simulation of the boundary conditions, generally acknowledged to be a difficult task whilst undertaking a panel buckling test, and the achievement of the correct loading conditions. The judicious placement of strain gauges allowed a description of the buckled shape to be obtained and enabled a distinction to be made between the instability failure and material failure of the system. The development of a finite element model representing the experimental tests and the analysis of the numerical model enabled the failure criteria of the system to be studied in detail. Following these investigations further modifications to the experimental set-up and boundary conditions were suggested to improve the co-relation between experimental and numerical models.