Truss Core Sandwich Structures Research Articles

Thin-walled high temperature alloy structures fabricated from additively manufactured polymer templates

Additive manufacturing is enabling a paradigm shift in design and production, but conventional techniques reach their limits when metallic structures require walls with <0.5mm thickness. Here we introduce an approach for indirect additive manufacturing of thin-walled alloy structures. First a polymer template is additively manufactured, then metal layers are deposited by electroplating, physical or chemical vapor deposition. After removal of the polymer, the metal layers can be interdiffused to form an alloy via homogenization heat treatments. Three different alloys designed for three elevated temperature regimes are demonstrated: Monel alloys based on Ni-Cu-Al-Ti, nickel superalloys based on Ni-Cr-Al and refractory rhenium alloys based on Re-Co. A process was developed to co-deposit rhenium and cobalt via aqueous electroplating, resulting in an alloy with a melting point of 2000°C and a Vickers hardness of 480±50HV0.2 after homogenization. Two applications of interest for the aerospace industry were chosen to demonstrate the technology. High temperature truss core sandwich structures and rocket engine thruster demos where fabricated.

Bending behavior of graded corrugated truss core composite sandwich beams

This study presented a new method for forming the graded corrugated truss core sandwich structures based on an auto-cutting and mould-press process. The bending stiffness, strength and failure mechanism were investigated. Analytical models were presented to estimate the performance and failure mode of the sandwich beams. In order to demonstrate sensitivity of geometric parameters on the bending behavior of the truss core sandwich beams, a uniform and two kinds of graded corrugated truss core sandwich panels were fabricated and tested to probe different failure modes. Results showed that the distributions of the truss cores have strong influences on the bending behaviors of the sandwich beams. The predicting results were also compared with the measurements investigated. In general, the measured failure loads showed good agreement with the analytical predictions, except the uniform truss core sandwich beam. The graded corrugated truss core sandwich structures investigated appear to be promising candidates for lightweight systems and multifunctional applications.

The effect of temperature on the bending properties and failure mechanism of composite truss core sandwich structures

The effects of temperature on the bending properties and failure mechanism of carbon fiber reinforced polymer composite sandwich structure with pyramidal truss cores were investigated and presented in this paper. The three-point bending tests of composite sandwich structures were performed at seven different temperatures, and the scanning electron microscope was used to examine the fiber-matrix interface properties in order to understand the deformation and failure mechanism. Then the effects of temperature on deformation modes, failure mechanism and bending failure load were studied and analyzed. The results showed that the temperature has visible impact on the deformation modes, failure mechanism, and bending failure load. The bending failure load decreased as temperature increased, which was caused by the degradation of the matrix properties and fiber-matrix interface properties at high temperature. The analytical formulae were also presented to predict the bending stiffness and failure load of composite sandwich structures at different temperatures.

Damage localization in composite lattice truss core sandwich structures based on vibration characteristics

Although much effort has been devoted to explore the behavior of the composite lattice truss core sandwich structures, little research has been undertaken into non-destructive evaluation (NDE) and health control of this new structure. This article presents the development of a baseline-free NDE method to determine the debonding of truss bar in composite lattice truss core sandwich structures. The method is proposed based on the uniform load surface (ULS) curvature, and developed according to the synergy of gapped smoothing method (GSM) and Teager energy operator (TEO), which is denoted as GSM-TEO method. The effects of local damage on the vibration characteristics of different composite lattice truss core sandwich structures are firstly investigated, and then, experiment and numerical simulation are conducted to assess the performance of the proposed method. It is demonstrated that the GSM-TEO method is reliable and applicable for damage localization in composite lattice truss core sandwich structures.

Compressive and bending behaviours of wood-based two-dimensional lattice truss core sandwich structures

In an effort to optimal the structure of wood engineering materials, wood-based two-dimensional lattice truss core sandwich structures made of wood composites and birch dowels were manufactured using a simple slotting and adhesive bonding approach. The out-of-plane compressive and bending behaviours of sandwich structures made of different facesheet materials were investigated. Analytical models were employed in this study to predict the compressive collapse strength and Young’s modulus of the sandwich structures. The theoretical predictions of the compressive Young’s modulus are in good agreement with experimental results based on the elastic deformation of the dowels. The failure modes of the sandwich structures are represented by the shear failure of the dowels and facesheets under out-of-plane compressive loads. The out-of-plane compressive behaviours of the sandwich structures demonstrate a good energy absorption capability which is an important factor for the safety of wooden construction. The bending behaviours of the sandwich structures indicate that the debonding of nodes was fatal to the sandwich structures, and the bending properties of the sandwich structures were found to depend on the fracture toughness of the adhesive and the strength of the facesheet materials used in their construction.

Fluid Flow and Heat Transfer Characteristics of Composite Lattice Core Sandwich Structures

The fluid flow and heat transfer performance of composite lattice truss core sandwich structures with a constant localized internal heat source are numerically investigated under conditions of forced water convection for a wide range of Reynolds numbers. Three kinds of heat transfer methods are adopted: normal convective heat transfer, incident flow enhancement, and column support enhancement. The local thermal and fluid flow characteristics for this structure are analyzed to reveal the heat transfer mechanism, verifying that the multiform local vortical structures greatly contribute to the improvement in heat transfer efficiency. The heat transfer performance is characterized and assessed in terms of the thermal field distribution and the nondimensional heat transfer parameters of structure. In comparison with other heat dissipation media, a significant advantage is displayed for the comprehensive heat transfer performance of the structures. Much improvement and development space remain for the structural heat transfer performance, even for the achievement of multifunctional integration.

