Flexural Creep Behaviour Testing | ISO 899-2 & ASTM D2990

Plastic and polymer components subjected to sustained bending loads can gradually deform over time, even when the applied stress is well below the material's short-term strength. This time-dependent behaviour, known as creep, can have a significant impact on the long-term dimensional stability and performance of a product.

Components such as panels, supports, housings and structural polymer parts may remain under flexural loading for months or years during service. Excessive creep can lead to permanent deflection, loss of stiffness, dimensional changes and, in severe cases, premature failure. Short-term flexural testing alone may therefore not provide enough information to predict long-term material behaviour.

Flexural creep testing to ISO 899-2 and ASTM D2990 provides valuable data on how plastics respond to sustained bending loads over time, supporting material selection, engineering design, product development and long-term performance assessment.

What Flexural Creep Behaviour Testing Involves

Flexural creep testing evaluates the time-dependent deformation of a material while it is subjected to a constant bending load or stress for a specified period.

ISO 899-2 specifies a method for determining the flexural creep behaviour of plastics using three-point loading.

ASTM D2990 covers methods for determining creep and creep-rupture behaviour of plastics under specified environmental conditions and can be used for the assessment of long-term mechanical behaviour.

In a three-point flexural creep test, a specimen is supported at two points while a controlled load is applied between the supports. The resulting deflection is measured over time while the load and environmental conditions are maintained.

Testing can be performed on materials including:

Thermoplastics

Thermosetting plastics

Engineering polymers

Reinforced plastics

Filled polymer compounds

Plastic sheets and panels

Moulded plastic materials

Polymer-based engineering materials

Materials intended for sustained flexural loading

Depending on the applicable method and test programme, testing can provide information including:

Flexural creep strain

Flexural creep modulus

Time-dependent deflection

Creep curves

Creep rate

Long-term stiffness behaviour

Comparative performance at different stress levels

Influence of temperature and environmental conditions

Creep-rupture behaviour where applicable

The resulting data provides valuable insight into how a material's flexural stiffness and dimensional stability change during prolonged loading.

Methodology

At Impact Solutions, flexural creep testing is carried out using controlled mechanical loading and measurement equipment in accordance with ISO 899-2 or the applicable requirements of ASTM D2990.

A typical testing programme includes:

Identification of the applicable test method, required stress level, test duration and environmental conditions.
Preparation of representative test specimens in accordance with the applicable standard.
Conditioning of specimens under specified environmental conditions.
Measurement of specimen dimensions prior to testing.
Positioning of the specimen on the specified supports within the flexural creep test arrangement.
Application of the specified load using a three-point loading configuration.
Maintenance of the applied load for the required test duration.
Measurement of specimen deflection at specified time intervals throughout the test.
Calculation of flexural creep strain, flexural creep modulus or other required creep properties.
Comprehensive reporting of test conditions, creep behaviour, results and relevant observations.

Where required, test programmes can incorporate multiple stress levels, temperatures or test durations to investigate their influence on long-term flexural behaviour.

Relevant Industry Applications

Flexural creep behaviour testing is widely applicable to:

Automotive components

Aerospace materials

Construction products

Plastic panels and sheets

Structural polymer components

Electrical and electronic housings

Industrial equipment

Consumer products

Engineering plastics

Reinforced polymer materials

Load-bearing supports and components

Material development

Product design and validation

Research and development

Quality assurance programmes

Benefits of Flexural Creep Behaviour Testing

Characterises long-term deformation under sustained bending loads

Determines flexural creep modulus

Measures time-dependent deflection

Supports selection of materials for long-term load-bearing applications

Enables comparison between different polymers and formulations

Evaluates changes in material stiffness over time

Assesses the influence of stress and environmental conditions

Supports engineering design and material modelling

Helps identify materials susceptible to excessive long-term deflection

Provides data for product development and technical documentation

Supports assessment of long-term polymer performance

Uses recognised ISO and ASTM test methods

Need to understand how your materials perform under sustained flexural loading?

Contact Impact Solutions to discuss three-point flexural creep testing to ISO 899-2 and ASTM D2990 and obtain reliable long-term mechanical performance data for your plastics and polymer materials.

FAQ

Q: What is flexural creep?

Flexural creep is the gradual, time-dependent deformation of a material while it is subjected to a sustained bending load. A plastic specimen can continue to deflect over time even though the applied load remains constant.

Q: What is ISO 899-2?

ISO 899-2 specifies a method for determining the flexural creep behaviour of plastics using three-point loading. The method can be used to determine properties such as flexural creep strain and flexural creep modulus over specified periods.

Q: What is ASTM D2990?

ASTM D2990 covers creep and creep-rupture testing of plastics under specified environmental conditions. It provides methods for evaluating the time-dependent mechanical behaviour of plastics subjected to sustained loading.