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Analysis of Local Fracture Strain and Damage Limit of Advanced High Strength Steels using Measured Displacement Fields and FEM
Get PDFThe local mechanical behaviors of advanced high strength steels undergoing a very large strain from uniform plastic deformation to fracture were investigated with the aid of a measured displacement field and a measurement based FEM. As a measurement method, a digital image grid method (DIGM) was developed and the three-direction transient displacement field on uniaxial tensile test pieces was measured. Combining the measured transient displacement field with the finite element method, a measurement based FEM (M-FEM) was developed for the computation of distribution of the local strains, local stresses and ductile damage accumulation in a tensile test piece. Furthermore, the local fracture strain and damage limit of several advanced high strength steel sheets (980MPa/t1.2mm, 980MPa/t1.6mm, 1180MPa/t1.6mm) were identified by uniaxial tensile tests and the measurement based FEM. The identified damage limit of materials agreed very well compared with that measured by a conventional press test, and the validity of the measuring method and measurement based FEM was verified
Research on damage distribution and permeability distribution of coal seam with slotted borehole
Get PDFIn order to study the effect of high pressure water jet cutting technology on the permeability of single coal seam, we use the damage variable to describe the fracture distribution of coal seam, develop the 3-D finite element program based on the damage theory, and then analyze the damage distribution of coal seam after drilling and slotting. Using MTS815 rock mechanics testing system and the permeability test system, we conduct the permeability test and get the relationship between permeability and damage. Based on the damage distribution of coal seam after drilling and slotting and the permeability change law, we analyze the permeability distribution of coal seam after drilling and slotting. The results show that: after slotting high damage appears in the coal seam around the slot, which is advantageous for gas flow and expands the effect range of the drill. The slot width has little effect on the permeability of coal seam while the slot height has the obvious effect on permeability of coal seam. It is necessary to expand the slot height for increasing the effect range of the drill
Minimizing Thermal Residual Stress in Ni/Al<sub>2</sub>O<sub>3</sub> Functionally Graded Material Plate by Volume Fraction Optimization
No full textThe thermal residual stress in the fabrication of functionally graded material (FGM) systems can give rise to various mechanical failures. For a FGM system under a given fabrication environment, the thermal residual stresses are determined by the spatial distribution of its constituent components. In this study, we optimize a Ni/Al2O3 FGM plate aiming at minimizing the thermal residual stresses through controlling its compositional distribution. Material properties are graded in the thickness direction following a power law distribution in terms of the volume fractions of constituents (P-FGM). An analytical model and a hybrid genetic algorithm with the pattern search are employed to predict and to minimize the thermal residual stresses, respectively. Simulation results show that an optimal design of the FGM plate could help fulfill its potential in reducing the thermal residual stresses
Molecular Dynamics Analysis of High-temperature Molten-salt Electrolytes in Thermal Batteries
Get PDFThe purpose of this research is to improve the discharge rate and to predict the melting point of high-temperature molten-salt electrolytes in thermal batteries. Using molecular dynamics (MD) simulation techniques, we tried to develop some novel ternary and quaternary molten electrolytes to replace conventional binary LiCl-KCl ones. The simulation results with greater ionic conductivity and lower melting point are consistent with experimental results reported by previous literatures. The MD results have found that the lithium ion mole fraction in the molten-salt electrolytes affects the ionic conductivity significantly. This paper demonstrates that MD simulation techniques are a useful tool to screen various design ideas on the multi-component electrolytes in a more efficient way. The molecular composition of each component of the molten-salt electrolytes can be optimized using this atomistic analysis instead of trial-and-error experiments
Guided Waves in Functionally Graded Rods with Rectangular Cross-Section under Initial Stress
Get PDFThe characteristics of the guided waves propagation in functionally graded rods with rectangular cross-section (finite width and height) under initial stress are investigated in this paper based on Biot’s theory of incremental deformation. An extended orthogonal polynomial approach is present to solve the coupled wave equations with variable coefficients. By comparisons with the available results of a rectangular aluminum rod, the validity of the present approach is illustrated. The dispersion curves and displacement profiles of various rectangular functionally graded rods are calculated to reveal the wave characteristics, and the effects of different width to height ratios and initial stress and gradient functions on the guided waves are discussed in detail
A Experimental Study on the Rhelogical and Mechanical Properties of Blends of Polyethylene and Modified Oil Shale Ash (MOSA)
Get PDFBlends of Polyethylene (PE) and modified-oil shale ash (MOSA) with different fractions of MOSA were prepared by the melting blend method. The effects of MOSA content on the rheological and mechanical properties of the blend were properly assessed via direct experimental analysis (more precisely, all rheological measurements were performed using a laboratory-scale XSS-300 torque rheometer with single screw extruder; the temperatures were maintained at 170°C, 180°C and 190°C under continuous extrusion). The prepared samples were observed to display a shear-thinning behaviour. Moreover, with increasing the MOSA content, we found the yield strength of the blends to increase, while its elongation at break tends to decrease. Notably, by adding 3 wt.% MOSA only, the tension yield strength of the blends was 61.18% higher than that of pure PE
Numerical Simulation of Entropy Generation in Hydrogen-Air Burner
Get PDFThe aim of this work is the numerical simulation of the combustion of hydrogen with air in a burner and the numerical solution of local entropy generation rate in the combustion chamber. The effects of equivalence ratio φ and oxygen percentage γ on combustion and entropy generation rates are studied for different φ(ranging from 0 to 1.0) and γ values (ranging from 10 to 30%). The predictions show that the increase of φ (or the decrease of λ ) reduces notably the reaction rate levels. The equations of continuity, of energy and momentum are solved by volume finite using commercial code CFD Fluent, the effects of turbulence will be modeled by the RNG-K-epsilon model, on the other hand the generation of the entropy will be introduced in post-processing
A Parallel Boundary Element Formulation for Tracking Multiple Particle Trajectories in Stoke’s Flow for Microfluidic Applications
Get PDFA new formulation for tracking multiple particles in slow viscous flow for microfluidic applications is presented. The method employs the manipulation of the boundary element matrices so that finally a system of equations is obtained relating the rigid body velocities of the particle to the forces applied on the particle. The formulation is specially designed for particle trajectory tracking and involves successive matrix multiplications for which SMP (Symmetric multiprocessing) parallelisation is applied. It is observed that present formulation offers an efficient numerical model to be used for particle tracking and can easily be extended for multiphysics simulations in which several physics involved
A New Coupled Fractional Reduced Differential Transform Method for the Numerical Solution of Fractional Predator-Prey System
Get PDFIn the present article, a relatively very new technique viz. Coupled Fractional Reduced Differential Transform, has been executed to attain the approximate numerical solution of the predator-prey dynamical system. The fractional derivatives are defined in the Caputo sense. Utilizing the present method we can solve many linear and nonlinear coupled fractional differential equations. The results thus obtained are compared with those of other available methods. Numerical solutions are presented graphically to show the simplicity and authenticity of the method
CFD Analysis of Pulsatile Flow and Non-Newtonian Behavior of Blood in Arteries
Get PDFCFD analysis plays an important role in the area of analysis of blood flow as in-vivo measurements of blood flow is costly and easily not accessible. This paper presents simulation of blood flow in healthy and stenosed coronary artery 2- D models. The simulation was done considering non-Newtonian behavior of blood and pulsatile nature of blood flow which is close to physical scenario. Pressure distribution, velocity distribution and wall shear were examined to understand their effect on Atherosclerosis