The standard demands that you calculate tensile strength by dividing the maximum force by the of the narrow portion. You need a thickness gauge accurate to 0.01mm.
You can find the JIS K 6251 standard in PDF format through various sources:
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Insight: While JIS and ISO are nearly identical today, ASTM D412 die profiles (specifically Die C) are slightly different. This can result in slight variations in reported tensile strength due to stress concentration differences in the narrow section of the specimen.
Proving your lab follows the latest version (e.g., the 2017 revision).
If you're interested in equivalent standards, you may refer to:
Setting up your Universal Testing Machine (UTM) correctly.
The official publisher of JIS standards. The JSA Web Desk allows you to purchase and instantly download the most recent, authenticated PDF version in either Japanese or English.
This is the International Organization for Standardization equivalent. JIS K 6251 is technically aligned with ISO 37, meaning their test piece shapes and testing speeds are highly compatible, though minor localized variations exist.
Tensile testing is fundamental to the rubber industry. It ensures that rubber components—such as automotive seals, gaskets, O-rings, and conveyor belts—can withstand mechanical forces during their operational lifespan. Core Materials and Parameters Measured
The percentage of increase in length at the moment of rupture. Tensile Stress (Modulus):
JIS K 6251 outlines the destructive testing procedures used to evaluate how a vulcanized or thermoplastic rubber material behaves under tension. When a rubber component is used in real-world applications—such as an engine belt stretching or an O-ring under pressure—it must withstand specific forces without tearing or permanently deforming.
JIS K 6251 is related to other international standards, such as:
JIS K 6251 is developed and maintained by the under the framework of Japan's Industrial Standardization Law. The standard is published by the Japanese Standards Association (JSA) and is administered through the Japan Rubber Manufacturers Association (JRMA). Because this is a Japanese industrial standard, many official publications are available in both Japanese (和文) and English translation (英訳) formats.
Often called "modulus" (e.g., 100% or 200% stress), measuring the force required to reach a specific stretch level. Test Specimen & Equipment
