An Introduction to Compression Testing

Compression testing is a technique that is used to determine how a material will react after crushed, compressed, or flattened. It identifies the behavior of the material by measuring its fundamental parameters.  This test is conducted by applying compressive pressure to a sample using platens or special fixtures on a testing machine. This technique is applied to those materials that have high compression, but their tensile strength is low.

  • Technical overview of compression testing machine: It is the most commonly used method to compress or crush the resistance of any material. In these machines, a sample is subjected to increasing compressive forces until there is failure. Calculation of the compressive strength is derived by dividing the maximum load achieved while testing the sample’s cross-sectional area. Various models of such machines with different capacities are available which are designed in such a manner that they can meet the needs of consistent, accurate, and reliable testing. These machines also test the ability of the material to recover after the execution of a specified compression force. The sample is then held for a while to measure its fundamental properties like deformation, stress, or strain.Compression testing machines can be fully or semi-automatic, hydraulic or servo controlled.
  • Fully automatic machine: Fully automatic machines have a fully automatic cycle of test. There is a closed-loop read-out unit in it. The test is completed by just pressing the start button after inserting features of samples in the machines’ system. In fully automatic machines, models a having digital control system with a button or touch screen are also available. These machines can be controlled by a computer that is directly connected to them.
  • Structure of machine:The structure of such machines includes a frame, power pack, and data acquisition control system. Frame includes a load frame, compression, limit switch, upper, and lower platens, distance pieces, loading cylindrical assembly, front, and rear protective doors. Power pack also called hydraulic power pack is responsible for supplying oil required by the load frames. There is an oil tank, oil filter, cylinder, hydraulic pump, pressure sensor, motor, delivery, and return valves in a power pack. The data acquisition control system is for processing data from load cells. They operate the machines mechanical system.

A reliable and accurate data can be given by these machines only when they are operated correctly. A sample must be tested in wet conditions in most of the cases. For correct results, parts of machines especially platens must be cleaned. The sample surface should also be clean. Sample’s alignment should be proper when it is placed for testing. While performing the examination, force must be applied without any shock and should increase at equal rates. If the sample fails, the process should be stopped by slowly releasing the pressure. In the case of an unusual result, the sample should be broken fully and then must be further tested. The machine should be selected that meet all the requirements and standards. The procedure should be followed properly for effective functioning and prompt results.

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