Pyramidal Truss Research Articles

Experimental investigation of composite pyramidal truss core sandwich panels with lightweight inserts

Composite sandwich structures with lattice truss cores have both lightweight characteristics and multifunctional potential, which attract a large number of studies on topological optimization, manufacture process and performance evaluation in recent years. However, reliability study on the joint is an inevitable research subject for engineering application, and few studies on inserts within sandwich panels with lattice truss cores are published. In this paper, composite pyramidal truss core sandwich panels with lightweight metallic quadrangular-prism inserts are designed and fabricated. Pull-out and shear tests are carried out to investigate their load capability and failure behaviors, respectively. It is observed that, compared to the honeycomb panels, the present sandwich panels with quadrangular-prism inserts normally can obtain a similar level of pull-out strength but a higher level of shear load capabilities.

Active Vibration Control of Composite Pyramidal Lattice Truss Core Sandwich Plates

AbstractThe vibration characteristics of composite pyramidal truss core sandwich plates with piezoelectric actuator/sensor pairs were investigated, and the active vibration control methods of the s...

Shear and bending performance of new type enhanced lattice truss structures

In this work, the new type enhanced lattice (defined as hourglass) truss structures with the improved resistance of their core members and attached face sheets have been fabricated by an innovative interlocking method. The shear and bending properties of the produced sandwich structures characterized by three different relative densities have been investigated using various analytical methods and the obtained results were in good agreement with the experimental data. The truss failure under shear loading was dominated by the inelastic buckling of the truss members, while the four possible analytical models describing the bending properties and failure mechanism of the hourglass truss beams included elastic face sheet buckling, face sheet yielding, elastic core member buckling, and core member yielding were studied. The bending specimens, which were designed by constructing failure mechanism maps, were used to examine the yielding behavior of the truss core members as well as the elastic buckling and yielding of the face sheet members. The obtained results revealed that the specific shear strengths and bending failure loads of the studied hourglass truss structures were superior to those of pyramidal truss structures, and that the former could be considered promising candidates for manufacturing lightweight structures with high specific strength.

Sound transmission through composite sandwich plate with pyramidal truss cores

In this paper, the sound transmission loss (STL) through sandwich structure with pyramidal truss cores immersed in the surrounding acoustic fluids is investigated. The periodic model is established in two dimensions. Trusses are replaced by translational and rotational springs and the stiffnesses are calculated by the theory of Euler beam. Fluid-structure coupling is considered by imposing velocity continuity condition at fluid-structure interfaces. The dynamic equations are derived by using space harmonic expansions and the principle of virtual work. The sound transmission characteristics of structure are studied by using the numerical calculation. Then, the effects of incident wave, geometry of truss and material properties are discussed for thorough understanding and system design.

Mechanical characterization of hybrid lattice-to-steel joint with pyramidal CFRP truss for marine application

As a novel type of composite structure in recent years, lattice structure with carbon fiber pyramidal truss core being applied to vessel superstructure because of its high stiffness ratio and strength ratio, structure design is the key to joint between superstructure and main hull. To investigate the mechanical property of hybrid joint and to solve the problem of engineering application, two kinds of specimens of hybrid joints are designed and their compressive and flexural properties are tested through experiments. Experimental result shows that lattice structure is weakest when joint carries in-plane compressive load and debonding induced by core macro-shear and facesheet wrinkling can result in buckling. When load alters to out-of-plane normal force, facesheet delamination becomes main failure mode, occurring where stiffness mutation of joint structure turns up, and bearing reaction can bring about resin base of lattice core fracture, further leading to debonding.

Parametric study on nonlinear vibration of composite truss core sandwich plate with internal resonance

Nonlinear vibrations of carbon fiber reinforced composite sandwich plate with pyramidal truss core are investigated. The governing equation of motion for the sandwich plate is derived by using a Zig-Zag theory under consideration of geometrically nonlinear. The natural frequencies of sandwich plates with different dimensions are calculated and compared with those obtained from the classic laminated plate theory and Reddy’s third-order shear deformation plate theory. The frequency responses and waveforms of the sandwich plate when 1:3 internal resonance occurs are obtained, and the characteristics of the internal resonance are discussed. The influences of layer number of face sheet, strut radius, core height and inclination angle on the nonlinear responses of the sandwich plate are analyzed. The results demonstrate that the strut radius and inclination angle mainly affect the resonance frequency band of the sandwich plate, and the layer number and core height not only influence the resonance frequency band but also significantly affect the response amplitude.

