ISO 13934-1

What the test does

A 50 mm wide strip of woven fabric is clamped across its entire width in two flat jaws set a fixed distance apart. One jaw travels away from the other at a constant speed until the strip ruptures, while force and jaw separation are recorded continuously. The peak of that curve, and the extension reached at the instant of the peak, are the two reported results.

What it measures, and why it matters

The method reports maximum force in newtons and elongation at maximum force as a percentage, separately for the warp and the weft, because a woven fabric is anisotropic. Maximum force is the figure written into purchase specifications for apparel, furnishing and technical wovens, so it governs lot acceptance and supplier qualification. Elongation at maximum force distinguishes a stable construction from one that will distort under load, and both figures drop measurably after abrasion, laundering or UV exposure, which is what makes the pair useful in failure investigations.

Specimen

The strip method grips the whole specimen width, unlike grab tests that clamp only a central portion, so the width must be exact. Strips are cut oversize and then fringed — threads are drawn off each long edge until precisely 50 mm of fabric remains between the outermost surviving threads. Strips are cut in both principal directions, avoiding selvedges, creases and the same warp or weft yarns twice. Conditioning follows the ISO 139 textile standard atmosphere, 20 °C ±2 °C and 65 % ±4 % RH, with 24 h of relaxed conditioning recommended before test. A wet-state variant soaks the specimen in Grade 3 water to ISO 3696 with a nonionic wetting agent and needs no prior conditioning. Specimens that slip in the jaws, or that rupture at the jaw line rather than in the free length, are discarded and replaced.

What the machine must be capable of

The method calls for a constant-rate-of-extension frame — the moving jaw holds its speed throughout, rather than tracking load. Most apparel and furnishing wovens break between roughly 100 N and 1.5 kN on a 50 mm strip, so a 5 kN load string covers the great majority of the work; heavy technical wovens such as sailcloth, airbag fabric and coated industrial cloth can push past 5 kN, which is why textile laboratories handling them specify 10 kN. Force indication must meet ISO 7500-1 Class 1.

Gauge length is 200 mm, reduced to 100 mm where elongation at maximum force is expected above 75 %. Speed is keyed to that expectation: 20 mm/min below 8 % elongation and 100 mm/min from 8 % to 75 % on the 200 mm gauge, and 100 mm/min on the 100 mm gauge above 75 %. Rate must hold to ±10 %, because fabric strength is rate-sensitive.

No extensometer is required — elongation is taken from jaw separation, so every millimetre of grip slip or frame compliance is counted as fabric stretch. Jaws must be flat-faced and at least 60 mm wide so the full 50 mm of fringed width is clamped uniformly; narrower faces load the centre of the strip and force an early edge failure. Capstan jaws are the fallback for fabrics that slip or break at the clamp. A pretension is applied to straighten the strip and define the starting length. The laboratory itself is part of the instrument: testing is done in the same conditioned atmosphere, and the alternative 23 °C / 50 % RH atmosphere may be used only by agreement between the parties and must be reported.

What goes wrong in practice

Jaw breaks are the standard invalidation — the strip fails at the clamp line, reads low, and must be replaced. Slippage is harder to catch, because with no extensometer the fabric creeping out of the jaws is recorded as extension and inflates elongation. Fringing errors are specific to this method: one thread too many leaves under 50 mm carrying the load, and maximum force falls proportionately. Conditioning drift is invisible — hygroscopic fibres change strength with moisture regain, so a warm, dry laboratory produces a consistent offset.

Related and equivalent standards

EN ISO 13934-1:2013 is the European adoption and is technically identical. ISO 13934-2 covers the grab method on the same fabrics, gripping only part of the width, so its forces are not comparable with strip results. ASTM D5035 is the nearest counterpart and is also a strip method, but differs in specimen and procedural conventions, so figures should not be transferred between the two without correlation work. ISO 139, ISO 7500-1 and ISO 3696 supply the conditioning atmosphere, force verification and water grade respectively.