Tensile strength and elongation testing service

Tensile Strength and Elongation Testing Service – Accredited ISO/IEC 17025 Mechanical Property Assessment for the Croatian Market

Tensile strength and elongation are fundamental mechanical properties that quantify the resistance of a material to failure under tensile (pulling) forces and its ability to deform plastically before fracture. These parameters are essential for ensuring the structural integrity, safety, and performance of materials and components used in construction, automotive, aerospace, manufacturing, medical devices, packaging, and consumer goods. 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 tensile strength and elongation is essential for product certification, supplier qualification, type testing, quality control in manufacturing, and import‑export processes. Our laboratory offers a comprehensive tensile strength and elongation testing service, applying standardized methods such as ASTM E8, ISO 6892, ASTM D638, ISO 527, ASTM D412, ISO 37, ASTM F2057, and HRN EN ISO 6892 to measure yield strength, ultimate tensile strength, elongation at break, and tensile modulus 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 Materials We Regularly Examine

Our laboratory receives a wide variety of materials and components for tensile strength and elongation testing. Typical samples include:

• Metals and alloys – steel, aluminum, copper, titanium, nickel alloys, and their various grades used in structural, automotive, and aerospace applications.
• Plastics and polymers – thermoplastics (PE, PP, PVC, ABS, PA, PC), thermosets (epoxy, polyester), and elastomers (rubber, silicone, EPDM).
• Composites and laminates – carbon fiber, glass fiber, and hybrid composites for aerospace, automotive, and construction.
• Textiles and fabrics – woven, knitted, and nonwoven textiles for technical and consumer applications.
• Films, sheets, and foils – packaging films, adhesive tapes, and metallic foils.
• Welded and joined assemblies – for evaluating the strength of welded, brazed, and adhesively bonded joints.
• Prototype and new material formulations – submitted by manufacturers for validation of tensile properties before series production.
• Field‑retrieved components – for failure analysis and remaining life assessment.

Static Tensile Testing – Standard Method for Metals and Alloys

The static tensile test for metals is the most fundamental method for determining tensile strength and elongation. A standardized specimen is pulled in tension at a controlled rate until fracture, and the force and elongation are recorded. Our procedures follow international standards and the requirements of the Croatian industrial, automotive, and construction sectors.

• Tensile test for metallic materials (ASTM E8 / ISO 6892 / HRN EN ISO 6892 / NTC 5700 – for metals and alloys) – we machine a standard tensile specimen (round or flat) from the material and mount it in a universal testing machine. The specimen is pulled at a constant strain rate (e.g., 0.015 mm/mm/min) until fracture. The load and the elongation are measured continuously. We calculate the yield strength (0.2 % offset), the ultimate tensile strength, the elongation at break (in %), and the reduction of area (in %). We report the stress‑strain curve, the yield strength (in MPa), the ultimate tensile strength (in MPa), the elongation at break (in %), and the reduction of area (in %).
• Tensile test at different temperatures (NTC 5701 – for the thermal effect on tensile properties) – we perform the tensile test at elevated temperatures (e.g., 100 °C, 200 °C, 400 °C) or at low temperatures (e.g., -10 °C, -20 °C) using a temperature‑controlled chamber. We report the tensile properties at each temperature and the temperature coefficients.
• Tensile test for welded joints (NTC 5702 – for the evaluation of weld strength) – we machine a tensile specimen that includes the welded joint and perform the tensile test to evaluate the strength of the weld metal and the heat‑affected zone. We report the tensile properties and the location of the failure (weld metal, HAZ, or base metal).
• High‑strain rate tensile test (NTC 5703 – for the dynamic tensile properties) – we perform the tensile test at a high strain rate (e.g., 0.1 s⁻¹ to 10 s⁻¹) using a servo‑hydraulic testing machine to evaluate the strain‑rate sensitivity of the material. We report the tensile properties at each strain rate.
• Tensile test after environmental exposure (NTC 5704 – for the durability assessment) – we expose the material to a corrosive environment (e.g., salt spray, acidic solution) or to thermal aging, and then we perform the tensile test. We report the tensile properties after exposure and the retention of strength (in %).

Tensile Testing for Plastics and Polymers – Standard Methods

Tensile testing for plastics and polymers is performed using dog‑bone shaped specimens, and the test is typically conducted at a slower strain rate to account for the viscoelastic behavior of the material. Our procedures follow international standards and the requirements of the Croatian plastics, packaging, and consumer goods industries.

