Direct Evidence for the Influence of Hydrostatic Pressure on Yield Behaviour

2 Direct Evidence for the Influence of Hydrostatic Pressure on Yield Behaviour 

There is a substantial inerease in the shear yield stress up to a hydrostatic pressure of about 300 MPa. After this pressure brittle failure oeeurs, unless prevented by protecting the specimens from the hydraulie fluid [36] (e.g. by eoating with a layer of solidified rubber solution). A study of polyethylene under conditions of combined pressure and tension has 

We will see that this simple form of pressure-dependent yield criterion is more satisfactory than the Coulomb criterion when a representation is developed which includes the effects of temperature and strain rate on the yield behaviour. In physical terms, the hydrostatic pressure can be seen as changing the state of the polymer by compressing the polymer significantly, unlike the situation in metals where the bulk moduli are much larger ( 100 GPa compared 

Recent studies of yield behaviour, using a variety of multi-axial stressing experiments, can all be adequately described by a generalisation of Equation (12.14), i.e. a generalised von Mises equation where r is replaced by the octahedral shear stress (see Section 12.5.1 for a fuller development). 

Finally, it can be noted that the coefficient a in Equation (12.14) depends on the temperature of measurement and increases markedly near a viscoelastic transition. Briscoe and Tabor [38] have pointed out that a is equivalent to the coefficient of friction p in sliding friction, and show that there is good numerical agreement between values of p and the values of a obtained from yield stress/pressure measurements. 

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Direct evidence for the influence of hydrostatic pressure on yield behaviour... 

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