DIN 52185 Testing of Wood - Determination of Compressive Strength Parallel to the Fiber Direction

The standard "DIN 52185 Testing of wood - Determination of compressive strength parallel to the grain direction," developed by the German Institute for Standardization (DIN), describes a method for determining the compressive strength of wood parallel to its grain using small, flawless samples. The compressive strength values ​​determined according to this standard cannot be readily applied to structural components because their strength depends on the dimensions and quality of the wood (growth characteristics, wood defects). A test procedure for determining Young's modulus has been omitted from this standard.

For the purposes of this standard, compressive strength refers to the maximum force developed under compressive load relative to the initial cross-section of the specimen.

To determine the compressive strength of wood in the grain direction, the following testing equipment is required:

• Length measuring device (micrometer or similar) that allows determination of sample dimensions with an accuracy of 0,1 mm.
• A compression testing machine (e.g., a compression testing machine of a tensile testing machine according to DIN 51 221 or a Class 1 compression testing machine according to DIN 51223 and DIN 51220) is a device in which a sample is compressed between two flat, centrally placed hardened steel plates. At least one of the two steel plates must be movably mounted on a spherical body and be movable in a vertical direction.
• The force measuring device must support measurement of up to 1 percent of the maximum compressive force.

For compressive strength determination, cubic specimens with a square cross-section and a side length of 20 mm should be used whenever possible. For wood with very irregular grain, especially those with extensive interlocking grain areas, larger cross-sectional dimensions (up to 50 mm side length) should be used, if possible, so that at least five growth rings or growth zones are recorded. The length (height) of the specimen in the direction of the grain should be between 1,5 mm and 3 mm. Specimen surfaces should be flat and smooth enough that dimensions can be determined to an accuracy of 0,1 mm. Production should be carried out in a climate-controlled environment, ensuring parallelism of opposing surfaces, especially end surfaces, and perpendicularity of adjacent surfaces.

Before testing, samples must be stored in a humid environment until they reach constant weight in a standard climate (20°C plus/minus 1°C and 65% plus/minus 3% relative humidity, in accordance with DIN 50014). In a climate-controlled environment, constant weight is considered to have been achieved if the sample weight does not change by more than 0,1% compared to the previous weighing at 24-hour intervals.

In the world of materials engineering and forestry, standardized testing procedures are essential to ensure the quality, reliability, and safety of wood products used in construction, furniture, and various industrial applications. One of these fundamental standards is DIN 52185. This standard provides a rigorous methodology for assessing the compressive strength of wood along its grain direction. While modern European and international standards have evolved to incorporate or replace elements of this standard, DIN 52185 remains a fundamental reference.

The DIN 52185 standard was created to address the need for a uniform method for assessing the mechanical properties of wood under compression, a critical factor for structural applications such as beams, columns, and load-bearing elements in buildings. Prior to these standards, testing methods varied widely, leading to inconsistencies in material properties and safety assessments.

Although this standard has not been officially withdrawn, it proposes a transition to new standards such as "DIN EN 408 Timber structures - Structural timber and glued-laminated timber - Determination of certain physical and mechanical properties," which build on and improve upon the original procedures. However, DIN 52185 remains in existence.

The primary purpose of this standard is to determine the compressive strength of wood parallel to the grain, a fundamental mechanical property that measures how much load a wood sample can withstand under axial compression before failing. This test is vital for:

• Structural design: Engineers use data to calculate safe load capacities for timber members in bridges, roofs, and frames.
• Quality control: Manufacturers ensure compliance with building regulations by assessing batch consistency in lumber production.
• Research and development: Scientists examine wood species differences, processing effects (e.g., drying or chemical impregnation), and environmental influences on strength.

This standard applies to solid wood samples, typically obtained from softwoods or hardwoods, and does not cover engineered products such as plywood or laminated veneer lumber unless otherwise specified. It emphasizes testing along the longitudinal grain direction, which is the wood's strongest direction due to the alignment of the cellulose fibers.

By standardizing variables such as specimen dimensions, loading rates, and fracture criteria, DIN 52185 minimizes experimental errors and ensures comparable results across laboratories and countries.

The DIN 52185 standard outlines a simple yet rigorous compression testing protocol designed for universal testing machines commonly found in materials laboratories. This procedure primarily involves the following steps:

• Sample preparation: Clean, flawless wood samples measuring 20 mm x 20 mm x 300 mm (section x length) are selected, with their lengths parallel to the grain direction. The samples are brought to a standard moisture content (typically 12 percent for construction-grade wood) in a controlled climate chamber to simulate service conditions. Initial dimensions and mass are accurately measured.
• Setup: The specimen is placed vertically between the loading plates of a testing machine, ensuring that the end surfaces are flat and perpendicular to the fiber direction. A light preload (approximately 1 percent of the maximum expected load) is applied to securely position the specimen.
• Loading and testing: Compressive force is applied at a constant rate of 1 mm per minute until failure, defined as a 10 percent decrease in load after the maximum or apparent buckling/crushing level is reached. Load-deformation data are continuously recorded to plot the stress-strain curve. The test speed ensures quasi-static conditions, avoiding dynamic effects.
• Calculation and reporting: Calculate the compressive strength by dividing the maximum load by the initial cross-sectional area. Results are reported along with the modulus of elasticity, if derived from a curve. Details about the wood species, density, and any anomalies are included.

Safety precautions such as using protective shields around the machine should be taken to prevent splinter hazards.

The DIN 52185 standard has profoundly impacted the timber industry by providing reliable data for design regulations governing timber structures in Europe. For example, the compressive strength values ​​derived from this test determine the permissible stresses in building codes, reducing over-engineering and material waste.

This standard is used in the following areas of application:

• Construction: For the purpose of verification of laminated timber beams for high-rise wooden buildings.
• Furniture production: To ensure that table legs or chair frames are resistant to daily loads.
• Research: Comparative studies on tropical and temperate climate trees for sustainable resource use.

Ultimately, DIN 52185 exemplifies the power of concise, practical standards in fostering innovation and safety. By standardizing pressure testing in line with texture, it has enabled engineers to build with confidence using wood. Whether in a mobile sawmill or a cutting-edge research laboratory, its principles continue to underpin the world's structural integrity.

Our organization, which has been serving for many years and meticulously following global developments in science and technology, employs a skilled team and extensive infrastructure to conduct testing, measurement, and analysis in a wide range of areas for businesses across all sectors. In this context, we also provide testing services in accordance with the DIN 52185 "Testing of wood - Determination of compressive strength parallel to the grain direction."