Simple Physically-based Model Research Articles

Prediction of flow stress characteristics of P92 steel using a simple physically-based constitutive modelling

This study reports the flow stress behavior of three P92 steels with different compositions. Uniaxial compression tests were conducted in the deformation temperature range of 575 °C to 650 °C and strain rate range of 0.001-0.5 s-1 using a Gleeble® 3500 thermo-mechanical simulator. A simple physically-based constitutive model was used to analyse the effects of deformation conditions (temperature and strain rate) on the metal flow stress behavior during the deformation process. The method accounts for the temperature dependence of Young’s modulus and the lattice self-diffusion coefficient of Fe in the ferrite. Constitutive equations describing the flow stress behavior of the three P92 steels were developed. From the results, the stress exponent n of 26.13(steel A), 21.61(steel B) and 27.55 (steel C) were obtained using the self-diffusion activation energy in the physically-based constitutive equation. From the results, the three steels had variation in the stress exponent values, which was attributed to differences in elemental content, such as chromium and tungsten. The developed constitutive equations were verified using statistical parameters: Pearson’s correlation coefficient (R) and average absolute relative errors (AARE). Statistical analysis showed that the three steels had the same R of 0.98, while AARE was: 1.68 (steel A), 1.72 (steel B), and 1.82 (steel C). The constitutive equations developed showed a good correlation between the experimental and predicted flow stress data. Hence, the method is applicable in describing flow stress behavior in the metalworking process in the industry.

A Simple Physically-Based Model for Wind-Turbine Wake Growth in a Turbulent Boundary Layer

The growth rate of wind-turbine wakes in the atmospheric boundary layer is a key parameter in analytical models used to predict wind-turbine wakes and their effects in wind farms. To date, the turbine-wake growth rate is determined empirically, owing to our limited understanding of the physical mechanisms leading to the recovery of the wakes in turbulent flows. Here, a simple physically-based model for wind-turbine wake growth is proposed based on the analogy with scalar dispersion in turbulent flows. The model is developed based on Taylor’s diffusion theory and intrinsically accounts for the effect of ambient turbulence intensity. In validations against large-eddy simulations of the wake flow of a turbine under different inflow turbulence conditions, it is found that the model yields good predictions of the growth of the turbine wakes. A slight underestimation of the wake growth rate is found only in the lowest ambient turbulence case, due to the non-negligible contribution of the turbine-induced turbulence in that case.

Prediction of the notched strength of woven-ply PolyPhenylene Sulfide thermoplastic composites at a constant high temperature by a physically-based model

A simple physically-based model – the Critical Damage Growth model – derived from fracture mechanics criteria has been applied to quasi-isotropic carbon fibers woven-ply reinforced PolyPhenylene Sulfide (PPS) laminates to predict their notched strength under constant high temperature conditions. The tested notched specimens are characterized by an elastic-brittle response resulting from transverse matrix cracking and fiber breakage near the notch tip. This model requires only, as input parameters, the unnotched strength and fracture toughness of the laminate determined from the measurements of critical strain energy release rates. The translaminar fracture toughness has been calculated by means of the compliance method applied to quasi-isotropic Single-Edge Notch specimens with different initial crack lengths. For various hole diameters, the capabilities of the Critical Damage Growth model are very good to predict the notched strength of quasi-isotropic C/PPS laminates tested at a temperature higher than glass transition temperature when PPS matrix ductility and toughness are exacerbated.

On the effect of pre-recovery on subsequent recrystallization

Abstract The effect of low temperature recovery treatments on recrystallization kinetics during subsequent annealing was examined using a simple physically-based model. The results suggest that recovery may accelerate recrystallization in high stacking fault energy materials. Otherwise, recovery is expected to retard recrystallization by reducing the driving force for the nucleation and growth of recrystallized grains. These calculations help reconcile a number of apparently conflicting reports on the effect of recovery on recrystallization.

A simple model for water table fluctuations in response to precipitation

Summary A simple physically-based model is developed for quantifying groundwater fluctuations in response to precipitation time-series. A semi-analytical solution of the governing differential equation is derived for relevant initial conditions and an efficient numerical algorithm is presented. Model performance is assessed by comparing predicted and observed groundwater fluctuations over a multi-year period in response to precipitation data for a site in the Hongcheon area of South Korea. Groundwater fluctuation and precipitation time-series during the year 2001 are used for model calibration. The calibrated model is then used to predict groundwater fluctuations for 2002–2004 from measured daily precipitation data. Prediction variance is only slightly larger than the calibration variance. Results indicate that model parameters are stable over time and that reliable water level fluctuation predictions can be made by the model from actual or projected precipitation data following calibration for a limited time-series.

A physically-based abrasive wear model for composite materials

A simple physically-based model for the abrasive wear of composite materials is presented based on the mechanics and mechanisms associated with sliding wear in soft (ductile)- matrix composites containing hard (brittle) reinforcement particles. The model is based on the assumption that any portion of the reinforcement that is removed as wear debris cannot contribute to the wear resistance of the matrix material. The size of this non-contributing portion (NCP) of reinforcement is estimated by modeling three primary wear mechanisms, specifically, plowing, cracking at the matrix/reinforcement interface or in the reinforcement, and particle removal. Critical variables describing the role of the reinforcement, such as relative size, fracture toughness and the nature of the matrix/reinforcement interface, are characterized by a single contribution coefficient, C. Predictions are compared with the results of experimental two-body (pin-on-drum) abrasive wear tests performed on a model aluminum particulate-reinforced epoxy-matrix composite material.

Simulating the radiation distribution within a barley-straw mulch

Mulching is a technique widely used to moderate soil microclimate. Modelling radiation transfer within mulches is a critical step in the development of comprehensive microclimate models of the soil–mulch–atmosphere system and similar hay-drying systems. The objective of this research was to develop a relatively simple physically-based model that predicts profiles of shortwave and longwave radiation flux densities within barley-straw mulches and to test it against hourly radiation flux measurements made above and below mulches applied at rates of 2, 5, 10, and 15 t ha −1 in successive field-plot experiments. Unique features of the model include accounting for upper-surface and lower-surface mulch element temperatures using effective view factors and neglecting all shortwave reflections beyond secondary ones, so that calculation of the fluxes above any layer is explicit and does not require matrix inversion. Model input parameters were for the most part measured completely independently of the field tests. Measured transmissivities demonstrated that mulch elements were uniformly distributed, as expected, for low mulch application rates but were clumped for higher rates, which was attributed to the greater effort then needed to separate the elements of baled straw. Sensitivity tests showed that solar irradiance, atmospheric emissivity, and mulch element reflectivity are important input parameters to the model and that measuring the difference between upper-surface and lower-surface mulch element temperatures is not as critical. Modelled and measured net radiation flux density above the mulch and total downward radiation flux density near the bottom of the mulch were generally in excellent agreement, with some exceptions. These were attributed mainly to measurement error (condensation on the upper dome of the net radiometer above the mulch before and just after sunrise and inadequate spatial averaging under the thin mulches). Modelled profiles of daytime and nighttime radiation fluxes in a 10 t ha −1 mulch and simulations of the effects of uniformity, randomness, and clumping of mulch elements are reported.