Testing standard
Standard Test Method for Tensile Properties of Yarns by the Single-Strand Method
Written and technically reviewed by Dak System Inc. engineeringLast reviewed
ASTM D2256 measures the tensile properties of yarn by the single-strand method. A single end is pulled to rupture at a rate giving an average time-to-break of 20 ± 3 s, with an alternate speed such as 300 ± 10 mm/min at a 250 mm gauge length. It reports breaking force and elongation, and provides for the calculation of breaking tenacity, initial modulus, chord modulus and breaking toughness. The clamping arrangement is left to the laboratory, provided the force-elongation curve is representative.
From the test method to your testing system
Explore the DAK machines already listed for ASTM D2256, then review the grips, measurement and setup requirements below.
Universal Testing MachineSeries 7200Explore the machine →
Universal Testing MachineSeries 9000Explore the machine →01Understand the method
A single end of yarn is drawn from a package and pulled to rupture, the machine recording force against elongation. Scope 1.1 covers monofilament, multifilament and spun yarns, single, plied or cabled. Clause 1.2.1 offers three specimen forms — straight, knotted or looped — and 1.2.2 six test conditions, from conditioned air to low temperature. The crosshead runs at a rate giving an average time-to-break of 20 ± 3 s, with an alternate speed such as 300 ± 10 mm/min at a 250 mm gauge length. Because yarn is variable, the test is repeated across many specimens sampled from different parts of the package.
Clause 1.2 measures breaking force and elongation, and gives directions for calculating four further properties: breaking tenacity, initial modulus, chord modulus and breaking toughness. Under 5.5.1 tenacity is what compares yarns of different counts, because breaking strength for a given fibre type is approximately proportional to linear density. Significance and Use 5.2 defines the rest — initial modulus as the resistance of the yarn to extension at forces below the yield point, chord modulus as an estimate of resistance to imposed strain, and breaking toughness as a measure of the work necessary to break the yarn. Those describe how the yarn survives weaving and knitting, which apply repeated shock loads rather than a steady pull. The variability across specimens matters as much as the average, because it is the weakest place in a yarn that causes an end-break.
02Prepare the specimen and test settings
A yarn is a bundle of fibres held together by twist. Anything that crushes it or lets the twist run out changes what is being measured — which is why D2256 sets the outcome the clamp has to achieve rather than naming the clamp.
Breaking force alone does not compare two yarns unless they are the same count. Under 5.5.1 the comparable quantity is breaking tenacity — the observed breaking strength converted using the linear density, in centinewtons per tex, grams-force per tex or grams-force per denier.
03Build the test setup on a DAK machine
Very small forces measured accurately. Fine spun yarns break below a newton, and a load cell sized for fabric or film reports them as noise, so the cell has to match the yarn count. The crosshead must offer a range of rates: a twenty-second break across yarns ranging from a few per cent elongation to well over a hundred cannot be had at one speed. The machine itself is the subject of Specification D76/D76M, which 5.9.2 names as the source of the 20 ± 3 s. The method names no grip: 5.4 leaves specimen clamping to the discretion of the individual laboratory, provided a representative force-elongation curve is obtained, and warns that high-modulus yarns such as glass or extended-chain polyolefin may need a special clamping adaptation.
5.4 asks for clamping that gives a representative force-elongation curve without slipping or damaging the yarn, and leaves the arrangement to the laboratory. Split capstan grips are our usual answer for yarn: the wrap spreads the clamping load around a curve, so tension decays gradually instead of concentrating on one line across the bundle.
Specifications
The same wrapped hold with faster loading, which matters because a yarn programme means tens of breaks per sample. 5.4 also flags high-modulus yarns — glass or extended-chain polyolefin — as the case where a special clamping adaptation is likely to be needed.
SpecificationsDak verifies against whichever standard the method names, and where a class applies our frames sit a class tighter than it asks.
| The method asks for | Dak supplies | |
|---|---|---|
| Capacity | Very low — from under 1 N on fine spun yarn to a few hundred newtons on industrial filament | Load cells from 1 kg to 60 ton on the Series 7200, and 0.5 to 100 kN on the Series 9000 |
| Force accuracy | Specification D76/D76M for the tensile testing machine, named in 5.9.2; the retrievable record prints no accuracy figure | ISO 7500-1 Class 0.5 — the method sets no class of its own |
| Gripping | No clamp type is named. 5.4 leaves specimen clamping to the discretion of the individual laboratory, provided a representative force-elongation curve is obtained; special adaptations may be needed for high-modulus yarns such as glass or extended-chain polyolefin | Our split capstan grips, built to the specimen |
04Run the test
05Calculate, report and interpret
The maximum force recorded before rupture
1.2 makes breaking force and elongation the two measured quantities; everything below is calculated from them.
