Permanent deformation

Property of plastics that permits the material to undergo deformation permanently and continuously without rupture from a force that exceeds the yield value of the material. 

When most materials are bent, stretched, or compressed, they alter their molecular structure or grain orientation to accommodate the deformation permanently, but this is not so with thermoplastics. They temporarily assume the deformed shape, but they always maintain the internal stresses that want to force the material back to its original shape. 

A clot with a greater inelastic component will deform permanently with stress, while one with a greater elastic component will return to its original shape. 

Creep is the term used to describe the tendency of a material to move or to deform permanently to relieve stresses. Material deformation occurs as a result of long term exposure to levels of stress (physics) that are below the yield strength or ultimate strength of the material. Creep is more severe in materials that are subjected to heat for long periods and near melting point. Creep is often observed in glasses. Creep is a monotonically increasing function of temperature. 

The ability of a material to deform permanently without rupture under application of a load. 

Malleability The ability to deform permanently under compressive loads without... 

When the elastic limit of a metal has been exceeded, it will undergo plastic flow beginning at the yield point. It is this property of metals that is exploited for cold and hot working into desired shapes. When a metal is deformed permanently from the tension force, it exhibits a property known as ductility. By comparison, the term... 

Figure l-3a illustrates the response of an elastomer sample to the application and removal of a load at different temperatures. The sample here is assumed to be cross-1 inked, so that the polymer does not deform permanently under stress. 

Strength A measure of a material s ability to resist loads without deforming permanently. To increase strength, a material with a higher yield stress must be used. 

The four-parameter model provides a crude quahtative representation of the phenomena generally observed with viscoelastie materials instantaneous elastie strain, retarded elastic strain, viscous flow, instantaneous elastie reeovery, retarded elastie reeovery, and plastic deformation (permanent set). Also, the model parameters ean be assoeiated with various molecular mechanisms responsible for the viscoelastic behavior of linear amorphous polymers under creep conditions. The analogies to the moleeular mechanism can be made as follows. 

Plastic Deformation Permanent distortion of a metal under the action of applied stresses. 

Metallic crystalline solids such as iron, nickel, or aluminum are hard stable materials. They conduct electricity and heat. They range in density from 2 g/cc up to the most dense solids known. Objects made from metallic crystalline materials respond to forces or loads applied in an elastic manner, that is, they deform in proportion to the applied force and recover to their original dimension when the distorting force is removed. When the applied force exceeds a characteristic value, the elastic limit, the material flows and the part deforms permanently. After the deformation, however, the part still behaves elastically at loads below the elastic limit. 

A thermoplastic is a material which can be deformed permanently and repeatedly by heat and pressure. Complete recycle is often difficult because of contamination or degradation, but polyethylene terephthalate (PETP) is easily recycled, i.e. the action of heat and pressure is reversible. 

Ductility the ability to deform permanently imder tensile stress without breaking. This is a desirable property for materials used in pressure piping and vessels. 

Deformation, permanent set The deformation remaining after a specimen has been stressed a prescribed amount in tension, compression, or shear for a specified time period and released for a specified time period. 

It is not advisable to flood cool the whole length of the screw with cooling water as high melt pressures, in excess of those required to deform permanently the barrel of the extruder, can be developed. 

Plasticity is the quality of being deformed permanently by a small force. When plasticizer is added to various kinds of binder, the glass transition point and melting point of the resin falls, giving it flexibility and making it easy to shape. The following qualities are required of the plasticizers for green sheets used in LTCCs. 

When materials are strained beyond their elastic limits, they deform permanently and then fracture. The measurement of hardness is a convenient method with which to evaluate these proper-... 

A substance exhibiting rubbery behaviour may become glassy if a very high rate of deformation is imposed. This is rather difficult to demonstrate, because extremely high rates are required. On the other hand, if the rate is very low, it deforms permanently, i.e., flows. This is also difficult to demonstrate, but is observable with relatively low MW rubber. When bales of such a rubber are stuck on top of the others, the bottom bale may show a cold flow over a long period of time. 

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