Bending degree testing service

Bending Degree Testing Service – Accredited ISO/IEC 17025 Flexural Deformation and Stiffness Assessment for the Croatian Market

Bending degree, often characterized by flexural strain, deflection, curvature, or bending stiffness, is a fundamental mechanical property that quantifies the deformation behavior of materials and components when subjected to bending or flexural loads. This parameter is essential for ensuring the structural integrity, dimensional stability, and functional performance of products used in construction, automotive, aerospace, packaging, electronics, medical devices, and consumer goods, where resistance to bending, flexibility, and springback are critical design considerations. In the Croatian market, where the Hrvatski zavod za norme (HZN), the Ministarstvo gospodarstva i održivog razvoja, the Državni inspektorat, the Ministarstvo graditeljstva i prostornoga uređenja, and the Carinska uprava enforce strict quality, safety, and performance standards aligned with EU directives and HRN EN (Croatian standards based on European norms), the accurate evaluation of bending degree is essential for product certification, supplier qualification, type testing, quality control in manufacturing, and import-export processes. Our laboratory offers a comprehensive bending degree testing service, applying standardized methods such as ASTM D790, ISO 178, ASTM E290, ISO 7438, ASTM D747, ASTM D522, ASTM E855, and HRN EN ISO 178 to measure flexural strain, deflection, bending stiffness, and springback under controlled loading conditions. All tests are performed under our ISO/IEC 17025 (CNAS) accreditation, and the resulting reports are fully accepted by Croatian authorities and notified bodies, making them indispensable for regulatory compliance, product validation, and market access in Croatia and the European Union.

Bending Test Samples and Materials We Regularly Examine

Our laboratory receives a wide variety of materials and components for bending degree testing. Typical samples include:

• Plastics and polymers – sheets, films, rods, and molded components of PE, PP, PVC, ABS, polyamide, polycarbonate, and other thermoplastics and thermosets.
• Metals and alloys – sheets, plates, bars, tubes, and profiles of steel, aluminum, copper, titanium, and their alloys.
• Composites and laminates – carbon fiber, glass fiber, and hybrid composites for aerospace, automotive, and construction applications.
• Wood and engineered wood products – timber beams, plywood, MDF, particleboard, and laminated veneer lumber.
• Paper and paperboard – for packaging, printing, and corrugated board applications.
• Textiles and flexible materials – fabrics, nonwovens, and coated textiles for technical and consumer applications.
• Prototype and new material designs – submitted by manufacturers for validation of bending behavior before series production.
• Field-retrieved components – for failure analysis and remaining life assessment.

Three‑Point and Four‑Point Bending Tests – Measuring Flexural Strain and Deflection

Three‑point and four‑point bending tests are the most common methods for measuring the bending degree of materials. These tests apply a controlled bending load to a specimen and measure the resulting deflection and strain, providing a direct measure of the material's flexural behavior. Our procedures follow international standards and the requirements of the Croatian construction, automotive, and industrial sectors.

• Three‑point bending test for flexural strain and modulus (ASTM D790 / ISO 178 / HRN EN ISO 178 / NTC 5800 – for plastics and polymers) – we place a rectangular specimen on two supports and apply a load at its center at a constant rate (e.g., 1 to 2 mm/min) until the specimen breaks or reaches a maximum deflection of 5 % of the span. The flexural strain (εf), flexural modulus (Ef), and the deflection at the maximum load are measured. We report the flexural strain (in %), the flexural modulus (in MPa), and the load‑deflection curve.
• Three‑point bending test for metals (ASTM E290 / ISO 7438 / NTC 5801 – for metallic materials) – we perform a three‑point bending test on a metal specimen (typically a bar or a plate) at a specified rate, and we measure the deflection and the bending angle. The test is performed until a specified deflection (or a specified angle) is reached, or until the specimen fractures. We report the bending angle (in °), the deflection (in mm), and the bending force (in N).
• Four‑point bending test (ASTM E855 / ISO 14125 / NTC 5802 – for composites and advanced materials) – we use a four‑point bending configuration (with two loading points) to apply a uniform bending moment over a central section of the specimen. The flexural strain and the flexural modulus are calculated from the load‑deflection data. We report the flexural strain and the flexural modulus.
• Flexural strain at break (NTC 5803 – for the maximum strain capacity) – we measure the strain at the point of fracture (or at the maximum deflection) to determine the maximum flexural strain capacity of the material. This is a critical parameter for flexible materials. We report the flexural strain at break (in %).
• Bending test at different temperatures (NTC 5804 – for the thermal effect on bending behavior) – we perform the bending test at elevated temperatures (e.g., 40 °C, 60 °C, 80 °C) or at low temperatures (e.g., -10 °C, -20 °C) to evaluate the effect of temperature on the bending degree and the flexural modulus. We report the flexural strain and the flexural modulus at each temperature.

