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Home >> Application >> By Standard >> ISO >> ISO 5000~9999 >> ISO 7800 Metal Wire Torsion twisting testing – Wire Simple torsion test

ISO 7800 Metal Wire Torsion twisting testing – Wire Simple torsion test

ISO 7800 Metallic materials -- Wire -- Simple torsion test

ISO 7800 specify a unidirectional simple torsion test to evaluate the plastic deformation ability of metallic wire under torsional loading in one direction. It applies to round and shaped wire with diameter or characteristic dimension from 0.1 mm up to and including 14 mm. (similar with ASTM A938 Standard Test Method for Torsion Testing of Wire).

Test Principle

A test piece of wire is twisted a specified number of turns through 360° around its own axis in one direction, and then a specified number of turns through 360° in the opposite direction. The wire is clamped at both ends by coaxial grips. One grip is rotated around the wire's longitudinal axis while the other remains fixed (no angular deflection). The wire is twisted in one direction only until it breaks, or until a specified minimum number of turns is reached.

Test Specimen Information

Size range	Round wire diameter d = 0.1–14 mm; shaped wire characteristic dimension h = 0.1–14 mm.
Free length between grips (L)	Round wire: 200d (0.1≤d<1); 100d (1≤d<5); 50d (5≤d≤10); 25d (10<d≤14, steel only); max 500 mm. Shaped wire: 100h (2≤h<5); 500 mm (5≤h<8).
Material	Metallic wire — round or shaped (Z, H, T profiles listed for shaped wire).
Condition	Must be as straight as possible. If straightening is needed, it must not damage the surface and must not pre-twist the wire. Wire with a sudden sharp curvature toward the neutral axis shall not be tested.

Test equipment required for ISO 7800

Torsion Testing Machine

Recommend UnitedTest NJS-X series Metal wire reverese torsion tester.

Axially aligned grips; one fixed, one rotatable; allows length change during contraction; speed control ±10% of nominal; with turn counter and protective shield.

Jaws / Grips

Minimum hardness 55 HRC; faces must be parallel.

Type depends on wire size: smooth jaw (d < 0.3 mm), lightly serrated (0.3–3 mm), V-grooved (3–10 mm), smooth or special (10–14 mm, steel only).

Key Test Parameter and stipulations:

Temperature: General: 10 °C … 35 °C ambient; Controlled conditions: 23 ± 5 °C.

Axial tension: Unless otherwise specified: apply a constant tensile stress ≤ 2% of the nominal tensile strength of the wire, just enough to keep it straight and aligned.

For steel wire > 10 mm dia., tension application is not necessary.

Temperature rise warning: Because this is treated as an isothermal test, temperature increase should be avoided / controlled — the standard suggests not exceeding roughly 60 °C for strain-rate-sensitive wires.

Twist speed:

Diameter d(mm)	Steel (turns/s)	Cu / Cu-alloys	Al / Al-alloys
0.1 ≤ d < 1	1 or 3	5	—
1 ≤ d < 1.5	0.5 or 1	2	1
1.5 ≤ d < 3.6	0.25 or 0.5	1.5 … 0.5	1
3.6 ≤ d ≤ 10	0.25 or 0.5	0.5	1
10 < d ≤ 14	0.1	—	—

ISO 7800 Details Test Procedure:

1, Prepare the specimen — straighten if needed (no surface damage, no pre-twist). Measure d or h.

2, Select grip type (smooth / serrated / V-groove) and install in the machine. Verify coaxial alignment.

3, Set the free length L between grips per stipulation.

4, Apply axial tension if required — ≤ 2% of nominal tensile strength (skip for steel > 10 mm unless specified).

5, Draw a coloured line along the wire surface to help verify rotation count visually.

6, Rotate one grip at the prescribed speed (±10%) — one direction only — until the wire breaks or the specified target turns is reached.

7, Record Nₜ= total complete turns at fracture (or at stop).

8, Check validity: if fracture occurs within 2d(or 2h) of either grip, the test is invalid — repeat with a new specimen.

