Yarn Tensile Testing: Breaking Force, Tenacity and Elongation

Decide which property the yarn needs

Suppose one yarn breaks at 3.6 N and another at 3.8 N. Which is stronger? The second withstands more force in those tests. But if it contains more fibre mass per metre, it may have lower tenacity. Neither result tells you how far the yarn stretched before it broke.

That is why a yarn tensile report should provide more than a headline “strength” value. Breaking force, tenacity and elongation describe different parts of the response. The test method and specimen condition give those numbers their meaning.

Begin with the intended decision. Are you comparing yarns of different counts? Checking a delivery against an agreed limit? Looking for weak specimens after winding? Studying how a yarn carries load as it stretches? Each question needs a suitable result and a sample that represents the material of interest.

The calculations below use invented data. They show how to read results and check units. They do not set acceptance limits or replace the full laboratory method.

Keep force, tenacity and elongation separate

Breaking force is a force result, commonly expressed in newtons or centinewtons. Tenacity relates that force to the yarn's linear density. Elongation expresses a length change relative to a stated starting length.

Confirm how the report defines its endpoint. For example, Uster Tensorapid 5 technical data defines breaking force as the maximum force in the test. Its breaking elongation is the elongation at that maximum force. Those definitions should not be silently changed to the travel at which the last visible fibre separates.

Use the full field name when exporting results. “Elongation at maximum force” and “extension at final separation” can be different values. A curve helps resolve doubt, especially when the yarn loses load in stages.

Tenacity also differs from stress expressed in MPa. MPa uses force per cross-sectional area. A cN/tex result uses force per mass per length. Converting between them needs a justified area or density basis. A fuzzy yarn outline does not supply an exact solid area on its own.

Calculate tenacity with the right count

One newton equals 100 centinewtons. Tex expresses grams per 1,000 m. With those units aligned:

Breaking tenacity (cN/tex) = breaking force (cN) / linear density (tex)

For the opening comparison, assume that suitable count tests on matched yarn give 18.0 tex for A and 20.0 tex for B. Both tensile results come from the same agreed method and condition.

Yarn B has the higher breaking force, but yarn A has the higher tenacity. This is not a conflict. B's greater mass per metre changes the comparison.

The relevant choice depends on the product. A fixed-count development trial may favour the yarn with higher tenacity. A process load acts on the actual strand and still needs adequate force capacity. Tenacity does not make count, fabric weight or the required yarn size irrelevant.

A nominal count can distort the answer

Suppose B is labelled 18 tex, but an appropriate count test finds 10.0 g in a measured 500 m. On that mass and length basis:

Linear density = 10.0 × 1,000 / 500 = 20.0 tex

Using the nominal 18 tex would give 380 / 18 = 21.11 cN/tex. Using 20 tex gives 19.00 cN/tex. The nominal-count result is 11.11% higher than the measured-count result.

Do not correct a supplier's report by guessing the true count. Establish which count basis the agreed procedure requires and how the reported value was obtained. The example shows the size of an error that can arise when a label is treated as a measurement.

Match the count sample to the tensile sample. A count measured on a different lot, blend or treatment cannot safely normalize the force result. Use a consistent moisture and preparation basis too. ApparelDiary's yarn count guide explains the main count systems and their conversions.

When several counts are tested, retain the count assigned to each group. Do not divide every force result by a single convenient nominal value. A change in reported tenacity may otherwise come from the denominator rather than from the yarn's load-bearing response.

Check how a combined tenacity was formed

If the two example yarns receive equal weight, the mean of their tenacities is:

(20.0 + 19.0) / 2 = 19.50 cN/tex

Their mean force is 370 cN and their mean count is 19 tex. Dividing those means gives 370 / 19 = 19.47 cN/tex. The results are close here, but the operations are different. A ratio of means does not generally equal a mean of ratios.