Failure maps and optimal design of metallic sandwich panels with truss cores subjected to thermal loading

Sandwich panels with truss cores have been widely investigated due to their superior mechanical performances. When being used in the thermal protection system of a high-speed aircraft, sandwich panels are usually subjected to intense thermal loading and may fail due to various mechanisms. This paper presents a theoretical and numerical analysis on the failure mechanisms and optimal design of metallic sandwich panels with truss cores subjected to uniform thermal loading. Five failure modes are considered: global buckling, face sheet buckling, face sheet yielding, core member buckling and core member yielding. Failure maps of sandwich panels with several truss core topologies are developed based on these failure modes. Taking the five failure modes as constraint conditions, sandwich panels with truss cores are optimally designed for the minimum weight at given thermal loadings. It is found from the optimal analysis that sandwich panels with Kagome and X-type truss cores are more efficient than those with tetrahedral and pyramidal truss cores. Sandwich panels with fully-clamped boundary conditions have superior thermal loading resistance than those with simply-supported boundary conditions.

Fabrication and mechanical properties of composite pyramidal truss core sandwich panels with novel reinforced frames

The novel composite pyramidal truss core sandwich panels with reinforced joints are manufactured by the water jet cut and interlocking assembly method. Here, the relative density [Formula: see text] of the carbon fiber composite pyramidal truss cores varies in the range 0.88–4.4%. The out-of-plane compression and shear performance of sandwich structures are investigated. Analytical estimates for sandwich panel strength are presented for possible competing failure modes. In general, the measured failure loads show good agreement with the analytical predictions. The measured quasi-static uniaxial compressive strength increases from 0.53 to 8.9 MPa with increasing [Formula: see text] over the relative density range investigated here. The shear strength of lattice cores is improved by eliminating core-to-face sheet bond failures. The measured quasi-static shear strength varies between 0.78 and 1.75 MPa. Compared with node non-reinforced composite pyramidal truss sandwich panels, under the relative density of 1.8%, the shear strength of node reinforced sandwich panels increases by 120%, and its shear modulus increases by 26.5%.

Effect of local damages on the buckling behaviour of pyramidal truss core sandwich panels

Truss core sandwich panels have been widely investigated due to their superior mechanical performances. However, local defects or damages during preparation and service may reduce the strength significantly. The objective of this paper is to examine the imperfection sensitive of this kind of structures under in-plane compression. The elastic and plastic buckling behaviour of pyramidal truss core sandwich panels with local damages under in-plane compression are studied experimentally and numerically. Local damages including unbound nodes between lattice truss and the facesheet, missing lattice cells and holes in the facesheet are considered. In-plane compression tests of truss core sandwich panels with prefabricated local damages are conducted, and then a finite element model in conjunction with random number is developed to simulate the buckling behaviour of the panel with randomly distributed damages in a specific region. Experimental and numerical results show that, besides the damage extent, the location of unbound nodes and missing lattice cells have significant effect on the buckling strength of the pyramidal truss core sandwich panel. In addition, the local damage sensitiveness of sandwich panel with round holes in the facesheet is lower than that with square holes.

Hybrid lightweight composite pyramidal truss sandwich panels with high damping and stiffness efficiency

Hybrid composite pyramidal truss sandwich panels combined with multiple damping configurations are fabricated in this work. Modal and quasi-static compressive tests are carried out to investigate the damping and stiffness efficiency of the candidate structures. Experimental results show that such structures combined with damping materials would significantly improve the damping loss efficiency but decrease simultaneously the stiffness efficiency in varying degrees compared with the bare hybrid sandwich panels. In order to evaluate the compatible effect of total damping and stiffness efficiency of the present sandwich structures, a synthetic evaluation criterion is developed, which shows that bare sandwich panels filled with hard polyurethane foam (B-II-HPF) and soft polyurethane foam (B-II-SPF) can yield the best performance up to 2–4times higher than the base hybrid sandwich panels. It is also shown that multiple patch damping treatments based on the finite element-modal strain energy (FE-MSE) approach are suitable and effective to further improve the total damping efficiency.

