ASTM C393 Core Shear Properties of Sandwich Constructions by Beam Flexure

ASTM C393 Introduction

ASTM C393 (Standard Test Method for Core Shear Properties of Sandwich Constructions by Beam Flexure) determines the flexural properties and the core shear properties of sandwich constructions. Sandwich constructions consist of light cores and strong facing material, which provides high stiffness and strength. So, these materials are widely used in aerospace panels, marine structures, and transportation components, among others. ASTM C393 measures core shear strength, core-to-facing shear strength, and flexural stiffness of sandwich beams. In addition, the test also provides load-deflection information for stiffness calculations in accordance with ASTM D7250/D7250M. Precise test results aid in the design and materials development, compliance with specifications, and quality control of bonded panels.

Get Certified ASTM C393 Testing for Reliable Sandwich Panel Performance

During service, structural sandwich panels experience bending and shear stresses. Hence, manufacturers need to confirm the core integrity as well as the bonding property prior to product application. Correct testing detects areas of poor bonding, low-density core, and stiffness issues. In addition, laboratory testing certification will enhance the reliability of the products and aid in the qualification of materials.

Testing Procedure and Requirements

ASTM C393 is a flexural test for flat sandwich beam specimens. The specimen is placed on support spans, and loading noses apply force to the specimen. When testing, the system continuously measures the load and deflection. These measurements are used to calculate core shear strength and stiffness behavior.

Scope of ASTM C393 Test Standard

• Calculates basic shear characteristics of flat sandwich structures.
• Test flexural-loaded sandwich beams.
• Covers all core bonding surfaces (continuous and discontinuous).
• Uses for foam, balsa wood, and honeycomb core materials.
• Helps in support and stiffness testing and evaluation.

Equipment and Sample Preparation

Use of ASTM C393 

• Tests the shear strength of the core in sandwich constructions.
• Evaluates key-to-key bond performance.
• Assists bonded panel quality control programs.
• Creates data that is allowed for structural design.

Why Is Core Shear Strength Important in Sandwich Structures?

Sandwich panels can withstand internal shear stresses during bending, which are controlled by core shear strength. Core materials may be weak and can bend or break under load. Thus, the ASTM C393 results are valuable for deciding on an appropriate core configuration for lightweight structures. Accurate shear data also enhances the safety and structural longevity.

How Does Core Density Influence ASTM C393 Results?

Shear strength and stiffness performance are directly related to core density. Low-density cores reduce weight and also compromise load-carrying ability. Higher density cores tend to have better stiffness and strength properties, however. Thus, the core density must be reported in ASTM C393 testing to allow correct material comparison.

Common Challenges and Troubleshooting

Multiple parameters affect the accuracy of the ASTM C393 test and must be carefully controlled. Results may be inaccurate due to poor specimen alignment, inconsistent adhesive thickness, and void formation. Moreover, when using thin facings with low-density cores, local loading effects can occur around failure points. Wider load pads with rubber padding could improve load distribution during testing. Other factors, such as environmental conditions, fabrication methods, and specimen conditioning, also influence performance. As a result, laboratories need to have controlled procedures, calibrated equipment, and accurate specimen preparation practices.

Testing Technique, Process, and Data Collection

The basic steps of testing are specimen preparation and dimension verification. Then the technicians use the support fixtures inside the testing machine to set the sandwich beam. The loading system then applies flexural force at a controlled rate, and the deflection behavior is recorded by sensors. Operators make continuous observations of load response and specimen deformations during testing. Finally, from the recorded data, technicians determine core shear strength, stiffness properties, and load-deflection characteristics.

Analysis Results and Interpretation

ASTM C393 reports results in either SI units or inch-pound units. Typical test reports include core shear and core-to-facing shear, flexural stiffness, and load-deflection curve information. The larger the shear strength value, the greater the resistance to internal failure of the core. The same applies to the stable load-deflection pattern, which is a reflection of the effective stiffness of the sandwich panel. Engineers use the measured value to compare it with the designed value and material specifications to determine the structure’s suitability.

Factors to Consider For ASTM C393 Testing

• Speed: An optimized lab workflow can help manufacturers to get test results fast while avoiding compromising testing accuracy.
• Expertise: The ASTM C393 test is performed with the help of experienced technicians who ensure the correct alignment of the specimen, controlled loading, and accurate calculation of stiffness.
• Cost: Reliable testing programs are also cost-effective to ensure that manufacturers have quality control and that they have the resources to carry out research and product development.

Link to ASTM C393

By Malhar Khole

Malhar Khole is a Material Testing Associate at MaTestLab Inc. and holds a postgraduate degree in Material Science and Technology from IIT...