Breaking Force and Elongation at Break Testing: Principles, Methods, and Applications

Breaking force and elongation at break testing is a fundamental mechanical evaluation used to determine the tensile strength and stretchability of textiles, yarns, plastics, and other materials before failure occurs. This comprehensive guide explains the testing principles, applicable standards such as ISO 13934 and ASTM D5034, sample preparation, test procedures, and practical applications across quality control and product certification. Whether you are a manufacturer, buyer, or quality engineer, understanding these two critical parameters helps ensure material performance, durability, and compliance with international specifications.

Technical Overview

Breaking force (also referred to as tensile strength or maximum force) and elongation at break are two of the most widely measured mechanical properties in material testing. Breaking force is defined as the maximum tensile force a specimen can withstand before rupturing, typically expressed in newtons (N) or pounds-force (lbf). Elongation at break refers to the percentage increase in length of a specimen at the moment of rupture relative to its original gauge length, reflecting the deformability and ductility of the material.

During a tensile test, a specimen of standardized dimensions is clamped between two jaws of a universal testing machine (tensile tester). The moving jaw extends the specimen at a constant rate while the instrument continuously records the force-extension curve. From this curve, the maximum force, elongation at maximum force, breaking force, and elongation at break can be determined. The shape of the force-extension curve also reveals important information about the elastic, viscoelastic, and plastic behavior of the material.

These two parameters are closely interrelated and together characterize how a material responds to tensile loading. A material with high breaking force and low elongation is strong but rigid, while a material with lower force but high elongation offers flexibility and energy absorption. For products such as apparel, industrial fabrics, geotextiles, medical textiles, packaging films, and safety equipment, both values must meet specified requirements to guarantee performance, safety, and service life.

Testing Samples

Breaking force and elongation at break testing can be applied to a broad range of materials. Sample types commonly submitted to accredited third-party laboratories include:

Woven Fabrics

Woven fabrics are tested in both warp (lengthwise) and weft (widthwise) directions because their strength is strongly direction-dependent. Specimens are cut as rectangular strips of specified width, and raveled strip or cut strip methods may be applied depending on the fabric construction.

Knitted Fabrics

Knitted fabrics, due to their loop structure, exhibit high elongation and relatively low breaking force. Special precautions, such as wider specimens or the use of grooved jaw faces and protective liners, are often necessary to prevent jaw slippage and specimen damage.

Yarns and Threads

Single yarns, plied yarns, and sewing threads are tested using yarn grips to determine breaking force, elongation, tenacity (force per unit linear density), and breaking toughness.

Nonwoven Fabrics and Geotextiles

Nonwoven materials used in filtration, hygiene, medical, and civil engineering applications are evaluated for machine-direction and cross-direction tensile properties to verify structural integrity under load.

Plastic Films and Sheets

Packaging films, composite membranes, and plastic sheets are tested to assess tensile strength, elongation at break, and yield behavior according to relevant plastic material standards.

Elastomeric and Coated Materials

Elastic fabrics, coated fabrics, coated webbings, and rubber-like materials require extended-capacity elongation measurement and appropriate grip systems to accommodate large deformations.

Webbings, Tapes, and Straps

Narrow fabric products such as seatbelt webbing, lifting slings, hook-and-loop fasteners, and adhesive tapes are tested in full width to reflect their actual end-use loading conditions.

Testing Items

Depending on the applicable standard and customer requirements, the following parameters are typically reported:

• Breaking force (maximum force) in newtons (N) or pounds-force (lbf)
• Elongation at break (%), calculated from gauge length at rupture
• Elongation at maximum force or at specified force levels
• Breaking tenacity (cN/tex) for yarns and threads
• Breaking toughness (work of rupture) expressed in joules (J)
• Force-extension (stress-strain) curve and test plot documentation
• Directional results for machine direction (MD) and cross direction (CD)
• Statistical evaluation: mean, standard deviation, coefficient of variation
• Seam breaking force for stitched or joined specimens where required

Testing Methods

Testing is performed on constant-rate-of-extension (CRE) tensile testing machines in accordance with internationally recognized standards. The most commonly applied methods are summarized below.

Strip Method

The strip method, described in ISO 13934-1, ASTM D5035, and GB/T 3923.1, uses a rectangular specimen of full specified width clamped along its entire width in the jaws. The specimen is extended to rupture at a constant rate, and the maximum force and corresponding elongation are recorded. This method is suitable for most woven fabrics, coated fabrics, and nonwovens.

Grab Method

The grab method, specified in ISO 13934-2, ASTM D5034, and GB/T 3923.2, clamps only the central portion of a wider specimen. It evaluates the effective strength of fabric as influenced by yarn interaction and is often preferred for high-strength fabrics, fabrics where raveling is difficult, and quality control comparisons.

