DIN 53293 Testing of Sandwich Structures - Bending Test

The standard “DIN 53293 Testing of sandwich structures - Bending test”, published by the German Institute for Standardization (DIN), describes a method for determining the bending properties of sandwich composites (sandwich panels). Sandwich structures are lightweight composite materials consisting of the following components:

Two thin, rigid outer layers (surface layers or coating layers) are typically made of materials such as glass fiber reinforced plastic, carbon fiber reinforced plastic, aluminum, or steel.
There is a thicker, lighter core in between, for example:
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Honeycomb structures (aluminum, paper, aramid or plastic)
Foam (e.g., polyurethane, PVC, or aluminum foam)

These materials are widely used in industries where a high hardness-to-weight ratio is critical, including:

Aviation and space
Automotive and railway vehicles
Maritime applications
Building and construction (e.g., facade panels, refrigerated trucks)
Wind energy (rotor blades)
Sports equipment

According to the DIN 53293 standard, bending tests evaluate the fundamental mechanical properties of sandwich panels under bending load. This test provides data on the following:

Bending rigidity (bending stiffness)
Maximum bending moment or load-carrying capacity before failure
Deviant behavior
Failure modes (e.g., surface layer wrinkling, core slip failure, surface layer compression/tension failure, layer separation, or indentation under loading points)

This test is particularly useful for quality control, material comparison, design verification, and research on lightweight structures.

The DIN 53293 standard defines a four-point bending test. This configuration is preferred over three-point bending for sandwich materials because:

It creates a constant bending moment between the internal loading points.
It minimizes shear stresses in the central region.
Compared to three-point installations, it reduces local effects (indentation) under the loading points.

The typical setup is as follows:

Rectangular test specimen (dimensions are defined in the standard, usually depending on core thickness and expected deflection).
It is supported by two external points.
It is loaded symmetrically at two internal points.
The test is typically performed under semi-static conditions until fracture or a defined deformation limit is reached.

The results typically include the following:

Load-deformation curve
Apparent bending stiffness (equivalent bending stiffness)
Critical load values
Type of fracture observed

The following standards are related to the DIN 53293 standard:

The described method is similar to, but not exactly the same as, the “ASTM C393 Standard test method for core shear properties of sandwich structures by beam bending” standard.
Relevant bending tests for general plastics or fiber-reinforced plastics include the DIN EN ISO 178 (three-point bending) or ISO 14125 standards.
In some contexts (e.g., fiber-reinforced panels), DIN 53293 is used in conjunction with, or in comparison to, DIN EN ISO 14125 or EN ISO 178 standards.

Even years after its publication, the DIN 53293 standard is still used as a reference in technical literature, testing laboratories, and product certifications, particularly in Europe, for sandwich panels used in transportation and construction.

In short, the DIN 53293 standard includes a method used to determine the bending behavior of sandwich structures, especially sandwich panels. This method is applied to evaluate the stiffness, strength, and fracture behavior of sandwich composites under load.

Sandwich structures typically consist of three layers:

Top surface: This is the thin and durable load-bearing layer.
Bottom surface: Provides bending resistance together with the top surface.
Core: Lightweight, thick, and usually has a honeycomb or foam structure.

This design allows for high bending rigidity with low weight.

The purpose of this test method is to determine the following:

Flexural strength
Flexural modulus
Maximum load carrying capacity
Fracture type (surface fracture, core crushing, cleavage, etc.)

The test is usually performed using a universal testing machine. The testing process essentially follows these steps:

Sample preparation: Rectangular samples of specific dimensions are prepared. Sample thickness and core type are reported.
Loading method: A three-point or four-point bending test can be applied. It is applied in a load-controlled or displacement-controlled manner.
Measurements: The following measurements are taken:
The force applied
Midpoint displacement
Maximum load at the moment of fracture

The following parameters are also determined:

Bending strength: The maximum stress a material can withstand before fracture.
Bending rigidity: The panel's resistance to bending. Core thickness significantly affects this value.
Damage mode analysis:
Tensile fracture of the surface layer
Sprain on the pressure side
Core shear fracture
Surface-core separation (delamination)

DIN 53293 is used particularly in the following sectors:

Aviation and space
Automotive
Marine
Construction (composite facade panels)
Wind turbine blades

Because sandwich structures are lightweight yet high-strength systems, the bending test defined in this standard is considered important. This test is crucial because...

It provides design validation.
It controls the quality of production.
It allows for material comparison.
It provides security-critical data.

For many years, our organization, with its competent and experienced staff, has been understanding the needs of its clients, providing the advanced testing services they require, and assisting them in the establishment, implementation, and improvement of management systems. Within this framework, we also provide testing services in accordance with the DIN 53293 standard.