Open Access Original Research Article

A Mathematical Model for Predicting the Relaxation of Creep Strains in Materials

Marc Delphin Monsia

Physical Science International Journal, Page 107-124

To describe the time dependent response of a variety of viscoelastic materials, a one-dimensional nonlinear rheological mathematical model with constant material parameters is developed by using the stress decomposition theory. The model represents, under relaxation of stress, the time versus deformation variation as a decay Gompertz-type function, which is able to reproduce the qualitative decay sigmoid shape of the experimental creep relaxation data of a variety of materials. Numerical applications performed shown that the model is very sensitive to material parameters variation and particularly to the total deformation experienced by the material of interest under creep process. It is also found that the damping viscosity relative increase reduces significantly the magnitude of the maximum value of the rate of recovery.

Open Access Original Research Article

Dependence of Viscosity and Density of Nigerian Lophira lanceolata Oil (Ochnaceae) on Temperature

J. B. Yerima, J. S. Madugu, P. Timtere, Y. M. David

Physical Science International Journal, Page 125-132

The viscosity at constant shear rate of 30 rpm and density of Lophira lanceolata oil (LLO) were measured at different temperatures. The viscosity at constant temperature, 285 K was measured at different shear rates. The results show that viscosity decreases with both shear rate and temperature and density decreases with temperature as well as while the cubic expansivity increases with temperature. From viscosity measurements, the following parameters: molar activation energy (G = 5.1 kJ/mol), molar volume (Vm = 11.91 × 10-3 m3), intermolecular distance (ᵟ = 2.71 × 10-9 m), consistency index (k = 148.4 Pa) and power index (n = 0.9886 ± 0.0054) were determined. Our results and that from previous works show that LLO may be a non-Newtonian liquid, a good lubricant and coolant in non-vehicle engines, desirable inhibitor of corrosion, and has bio-fuel potentials.