ASTM A938 Test Method for Torsion Testing of Wire

Information on the most widely used ASTM standards within the materials testing industry

Descriptions of the most prominent lSO standards within the materials testing industry

Standards including EN, DIN, JlS, and more

Mechanical testing of polymer materials in the automotive industry is directly related to the safety of components and the reliability of the entire vehicle. UnitedTest can cover mechanical performance testing for automotive interior and exterior parts, as well as functional components, adapting to automaker standards and providing comprehensive testing solutions including tensile, impact, and fatigue tests.

Mechanical testing in the battery industry determines the tensile and puncture resistance of core components such as separators and electrodes, directly affecting battery safety and cycle life. UnitedTest can cover full-dimensional mechanical testing of battery materials, compatible with national and international standards, and provide customized testing solutions.

Mechanical testing in the consumer goods industry determines product durability and safety, such as impact resistance for toys and fatigue resistance for home appliances, making it core to compliance and quality. UnitedTest can cover mechanical tests for all categories of consumer goods, including tensile, impact, and hardness tests, compatible with national and international standards, and offers customized testing solutions.

In the field of medical and biomedical sciences, mechanical testing determines the safety and compatibility of implanted devices and biomaterials, making it a core part of regulatory approval. UnitedTest can cover a full range of tests including tensile, fatigue, and wear tests, compatible with national and international standards, and provides customized biomechanical testing solutions.

Material strength is a course that most engineering fields are required to study in university education. This interesting course is very practical and makes use of testing equipment in the materials laboratory.

Mechanical testing of industrial products and components is essential to ensure their load-bearing, fatigue resistance, and impact resistance, directly preventing production accidents and ensuring stable operation of equipment. UnitedTest can cover a full range of tests including tensile, hardness, and fatigue, complying with national and international standards, and provides customized industrial mechanical testing solutions.

Mechanical testing in the plastic pipe industry determines ring stiffness, impact resistance, and tensile performance, directly preventing pipe bursts and deformation risks. UnitedTest can cover full-dimensional mechanical testing of pipes, complies with ISO,ASTM,EN et.c, international standards, and provides customized testing solutions.

In the construction engineering and building materials industry, mechanical testing determines the compressive and tensile properties of materials such as concrete and steel, which is core to ensuring the safety and durability of buildings. UnitedTest can cover the full range of building material mechanical tests, complies with ISO, ASTM international standards, and provides customized testing solutions for compressive, tensile, and other properties.

Mechanical testing in the food and beverage industry involves the compressive and tensile performance of packaging and the safety of food texture, directly ensuring storage, transportation safety, and the eating experience. UnitedTest can cover all-dimensional mechanical testing for packaging and food texture, comply with national and international standards, and provide customized testing solutions.

Mechanical testing in the packaging industry determines the packaging's resistance to compression, impact, and tension, directly ensuring the safety of contents during storage and transportation. UnitedTest can cover comprehensive mechanical testing for packaging, complying with ISO, ASTM Standards, and provides customized testing solutions for compression, drop, tear, and more.

Mechanical testing in the transportation industry concerns the load-bearing and fatigue resistance performance of core components such as vehicles, tracks, and containers, directly ensuring transport safety and equipment durability. UnitedTest can cover mechanical testing for all types of transportation materials, complying with national and international standards, and provides customized testing solutions including tensile, fatigue, and impact tests.

Metallurgical testing examines the properties of metallic materials to determine if a particular metal is appropriate for its intended use.

Testing of polymer materials covers mechanical, thermal, and chemical properties, verifying strength, heat resistance, composition, and ensuring product quality and compliance.

UnitedTest offer world-class testing solution in testing for polymeric materials, including elastomers, thermoplastics, composites, coatings, and structural adhesives in a variety of industries.

Testing of rubber and elastomers is used to assess the various properties and performance of materials under different conditions. This is crucial for ensuring the safety, functionality, and quality of rubber and elastomer products used in industries such as automotive, construction, consumer goods, and aerospace.

