Aramid Honeycomb Core Research Articles

Repair Effectiveness Studies on Impact Damaged Sandwich Composite Constructions

Experimental studies were carried out using sandwich composite panel specimens, consisting of both polyurethane foam core (PUF) and aramid honeycomb core (Nomex) type constructions. These specimens were subjected to impact damage at energy levels ranging between 7.56 and 15.6 J. A ply-drop-patching technique was employed to repair the impact damaged sandwich specimens. The undamaged (virgin), impact damaged, and repaired specimens were then subjected to flexural (four point bending) and edgewise compression tests and strength recoveries were measured to determine the efficacy of the repair technique employed. In flexure, strength recoveries of up to 97% in PUF core and 90% in honeycomb core sandwich specimens were realized after repair, whereas in compression, the corresponding values were up to 90% in PUF core and 88% in honeycomb core sandwich specimens. A repair effectiveness factor (Ref) has been conceived and introduced to quantify the efficiency of the repair technique. Further, the repair quality was assessed using a simple NDT method prior to subjecting the sandwich specimens for destructive tests.

Basic mechanical properties of balloon-type TEEK-L polyimide-foam and TEEK-L filled aramid-honeycomb core materials for sandwich structures

The objectives of this study are to investigate the basic mechanical properties of TEEK-L polyimide-foam of a balloon type and TEEK-L filled aramid-honeycomb core-materials for sandwich structures and to compare their mechanical properties with those of AIREX R82 and ROHACELL WF foam core-materials. Compression, tension, and plate-shear tests provided their stress–strain relationships, elastic modulus, and strength. The test results are compared and discussed. The major results obtained are: (1) Filling the aramid honeycomb cells with TEEK-L can improve the basic mechanical properties of an aramid-honeycomb core-material, in particular making them higher than the values expected from the principle of superposition for compression tests and equal to the values expected from superposition for plate-shear tests. (2) The basic mechanical properties of the TEEK-L filled aramid honeycomb are superior to those of AIREX R82 110 and equivalent to those of ROHACELL WF 110, where the three materials have equal densities. (3) The basic mechanical properties of TEEK-L are inferior to those of AIREX R82 60 and ROHACELL WF 51, when materials with equivalent densities are compared. (4) TEEK-L filled aramid honeycomb has high potential as a new core material for aerospace sandwich structures.

225 Time and Temperature Dependence on Flexural Fracture Behavior of Honeycomb Core Sandwich Panels

Honeycomb core sandwich panels with the GFRP laminates as skin layer and aramid honeycomb core were employed for this study. The three point bending tests for the sandwich panels as well as the GFRP laminates were carried out at wide ranges of both deflection rate and temperature. The flexural strength for laminates and panel strongly depend on time and temperature. The time-temperature superposition principle holds for the flexural strength of the sandwich panel as well as GFRP laminates. The time-temperature shift factors for both strengths agreed well with each other in the temperature range of which the compressive fracture of GFRP occurred.

Pin Reinforcement of Delaminated Sandwich Beams Under Axial Compression

The present study is concerned with translaminar reinforcements in a sandwich beam for preventing buckling of the delaminated face sheet under edge-wise axial compression. Sandwich beams consisting of graphite/epoxy face sheets and an aramid honeycomb core were reinforced in the thickness direction using two techniques: Z-pinning using graphite/epoxy pins and a novel “C-pinning technique” developed by the authors. To evaluate the effect of reinforcement type and reinforcement spacing on the ultimate compressive strength of delaminated beams, compression tests were performed. Critical buckling loads and post-buckling behavior of sandwich beams under axial compression were evaluated by finite element analysis to provide insight into the effectiveness of translaminar reinforcement. Pin reinforcement has been shown to significantly improve the ultimate compressive load of a delaminated sandwich beam.

Analysis of Mechanical Properties of Aramid Honeycomb Core. Investigation on the Compression Strength and the Shear Modulus.

The compression strength and the shear elastic modulus of an aramid honeycomb core have been studied theoretically and experimentally. Equations have been proposed for calculation of these characteristics based on the longitudinal and shear elastic moduli of the paper material composing the core and the detailed geometry of the honeycomb shape. The effects of single and double wall thickness of the materials are taken into account in the equation. The predicted mechanical properties showed good agreement with the test results although a difficulty was found in the determination of the shear elastic modulus of the paper material. It also became clear that the aramid papers used showed considerable anisotropy which seemed to strongly influence the shear property of the core.