A breaking force test report is a formal technical document that records the maximum tensile load a specimen can withstand before fracture, together with the methods, equipment, and conditions used to obtain the result. This guide explains the structure, applicable standards, test procedures, and data interpretation of a professional breaking force test report for wires, cables, crimped terminals, yarns, films, and other products. It is written for engineers, quality managers, and procurement specialists who need to understand or verify tensile breaking force results.
Technical Overview
Breaking force, also known as pull-off force or ultimate tensile load, is the maximum force a specimen sustains during a tensile test before it ruptures. It is expressed in newtons (N) and, in many legacy reports, in kilogram-force (kgf) or pound-force (lbf), where 1 kgf equals 9.80665 N and 1 lbf equals 4.448 N. Breaking force is a raw force value, whereas tensile strength is the force normalized by the original cross-sectional area of the specimen, expressed in MPa or N/mm². A professional breaking force test report clearly distinguishes between these two quantities.
A breaking force test report typically serves three purposes. First, it verifies that a product meets the minimum force requirements defined in product standards, customer specifications, or regulatory documents. Second, it provides statistical evidence for incoming inspection, supplier qualification, and lot release decisions. Third, it documents failure analysis by describing the break location and failure mode, which helps diagnose crimping defects, material degradation, or processing anomalies. Reports issued by accredited third-party laboratories operating under ISO/IEC 17025 management systems carry additional credibility for export certification and dispute resolution.
Testing Samples
Wires and Cables
Bare and insulated conductors are tested to determine the breaking force of the conductor itself or the pull-out force between the conductor and its insulation. For cable products, IEC 60811-501 defines the tensile strength and elongation test on conductor wires, while IEC 60228 specifies conductor classes whose mechanical requirements are verified by this method. Typical specimens are straight wire sections with sufficient length for clamping, and the reported value is the maximum force at rupture of a single wire or a stranded conductor.
Crimped Terminals and Connectors
The tensile test on crimped connections, often called a pull-off or pull-out force test, evaluates the mechanical integrity of a crimp joint between a wire and a terminal. UL 486A/B and IEC 60999 series standards define minimum pull-off forces according to wire cross-section, and the test is widely used in the automotive, appliance, and aerospace wire harness industries. The specimen is a terminated wire pulled axially at a constant rate until the crimp separates or the wire breaks.
Yarns, Threads, and Fabrics
Single-end breaking force of yarns is determined according to ASTM D2256, ISO 2062, or GB/T 3923.1, using either constant-rate-of-extension or constant-force testing. Fabric breaking force is measured by the strip method in ISO 13934-1 and ASTM D5035 or by the grab method in ASTM D5034. These tests are essential for sewing thread, industrial yarn, geotextile, and apparel supply chains, and the report usually includes breaking tenacity in cN/tex alongside the force value.
Plastic Films and Flexible Packaging
Thin plastic sheeting and packaging films are tested in accordance with ASTM D882, ISO 527-3, or GB/T 1040.3 to measure breaking force, tensile strength, and elongation at break. Heat seals on pouches and bags are additionally evaluated by seal strength tests under ASTM F88. Because film results are highly sensitive to specimen width, the report must state whether tests were performed on strips, and the nominal width used for normalization.
Ropes, Cords, Cables, and Webbing
Natural and synthetic fibre ropes are tested under ISO 2307, which specifies specimen length, pretension, and the calculation of measured breaking force from the maximum force. Lifting slings, safety lanyards, seat belts, and parachute cords are governed by product-specific EN standards that require breaking force verification as part of type testing and routine factory production control.
Medical Devices
Absorbable and non-absorbable surgical sutures are tested for tensile breaking force according to the pharmacopeial method for tensile strength of sutures, with minimum forces assigned by suture size. Catheters, ligatures, and medical tubing also rely on breaking force data to demonstrate secure attachment of hubs and connectors during device validation.
Testing Items
A complete breaking force test report covers the following measured and derived parameters, depending on the applicable standard:
- Maximum breaking force in N, kgf, or lbf, including individual values for each specimen.
- Breaking strength or tensile strength in MPa, calculated from breaking force divided by original cross-sectional area.
- Elongation at break in percent, referenced to the initial gauge length.
- Breaking tenacity in cN/tex or g/den for textile yarns.
- Break location, such as mid-span, at the grip line, inside the jaw, or at the crimp joint.
- Failure mode description, for example wire fracture, crimp slippage, yarn fibrillation, or film necking.
