Impact response of polyethylene sandwich panel obtained by rotational moulding

Abstract

A B S T R A C T Sandwich panels are more and more used in load bearing structures because of their high specific stiffness and high specific strength. Impact energy absorption is a characteristic required for some specific application, that is, in high-speed transportations. In this article, the impact response of a new sandwich panel made up of two polyethylene skins separated by lightweight polyethylene foam, built with an innovative manufacturing process called rotational moulding, is investigated by both the impact test and the finite element analysis. To characterize the low-velocity impact response of this new material, three homogenous polyethylene sandwich panels, 44 ± 1 mm thick, are studied under seven impact test energy levels, from 5 to 70 J. Experimental tests have allowed obtaining absorbed energy and the load-time plot for each impact energy level. Furthermore, a quantitative analysis of the damage is presented. Finally, a finite element model was implemented to evaluate the damping effect of the core. E = Young's modulus of the skin E pl = plastic modulus of the skins J = elastic volume ratio U(λ i ,η) = modified strain energy function U λ i ð Þ = foam strain energy function ϕ(η) = damage function η = damage variable λ i = principal stretches μ i , β i , α i = temperature-dependent material parameters ν = Poisson's ratio of the skins σ sn = yield stress of the skins I N T R O D U C T I O NSandwich panels, made up of two polyethylene skins separated by a lightweight polyethylene foam, could represent a good solution in many technical uses where a high damping impact effect is required (e.g. car bumpers). 1 The panel studied in the present work was built with an innovative manufacturing process called rotational moulding (or rotomoulding) whose peculiarity is the possibility of creating in a unique step the entire sandwich component, so as to obtain a better adhesion and continuity between the skins and the core. Rotomoulding is the principal process for making hollow shapes. In rotomoulding, polymer in powder form is introduced into a mould, which is then closed and rotated. If the mould temperature is set with appropriate regard to the melting temperature range of the polymer powder, a viscous molten layer is built up next to the mould surface, which gradually extends inward. 2 To fill the interior part of the panel, special polymeric beads are introduced into the mould with the powder. These beads have the characteristic to explode and to foam at a higher temperature than polymer melting temperature. This technology should permit a reduction of production time and an increase of material mechanical characteristics.Sandwich structures are known to be susceptible to impact damage by foreign objects. 3,4 The impact represents, therefore, an indispensable issue to characterize this kind Correspondence: C. Casavola.

Morphological and Mechanical Properties of Bilayers Wood-Plastic Composites and Foams Obtained by Rotational Molding

“…Casavola et al [22] studied the low impact behavior of three-layer materials produced by rotational molding made from two polyethylene layers enclosing a foam layer. The results showed that the average force to penetrate the external face was about 28% higher compared to the internal face, which is related to the compression behavior of the foam absorbing a part of the impact energy and also reducing the plastic deformation of the skin (force needed to penetrate in the layer), which is convenient for some applications.…”

Viscosity contrast effects on the structure – Property relationship of multilayer soft film/foams

“…In addition, a number of research works have been carried out to improve the performance of PE foams such as by adding small amounts of micro or nano particles [12][13][14][15][16] or by sandwiching them in between two rigid polymers [17][18][19]. Such PE foam composites exhibited improved thermal and mechanical behavior [12][13][14][15][16][17][18][19].…”

An Investigation of Low Velocity Impact Properties of Rotationally Molded Skin–Foam–Skin Sandwich Structure

“…Sandwich composite structures are made from a single material such as polyethylene (PE) using the rotational molding process, have two solid skins separated by a foam core (Fig. ) . The main advantages of these sandwich structures are high specific stiffness and strength, good bending stiffness, lower weight, excellent thermal insulation and acoustic damping when compared to a solid structure .…”