Plastic Deformation under Uniaxial Tension

G Sell Ch, Bai S L and Hiver J M (2004) Polypropylene/polyainide 6/polyethyleue-octene elastomer blends. Part 2 Volume dilatation during plastic deformation under uniaxial tension. Polymer 45 5785-5792. 

Aboulfaraj M, G Sell C, Ulrich B and Dahoun A (1995)/n situ observation of the plastic deformation of polypropylene spherulites under uniaxial tension and simple shear in the scanning electron microscope. Polymer 36 731-742. 

Dahoun A, Aboulfaraj M, G Sell C, Molinari A and Canova G R (1995) Plastic behavior and deformation textures of poly(etherether ketone) under uniaxial tension and simple shear, Polym Eng Sd 35 317-330. 

The toughness of a polymer can manifest itself in a complementary manner, in several different forms. In uniaxial tension of a smooth bar, the toughness is the plastic work required in order to fracture, per unit volume, which is given by the area under the stress-strain curve as shown in Fig. 13.1, where deformation under various strain rates e is terminated when the flow stress reaches a fracture strength fff that is flaw-sensitive but otherwise relatively insensitive to the deformation rate. 

Figure 14.5b represents the uniaxial compression test, which uses samples with cylindrical or rectangular cross section. The stress and strain are defined in an analogous way to that of the tensile test. This test overcomes the disadvantages mentioned in relation to a tensile test. The stress is compressive, and consequently there is no possibility of the brittle fracture observed in tensile deformation. Plastic yield can even be seen in thermostable materials, which, under other conditions, can be brittle. In addition, the determination of the yield stress is made under conditions of stable deformation since there is no geometrical reason for the formation of a neck such as occurs in tension. A problem that can arise in this test concerns the diameter/height ratio of the sample. If this ratio is too large friction between plates and sample will introduce a constraint, and if it is very small... 

The challenges inherent in the measurement of stress-strain response of thin film materials by means of direct tensile testing are commonly more than offset by the distinct advantage that properties characterizing deformation resistance of the material in the plastic range can be determined under isothermal conditions for a relatively simple state of stress on the specimen. However, these techniques are not readily amenable to modifications that can accommodate uniaxial compression, simple shear stress, equi-biaxial stress or states stress on the specimen. As a result, it is difficult to draw conclusions concerning the dependence of plastic response on stress path history. It is noted that results for some cyclic tension-compression experiments were reported by Hommel et al. (1999). 

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