Free Vibration and Hardening Behavior of Truss Core Sandwich Beam

The dynamic characteristics of simply supported pyramidal truss core sandwich beam are investigated. The nonlinear governing equation of motion for the beam is obtained by using a Zig-Zag theory. The averaged equations of the beam with primary, subharmonic, and superharmonic resonances are derived by using the method of multiple scales and then the corresponding frequency response equations are obtained. The influences of strut radius and core height on the linear natural frequencies and hardening behaviors of the beam are studied. It is illustrated that the first-order natural frequency decreases continuously and the second-order and third-order natural frequencies initially increase and then decrease with the increase of strut radius, and the first three natural frequencies all increase with the rise of the core height. Furthermore, the results indicate that the hardening behaviors of the beam become weaker with the increase of the rise of strut radius and core height. The mechanisms of variations in hardening behavior of the sandwich beam with the three types of resonances are detailed and discussed.

Localized damage response of carbon fiber reinforced polymer composite sandwich panel after thermal exposure

An experimental study was conducted to investigate the effect of thermal exposure on indentation behavior of carbon fiber reinforced polymer composite sandwich panel (CFRPCSP) with pyramidal truss cores. Composite sandwich panels were fabricated by the hot press molding method. Subsequently, composite sandwich panels were exposed to different temperatures for 6 h. After thermal exposure, quasi-static indentation tests were carried out at room temperature. Then, the effect of thermal exposure on the failure mechanism, indentation load and energy absorption were analyzed and discussed. The results showed that the indentation load and energy absorption decreased as exposure temperature increased, which was caused by the degradation of the matrix properties and fiber-matrix interface properties at high temperature. In addition to the decrease of the indentation load and energy absorption, the failure modes also changed with exposure temperature. It is expected that this study can provide useful information for the design and application of composite sandwich panel with pyramidal truss cores at high temperature.

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.

Damping Properties of Sandwich Truss Core Structures by Strain Energy Method

Sandwich panel structures with stiff face sheets and cellular cores are widely used to support dynamic loads. Combining face sheets made of carbon fibre reinforced plastics (CFRPs) with an aluminium pyramidal truss improves the damping performance of the structure due to viscoelastic character of CRFP composites. To predict the damping characteristics of the pyramidal truss core sandwich panel the strain energy method is adopted. The procedure for evaluating the damping of the sandwich panel was performed using commercial finite element software NASTRAN and MATLAB. Non-contact vibration tests were performed on the real sandwich panels in order to extract the modal characteristics and compare them with the numerical predictions.

Comparison of Brazed Residual Stress and Thermal Deformation between X-Type and Pyramidal Lattice Truss Sandwich Structure: Neutron Diffraction Measurement and Simulation Study

Abstract This paper uses finite element method and neutron diffraction measurement to study the residual stress in lattice truss sandwich structure. A comparison of residual stress and thermal deformation between X-type and pyramidal lattice truss sandwich structure has been carried out. The residual stresses are concentrated in the middle joint and then decreases gradually to both the ends. The residual stresses in the X-type lattice truss sandwich structure are smaller than those in pyramidal structure. The maximum longitudinal and transverse stresses of pyramidal structure are 220 and 202 MPa, respectively, but they decrease to 190 and 145 MPa for X-type lattice truss sandwich structure, respectively. The thermal deformation for lattice truss sandwich panel structure is of wave shape. The X-type has a better resistance to thermal deformation than pyramidal lattice truss sandwich structure. The maximum wave deformation of pyramidal structure (0.02 mm) is about twice as that of X-type (0.01 mm) at the same brazing condition.

