ISO 3384-1 Rubber, Vulcanized or Thermoplastic - Determination of Stress Relaxation Under Pressure - Part 1: Constant Temperature
The ISO 3384-1 “Rubber, vulcanized or thermoplastic – Determination of stress relaxation under compression – Part 1: Test at constant temperature” standard, published by the International Organization for Standardization (ISO), describes two procedures for determining the reduction in the counterforce applied to a test piece made of vulcanized or thermoplastic rubber, compressed to a constant deformation and held in this manner at a predetermined test temperature.
In Method A, compression and all counterforce measurements are performed at the test temperature, while in Method B, compression and all counterforce measurements are performed at the standard laboratory temperature. Methods A and B do not yield the same results because Method B includes the shrinkage of the material from the test temperature to the standard laboratory temperature in the result.
This standard specifies two test piece shapes: cylindrical test pieces and rings. Comparison of results is only valid when performed on test pieces of similar size and shape.
The use of ring test pieces is particularly suitable for determining stress relaxation in liquid environments.
This standard only addresses tests performed in a steady environment or at high temperatures. Testing at temperatures below the standard laboratory temperature is not specified. The methods have been used for low-temperature testing, but their reliability under these conditions has not been proven.
For the purposes of this standard, compressive stress relaxation refers to the decrease in compressive force over time, expressed as a percentage of the initial force, after a constant compressive stress has been applied.
In short, ISO 3384-1 is an internationally accepted test standard that specifies methods for determining the stress relaxation of vulcanized and thermoplastic rubber materials under compression at a constant temperature. This standard is widely used in the automotive, aerospace, industrial sealing, medical, and manufacturing industries to evaluate how well elastomeric materials maintain their sealing strength during prolonged compression.
Rubber components such as O-rings, gaskets, seals, vibration isolators, and bushings are designed to remain compressed throughout their service life. Although these materials appear unchanged, the force they exert gradually decreases due to a phenomenon known as stress relaxation.
Stress relaxation differs from compressive permanent deformation. Compressive permanent deformation measures the permanent deformation remaining after the load is removed, while stress relaxation measures the loss of sealing force while the material is under compression. Since sealing performance depends on maintaining adequate contact pressure, stress relaxation is generally a more realistic indicator of long-term service performance.
The ISO 3384-1 standard provides a standardized procedure for measuring this behavior, allowing engineers to compare different rubber compounds and predict long-term sealing reliability. This standard specifies procedures for determining the reduction in the counterforce exerted by a rubber sample compressed to a constant deformation and held at a predetermined temperature.
This standard applies to:
This standard covers tests performed in a constant environment or at high temperatures. It does not cover tests performed below standard laboratory temperatures.
In principle, a rubber sample is compressed to a specific deformation between two parallel plates. The sample remains compressed throughout the test while being exposed to a controlled temperature. As time passes, the internal stress within the rubber decreases, causing the compressive force acting on the plates to decrease. The remaining force is measured periodically to determine how much stress relaxation has occurred. Materials exhibiting lower stress relaxation generally provide better sealing performance over longer service lives.
The ISO 3384-1 standard specifies two test methods:
Since cooling causes thermal shrinkage, Method B produces different results than Method A.
This standard allows two specimen geometries: cylindrical specimens and ring specimens. Ring specimens are particularly useful when evaluating stress relaxation in liquid media such as oils or fuels. The standard also states that comparisons should only be made using specimens with similar geometries and dimensions, as the specimen shape influences the measured relaxation behavior.
Although the ISO 3384-1 standard allows for flexibility depending on material properties, the common test parameters are as follows:
Many automotive manufacturers refer to the ISO 3384-1 standard when specifying their own temperatures and exposure times.
The main finding in the tests is a decrease in compressive force over time. Lower stress-relaxation values indicate better long-term force retention.
The ISO 3384-1 standard is widely used in the evaluation of the following:
This standard is particularly valuable where components need to maintain their sealing pressure for many years.
The ISO 3384-1 standard is frequently used in the following sectors:
Modern vehicles contain hundreds of rubber sealing compounds that are exposed to the following:
Even if a gasket doesn't permanently deform, excessive stress relaxation can reduce its sealing strength, leading to leaks, noise, dust ingress, or water ingress. This standard helps manufacturers select compounds that maintain adequate sealing strength for the expected service life of a vehicle.
In conclusion, the ISO 3384-1 standard is one of the most important international standards for evaluating the long-term compression performance of rubber materials. By measuring the reduction in sealing strength under constant deformation, it provides a realistic assessment of how elastomeric products will perform in service. Its widespread adoption in automotive, aerospace, industrial, and sealing applications makes it an indispensable tool for material development, product qualification, and quality assurance.
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 compliant with the ISO 3384-1 standard.
To get an appointment, to get more detailed information or to request an evaluation, you can ask us to fill in our form and reach you.
