Sandwich construction materials are versatile materials with high strength, high stiffness, and low density. They are commonly used in the aerospace, marine, and construction industries. This post discusses the construction of sandwich materials, definitions, and mechanical testing and equipment.

What are sandwich construction materials? 

Sandwich construction materials are composite structures composed of a sandwich material of at least two different materials such as foam, honeycomb, polymers, wood, and ceramic. The structure of a sandwich construction includes two face plates, optional adhesive layers, and a core. The facings are usually solid materials that are thin, dense, and high-strength whereas the core is a lower-strength, lower-density material. When these materials are joined together in the sandwich structure, the overall material is a highly efficient element. Sandwich construction materials are often used in industries such as aerospace, construction, and more.  

What are some examples of materials used in the outer facing layers and in the core of a sandwich construction?

Face materials can be selected from Aluminum, Steel, Titanium alloys, fiber-reinforced polymers, and wood. 

The core material may be a foamed polymer, synthetic rubber, honeycomb, or foam.

What are sandwich materials used for?

Sandwich construction materials can be designed from a combination of a variety of facing and core materials. They are commonly used in aerospace, marine, and construction industries. Depending on the final application, the materials selected will have different properties. For example, sandwich composite materials used in aerospace vehicles have high strength, high stiffness, are light in weight and need to have the ability to resist high velocity impacts. For packaging applications, high strength-to-weight ratio, as well as resistance to corrosion, moisture and chemical reactions, become a priority. 

What mechanical properties make sandwich construction materials preferred in certain applications? 

Overall, sandwich construction materials have a high strength-to-weight ratio, high stiffness-to-weight ratio, low density, and are resistant to corrosion. The face plates combined with the core material provide greater flexural rigidity while the core provides adequate shear strength and greater stiffness. In addition, sandwich construction materials have a uniform energy absorption capacity and provide good thermal insulation [1]. 

What are some testing standards for sandwich construction material mechanical testing?

Sandwich construction materials are versatile materials. Thus, the determination and analysis of mechanical properties play an important role in the selection of a material for its final use. Testing standards organizations have developed testing methods tailored to sandwich construction materials and the determination of their mechanical properties. Some standard methods include:

What are some of the factors that need to be taken into account when preparing sandwich panel test specimens? 

Important aspects of sandwich panel specimen preparation that contribute to data scatter are incomplete or nonuniform core bonding to facings, misalignment of core and facing elements, the existence of joints, voids or other core and facing discontinuities, out of plane curvature, facing thickness variation, and surface roughness.

What are some of the test types to measure the mechanical properties of sandwich construction materials? 

Below is a list of different test types to measure the mechanical properties of sandwich construction materials.

Tension Testing

Tension testing on sandwich construction materials provides information on the strength and quality of core-to-facing bonds and produces flatwise tensile strength data for the core material.

ASTM C297 Sandwich Constructions Flatwise Tensile Testing on an dual column universal testing machine

ASTM C297 Sandwich Constructions Flatwise Tensile Testing on an eXpert 2613

Compression Testing

Compression testing in the flatwise direction or in the edgewise direction is performed to determine the core strength and modulus. 

Flexural (Bend) Testing

Sandwich construction materials can be tested in flexion to calculate the flexural stiffness, core shear strength, shear modulus, compressive, and tensile strength. The standard bending test setup for sandwich constructions is in a 4-point bend, thus a 4-point bend fixture is required to load the test specimen.

3-point bend test on a piece of sandwich construction material according to ASTM D7249

ASTM D7249 Bend Fixture – Sandwich Construction Materials Long Beam Flexure Test Setup

Shear Strength Testing

Shear properties are fundamental to the design of sandwich panels. By running shear strength tests, researchers and developers can gather data on the force-deflection behavior of the core material used in sandwich constructions. Shear strength testing can be conducted in tension or in compression. The short beam flexure test method is another method to measure the core shear strength.

Calculations include the core shear modulus and shear strength. In addition, if shear strain is calculated, a displacement transducer can be added to the test setup to acquire strain data. 

ASTM C273 Lap Shear Testing on a universal testing machine

ASTM C273 Lap Shear Testing on an eXpert 2610

Peel Testing

Peel testing on sandwich construction materials is a special type of test called the climbing drum peel test and is run using a climbing drum peel fixture. The peel resistance of the adhesive bond between the facing plate and the core material is measured.

ASTM D1781 Climbing Drum Peel Fixture on a universal testing machine