Finite Element Study of the Stress Response of Bi-Directional Corrugated-Strip Core Sandwich Beam

Problem statement: In engineering design, stress affects the size of structural member. A suitable topology of structure should be designed to optimize the stress. Approach: This study presents an alternative topology of truss-like core sandwich beam referred to here as bi-directional corrugated-strip core topology. A finite element me thod is used to study the stress response of three point loaded truss-like core sandwich beams. Two ki nds of core topologies: a truss core and a bidirectional corrugated-strip core are chosen to b e analyzed and compared to each other. Results: The results showed that the bi-directional corrugat ed-strip core topology provided less surfaced normal stress than the truss core topology. Conclusion: From the finding, the stress of truss-like core sandwich beam can be optimized by arranging th e core in the alternative bidirectional corrugated-strip core topology.


INTRODUCTION
In recent design of engineering structures, the need for structures with optimized stress responses is increasing. To deliver such structures, engineering designers may design a new structural topology such as a sandwich structure.
In truss-like core sandwich construction, a core formed in various corrugation profiles may be arranged in either a one-way or a two-way pattern. In addition, the core can also be designed in various advanced patterns such as an offset-corrugated core (Ray, 1995), a bi-directional corrugated core (Ray, 1996), a cross corrugated core (Ray, 1997) and a bi-directional corrugated-strip core (Leekitwattana et al., 2011;Paknejad et al., 2009;Kumar and Singh, 2010;Souiyah et al., 2009;Thomas and Dozier, 2010;Urgessa, 2009).
This study aims to presents an alternative to the truss-like core sandwich beam in which a bi-directional corrugated-strip core is proposed. This study also aims to outline the advantage in stress response of this alternative in comparison with a truss core.

MATERIALS AND METHODS
Finite element software: The commercial finite element software ANSYS Release 11 is used in this study. The ANSYS is run under the operating software MS Windows XP Professional Version 2002. The hardware condition is a desktop computer with Intel ® Core TM 2 CPU 6600 @ 2.40 GHz and 1.98 GB of RAM.
Finite element models: Three-dimensional finite element models of bi-directional corrugated-strip core sandwich beam, as shown in Fig. 1, are analyzed. The sandwich beam consists of the top and bottom steel faceplates and a series of corrugated-strip core. These parts are modeled using the SOLID45 element type-an eight-node element having three degrees of freedom in nodal translations at each node. In this study, the typical 2-mm finite element mesh size is used. The connections between the faceplates and core elements are defined as fully rigid.
The sandwich beam, as shown in Fig. 1, has simply supports at the lines 1-1' and 2-2'. An additional constraint boundary condition is set up along the lines 3-3' and 4-4' to reduce the local deformation effect beneath the loading line 5-5' which is subjected to a unit transverse force per unit width of the sandwich beam (Table 1).
In addition to the bi-directional corrugated-strip core, the truss core, as shown in Fig. 2a, is also investigated and compared.

Material properties of steel:
In this finite element study, the steel with perfectly elastic-plastic property is used. In the ANSYS, this material property of steel is defined using the bi-linear model. The tension and compression behaviors of steel are assumed the same. The physical properties of steel are defined in Table 2.

RESULTS
Based on the finite element method presented in the materials and methods section, the normal stress, σ y , at the surface of the top face plate of sandwich beam with two core topologies, i.e., the truss core topology and the bi-directional corrugated-strip core topology, obtained from the ANSYS are presented in Fig. 3.
In Fig. 3, only left-side a half sandwich beam is presented, i.e., any point of the sandwich beam locates in the range of 0≤y≤1. Due to the symmetry of the beam, this figure can present the right-side a half sandwich beam.

DISCUSSION
In comparison, it can be seen that the response of the normal stress, σ y , of the bi-directional corrugatedstrip core is similar to the response of the truss core. Both responses distribute in the zigzag pattern along the top face plate.
It can be seen from Fig. 3 that, however, the surfaced normal stress, σ y , at the upper peak of each unit cell of the bi-directional corrugated-strip core sandwich beam is significantly less than the stress σ y at the same peak of the truss core sandwich beam. Compared with the truss core, the stress σ y at, for example, y~140 is about sixty per cent less. This may imply that introducing the core in the bi-directional corrugated-strip core format can optimize the surfaced normal stress, σ y . Consequently, the thickness t of the top face plate of this sandwich beam can be reduced. Compared with the truss core, the thickness t of the bi-directional corrugated-strip core sandwich beam can be less than the thickness t of the truss core sandwich beam.

CONCLUSION
This study presents the alternative core topology to the truss-like core sandwich beam. The alternative core topology is referred to here as the bi-directional corrugated-strip core is presented. The surfaced normal stress response of three-point loaded bi-directional corrugated-strip core sandwich beam is studied using the finite element software ANSYS. The stress response of the bi-directional corrugated-strip core sandwich beam is compared with the stress response of the truss core sandwich beam. It is found that the sandwich beam with bi-directional corrugated-strip core topology can provide less normal stress at the surface of the top face plate of the sandwich beam in comparison with the truss core topology. From the finding, therefore, the normal stress of the truss-like core sandwich beam can be optimized by arranging the core in the alternative bidirectional corrugated-strip core topology.