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Material Properties of Plastics 1.1 Formation and Structure The basic structure of plastics (or polymers) is given by macromolecule chains, formulated from monomer units by chemical reactions. Typical reactions for chain assembling are polyaddition (continuous or step wise) and condensation polymer-ization (polycondensation) [1] (Figure 1.1)..
plasticity is usually employed (see below), and use is made of special limit theorems which hold for such models. Plastic deformations are normally rate independent, that is, the stresses induced are independent of the rate of deformation (or rate of loading). This is in marked
proportionality limit, the stress is no longer linearly proportional to the strain. However, if the stress is slowly removed then the material will still return to its original state; the material behaves elastically. If the stress is above the proportionality limit, but less then
Once the elastic limit of the material is reached, Hooke’s law is no longer obeyed and the material will not return to its original shape. Hooke’s law states that F ∝ x, and this can be expressed as a formula . F = k. x, where k is the . force constant. of the material. K is a measure of stiffness, and the larger it is, the stiffer the ...
Plastic (or inelastic) means that an object deformed by an external force is permanently deformed even after the force is removed. Work done deforming the object is irreversible. All or most of work done is converted to thermal energy. e.g. wet clay, plasticine.
Stress, strain and modulus are related to each other by the following equation. The modulus or stiffness of a material can be determined when the material is loaded in different ways, such as tension, compression, shear, flexural (bending) or torsion (twisting).
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