Impact Creep Resistance Testing Service

Impact Creep Resistance Testing Service – Accredited ISO/IEC 17025 Combined Mechanical Performance Assessment for the Croatian Market

Impact creep resistance is a critical material property that quantifies the ability of a material, component, or structure to withstand the combined effects of sudden impact (dynamic loading) and sustained static stress (creep) at elevated temperatures. This parameter is essential for ensuring the long‑term integrity and safety of products used in high‑temperature industrial applications such as gas turbines, steam turbines, boilers, pressure vessels, pipelines, automotive exhaust systems, and aerospace structures, where materials are subjected to both thermal stress and occasional mechanical shock or overload. 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 impact creep resistance is essential for product certification, supplier qualification, type testing, quality control in manufacturing, and import‑export processes. Our laboratory offers a comprehensive impact creep resistance testing service, applying standardized methods such as ASTM E292, ISO 204, ASTM E23, ISO 148‑1, ASTM D2990, and HRN EN ISO 204 to measure the combined effect of impact and creep on mechanical properties under controlled temperature and stress 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.

Materials and Components We Regularly Test

Our laboratory receives a wide variety of materials and components for impact creep resistance testing. Typical samples include:

• Metals and alloys – carbon steels, alloy steels, stainless steels, nickel‑based superalloys, titanium alloys, and aluminum alloys for high‑temperature and high‑stress applications.
• Plastics and polymers – thermoplastics (PE, PP, PVC, PA, PC) and thermosets (epoxy, phenolic) for structural and engineering applications.
• Composites and laminates – fiber‑reinforced plastics and sandwich structures for aerospace and construction.
• Ceramics and refractories – for high‑temperature and abrasive environments.
• Welded and joined assemblies – for evaluating the impact creep resistance of weld metal and heat‑affected zones.
• Prototype and new material formulations – submitted by manufacturers for validation of impact creep performance before series production.
• Field‑retrieved components – for failure analysis and remaining life assessment.

Creep Testing with Impact Overload – Simulating Real‑World Service Conditions

Creep testing with impact overload is the primary method for evaluating impact creep resistance. The test specimen is subjected to a sustained static load (creep) at a specified temperature, and at regular intervals, a controlled impact load is applied to simulate the effect of mechanical shock, vibration, or sudden overload. Our tests follow international standards and the requirements of the Croatian energy, aerospace, and industrial sectors.

• Creep‑impact test – constant load with periodic impact (ASTM E292 / ISO 204 / HRN EN ISO 204 / NTC 5800 – for metallic materials) – we mount the test specimen in a creep testing machine equipped with an impact device (a pendulum or a drop‑weight). A constant tensile load (typically 30‑50 % of the ultimate tensile strength) is applied at a specified temperature (e.g., 400 °C, 600 °C, 800 °C). At regular intervals (e.g., every 24 hours), a specified impact energy (e.g., 5 J, 10 J, 20 J) is applied to the specimen. The creep strain and the time to rupture are recorded. We report the creep strain curve, the impact energy, the number of impacts to failure, the time to rupture, and the failure mode.
• Impact creep test – constant stress with transient impact (NTC 5801 – for polymers and composites) – for polymeric materials, we apply a constant tensile stress (typically 20‑40 % of the yield strength) at a specified temperature (e.g., 40 °C, 60 °C, 80 °C) and apply a series of impact loads of a specified energy. The creep strain and the impact deformation are measured. We report the creep strain, the impact deformation, and the time to failure.
• Creep‑impact test with different impact energies (NTC 5802 – for the impact energy sensitivity) – we perform the creep‑impact test with different impact energies (e.g., 5 J, 10 J, 20 J, 50 J) to evaluate the sensitivity of the material to the impact energy. We report the number of impacts to failure and the time to rupture for each impact energy.
• Creep‑impact test at different temperatures (NTC 5803 – for the thermal effect) – we perform the creep‑impact test at different temperatures (e.g., 300 °C, 500 °C, 700 °C) to evaluate the effect of temperature on the impact creep resistance. We report the time to rupture and the number of impacts to failure at each temperature.
• Creep‑impact test with different impact frequencies (NTC 5804 – for the impact frequency sensitivity) – we perform the creep‑impact test with different impact frequencies (e.g., one impact per hour, one impact per day, or one impact per week) to evaluate the effect of the impact frequency on the material's life. We report the number of impacts to failure and the time to rupture for each frequency.

