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Keywords: composite materials, sandwich structures, flexural behaviour, FEM.

Summary

Refrigerated transportation is a very important market for the Portuguese economy, both in services and in the industrial building of refrigerated trailers and cold storage installations. In this type of construction, non-metallic sandwich panels with faces in Glass Reinforced Polymer (GRP) and polymeric foam core are usually employed. Depending on the size of the trailer, it's common practise to reinforce the foam core to increase the sandwich structural performance. These reinforcements, also called stiffeners, must be polymeric so that the sandwich panels maintain their isothermal capacity. In this paper three configurations of stiffened-core sandwich beams, with three types of adhesives are tested in three point bending (3PB) tests. The flexural results are analysed in terms of the beam stiffness and mid-span deflection, and the different kinds of stiffened foam cores are compared. The three configurations of stiffened core sandwich beams are studied by finite element modelling (FEM). Several strategies are used to model the different beam stiffeners configurations: solid modelling, solid/shell and shell/beam models. FEM results are analysed for the beam mid span deflection in 3PB test and compared with analytical and experimental results. Different strategies for modelling sandwich structures were established, providing engineering capacity to model real sandwich structures, like refrigerated trailers.

In lightweight refrigerated trailers it's common to reinforce the foam core to increase the sandwich structural performance. These stiffeners must be also polymeric so that the sandwich panels maintain their isothermal capacity. In this paper several configurations of stiffened core sandwich beams, with three types of adhesives are tested in three point bending test. The results are analysed in terms of the beam stiffness and mid span deflection, and the different kinds of reinforced foam cores are compared.

All results show that:

Polyurethane adhesive bonding has the worst structural performance in stiffness and resin reinforced adhesive has the best performance in stiffness. Polyester resin adhesive shows average performance. This happens for two reasons, first the mechanical properties of polyester resin are better than polyurethane adhesive, second because the resin reinforced adhesive increases slightly the overall beam thickness.
Polyurethane adhesive proves to be a not so good solution in reinforced sandwiches. Results show that the mid span deflection of the beams is about 1/3 of the expected analytical solution.
To increase shear beam rigidity one has to increase foam density, or introduce stiffeners, or both. Stiffeners increase flexural rigidity in flexural bending and shear deflection. Foam density increase only influences shear deflection behaviour.
Increasing foam core rigidity results on heavier beams with increased price on materials and increased thermal conductivity. Stiffeners increase not only materials price, but also manufacturing prices, so one must have great care when choosing a solution.
Analytical solutions for unreinforced sandwich beams describe correctly their elastic behaviour. Analytical solutions developed for reinforced sandwiches also showed to be accurate in predicting the correct displacements in three point bending tests.

Finite element analysis is an extreme help for engineers and designers, however sandwich structures are somewhat more difficult to model than an isotropic material such as iron or steel. Solid, shell and layered solid analysis are accurate and appropriated when modelling 3D structures. Shell approach is only possible when using the sandwich logic special feature.

Conclusion is that not all elements proposed to model layered composite materials are accurate in the sandwich construction studied. SHELL99 is inadequate to model sandwich beams, predicting a stiffer behaviour of the beams. Being a shell element, it neglects shear deflections witch is very important in this construction. As the stiffener influence increases, shear effects are relatively less important and results from all strategies tend to approximate and all the approaches are valid.

Another conclusion is that computational time can be extremely expensive in the full solid models, making a very difficult task when modelling real structures. To maintain an appropriate element shape one has to have a very refined mesh, increasing computational time. Solid layered elements are an extreme help for engineers and designers when modelling sandwich structures, since it is a very simple solution, requiring coarse mesh with same deflection results.

Different strategies for modelling sandwich structures were established, providing engineering capabilities to model real sandwich structures such as refrigerated trailers.

