A concise, self-contained introduction to solid polymers, the mechanics of their behavior and molecular and structural interpretations. This updated edition provides extended coverage of recent developments in rubber elasticity, relaxation transitions, non-linear viscoelastic behavior, anisotropic mechanical behavior, yield behavior of polymers, breaking phenomena, and other fields.

Mechanical properties of solid polymers

Deformation bands are the most common strain localization feature found in deformed porous sandstones and sediments, including Quaternary deposits, soft gravity slides and tectonically affected sandstones in hydrocarbon reservoirs and aquifers. They occur as various types of tabular deformation zones where grain reorganization occurs by grain sliding, rotation and/or fracture during overall dilation, shearing, and/or compaction. Deformation bands with a component of shear are most common and typically accommodate shear offsets of millimetres to centimetres. They can occur as single structures or cluster zones, and are the main deformation element of fault damage zones in porous rocks. Factors such as porosity, mineralogy, grain size and shape, lithification, state of stress and burial depth control the type of deformation band formed. Of the different types, phyllosilicate bands and most notably cataclastic deformation bands show the largest reduction in permeability, and thus have the greatest potential to influence fluid flow. Disaggregation bands, where non-cataclastic, granular flow is the dominant mechanism, show little influence on fluid flow unless assisted by chemical compaction or cementation.

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Deformation bands in sandstone: a review

A review is given of the structure of semi-crystalline polymers and the mechanisms of plastic deformation in them. High-density polyethylene (HDPE) is taken as the specific example because of the large number of detailed studies performed on this material. The early findings are also compared and contrasted with very recent detailed large-strain deformation studies and computer simulations of deformation-induced texture development in HDPE.

Structure and plastic deformation of polyethylene

Evolution of plastic anisotropy in amorphous polymers during finite straining

Recent research on the yield behaviour of polymers is reviewed. Particular attention is given to the importance of the hydrostatic component of stress, the viscoelastic nature of the yield process, and the behaviour of oriented polymers.

Review: The yield behaviour of polymers

Oriented sheets of polyethylene terephthalate have been deformed in tension and simple shear, with the primary variable as the angle between the tensile stress or the shear stress and the initial draw direction. In tension, deformation bands were observed in all cases, as has been reported previously (Brown and Ward 1968 a), and a clear yiold point was observed in all cases. The stress–strain curves for simple shear on the other hand showed very appreciable changes with the direction of the shear stress, and deformation bands were observed only in certain cases. These qualitative features are consistent with the principles proposed in the previous paper, on the basis of the tensile behaviour. An attempt is made to obtain a yield criterion which is consistent with both the tensile and shear data. It was found that neither a critical resolved shear stress criterion nor this modified by a normal stress term was adequate to explain the tensile yield data. However, a modification of the von Mises yiel...

The yield behaviour of oriented polyethylene terephthalate

Polyethylene terephthalate sheet which had been oriented by drawing was subsequently deformed in tension where the primary variable was the angle between the stress and the initial drawing direction. The beginning of yielding was marked by the formation of a narrow deformation band which had the following important characteristics: (1) the shear strain in the band was about 200%, (2) the direction of the band was nearly but definitely not parallel to the initial drawing direction and (3) the direction of optical extinction under crossed polarizers rotated from the initial drawing direction toward the axis of stress. Simple ideas of the structure of oriented polymers are used to explain the main features of the deformation behaviour, including the change in the extinction direction within the deformation band. These ideas are of a sufficiently general nature to be applicable to all oriented linear polymers.

Deformation bands in oriented polyethylene terephthalate

A study has been undertaken of the change in optical extinction direction in deformation bands produced by tensile and shear tests on oriented polyethylene terephthalate sheets The change in extinction direction has been related theoretically to the band direction, the shear strain and the normal strain Good agreement was obtained between experimental results and the prediction of this theory It can be concluded that under the conditions of initial orientation and deformation within the bands, the optical anisotropy is directly related to the strain history

Deformation bands in polyethylene terephthalate

Structural and mechanical studies have been made on low-density polyethylene sheets, in some of which mechenical twins were introduced by uniaxial plastic deformation. In Part I of the paper the results on isotropic sheets, cold-drawn to different extents (up to 150%), are discussed. Measurements on specially annealed sheets, cold-drawn to different extents (up to 150%), are presented in Part II of the paper. The effects of mechanical twinning are discussed in semi-quantitative terms, based on a distribution of twin planes and directions in the oriented sheets.

I. M. Ward

Papers

The yield behaviour of oriented polyethylene terephthalate

Deformation bands in oriented polyethylene terephthalate

Deformation bands in polyethylene terephthalate

The effect of mechanical twinning on the tensile modulus of polyethylene