Elsevier

Composites Science and Technology

Volume 125, 23 March 2016, Pages 114-122
Composites Science and Technology

Fabrication and mechanical behaviors of corrugated lattice truss composite sandwich panels

https://doi.org/10.1016/j.compscitech.2016.02.003Get rights and content

Abstract

To get a strong, stiff and weight-efficient structure, a novel carbon fiber reinforced composite (CFRC) lattice truss sandwich panel (LTSP) was designed and fabricated. The lattice core is made up of orthogonal corrugated lattice trusses (CLTs) and manufactured by mould pressing method. Compression and shearing experiments were carried out to reveal the strength and failure modes of the structure. A coupled compression-shear failure mode was observed in compression and the compression strength of the lattice truss structure is over 13 MPa. In shearing, the enlarged area of the node enhances the shear strength to 3.4 MPa. Structural models were built to evaluate the strength in compression and shearing. Failure maps were supplied to instruct optimal design of the CFRC LTSP.

Introduction

Benefited from light but strong carbon fibers and stretching-dominated topology, CFRC lattice truss composite structure (LTCS) is weight-efficient for its high specific stiffness and strength [1], [2], [3]. This structure has the potential to enhance innumerable applications ranging from aerospace structures to marine structures to civil infrastructure. In last two decades, Octet truss [1], tetrahedral truss [4], pyramidal truss [5], Kagome lattice [6], hierarchical lattice [7], woven lattice [8], IsoTruss® [9], [10] and Isogrid [11], [12], [13], [14], [15] have been developed. Interlacing method [2], [3], mould pressing method [4], [16], cutting method [17], filament winding method [9], [10], [11], [12], [13], [14], [15] and woven method [8] have been developed to fabricate the LTCS. Usually shear strength of the CFRC LTSP is limited by the node failure. According to previous works [4], [16], the shear strength is usually smaller than 1 MPa. To enhance the shear strength, nodes were epoxy bonded and buried in milled facesheet pockets [17]. Through this way, the shear strength can be greatly improved but the facesheet is severely damaged. Another efficient way to enhance the anti-shear ability is enlarging the node area, such as corrugated topology for the lattice truss structure.

In this paper, a novel CFRC LTSP was designed and manufactured. To enhance the interfacial shear strength, corrugated lattice truss core structure was developed. Mould pressing method and co-curing scheme were applied to make the sandwich panel. Mechanical behaviors of the structure were revealed by experiments and theoretical analyses.

Section snippets

Structure

The sandwich panel has two facesheets and an orthogonal corrugated lattice truss structure performing as the core, as shown in Fig. 1. Compared with other lattice truss structures, corrugation design lets the skin and the core have enough adhesive area to guarantee the interfacial strength. The truss member has plate-like structure, whose width enlarges the adhesive area and improves the anti-shear resistance of the truss member. Bi-directional corrugation design avoids the cross-linking of the

Flatwise compression

Flatwise compression experiments were carried out at a loading rate of 0.2 mm/min, as shown in Fig. 3, where two failure modes and two typical deformation curves were observed. For A1 and A2, the compression strength is 10.1 MPa and 9.8 MPa, respectively. These two panels fail at adhesive shear failure and truss member compression failure successively. When loaded to about 96.6 kN or 6.7 MPa, the adhesive layer between y-axis directional corrugated trusses and the skin delaminated, induced by

Compression model

Under vertical displacement, δz, displacements along the strut, δN, and transverse to strut, δQ, are given by Ref. [18].δN=δzsinα,δQ=δzcosα.

Axial force, N, shear force, Q, and bending moment, M, in the strut are given byN=EAδzcsin2α,Q=12EIc3δzsin3αcosα,M=6EIc2δzsin2αcosα,where E, A and I are the Young's modulus, the cross section area, the second moment of area of the strut, respectively. Compression stress, σz, is given byσz=8Au(Nsinα−Qcosα)=8AuEbtcsin3α(1−tc2c2cos2α)εz.where the compression

Column failure

For CLTSP, the interfacial property dominates its behavior in edgewise compression. The column length (H) varies from 80 mm to 240 mm, as shown in Fig. 9. The width (B) is 120 mm. The failure turns from end-crushing of the 80 mm column to facesheet debonding of the 240 mm column. Their peak loads (P) have little difference, varying from 70.6 kN to 64.6 kN. It is concluded that the corrugation design lets the debonding strength close to the skin compression failure strength (σfs), 294 MPa,

Predictions

From Eq. (11), the compression strength controlled by the interface shear failure isσzs=4τasba/(c+a)2.

From Eq. (25), τas = 14 MPa. The compression strength controlled by the interface shear failure is 14.0 MPa, very close to the tested strength, 13.6 MPa. In the experiments, the ratio of σzs to σzf is 1.48. According to Eq. (12), the predicted value is 1.40 for τas = 13.6 MPa and σs = 294 MPa. All these predictions demonstrate that the models proposed in Section 4 are reasonable.

Advantages of corrugation design

Node area

Conclusions

In this research, a novel corrugated lattice truss sandwich panel reinforced by carbon fibers was designed and fabricated through mould pressing method. The fabrication method proposed in this research makes the structure have advantages compared with previous lattice truss composites: (a) Co-curing guarantees the adhesive strength; (b) Mould pressing improves the volume fraction of the carbon fiber in the lattice structure and guarantees the strut strength; (c) Corrugation design enlarges the

Acknowledgments

Supports from National Natural Science Foundation of China (11372095) and State Key Laboratory of Mechanics and Control of Mechanical Structures (MCMS-0215G01) are gratefully acknowledged.

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