Definition
The low-temperature tensile testing machine is a special equipment for testing the mechanical properties of materials or components such as tensile, compression, and bending in a controlled low-temperature environment. It simulates the stress state of materials under low temperature conditions and obtains their mechanical behavior data, which provides a key basis for the reliability evaluation and application of materials in cold environments. This equipment is widely used in materials science, aerospace, automobile manufacturing, wire and cable, polymer materials, and other fields, making it an indispensable tool for studying the low-temperature properties of materials.
Principle
The low-temperature tensile testing machine is mainly composed of mechanical loading system, low-temperature environment box, control system and data acquisition system. Mechanical loading systems typically employ servo motors or hydraulic drives to apply a controlled tensile force to the specimen. The low-temperature environment chamber uses compressor refrigeration or liquid nitrogen refrigeration to quickly reduce the temperature inside the chamber to the set value (the common range can reach -70°C or even lower) and maintain the temperature stability during the test. The specimen is placed in an environmental chamber and the ends are clamped by a fixture. The control system coordinates the temperature with the loading process to ensure mechanical testing at the target temperature. The data acquisition system records parameters such as temperature, load, and displacement in real time, and calculates the elastic modulus, yield strength, tensile strength, elongation at break, and other indicators of the material accordingly.
Measurement method
Measurements usually follow relevant international or national standards, such as ISO 527, ASTM D638, etc. First, a standard-sized specimen is installed in a fixture in the environmental chamber. Subsequently, the refrigeration system is started to reduce the temperature in the environmental chamber to the preset test temperature at a specified rate and maintain sufficient time to uniformize the specimen temperature. Once the temperature stabilizes, the loading system is started to apply a tensile load to the specimen at a constant rate until it breaks. The system synchronizes the load-displacement curve throughout the process. Based on this curve, the key mechanical parameters can be calculated using the following formula:
Yield strength σy = Fy / A0
Tensile strength σm = Fm / A0
where FyFor yield point load, Fmis the maximum load, A0is the initial cross-sectional area of the specimen. The elongation at break is calculated by the change of gauge distance at fault.
Influencing factors
The accuracy of test results is influenced by various factors. Uniformity and stability of temperature control are key, and temperature gradients can lead to uneven stress on the specimen. The cooling rate should be appropriate, too fast may cause internal thermal stress of the specimen. The design of the fixture should ensure that the grip is firm and does not damage the specimen, avoiding stress concentration at the clamping site. The loading rate needs to be selected according to the standard or material properties, and different rates may affect the yield and fracture behavior of the material. The quality of sample preparation, such as dimensional accuracy and surface condition, also directly affects data reliability. In addition, the calibration status of the sensor and the frequency of data acquisition have an impact on the measurement accuracy.
Applications
Cryogenic tensile testing machines play an important role in many industrial and scientific research fields. In the aerospace field, it is used to test the mechanical properties of metal alloys and composites in high-altitude and low-temperature environments. In the automotive industry, it is used to evaluate the low-temperature resistance of plastic components, rubber seals, and metal materials in cold regions. The wire and cable industry uses this equipment to test the flexibility and crack resistance of insulation materials at low temperatures. In the study of polymer materials and composites, it is a basic means to analyze the mechanical behavior of materials below the glass transition temperature. In addition, it is also applied in the fields of polar scientific research equipment and cold chain logistics packaging materials.
Equipment selection considerations
When selecting, it is necessary to comprehensively consider technical parameters and actual needs. First, the type of test material, the size of the specimen and the range of required force values should be clarified to determine the load capacity and stroke of the testing machine. The temperature range should cover the minimum temperature of the application scenario, and pay attention to the cooling speed and temperature control accuracy of the equipment. The interior of the chamber should be able to accommodate fixtures and specimens, and ensure that the airflow is designed for uniform temperature. The control system should support programming complex temperature-load coupling test flows. The data acquisition system needs to have sufficient channels and sampling rates. At the same time, the reliability of the equipment, safety (e.g., overload protection, emergency braking), and the availability of subsequent maintenance and calibration services should also be evaluated. Compliance with relevant international or national standards is a fundamental requirement for the functional integrity of the equipment.