Compressive creep test

Compressive Creep Testing Service – Comprehensive Evaluation of Time‑Dependent Deformation Under Sustained Compressive Loading

As an ISO/IEC 17025 accredited independent testing laboratory, we offer specialised compressive creep testing services to manufacturers, engineering contractors, and quality assurance teams across the construction, automotive, aerospace, polymer processing, and energy sectors. Compressive creep – the time‑dependent, permanent deformation of a material under a sustained compressive load – is a critical performance parameter for a wide range of products, including concrete, polymer foams, composites, elastomeric seals, and metal alloys operating at elevated temperatures. Accurate compressive creep data is essential for predicting long‑term dimensional stability, estimating service life, verifying design calculations, and ensuring the safety and reliability of components subjected to sustained loading. Our test protocols are performed under controlled temperature, humidity, and load conditions, and are aligned with ISO, ASTM, EN, and GB standards, including ISO 899‑1 (Plastics – Determination of creep behaviour – Part 1: Tensile creep), ASTM D2990 (Standard Test Methods for Tensile, Compressive, and Flexural Creep and Creep‑Rupture of Plastics), ISO 7850 (Cellular plastics – Determination of compressive creep), ASTM D695 (Standard Test Method for Compressive Properties of Rigid Plastics), GB/T 11546 (Plastics – Determination of creep behaviour), and GB/T 8813 (Determination of compressive properties of rigid cellular plastics). Our inspection and test reports are recognised by the National Medical Products Administration (NMPA), the State Administration for Market Regulation (SAMR), the Ministry of Industry and Information Technology (MIIT), and international certification bodies for product registration, type approval, and quality assurance.

Materials and Products We Regularly Test

Our compressive creep testing facilities accommodate a wide range of material types and finished products. Typical test articles include:

Polymers and plastics – thermoplastics (PE, PP, PVC, PA, PC, POM), thermosets (epoxy, phenolic, polyurethane), and engineering plastics
Elastomers and rubber materials – EPDM, NBR, FKM (Viton®), silicone, polyurethane, and natural rubber for seals, gaskets, and vibration mounts
Polymer foams and cellular plastics – polyurethane foam, polyethylene foam, polystyrene foam, and structural foams for cushioning, insulation, and lightweight structural applications
Concrete, mortar and cementitious materials – concrete cylinders, mortar cubes, and grouts for structural applications
Composites and fibre‑reinforced plastics – glass fibre reinforced plastics (GFRP), carbon fibre reinforced plastics (CFRP), and hybrid composites
Metals and alloys – aluminium alloys, magnesium alloys, zinc alloys, and lead‑based alloys, for applications at elevated temperatures (creep testing of metals is typically performed at high temperatures, > 0.4 Tm)
Wood and wood‑based materials – solid wood, plywood, oriented strand board (OSB), and medium density fibreboard (MDF)
Building and construction materials – insulation materials, flooring materials, and roofing membranes

Test Methods – Constant Load, Constant Stress and Incremental Loading

Constant load compressive creep test – ISO 899‑1 / ASTM D2990 / GB/T 11546 – We apply a constant compressive load (or a constant force) to a cylindrical or prismatic specimen using a creep frame or a universal testing machine. The load is maintained for a specified period (typically 1 000 hours, 10 000 hours, or until failure). The specimen deformation (strain) is measured continuously (or at specified intervals) using extensometers, LVDTs, or other displacement transducers. The creep strain is plotted against time to generate a creep curve (creep strain vs. time). The creep rate (the slope of the creep curve) and the total creep strain are calculated.
Constant stress compressive creep test – ASTM D2990 / ISO 899‑1 – In constant stress creep testing, we adjust the compressive load during the test to maintain a constant stress (force divided by the current cross‑sectional area) on the specimen. This is achieved using a lever‑arm or computer‑controlled loading system. Constant stress testing is more representative of service conditions where the stress is constant (e.g., in a building column).
Incremental compressive creep test (creep‑rupture test) – ASTM D2990 / ISO 7850 – We apply a stepwise‑increasing load to the specimen, holding each load level for a specified time (e.g., 1 hour, 24 hours) until the specimen fails (creep‑rupture). The test determines the creep‑rupture strength (the load or stress that causes failure at a specified time) and the creep‑rupture time (the time to failure at a specified load).
Compressive creep at elevated temperatures – ASTM E139 / ISO 204 – for metals and high‑temperature polymers – For materials that are used at elevated temperatures (e.g., metals in power generation, plastics in hot water systems), we perform compressive creep testing in a temperature‑controlled furnace or chamber, with the temperature maintained to ±1 °C. The test is performed at a specified temperature (e.g., 100 °C, 150 °C, 200 °C) and under a constant compressive load. The creep deformation and the creep rate are plotted as a function of temperature.
Compressive creep at reduced temperatures – for materials used in cold environments – For materials used in cold environments (e.g., arctic conditions, refrigeration systems), we perform compressive creep testing at sub‑zero temperatures (e.g., -20 °C, -40 °C) using a temperature‑controlled chamber.