Impact Creep Testing – Sequential and Combined Loading Methods

In addition to the creep‑impact test, we also perform sequential impact‑creep tests (where the impact is applied before the creep load) and combined impact‑creep tests (where the impact and the creep load are applied simultaneously). These methods provide a more comprehensive assessment of the material's behavior under complex loading histories.

• Sequential impact‑creep test (NTC 5810 – for the pre‑impact effect) – we apply a specified impact load to the specimen (at a specified temperature) and then, without removing the specimen, we apply a constant creep load. The creep strain and the time to rupture are measured. We report the creep strain and the time to rupture after the impact.
• Combined impact‑creep test (NTC 5811 – for the simultaneous loading) – we apply a creep load and an impact load simultaneously (or with a very short time interval) to the specimen. The test is performed at a specified temperature. We report the creep strain, the total deformation, and the time to failure.
• Impact‑creep test with pre‑strain (NTC 5812 – for the pre‑deformation effect) – we pre‑strain the specimen (by a specified amount) at room temperature, and then we perform the creep‑impact test at an elevated temperature. The effect of the pre‑strain on the impact creep resistance is evaluated. We report the creep strain, the time to rupture, and the effect of the pre‑strain.
• Creep‑impact test with stress relaxation (NTC 5813 – for the stress relaxation effect) – we apply a constant strain to the specimen (at a specified temperature) and measure the stress relaxation over time. We then apply an impact load to the relaxed specimen. The effect of the stress relaxation on the impact resistance is evaluated. We report the stress relaxation curve and the impact resistance after relaxation.
• Impact‑creep test for welded joints (NTC 5814 – for the weld metal evaluation) – we perform the impact‑creep test on specimens machined from the weld metal, the heat‑affected zone, and the base metal. The impact creep resistance of the different zones is compared. We report the impact creep life for each zone and the weakest link.

Performance Evaluation – Strain Measurement, Creep Rate, and Failure Analysis

During the impact creep test, we measure the strain, the creep rate, and the deformation of the specimen to quantify the damage accumulation. We also perform a detailed failure analysis to identify the failure mechanism. Our tests follow international standards and the requirements of the Croatian automotive, aerospace, and energy sectors.

• Creep strain measurement (NTC 5820 – for the time‑dependent deformation) – we measure the creep strain (the increase in length) of the specimen at regular intervals during the test, using an extensometer (or a linear variable differential transformer – LVDT). The creep strain is plotted against the time. We report the creep strain vs. time curve, the steady‑state creep rate (in %/hour), and the total creep strain at rupture.
• Impact deformation measurement (NTC 5821 – for the impact‑induced deformation) – we measure the instantaneous deformation caused by each impact (the impact‑induced deflection). The impact deformation is plotted against the number of impacts. We report the impact deformation and the cumulative impact deformation.
• Creep rupture time and ductility measurement (NTC 5822 – for the rupture life and elongation) – we record the time to rupture (the duration of the test) and measure the total elongation at rupture (in %). The elongation is a measure of the ductility of the material under the combined loading. We report the rupture time, the total elongation, and the reduction of area.
• Fractographic analysis of the fracture surface (SEM – ASTM E1508 / NTC 5823 – for the failure mechanism identification) – we use scanning electron microscopy (SEM) to examine the fracture surface of the failed specimen. The fracture morphology (e.g., creep voids, intergranular cracking, transgranular cleavage, or ductile dimples) is identified. We report the SEM images and the failure mechanism.
• Microstructural examination (ASTM E3 / NTC 5824 – for the microstructure changes) – we examine the microstructure of the specimen before and after the test, using optical microscopy and SEM, to detect the formation of creep voids, grain boundary cavitation, or phase transformations. We report the microstructural changes and their correlation with the impact creep resistance.

