Torsion testing service

Torsion Testing Service – Accredited ISO/IEC 17025 Mechanical Performance and Structural Integrity Assessment for the Croatian Market

Torsion testing is a critical mechanical evaluation method used to measure the response of materials, components, and assemblies to twisting forces (torque) applied about their longitudinal axis. This test determines key mechanical properties such as shear modulus, torsional yield strength, ultimate torsional strength, and angular deformation, which are essential for ensuring the reliability, safety, and performance of shafts, axles, springs, fasteners, couplings, and structural components used in automotive, aerospace, marine, construction, and industrial machinery applications. In the Croatian market, where the Hrvatski zavod za norme (HZN), the Državni inspektorat, the Ministarstvo gospodarstva i održivog razvoja, 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 torsional properties is essential for product certification, supplier qualification, type testing, quality control in manufacturing, and import-export processes. Our laboratory offers a comprehensive torsion testing service, applying standardized methods such as ASTM E143, ISO 1100, ASTM F734, ISO 6802, ASTM A938, and HRN EN ISO 1100 to measure torque, angle of twist, shear modulus, and torsional fatigue resistance 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.

Test Samples and Components We Regularly Examine

Our laboratory receives a wide variety of materials, components, and assemblies for torsion testing. Typical samples include:

• Shafts and axles – solid and hollow shafts, drive shafts, propeller shafts, and axle shafts for automotive, marine, and industrial applications.
• Torsion bars and springs – torsion bar suspensions, torsion springs, and anti-roll bars for automotive and machinery applications.
• Fasteners and threaded connections – bolts, screws, and studs subjected to torsional loads during tightening and service.
• Couplings and universal joints – for power transmission and driveline systems.
• Pipes and tubular components – for structural and fluid-carrying applications.
• Composite and plastic components – for lightweight and corrosion-resistant applications.
• Prototype and new designs – submitted by manufacturers for validation of torsional performance before series production.
• Field-retrieved components – for failure analysis and remaining life assessment.

Static Torsion Testing – Torque and Angle of Twist Measurement

Static torsion testing measures the torque applied to the specimen and the resulting angle of twist. From these measurements, we calculate the shear modulus, the torsional yield strength, and the ultimate torsional strength. Our tests follow international standards and the requirements of the Croatian automotive, aerospace, and industrial sectors.

• Static torsion test (ASTM E143 / ISO 1100 / HRN EN ISO 1100 / NTC 5800 – for metallic materials) – we mount the test specimen in a torsion testing machine (with a torque capacity of up to 50,000 N·m) and apply a static torsional load at a constant rate (e.g., 1‑5 °/min) until the specimen fails or reaches a specified angle of twist. The torque and the angle of twist are measured continuously. The shear modulus (G), the torsional yield strength (τ_y), and the ultimate torsional strength (τ_u) are calculated from the torque‑angle curve. We report the torque‑angle curve, the shear modulus (in GPa), the yield torque (in N·m), the ultimate torque (in N·m), and the failure mode.
• Static torsion test for plastics and composites (ASTM D695 / ISO 527 / NTC 5801 – for polymer materials) – we perform a torsion test on plastic and composite specimens at a lower torque range and at a slower strain rate to account for the viscoelastic behavior of the materials. We report the shear modulus, the torsional strength, and the angle of twist at failure.
• Torsion test for shafts and axles (NTC 5802 – for the component-level testing) – we test complete shafts and axles in torsion, applying the torque at one end and restraining the other end. The torque and the angle of twist are measured, and the torsional stiffness (torque per unit angle) is calculated. We report the torsional stiffness (in N·m/°), the yield torque, and the ultimate torque.
• Torsion test at different temperatures (NTC 5803 – for the thermal effect on torsion strength) – we perform the torsion test at elevated temperatures (e.g., 40 °C, 80 °C, 120 °C) or at low temperatures (e.g., -10 °C, -20 °C) using a temperature‑controlled chamber, to evaluate the effect of temperature on the torsional properties. We report the shear modulus and the torsional strength at each temperature.
• Torsion test with strain measurement (NTC 5804 – for the shear strain determination) – we attach strain gauges (or use a torsion extensometer) to the specimen to measure the shear strain directly. The shear stress‑shear strain curve is plotted. We report the shear modulus and the shear strain at yield.

Shear Modulus and Torsional Stiffness – Evaluating the Material's Resistance to Twist

The shear modulus (G) and the torsional stiffness are measures of the material's resistance to twisting. Our tests determine these parameters from the linear region of the torque‑angle curve, providing essential data for the design of shafts and torsionally loaded components.

