DIN 53423 Testing of Rigid Cellular Materials - Bending Test

The standard “DIN 53423 Testing of rigid cellular materials - Bending test,” published by the German Institute for Standardization (DIN), describes how to perform bending tests on rigid cellular materials such as rigid foams. This standard is widely referenced in material data sheets, particularly for polyurethane (PU) foams, polymethacrylamide (PMI) foams, melamine foams, and similar rigid foam products used in insulation, construction, aerospace, modeling boards, and composite core materials.

Older rigid foam tests were generally based on this DIN standard series, for example, DIN 53421 for compression and DIN 53423 for bending/flexure. Nowadays, most international tests have shifted towards compatible international standards such as:

• EN ISO 1209 Rigid cellular plastics - Determination of bending properties
• ISO 178 Plastics - Determination of flexural properties (this standard has been adapted for foams in some contexts)
• ASTM D790 Standard test methods for flexural properties of unreinforced and reinforced plastics and electrical insulation materials.

Many material manufacturers still list DIN 53423 standard values ​​in older technical data sheets for historical comparison or because older certificates/products refer to them.

According to the DIN 53423 standard, bending tests determine the behavior of rigid foam specimens under three-point or four-point bending loads, up to fracture or a defined deformation. The basic characteristics typically reported are:

• Bending strength: Usually expressed in N/mm2 or MPa (stress at fracture or at a specific deflection)
• Flexural modulus: Stiffness in bending, in N/mm².

A typical test setup is as follows:

• Rectangular rod-shaped specimens (dimensions typically 20 x 20 x 120 mm or similar)
• Three-point bending with specific support span and loading rate.
• Measurement up to fracture or a specified strain.

Rigid foams exhibit a wide variation depending on their density and type:

• Low-density polyurethane mounting/expanding foams: Bending strength approximately 0,7-7 N/cm2.
• High-density rigid PU foams: Bending strength approximately 20-34 N/mm2.
• PMI structural foams: Significantly higher values, typically compared to DIN 53423, ISO 1209 and ASTM D790 standards.
• Foam sheets: Typical display/modeling grades have a flexural strength of approximately 2-4 N/mm2.

These values ​​are frequently found in technical data sheets for insulation foams, sandwich panel cores, door frame foams, and composite materials.

Until recently, the DIN 5342x standard series formed the backbone of many European foam characterization methods. Even after its withdrawal, it remains a recognizable point of reference when comparing historical material performance or reading old certificates or patents.

Today, if testing of rigid cellular plastics is required, the following standards are used:

• ISO 1209 or EN ISO 1209 standards for the direct bending properties of rigid foams.
• Sample preparation, testing speed, and calculation methods are very similar.

In short, the DIN 53423 standard provides a method for determining the bending behavior of rigid cellular materials such as rigid foams. However, since the DIN 53423 standard is now obsolete, international standards such as ISO 1209-1 and ISO 1209-2 are proposed as modern alternatives.

The primary purpose of the DIN 53423 standard is to evaluate the resistance of rigid cellular materials to bending loads. By applying a controlled force to a specimen, the test determines how much load the material can withstand before deforming or fracturing.

This information helps manufacturers and researchers in the following areas:

• Evaluating the structural integrity of rigid foams.
• Comparing different foam formulations or densities
• Evaluating quality consistency in production.
• To determine suitability for load-bearing or insulation applications.

Typical materials tested include:

• Rigid polyurethane (PUR/PIR) foams
• Polystyrene foams (EPS, XPS)
• Phenolic foams
• Other rigid cellular plastics used in insulation or sandwich structures.

The DIN 53423 standard uses a three-point bending configuration. The basic principle is as follows:

• A rectangular test specimen is supported at two points (supports).
• A charge is applied to the center of the sample.
• The force causes the sample to bend.

The applied load and resulting deformation are recorded until a defined deflection or fracture occurs. This method provides a measure of the bending behavior of a material under bending stress, which is critical for rigid cellular materials that are frequently subjected to bending loads in real-world applications.

The test usually requires the following:

• Controlled Loading Universal Testing Machine (UTM)
• Three-point bending fixture with two supports and a central loading nose.
• Deviation measurement system for recording displacement.
• Data collection system for capturing load-deflection curves.

The load is applied gradually at a constant rate while monitoring the sample's response.

The samples used in the test typically have the following characteristics:

• Rectangular shape
• Defined length, width, and thickness
• Smooth cellular structure undamaged during cutting.

Proper conditioning of samples (temperature and humidity) before testing is usually necessary to ensure reproducible results.

A simplified testing procedure includes the following:

• Sample preparation: Samples are cut to the specified dimensions. They are conditioned under controlled laboratory conditions.
• Sample assembly: The sample is placed between the two supports of the bending fixture.
• Loading: Force is applied to the center of the sample with a constant crosshead velocity.
• Measurement: Load and deflection are recorded during the test.
• Fracture or target deviation: Testing continues until the sample fractures or reaches a defined deformation.

The bending test allows for the determination of the following parameters:

• Bending load at the moment of fracture
• Load at the specified deviation
• Load-deflection curve
• Relative bending stiffness

These values ​​help to characterize the mechanical behavior of rigid cellular plastics, especially in applications where bending stresses occur.

The DIN 53423 standard is no longer valid and has been largely replaced by the following international standards:

• ISO 1209-1 Basic bending test for rigid cellular plastics.
• ISO 1209-2 Determination of flexural strength and modulus of elasticity.

These standards provide more comprehensive methods, including the calculation of bending strength and modulus of elasticity using a three-point bending system.

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 53423 standard.