Choose the summary that matches the stated reporting basis. For an equal-weight average of group tenacities, calculate each group first. Keep the underlying force and count values so the calculation can be checked. Do not mix counts or change group weights without saying so. Where a standard specifies the calculation, follow that definition rather than substituting a preferred summary.

Choose a method that covers the material

ISO 2062:2009 covers single-end breaking force and elongation of yarns from packages using constant-rate-of-extension equipment. Its scope distinguishes tests from conditioned packages, relaxed conditioned skeins and wetted specimens. It also identifies a route for disputes about elongation.

The scope has exclusions, including glass, elastomeric, aramid, carbon and certain high-performance polyethylene yarns. Check the complete scope for the actual material. A machine's ability to pull a yarn does not establish that a chosen standard applies to it.

At the time of review, ISO still listed the 2009 edition as published and current. ISO/CD 2062 was a committee draft under development. A replacement project is not yet a published replacement. Confirm the edition when preparing a purchase or test agreement.

ASTM D2256/D2256M-21 is another single-strand tensile method. Its public scope includes straight, knotted and looped forms and several specimen conditions. Its acceptance-testing statement is qualified; it does not give every option the same standing.

Write down the method, edition, option and condition before comparing reports. “Tested to ASTM” is not enough. A wet loop test and a conditioned straight-yarn test answer different questions even if both reports use newtons.

Also keep single-end results separate from hank or lea strength. A skein loads many lengths together. Dividing its result by the number of lengths does not automatically reproduce an individual-yarn test. Use the method that matches the agreed property and retain its identity throughout the report.

Establish the starting length carefully

Elongation is a ratio, so the starting length matters as much as the extension:

Elongation (%) = 100 × extension / defined initial gauge length

If a specimen extends by 20 mm from an initial gauge length of 250 mm, its elongation is 8%. The same 20 mm extension over 500 mm is 4%. A percentage copied from one test cannot be checked without its gauge length.

Conversely, 8% elongation over 500 mm requires 40 mm of extension. These figures are geometry, not recommended settings. The selected method determines how the starting length and its initial tension are established.

A slack strand can move before it carries the intended tensile load. A strand pulled too hard during mounting can begin the test already stretched. That is why initial tension and the point where extension is zeroed belong in the method record.

Keep specimen preparation consistent with the intended comparison. Do not hand-stretch one group to make mounting easier while leaving the other relaxed. For textured or highly extensible yarns, first confirm that the method and equipment cover that structure. Preparation can change which part of its response the test records.

Crosshead travel needs a valid measurement basis

Crosshead movement can be used for extension in a suitable test arrangement. It is not automatically equal to the extension of the intended free yarn length in every grip system.

ZwickRoell's yarn-testing guidance shows different grip and extension arrangements. Some examples use crosshead travel. Its multifilament example uses optical extension measurement because the reference for crosshead-based strain cannot be defined precisely in that arrangement. The equipment choice follows the specimen and setup.

Consider a hypothetical 500 mm gauge length. If the yarn itself extends 25 mm, its elongation is 5%. If the recorded movement also contains 3 mm from unwanted slip or other movement, the apparent value becomes 28 / 500 × 100 = 5.6%.

The difference is 0.6 percentage points, or 12% relative to the true 5% in this example. Do not subtract an assumed 3 mm from real results. Find and control the source of movement, or use the appropriate extension measurement. The calculation only shows why a small displacement error can matter.

Make the grips part of the investigation

The grip must hold the yarn without turning the clamp into the weak point. A low force result may reflect the specimen, damage during gripping, or loss of grip. Raising pressure without checking the failure can trade one problem for another.

ZwickRoell describes capstan arrangements that reduce the load reaching the final clamping point. It also shows that yarn types require different grips and inserts. These are equipment examples, not a reason to apply one wrap count or jaw pressure to every yarn.

Observe where the break occurs. Keep the original curve and any evidence of slip, clamp damage or unusual mounting. Follow the selected method's rules for invalid tests and replacement specimens. Do not reject a result merely because it is lower than expected.

