Lab 01: Honeycomb Compression Test

Lab Overview

Course: AE 417 – Aerospace Structures and Instrumentation Laboratory (David Sypeck / Reshma Kubsad) | September 19, 2025
Objective: Measure the out-of-plane compressive behavior of an aluminum honeycomb structure per ASTM D 7336/D 7336M-07 and compare results to manufacturer-reported values for the 5056 Alloy Hexagonal Aluminum Honeycomb.
Specimen: Aluminum honeycomb block; mean dimensions: L = 79.81 mm, W = 81.14 mm, H = 76.10 mm, cell size = 6.11 mm, foil thickness = 0.071 mm, mass = 36.39 g
Instrumentation: Tinius Olsen 150ST Electromechanical Universal Testing Machine, digital calipers, mass scale, Motic stereo zoom microscope with digital camera
Standard: ASTM D 7336/D 7336M-07 — Crushing Resistance of Sandwich Cores

Honeycomb specimen — side view (Fig. 1)

Honeycomb specimen — top view (Fig. 2)

Tinius Olsen 150ST testing machine (Fig. 8)

Procedure & Methodology

Four teams each measured five specimens, recording foil thickness, length, width, height, cell size, and mass. A total mean was calculated across all teams; the specimen closest to that mean and showing the least visible damage was selected for compression testing. An additional in-plane crushed specimen was used to measure foil thickness via caliper with full cell wall access.

The selected specimen was placed in the Tinius Olsen 150ST with compression plates attached and the machine set to the "ERAU Honeycomb Compression" method. A pre-load of approximately −45 N was applied and the position zeroed before the automated test ran to completion. Post-compression, the crushed cell walls were imaged under a Motic stereo zoom microscope at multiple magnifications to document the buckling morphology.

Foil thickness measurement (Fig. 12)

Specimen in machine pre-compression (Fig. 13)

Specimen post-compression (Fig. 16)

Results & Analysis

The force-displacement curve showed the expected three-stage response: initial linear elastic region, progressive crushing plateau, and final densification.
F_peak = 29,300 N at 0.535 mm displacement (initial peak before cell wall buckling onset).
F_crush = 12,000 N — average crush force over the plateau region.
σ_peak = 4.5 MPa — confirmed against manufacturer value of 4.3 pcf / σ_peak ≈ 620 psi.
σ_crush = 1.87 MPa (270 psi) vs. manufacturer target of 300 psi for the 5056 alloy at 4.3 pcf density.
Energy absorbed ≈ 798.9 MPa·cm³ (area under stress-strain curve × specimen volume of 492.8 cm³).
Specimen density: 4.6 pcf — consistent with 5056 alloy designation ¼-5056-0.002.
Microscopy confirmed progressive cell-wall local buckling and folding, consistent with the known energy absorption mechanism of metallic honeycombs.

Force vs Position curve (Fig. 18)

Stress vs Strain curve (Fig. 19)

Manufacturer spec comparison (Fig. 22)

Microscopy & Failure Observation

Microscopy images (Figs. 20a–20c) showed bent and buckled cell walls with periodic fold lines characteristic of progressive axial crushing.
Top-view images revealed collapsed hexagonal geometry with cell walls folded against adjacent cells, demonstrating the progressive buffering mechanism.
Even as individual cell sections failed, the buckled material strengthened adjacent sections — explaining the near-constant plateau force and high specific energy absorption.
The test specimen was identified as most likely a 5056 Alloy Hexagonal Aluminum Honeycomb, designation ¼-5056-0.002, based on σ_crush, σ_peak, density, and cell size matching the Hexcel Hexweb datasheet.

Buckled cell walls — close-up (Fig. 20a)

Collapsed hexagonal geometry (Fig. 20b)

Adjacent cell wall bending (Fig. 20c)