Glassy epoxy polymers deformability

J.N. Sultan and F.J. McGarry, "Effect of Rubber Particle Size on Deformation Mechanisms in Glassy Epoxy, Polym. Eng. Sci., (1) 29 (1973). 

Sultan J N and McGarry F J (1973) Effect of rubber particle size on deformation mechanisms in glassy epoxy, Polym Eng Sci 13 29-34. 

However, experimental results do not support these expectations. Young moduli of all the polymers considered here are rather close to those of organic glasses (polymeric and non-polymeric)40,62) (see also Sect. 5) at 25 °C, E25 = 3.0-3.7 GPa. These values show that the U term, even in densely crosslinked epoxy network glasses, has an intermolecular origin and is determined by Van-der-Waals interactions. Also the deformation of H bonds and the deformation of chemical bonds and valence angles of network chains do not play any role in the elasticity of glassy networks. 

The analysis of the deformational behaviour of linear polymers allows us to understand the importance of plasticity in fracture behaviour of the glassy state. The same result is valid for the network glasses considered. Fracture processes in glassy polymers of epoxy-aromatic amines type were investigated in Refs. 87and64). The main results of the investigations can be summarized as follows ... 

Glassy polymers with highercohesiveness, like polycarbonate and cross-linked epoxies, preferentially exhibit shear yielding [7], and some materials, such as rubber-modified polypropylene, can either craze or shear yield, depending on the deformation conditions [8]. Application of a stress imparts energy to a body which... 

Tg especially wl en deformed under the influence of an overall hydrostatic compressive stress. This behaviour is illustrated in Fig. 5.37 where true stress-strain curves are given for an epoxy resin tested in uniaxial tension and compression at room temperature. The Tg of the resin is 100°C and such cross-linked polymers are found to be brittle when tested in tension at room temperature. In contrast they can show considerable ductility in compression and undergo shear yielding. Another important aspect of the deformation is that glassy polymers tend to show strain softening . The true stress drops after yield, not because of necking which cannot occur in compression, but because there is an inherent softening of the material. 

---