That last distinction protects the decision. A weak break within the valid gauge length may be the feature the test was meant to find. Removing it because it spoils the average turns a useful measurement into a biased sample.

If many tests fail at the grip, stop and resolve the setup. Repeating the same unsuitable arrangement produces more numbers without answering the material question. A short trial with appropriate grip options can be more useful than a long run with an unexplained failure pattern.

Keep attempted pulls separate from valid results. An invented setup trial might contain 112 pulls, of which 100 meet the method's validity rules. If the other 12 are confirmed grip-related invalid tests, report that reason. They are neither 12 proven yarn defects nor 12 extra observations to include in the accepted mean.

Their removal also does not erase the setup problem. Review whether it could have affected the remaining tests. A stable grip arrangement should be demonstrated before relying on a larger run. The numbers in this example illustrate report accounting; they do not prescribe a sample size or an allowed rate of invalid tests.

Align speed and gauge length before comparing

The rate of extension is a length per time. The nominal rate of strain also depends on the starting gauge length:

Nominal strain rate per minute = extension speed / initial gauge length

For illustration, 250 mm/min over 250 mm gives 1 per minute, or 100% of the initial length per minute. At the same speed over 500 mm, the value is 0.5 per minute, or 50% per minute.

To reach 100% per minute over 500 mm would require 500 mm/min. These examples assume the moving system creates the intended specimen extension without slip. They explain the ratio; the chosen test method still controls the permitted settings.

At 250 mm/min, reaching 20 mm of extension would take 0.08 minute, or 4.8 seconds, under ideal constant-speed motion. Time to break, crosshead speed and strain rate are therefore related, but they are not interchangeable labels.

ASTM's public guidance discusses rate effects and warns that different machine principles do not always give equivalent results. Do not apply a generic correction percentage to reconcile different speeds. Align the method or establish a justified comparison for the material and conditions involved.

High-speed screening also needs its own identity. Uster Tensojet 5 data specifies a much faster tensile system and reports individual weak places and lower-tail values. It separately labels an expected traditional tensile value. A modelled comparison value should not be presented as a directly measured result from another method.

Condition the yarn for a fair comparison

ISO 139 defines textile conditioning and test atmospheres, including an alternative by agreement. Follow the atmosphere and preparation required for the selected tensile method. Record the condition actually used, including whether the specimen was wet or dry under the method's definition.

Moisture history can matter as well as the room reading. A USDA ARS study summary on cotton moisture explains that fibre moisture at a given humidity depends on the previous humidity exposure. The work concerns cotton fibres; it does not supply a universal tensile correction for all yarns.

For a supplier comparison, samples taken from different storage conditions need the agreed preparation before testing. Measuring one straight from a damp package and another after suitable conditioning introduces an avoidable difference. A room display alone does not establish that both specimens reached the required state.

Do not infer wet performance from a conditioned-dry result. Nor does a wet test automatically describe a yarn's performance after drying again. These are separate material histories. Match the test condition to the question, then label it clearly so later users do not merge unlike results.

Read the curve beyond its highest point

A force–extension curve shows how load changes as the yarn extends. Two specimens may reach the same maximum force while taking different paths to it. The area under those paths can differ, as can their behaviour at a smaller working extension.

The Tensorapid definitions include breaking work and values at selected points on the curve. These help distinguish the force at a chosen extension from the ultimate force. A yarn that reaches a high peak only after substantial stretch may not suit a process that permits little extension.

Calculate work from an invented curve

Take the following four points, with straight lines between them. Assume a 500 mm initial gauge length and choose the final point as the calculation endpoint.

The final elongation is 30 / 500 × 100 = 6%. Calculate the area of each strip using its average force multiplied by its width:

First strip = (0 + 1.2) / 2 × 10 = 6 N·mm

Second strip = (1.2 + 2.4) / 2 × 10 = 18 N·mm

Third strip = (2.4 + 3.0) / 2 × 10 = 27 N·mm

Total work = 6 + 18 + 27 = 51 N·mm = 0.051 J

Multiplying the peak force by the final extension would give 3.0 × 30 = 90 N·mm. That assumes the peak force acted throughout the movement, which this curve does not show. The area calculation preserves the changing load.