• Shear modulus measurement (ASTM E143 / NTC 5810 – for the elastic torsional behavior) – we calculate the shear modulus (G) from the slope of the torque‑angle curve in the linear (elastic) region, using the formula G = (T × L) / (J × θ), where T is the torque, L is the gauge length, J is the polar moment of inertia, and θ is the angle of twist. We report the shear modulus (in GPa) and the linearity of the elastic region.
• Torsional stiffness measurement (NTC 5811 – for the component-level stiffness) – we calculate the torsional stiffness (K = T / θ) of the component (e.g., a shaft or an axle) from the torque‑angle curve. The stiffness is expressed in N·m/° or N·m/rad. We report the torsional stiffness and the stiffness‑torque relationship.
• Effect of geometry on torsional stiffness (NTC 5812 – for the design optimization) – we test specimens with different geometries (e.g., different diameters, lengths, or cross‑sectional shapes) to evaluate the effect of the geometry on the torsional stiffness. We report the stiffness for each geometry.
• Torsional stiffness at different temperatures (NTC 5813 – for the thermal effect) – we measure the torsional stiffness at elevated and low temperatures to evaluate the effect of temperature on the stiffness. We report the stiffness at each temperature.
• Torsional stiffness of composite and layered materials (NTC 5814 – for the anisotropic materials) – we test composite and layered materials (e.g., carbon fiber shafts, laminated torsion bars) in torsion to determine their effective shear modulus and stiffness. We report the effective shear modulus and the stiffness.

Torsional Strength and Yield Point – Evaluating the Load‑Carrying Capacity

The torsional yield strength and the ultimate torsional strength determine the maximum torque that a component can withstand before permanent deformation or fracture. Our tests measure these parameters, which are essential for the design of safe and reliable components.

• Torsional yield strength measurement (NTC 5820 – for the offset yield method) – we determine the torsional yield strength (τ_y) using the offset method (typically 0.2 % offset) on the torque‑angle curve. The yield torque is the torque at which the shear strain reaches the offset value. We report the torsional yield strength (in MPa) and the yield torque (in N·m).
• Ultimate torsional strength measurement (NTC 5821 – for the maximum torque capacity) – we determine the ultimate torsional strength (τ_u) from the maximum torque (the peak of the torque‑angle curve) before fracture. The ultimate torque is recorded. We report the ultimate torsional strength (in MPa) and the ultimate torque (in N·m).
• Torque‑angle curve and the failure mode (NTC 5822 – for the ductile and brittle behavior) – we analyze the torque‑angle curve to identify the ductile or brittle nature of the material. A ductile material exhibits a large plastic deformation region, while a brittle material fails abruptly. We report the torque‑angle curve, the type of failure (ductile or brittle), and the fracture appearance.
• Torsional strength at different temperatures (NTC 5823 – for the temperature dependence) – we measure the torsional yield strength and the ultimate torsional strength at different temperatures to evaluate the temperature dependence. We report the strengths at each temperature.
• Torsional strength after aging and environmental exposure (NTC 5824 – for the durability assessment) – we age the material (e.g., by thermal aging, UV exposure, or corrosion) and then perform the torsion test to evaluate the long‑term stability of the torsional strength. We report the torsional strength after aging and the retention of strength (in %).

Torsional Fatigue and Cyclic Loading – Evaluating the Durability under Repeated Torsion

Torsional fatigue testing evaluates the resistance of a material or component to repeated torsional loading, which is essential for shafts, springs, and components that are subject to cyclic twisting forces. Our tests determine the fatigue life and the fatigue limit under torsional loading.

• Torsional fatigue test (ASTM A938 / ISO 1350 / NTC 5830 – for metallic materials) – we apply a cyclic torsional load (sinusoidal or constant amplitude) with a specified torque amplitude and frequency (e.g., 1‑10 Hz) until the specimen fails or until a specified number of cycles (e.g., 10⁶ cycles) is reached. The S‑N curve (torque amplitude vs. cycles to failure) is constructed. We report the fatigue limit, the number of cycles to failure, and the failure mode.
• Torsional fatigue test for plastics and composites (ASTM D7791 / ISO 13003 / NTC 5831 – for polymer materials) – we perform the torsional fatigue test at a lower frequency (e.g., 1‑5 Hz) to avoid heating. We report the S‑N curve and the fatigue limit.
• Torsional fatigue at different temperatures (NTC 5832 – for the thermal effect) – we perform the torsional fatigue test at elevated temperatures (e.g., 40 °C, 60 °C) to evaluate the effect of temperature on the fatigue life. We report the fatigue life at each temperature.
• Torsional fatigue under variable amplitude loading (NTC 5833 – for spectrum loading) – we apply a variable amplitude torque sequence (based on a real‑world load spectrum) to evaluate the cumulative fatigue damage. We report the predicted service life and the Palmgren‑Miner damage sum.
• Torsional fatigue with monitoring of modulus degradation (NTC 5834 – for stiffness reduction during fatigue) – during the fatigue test, we measure the specimen's torsional stiffness at intervals to monitor the degradation of stiffness, which is an indicator of fatigue damage. We report the stiffness degradation curve.

