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Lightweight and high-strength sandwich structures with advanced materials are essential for the sustainable development of future industrial development. This paper focuses on investigating the fabrication technology and compression properties of the three-dimensional sandwich structure with lattice cores fabricated by using the continuous carbon fiber reinforced thermoplastic polyether ether ketone (CCF/PEEK). A novel fabrication technology for continuous carbon fiber reinforced thermoplastic polyether ether ketone lattice core is proposed utilizing the unique characteristic of repeated thermoforming of continuous carbon fiber reinforced thermoplastic polyether ether ketone. A mould was designed and then the continuous carbon fiber reinforced thermoplastic polyether ether ketone lattice cores were fabricated. Typical adhesive technology is selected to connect facesheets and lattice cores. The out-of-plane compression behaviors of continuous carbon fiber reinforced thermoplastic polyether ether ketone sandwich structures with lattice cores were investigated by experiment and simulation. Compared with the experimental results, the reliability and correctness of the simulation model were verified. By dint of the simulation model, the effect of stacking sequence of the lattice cores on the structural compression properties was investigated, and the correctness of lattice cores adopted [Formula: see text] stacking sequence in this paper was proved. The continuous carbon fiber reinforced thermoplastic polyether ether ketone lattice sandwich structures exhibit the competitive compression strength with other thermoplastic sandwich structures and surpasses some metal foams at a range of densities.

This paper experimentally and numerically investigates the free vibration, quasi-static compressive and split Hopkinson pressure bar impact responses of hybrid composite pyramidal truss sandwich panels. Such sandwich panels made of carbon fibre composite face sheets and aluminium alloy pyramidal truss cores are fabricated using an interlocking and adhesive bonding approach. Modal tests and quasi-static compression tests are conducted. A good consistency for natural frequencies, modal shapes and static stress–strain curves of the specimen with the same specification is obtained, which ensures the good repeatability of the present specimens. Considering the effect of strain rate, a series of split Hopkinson pressure bar tests combined with numerical simulations is carried out to investigate their dynamic compression responses. A good agreement between simulation results and experimental data is observed, which shows that the adopted split Hopkinson pressure bar testing device and the modified Johnson-Cook model are reasonable and reliable. Results show that the dynamic compression modulus and strength of specimen are strongly influenced by the relative density of the truss cores and much higher than the corresponding static compression modulus and strength. Furthermore, it is also revealed that all the specimens have excellent energy absorption performance, which may have greatly advantage in shock isolation application.

A new theoretical model based on the extended high order sandwich panel theory is established to predict the mechanical response of sandwich panels under static loads with the bilinear constitutive stress–strain relation in the core. The constitutive relations of normal stresses related to the longitudinal and vertical normal strains in the bilinear isotropic hardening core are first formulated. The influence of the in-plane rigidity on the elastoplastic response of sandwich structures is analyzed. An in-plane loaded sandwich structure with the bilinear core is first studied based on extended high order sandwich panel theory, and the effect of the bilinear ratio on the mechanical response is evaluated. The governing equations are derived from the principle of minimum potential energy, and a Ritz-based half-analytical method is applied to get the solutions. The plastic response is acquired by an iterative procedure along with the convergence criteria. The results reveal that the local effect can be captured when the axial rigidity of the core is considered. The bilinear characteristic of the core decreases the maximum normal stress with an increase of the average value. The equivalent plastic region extends with the increase of the bilinear ratio when the sandwich structure is loaded in plane. By comparison with open literatures and finite element results, the present theoretical model is proved to be effective and efficient.

This research focuses on the dynamic response of sandwich panels with multilayered graded hourglass lattice core subjected to blast loading. A three-layer lattice core configuration is proposed to improve the absorption efficient of kinetic energy resulted from blast shock wave. The relative density of each core layer is changed with sectional dimension of core truss members to regulate the energy absorption of each core layer. Three-dimensional numerical simulation analyses of dynamic response are carried out, and the applied impulsive pressure distribution on the surface of the panels is calculated using the CONWEP code. The panels are made of stainless steel AL6XN, which is assumed to follow bilinear strain hardening and strain rate-dependence. Peak back sheet deflection and energy absorption of core layers for four types of hourglass lattice panels are comparatively analyzed and the effects of load intensity on the peak deflection are discussed. Furthermore, the near-optimal configuration under blast loadings is proposed.

Topological-reinforcement and material-strengthening were used and employed to improve the mechanical properties of lattice truss sandwich structures. This new type of three-dimensional aluminum alloy lattice truss (named enhanced lattice truss) sandwich structure, with a relative density ranging from 1.7% to 4.7%, was designed and fabricated by interlocking and vacuum-brazing method. The out-of-plane compression and shear properties of the enhanced lattice truss sandwich structures (both as-brazed and age-hardened cores) were experimentally and analytically investigated. Good correlations between analytical predictions and experiment results were achieved. Experimental results showed that the mechanical properties of the enhanced lattice truss cores were sensitive to the unit-cell size and parent-alloy properties (i.e. inelastic buckling and tangential modulus). The compressive and shear characteristics of enhanced lattice truss sandwich structures were discussed and found superior to competing lattice truss structures in low density area (0.046–0.124 g/cm3) of material property charts. The combination of topological-reinforcement and material-strengthening provided a way to achieve lightweight sandwich structures with high specific strengths and low densities.

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%.

Composite lattice structures can be regarded as hierarchical when trusses have their own structure (e.g. different stacking sequences are incorporated). In this study, hollow composite pyramidal lattice sandwich structures in end compression were analyzed, measured and evaluated with respect to the designable properties of sandwich cores, such as relative density and truss stacking sequence. Collapse mechanism charts were constructed for both component elements and sandwich columns to illustrate the influence of structural geometries and properties of composite pyramidal lattice cores on failure modes. Operative failure modes were identified and the analytical models were shown to be accurate when compared to the measured response. The minimum weight design for the hollow composite pyramidal lattice sandwich column in end compression was carried out and the structural efficiency was also discussed.

A laminated mechanical model has been developed that can predict the mechanical properties of 3D braided composites with internal transverse crack. By using the principle of minimum complementary energy, the stress components are obtained in closed-form expressions in terms of a perturbation function, which is governed by two fourth-order inhomogeneous ordinary differential equations. The effective Young’s modulus and Poisson’s ratio of 3D braided composites with internal crack are calculated using the homogenization theorem. To demonstrate the solution, some examples are analyzed. Good agreement is obtained between the presented results and the values predicted by the modified finite element method.