Breaking tenacity = breaking force / linear density
5.5.1, expressed in centinewtons per tex, grams-force per tex or grams-force per denier. This is the quantity that compares yarns of different counts, and it is why the linear density has to be known for the yarn actually tested.
ε = ΔL / L₀ × 100
5.7 lists elongation at break among the values the force-elongation curve permits, and 5.6 is why it is wanted: yarn elongation drives the stretch behaviour of the fabric or cord made from it.
A measure of the work necessary to break the yarn
5.2. Under 5.7 the area under the force-elongation curve is a measure of toughness, proportional to the work done. It is often the better predictor of how a yarn survives weaving or knitting, where shock loads matter more than a peak force.
The resistance of the yarn to extension at forces below the yield point
5.2. It is the property that separates two yarns of similar breaking force but very different handle, because it describes the first part of the curve rather than its end.
Used to estimate the resistance to imposed strain
5.2. Taken between two points on the curve rather than at its origin, which is what makes it usable on yarns with no straight initial portion.
The catalogue record for D2256/D2256M-21 carries the Scope and Significance and Use only; its test-report clause is not retrievable, so nothing below is quoted as a reporting requirement. These are the choices the readable clauses make load-bearing — each of them changes what the number means, and Dak's practice is to put every one on the certificate.
Jaw breaks and slippage account for most rejected specimens, with opposite signatures — a jaw break gives a low force, slippage a normal force with an inflated elongation, because the slip is counted as extension. Both are clamping problems, and 5.4 is the clause that lets you solve them: change the arrangement until the curve is representative, rather than clamping harder. Not saying which of the six conditions in 1.2.2 was run is the next error: 5.1 does not extend its acceptance-testing statement to the wet, oven-dried, knot, loop or temperature options, so a certificate that omits the condition cannot be relied on for acceptance. Sampling one continuous length instead of across the package understates variability, which is precisely the information the single-strand method exists to provide. And an assumed rather than known linear density puts a quiet bias into every tenacity figure.
06Compare methods and find answers
Both methods break a single end of yarn and report breaking force, elongation and tenacity, so a buyer is often asked for either. They set the test up differently, and each difference below moves the number.
| This method (D2256/D2256M-21) | ISO 2062:2009 | |
|---|---|---|
| Rate principle | A time: an average time-to-break of 20 ± 3 s, with alternate speeds such as 300 ± 10 mm/min at a 250 mm gauge | A rate: 100 % of the gauge length per minute, so 500 mm/min at the usual gauge |
| Machine types | CRT, CRE and CRL all recognised, with the CRE type preferred | CRE only in the body; CRT and CRL held in informative Annex A as deprecated |
| Gauge length | Not fixed in the retrievable record; 250 mm is named once, as the gauge the alternate rate is written for | 500 mm usually, with 250 mm only where machine travel is short or the parties agree |
| Clamping | Left to the individual laboratory, provided a representative force-elongation curve is obtained (5.4) | Flat-faced unlined jaws are the normal type; bollards and other snubbing devices only where flat jaws cannot prevent slipping, and then by agreement |
| Named variants | Straight, knotted or looped specimens; conditioned air, wet, oven-dried, or at high or low temperature | Four lettered methods — A manual, B automatic, C relaxed skein, D wet |
The clamp is the difference most often missed, and it runs the opposite way to the usual assumption. ISO 2062 names a normal clamp and treats anything else as a by-agreement fallback; D2256 names none and leaves the choice to the laboratory, subject to the curve being representative. Because the clamp type changes the elongation reading, the two setups still cannot simply be swapped. Run the document the specification names, and say which one was run.
Note 2 to D2256's scope points the skein method to Test Method D1578, Breaking Strength of Yarn in Skein Form; Note 1 to D1578's own scope points back. They are the two halves of the same question and they do not answer it the same way.
