Softening breakdown test

Softening Breakdown Test Service – Accredited ISO/IEC 17025 Thermal and Mechanical Property Assessment for the Croatian Market

The softening breakdown test is a critical thermal and mechanical evaluation method used to determine the resistance of polymeric materials, elastomers, and composites to deformation and failure under the combined effects of elevated temperature and applied load. This test measures the temperature at which a material softens to a predetermined extent (Vicat softening temperature) or the temperature at which it undergoes a specified deflection under a bending load (heat deflection temperature – HDT). These parameters are essential for ensuring the thermal stability, dimensional integrity, and performance of materials used in automotive components, electrical enclosures, piping systems, packaging, consumer goods, and structural applications. In the Croatian market, where the Hrvatski zavod za norme (HZN), the Ministarstvo gospodarstva i održivog razvoja, the Državni inspektorat, 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 softening breakdown resistance is essential for product certification, supplier qualification, type testing, quality control in manufacturing, and import-export processes. Our laboratory offers a comprehensive softening breakdown testing service, applying standardized methods such as ISO 306, ASTM D1525, ISO 75, ASTM D648, and HRN EN ISO 306 to measure Vicat softening temperature, heat deflection temperature, and the softening breakdown characteristics of materials under controlled loading and temperature 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.

Material Samples We Regularly Test

Our laboratory receives a wide variety of polymeric and composite materials for softening breakdown testing. Typical samples include:

• Thermoplastics – polyethylene (PE), polypropylene (PP), PVC, polyamide (PA), polycarbonate (PC), polymethyl methacrylate (PMMA), and acrylonitrile butadiene styrene (ABS).
• Thermosets – epoxy resins, phenolic resins, and polyester resins.
• Elastomers and rubber compounds – silicone, EPDM, and other heat‑sensitive elastomers.
• Composite materials – fiber‑reinforced plastics and laminates.
• Prototype and new material formulations – submitted by manufacturers for validation of softening breakdown temperature before series production.
• Field‑retrieved components – for failure analysis and remaining life assessment.

Vicat Softening Temperature (VST) Testing – Standard Method for Softening Point Determination

The Vicat softening temperature (VST) is the temperature at which a specified needle penetrates a material to a depth of 1 mm under a specified load. This test is widely used for quality control and material characterization of thermoplastics and is essential for evaluating the heat resistance of polymeric components. Our procedures follow international standards and the requirements of the Croatian automotive, electrical, and consumer goods sectors.

• Vicat softening temperature test (ISO 306 / ASTM D1525 / HRN EN ISO 306 / NTC 5700) – we place a test specimen (typically 10 mm × 10 mm × 3‑4 mm) in a temperature‑controlled heating bath (oil or silicone oil) and apply a specified load (10 N or 50 N) to a flat‑ended needle that rests on the specimen. The specimen is heated at a controlled rate (50 °C/h or 120 °C/h). The temperature at which the needle penetrates the specimen to a depth of 1 mm is recorded as the Vicat softening temperature (VST). We report the VST (in °C), the test load, the heating rate, and the specimen thickness.
• Vicat softening temperature at different loads (NTC 5701 – for the load sensitivity) – we perform the Vicat test at different loads (e.g., 10 N, 50 N, 100 N) to evaluate the effect of the load on the softening temperature. The VST is reported for each load. We report the VST at each load and the load‑sensitivity curve.
• Vicat softening temperature at different heating rates (NTC 5702 – for the heating rate sensitivity) – we perform the Vicat test at different heating rates (e.g., 50 °C/h, 120 °C/h, 200 °C/h) to evaluate the effect of the heating rate on the softening temperature. The VST is reported for each heating rate. We report the VST at each heating rate and the heating‑rate sensitivity.
• Vicat softening temperature after aging (NTC 5703 – for the durability assessment) – we age the material (e.g., by thermal aging, UV exposure, or humidity) and then perform the Vicat test. The change in the VST is reported. We report the VST after aging and the retention of the heat resistance.
• Vicat softening temperature on different material grades (NTC 5704 – for the comparative evaluation) – we perform the Vicat test on different grades of the same material (e.g., different molecular weights or different filler contents) to compare their heat resistance. We report the VST for each grade and the ranking.

