🔩 Metallic wire with a diameter or thickness of 0.3–10 mm — reverse bend test: bending through 90° alternately in both directions over cylinders with a radius chosen for the diameter, number of bends Nb until a crack visible to the naked eye; PN-ISO 7801

Materials and NDT PN-ISO 7801

Overview

WHAT THE STANDARD COVERS. ISO 7801:1984 (clauses 1–2) specifies a method for determining the ability of metallic wire with a diameter or thickness from 0.3 to 10 mm inclusive to undergo plastic deformation during reverse bending; the range of diameters to which the standard applies may be specified more precisely by the product standard. The test consists of repeatedly bending through 90° in opposite directions a test piece held at one end, each bend being made over a cylindrical support of specified radius. The standard replaced ISO 144-1973 and ISO 2625-1973. The "Scope" field of the PKN card of PN-ISO 7801:1996 (Polish version): "The scope of application of the standard, the requirements for bend testing machines, the method of sampling and preparing test pieces, the conditions and method of carrying out the test and the requirements for the test report are specified" (our translation).

APPARATUS (clauses 3–4, Table 2). The machine shall conform to the principle of Figure 1: two cylindrical supports with gripping faces, a bending arm with a guide and a hole for the wire. The supports and jaws shall have sufficient hardness for rigidity and wear resistance; the axes of the supports are perpendicular to the plane of bending, parallel and in one plane to within 0.1 mm; the gripping faces project beyond the supports by not more than 0.1 mm, and their upper edge lies below the centres of curvature of the supports by y = 1.5 mm for a support radius up to 2.5 mm and by 3 mm for a larger one; the axis of rotation of the arm lies 1.0 mm above the top of the supports. Table 2 assigns to the wire diameter (thickness) the support radius r, the distance h and the diameter of the guide hole: 0.3–0.5 mm — r = 1.25 ± 0.05 mm, h = 15 mm, hole 2.0 mm; over 0.5 to 0.7 — 1.75 ± 0.05, 15, 2.0; over 0.7 to 1.0 — 2.5 ± 0.1, 15, 2.0; over 1.0 to 1.5 — 3.75 ± 0.1, 20, 2.0; over 1.5 to 2.0 — 5 ± 0.1, 20, 2.0 and 2.5; over 2.0 to 3.0 — 7.5 ± 0.1, 25, 2.5 and 3.5; over 3.0 to 4.0 — 10 ± 0.1, 35, 3.5 and 4.5; over 4.0 to 6.0 — 15 ± 0.1, 50, 4.5 and 7.0; over 6.0 to 8.0 — 20 ± 0.1, 75, 7.0 and 9.0; over 8.0 to 10.0 — 25 ± 0.1, 100, 9.0 and 11.0 (the smaller hole for the smaller diameter; the hole shall ensure free movement of the wire).

TEST PIECE AND PROCEDURE (clauses 5–7). The length of wire shall be as straight as possible (slight curvature in the plane of bending is permissible); it is straightened by hand, and if that is not possible — with a hammer of wood, plastic or copper on a flat surface of such a material, without damaging the surface and without twisting; wire with a local sharp bend is not straightened. The test is normally carried out at an ambient temperature of 10–35 °C, and under controlled conditions at 23 ± 5 °C. The test piece is inserted with the arm vertical through the guide hole and the lower end is clamped so that it is perpendicular to the axis of the supports (non-circular test pieces — with the larger dimension parallel to the jaws). One bend is bending the free end through 90° and returning it to the original position, the next — in the opposite direction, without interruption; bending is uniform, without jerks, not faster than one bend per second, and slower if necessary so that heat does not affect the result. To ensure constant contact with the supports, a tensile stress of not more than 2 % of the nominal tensile strength may be applied, unless otherwise specified in the product standard. The test is ended after the required number of bends or when a crack visible without magnifying aids appears, and if the product standard so provides — only after complete fracture. The bend during which failure occurred is not counted in the number of bends Nb. Report: reference to the standard, identification of the test piece, diameter or smallest thickness, preparation (e.g. straightening), conditions (support radius, stress), criterion for ending the test, result.

EDITIONS. PN-ISO 7801:1996 adopts the first edition ISO 7801:1984. According to the foreword of ISO 7801:2024 (second edition, ISO/TC 164/SC 2), the technical changes include: symbols for shaped wires, cross-sections of round, shaped and clad wire in Figure 1, table supplemented with diameter limits and the distance y with tolerance, updated tensile force principle, changed definition of the criterion for ending the test, new annexes: A (normative — parameters for shaped steel wires) and B (informative — examples of force-applying devices). The scope of the 2024 edition remained: wires with a diameter or characteristic dimension of 0.3–10 mm. In the iTeh catalogue (read on 27.10.2026) ISO 7801:1984 has the status "Withdrawn", and ISO 7801:2024 — "Published".