Effects of local damage on vibration characteristics of composite pyramidal truss core sandwich structure

The effects of local damage on the natural frequencies and the corresponding vibration modes of composite pyramidal truss core sandwich structures are studied in the present paper. Hot press molding method is used to fabricate intact and damaged pyramidal truss core sandwich structures, and modal testing is carried out to obtain their natural frequencies. A FEM model is also constructed to investigate their vibration characteristics numerically. It is found that the calculated natural frequencies are in relatively good agreement with the measured results. By using the experimentally validated FEM model, a series of numerical analyses are conducted to further explore the effects of damage extent, damage location, damage form on the vibration characteristics of composite pyramidal truss core sandwich structures as well as the influence of boundary conditions. The conclusion derived from this study is expected to be useful for analyzing practical problems related to structural health monitoring of composite lattice sandwich structures.

The residual compressive strength of impact-damaged sandwich structures with pyramidal truss cores

A combined experimental and numerical study is conducted to assess the effects of impact energy, impact site and core density on the compression-after-impact (CAI) strength of pyramidal truss core sandwich structures. It is found that the severity of impact damage highly depends on the impact site. The CAI tests show that the local buckling occurs for both the un-impact specimens and the specimens impacted under lower energy, while debonding is observed for the specimens impacted under higher energy. In case of the specimens impacted on the middle point of the four adjacent nodes, only a crack appears in the impact-damaged facesheet, which propagates transversely across the facesheet. It is observed that the CAI strength of specimens impacted on the middle point of four adjacent nodes drop much more than that of specimens impacted on the node, and that the specimens with higher density cores have slightly lower normalized CAI strength reduction. Moreover, it is found that the CAI strength of specimens impacted on the node decreases with the impact energy increasing. In addition to experimental tests, the numerical simulation performs well in capturing the failure modes for impact-damaged specimens under compressive load.

Response of sandwich structures with pyramidal truss cores under the compression and impact loading

In this paper, the pyramidal truss core sandwich structures consisting of carbon fiber reinforced polymer (CFRP) facesheets and aluminum alloy cores were manufactured based on the slot-fitting method. This hybrid concept is to maximize the specific bending stiffness/strength as well as obtain excellent energy absorption ability. Quasi-static compression tests were conducted to get the stress–strain curves and to evaluate the energy absorption mechanism. Low velocity impact tests were carried out to investigate the damage resistance of such structures. The compressive measurements show that the low density aluminum alloy pyramidal truss cores have superior energy absorption ability compared with other lightweight lattice cores. In the impact tests, the failure of matrix cracking, fiber breakage, delamination of CFRP facesheets and buckling of truss members occurred and the extent of damage was significantly affected by the impact site. In addition to experimental testing, finite element models for compression and impact simulations have been developed using ABAQUS software. The numerical results were validated compared with the experimental tests.

Mechanical behaviour of CFRP sandwich structures with tetrahedral lattice truss cores

A method of manufacturing carbon fibre reinforced polymer (CFRP) tetrahedral lattice truss core sandwich structure by thermal expansion silicon rubber mould was developed. The sandwich structure was manufactured integrally without secondary bonding and the silicon rubber mould can be made mass-production with low cost in this approach. The intrinsic property of the CFRP was fully exploited because of carbon fibres aligned in the axial orientation of the truss member. The mechanical properties of CFRP tetrahedral lattice truss core sandwich structures were investigated by flatwise compression and shear test. The experimental results indicate that CFRP tetrahedral lattice truss core sandwich structures have higher weight-specific compressive strength than some metal truss cores, and are competitive with conventional honeycombs.

Mechanical Response of All-composite Pyramidal Lattice Truss Core Sandwich Structures

The mechanical performance of an all-composite pyramidal lattice truss core sandwich structure was investigated both theoretically and experimentally. Sandwich structures were fabricated with a hot compression molding method using carbon fiber reinforced composite T700/3234. The out-of-plane compression and shear tests were conducted. Experimental results showed that the all-composite pyramidal lattice truss core sandwich structures were more weight efficient than other metallic lattice truss core sandwich structures. Failure modes revealed that node rupture dominated the mechanical behavior of sandwich structures.

Design optimization of truss-cored sandwiches with homogenization

Lightweight metallic sandwich plates comprising periodic truss cores and solid facesheets are optimally designed against minimum weights. Constitutive models of the truss core are developed using homogenization techniques which, together with effective single-layer sandwich approaches, form the basis of a two-dimensional (2D) single-layer sandwich model. The 2D model is employed to simulate the mechanical behaviors of truss-cored sandwich panels having a variety of core topologies. The types of loading considered include bending, transverse shear and in-plane compression. The validities of the 2D model predictions are checked against direct FE simulations on three-dimensional (3D) truss core sandwich structures. Optimizations using the 2D sandwich model are subsequently performed to determine the minimum weights of truss-cored sandwiches subjected to various failure constraints: overall and local buckling, yielding and facesheet wrinkling. The performances of the optimized truss core sandwiches with 4-rod unit cell and solid truss members and pyramidal unit cell with hollow truss members are compared with benchmark lightweight structures such as honeycomb-cored sandwiches, tetrahedral core sandwiches and hat-stiffened single layer plates.

Wrought aluminum truss core sandwich structures

Wrought metallic sandwich structures with open cell truss cores are a relatively new class of multifunctional material systems that can be made using affordable deformation, assembly, and joining processes. Here, the design and fabrication of these types of structures from wrought, heat-treatable aluminum alloys is reported. Tetrahedral truss cores were made by bending perforated aluminum alloy sheets. Plain square weave truss cores were made by stacking and aligning precrimped aluminum alloy weaves. Both core types were metallurgically bonded between braze clad aluminum alloy facesheets using a vacuum brazing approach. With this method, affordable truss core sandwich structures can be made from a variety of wrought aluminum and other alloys. Design methodology and multifunctional applications are discussed.