Cellular Sandwich Panels Research Articles

ELIMINATION OF THE DEFECTIVE LAYER AND STRESS CONCENTRATORS DURING MICROMACHINING OF HOLES IN THIN SHEET BLANKS OF METAL CELLULAR PANELS

Thin-sheet blanks made of aluminum (in particular, AMg2-N), titanium (VT-15, VT-19) or stainless (12X17) alloys are widely used in the production of honeycomb panels in the aviation and space industries. Foil (thickness 0.025-0.055 mm) is used for the production of fillers for cellular sandwich panels; it is pre-perforated with holes of 0.05-0.18 mm and laid out in a corrugated box with adhesive strips. The possibility of making holes by the laser jet method is considered, as it precedes the occurrence of mechanical damage and thermal defects of the surface adjacent to the treatment zone. It is shown that the Water Jet Guided Laser (WJGL) is an effective and efficient method of obtaining profile holes in the fillers of cellular panels and in the panels themselves, which is characterized by high productivity and allows obtaining holes without thermal and mechanical defects. The method can be used both for foil fillers and for metal panels made of stainless steel up to 1.5 mm thick.

Thermal protection system integrating graded insulation materials and multilayer ceramic matrix composite cellular sandwich panels

Current integrated thermal protection systems (ITPS) are generally devised with single layer metal sandwich panel and uniform insulation material, inevitably leading to limited thermal insulation effect and high risk of buckling failure. By contrast, here, ITPS, which incorporates graded insulation materials and multilayer ceramic matrix composite cellular sandwich panels, is devised to raise both thermal insulation effect and buckling strength. The effective thermal and mechanical properties are theoretically established. Transient heat transfer characteristics are numerically calculated. The results reveal that ITPS with specific graded insulation materials can present lower temperature and better temperature distribution uniformity than those of ITPS filled with uniform insulation material, demonstrating that graded insulation layers can firmly enhance the insulation effect. Besides, the insulation effect of ITPS, in which the densities and thermal conductivities of graded layers are taken arranged from low to high, is much better than those of ITPS which have opposite sequence. Moreover, the buckling strength is demonstrated to be significantly improved through the approach of integrating multilayer sandwich panels. The thermal short effect can be also suppressed, since it is demonstrated that the multilayer sandwich panels in the ITPS can reduce the temperature on bottom facesheet and raise the temperature distribution uniformity.

Low-energy drop weight performance of cellular sandwich panels

Purpose – The aim of this study is to perform a comparative study on sandwich structures with several types of three-dimensional (3D) reticulate cellular structural core designs for their low-energy impact absorption abilities using powder bed additive manufacturing methods. 3D reticulate cellular structures possess promising potentials in various applications with sandwich structure designs. One of the properties critical to the sandwich structures in applications, such as aerospace and automobile components, is the low-energy impact performance. Design/methodology/approach – Sandwich samples of various designs, including re-entrant auxetic, rhombic, hexagonal and octahedral, were designed and fabricated via selective laser sintering (SLS) process using nylon 12 as material. Low-energy drop weight test was performed to evaluate the energy absorption of various designs. Tensile coupons were also produced using the same process to provide baseline material properties. The manufacturing issues such as geometrical accuracy and anisotropy effect as well as their effects on the performance of the structures were discussed. Findings – In general, 3D reticulate cellular structures made by SLS process exhibit significantly different characteristics under low-energy drop weight impact compared to the regular extruded honeycomb sandwich panels. A hexagonal sandwich panel exhibits the largest compliance with the smallest energy absorption ability, and an octahedral sandwich panel exhibits high stiffness as well as good impact protection ability. Through a proper geometrical design, the re-entrant auxetic sandwich panels could achieve a combination of high energy absorption and low response force, making it especially attractive for low-impact protection applications. Originality/value – There has been little work on the comparative study of the energy absorption of various 3D reticulate cellular structures to date. This work demonstrates the potential of 3D reticulate cellular structures as sandwich cores for different purposes. This work also demonstrates the possibility of controlling the performance of this type of sandwich structures via geometrical and process design of the cellular cores with powder bed additive manufacturing systems.

Deformation and impact energy absorption of cellular sandwich panels

The response and energy absorption capacity of cellular sandwich panels that comprises of silk-cotton wood skins and aluminum honeycomb core are studied under quasi-static and low velocity impact loading. Two types of sandwich panels were constructed. The Type-I sandwich panel contains the silk-cotton wood plates (face plates) with their grains oriented to the direction of loading axis and in the case of Type-II sandwich panel, the wood grains were oriented transverse to the loading axis. In both of the above cases, aluminum honeycomb core had its cell axis parallel to the loading direction. The macro-deformation behavior of these panels is studied under quasi-static loading and their energy absorption capacity quantified. A series of low velocity impact tests were conducted and the dynamic data are discussed. The results are then compared with those of quasi-static experiments. It is observed that the energy absorption capacity of cellular sandwich panels increases under dynamic loading when compared with the quasi-static loading conditions. The Type-I sandwich panels tested in this study are found to be the better impact energy absorbers for low velocity impact applications.

Damage Localization in Plates Using Mode Conversion Characteristics of Ultrasonic Guided Waves

The present study provides a concise description of wave propagation in cellular sandwich panels. A novel approach of damage detection based on mode conversion is proposed which can be useful for detecting relatively small damages in cellular sandwich structures using high frequency guided waves. The new methodology applies the continuous wavelet transform (CWT) and the cosine formula to extract the damage location from the time signal of displacements. Experiments conducted on a honeycomb and a metallic hollow sphere sandwich plate highlight the feasibility of the novel technique.

Homogenization of cellular sandwich panels

The Bending-Gradient plate theory originally presented in Lebée and Sab (International Journal of Solids and Structures 48 (2011) 2878–2888) is applied to cellular sandwich panels. This theory is the extension of the Reissner–Mindlin theory to heterogeneous plates. Its application clarifies common assumptions made in sandwich theory. It also enables to define a direct homogenization scheme for deriving the shear forces stiffness of sandwich panels. Finally, the conventional bounds used for estimating sandwich panels stiffnesses are justified.