Information on the most widely used ASTM standards within the materials testing industry
Material Torsion Testing Machine
Torsion tests twist a material or test component to a specified degree, with a specified force, or until the material fails in torsion. The twisting force of a torsion test is applied to the test sample by anchoring one end so that it cannot move or rotate and applying a moment to the other end so that the sample is rotated about its axis. The rotating moment may also be applied to both ends of the sample but the ends must be rotated in opposite directions. The forces and mechanics found in this test are similar to those found in a piece of string that has one end held in a hand and the other end twisted by the other.
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What's torsion testing?
The torsion test applies a rotational torque to a cylindrical or tubular specimen, measuring its torsional behavior under static or dynamic loading. It assesses key mechanical indicators including shear strength, torsional modulus of elasticity, yield torque, torsional ductility, and fracture toughness. Unlike tensile or compression tests, it focuses on a material’s performance under shear stress, revealing properties such as fatigue resistance and plastic deformation capacity under rotational forces. The test process involves gradually increasing torque until the specimen twists, yields, or fractures, while recording torque-twist angle data to generate characteristic curves.
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Torsion tests twist a material or test component to a specified degree, with a specified force, or until the material fails in torsion. The twisting force of a torsion test is applied to the test sample by anchoring one end so that it cannot move or rotate and applying a moment to the other end so that the sample is rotated about its axis. The rotating moment may also be applied to both ends of the sample but the ends must be rotated in opposite directions. The forces and mechanics found in this test are similar to those found in a piece of string that has one end held in a hand and the other end twisted by the other.
Purpose of torsion testing
The purpose of a torsion test is to determine the behavior a material or test sample exhibits when twisted or under torsional forces as a result of applied moments that cause shear stress about the axis. Measurable values include: the modulus of elasticity in shear, yield shear strength, torsional fatigue life, ductility, ultimate shear strength, and modulus of rupture in shear. These values are similar but not the same as those measured by a tensile test and are important in manufacturing as they may be used to simulate the service conditions, check the product’s quality and design, and ensure that it was manufactured correctly.
Tosion test provides valuable insights into several important aspects:
| Determining torsional strength | Understanding the maximum torsional stress a material can withstand before failure helps in selecting materials for specific applications where torsional forces are common. |
| Measuring shear modulus | By assessing a material's stiffness and its deformation under shear stress, engineers can predict how the material will perform under real-world conditions. |
| Evaluating torsional rigidity | The relationship between applied torque and the resulting angular deformation provides deeper insight into a material's resistance to twisting, which is crucial for designing components such as axles and shafts. |
| Assessing brittleness and ductility | Torsion testing can reveal a material's tendency to fail in a brittle manner or its ability to deform plastically without breaking. |
| Studying fatigue performance | In dynamic torsion tests, the behavior of materials under repeated or fluctuating torsional loads can be analyzed, which is vital for components subjected to cyclic loading. |
| Compliance with standards | Torsion testing helps ensure that materials meet specific industry standards, supporting quality control and safety. |
| Material comparison and selection | By comparing the torsional properties of different materials, engineers and designers can make informed decisions and choose the most suitable materials for various applications, such as automotive, aerospace, construction, and manufacturing. |
What does a torsion test measure?
A torsion test measures several key properties and characteristics related to the behavior of materials under twisting forces:
| Torsional Strength | The maximum twisting force a material can withstand before failure. This is crucial for determining whether a material is suitable for applications with high torsional stress. |
| Shear Modulus (G) | Also known as the modulus of rigidity, this property quantifies how a material deforms under shear stress. It indicates the stiffness of the material and is expressed as the ratio of shear stress to shear strain. |
| Torsional Stiffness | Measures a material's resistance to twisting, defined as the torque required to produce a unit angle of twist. It helps understand the stiffness of a material when subjected to torsional loads. |
| Yield Strength under Torsion | The level of torsional stress at which a material begins to deform plastically. Beyond this point, the material will not return to its original shape once the stress is removed. |
| Brittleness | Analyzing how a material fractures under torsional stress provides insight into its brittleness. Brittle materials may fail suddenly under torsion, while more ductile materials may deform more before breaking. |
| Ductility and Toughness | Torsion tests give insight into a material's ability to deform without losing strength. This is critical for materials that need to absorb energy without failing. |
| Fatigue Properties | In dynamic torsion tests, the behavior of materials under repeated or fluctuating twisting loads is analyzed. This is especially important for components subject to cyclic loads, such as engine shafts and suspension systems. |
| Torque-Angle Curve | The relationship between applied torque and the resulting angle of twist is often plotted as a curve, providing a comprehensive understanding of material behavior across the entire applied torque range. |
| Strain Hardening and Elastic Limit | This test can reveal how a material hardens with deformation and its elastic limit, guiding the design of components that must withstand specific torsional stresses. |
Types of materials and standards
Many materials experience torques or torsional forces in their applications and so will benefit from or require torsion testing. Materials used in structural, biomedical and automotive applications are among the more common materials to experience torsion in their applications. These materials may be composed of metals, plastics, woods, polymers, composites, or ceramics among others and commonly take the forms of fasteners, rods, beams, tubes and wires.
