The model underpredicts extensional viscosity when compared with experimental data for the [150 rpm, 5 min] blends, although it shows reasonable agreement with data insofar as predicting the onset of strain hardening
at higher stretch rates.
Due to continuous loading the plastic deformations of the metal increases and hence strain hardening
where [sigma] is flow stress, A is the yield stress at reference temperature and strain rate, B is the coefficient of strain hardening
, n is the exponent of strain hardening
, [epsilon] is the true strain, [??]* = [??]/[[??].sub.ref] is the dimensionless strain rate with [??] being the strain rate ([s.sup.-1]), [[??].sub.ref] the reference strain rat ([s.sup.-1]), and T* is homologous temperature, expressed as:
Li, "Introduction of strain hardening
engineered cementitious composites in design of reinforced concrete flexural members for improved durability," ACI Structural Journal, vol.
Ainsworth, "The assessment of defects in structures of strain hardening
material," Engineering Fracture Mechanics, vol.
where [[sigma].sub.s] is the Von Mises equivalent flow stress (MPa), A is the yield stress at a given reference temperature and a given reference strain rate, B is the coefficient of strain hardening
, C is the coefficient of strain rate hardening, n is the strain hardening
exponent, [[epsilon].sup.p] is the equivalent plastic strain, and [mathematical expression not reproducible] is the dimensionless strain rate with [??] being the strain rate and [[??].sub.0] the reference strain rate.
Stl_mp model does not consider a yield plate in its stress-strain curve or have a strain hardening
For a given value of 0 < n < 1, the stress-strain curve defined by (1) can result in a rapid increase in the yield stress for small strains or strain hardening
. However, it can be the opposite for values of n > 1, for which large strains produce small stress or softening.
Obtained results can contribute to analyze deformation behavior during repeated loading for several cycles and strain path changes, when twin-twin junctions can form, and they have been shown to play a crucial role in increasing strain hardening
and controlling microstructure evolution.
Calculation of the strain hardening
behaviour of steel structures based on mill tests, Journal of Constructional Steel Research 61(2): 133-150.