Bottom Face Sheets Research Articles

Effect of physical and geometrical parameters on transverse low-velocity impact response of sandwich panels with a transversely flexible core

The effects of important physical and geometrical parameters on transverse low-velocity impact response of composite sandwich panels have been studied in this paper. Impacts are assumed to occur normally over the top and/or the bottom face sheets, at arbitrary locations and with different impactor masses and initial velocities. For deriving closed-form solutions for the contact force, displacements of the impactor and the panel in the transverse direction, the sandwich panel has been modeled as a discrete three-degrees-of-freedom dynamic system with equivalent masses and springs (SM). The dynamic response of the panel is based on the improved higher-order sandwich plate theory (IHSAPT) and both thick and thin panels have been analyzed. The effects of transverse flexibility of the core, and boundary conditions are considered. Also, the area of the contact patch between the impactor and the panel can be varied as it changes with contact duration. The numerical results of the analysis have been compared either with the available experimental results or with some theoretical results. It is established that the dynamic behavior of the sandwich panel depends on various parameters, such as the aspect ratio and the length-to-thickness ratio of the panel, core thickness, boundary conditions of the panel and impactor parameters like its potential energy, velocity and the location of contact point, etc.

Perforation of Sandwich Panels with Honeycomb Cores by Hemispherical Nose Projectiles

Analytical models for the static and low-velocity perforation of composite sandwich panel with woven E-glass/epoxy prepreg facesheets and aluminum honeycomb core are developed. The analytical models are based on a set of experimental results. A three-stage perforation process involving consecutive failures of top facesheet, core, and bottom facesheet is proposed. The analytical predictions of static failure loads and deformation are within 10 and 8% of the test data, respectively. The predicted ballistic limit is within 10% of the test data, while the total energy dissipated at the ballistic limit is within 18% of the test results.

Low velocity impact of combination Kevlar/carbon fiber sandwich composites

Impact, compression after impact, and tensile stiffness properties of carbon fiber and Kevlar combination sandwich composites were investigated in this study. The different samples consisted of impact-side facesheets having different combinations of carbon fiber/Kevlar and carbon fiber/hybrid. The bottom facesheets remained entirely carbon fiber to maintain the high overall flexural stiffness of the sandwich composite. The focus of this research was to determine if any improvement in impact properties existed as a result of replacing the impact-side facesheet layers of carbon fiber with Kevlar or hybrid. Impact tests were conducted on different sample types to obtain information about absorbed energy and maximum impact force. Also, compression after impact tests were conducted to determine the reduction in compressive strength when comparing impacted to non-impacted samples. The elastic moduli of carbon fiber, Kevlar, and hybrid were determined from tensile testing. This data was used to characterize the reduction in stiffness from replacing carbon fiber layers with the Kevlar or hybrid layers. The experimental data in its entirety helps define the benefits and disadvantages of replacing carbon fiber layers with Kevlar or hybrid.

Perforation of honeycomb sandwich plates by projectiles

An analytical solution for the ballistic limit of a honeycomb plate subjected to normal impact by blunt and spherical projectiles is presented. The solution involves a three-stage, perforation process that results in complete perforation of the sandwich. Stages 1–3 describe perforation of the top facesheet, honeycomb core, and bottom facesheet, respectively. Residual velocities in Stages 1 and 2 are found from energy balances between each stage. The plastic work dissipated in deformation and fracture at each stage is approximated from the solution of the previous stage. Shear forces are transmitted in the bond between facesheets and honeycomb core. The predicted ballistic limits are found to be within 5% of the measured ballistic limits for sandwich plates perforated by the blunt and spherical projectiles. The lateral extent and deformation of the damaged facesheets are also found to be within 34 and 51% of limited test results, respectively. It has also been found that most of the work is dissipated in perforation of the bottom facesheet during impact. The work to perforate the bottom facesheet by the blunt and spherical projectiles accounts for 63–85 and 55% of the initial kinetic energy, respectively. Therefore, the perforation resistance of the bottom facesheet, rather than the top facesheet or honeycomb core, would be an important parameter in determining the perforation resistance of the entire sandwich panel.

Low-Velocity Impact Response of Cross-Ply Laminated Sandwich Composites with Hollow and Foam-Filled Z-Pin Reinforced Core

Sandwich composites offer unique lightweight and high bending stiffness advantages for a wide variety of engineered structures. Traditional foam core sandwich constructions exhibit low transverse stiffness and catastrophic compression failure of the core, besides being inaccessible in terms of space. In this study, two configurations including a hollow truss/Z-pin core comprising a three-dimensional (3-D) open network of titanium pins and a foam core reinforced with a 3-D arrangement of titanium pins have been considered in conjunction with traditional foam core sandwich composites. These innovative core designs have the potential to enhance the impact damage resistance, and provide damage containment mechanisms and space/core accessibility advantages. The top and bottom facesheets in all three types of sandwich constructions are made from 16 layers of E-glass/epoxy prepregs stacked in crossly orientation. The low-velocity impact response of the composites is studied at five energy levels, ranging from 11 to 40 J, with an intention of investigating the damage initiation, damage propagation, and failure mechanisms. The influence of spacing the Z-pins in a foam core has also been studied at the same five energy levels. Detailed microscopic inspection has been conducted to determine the impact failure characteristics of the three types of sandwich composites. For the energy levels considered, the results demonstrate that by reinforcing the foam cells with Z-pins, low-velocity impact damage is contained effectively and is limited to the localized dimensions of the core and facesheet that lie within a pain cluster dimension.