Compression testing is one of the most fundamental types of mechanical testing, alongside tensile and flexion tests. Compression tests are used to determine a material’s behavior under applied crushing loads, and are typically conducted by applying compressive pressure to a test specimen (usually of either a cuboid or cylindrical geometry) using platens or specialized fixtures on a universal testing machine. During the test, various properties of the material are calculated and plotted as a stress-strain diagram which is used to determine qualities such as elastic limit, proportional limit, yield point, yield strength, and, for some materials, compressive strength.
WHY PERFORM A COMPRESSION TEST?
Compression testing allows manufacturers to assess the integrity and safety of materials, components, and products during several phases of the manufacturing process. In order for a material to be selected for a new application or product, it needs to demonstrate the ability to withstand whatever mechanical forces it will encounter in its end-use application. The potential applications can vary from strength testing of a car windshield to endurance testing of concrete beams used in construction. Foam used in seating must be comfortable for the consumer while drug delivery devices must be easy for medical providers to deploy. Furthermore, materials and products might be exposed to mechanical forces for short or long periods of time, through cyclical or repeated use, and in a wide variety of different temperature and environmental conditions. Seating cushions are expected to last for a certain length of time, while automotive tires must maintain their elasticity in all types of weather. Materials that exhibit high tensile strength tend to (but do not always!) exhibit low compressive strength. Likewise, materials high in compressive strength tend to exhibit low tensile strength. Therefore, compression testing is often used on brittle materials such as concrete, metals, plastics, ceramics, composites, and corrugated materials like cardboard. These materials are often used in a load-bearing capacity where their integrity under compressive forces is critical.
Unlike tensile tests, which are usually conducted to determine the tensile properties of a specific material, compression tests are often performed on finished products. Common items such as tennis balls, golf balls, water bottles, protective cases, plastic pipes, and furniture are all examples of products that need to be evaluated for their compressive strength. For example, an engineer may want to conserve plastic by creating water bottles with thinner walls, but the bottles must still be strong enough to be packed in pallets and stacked on top of each other for transport. Compression testing can help the engineer fine tune the balance between product strength and material conservation.
In addition to its importance to the R&D process, compression testing is also used by quality assurance departments to ensure that batches of finished product are meeting the required specifications for compressive properties. This is important from both a safety and a business perspective, as defective products can be dangerous to the end user and can also cause significant harm to manufacturers in the form of product delays, lost revenue, and damaged reputations.
