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The influence of five different types of morphological imperfection – curved cell wall, corrugation, cell shape irregularity, missing cell walls and non-uniform distribution of cell wall thickness – on steady state creep of closed-cell aluminum foams is systematically studied under uniaxial compressive loading. A refined theoretical model is developed to predict the steady state creep rate of idealized tetrakaidecahedral (TKD) closed-cell foams. Based upon the TKD model, finite element modeling is also carried out. The presence of imperfections usually leads to significant increase in steady state creep rate. The creep rate increases linearly with the degree of cell shape irregularity and the curvature of curved cell walls, while increases as a power law function of the area fraction of missing cell walls and the dispersion degree of non-uniform distributed cell wall thickness. The combined effect of three different random defects—cell shape irregularity, missing cell walls and non-uniform distribution of cell wall thickness—causes more drastic increase in creep rate than any single or dual imperfections. Interactions among the three are small and can be neglected. Finally, an empirical formula of steady state creep rate is proposed to give a good prediction for closed-cell foams with random imperfections. Keywords: Imperfections, Steady state creep, Closed-cell foam, Finite element modeling, Theoretical modeling

A novel sandwich core topology – corrugated channels (periodic fluid-through wavy passages) – was proposed for simultaneous load-bearing and active cooling applications. Relative to a sandwich panel with parallel plate channels, the sandwich with corrugated channel core exhibits not only significantly enhanced convective heat transfer rate but also superior mechanical performance. To explore the underlying deformation and failure mechanisms, corrugated-channel-cored sandwich panels (3CSPs) with low relative densities (

The authors recently reported a novel in-situ method of fabricating self-lubricating coatings derived nickel based alloy and ferrous sulfide film by ion sulfurizing at an atmospheric H2/Ar/H2S flow. In the present work, thin 3 μm FeS film was deposited on 1.1 mm Ni55 coating with a hardness of about 635 HV. The microstructural evolution, the bond strength with substrate and antifriction properties in artificial seawater of the processed film are reported. The surface roughness value of FeS film is 0.08 μm. The diameters of FeS nano-spheres in the film are in the range of 80–230 nm. FeS self-lubricating film exhibited the best self-lubricating effect on Ni55 coating in artificial seawater, compared with that in dry friction and deionized water. This was attributed to its close-packed hexagonal structure, the separation of the salts, and the auxiliary lubrication and cool effect of artificial seawater. Keywords: Laser cladding, FeS self-lubricating film, Ion sulfurizing, Scratch test, Artificial seawater

A novel lightweight sandwich construction with honeycomb–corrugation hybrid core is fabricated by filling the interstices of aluminum corrugations with trapezoidal aluminum honeycomb blocks. The performance of the hybrid structure under quasi-static out-of-plane uniform compression is investigated, both experimentally and theoretically. When all the interfaces in the hybrid structure are fixed using epoxy glue, the proposed structure is found to have strength and energy absorption capacity significantly greater than the sum of those of empty corrugated sandwich and honeycomb-cored sandwich. It is demonstrated that the interaction effect between honeycomb insertions and corrugated plates stabilizes buckling and changes the crushing deformation mechanisms of both constituents, leading to enhanced strength and energy absorption. Comparison with competing lightweight sandwich constructions having equal mass reveals that the proposed hybrid structure exhibits superiority in both strength and energy absorption in the low-density regime. Keywords: Honeycomb–corrugation hybrid, Strength, Energy absorption, Finite element analysis

Honeycomb as sandwich core construction has been established as one of the best candidates among ultralight cellular materials for load-bearing and energy absorption applications. In this paper, by introducing non-uniform mass distribution (gradient) in the core, substantially improved structural performance of a fully-clamped sandwich plate with square honeycomb core is achieved for out-of-plane uniform pressure loading. In-plane gradient of core is defined and achieved via two approaches: web thickness variation and cell size variation. Response of sandwich plates with linear in-plane core gradient is systematically investigated with finite element (FE) simulations. For both quasi-static and blast loading cases, it is found that positively graded cores exhibit advantage in stiffness, strength as well as plastic energy dissipation compared to cores without gradient or with negative gradient. Examination of plastic energy dissipation in a graded core reveals that ribs placed next to its symmetry plane are more sensitive to changes in thickness or location compared to those placed adjacent to the clamped edges. With the total mass of the core constrained, the constituent material can be more efficiently utilized by either increasing the thickness of ribs close to symmetry planes or moving ribs towards the symmetry planes. Keywords: Graded honeycomb, Sandwich plate, Flexural behavior, Energy absorption

Sandwich panels having metallic corrugated cores had distinctly different attributes from those having metal foam cores, the former with high specific stiffness/strength and the latter with superior specific energy absorption capacity. To explore the attribute diversity, all-metallic hybrid-cored sandwich constructions with aluminum foam blocks inserted into the interstices of steel corrugated plates were fabricated and tested under three-point bending. Analytical predictions of the bending stiffness, initial failure load, peak load, and failure modes were obtained and compared with those measured. Good agreement between analysis and experiment was achieved. Failure maps were also constructed to reveal the mechanisms of initial failure. Foam insertions altered not only the failure mode of the corrugated sandwich but also increased dramatically its bending resistance. All-metallic sandwich constructions with foam-filled corrugated cores hold great potential as novel lightweight structural materials for a wide range of structural and crushing/impulsive loading applications.

Density-graded metallic foam projectiles are proposed for shock loading simulation, with special focus placed upon designing pressure pulses having specific shapes. Experiments are performed to explore the potential of density-graded foam projectiles in generating shock loadings of various pulse shapes. Subsequently, three-dimensional Voronoi foam models with varying gradient profiles along the length direction are constructed for finite element (FE) simulations, which are validated against the experimental data. Then, FE simulations of density-graded foam projectiles impacting a stationary rigid wall are conducted to quantify the effect of density gradient on the shape of the pressure pulse generated and explore the physical mechanisms underlying such effect. It is demonstrated that density gradient affects significantly local crushing stress and local density within the shock front when it propagates from the impact end to the other end of the foam projectile. Inspired by the FE simulation results and the classical Taylor impact model, one-dimensional theoretical model for density-graded foam projectiles is developed to predict the contact force between the projectile and the fixed rigid wall. Finally, the theoretical model is employed to determine the geometry, density gradient, and firing velocity of foam projectiles needed to generate shock loadings with prescribed pulse shapes. Keywords: Density-graded foam projectile, Shock loading simulation, Pulse shape design

During laser surface melting of steel components, obtaining the desired distribution of microstructure and residual stresses with minimum distortion is essential for production goals and reliable service performance. In this study, a three-dimensional finite element based model, which is integrated into commercial finite element analysis (FEA) software SYSWELD by means of user subroutines, has been developed to simulate the wide-band laser surface melting (LSM) processing and predict temperature history and stress field with different laser scanning speed. In the proposed computational procedure, thermal, metallurgical transformation and mechanical aspects were taken into account, and the heat transfer analysis, the temperature dependent on material properties and a coupled transient thermo-mechanical analysis were used. Effects of laser scanning speed on melting temperature field and residual stress were investigated. The simulation results show that laser scanning speed changes have significant effects on melting residual stress. For experimental verification, laser surface melting of thin plate 42CrMo4 steel was achieved by a 5 kW continuous wave CO2 laser with laser scanning speed from 10 m/s to 30 m/s. The computational results are in good agreement with experimental measurements.