Plastic foams creep

Creep. The creep characteristic of plastic foams must be considered when they are used in stmctural appHcations. Creep is the change in dimensions of a material when it is maintained under a constant stress. Data on the deformation of polystyrene foam under various static loads have been compiled (158). There are two types of creep in this material short-term and long-term. Short-term creep exists in foams at all stress levels however, a threshold stress level exists below which there is no detectable long-term creep. The minimum load required to cause long-term creep in molded polystyrene foam varies with density ranging from 50 kPa (7.3 psi) for foam density 16 kg/m (1 lb /ft ) to 455 kPa (66 psi) at foam density 160 kg/m (10... 

Creep - [PLASTIC TESTING] (Vol 19) -of plastic foams [FOAMED PLASTICS] (Vol 11) -in tire cord [TIRE CORD] (Vol 24)... 

The creep characteristic of plastic foams is important in structural applications. Creep, either short-term or long-term, is the change in dimensions caused by constant stress. The deformation of polystyrene foam under various static loads... 

Compression set n. A permanent deformation remaining after release of a compressive stress. It is a property of interest in elastomers and cushioning materials, such as plastic foams. See, for example, ASTM tests D 395 and D 1565. Sometimes used to mean creep. 

It will be necessary to describe the definition and measurement of the parameters used to quantify viscoelastic effects, in the sense that elastic moduli allow one to quantify elastic effects. For example how do you design the size of a torsional shaft when the pofymer creeps for a plastic bolt after it is tightened, how do you conqwte the rate of stress deca or, for the damping of mechankal vibrations what parameters would you require to design the pofyurethane foam used to control and dampen vibrations and resonances in a hi-fi tone arm ... 

Butyl octyl phthalate (BOP), butyl decyl phthalate (BDP), and butyl benzyl phthalate (BBP) are mixed together to obtain special creep properties or to modify the processibility of PVC blends. These plasticizers have a good solvency and they are used to adjust melt viscosity and fusion time in the production of high-quality foams. 

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