How to Evaluate Wire Performance at Low Temperatures?

The core objective of evaluating wire performance in low-temperature environments is to verify whether its mechanical properties, electrical properties, and structural integrity meet the requirements of severe cold-weather operating conditions. This is primarily achieved through a series of standardized low-temperature tests.

I. Key Evaluation Items and Methods

1. Low-Temperature Tensile Testing

Evaluates the wire's tensile strength, elongation at break, and yield strength at low temperatures to determine whether the material becomes brittle due to the cold.

Testing Standards: Reference standards such as GB/T 31527-2015 for comparative testing between room temperature and low temperatures.

Testing Conditions: Typically conducted in representative low-temperature environments, such as liquid nitrogen temperatures (77K, approx. -196°C) or -40°C. The loading rate is controlled at 0.5 mm/min, and force-displacement data is recorded in real-time.

2. Low-Temperature Bending Testing (Cold Bend/Cold Wrap Test)

Assesses the flexibility and crack resistance of the wire's insulation layer and sheath at low temperatures; this is the most common method for evaluating cold resistance.

Testing Procedure: After conditioning the wire specimen at -30°C (or lower) for one hour, it is rapidly wound around a cylindrical rod of a specified diameter. The surface is then inspected for any signs of crazing or cracks.

Applicable Standards: UL-158, CNS-689, JIS-C3005, etc.

Typical Equipment: Wire Low-Temperature Cold Bend Tester (e.g., Model HD-212), capable of testing multiple samples simultaneously.

3. Low-Temperature Impact Testing

Evaluates the wire's ability to withstand sudden mechanical impacts at low temperatures, observing whether cracking or damage occurs after the impact.

This test is frequently used to verify the low-temperature toughness of sheath materials, and is particularly relevant for cables intended for installation in cold regions.

4. Thermal Cycling Testing

Simulates the wire's adaptability to environments characterized by drastic temperature fluctuations, verifying whether the material suffers from delamination, cracking, or loose connections caused by thermal expansion and contraction.

The typical temperature cycling range is from -40°C to 85°C; the wire's physical appearance and electrical properties are inspected after undergoing multiple cycles. 5. Electrical Performance Testing

This includes measurements such as insulation resistance, dielectric strength, and conductor resistance at low temperatures, ensuring that the wires can safely transmit electrical energy even under cold conditions.

Particular attention is paid to whether superconducting materials exhibit the "zero-resistance effect" at extremely low temperatures (e.g., the disappearance of resistance in mercury at -268.98°C).

II. Typical Application Scenarios and Testing Focus Areas