International Standards:
ISO 7800: Specifies static torsion testing methods for metallic materials.
ISO 9649: Metallic Wire Reverse torsion test
ISO 1397: Covers torsion testing of tubes for pressure purposes.
ISO 7206: Implants for surgery — Partial and total hip-joint prostheses — Part 10: Determination of resistance to static load of modular femoral heads — Amendment 1
ISO 6475: Implants for surgery; metal bone screws with asymmetrical thread and spherical under-surface; mechanical requirements and test methods.
ISO 1043: Plastics — Symbols and abbreviated terms — Part 1: Basic polymers and their special characteristics
ASTM A938: Standard Test Method for Torsion Testing of Wire
ASTM F543: Medical Bone Screw Testing
ASTM E143: Standard test method for torsion testing of metallic materials.
ASTM E2207: Standard Practice for Strain-Controlled Axial-Torsional Fatigue Testing with Thin-Walled Tubular Specimens.
ASTM F383: Static Bend and Torsion Testing of Intramedullary RodsISO 80369-7 Small-bore connectors for liquids and gases in healthcare applications Part 7: Connectors for intravascular or hypodermic applications
UNE-EN 1707 CONICAL FITTINGS WITH A 6% (LUER) TAPER FOR SYRINGES, NEEDLES AND CERTAIN OTHER MEDICAL EQUIPMENT. LOCK FITTINGS.
Material-Specific Standards: Separate standards exist for non-metals (e.g., plastics, composites) and components (e.g., fasteners, shafts) to adapt to their unique properties.
| Feature | ASTM A938 | ISO 7800 (Metallic Wire – Torsion Test) |
|---|---|---|
| Units | U.S. customary primary, SI approximate | SI units (mm, N) primary |
| Test Length | 5 in or 10 in based on diameter | 100 mm or 200 mm based on diameter |
| Tensile Force | Specific lbf values by diameter | Calculated based on wire cross-sectional area |
| Speed Limits | Maximum rpm specified | Rotation speed based on angular velocity (degrees/second) |
| Clamping | Bending ends permitted | No specific mention of end bending |
| Reporting | Emphasizes total turns to fracture | Includes additional torsion stress calculations |
Types of torsion tests:
The three common forms that torsion testing take include failure, proof and operational. A torsion test for failure requires that the test sample be twisted until it breaks and is designed to measure the strength of the sample. A proof test is designed to observe the material under a specified torque load over a set period of time.
Mainly torsion test type include: static torsion test, dynamic torsion test; by specimen can divided to Wire/Rod Torsion Test, Tube/Pipe Torsion Test, Solid Bar Torsion Test. Also Micro-Torsion Test, Combined Loading Torsion Test.
| Test Type | Core Feature | Typical Standard |
|---|---|---|
| Static Torsion (to fracture) | Slow, constant torque to rupture | ASTM A938, ASTM E143 |
| Reverse Torsion | Cyclic clockwise/counterclockwise twist | ISO 7800 |
| Torsional Fatigue | Repeated cyclic torque | ASTM E466 |
| High-Speed Torsion | Rapid torque application (high strain rate) | Custom protocols |
| Micro-Torsion | Tiny specimens for micro/nanomaterials | ASTM E2207 (for micro-mechanical testing) |
Finally, operational testing is measures the material’s performance under the expected service conditions of its application. All of these forms of tests may be performed with either torsion only loading or a combination of torsion and axial (tension or compression) loading depending upon the characteristics to be measured.
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