Material properties uniaxial stress-strain curve

The material properties used in the simulations pertain to a new X70/X80 steel with an acicular ferrite microstructure and a uniaxial stress-strain curve described by er, =tr0(l + / )", where ep is the plastic strain, tr0 = 595 MPa is the yield stress, e0=ff0l E the yield strain, and n = 0.059 the work hardening coefficient. The Poisson s ratio is 0.3 and Young s modulus 201.88 OPa. The system s temperature is 0 = 300 K. We assume the hydrogen lattice diffusion coefficient at this temperature to be D = 1.271x10 m2/s. The partial molar volume of hydrogen in solid solution is... 

Figure 14.8 shows stress-strain curves for polycarbonate at 77 K obtained in tension and in uniaxial compression (12), where it can be seen that the yield stress differs in these two tests. In general, for polymers the compressive yield stress is higher than the tensile yield stress, as Figure 14.8 shows for polycarbonate. Also, yield stress increases significantly with hydrostatic pressure on polymers, though the Tresca and von Mises criteria predict that the yield stress measured in uniaxial tension is the same as that measured in compression. The differences observed between the behavior of polymers in uniaxial compression and in uniaxial tension are due to the fact that these materials are mostly van der Waals solids. Therefore it is not surprising that their mechanical properties are subject to hydrostatic pressure effects. It is possible to modify the yield criteria described in the previous section to take into account the pressure dependence. Thus, Xy in Eq. (14.10) can be expressed as a function of hydrostatic pressure P as... 

Young s modulus of elasticity quantifies the elasticity of the polymer. Like tensile strength, this is highly relevant in polymer applications involving physical properties of polymers. It is defined as the ratio of the uniaxial stress over the uniaxial strain in the range of stress in which Hooke s law holds. This can be experimentally determined from the slope of a stress-strain curve created during tensile tests conducted on a sample of the material. 

Thus, the properties E and v for PVP and mannitol must be determined as well as E denotes the elastic modulus, which relates to the stress-strain curve obtained through uniaxial tensile testing [29]. As the mechanical behavior of dried mannitol is unknown, in this study, a linear stress-strain relation is assumed. If a dried particle is deformed, its deformation is assumed to be permanent. The ultimate tensile stress of the material is denoted as R. Here, is considered to be the stress at which the material (i.e., the solid layer) fails and a crack develops, independently of the type of failure. The negative ratio of the transverse to axial strain is given by Poisson s ratio, v, cf. Eq. (9.7). 

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