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Front Page Browse CCP CSETS CTR IJRT Other Authors Search Purchase Guide FAQ Contact us	Civil-Comp Proceedings ISSN 1759-3433 CCP: 79 PROCEEDINGS OF THE SEVENTH INTERNATIONAL CONFERENCE ON COMPUTATIONAL STRUCTURES TECHNOLOGY Edited by: B.H.V. Topping and C.A. Mota Soares Paper 27 Elastic Behaviour of Reinforced Sandwich Beams M. Leite, A. Silva and M. Freitas Department of Mechanical Engineering, ICEMS, Instituto Superior Técnico, Lisbon, Portugal doi:10.4203/ccp.79.27 purchase the full-text of this paper Full Bibliographic Reference for this paper M. Leite, A. Silva, M. Freitas, "Elastic Behaviour of Reinforced Sandwich Beams", in B.H.V. Topping, C.A. Mota Soares, (Editors), "Proceedings of the Seventh International Conference on Computational Structures Technology", Civil-Comp Press, Stirlingshire, UK, Paper 27, 2004. doi:10.4203/ccp.79.27 Keywords: composite materials, sandwich structures, flexural behaviour, FEM. Summary Refrigerated transportation is a very important market for the Portuguese economy, both in services and in the industrial building of refrigerated trailers and cold storage installations. In this type of construction, non-metallic sandwich panels with faces in Glass Reinforced Polymer (GRP) and polymeric foam core are usually employed. Depending on the size of the trailer, it's common practise to reinforce the foam core to increase the sandwich structural performance. These reinforcements, also called stiffeners, must be polymeric so that the sandwich panels maintain their isothermal capacity. In this paper three configurations of stiffened-core sandwich beams, with three types of adhesives are tested in three point bending (3PB) tests. The flexural results are analysed in terms of the beam stiffness and mid-span deflection, and the different kinds of stiffened foam cores are compared. The three configurations of stiffened core sandwich beams are studied by finite element modelling (FEM). Several strategies are used to model the different beam stiffeners configurations: solid modelling, solid/shell and shell/beam models. FEM results are analysed for the beam mid span deflection in 3PB test and compared with analytical and experimental results. Different strategies for modelling sandwich structures were established, providing engineering capacity to model real sandwich structures, like refrigerated trailers. In lightweight refrigerated trailers it's common to reinforce the foam core to increase the sandwich structural performance. These stiffeners must be also polymeric so that the sandwich panels maintain their isothermal capacity. In this paper several configurations of stiffened core sandwich beams, with three types of adhesives are tested in three point bending test. The results are analysed in terms of the beam stiffness and mid span deflection, and the different kinds of reinforced foam cores are compared. All results show that: Polyurethane adhesive bonding has the worst structural performance in stiffness and resin reinforced adhesive has the best performance in stiffness. Polyester resin adhesive shows average performance. This happens for two reasons, first the mechanical properties of polyester resin are better than polyurethane adhesive, second because the resin reinforced adhesive increases slightly the overall beam thickness. Polyurethane adhesive proves to be a not so good solution in reinforced sandwiches. Results show that the mid span deflection of the beams is about 1/3 of the expected analytical solution. To increase shear beam rigidity one has to increase foam density, or introduce stiffeners, or both. Stiffeners increase flexural rigidity in flexural bending and shear deflection. Foam density increase only influences shear deflection behaviour. Increasing foam core rigidity results on heavier beams with increased price on materials and increased thermal conductivity. Stiffeners increase not only materials price, but also manufacturing prices, so one must have great care when choosing a solution. Analytical solutions for unreinforced sandwich beams describe correctly their elastic behaviour. Analytical solutions developed for reinforced sandwiches also showed to be accurate in predicting the correct displacements in three point bending tests. Finite element analysis is an extreme help for engineers and designers, however sandwich structures are somewhat more difficult to model than an isotropic material such as iron or steel. Solid, shell and layered solid analysis are accurate and appropriated when modelling 3D structures. Shell approach is only possible when using the sandwich logic special feature. Conclusion is that not all elements proposed to model layered composite materials are accurate in the sandwich construction studied. SHELL99 is inadequate to model sandwich beams, predicting a stiffer behaviour of the beams. Being a shell element, it neglects shear deflections witch is very important in this construction. As the stiffener influence increases, shear effects are relatively less important and results from all strategies tend to approximate and all the approaches are valid. Another conclusion is that computational time can be extremely expensive in the full solid models, making a very difficult task when modelling real structures. To maintain an appropriate element shape one has to have a very refined mesh, increasing computational time. Solid layered elements are an extreme help for engineers and designers when modelling sandwich structures, since it is a very simple solution, requiring coarse mesh with same deflection results. Different strategies for modelling sandwich structures were established, providing engineering capabilities to model real sandwich structures such as refrigerated trailers. purchase the full-text of this paper (price £20) go to the previous paper go to the next paper return to the table of contents return to the book description purchase this book (price £135 +P&P)
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