Standard Test Method for Core Shear Properties of Sandwich Constructions by Beam Flexure
APP-C393Always place the specified elastomer pads between the anvils and the panel to spread out high localized line loads.
Challenge & Testing Gap
Localized skin crushing under the loading anvils induces premature failure, masking true core shear propagation limits.
The Solution
Incorporate thick rubber or elastomer padding strips between the loading anvils and the sandwich panel skin faces.
Mechanics & Specimen Behavior
Primary Mechanics
Three-point bend flexural configuration applying a centralized vertical force to a long sandwich beam to induce core shear.
Specimen Details
Long rectangular sandwich beam specimen featuring dense structural skins bonded to a lightweight core matrix.
Mechanical Ratios & Properties
Short support span-to-thickness ratio explicitly selected to maximize internal vertical shear stresses while suppressing skin bending.
Expert Engineering Commentary
Core Problem Identification
Localized puncture or dimpling of the thin facing material directly beneath the central loading anvil before core shear occurs.
Root Cause Analysis
High localized contact stress concentrations pushing into thin composite facings from rigid steel loading rollers.
Hardware Specific Solutions
Heavy-duty flexure base with broad adjustable support anvils, integrated rubber pad kits, and a central mid-span deflectometer.
Analysis & Calculation Standards
Event & Failure Detection
Yield inflection monitoring paired with abrupt load-drop tracking during catastrophic core web diagonal cracking.
Required Calculations
Core Shear Strength, Facing Stress, Mid-Span Deflection, Peak Flexural Force, and Apparent Sandwich Flexural Rigidity.
Statistical Outputs
Lot parameter reports detailing mean core shear limits, deflection variances, and standard deviations across 5 panels.
Advanced Newton controller to process mid-span deflection data continuously to separate structural core shear from skin compression.
Additional Commentary
Distributing the contact load prevents premature localized face skin indentation, ensuring the core reaches its ultimate shear design limit.
Select a short span intentionally if your goal is core shear characterization, as long spans will favor skin tensile failure.
Common Pitfalls
Using a standard long-span bend setup that forces skin tension failure while misapplying the core shear equations to the data.