• Tensile test for plastics (ASTM D638 / ISO 527 / HRN EN ISO 527 / NTC 5710 – for thermoplastics and thermosets) – we machine a dog‑bone specimen (Type I, II, or IV) from the plastic material and test it in tension at a constant crosshead speed (e.g., 1, 5, or 50 mm/min). The tensile strength, the yield strength, the elongation at break (in %), and the tensile modulus (in MPa) are calculated. We report the stress‑strain curve, the tensile strength (in MPa), the yield strength (in MPa), the elongation at break (in %), and the tensile modulus (in MPa).
• Tensile test for films and sheets (ASTM D882 / ISO 527-3 / NTC 5711 – for thin films and sheets) – we test strips of film or sheet (thickness < 1 mm) at a specified crosshead speed (e.g., 50 mm/min). The tensile strength, the elongation at break, and the tensile modulus are reported. We report the tensile properties and the stress‑strain curve.
• Tensile test for elastomers and rubbers (ASTM D412 / ISO 37 / NTC 5712 – for rubber and elastomeric materials) – we test dumb‑bell or ring‑shaped specimens at a constant crosshead speed (e.g., 500 mm/min). The tensile strength, the elongation at break (in %), and the modulus at 100 % and 300 % elongation are measured. We report the tensile properties and the stress‑strain curve.
• Tensile test for composites (ASTM D3039 / ISO 527-4 / NTC 5713 – for fiber‑reinforced composites) – we test rectangular specimens of fiber‑reinforced composites in the 0°, 90°, and 45° directions. The tensile strength, the tensile modulus, and the failure mode (e.g., matrix cracking, fiber breakage, or delamination) are reported. We report the tensile properties and the failure mode.
• Tensile test at different temperatures (NTC 5714 – for the thermal effect on the tensile properties) – we perform the tensile test at elevated temperatures (e.g., 40 °C, 60 °C, 80 °C) or at low temperatures (e.g., -10 °C, -20 °C) using a temperature‑controlled chamber. We report the tensile properties at each temperature and the temperature coefficients.

Elongation and Ductility Measurement – Evaluating the Material's Deformation Behavior

Elongation is a measure of the material's ductility, which is its ability to deform plastically before fracture. Our tests measure the elongation at break (the total elongation) and the uniform elongation (the elongation up to the maximum load), providing essential data for the design of components that require a certain level of ductility.

• Elongation at break measurement (NTC 5720 – for the total elongation at fracture) – we measure the elongation at break (in %) from the stress‑strain curve or by measuring the change in the gauge length of the specimen after the test. We report the elongation at break (in %) and the gauge length.
• Uniform elongation measurement (NTC 5721 – for the elongation up to the maximum load) – we measure the elongation at the point of maximum load (the onset of necking) from the stress‑strain curve. The uniform elongation (in %) is reported. We report the uniform elongation.
• Strain hardening exponent (n‑value) measurement (NTC 5722 – for the work‑hardening behavior) – we calculate the strain hardening exponent (n) from the stress‑strain curve (in the region of uniform plastic deformation). The n‑value is a measure of the material's ability to strain‑harden. We report the n‑value and the strain hardening coefficient.
• Plastic strain ratio (r‑value) measurement (NTC 5723 – for the anisotropy of the sheet metals) – we measure the plastic strain ratio (r) from the width and the thickness strains of a tensile specimen. The r‑value is a measure of the material's resistance to thinning and its formability. We report the r‑value and the plastic anisotropy.
• Elongation after environmental exposure (NTC 5724 – for the durability assessment) – we measure the elongation at break after the material has been exposed to a corrosive environment or to thermal aging. The retention of the elongation (in %) is reported. We report the elongation after exposure and the retention of ductility.

Tensile Modulus and Stiffness Measurement – Evaluating the Elastic Deformation

The tensile modulus (Young's modulus) is a measure of the material's stiffness, which is its resistance to elastic deformation. Our tests measure the tensile modulus from the initial linear portion of the stress‑strain curve, providing essential data for the design of components that require a certain level of stiffness.