Heat Deflection Temperature (HDT) Testing – Standard Method for Deflection Temperature

The heat deflection temperature (HDT) is the temperature at which a standardized test specimen deflects by a specified amount (typically 0.25 mm) under a specified bending load. This test is essential for evaluating the short‑term heat resistance of polymeric materials under load, and it is widely used for material selection and quality control. Our procedures follow international standards and the requirements of the Croatian construction, automotive, and industrial sectors.

• Heat deflection temperature test (ISO 75 / ASTM D648 / HRN EN ISO 75 / NTC 5710) – we place a test specimen (typically 80 mm × 10 mm × 4 mm) in a three‑point bending fixture and apply a specified bending stress (1.8 MPa, 0.45 MPa, or 8.0 MPa) to the specimen. The specimen is heated at a controlled rate (120 °C/h) in a temperature‑controlled oil bath. The temperature at which the specimen deflects by 0.25 mm is recorded as the heat deflection temperature (HDT). We report the HDT (in °C), the bending stress, the heating rate, and the specimen dimensions.
• Heat deflection temperature at different stresses (NTC 5711 – for the stress sensitivity) – we perform the HDT test at different bending stresses (e.g., 0.45 MPa, 1.8 MPa, 8.0 MPa) to evaluate the effect of the stress on the deflection temperature. The HDT is reported for each stress level. We report the HDT at each stress and the stress‑sensitivity curve.
• Heat deflection temperature after aging (NTC 5712 – for the durability assessment) – we age the material (e.g., by thermal aging, UV exposure, or humidity) and then perform the HDT test. The change in the HDT is reported. We report the HDT after aging and the retention of the heat resistance.
• Heat deflection temperature of filled and reinforced materials (NTC 5713 – for the composite materials) – we perform the HDT test on materials with different filler contents (e.g., glass‑filled, mineral‑filled) to evaluate the effect of the filler on the heat resistance. The HDT is reported for each filler content. We report the HDT as a function of the filler content.
• Heat deflection temperature and Vicat softening temperature comparison (NTC 5714 – for the method correlation) – we perform both the HDT and the Vicat tests on the same material and compare the results. The correlation between the two temperatures is established. We report the HDT, the VST, and the correlation.

Softening Breakdown Characteristics – Evaluating the Material's Behavior at Elevated Temperatures

In addition to the standard VST and HDT tests, we perform a detailed analysis of the softening breakdown behavior, including the measurement of the load‑deflection curve, the deformation under sustained load, and the visual observation of the material's failure mode. This provides a more comprehensive understanding of the material's performance at elevated temperatures.

• Load‑deflection curve at elevated temperature (NTC 5720 – for the deformation analysis) – we measure the load‑deflection curve (or the temperature‑deflection curve) during the HDT test. The curve reveals the elastic, plastic, and rupture regions. We report the load‑deflection curve and the deformation characteristics.
• Creep and stress relaxation at elevated temperature (NTC 5721 – for the long‑term deformation) – we apply a constant load (or a constant strain) to the specimen at a specified temperature (e.g., the HDT temperature) and measure the deflection (or the stress) over time. The creep and the stress relaxation are reported. We report the creep curve and the stress relaxation curve.
• Softening breakdown failure mode analysis (NTC 5722 – for the failure mechanism identification) – we examine the failed specimen (from the HDT or the Vicat test) to identify the failure mode (e.g., brittle fracture, ductile deformation, melting, or delamination). We report the failure mode and the fractographic analysis.
• Visual observation of the softening process (NTC 5723 – for the thermal degradation) – we observe the material during the heating process for any visible signs of softening, melting, or discoloration. The onset temperature of the visual changes is recorded. We report the visual observations and the onset temperature.
• Softening breakdown at different heating rates (NTC 5724 – for the kinetics analysis) – we perform the Vicat and HDT tests at different heating rates (e.g., 50 °C/h, 120 °C/h, 200 °C/h) to evaluate the kinetics of the softening process. The activation energy of the softening is calculated. We report the VST, the HDT, and the activation energy at each heating rate.

Environmental and Aging Effects – Evaluating the Long‑Term Heat Resistance

The softening breakdown temperature and the heat resistance 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 softening resistance, ensuring the reliability of the material over its service life in the diverse Croatian climate (coastal, continental, and mountainous).