Deflection and Bending Stiffness Measurement – Evaluating the Resistance to Deformation

Deflection is the displacement of a point on a bending specimen under load. Bending stiffness is the resistance of the specimen to bending deflection. Our tests measure the deflection and the bending stiffness under specified loads, providing essential data for the design of beams, panels, and structural components.

• Deflection measurement under a specified load (NTC 5810 – for the load‑deflection relationship) – we apply a specified load (e.g., 10 N, 100 N, or the design load) to the specimen and measure the resulting deflection at the center (or at the point of load application) using a dial gauge, an LVDT, or a laser displacement sensor. We report the deflection (in mm) at the specified load.
• Bending stiffness measurement (NTC 5811 – for the stiffness determination) – we calculate the bending stiffness (EI) from the load‑deflection curve, using the equation for the beam deflection (e.g., for a three‑point bending: EI = (P × L³) / (48 × δ), where P is the load, L is the span, and δ is the deflection). We report the bending stiffness (in N·mm²).
• Load‑deflection curve and stiffness profile (NTC 5812 – for the non‑linear behavior) – we record the complete load‑deflection curve, including the initial linear region and the non‑linear region (if any). The curve is used to identify the yield point, the maximum load, and the stiffness at different load levels. We report the load‑deflection curve and the stiffness profile.
• Effect of span length on deflection (NTC 5813 – for the geometry effect) – we perform the deflection test at different support spans (e.g., 25 mm, 50 mm, 100 mm) to evaluate the effect of the span on the measured deflection. We report the deflection at each span.
• Creep under a sustained bending load (NTC 5814 – for the time‑dependent deflection) – we apply a constant bending load (e.g., 50 % of the maximum load) to the specimen and measure the deflection over time (e.g., 1 hour, 24 hours, 100 hours). The creep deflection (the increase in deflection over time) is reported. We report the creep deflection and the creep rate.

Springback and Bend Radius Testing – Evaluating the Elastic Recovery after Bending

Springback is the elastic recovery of a material after the removal of a bending load. The bend radius is the minimum radius to which a material can be bent without fracture. These parameters are critical for the forming and shaping of sheet metals, plastics, and other materials.

• Springback measurement (ASTM E290 / NTC 5820 – for the elastic recovery after bending) – we bend a specimen to a specified angle (e.g., 90°) using a bending die, and then we release the load and measure the final angle (the springback angle). The springback is calculated as the difference between the initial bend angle and the final angle. We report the springback angle (in °) and the springback ratio.
• Minimum bend radius test (ASTM D522 / NTC 5821 – for the formability assessment) – we bend the specimen around a series of mandrels of decreasing radius until cracking occurs. The minimum bend radius (the smallest radius without cracking) is determined. We report the minimum bend radius (in mm) and the bend angle.
• Bend angle and springback under different temperatures (NTC 5822 – for the thermal effect) – we perform the springback test at elevated temperatures (e.g., 40 °C, 60 °C) to evaluate the effect of temperature on the springback. We report the springback angle at each temperature.
• Bend radius for sheet metals and strips (ASTM E290 / NTC 5823 – for the forming limit) – we test sheet metals and strips in bending to determine the bend radius and the angle of bend before fracture. We report the bend radius and the bend angle.
• Effect of the grain direction on the bend radius (NTC 5824 – for the anisotropic materials) – for materials with a pronounced grain direction (e.g., rolled sheets), we perform the bend test in the direction parallel to the grain and perpendicular to the grain. The bend radius and the springback are reported for each direction.