Specimen Preparation and Instrumentation – Ensuring Representative Results

Specimen dimensions – ISO 899‑1 / ASTM D695 / GB/T 11546 – For polymers and plastics, we use cylindrical (12.7 mm diameter × 25.4 mm height) or prismatic (10 mm × 10 mm × 25 mm) specimens. For concrete, we use 150 mm diameter × 300 mm height cylinders (or smaller 100 mm × 200 mm cylinders). For foams, we use specimens with a height‑to‑thickness ratio of at least 2:1. The specimen dimensions are measured precisely, and the exact cross‑sectional area is calculated.
Conditioning – to achieve equilibrium moisture and temperature – ISO 291 / ASTM D618 / GB/T 2918 – Before testing, the specimens are conditioned at the specified temperature (typically 23 °C) and humidity (typically 50 % RH) for a minimum of 48 hours. The conditioning ensures that the material properties are stable at the start of the test.
Extensometer and displacement measurement – for accurate strain measurement – We use a high‑precision extensometer (axial extensometer) or LVDT (linear variable differential transformer) to measure the deformation of the specimen. The extensometer is attached to the specimen at two points (typically at the mid‑height) to measure the strain directly, eliminating the effect of end‑effects and machine compliance. The displacement measurement is accurate to ±0.001 mm.
Environmental chamber – for controlling temperature and humidity during the test – For tests at elevated or reduced temperatures, we use a computer‑controlled environmental chamber (or furnace) that maintains the temperature to ±1 °C and the humidity to ±2 % RH (for humidified tests).

Data Analysis – Determining Creep Parameters and Predicting Long‑Term Behaviour

Creep curve (strain vs. time) – the primary output of the test – The creep curve plots the compressive strain (or the percentage deformation) against time. The curve typically shows three stages:
- Primary creep (transient creep) – the strain rate decreases with time.
- Secondary creep (steady‑state creep) – the strain rate is constant (the minimum creep rate).
- Tertiary creep (accelerated creep) – the strain rate increases with time, leading to failure (creep‑rupture).
Creep strain (ε_c) and creep modulus (E_c) – quantifying the deformation – The creep strain is the total strain after a specified time under load. The creep modulus (E_c) is the ratio of the applied stress to the total strain at a specified time. It is a measure of the material's resistance to creep.
Creep rate (ε̇) – the rate of deformation during secondary creep – The creep rate (ε̇) is calculated from the slope of the creep curve during the secondary creep stage. It is a key parameter for predicting the long‑term deformation of the material. For most engineering applications, the creep rate should be less than 0.1 % per year.
Creep‑rupture time (t_r) and creep‑rupture strength (σ_r) – for assessing long‑term durability – The creep‑rupture time (t_r) is the time at which the specimen fails under the applied load. The creep‑rupture strength (σ_r) is the stress at which the specimen fails at a specified time (e.g., 100 hours, 1 000 hours, 10 000 hours). The creep‑rupture data is often plotted as a stress‑rupture curve (stress vs. time to failure), which is used for design and life estimation.
Creep recovery – for assessing the elastic and permanent deformation components – After the creep test, we release the load and measure the recovery of the specimen over time. The recovery strain is the strain that recovers (elastic and viscoelastic components), while the permanent strain is the strain that remains (plastic creep). The creep recovery provides insight into the material's viscoelastic behaviour.
Time‑temperature superposition (TTSP) – for predicting long‑term creep from short‑term tests – For polymers and other viscoelastic materials, we apply time‑temperature superposition to extrapolate the short‑term creep data (at elevated temperatures) to predict the long‑term creep behaviour (at service temperature). The data is shifted along the time axis using the Williams‑Landel‑Ferry (WLF) equation.

Regulatory Compliance and Material Characterisation – Supporting Design and Service Life Estimation

ISO 899‑1 – Plastics – Determination of creep behaviour – Part 1: Tensile creep – the international standard for creep testing of plastics (also applicable to compressive creep with appropriate modifications)
ASTM D2990 – Standard Test Methods for Tensile, Compressive, and Flexural Creep and Creep‑Rupture of Plastics – the North American standard for creep testing of plastics
ISO 7850 – Cellular plastics – Determination of compressive creep – the international standard for creep testing of cellular plastics
ASTM D695 – Standard Test Method for Compressive Properties of Rigid Plastics – for determining the compressive properties, often used as a preliminary test before creep testing
GB/T 11546 – Plastics – Determination of creep behaviour – the Chinese national standard for creep testing
GB/T 8813 – Determination of compressive properties of rigid cellular plastics – the Chinese national standard for compression testing of foams

Report Acceptance and Regulatory Recognition

All compressive creep tests are conducted under our ISO/IEC 17025 accreditation, using calibrated creep frames, extensometers, and environmental chambers, all traceable to national and international reference standards. Our final test reports include: a complete description of the test article (material, dimensions, manufacturer), the test method and conditions (temperature, load/stress, test duration), the measured parameters (creep strain, creep rate, creep modulus, creep‑rupture time), the creep curve (strain vs. time), a statistical summary (mean, standard deviation, coefficient of variation), and a clear pass/fail verdict against your specified acceptance criteria. These reports are accepted by the National Medical Products Administration (NMPA), the State Administration for Market Regulation (SAMR), the Ministry of Industry and Information Technology (MIIT), and international certification bodies for product registration, type approval, and quality assurance. Bilingual (Chinese/English) versions are available to facilitate submissions to domestic and international authorities and to support your global market access.