Test Applications — Industry Fields

Sector	Why ISO 7800 Matters
Steel wire & rope (spring wire, ACSR core wire, crane rope, fishing net wire)	Wires in service are twisted/torqued during stranding, spooling, and loading — torsional ductility must be there
Prestressed concrete / PC wire & strand	Torsional checks catch drawing/patenting defects that tensile alone misses
Electrical / conductor wire (copper, aluminium alloy wire for stranded conductors)	Spiral cracking under torsion = bad news for bending-in-installation
Fastener & spring industry	Surface seam or inclusion revealed by early torsional crack = rejected batch before it goes into a safety-critical spring
Automotive & aerospace (control cables, small diameter alloy wires)	Wire that snaps under torsion can cause catastrophic remote failures

ISO 7800 Metal Wire Reverse Torsion twisting testing – Wire Simple torsion test

Related Standard

ASTM A938	Standard Test Method for Torsion Testing of Wire
GBT 239.1	China equivalent torsion test standard
AS 2505.5	Metallic materials, Method 5: Wire - Simple torsion test
UNE 7468	METALLIC MATERIALS. WIRE. SIMPLE TORSION TEST
EN 10218‑1	Steel wire and wire products – General – Part 1: Test methods (often cited alongside wrapping tests).
ISO 15630‑3	Steel for reinforcement & prestressing – test methods for prestressing steel

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

Related products and device

ISO 7800 metal wire torsion testing machine

Metal Wire Reverse 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.

Related Standard

ASTM A938 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.

ISO 9649 Metallic materials - Wire - Reverse torsion test –

ISO 9649 specifies a method for determining the ability of metallic wire of diameter dimension from 0,3 mm to 10,0 mm inclusive to undergo plastic deformation during reverse torsion. This test is used to detect surface defects, as well as to assess ductility.

A test piece of wire is twisted a specified number of turns through 360° around its own axis in one direction, and then a specified number of turns through 360° in the opposite direction.

ISO 7802: Metal Wire Wrapping test –

ISO 7802 specifies the method for determining the ability of wire of diameter or thickness 0,1 to 10 mm inclusive to undergo plastic deformation during wrapping. The test consists of winding a wire to a specified number of turns around a mandrel of the diameter specified in the relevant standard to form a closely wrapped helix. It may also include a specified sequence of windings and unwindings, or even rewindings.

FAQs about the ISO 7800 Simple Torsion Test for metallic wire

Q1: What is the ISO 7800 test?

A: ISO 7800:2012 is an international standard that specifies a simple torsion test for metallic wire. It determines the wire’s ability to undergo plastic deformation when twisted around its own axis in one direction, measuring either the number of turns to failure or verifying that a specified minimum number of turns can be achieved without fracture.

Q2: What does this test actually evaluate?

A: The test evaluates torsional ductility—the wire’s capacity to withstand shear strain without cracking or breaking. It also reveals surface and internal defects (seams, inclusions, improper heat treatment, decarburization, hydrogen embrittlement) that are not detectable by tensile tests alone.

Q3: Why is torsion testing important if we already do tensile tests?

A: Tensile tests load the wire axially, while torsion places maximum shear stress at the surface—the region where most manufacturing defects hide. A wire may pass tensile strength requirements but fail catastrophically in service due to poor torsional ductility. ISO 7800 catches these hidden flaws early.

Q4: What types and sizes of wire can be tested?

A: The standard applies to metallic wire (round or shaped) with:

Round wire: diameter 0.1 mm to 14 mm

Shaped wire (e.g., Z, H, T profiles): characteristic dimension 2 mm to 8 mm

It covers steel, copper, copper alloys, aluminum, and aluminum alloys.

Q5: Why must the grips allow free axial contraction?

A: During torsion, the wire shortens (contracts) due to plastic deformation. Restraining this movement introduces unwanted axial stress, invalidating the pure torsion condition and potentially causing premature failure.

Q6: Can I use ISO 7800 for quality control of coated wire?

A: Absolutely. The test is excellent for detecting coating adhesion problems (e.g., zinc flaking on galvanized wire) and substrate defects masked by coating. Fracture types often reveal whether failure initiated at the coating interface or within the base metal.

Q7: How does ISO 7800 differ from ISO 7802?

A:ISO 7800 = Torsion (twist around own axis) → tests shear ductility, surface integrity.

ISO 7802 = Wrapping (wind around a mandrel) → tests bend ductility, formability.

They complement each other—many critical wire applications require both.

Q8: What must be in the test report?

A: Standard reference; specimen ID; diameter/h; preparation details; grip length; speed; tension; number of turns; fracture evaluation (optional).

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