STATUS (PKN card as of 27.10.2026). The card of PN-ISO 7801:1996 (Polish version) has no withdrawal label: publication 05-02-1996, 8 pages, Logistics, Transport and Packaging Sector, KT 163 Ropes and Rope Transport, "Adopts: ISO 7801:1984 [IDT]", "Replaces: PN-M-80002:1983 - Polish version", ICS 77.140.65. PKN search, search term "ISO 7801" (27.10.2026): with this number there is only PN-ISO 7801:1996 — the results contain no Polish standard adopting ISO 7801:2024. The Polish standard is therefore current, although it adopts an edition which ISO has withdrawn.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database refreshed from the production server on 27.10.2026 and current PCA documents downloaded on that day). Number 7801 appears in 7 records at 7 Polish laboratories: AB 005, AB 023, AB 024, AB 273, AB 771, AB 1141, AB 1348. In all 7 current PCA documents the standard is in the same entries; none is suspended. Forms: "PN-ISO 7801:1996" (6 laboratories; AB 024 in one cell with "PN-EN ISO 15630-3:2019 p. 7") and "PN-ISO 7801" without the year (AB 023). The "Laboratories" tab ("PN-ISO 7801") shows 10 laboratories: these 7 Polish ones and 3 Czech ones (tab query on labcoda.pl, 27.10.2026).

WHAT THE LABORATORIES TEST (database copy and PCA documents). Wires (AB 005: diameters 0.7–4.0 mm; AB 1348: 0.5–8.0 mm; AB 771: up to 5.0 mm), steel wire (AB 023: 1.0–7.0 mm), wire with a diameter of 0.3–5.0 mm (AB 1141: number of bends), wires as one of the metal products (AB 024: below 6.0 mm, together with the test according to PN-EN ISO 15630-3 point 7), metal wire for brushes and materials for their production (AB 273: 0.3–1.5 mm and over 2.0 to 10.0 mm).

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. First — counting: the bend at which the wire cracked is not counted in Nb; "a crack at the tenth" gives a result of 9. Second — criterion for ending: the product standard decides whether the test is ended by the number of required bends, a crack visible to the naked eye or complete fracture — the report must state it. Third — support radius: it is chosen for the wire diameter according to Table 2; a different radius (e.g. from an older national standard or from the product standard) changes the result, so it is stated in the report. Fourth — speed: at most one bend per second, and slower if the wire heats up; bending too fast heats the wire and falsifies the result. Fifth — straightening: wire with a sharp local bend is not straightened, and straightening must not damage the surface or twist the wire. Sixth — edition: the Polish standard adopts the ISO of 1984, and the ISO 2024 edition changed, among other things, the tensile force principle and the definition of the criterion for ending; a laboratory citing PN-ISO 7801:1996 works according to the first edition.

WHAT WE DO NOT GIVE. We read the full text of ISO 7801:1984 (4 pages); of the ISO 7801:2024 edition — the foreword, scope and the beginning of clause 4 (symbols). We do not give the new values and figures of the 2024 edition or Annexes A and B.

Method principle

A wire test piece clamped at one end is bent alternately through 90° in opposite directions over cylindrical supports with a radius r chosen for the wire diameter (Table 2: from 1.25 mm for wire of 0.3–0.5 mm to 25 mm for wire over 8 to 10 mm); one bend is bending through 90° and returning. Bending is uniform, not faster than 1 bend/s, up to the required number of bends or until a crack visible to the naked eye; the result is the number of bends Nb without the bend in which failure occurred (ISO 7801:1984, clauses 2 and 6).

Applications

• Round metallic wires with a diameter of 0.3–10 mm and non-circular wires with a thickness in this range (ISO 7801:1984, clause 1)
• Testing the conformity of wires with a product standard which specifies the required number of bends and the criterion for ending
• In accreditation scopes: 7 Polish laboratories — wires, steel wire, metal products, brush wire

Key parameters

Standard

Standard number

PN-ISO 7801:1996 (wersja polska; wprowadza ISO 7801:1984 [IDT])

Title (PL)

Metale — Drut — Próba przeginania dwukierunkowego

Title (EN)

Metallic materials — Wire — Reverse bend test

Step-by-step procedure

1. Test piece

   Length of wire as straight as possible; straightening by hand or with a hammer of soft material, without damaging the surface and without twisting; wire with a sharp local bend is not straightened (clause 5).

2. Choice of supports and guide

   Radius r, distance h and guide hole according to the wire diameter from Table 2; temperature 10–35 °C or 23 ± 5 °C (points 6.1–6.2).

3. Clamping

   Arm vertical, wire through the guide hole, lower end in the jaws, perpendicular to the axis of the supports; non-circular test pieces with the larger dimension parallel to the jaws (point 6.3).

4. Bending

   Alternately through 90° in both directions, without interruption, uniformly and without jerks, ≤ 1 bend/s; any tension ≤ 2 % of the nominal strength (points 6.4–6.6).

5. End and result

   After the required number of bends or after a crack visible to the naked eye (or after fracture, if required by the product standard); the bend in which failure occurred is not counted in Nb (points 6.7–6.8).

6. Report

   Standard, test piece, diameter or thickness, preparation, support radius, stress, criterion for ending, result (clause 7). PN-ISO 7801:1996 — current (PKN card as of 27.10.2026), although it adopts the withdrawn ISO 7801:1984.

Required equipment and apparatus

Health and safety (OHS)

• TECHNICAL NOTE: the bend at which the wire cracked does not count in the result Nb (point 6.8)
• TECHNICAL NOTE: at most one bend per second, and slower if the wire heats up — heat affects the result (point 6.5)

Frequently asked questions