Flexural Fatigue and Cyclic Bending Testing – Evaluating the Resistance to Repeated Flexing

Flexural fatigue and cyclic bending testing evaluate the resistance of a material to repeated bending loads, which is essential for components that are subjected to cyclic flexing, such as springs, flexible circuits, and folding structures.

• Flexural fatigue test (ASTM D7791 / ISO 13003 / NTC 5830 – for plastics and composites) – we apply a cyclic bending load (with a constant amplitude or a variable amplitude) to the specimen at a specified frequency (e.g., 1‑5 Hz) until the specimen fails or until a specified number of cycles (e.g., 10⁶ cycles) is reached. The S‑N curve (stress vs. cycles to failure) is constructed. We report the S‑N curve and the fatigue limit.
• Cyclic bending test for flexible materials (NTC 5831 – for the fold endurance) – we subject the specimen (e.g., a film, a textile, or a paper) to repeated bending over a specified angle (e.g., ±90°) at a specified frequency (e.g., 1 Hz) for a specified number of cycles. The number of cycles to failure is recorded. We report the number of cycles to failure and the failure mode.
• Bending fatigue at different temperatures (NTC 5832 – for the thermal effect) – we perform the bending fatigue test at elevated temperatures (e.g., 40 °C, 60 °C) to evaluate the effect of temperature on the fatigue life. We report the S‑N curve at each temperature.
• Bending fatigue with crack propagation monitoring (NTC 5833 – for the damage evolution) – during the bending fatigue test, we monitor the crack initiation and propagation using an optical microscope or a video camera. The crack length vs. cycles curve is plotted. We report the crack initiation time and the crack growth rate.
• Bending fatigue under corrosive environment (NTC 5834 – for the corrosion‑fatigue assessment) – we perform the bending fatigue test in a corrosive environment (e.g., salt spray or acidic solution) to evaluate the combined effect of cyclic bending and corrosion. We report the corrosion‑fatigue life and the failure mechanism.

Environmental and Aging Effects on Bending Degree – Evaluating Long‑Term Stability

The bending degree and the bending stiffness of materials can change over time due to environmental exposure, thermal aging, moisture absorption, and UV degradation. Our environmental and aging tests evaluate the long‑term stability of the bending properties, ensuring the reliability of the product over its service life in the diverse Croatian climate (coastal, continental, and mountainous).

• Thermal aging effect on bending properties (ASTM D573 / ISO 188 / NTC 5840 – for the heat‑aged materials) – we age the material in an oven at a specified temperature (e.g., 70 °C, 100 °C) for a specified duration (e.g., 7, 14, or 28 days), and then we re‑measure the flexural strain and the flexural modulus. We report the change in the bending properties (in %) and the effect of the aging.
• Humidity and moisture effect on bending (ASTM D570 / NTC 5841 – for the moisture‑exposed materials) – we condition the material at a high‑humidity environment (e.g., 40 °C, 95 % RH) for a specified duration (e.g., 7 days), and then we re‑measure the bending properties. We report the bending properties after the humidity exposure and the moisture uptake.
• UV and weathering effect (ASTM G154 / NTC 5842 – for the outdoor‑exposed materials) – we expose the material to UV radiation (UVA‑340) and condensation cycles for a specified duration (e.g., 500 hours), and then we re‑measure the bending properties. We report the bending properties after UV exposure and the change.
• Chemical exposure effect on bending (ASTM D543 / NTC 5843 – for the chemically exposed materials) – we immerse the material in various chemicals (e.g., mineral oil, 10 % HCl, 10 % NaOH, or a solvent) for a specified duration (e.g., 7 days), and then we re‑measure the bending properties. We report the bending properties after the chemical exposure and the compatibility.
• Freeze‑thaw effect on bending (NTC 5844 – for the cold‑climate applications) – we subject the material to repeated freeze‑thaw cycles (e.g., -20 °C to +20 °C) and then we re‑measure the bending properties. We report the bending properties after the freeze‑thaw cycles and the effect.

