Selection method of electronic tensile testing machine fixture
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Electronic Tensile Testing Machine Fixtures:
A fixture is an essential component of an electronic tensile testing machine, often overlooked but crucial for accurate and reliable results. Many people wonder what a fixture actually is and how it functions. In this article, we’ll explore the different types of fixtures and their roles in material testing.
Depending on the type of test being conducted, fixtures can be categorized into several types such as tensile, compressive, bending, peeling, shearing, and more. Among these, tensile fixtures are the most commonly used, accounting for about 80% of all fixtures. These tools are designed to hold samples securely during testing, ensuring that the applied force is accurately measured.
Key characteristics of testing machine fixtures include their ability to withstand the test force, which varies greatly depending on the sample. For example, some materials like spandex may only require a few Newtons of force, while others like steel can require several tons. The largest electronic universal testing machines in China can handle up to 600 kN, with samples ranging from tiny gold wires (as small as 0.006 mm in diameter) to large PVC pipes (up to 1 meter in diameter). This variation requires custom-designed fixtures tailored to specific test conditions.
Material selection for fixtures is also critical. Most metal and non-metal samples use high-quality alloy steels or carbon steels, often heat-treated to improve strength and wear resistance. Some fixtures feature special coatings, like gold sand or hardened surfaces, to enhance grip. For low-force applications, soft rubber is sometimes used to avoid damaging delicate samples like plastic films or fiber yarns.
The design of fixtures is heavily influenced by international standards such as ISO, ASTM, DIN, GB, and others. Each standard specifies exact requirements for sample preparation and testing methods, which directly impacts the fixture’s structure. Some fixtures are made from lightweight materials like aluminum to reduce weight, while others use cast metals for durability.
Fixtures come in various structural designs, including wedge-shaped, threaded, eccentric, lever, and shoulder-type clamps. Each has its own advantages and limitations. For instance, wedge clamps start with a low initial clamping force but increase as the load rises, while threaded clamps provide strong initial grip that decreases under heavy loads.
In recent years, the development of fixtures has focused on efficiency, automation, and adaptability. Traditional mechanical clamping methods have given way to pneumatic and hydraulic systems, reducing labor and increasing throughput. Fully automatic fixtures now handle everything from sample measurement to test execution, though they are typically reserved for high-volume production lines.
Environmental testing, such as high and low-temperature chambers, has also increased demand for specialized fixtures. These must not only withstand extreme temperatures but also fit within the limited space of the testing chamber. Additionally, new industries like aerospace and biotechnology require fixtures with unique properties—such as non-magnetic, corrosion-resistant, or compact designs.
As technology advances, the role of fixtures continues to evolve. Whether for traditional materials or cutting-edge composites, the right fixture ensures accurate, repeatable, and meaningful test results. Understanding the function and variety of fixtures is key to optimizing any testing process.