Repetitive bending test

Repetitive Bending Testing Service – Comprehensive Evaluation of Flexural Fatigue Resistance for Cables, Wires, Plastics, Metals and Flexible Materials

As an ISO/IEC 17025 accredited independent testing laboratory, we offer specialised repetitive bending testing services to manufacturers, engineering contractors, and quality assurance teams across the cable and wire, automotive, aerospace, construction, medical device, and flexible material sectors. Repetitive bending – the ability of a material or component to withstand repeated flexing, folding, or bending without cracking, breaking, or losing functional performance – is a critical performance parameter for products subjected to cyclic flexural stresses during service, handling, or installation. Our test protocols simulate the repeated bending stresses that occur in flexible cables, wire harnesses, polymer films, metal strips, textiles, and composite materials. All methods are aligned with ISO, ASTM, EN, and GB/T standards, including ISO 6722 (Road vehicles – 60 V and 600 V single‑core cables – Test methods), IEC 60227 (Polyvinyl chloride insulated cables), ASTM D2176 (Folding endurance of paper by the MIT tester), ISO 7854 (Rubber‑ or plastics‑coated fabrics – Determination of resistance to damage by flexing), ASTM D4300 (Flexural fatigue of plastics), ISO 148‑1 (Metallic materials – Charpy pendulum impact test), GB/T 238 (Metallic materials – Wire – Reverse bend test), and GB/T 2951.14 (Cables – Flexing test). Our inspection and test reports are recognised by the National Medical Products Administration (NMPA), the State Administration for Market Regulation (SAMR), the Ministry of Industry and Information Technology (MIIT), and international certification bodies for product registration, type approval, and quality assurance.

Materials and Products We Regularly Test

Our repetitive bending test facilities accommodate a wide range of material types and product forms. Typical test articles include:

Cables and wires – flexible cables, power cables, control cables, coaxial cables, ribbon cables, and wire harnesses
Metals and metallic strips – steel wires, aluminium strips, copper strips, spring steels, and thin metal foils
Plastics and polymer films – flexible films, thin sheets, laminates, and coated fabrics
Textiles and coated fabrics – rubber‑coated fabrics, tarpaulins, conveyor belts, and protective clothing materials
Composite materials – flexible composites, laminated composites, and fibre‑reinforced plastics
Paper and paperboard – packaging materials, folding cartons, and printing papers
Medical devices – catheter tubing, flexible endoscope components, and surgical glove materials
Automotive components – flexible hoses, bellows, and interior trim materials

Reverse Bend Test for Metallic Wires and Strips – ASTM E290 / ISO 7438 / GB/T 238

Test specimen preparation – wire or strip specimens of specified diameter or thickness – We prepare specimens of the metallic wire or strip (typically 200‑500 mm long) and mount them in a reverse bend testing machine. The specimen is bent through a 90° or 180° angle around a mandrel of a specified diameter (typically 3‑6× the wire diameter) and then bent back in the reverse direction. The process is repeated until failure (cracking or fracture). The number of reverse‑bend cycles to failure is recorded.
Test conditions – bending angle, mandrel diameter, and bend rate – standardised conditions for comparison – The bending angle is typically 90° or 180°, and the bend rate is typically 10‑60 bends per minute. The mandrel diameter is specified by the product standard or the client’s specification (e.g., for steel wires, the mandrel diameter is typically 3× the wire diameter).
Failure mode assessment – for identifying ductility and brittleness – After the test, we examine the specimen for any signs of cracking, fracture, or surface defects. The failure mode (ductile, brittle, or mixed) is recorded and correlated with the number of cycles to failure.
Temperature‑conditioned reverse bend testing – for assessing low‑temperature ductility – For materials used in cold climates, we perform the reverse bend test at sub‑zero temperatures (e.g., -20 °C, -40 °C) by conditioning the specimen and the test equipment in a temperature‑controlled chamber.