Conduct adhesive testing using various testing methods to determine their performance and characteristics in applications across multiple industries such as aerospace, automotive, construction, packaging, industrial, medical, and energy, thereby supporting application development and quality assurance.

UnitedTest supply machine and testing solution for tension, compression, fracture toughness, direct shear, triaxial and ultrasonic velocity are common concrete and rock testing applications.

UnitedTest has helped a number of companies involved in the wood, paper, cardboard, and corrugated industry with their testing needs. Our materials testing systems are capable of testing raw materials, components, and finished products.

UnitedTest testing system is trusted by leading medical device manufacturers, universities, and medical research laboratories worldwide. Whether testing tissues or bioresorbable materials, stents, or sutures, UnitedTest offers a variety of single-actuator and dual-actuator systems to meet your biomedical testing needs.

Mechanical testing in the textile fabric industry determines core properties such as fabric tensile strength, tear resistance, and wear resistance, directly affecting product durability and safety. UnitedTest can cover comprehensive mechanical tests for textiles, complying with national standards / ISO standards, and provides customized testing solutions including tensile, tear, and puncture tests.

The mechanical testing of industrial components directly determines the load-bearing, fatigue resistance, and wear resistance of the parts, helping to avoid equipment failure risks. UnitedTest can cover a full range of tests including tensile, hardness, and fatigue, is compatible with ISO/ASTM/GB standards, and provides customized mechanical testing solutions for industrial components.

Mechanical testing in the glass-ceramics industry determines core properties such as flexural strength, hardness, and fracture toughness, directly helping to avoid brittleness and failure risks. UnitedTest can cover comprehensive testing for flexural strength, hardness, and fracture toughness, compatible with national and ISO/ASTM standards, and provides customized testing solutions.

Tensile test evaluates material resistance to stretching, measuring strength/elongation critical for quality control. UnitedTest offers universal tensile testers (10-600KN) compliant with ASTM/ISO standards, providing tailored solutions for metals, polymers, medical & industrial materials.

Compression test assesses material resistance to compressive loads, measuring strength/deformation critical for quality validation. UnitedTest offers compression testing machines compliant with ASTM/ISO standards, providing tailored solutions for concrete, plastics, metals and industrial components.

Flexural & Bend tests evaluate material resistance to bending forces, measuring strength, stiffness and ductility for quality assurance. UnitedTest provides flexural testing machines (3-point/4-point bend) compliant with ASTM/ISO standards, offering tailored solutions for composites, plastics, metals and construction materials.

Torsion Test evaluates material resistance to rotational forces, measuring torsional strength/ductility critical for fasteners, insulators, shafts. UnitedTest offers torsion testers compliant with ASTM A938/ISO 16047, providing tailored solutions for automotive, aerospace, fastener industries.

Fatigue Test assesses material durability under cyclic loading, critical for predicting service life of industrial components. UnitedTest offers fatigue testing systems (axial/bending/torsion) compliant with ASTM E466/ISO 12106, providing tailored solutions for automotive, aerospace and manufacturing sectors.

Peel Test measures material adhesion strength by evaluating resistance to peeling forces, critical for adhesives, films, packaging. UnitedTest offers peel testers compliant with ASTM D903/ISO 8510, covering 90°/180° peel tests, and tailored solutions for packaging, automotive, textile industries.

Impact Test evaluates material resistance to sudden shock loads, critical for assessing toughness and fracture risk. UnitedTest offers impact testers (Charpy/Izod/fall weight) compliant with ASTM E23/ISO 148, providing tailored solutions for metals, plastics, glass and industrial components.

Tear & Shear Test evaluates material resistance to tearing and shearing forces, measuring critical strength parameters for quality control. Tear tests (Elmendorf/trouser/trapezoidal) assess resistance to crack propagation in films/fabrics, while shear tests measure resistance to parallel forces in joints/bolts. UnitedTest provides universal testing machines (10KN-600KN) with specialized fixtures for both tests, compliant with ASTM D624/D3164 and ISO standards, serving automotive, packaging and construction industries.