- Statistical summary: mean value, standard deviation, coefficient of variation, and the number of valid specimens after discarding jaw breaks.
- Pass or fail judgment against the specified minimum force requirement, with the judgment basis explicitly cited.
Testing Methods
Equipment and Calibration
The core instrument is a universal testing machine or a dedicated tensile tester equipped with a calibrated load cell whose capacity matches the expected breaking force, ideally so that the break occurs between 20 percent and 80 percent of the range. Pneumatic, mechanical, capstan, or bollard grips are selected to suit wire, yarn, film, or rope specimens. The load verification system, grip alignment, and extensometer must be traceable to national or international measurement standards, and calibration status is stated in the report.
Specimen Preparation and Conditioning
Specimens are cut to the length required by the method standard, avoiding nicks, kinks, and pre-tension that could bias the result. Textile and film specimens are conditioned in a standard atmosphere of 20 ± 2 °C and 65 ± 4 percent relative humidity, as specified in ASTM D1776 or ISO 139, until moisture equilibrium is reached. The report identifies the conditioning atmosphere and duration, because humidity strongly influences the breaking force of hydrophilic fibres such as cotton, viscose, and nylon.
Test Procedure
The general procedure consists of mounting the specimen in the grips, setting the gauge length, applying any specified pretension, and extending the specimen at a constant crosshead speed until rupture. Method standards prescribe speed precisely: single-strand yarn tests under ASTM D2256 commonly use a speed selected to produce rupture within 20 ± 3 seconds, film tests under ASTM D882 use 50, 250, or 500 mm/min depending on the material, and crimp pull-off tests apply a steady separation rate of 25 to 50 mm/min until failure. Force and extension data are sampled continuously, and the peak force is captured as the breaking force.
Data Processing and Report Content
After testing, invalid results such as breaks inside the jaws or at the grip line are excluded in accordance with the standard, and at least the minimum number of valid specimens is retested if necessary. The report then presents individual values, the arithmetic mean, and the statistical spread, followed by a conformity statement against the acceptance criterion. A professional report contains sample identification and description, the client and lot information, the sampling basis, test standards cited with edition years, equipment name and calibration due date, environmental conditions, test parameters, results with units and rounding rules, photographs of typical failures where relevant, and the signatures of the operator and technical approver.
Applications
Breaking force test reports are used across a wide range of industries for design verification, production control, and certification:
- Wire and cable manufacturing, for conductor strength and terminal pull-off force acceptance.
- Wire harness and connector production, for crimp quality monitoring in automotive and appliance supply chains.
- Textile and garment production, for yarn, thread, and fabric strength grading.
- Packaging and printing, for film tensile performance and heat seal integrity.
- Marine, lifting, and fall protection equipment, for rope and webbing certification.
- Medical device manufacturing, for suture and catheter validation and lot release.
- Construction and geosynthetics, for geotextile and geogrid strength verification.
FAQ
What is the difference between breaking force and tensile strength?
Breaking force is the absolute maximum load at rupture in newtons, while tensile strength is that force divided by the original cross-sectional area, giving a stress in MPa. Wire harness and suture specifications usually quote minimum breaking force, whereas metal and plastic material standards quote tensile strength. The report must state which quantity is being judged.
How many specimens are tested for one report?
Most textile and film standards require at least five valid specimens per direction or condition, while wire pull-off tests typically require three to five terminations per wire size. If a specimen breaks inside the grips or shows an anomalous low value caused by a preparation flaw, it is discarded and an additional specimen is tested, and all exclusions are documented.
What happens if a crimped sample breaks outside the crimp?
If the wire breaks in the free span rather than pulling out of the crimp, the recorded force is the wire breaking force, and the crimp is considered mechanically stronger than the wire. Such a result is recorded as wire break with the force value, which still demonstrates compliance when the specification requires the joint to withstand a minimum force.
Why did two laboratories report different breaking forces for the same product?
Differences commonly arise from gauge length, crosshead speed, grip type, conditioning atmosphere, and specimen width, all of which influence the measured force. A credible comparison requires identical standards, identical parameters, and comparable calibration traceability, which is why the report must disclose every test condition in full.
Can a breaking force test report be used for export certification?
Yes, provided the report is issued by an accredited third-party laboratory with the relevant standard in its scope of accreditation, includes traceable sample identification, and is signed by authorized personnel. Buyers and regulators generally accept such reports for conformity demonstration, lot release, and customs inspection purposes.
