Determination of Percentage Elongation After Fracture of PVC-Coated Wire Mesh

PVC-coated wire mesh is a galvanized or plain steel wire fabric protected by an extruded polymer layer, and its percentage elongation after fracture is a key ductility indicator that determines how well the mesh withstands weaving, welding, bending, and in-service deformation. This article explains the principles, sampling, test items, and step-by-step determination methods for the percentage elongation after fracture of PVC-coated wire mesh in accordance with ISO 6892-1, GB/T 228.1, and ASTM E8/E8M (ASTM A370), as commonly performed by accredited third-party laboratories. It also covers typical applications and answers frequently asked questions about specimen preparation, gauge length selection, and result validity.

Technical Overview

PVC-coated wire mesh, also known as plastic-coated mesh or vinyl-coated mesh, is manufactured from low-carbon steel wire (frequently galvanized for corrosion protection) that is covered with a polyvinyl chloride or polyethylene layer through extrusion or dipping, and then woven, welded, or crimped into mesh panels or rolls. The polymer coating provides weathering resistance and an attractive finish, while the steel core carries the mechanical load. Because mesh products are routinely bent, stretched, stapled, and impacted during installation and service, the ductility of the wire is as important as its strength.

Percentage elongation after fracture, denoted by the symbol A, is the standard measure of this ductility. It is defined as the permanent plastic extension of the gauge length after the specimen has fractured in a uniaxial tensile test, expressed as a percentage of the original gauge length L0. Elongation after fracture is calculated as follows:

• A = (Lu − L0) / L0 × 100%
• L0 = original gauge length marked before testing (for example 100 mm or 200 mm for wire specimens)
• Lu = final gauge length measured after carefully piecing the fractured specimen parts together

A higher elongation after fracture indicates greater plastic deformation capacity, which reduces the risk of brittle cracking during fence fabrication, mesh tensioning, and long-term exposure to wind loads, thermal movement, and accidental impact. For PVC-coated wire mesh, the tensile properties are governed primarily by the steel core, while the coating contributes to corrosion protection and, in some specifications, is evaluated separately for its own elongation and adhesion.

The determination is typically carried out in accordance with the following reference standards, and equivalent national standards are accepted when mutually agreed in the purchase contract:

• ISO 6892-1, Metallic materials — Tensile testing — Part 1: Method of test at room temperature
• GB/T 228.1, the Chinese national standard technically aligned with ISO 6892-1
• ASTM E8/E8M, Standard Test Methods for Tension Testing of Metallic Materials
• ASTM A370, Standard Test Methods and Definitions for Mechanical Testing of Steel Products, including wire
• ASTM D412 or ASTM D638, when the elongation of the polymer coating itself is separately assessed

Testing Samples

PVC-Coated Welded Wire Mesh Panels and Rolls

Specimens are cut from production panels or rolls at locations away from edges, weld line ends, and damaged areas. Individual straight wires running in the principal test direction are separated from the mesh so that each specimen consists of a single coated wire of sufficient free length, normally at least L0 plus two grip lengths plus a handling margin. The welded junctions are excluded from the gauge length unless the purchase specification explicitly requires the junction to be tested.

PVC-Coated Woven and Hexagonal Mesh

For woven products such as hexagonal netting and chain-link fabric, wires are carefully unpicked or cut from the fabric with minimal bending. Because weaving introduces residual curvature, specimens are straightened gently by hand or with a soft non-metallic tool without stretching, heating, or surface scoring, since cold work or notch marks introduced during preparation can depress the measured elongation.

Base Steel Wire Specimens

When the purchase specification defines mechanical properties for the bare core wire, the PVC coating is stripped mechanically or with a suitable solvent-based method that does not attack the steel or zinc layer. Testing the base wire eliminates the contribution of the coating to the load signal and gives values directly comparable to the wire grade declared by the manufacturer.

Polymer Coating Specimens (Optional)

Where the specification requires the coating ductility itself to be reported, strips or dumbbell specimens are die-cut from the coating after peeling, or coating integrity is assessed indirectly by checking for cracks after a mandrel bend of the coated wire. Coating elongation, when measured directly, is tested per ASTM D412 or ASTM D638 rather than the metallic-materials standards.

Unless otherwise specified, a minimum of three valid specimens per lot or per coil are tested, and the arithmetical mean of valid results is reported together with the individual values.

Testing Items

The core determination is the percentage elongation after fracture of the wire, and it is usually reported alongside the other tensile characteristics obtained from the same test curve:

• Percentage elongation after fracture (A), with the gauge length clearly stated, for example A100 mm or A200 mm
• Tensile strength (Rm), calculated from the maximum force and the cross-sectional area of the steel core
• 0.2% proof strength (Rp0.2) or yield strength, when required by the wire grade
• Fracture position assessment to confirm whether the result is valid
• Verification of wire diameter and cross-sectional area, determined by direct measurement or, for very fine wire, by the mass-per-length method given in ISO 6892-1
• Optional coating-related observations, such as coating cracking or peeling after fracture, recorded as supplementary information

Testing Methods

Specimen Preparation

Specimens are cut to a total length that accommodates the gauge length plus the gripping lengths. The coating is either retained or removed in accordance with the specification, and the treatment used is stated in the report. Sharp bends, kinks, and transverse scratches within the gauge length are avoided, because stress concentrators can cause premature fracture and artificially low elongation. Specimens are identified at the ends, outside the gauge length, and conditioned at room temperature before testing.