Hardness test measures material's resistance to permanent indentation, critical for quality control. UnitedTest offers universal hardness testers (Rockwell/Brinell/Vickers) compliant with ASTM/ISO standards, plus tailored hardness testing solutions for diverse industrial needs.

Biaxial/triaxial tests evaluate material performance under multi-axis loads, critical for biomaterials, metals and composites. UnitedTest provides compliant testing machines (ASTM/ISO) for planar biaxial, static/fatigue triaxial tests, with tailored solutions for industrial & biomedical needs.

Friction and wear tests assess material resistance to friction, abrasion and wear, critical for industrial material performance validation. UnitedTest offers tribometers compliant with ASTM G99/ISO standards, covering pin-on-disk, four-ball tests, and tailored friction & wear testing solutions for diverse industries.

Pressure test evaluates material/component resistance to static/dynamic pressure, critical for sealing, strength and safety validation. UnitedTest offers pressure testing machines compliant with ASTM/ISO standards, covering burst, hold-pressure tests, and tailored solutions for industrial, automotive & medical sectors.

Fire test assesses material flammability, heat resistance and fire-retardant performance, critical for safety compliance across industries. UnitedTest offers fire testing equipment compliant with ASTM/ISO/UL standards, providing tailored fire test solutions for building materials, plastics and industrial components.

Non-destructive Test (NDT) evaluates material/component integrity without damage, critical for safety & quality across industries. UnitedTest offers ultrasonic/X-ray/magnetic particle NDT equipment compliant with ASTM/ISO standards, plus tailored NDT solutions for aerospace, automotive & manufacturing sectors.

ASTM A938 : Standard Test Method for Torsion Testing of Wire

ASTM A938 test methods covers torsion testing of wire. It provides knowledge of the ductility of a wire when under torsion loading. A torsional test machine with proper gripping solutions is necessary for the test practices of ASTM A938. It is a testing standard that describes the torsion (or twist) testing procedures of metallic wire. The results of torsion tests can be used to assess wire ductility under torsional loading.

The torsion testing machine should have chuck jaws that will remain coaxial during the test. One of the chucks should be easily displaceable in the direction of the wire axis. The wire should be twisted only along the test length, and not at the point of clamping. We recommend UnitedTest metal wire reverse torsion testing machine.

ASTM A938 Test Method for Torsion Testing of Wire

Keywords

Ductility - Fracture - Metallic Wire Specimens - Test Specimens And Test Engines - Torsion - Torsion Test

Key Concept: Unlike a tension test that pulls the wire, a torsion test twists it. This reveals flaws like seams, inclusions, or brittleness that might not be apparent in a simple tensile test. It simulates service conditions encountered in spring winding, cable manufacturing, and other forming operations.

ASTM A938 Test Scope: It is applicable to round wire of any diameter, but is most commonly used for wires ranging from about 0.020 in. (0.51 mm) to 0.500 in. (12.7 mm). The test is performed at room temperature.

Principle of the ASTM A938 Torsion Test

A length of wire (the test specimen) is gripped at both ends. One grip is rotated (twisted) at a uniform speed in one direction, while the other grip remains fixed. The test continues until the wire fractures. The number of complete 360-degree turns (twists) to failure is counted and serves as the primary measure of torsional ductility.

ASTM A938 Test Method for Torsion Testing of Wire

ASTM A938 Torsion Test Apparatus:

Torsion Testing Machine: Must have two chucks or grips aligned on a common axis.

One Fixed Chuck: Holds one end of the wire stationary.

One Rotating Chuck: Driven at a uniform, controllable speed. It must be capable of rotating continuously in one direction.

Grips/Chucks: Must clamp the wire firmly without causing slippage or initial damage (e.g., crushing, notching) at the gripping points. They should be aligned to prevent axial bending or load during the test.

Rotation Counter: A device to accurately count the number of complete revolutions of the rotating chuck.