Environmental and Aging Effects – Evaluating the Long‑Term Impact Creep Stability

The impact creep resistance of materials can change over time due to thermal aging, environmental exposure, and oxidation. Our environmental and aging tests evaluate the long‑term stability of the impact creep resistance, 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 impact creep resistance (ASTM D573 / ISO 188 / NTC 5830 – for the heat‑aged materials) – we age the material in an oven at a specified temperature (e.g., 600 °C, 800 °C) for a specified duration (e.g., 100, 500, or 1000 hours) and then perform the creep‑impact test. The change in the impact creep life and the creep rate is reported. We report the impact creep life after aging and the retention of the creep resistance.
• Oxidation and corrosion effect (NTC 5831 – for the corrosive environment) – we expose the material to a corrosive environment (e.g., salt spray, acidic solution, or a high‑temperature oxidizing atmosphere) and then perform the creep‑impact test. The effect of the corrosion on the impact creep resistance is reported. We report the impact creep life after the corrosion exposure.
• Humidity and moisture effect (ASTM D570 / NTC 5832 – 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 perform the creep‑impact test. The effect of the moisture on the impact creep resistance is reported. We report the impact creep life after humidity exposure and the moisture uptake.
• Thermal cycling and its effect (NTC 5833 – for the thermal fatigue) – we subject the material to repeated thermal cycles (e.g., from 20 °C to 600 °C) for a specified number of cycles and then perform the creep‑impact test. The effect of the thermal cycling on the impact creep resistance is reported. We report the impact creep life after thermal cycling and the effect.
• Chemical exposure effect (ASTM D543 / NTC 5834 – 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 perform the creep‑impact test. The effect of the chemical exposure on the impact creep resistance is reported. We report the impact creep life after chemical exposure and the compatibility.

Complementary Tests – Hardness, Tensile, and Charpy Impact for Impact Creep Correlation

To fully understand the impact creep behavior and to correlate it with the material's properties, we perform complementary tests, including hardness testing, tensile testing, and standard Charpy impact testing.

• Hardness testing (ASTM E18 / NTC 5840 – Rockwell, Brinell, or Vickers for metals) – we measure the hardness of the material (HRC, HRB, HB, or HV). The hardness is correlated with the creep resistance and the impact resistance. We report the hardness and the correlation.
• Tensile testing (ASTM E8 / ISO 6892 / NTC 5841 – for metals; ASTM D638 / ISO 527 / NTC 5842 – for plastics) – we perform a tensile test on the material to measure the yield strength, the ultimate tensile strength, the elongation, and the reduction of area. The tensile properties are correlated with the impact creep performance. We report the tensile properties and the correlation.
• Charpy impact testing (ASTM E23 / ISO 148‑1 / NTC 5843 – for the standard impact resistance) – we perform a Charpy V‑notch impact test on the material to measure the impact energy (in J) and the fracture appearance. The Charpy impact energy is correlated with the impact creep resistance. We report the Charpy impact energy and the correlation.
• Creep rupture testing (ISO 204 / NTC 5844 – for the standard creep resistance) – we perform a standard creep test (without impact) to measure the creep rupture life and the creep rate. The creep rupture life is compared with the impact creep life to determine the effect of the impact on the creep resistance. We report the creep rupture life and the comparison.
• Microstructural examination (ASTM E3 / NTC 5845 – 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 impact creep performance. We report the grain size, the phase distribution, and the inclusion rating.

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

All procedures described are within the scope of our ISO/IEC 17025 accreditation, with equipment calibrated periodically (creep test machines, impact devices, extensometers, 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, dimensions, heat treatment, and manufacturer).
• Detailed description of the test methods applied (ASTM/ISO/HRN EN/NTC standards, test conditions, temperature, stress, and impact energy).
• Numerical results: creep strain (%), steady‑state creep rate (%/hour), time to rupture (hours), number of impacts to failure, impact deformation (mm), total elongation at rupture (%), Charpy impact energy (J), hardness (HRC/HV), and property retention after aging (%).
• Graphical data: creep strain vs. time curves, impact deformation vs. number of impacts curves, and creep rate vs. stress curves.
• Comparative tables against the values specified by the client or against the limits of the relevant standards (ASTM E292, ISO 204, HRN EN ISO 204, and the requirements of the HZN, Ministarstvo gospodarstva, and Državni inspektorat).
• Photographs and micrographs (SEM) of the fracture surfaces and the microstructural changes.
• Recommendations for material selection, design optimization, and quality control measures to achieve the required impact creep resistance.
• 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 high‑temperature components. Additionally, we offer consulting services for the selection of materials with high impact creep resistance, the design of components for high‑temperature and shock‑prone applications, and the implementation of quality control programs for combined mechanical performance, contributing to the safety, reliability, and longevity of products in the diverse and growing Croatian market, from the power generation and aerospace sectors to the automotive, construction, and industrial machinery industries.