Flexing Test for Cables and Wires – ISO 6722 / IEC 60227 / GB/T 2951.14

Test setup – cable flexing apparatus with a specified bending radius and reciprocating motion – We mount the cable or wire specimen in a flexing apparatus that bends it through a specified bending radius (typically 5‑10× the cable diameter) and a specified angle (typically 90° or 180°). The specimen is moved back and forth (reciprocating motion) at a specified speed (typically 10‑30 cycles per minute).
Test conditions – bending radius, bending angle, and flexing speed – simulating service conditions – The bending radius and the bending angle are selected to simulate the service conditions of the cable (e.g., for automotive cables, the bending radius is typically 5‑10× the cable diameter, and the flexing angle is 90°). The test is continued until failure (conductor breakage, insulation cracking, or loss of electrical continuity) or until a specified number of flex cycles (typically 10 000‑100 000) is reached.
Electrical continuity monitoring – for detecting conductor breakage – We continuously monitor the electrical resistance of the cable or wire during the flexing test. A sudden increase in resistance (or an open circuit) indicates conductor breakage, and the test is terminated. The number of flex cycles at the point of failure is recorded.
Visual inspection after test – for assessing insulation and sheath damage – After the test, we inspect the cable for any damage to the insulation or the outer sheath (cracking, abrasion, or deformation). The type and extent of the damage are recorded.

MIT Folding Endurance Test for Paper, Film and Thin Sheets – ASTM D2176 / ISO 5626 / GB/T 2679.5

Test specimen preparation – narrow strips of paper, film, or thin sheet – We cut narrow strips (typically 15 mm wide × 100‑200 mm long) from the test material. The specimens are conditioned at 23 °C and 50 % RH for a minimum of 48 hours.
Folding endurance test – using a MIT folding tester – We mount the specimen in a MIT folding tester, apply a specified tension (typically 1 kgf or 9.8 N), and fold the specimen through a 135° or 180° angle at a specified speed (typically 100‑200 folds per minute). The number of double‑fold cycles to failure (fracture of the specimen) is recorded.
Test conditions – tension, folding angle, and folding speed – standardised for reproducibility – The tension, folding angle, and folding speed are specified by the standard or the client’s specification. The test is performed until failure or until a specified number of folds is reached.
Failure analysis – for assessing the causes of failure (fatigue, delamination, or surface cracking) – We examine the failed specimen under a microscope to determine the failure mechanism (fatigue cracking, delamination, or surface wear).

Flex Resistance Test for Coated Fabrics and Textiles – ISO 7854 / GB/T 12586

Test specimen preparation – rectangular specimens of coated fabric or textile – We prepare rectangular specimens (typically 100 mm × 200 mm) from the coated fabric or textile material. The specimens are conditioned at 23 °C and 50 % RH for a minimum of 24 hours.
Flex resistance test – using a flexometer (De Mattia or similar) with a specified flexing angle and rate – We mount the specimen in a flexometer that repeatedly bends it through a 90° or 180° angle at a specified rate (typically 100‑300 flexes per minute). The test is performed for a specified number of flexes (typically 100 000‑1 000 000) or until failure (cracking, delamination, or loss of coating adhesion).
Inspection and rating – for assessing crack density and severity – After the test, we inspect the specimen for any cracks, delamination, or loss of coating adhesion. The damage is rated using a standard rating scale (e.g., a 0‑5 scale, where 0 = no damage, 5 = severe damage).
Temperature‑conditioned flex resistance – for assessing low‑temperature performance – For materials used in cold climates, we perform the flex resistance test at sub‑zero temperatures (e.g., -20 °C) using a temperature‑controlled chamber.