Complementary Tests – Hardness, Tensile, and Microstructure for Bending Correlation

To fully understand the bending behavior and to correlate it with the material's properties, we perform complementary tests, including hardness testing, tensile testing, and microstructural examination.

• Hardness testing (ASTM D2240 / NTC 5850 – Shore A or Shore D for plastics; ASTM E18 / NTC 5851 – Rockwell, Brinell, or Vickers for metals) – we measure the hardness of the material. The hardness is correlated with the flexural strength and the bending stiffness. We report the hardness and the correlation.
• Tensile testing (ASTM D638 / ISO 527 / NTC 5852 – for plastics; ASTM E8 / ISO 6892 / NTC 5853 – for metals) – we perform a tensile test on the material to measure the tensile strength (in MPa), the elongation at break (in %), and the tensile modulus (in MPa). The tensile properties are correlated with the bending performance. We report the tensile properties and the correlation.
• Metallographic examination (ASTM E3 / NTC 5854 – for the grain size and the phase distribution) – we examine the microstructure of the material (the grain size, the phase distribution, and the inclusion content) using optical microscopy and SEM. The microstructure is correlated with the flexural properties. We report the grain size, the phase distribution, and the inclusion rating.
• Density measurement (ASTM D792 / NTC 5855 – for the material density) – we measure the density of the material (in g/cm³) using the Archimedes method. The density is used in the calculation of the bending stiffness. We report the density.
• FTIR spectroscopy for polymer identification (ASTM E168 / NTC 5856 – for the chemical composition) – we use FTIR spectroscopy to identify the chemical composition of the polymer material and to detect any degradation. We report the FTIR spectra and the chemical identification.

Test Report and Recognition in the Croatian Construction, Automotive, and Industrial Sector

All procedures described are within the scope of our ISO/IEC 17025 accreditation, with equipment calibrated periodically (universal testing machines, extensometers, displacement sensors, and thermal chambers) and traceability to international standards (NIST, PTB). Our test reports are issued in English (with a Croatian summary available on request) and include:

• Full identification of the test sample (material, dimensions, orientation, and conditioning history).
• Detailed description of the test methods applied (ASTM/ISO/HRN EN/NTC standards, test conditions, temperature, and test speed).
• Numerical results: flexural strain (%), flexural modulus (MPa), deflection (mm), bending stiffness (N·mm²), springback angle (°), minimum bend radius (mm), fatigue life (cycles), and property retention after aging (%).
• Graphical data: load‑deflection curves, stress‑strain curves, S‑N curves, and springback angle vs. temperature curves.
• Comparative tables against the values specified by the client or against the limits of the relevant standards (ASTM D790, ISO 178, HRN EN ISO 178, ASTM E290, and the requirements of the HZN, Ministarstvo graditeljstva, and Državni inspektorat).
• Photographs of the test specimens before and after the test, and the fracture surfaces.
• Recommendations for material selection, design optimization, and quality control measures to achieve the required bending performance.
• Expanded uncertainty (k=2) for all key measurements, calculated according to the ISO/IEC 98‑3 Guide.

These reports are fully accepted by the Hrvatski zavod za norme (HZN) for the verification of product conformity, by the Ministarstvo gospodarstva i održivog razvoja for industrial and energy compliance, by the Državni inspektorat for market surveillance, by the Ministarstvo graditeljstva i prostornoga uređenja for building materials approval, and by the Carinska uprava (Croatian Customs) for tariff classification and quality verification in the import of materials and components. Additionally, we offer consulting services for the selection of materials with optimal bending performance, the design of flexural members and structures, and the implementation of quality control programs for bending properties, contributing to the safety, reliability, and performance of products in the diverse and growing Croatian market, from the automotive and aerospace sectors to the construction, packaging, and consumer goods industries.

This service description provides a comprehensive overview of the bending degree testing capabilities offered by our ISO/IEC 17025 accredited laboratory for the Croatian market. For specific test requirements, detailed quotations, or to discuss your unique material testing needs, please contact our technical team. All testing is performed in compliance with relevant HRN EN, ISO, and ASTM standards, and reports are issued in English with Croatian summaries available upon request.