Environmental and Aging Effects – Evaluating the Long‑Term Torsional Stability

The torsional strength and the shear modulus of materials can change over time due to thermal aging, UV exposure, humidity, and chemical attack. Our environmental and aging tests evaluate the long‑term stability of the torsional properties, ensuring the reliability of the component over its service life in the diverse Croatian climate (coastal, continental, and mountainous).

• Thermal aging and its effect on torsional 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 re‑measure the shear modulus and the torsional strength. We report the torsional properties after aging and the retention of properties (in %).
• UV and weathering effect (ASTM G154 / NTC 5841 – 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 re‑measure the torsional properties. We report the torsional properties after UV exposure and the change.
• Humidity and moisture effect (ASTM D570 / NTC 5842 – 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 re‑measure the torsional properties. We report the torsional properties after humidity exposure and the moisture uptake.
• Chemical exposure effect (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 re‑measure the torsional properties. We report the torsional properties after chemical exposure and the compatibility.
• Corrosion effect on torsional strength (NTC 5844 – for the corrosion‑exposed materials) – we expose the material to a corrosive environment (e.g., salt spray, acidic solution) and then perform the torsion test. We report the torsional strength after corrosion and the reduction in strength.

Complementary Tests – Hardness, Tensile, and Microstructure for Torsional Performance Correlation

To fully understand the torsional 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 E18 / NTC 5850 – Rockwell, Brinell, or Vickers) – we measure the hardness of the material (HRC, HRB, HB, or HV). The hardness is correlated with the torsional yield strength and the ultimate torsional strength. We report the hardness and the correlation.
• Tensile testing (ASTM E8 / ISO 6892 / NTC 5851 – for metals; ASTM D638 / ISO 527 / NTC 5852 – for plastics) – we perform a tensile test on the material to measure the yield strength, the ultimate tensile strength, and the elongation. The tensile properties are correlated with the torsional properties. We report the tensile properties and the correlation.
• Metallographic examination (ASTM E3 / NTC 5853 – for the grain size and the microstructure) – 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 torsional performance. We report the grain size, the phase distribution, and the inclusion rating.
• Chemical composition analysis (ASTM E415 / NTC 5854 – for the alloy composition) – we use X‑ray fluorescence (XRF) or optical emission spectroscopy (OES) to determine the chemical composition of the material. The composition is correlated with the torsional properties. We report the composition and the compliance with the specified grade.
• Surface roughness and defect inspection (NTC 5855 – for the surface condition) – we measure the surface roughness (Ra, Rz) of the test specimen and inspect the surface for any defects (scratches, pits, or cracks) that could affect the torsional strength. We report the roughness values and the surface condition.

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

All procedures described are within the scope of our ISO/IEC 17025 accreditation, with equipment calibrated periodically (torsion testing machines, strain gauges, extensometers, 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, heat treatment, and manufacturer).
• Detailed description of the test methods applied (ASTM/ISO/HRN EN/NTC standards, test conditions, temperature, and strain rate).
• Numerical results: shear modulus (GPa), torsional yield strength (MPa), ultimate torsional strength (MPa), yield torque (N·m), ultimate torque (N·m), torsional stiffness (N·m/°), fatigue limit (MPa), and property retention after aging (%).
• Graphical data: torque‑angle curves, shear stress‑shear strain curves, S‑N curves, and stiffness vs. temperature curves.
• Comparative tables against the values specified by the client or against the limits of the relevant standards (ASTM E143, ISO 1100, ASTM A938, HRN EN ISO 1100, and the requirements of the HZN, Ministarstvo gospodarstva, and Državni inspektorat).
• Photographs and micrographs (SEM) 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 torsional 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 shafts, axles, and torsionally loaded components. Additionally, we offer consulting services for the design of torsionally loaded structures, the selection of materials with high torsional strength, and the implementation of quality control programs for torsional 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 industrial machinery and renewable energy industries.