Aerothermoelastic analysis of lattice sandwich composite panels in supersonic airflow

This paper is devoted to investigate the aerothermoelastic properties of the composite sandwich panels with two- and three-dimensional lattice cores in supersonic airflow. Both the top and bottom face sheets of the sandwich panels are composite laminated panels. The two- and three-dimensional lattice cores are composed of triangular grids and pyramidal trusses, respectively. The first-order shear deformation theory is used in the structural modeling. The equivalent thermal expansion coefficients of the triangular grid are obtained by the physical and geometric relations of the deformed core only under the temperature change. The equation of motion of the structural system is formulated using the Hamilton’s principle. The supersonic piston theory is used to evaluate the aerodynamic pressure. The aerothermoelastic properties of the lattice sandwich panels are analyzed by the frequency-domain method. The influences of parameters of the lattice core on the aeroelastic stability of the sandwich panel are investigated. The aerothermoelastic properties of the sandwich composite panels with two- and three-dimensional lattice cores are compared. Some useful results are obtained from the present study.

Macroscopic response of carbon-fiber pyramidal truss core panel taking account of local defect

In present paper, the macroscopic responses of carbon-fiber pyramidal truss core panel subject to uniaxial compressive loading are investigated through experimental, theoretical and finite element analysis (FEA) methods, taking account of local defect. The local defect is introduced in the form of missing strut for the unit cell. A theoretical model is proposed to predict the effect of defect on the compressive stiffness and ultimate strength of pyramidal truss core sandwich panel. To study the buckling and crushing behavior, a progressive damage model based on the Hashin failure criteria is implemented in ABAQUS software by means of a user subroutine VUMAT. The sensitivity of sandwich panel to the percentage of missing struts, defect type, and defect spatial configuration are respectively discussed. Comparing with the open-cell foam and honeycombs, the pyramidal truss has better defect tolerant than bending dominated construction. Moreover, the effects of defect type and defect spatial configuration on the strength of pyramidal truss panel are significant under the same percentage of missing struts. The numerical results reveal that the discrepancy can be up to 14% and 29%, respectively. The local defect should be considered in the design and application of pyramidal truss structure.

High temperature indentation behaviors of carbon fiber composite pyramidal truss structures

The composite sandwich panels with pyramidal truss cores were fabricated by the hot-press method. Subsequently, the experimental studies were performed to investigate the quasi-static indentation response of composite sandwich panel at high temperature. The quasi-static indentation tests of composite sandwich panels were conducted at temperatures ranging from 20°C to 200°C. The damage mechanism, load–displacement curves, indentation load and absorbed energies at high temperature were investigated and compared with that at room temperature. The results showed that high temperature induced a change in the failure mechanism and had the significant effect on the load–displacement curves, indentation load and energy absorption. The indentation load and absorbed energies decreased as temperature increased. Especially at 200°C, the reduction in indentation load and absorbed energies was more severe, which was are mainly due to the degradation of matrix properties and fiber–matrix interface properties at higher temperature.

The compressive responses of glass fiber composite pyramidal truss cores sandwich panel at different temperatures

A new method for fabricating glass fiber composite sandwich panel with pyramidal truss cores was developed based on the vacuum assisted resin transfer molding technology. The microstructure and organizations of fabricated sandwich panels were examined by the scanning electron microscope. The out-of-plane compressive tests of composite sandwich panels were performed throughout the temperature range from −60°C to 125°C. Then the effects of temperature on the compressive strength, compressive modulus and failure mechanism were investigated and analyzed. Our results indicated that cryogenic temperature resulted in the increasing of the compressive modulus and strength, while high temperature caused the degradation of the compressive modulus and strength. The effect of temperature on failure mode of composite sandwich panel was also observed. Analytical expressions were presented to predict the compressive modulus and strength of composite sandwich panels at different temperatures.

Effect of Defect on the Compressive Response of Sandwich Structures with Carbon Fiber Pyramidal Truss Cores

In the present study, the defect was introduced in the form of missing strut for the individual cell. The effect of defect on the compressive response of carbon-fiber pyramidal truss cores sandwich panel was investigated through experimental and theoretical methods. A series of sandwich panel sample with or without defect was fabricated, and compressive tests were performed at ambient temperature. Scanning electron microscopy (SEM) was conducted on the samples to evaluate the carbon-fiber distribution and failure mode. A revised theoretical model was proposed to predict the effect of defect considering the strut bending and shear behavior. Our results revealed that the compressive moduli of sandwich panel decrease linearly with the fraction of missing struts. Comparing with open-cell foams and honeycombs, the pyramidal truss has better defect tolerance. The theoretical result calculated by the proposed model was in general agreement with experimental result.