This is raw work to a specified endpoint. It is not automatically work per gram or per unit volume. State any further normalization and its mass, length or area basis. Also state the integration endpoint; stopping at the peak and continuing through later failure can give different totals.

A 2025 study of hybrid yarns by Islam and colleagues illustrates why this distinction matters. Some glass-core constructions showed staged component failure. The authors examined the load–extension curves to assess breaking energy. This bounded research example does not establish the behaviour of ordinary cotton yarn or extend ISO 2062 to excluded materials.

Look for weak specimens hidden by the mean

Imagine two small sets of five valid breaking forces. Set A is 3.0, 3.0, 3.0, 3.0 and 3.0 N. Set B is 2.2, 3.2, 3.2, 3.2 and 3.2 N.

Both total 15 N and have a mean of 3.0 N. Their minimum values are quite different. If an illustrative process concern is force below 2.5 N, B contains one such result and A contains none.

Five values are not a recommended acceptance sample. The example only shows that the mean can hide a low result. It does not establish how often either yarn would fail in a full delivery or on a machine.

Retain individual values, valid test counts and sample identities. Examine variation within packages and differences between packages. Many adjacent specimens from one package provide more information about that package; they do not replace coverage of other packages or production periods.

Be precise about uncertainty too. NIST's guidance on confidence limits for a mean treats the interval as uncertainty in the estimated mean. A 95% confidence interval for mean breaking force is not a range containing 95% of all individual yarn breaks.

Lower-tail estimates need enough relevant data and a stated method. A report cannot support an extremely rare-failure claim merely by displaying many decimal places. Use the sample design and analysis required by the decision, with statistical help where the claim is demanding.

Use a matched trial to explain a change

When strength changes after a process stage, compare linked material before and after it. Keep count, conditioning, method and mounting aligned. Spread sampling across the relevant source packages and positions so that a single package does not decide the result by chance.

Record the expected change before testing. A suspected damaged guide may affect particular positions. A count shift may change force while leaving tenacity closer to its previous value. A mounting problem may produce a distinct break location. Those explanations lead to different checks.

Preserve failures and unusual curves for review. If a test is invalid under the method, record the reason and its treatment. If it is valid but low, investigate it as material evidence. Do not keep testing until the average reaches a preferred value.

For ongoing production, comparable results can support statistical process control. Keep that process signal separate from the contractual acceptance rule. A control limit describes observed process behaviour; a buyer's limit describes the agreed requirement.

Finally, check the intended fabric or process outcome. ASTM notes that fabric strength also depends on construction and manufacturing. A stronger isolated yarn does not guarantee a stronger finished fabric, fewer machine stops or better seam performance in every application.

The report should leave a clear path back to the decision: which yarn was tested, how it was prepared, what method was used, which events were valid, and how force, count and extension produced the stated results. That makes a tensile value useful beyond the test machine.

References

• ISO 2062:2009: Single-end breaking force and elongation of yarns from packages, public scope and status.

• ISO/CD 2062: Revision project, committee-draft status.

• ASTM D2256/D2256M-21: Tensile properties of yarns by the single-strand method, public scope and significance.

• Uster Tensorapid 5 technical data, June 2022.

• ZwickRoell: Testing threads, yarns and twine.

• Uster Tensojet 5 technical data, April 2022.

• ISO 139:2005: Standard atmospheres for conditioning and testing.

• Rousselle, Thibodeaux and French, 2005: Cotton Fiber Properties and Moisture—Water of Imbibition; USDA ARS research summary.

• Islam and colleagues, 2025: Mathematical model for breaking energy of component yarns in a hybrid yarn.

• NIST Engineering Statistics Handbook: Confidence limits for the mean.