Standard Test Method for Flatwise Compressive Properties of Sandwich Cores
APP-C365Always use a direct-contact deflectometer setup to measure core deflection; crosshead travel includes platen-seating errors.
Challenge & Testing Gap
Specimen edge burrs and non-parallel core surfaces introduce localized crushing artifacts, inflating initial displacement metrics.
The Solution
Utilize a spherical seat self-aligning upper compression platen paired with direct-on-sample extensometers or LVDTs.
Mechanics & Specimen Behavior
Primary Mechanics
Out-of-plane vertical compressive force applied to sandwich cores to determine core crushing strength and compressive modulus.
Specimen Details
Square or circular core block, typical dimensions measuring 50mm x 50mm, with unbonded or bonded facings.
Mechanical Ratios & Properties
Surface area to core thickness ratios optimized per standard to prevent structural column instability during cell crushing.
Expert Engineering Commentary
Core Problem Identification
Artificial softening on the initial stress-strain slope caused by the compression platens seating against uneven cell walls.
Root Cause Analysis
Minor macro-surface waves across the core sample face creating non-simultaneous contact across the platen area.
Hardware Specific Solutions
Hardened steel compression platens with an integrated sub-press spherical alignment seat and a direct-deflection displacement cage.
Analysis & Calculation Standards
Event & Failure Detection
Initial touch-point contact force auto-zeroing followed by multi-stage proportional crush-limit termination thresholds.
Required Calculations
Flatwise Compressive Strength, Core Compressive Modulus, Compressive Stress at Specified Strain, and Ultimate Crush Force.
Statistical Outputs
Production batch averages, cell-collapse plateau analysis tracking, standard deviations, and lot conformance profiles.
Synchronous 32-bit hardware layer samples the direct-contact deflectometer natively, bypassing frame compliance error completely.
Additional Commentary
Direct displacement tracking captures the true elastic deformation slope of delicate cell walls without systemic compliance noise.
Ensure honeycomb core cell axes are aligned perfectly parallel to the loading vector to capture true out-of-plane strength.
Common Pitfalls
Ignoring the initial non-linear toe region of the load curve instead of performing a proper mathematical toe-compensation correction.