Document ID: APP-C393
Public Compliance Release

ASTM C393 Test Guide: Flexural Testing for Composites

Architecture
NEWTON™ 32-BIT

Application Details

Standard:
ASTM C393
Material Type:
Composites
Specimen Type:
Test Type:
Flexural
Industry:
Aerospace
Mechanicaltest.org | Applications

The Challenge 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.

Insight

Always place the specified elastomer pads between the anvils and the panel to spread out high localized line loads.

Required Test Equipment for ASTM C393

Software

Driven by the Newton N-C393 software module to calculate core shear strength, facing stresses, and flexural stiffness of sandwich constructions under 3-point loading.

Grips/Fixtures

Includes a sandwich core 3-point flexure fixture featuring large-radius cylindrical loading and support rollers to prevent localized skin crushing.

Extensometer

Equipped with a mid-span deflectometer assembly mounted to the neutral axis to capture accurate true core deflection data.

Insight

Always place the specified elastomer pads between the anvils and the panel to spread out high localized line loads.

The Newton Advantage

Advanced Newton controller to process mid-span deflection data continuously to separate structural core shear from skin compression.

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.

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.

Additional Commentary

Distributing the contact load prevents premature localized face skin indentation, ensuring the core reaches its ultimate shear design limit.

Pro Tip

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.

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.
Let's Find the Right ASTM C393 Equipment for Your Application

The Newton™ 32-Bit
Difference

Typical testing system controllers rely on 24-bit resolution. Under high-accuracy flexural analysis, this creates a data phenomenon called **”stair-stepping”** or quantization error. When trying to track minor micro-deflection in rigid polymers, 24-bit electronic circuits suffer from resolution limits, dropping critical transition points during initial load curves.

Newton Characterization™ architecture utilizes a 32-bit analog-to-digital processor converter. This increases measurement fidelity by a factor of 256x, outputting 4.29 billion discrete signal thresholds. Electrical chatter is actively muted under a dedicated 100,000:1 Signal-to-Noise Ratio (SNR).

Simulate Signal Mode

Real-Time Continuous Sampling Simulation

Comparing standard 24-bit quantization with Newton™ 32-bit resolution

Observe the stepped resolution blocks in the legacy 24-bit curve (Red) versus the absolute **analog-smooth response curve** captured by Newton™ 32-bit architectures (Green). This fidelity is what prevents mechanical data variance during modulus evaluation.

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