Torsional Load Cell: Some machines measure torque during twisting, but ASTM A938 is primarily concerned with the count of twists to failure, not the torque value.

Specimen Preparation

Sampling: Follow product-specific requirements; select representative wire segments free from defects, kinks, or surface damage

Diameter Measurement: Measure wire diameter at three locations using a micrometer; calculate average for test reporting

Straightening: Gently straighten the specimen without causing plastic deformation or surface damage

Test Length Selection: Standard test lengths based on wire diameter:

For wires ≤ 0.032 in (0.81 mm): 5 in (127 mm)

For wires > 0.032 in: 10 in (254 mm)

Custom lengths may be specified by material standards

End Preparation: Optional bending of short end sections (to prevent clamping damage) while keeping the test length straight.

ASTM A938 Test Method for Torsion Testing of Wire

ASTM A938 Torsion Test Procedure:

Mounting: Insert one end of the wire securely into the fixed chuck. Slide the other end into the rotating chuck, ensuring the wire is straight and coaxial. Apply the gripping force uniformly.

Applying Pre-Tension Force (Critical Step): A small, constant axial tension is applied along the length of the wire. This is typically just enough to keep the wire straight during twisting (often 2% to 5% of the wire's tensile strength). This prevents the wire from buckling or forming helical loops during the test, which would invalidate the twist count.

Wire Diameter (in)	Recommended Tensile Force (lbf)
≤ 0.012	0.25
0.013–0.032	0.50
0.033–0.063	1.0
0.064–0.125	2.0
> 0.125	5.0

Initiate Twisting: Start the rotating chuck at a uniform speed. The standard specifies a maximum fiber strain rate. In practice, a common rotational speed is 30 revolutions per minute (RPM) for wires up to 0.1 in. (2.5 mm), and slower speeds (e.g., 10-15 RPM) for larger diameters, unless otherwise specified.

Wire Diameter (in)	Maximum Speed (rpm)
≤ 0.032	60
0.033–0.063	30
> 0.063	15

Twisting to Fracture: Continue twisting in one direction only until the specimen fractures. The wire will initially deform uniformly, then localize deformation prior to fracture.

Counting: The number of complete turns (N) required to cause fracture is recorded. A "turn" is one full 360° revolution of the rotating chuck.

Interpretation of Results & Failure Modes:

The primary reported result is the Number of Turns to Fracture (N), torsional angle, and peak loading torque.

Peak Torque: Document the maximum torque measured during the test (optional but recommended)

High N Value: Indicates good torsional ductility and uniformity of the wire material.

Low N Value: Suggests low ductility, potential embrittlement, or the presence of defects.

The standard also describes observing the fracture and the nature of the failure, which is often as informative as the twist count itself:

Clean, 45° Shear Fracture: Typical of a ductile failure in torsion.

Longitudinal Split (Fishmouth or "Cracked Barrel"): Indicates a brittle or segregated material. This is a common failure mode in torsion.

Surface Defects Revealed: Cracks, seams, or inclusions on the wire surface often open up and become visible as helical marks during twisting, pinpointing material flaws.

Typical Applications:

Spring Wire: Critical for evaluating wire that will be coiled.

Rope and Cable Wire: Assesses ductility for stranding operations.

Cold Heading and Fastener Wire: Ensures it can withstand twisting during manufacturing.

Piano Wire and Other High-Carbon Steels: Checks for uniformity and absence of brittle seams.

Quality Assurance: A simple, fast test to detect inconsistencies between batches of wire.

Torsion Testing Machine is mainly used to execute torsion test on various materials, measure torsion angles, angular stiffness and other content; record the testing data. Replace only with the appropriate clamps, it can complete the other component, bolts torsion test.

UnitedTest Metal Wire Torsion Tester is used to execute metal wire torsion test, measure the metal wire endure of plastic distortion ability in single or double direction torsion condition; check the surface or internal defect.

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

We offer customization to meet your specific needs. Our expert team will collaborate with you to develop the perfect product for you