Alexei Volkov
Compression testing is a controlled and measured application of compressive force to a standardized sample of material. It is used to determine a material's ability to withstand a compressive load and is essential for studying plasticity and investigating mechanisms responsible for the higher strength of materials at nanoscales. Compression testing is particularly useful for plastics, which vary from inexpensive, low-performance options to high-end engineering materials. Testing helps engineers find plastics that balance cost and capability. This is especially important in the construction industry, where plastic materials are now the second-largest market.
| Characteristics | Values |
|---|---|
| Purpose | To determine the ability of a material to withstand a compressive load |
| Application | Controlled and measured application of compressive force to a standardized sample of material |
| Sample preparation | Depends on the material type and expected properties |
| Sample shape | Cylindrical or rectangular cross-section |
| Testing machine | Universal testing machine |
| Output | Stress vs strain plot |
| Parameters | Compressive strength, modulus of elasticity, yield stress, deformation beyond yield point, compressive modulus, etc. |
| Use case | Optimizing raw material composition, ensuring structural integrity, quality control, etc. |
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What You'll Learn
To determine the mechanical properties of plastics
Compression testing is a fundamental mechanical test used to determine how a material behaves under applied crushing loads. This is done by applying compressive pressure to a test specimen, which is usually a cuboid or cylinder, using platens or specialised fixtures on a universal testing machine. The test is used to determine a material's mechanical properties, such as its elastic limit, yield point, and compressive strength.
When it comes to plastics, compression testing is used to determine the mechanical properties of the material, such as its compressive modulus and compressive yield strength. This is important for predicting how a plastic product will behave when subjected to compression during use. For example, an engineer may want to reduce the amount of plastic used in a water bottle by thinning the walls, but the bottles must still be strong enough to be stacked during transport. Compression testing can help engineers optimise the design of products like these.
The mechanical properties of plastics are extremely sensitive to temperature. Therefore, testing labs use environmental chambers to test materials at temperatures ranging from -50°C to 200°C. Dynamic mechanical analysis (DMA) is another method used to assess the thermal properties of plastics, as well as their viscoelastic properties and transition temperatures. DMA is, however, a complex method that requires a lot of work to interpret the results, so other techniques are often favoured for simple mechanical evaluations.
There are various standards that apply to the compression testing of plastics, such as ASTM D695 for rigid plastics and BS EN ISO 3386-1 for low-density polymeric materials. The standards that apply depend on the industry, with each manufacturer in the automotive industry, for example, having its own testing requirements for plastic components.
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To ensure packaging doesn't collapse under pressure
Compression testing is a controlled and measured application of compressive force to a standardised sample of material. It is used to determine a material's ability to withstand a compressive load.
In the context of plastic, compression testing is essential to ensure packaging doesn't collapse under pressure. This is especially important for manufacturers who want to ensure their products remain protected during storage and transport.
The test involves applying pressure to a standardised sample of the plastic packaging material. The deformation of the sample is then measured, and the data is used to determine the plastic's compressive strength and modulus. This information can be used to predict how the plastic will behave when subjected to compression in real-world scenarios, such as when heavy items are placed on top of it during transport or storage.
By understanding the compressive properties of the plastic, manufacturers can optimise the raw material composition, durability, and production processes. For example, if a packaging design requires a plastic that can withstand a certain amount of weight, manufacturers can use compression testing to find a plastic with the right balance between cost and capability.
Additionally, compression testing can also be used to compare the performance of different plastics. This allows manufacturers to select the most suitable plastic for their specific application, ensuring that the packaging doesn't collapse under expected pressure.
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To compare with international standards
Compression tests are performed on plastics to compare their properties with international standards. ASTM D695 is the standard for compressive testing of rigid plastics. This standard is reviewed every five years to address advancements in materials and technologies. The standard specifies the use of test specimens of a standard shape, such as a prism or a cylinder, which are conditioned to the appropriate standard before testing. The test is carried out in a controlled environment with consistent temperature and humidity. The specimens are slowly compressed between two hardened blocks until the point of fracture or distortion. This allows for the measurement of the compressive modulus and strength of the material.
ISO standards are also referenced in compression testing. ISO 604, for instance, applies to the compression testing of rigid and semirigid plastics. ISO 844, Method B, describes the direct compressive deformation measurement of the specimen, providing deformation data with reduced influence from force application effects. Other ISO standards mentioned in relation to plastic testing include ISO 178 for flexural testing and ISO 7743 for the determination of compression stress-strain properties of rubber and thermoplastic materials.
In addition to ASTM and ISO, other international standardization bodies include EN and DIN. These organizations publish mechanical testing standards for plastics, such as EN ISO 3386-1 and EN ISO 3386-2, which outline the determination of stress-strain characteristics in compression for low-density and high-density flexible cellular polymeric materials, respectively.
Compression testing is essential for ensuring compliance with international standards, maintaining product quality, and verifying the performance characteristics of plastic materials. By comparing test results with established standards, manufacturers can make informed decisions about material selection and application suitability.
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To test the elasticity of plastics
Compression testing is a standard procedure for determining the mechanical properties of plastics. It involves applying a compressive force to a plastic specimen and measuring its deformation. This deformation is typically measured using a strain gauge or a compressometer, which records the change in distance between two fixed points on the specimen. The test is performed at a slow rate of 0.05 inches per minute. While compression testing is less common than tensile and flexural testing, it is crucial for certain applications, especially in construction and packaging.
For example, when designing a plastic bag, engineers would want to test its elasticity by applying weight to see how much it stretches and whether it can bear the load without ripping. This is an important consideration for selecting the most suitable plastic for a specific application.
Additionally, compression testing can be used to study the plasticity of materials and investigate the mechanisms behind their strength at nanoscales. This is particularly relevant for nanowires used in sensors, transistors, and AFM tips, which must withstand compressive forces without buckling. By compressing the specimen along a single axis, the change in dimensions and resulting load can be recorded and analyzed.
Overall, compression testing plays a vital role in understanding the mechanical behaviour of plastics, including their elasticity, and in ensuring the optimal selection and design of plastic materials for various applications.
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To determine the compressive strength of plastics
Compression testing is a fundamental mechanical testing method used to determine a material's behaviour under applied crushing loads. It is often performed on finished products to evaluate their compressive strength.
The compressive yield limit, or yield strength, is the stress at which the material begins to deform plastically and fails to return to its original shape once the load is removed. This is determined by the amount of load required to produce a set amount of deformation, typically measured as a percentage of the specimen's original size.
Compression testing provides a quantifiable way of assessing a material's performance under compressive loads, which is crucial for quality assurance and product development. It is particularly important for plastic materials that will undergo compressive forces during their product life cycle, such as plastic pipes, water bottles, and other common, everyday items.
The results of compression tests can be influenced by factors such as strain rate and temperature, which can affect the plastic's behaviour under load and must be considered when interpreting the data.
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Frequently asked questions
A compression test is a controlled and measured application of compressive force to a standardised sample of material.
Compression testing helps determine a material’s ability to withstand a compressive load. This is important for quality control and can help engineers find plastics with the right balance between cost and capability.
The main mechanical properties determined from a compression test are the compression modulus and compression yield strength.
Compression testing is slower than tensile testing, which is always found on a material analysis data sheet. Compression testing is more commonly performed in civil engineering to check the strength of concrete columns, steel beams, flooring, and other construction materials.