Flexural Fatigue Test for Plastics and Composites – ASTM D7774 / ISO 178 / GB/T 14485

Test specimen preparation – rectangular or cylindrical specimens for flexural fatigue testing – We prepare rectangular or cylindrical specimens (typically 80 mm × 10 mm × 4 mm) from the test material. The specimens are conditioned at 23 °C and 50 % RH for a minimum of 48 hours.
Flexural fatigue test – applying a cyclic bending load at a specified stress amplitude and frequency – We apply a cyclic bending load (sinusoidal or other waveform) to the specimen at a specified stress amplitude (typically 20‑80 % of the static flexural strength) and a specified frequency (typically 1‑10 Hz). The test is performed until failure (fracture, excessive deflection, or loss of stiffness) or until a predetermined cycle count (typically 10⁶‑10⁷ cycles) is reached.
S‑N curve generation – for determining the fatigue life and the fatigue limit – We perform flexural fatigue tests at multiple stress amplitudes and plot the stress amplitude (S) versus the number of cycles to failure (Nf) to generate an S‑N curve. The fatigue limit (the stress amplitude that allows infinite life) is determined from the S‑N curve.
Failure analysis – for identifying the failure mode (fatigue, delamination, or creep) – We examine the fracture surface of the failed specimens under a microscope to determine the failure mechanism (fatigue cracking, delamination, or creep).

Data Analysis and Interpretation – Quantifying Bending Fatigue Resistance

Number of cycles to failure (Nf) – the primary output of the repetitive bending test – The number of cycles to failure (Nf) is the number of bending cycles (or double‑fold cycles) that the specimen can withstand before failure. A high Nf indicates good resistance to repetitive bending; a low Nf indicates poor resistance.
Stress‑life (S‑N) curve – for assessing the fatigue behaviour of materials – For flexural fatigue tests, we generate an S‑N curve (stress amplitude vs. number of cycles to failure). The S‑N curve is used to predict the service life of the component under a given service stress.
Failure mode analysis – for identifying the type of failure (fatigue, delamination, or overload) – We analyse the fracture surface to identify the failure mode (fatigue cracking, delamination, or overload). The failure mode is correlated with the test conditions and the material properties.
Statistical analysis – for batch‑to‑batch consistency and material qualification – For multiple specimens, we report the mean Nf, the standard deviation, and the coefficient of variation (CV). A CV of less than 20 % is typically considered acceptable for fatigue testing.

Regulatory Compliance and Product Certification – Supporting Industry Standards

Our repetitive bending testing services are performed in accordance with the most widely used international and national standards. The most commonly requested include:

ISO 6722 – Road vehicles – 60 V and 600 V single‑core cables – Test methods – for automotive cable flex testing
IEC 60227 – Polyvinyl chloride insulated cables – for cable flex testing
ASTM D2176 – Standard Test Method for Folding Endurance of Paper and Paperboard by the MIT Tester – for paper and paperboard
ISO 7854 – Rubber‑ or plastics‑coated fabrics – Determination of resistance to damage by flexing – for coated fabrics
ASTM D4300 – Standard Test Method for Flexural Fatigue of Plastics – for flexural fatigue of plastics
GB/T 238 – Metallic materials – Wire – Reverse bend test – the Chinese national standard for reverse bend testing of wires
GB/T 2951.14 – Common test methods for cables – Flexing test – the Chinese national standard for cable flexing
GB/T 2679.5 – Paper and board – Determination of folding endurance – MIT method – the Chinese national standard for folding endurance

Report Acceptance and Regulatory Recognition

All repetitive bending tests are conducted under our ISO/IEC 17025 accreditation, using calibrated flexing testers, folding testers, and fatigue testers, all traceable to national and international reference standards. Our final test reports include: a complete description of the test article (material, dimensions, manufacturer), the test method and conditions (bending angle, mandrel diameter, flexing rate, temperature, number of cycles), the measured parameters (number of cycles to failure, failure mode, load‑deflection curve, S‑N curve), a statistical summary (mean, standard deviation, coefficient of variation), and a clear pass/fail verdict against your specified acceptance criteria. These reports are accepted by the National Medical Products Administration (NMPA), the State Administration for Market Regulation (SAMR), the Ministry of Industry and Information Technology (MIIT), and international certification bodies for product registration, type approval, and quality assurance. Bilingual (English/Chinese) versions are available to facilitate submissions to domestic and international authorities and to support your global market access.