• Thermal aging and its effect on softening temperature (ASTM D573 / ISO 188 / NTC 5730 – 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 VST and the HDT. The change in the softening temperature is reported. We report the VST and the HDT after aging and the retention of the heat resistance.
• UV aging and its effect on softening temperature (ASTM G154 / NTC 5731 – for the UV‑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 VST and the HDT. The change in the softening temperature is reported. We report the VST and the HDT after UV exposure and the change.
• Humidity and moisture effect (ASTM D570 / NTC 5732 – 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 VST and the HDT. The effect of the moisture on the softening temperature is reported. We report the VST and the HDT after humidity exposure and the moisture uptake.
• Chemical exposure effect (ASTM D543 / NTC 5733 – for the chemically exposed materials) – we immerse the material in various chemicals (e.g., mineral oil, acids, bases, or solvents) for a specified duration and then re‑measure the VST and the HDT. The change in the softening temperature is reported. We report the VST and the HDT after chemical exposure and the compatibility.
• Thermal cycling effect (NTC 5734 – for the thermal fatigue) – we subject the material to repeated thermal cycles (e.g., from 20 °C to 80 °C) for a specified number of cycles and then re‑measure the VST and the HDT. The change in the softening temperature is reported. We report the VST and the HDT after the thermal cycling and the effect.

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

To fully understand the softening breakdown 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 5740 – Shore A or Shore D for plastics and elastomers) – we measure the Shore A or Shore D hardness of the material at room temperature. The hardness is correlated with the softening temperature (harder materials generally have a higher VST and HDT). We report the hardness and the correlation.
• Tensile testing (ASTM D638 / ISO 527 / NTC 5741 – for the tensile strength and elongation) – we perform a tensile test on the material to measure the tensile strength (in MPa) and the elongation at break (in %). The tensile properties are correlated with the softening temperature. We report the tensile properties and the correlation.
• Density measurement (ASTM D792 / NTC 5742 – for the material density) – we measure the density (in g/cm³) of the material using the Archimedes method. The density is correlated with the softening temperature. We report the density and the correlation.
• Microstructural examination (SEM – ASTM E1508 / NTC 5743 – for the grain size and the phase distribution) – we use scanning electron microscopy (SEM) to examine the microstructure of the material (the grain size, the phase distribution, and the presence of voids or inclusions). The microstructure is correlated with the softening temperature. We report the SEM images and the microstructural observations.
• Thermogravimetric analysis (TGA) – ASTM E1131 / NTC 5744 – for the thermal stability) – we use TGA to measure the thermal stability and the decomposition temperature of the material. The decomposition temperature is correlated with the softening temperature. We report the decomposition temperature and the mass loss.

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

All procedures described are within the scope of our ISO/IEC 17025 accreditation, with equipment calibrated periodically (Vicat testers, HDT testers, universal testing machines, and environmental 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 type, manufacturer, thickness, and intended application).
• Detailed description of the test methods applied (ISO/ASTM/HRN EN/NTC standards, test conditions, load, and heating rate).
• Numerical results: Vicat softening temperature (VST, °C), heat deflection temperature (HDT, °C), load‑deflection curve, creep strain (%), stress relaxation (%), and property retention after aging (%).
• Graphical data: temperature‑deflection curves, creep curves, and stress relaxation curves.
• Comparative tables against the values specified by the client or against the limits of the relevant standards (ISO 306, ASTM D1525, ISO 75, HRN EN ISO 306, and the requirements of the HZN, Ministarstvo gospodarstva, and Državni inspektorat).
• Statement of compliance and pass/fail status.
• Photographs of the test specimens before and after the test, and the failure mode.
• Recommendations for material selection, heat resistance improvement, and quality control measures to achieve the required softening breakdown 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, and by the Carinska uprava (Croatian Customs) for tariff classification and quality verification in the import of polymeric and composite materials. Additionally, we offer consulting services for the selection of heat‑resistant materials, the design of thermally stable products, and the implementation of quality control programs for softening breakdown performance, contributing to the safety, reliability, and performance of products in the diverse and growing Croatian market, from the automotive and electrical sectors to the construction and consumer goods industries.