• Tensile modulus measurement (NTC 5730 – for the elastic behavior) – we calculate the tensile modulus (E) from the slope of the initial linear portion of the stress‑strain curve, using an extensometer or a strain gauge to measure the strain accurately. We report the tensile modulus (in GPa or MPa) and the strain range used for the measurement.
• Secant modulus measurement (NTC 5731 – for the non‑linear materials) – for materials that do not exhibit a linear elastic region, we calculate the secant modulus (the slope of the line connecting the origin to a specified strain point, e.g., 0.2 %). We report the secant modulus and the reference strain.
• Chord modulus measurement (NTC 5732 – for the non‑linear elastic behavior) – we calculate the chord modulus (the slope of the line connecting two specified strain points, e.g., 0.1 % and 0.5 %) for materials with a non‑linear stress‑strain curve. We report the chord modulus and the strain range.
• Tensile modulus at different temperatures (NTC 5733 – for the thermal effect) – we measure the tensile modulus at elevated and low temperatures to evaluate the effect of temperature on the stiffness. We report the tensile modulus at each temperature.
• Dynamic modulus measurement (ASTM E1876 / NTC 5734 – for the non‑destructive modulus measurement) – we use the resonant frequency method to measure the dynamic modulus of elasticity (the non‑destructive method). The dynamic modulus is correlated with the static tensile modulus. We report the dynamic modulus and the comparison.

Yield Strength and Proof Stress Measurement – Evaluating the Onset of Plastic Deformation

Yield strength is the stress at which a material begins to deform plastically. Our tests measure the yield strength (the 0.2 % offset yield strength) and the proof stress (the stress at a specified strain), providing essential data for the design of components that must not undergo permanent deformation.

• 0.2 % offset yield strength measurement (ASTM E8 / ISO 6892 / NTC 5740 – for metallic materials) – we determine the 0.2 % offset yield strength from the stress‑strain curve by drawing a line parallel to the elastic portion of the curve at a strain offset of 0.2 %. The intersection of this line with the stress‑strain curve gives the yield strength. We report the yield strength (in MPa).
• Proof stress measurement (NTC 5741 – for the non‑linear materials) – for materials that do not exhibit a distinct yield point, we measure the proof stress at a specified strain (e.g., 0.5 % strain). We report the proof stress (in MPa) and the reference strain.
• Upper and lower yield point measurement (NTC 5742 – for the materials with a yield point phenomenon) – for materials that exhibit a yield point phenomenon (e.g., low‑carbon steel), we measure the upper yield point (the peak stress before the yield drop) and the lower yield point (the minimum stress during the yield drop). We report the upper and lower yield points (in MPa).
• Yield strength at different temperatures (NTC 5743 – for the thermal effect) – we measure the yield strength at elevated and low temperatures to evaluate the effect of temperature on the yield behavior. We report the yield strength at each temperature.
• Yield strength after environmental exposure (NTC 5744 – for the durability assessment) – we measure the yield strength after the material has been exposed to a corrosive environment or to thermal aging. The retention of the yield strength (in %) is reported. We report the yield strength after exposure and the retention.

Complementary Tests – Hardness, Microstructure, and Chemical Composition for Tensile Property Correlation

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

• Hardness testing (ASTM E18 / NTC 5750 – Rockwell, Brinell, or Vickers) – we measure the hardness of the material (HRC, HRB, HB, or HV). The hardness is correlated with the tensile strength (the empirical hardness‑tensile strength relationship). We report the hardness and the estimated tensile strength.
• Metallographic examination (ASTM E3 / NTC 5751 – 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 tensile properties. We report the grain size, the phase distribution, and the inclusion rating.
• Chemical composition analysis (ASTM E415 / NTC 5752 – 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 tensile properties. We report the composition and the compliance with the specified grade.
• Surface roughness and defect inspection (NTC 5753 – for the effect of the surface condition) – we measure the surface roughness (Ra, Rz) of the tensile specimen and inspect the surface for any defects (scratches, pits, or cracks) that could affect the tensile properties. We report the roughness values and the surface condition.
• Density measurement (ASTM D792 / NTC 5754 – for the material density) – we measure the density of the material (in g/cm³) using the Archimedes method. The density is correlated with the tensile properties (for composite and porous materials). We report the density.

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

All procedures described are within the scope of our ISO/IEC 17025 accreditation, with equipment calibrated periodically (universal testing machines, extensometers, strain gauges, 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: yield strength (MPa), ultimate tensile strength (MPa), elongation at break (%), tensile modulus (GPa), reduction of area (%), n‑value, r‑value, and property retention after environmental exposure (%).
• Graphical data: stress‑strain curves, yield strength vs. temperature curves, and elongation vs. temperature curves.
• Comparative tables against the values specified by the client or against the limits of the relevant standards (ASTM E8, ISO 6892, HRN EN ISO 6892, ASTM D638, ISO 527, 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 tensile properties.
• 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 metallic, polymeric, and composite materials. Additionally, we offer consulting services for the selection of materials with optimal tensile properties, the design of tension‑loaded structures, and the implementation of quality control programs for tensile performance, 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.