| Single strand (D2256/D2256M-21) | Skein (D1578-93(2022)) | |
|---|---|---|
| What is broken | One end of yarn | A skein — 80, 40 or 20 turns on a 1.50 m reel, or 50 turns on a 1 m reel (1.3) |
| Yarns it applies to | Monofilament, multifilament and spun, single, plied or cabled (1.1) | Spun yarns only, single or plied (1.2); 5.7 says it is rarely used for filament yarns, whose uniformity makes the single-strand method economical |
| What is reported | Breaking force and elongation, plus breaking tenacity, initial modulus, chord modulus and breaking toughness (1.2) | Breaking strength in units of force, converted to skein breaking tenacity and skein break factor (1.1) — no elongation |
| Speed | A time: 20 ± 3 s to break, or 300 ± 10 mm/min at a 250 mm gauge (5.9.2) | 300 mm/min for Options 1 and 2; a 20 s break for Option 3 (1.3) |
| How the two numbers relate | 5.3: a more accurate measure of breaking force, using less material | D2256 5.3: the skein breaking force is always lower than the sum of the breaking forces of the same number of ends broken individually |
D1578 is not simply a faster D2256. Its own 5.6 describes what it gives as an index that combines the effects of yarn unevenness and single-strand strength, and warns that its three options are not fully comparable with each other — a 1 m skein can read up to 4 % higher than a 1.5 yd one. Where the specification wants the distribution of individual breaks, only the single-strand method supplies it.
It is the ASTM method for the tensile properties of yarns by the single-strand method. Scope 1.1 covers monofilament, multifilament and spun yarns, single, plied or cabled. A single end is pulled to rupture at a rate giving an average time-to-break of 20 ± 3 s, and 1.2 makes breaking force and elongation the measured quantities, with directions for calculating breaking tenacity, initial modulus, chord modulus and breaking toughness.
No. The method names no clamp type at all. Significance and Use 5.4 says specimen clamping may be modified as required at the discretion of the individual laboratory, provided a representative force-elongation curve is obtained and the described procedure is maintained, and it notes that special clamping adaptations may be necessary for high-modulus yarns such as glass or extended-chain polyolefin to prevent slippage or gripping damage. Capstan and bollard grips are a common and effective answer for yarn — the wrap spreads the load around a curve rather than crushing the bundle on one line — but they are our recommendation, not the standard's requirement. Note that ISO 2062 runs the other way: its Clause 5.1 does name flat-faced unlined jaws as the normal type.
Breaking tenacity is breaking force divided by linear density, expressed under 5.5.1 in centinewtons per tex, grams-force per tex or grams-force per denier. Breaking force alone only compares yarns of the same count — a thicker yarn is stronger simply because there is more of it. 5.5.1 makes the conversion the way strands of different sizes are compared at all, because breaking strength for a given fibre type is approximately proportional to linear density.
They describe the part of the curve before the break, which is often what decides whether a yarn runs. Under 5.2 the initial modulus is a measure of the resistance of the yarn to extension at forces below the yield point, and the chord modulus is used to estimate the resistance to imposed strain. Both are named in 1.2 as properties the method gives directions for calculating, alongside breaking tenacity and breaking toughness — so a D2256 report that quotes only a breaking force is leaving most of the method's output on the table.
1.2.2 gives six: conditioned air, wet but not immersed, wet and immersed, oven-dried, exposed to elevated temperature, and exposed to low temperature. The choice matters commercially as well as technically, because 5.1 restricts the acceptance-testing statement to Option A1 — it does not extend to knot and loop tests, wet tests, oven-dried tests, or tests at low or high temperature, since between-laboratory precision and bias data are not available for them. 5.10 to 5.12 say when each is usually wanted: wet tests for yarns that lose strength when wet, oven-dried and high-temperature tests for industrial yarns such as rayon tyre-cord yarns, low-temperature tests for cold-climate and coated yarns.
Because a longer specimen contains more opportunities for a weak place, and a yarn breaks at its weakest point — so increasing the gauge length lowers the average breaking force. That is a statistical effect rather than an artefact of the machine, and it is why results obtained at different gauge lengths cannot be compared directly. The retrievable ASTM record does not fix a gauge length; it names 250 mm [10 in.] once, in 5.9.2, as the length the alternate speed of 300 ± 10 mm/min is written for. Whatever length is used, state it with the result.
The retrievable record sets no number, so we will not quote one as though it did — the specimen count sits in the procedure clause of the standard itself. In practice, considerably more than for a moulded plastic: yarn is variable along its length and between packages, so single-strand testing normally means tens of breaks rather than five, and the coefficient of variation is worth reporting alongside the mean. That variability is itself useful information, because a yarn with a good average and a wide spread will still break on a loom.
By the elongation. A specimen that slipped in the clamps shows an unusually high elongation with an otherwise ordinary breaking force, because the slip is counted as extension. If a set shows a few points with markedly higher elongation and no corresponding strength increase, slippage is the likely cause. 5.4 treats that as a clamping problem to be designed out rather than a result to be kept — it is the clause that lets you change the clamping arrangement, so long as the curve you end up with is representative.
Discuss your specimen, test requirements and reporting needs with DAK engineering.
This page describes the method as practised. The governing text is the current edition from the issuing body. Tell us what you are testing and we will answer with the machine, the fixture and a quotation.
