GB/T 15047-2025Test method for stiffness properties in torsion of plastics (English PDF)

3.1 Apparent modulus of rigidity

When the specimen is distorted due to exceeding its elastic limit and the creep characteristics of the material are taken into account, the measured modulus of rigidity is different from its value within the elastic limit.

3.2 Elastic limit

The maximum stress a material can withstand without undergoing permanent plastic deformation.

5.1 Torsion testing machine

The torsion testing machine shall be able to apply a controllable torque to induce a deflection of the specimen within the range of 5°~100°. The specific deflection angle depends on the stiffness characteristics, thickness, and span of the specimen. A typical schematic diagram of a torsion testing machine is shown in Figure 1. The torsion testing machine shall be able to apply and measure torque within the range of 0.0113 N · m to 1.81 N · m; this range can be achieved by using a single torsion testing machine or by combining two devices with different ranges (e.g., torsion testing machine A. 0.0113 N·m~0.113 N · m, torsion testing machine B. 0.113 N · m~1.81 N · m). It shall be equipped with replaceable standard counterweights to allow for precise torque adjustment based on specimen stiffness, ensuring effective testing within the target deflection angle range. The torsion testing machine should preferably be designed to allow for span adjustment, which is particularly important when testing materials prone to shear failure (such as laminates with a span-to-width ratio of 6). When the torsion testing machine is intended to be used in a low-temperature environment, its spindle (especially the shaft end part near the lower bearing) shall be equipped with a heating jacket or other effective antifreeze device to prevent the shaft from freezing and affecting the torque transmission accuracy and normal operation of the torsion testing machine. […]

5.2 Temperature control device

5.2.1 Insulated container

A properly sized insulated container shall be able to keep the internal temperature stable within ±1 °C during the test.

5.2.2 Thermometer

A thermometer with the necessary temperature range and an accuracy of not less than ±1 °C shall be provided, with a display resolution of 0.1 °C (digital) or a minimum division value of <=0.5 °C (analog). The thermometer's sensing bulb or inductive head shall be placed close to the sample.

5.2.3 Heat transfer medium

A liquid that remains liquid within the required temperature range and does not soften or affect the sample shall be used as the heat transfer medium. Commonly used heat transfer media include, but are not limited to, water, acetone, ethanol, butanol, methanol, n-hexane, silicone oil, and a mixture of methyl phosphate and water in a volume ratio of 87.13. Furthermore, a mixture of 50 portions of ethanol, 30 portions of ethylene glycol, and 20 portions of water is suitable for temperature conditions down to -70 °C.

An appropriate heat transfer medium should be chosen according to the physical properties of different liquids (such as the applicable temperature range). For example, water is suitable for 0 °C~100 °C, ethanol is suitable for -70 °C~78 °C, and silicone oil is suitable for -40 °C~300 °C.

5.2.4 Refrigeration

Effective cooling methods shall be provided to cool the heat transfer medium. This can be achieved through immersion cooling coils built into the instrument, or by pre-cooling the insulated container filled with the heat transfer liquid in a low-temperature environment.

To ensure efficient use of the equipment for low-temperature testing, sufficient space should be reserved to cool the heat transfer medium container required for one day. For different temperature ranges, mechanical refrigeration, dry ice, or a combination of both can be used.

5.2.5 Heater

A controllable immersion electric heater shall be used in conjunction with a stirrer in the insulated container.

5.3 Micrometer

The accuracy is no less than ±0.001 mm.

5.4 Counterweight

The precision is 1 g.

5.5 Timer

A timing device with an accuracy of 0.1 seconds.

6.1 Preparation

Specimens are prepared using compression molding, injection molding, or machining methods. If the specimen exhibits anisotropy, specimens shall be taken from different directions for testing. […]