Yarn Tensile Testing

Single-end yarn testing is conducted according to ASTM D2256, ISO 2062, and GB/T 3916. Yarn is mounted between pneumatic or capstan grips at a pretension load, extended to break, and evaluated for breaking force, elongation, and tenacity.

Plastics Tensile Testing

Rigid and semi-rigid plastics are tested using dumbbell-shaped specimens according to ISO 527 and ASTM D638, while thin plastic films are tested according to ASTM D882. Elongation at break is measured with extensometers or crosshead displacement, depending on the material rigidity.

Test Procedure and Key Conditions

• Conditioning: specimens are conditioned in a standard atmosphere of 20 ± 2 °C and 65 ± 4% relative humidity (or 23 ± 2 °C and 50 ± 5% RH for plastics) before testing
• Gauge length: commonly 200 mm for fabrics and yarns, or 100 mm where specified; 50 mm for high-elongation materials
• Specimen width: 50 mm for the strip method; effective clamped width of 25 mm for the grab method
• Speed of extension: selected according to the expected elongation of the material, typically 20 to 500 mm/min
• Pretension: applied according to material linear density or standard requirements to remove slack without stretching
• Replicates: typically five specimens per direction, with sampling spaced across the full width of the sample and away from edges, creases, and selvedges
• Slippage and jaw breaks: results from specimens that slip in the jaws or break within 5 mm of the jaw line are rejected and retested

Calculation of Results

Elongation at break is calculated as the extension at the breaking point divided by the initial gauge length, multiplied by 100. Breaking force is read directly from the force-extension curve at rupture. The arithmetic mean of valid specimens is calculated for each direction, and results are reported with statistical measures to assess uniformity. A sufficient coefficient of variation indicates consistent material quality, while excessive scatter may signal uneven yarn tension, processing defects, or non-uniform material structure.

Applications

Breaking force and elongation at break data support a wide range of industrial and commercial purposes:

• Quality control during textile manufacturing, dyeing, and finishing to verify that processing has not degraded fabric strength
• Incoming material inspection for garment manufacturers, converters, and brand supply chains
• Product certification and compliance demonstration against national and international standards
• Comparison of alternative materials, fiber types, fabric constructions, and finishing recipes during product development
• Performance verification of safety-critical products such as seatbelts, parachutes, lifting slings, personal protective equipment, and medical textiles
• Assessment of geotextiles, filtration media, construction membranes, and reinforcement fabrics used in civil engineering
• Packaging film evaluation for form-fill-seal compatibility, drop resistance, and puncture performance
• Failure analysis and claim investigation to determine whether breakage results from material deficiency or misuse
• Research and development of high-performance fibers, technical textiles, and composite materials

FAQ

What is the difference between breaking force and tensile strength?

Breaking force is the absolute maximum force a specimen withstands, expressed in newtons. Tensile strength is the maximum stress, calculated by dividing the force by the original cross-sectional area of the specimen, expressed in megapascals (MPa) for plastics and metals or as tenacity in cN/tex for yarns. For fabrics, breaking force is the directly reported quantity.

Why do warp and weft results differ so much?

Woven fabrics are anisotropic. The warp direction usually contains higher-twist, higher-strength yarns under greater tension during weaving, while the weft direction typically shows greater elongation. Testing both directions is therefore essential for a complete evaluation.

What causes specimen slippage in the jaws, and how is it handled?

Slippage occurs with smooth, coated, or high-strength fabrics when jaw pressure is insufficient. It is mitigated by using serrated, pneumatic, or wrapped jaws, adding protective liners, and adjusting clamping pressure. Any test in which visible slippage occurs is invalid and must be repeated.

Which standard should be selected: strip method or grab method?

The choice depends on the fabric type and the specification referenced by the buyer or product standard. The strip method measures the strength of a defined width of fabric and is preferred for research and precise comparison, while the grab method is faster and better suited to fabrics that ravel easily or require routine quality control.

How many specimens should be tested?

Most standards require a minimum of five valid specimens per direction. Additional specimens may be tested when results are variable or when a specification demands higher statistical confidence.

Why is conditioning important before testing?

Moisture content significantly affects the mechanical behavior of hygroscopic fibers such as cotton, viscose, and wool. Conditioning in a standard atmosphere ensures reproducible, comparable results between laboratories and test dates.

Can elongation at break predict product durability?

Elongation at break indicates ductility and energy absorption, which correlate with resistance to tearing, puncture, and impact. However, durability also depends on cyclic fatigue behavior, creep, abrasion resistance, and environmental exposure, so elongation data should be considered alongside other performance tests.