Gauge Length Marking

The original gauge length L0 is marked on the specimen using a contrasting paint marker, a fine punch, or a light scoring method that does not create notches. For wire specimens, non-proportional gauge lengths of 100 mm or 200 mm are most common; alternatively, a proportional gauge length L0 = k√S0 (commonly k = 5.65) may be used if the specification requires it, in which case the area S0 is determined from diameter measurement or from mass per unit length. The gauge length tolerance and the distance of the marks from the grips follow the requirements of ISO 6892-1 or ASTM E8/E8M.

Equipment and Calibration

A universal tensile testing machine with wedge or capstan-type grips suited to round wire is used. The machine force measuring system, extensometer, calipers, and temperature measuring devices must be calibrated and traceable to national or international standards. The test is normally performed at room temperature within 10 °C to 35 °C, and the ambient temperature is recorded.

Tensile Test Procedure

The specimen is mounted axially in the grips so that bending and torsion are minimized. Loading is applied under controlled rates consistent with the selected standard method, for example controlling the stress rate in the elastic range and then the strain rate through yield and up to maximum force, typically on the order of 0.00025 s⁻¹ for the plastic range per ISO 6892-1 Method A, or an equivalent crosshead separation rate per Method B or per ASTM A370 for wire. Testing continues until the specimen fractures completely, and the maximum force and force-elongation curve are recorded.

Measurement After Fracture

After fracture, the two broken pieces are carefully fitted back together so that their axes form a straight line, applying the light axial contact pressure described in the standard to close the fracture surfaces without distorting the specimen. The final gauge length Lu is then measured to the nearest 0.1 mm (or better) using calipers, as the distance between the original marks on the pieced specimen. Alternatively, when a class-appropriate extensometer or video extensometer is used and the specification permits, the extension at fracture may be taken directly from the instrument record.

Calculation and Rounding

The percentage elongation after fracture is calculated from A = (Lu − L0)/L0 × 100%. Each valid specimen result is rounded to the nearest 0.5%, and the reported value includes the gauge length, for example A100 mm = 18.5%. The report states whether the coating was present or removed during testing, the specimen orientation (warp or weft direction of the mesh), the standard method applied, and the individual and mean results.

Validity of Results

A test is generally considered invalid, and a retest on a reserve specimen is performed, when fracture occurs within the grips or within the transition region between the grip and gauge length, or when the specimen fails at a preparation defect. If the specification sets a minimum elongation requirement, a fracture inside the gauge length that still meets the minimum may be accepted per the rules of the standard. Retest rules, including the number of additional specimens, follow ISO 6892-1, ASTM E8/E8M, or the product specification.

Applications

Determination of elongation after fracture is applied throughout the supply chain of PVC-coated wire mesh products, from wire drawing and annealing control to finished-product acceptance:

• Factory quality control of annealed, galvanized, and coating lines to verify that drawing and thermal treatment have delivered the required ductility
• Incoming inspection of mesh rolls and panels by fence fabricators and installers
• Compliance verification for highway and railway fencing, stadium perimeter fences, airport security fencing, and bridge and embankment protection mesh
• Agricultural uses such as poultry and livestock enclosures, aviaries, predator-proof netting, and garden fencing
• Double-twist hexagonal PVC-coated mesh for gabion baskets, retaining walls, riverbank and slope stabilization, and marine and aquaculture cages
• Construction applications including stucco and plaster mesh, partition reinforcement, machine guarding, shelving, and window security screens
• Independent verification by accredited third-party laboratories for tender submissions, product certification, export documentation, and failure analysis of broken fences in service

In all of these applications, a verified elongation after fracture value gives engineers and buyers confidence that the mesh will survive forming, tensioning, and long-term service loads without brittle failure of the steel core.

FAQ

Should the PVC coating be removed before the tensile test?

It depends on the purchase specification. When properties are specified for the steel core, the coating is removed so that the result reflects the wire grade; when the specification covers the finished coated product, the coating may be retained and the report must state which condition was tested. Whatever the choice, the condition is always disclosed in the test report because it influences comparability of results.

What gauge length is normally used for PVC-coated wire specimens?

Non-proportional gauge lengths of 100 mm or 200 mm are the customary choice for wire, because the small cross-section makes proportional gauge lengths impractically short. If a proportional gauge length L0 = 5.65√S0 is required, the cross-sectional area may be determined from the measured wire diameter or from the mass per unit length as permitted by ISO 6892-1. The gauge length must always be quoted together with the elongation symbol.

What happens if the specimen breaks inside the grips?

A fracture inside the grips or in the transition region usually produces an artificially low elongation and the result is treated as invalid. The test is then repeated on a reserve specimen. Slight adjustments to grip pressure, the use of appropriate liner material, or capstan winding for fine wire help prevent premature grip failures.

Can elongation after fracture be measured without an extensometer?

Yes. The classic method permitted by ISO 6892-1 and GB/T 228.1 is to piece the two fractured parts together and measure the final gauge length Lu directly with calipers. This manual method is appropriate for ductile wire, but care must be taken to align the parts correctly and not to bend or stretch them during fitting. Machine crosshead displacement alone must not be substituted for gauge length extension, because grip seating and machine compliance would inflate the result.

What elongation values are typical for PVC-coated mesh wire?

Elongation depends on the wire processing route. Annealed low-carbon steel wire commonly shows elongation after fracture in the range of roughly 10% to 25% or more on a 100 mm gauge length, whereas hard-drawn or high-strength wires may show considerably lower values. The acceptance criterion is set by the relevant product or wire specification, so the measured value should always be judged against the grade declared in the contract documents.

Who can perform this determination?

Testing can be performed in the manufacturer's own laboratory for process control. For certification, tender compliance, dispute resolution, and import or export documentation, the determination should be carried out by accredited third-party laboratories with tensile testing scopes covering ISO 6892-1, GB/T 228.1, or ASTM E8/E8M, ensuring that equipment calibration, method validation, and reporting all meet the requirements of the standard.