Compression/deflection test methods

Two techniques allow determination of the compressibility of foam. The methods are related and the application dictates which method better defines the quality of the product. For example, for furniture cushions, indentation force deflection (IFD) is a more common test technique than compression force deflection. Both methods determine the amount of force required to compress a foam to a percentage of its thickness. In the IFD test, the plunger that compresses the foam is smaller than the foam sample. This presumably correlates to a person sitting in the center of a chair cushion. 

Representative test methods of flexible foam properties, as defined by the ASTM D-3574 are density, IFD (indentation force deflection), CFD (compression force deflection), sag factor, compression set, tensile and tear strengths, elongation, resilience, dry-heat aging and steam autoclave aging. 

D638-98 Standard Test Method for Tensile Properties of Plastics D648-98c Standard Test Method for Deflection Temperature of Plastics Under Flexural Load in the Edgewise Position D695-96 Standard Test Method for Compressive Properties of Rigid Plastics... 

Tests can be carried out under constant deflection Method B according to ASTM D395 [32], ISO 815 [33], and UNI 6121 [35]. This method applies a constant compression stress to specimens having a diameter of 29 0.5 mm or 13 0.2 mm with a thickness of 12.5 0.5 mm or 6 0.2 mm. After the introduction of the specimens the apparatns is placed in a conditioning chamber for a preset time at a preset temperature. At the end of the heating period the final thickness of the specimen is measnred. 

Method A. Indentation force deflection (IFD) consists of measuring the load necessary to produce deflection (generally 25-65 percent) in the foam product. The test is carried out by pushing a flat circular indentor foot down into the foam specimen and measuring the force on the foot at various compression amounts. The test is widely used in the cushioning and bedding industry. Higher IFD values indicate a stiffer foam. 

Method D, the dynamic fatigue test for carpet cushion, was developed to evaluate the specimen by repeatedly deflecting the carpet cushion by a rubber-covered roller exerting a specified force on the test specimens. The test determines the retention of force support at 65% compression force deflection (CFD), loss of thickness, and structural breakdown as determined by visual inspection. 

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