Asymmetrical rolling analysis of bonded two-layer sheets and evaluation of outgoing curvature

A theoretical model based on slab method is proposed to analyze asymmetrical rolling of bonded two-layer sheets where the ingoing sheet is forced to horizontally enter the roll gap. Separate equilibrium equations as well as yield relations are derived for each layer by considering different stress fields for the two layers of any slab within the roll gap. A large angle of bite is considered in the governing equations as the experimental data used for verifying the results belong to the rolling conditions where small bite angle assumption is not reasonable. The curvature of the sheet at exit from the roll gap is estimated by studying variations of the normal and the shear strains within the whole roll gap. A very good agreement is shown to exist between the rolling force as well as the outgoing curvature predicted by the present model and the available analytical and experimental results reported by other investigators. By studying the outgoing curvature at different conditions, some practical suggestions to minimize the strip curvature at exit from the roll gap are proposed.     

Slab analysis of asymmetrical sheet rolling

In this paper, a theoretical model based on slab method of analysis for plane strain asymmetrical rolling is presented. In this model the non-uniformity of the normal and shear stresses in deriving of the governing equations are considered. This model can predict the required external loading to the plate at entry to keep the plate horizontal. The analytical rolling force, torque and pressure of this model were compared with the experimental and analytical results of other investigators. Numerical and experimental results are shown to be in good agreements.     

Numerical and clinical investigation on the material model of the cornea in Corvis tonometry tests: differentiation between hyperelasticity and viscoelasticity

Mechanics of Time-Dependent Materials - Non-contact tonometers, including ORA and Corvis ST, are not only used to estimate intraocular pressure (IOP) in clinical surveys but are also utilized to...     

Recovery and partial purification of thermophilic β-xylosidase derived from recombinant Bacillus megaterium MS941 by aqueous two-phase system

A polymer–salt-based aqueous two-phase system (ATPS) was developed for the effective extraction and purification of extracellular β-xylosidase from the fermentation broth of recombinant Bacillus megaterium MS941. The effect of molecular weight (MW) of polyethylene glycol (PEG), tie-line length (TLL), volume ratio (V_R), crude loading and pH on the recovery performance was evaluated. Under the optimal extraction conditions, β-xylosidase was successfully purified up to 23-fold with a recovery yield of 99% in the bottom salt-rich phase at PEG 4,000/potassium phosphate ATPS comprising TLL of 41.8, V_R of 2.3, crude loading (C_L) of 30% (w/w) at pH 6.     

Flaw insensitive fracture in nanocrystalline graphene

We show from a series of molecular dynamics simulations that the tensile fracture behavior of a nanocrystalline graphene (nc-graphene) nanostrip can become insensitive to a pre-existing flaw (e.g., a hole or a notch) below a critical length scale in the sense that there exists no stress concentration near the flaw, the ultimate failure does not necessarily initiate at the flaw, and the normalized strength of the strip is independent of the size of the flaw. This study is a first direct atomistic simulation of flaw insensitive fracture in high-strength nanoscale materials and provides significant insights into the deformation and failure mechanisms of nc-graphene.     

Analysis of asymmetrical sheet rolling by a genetic algorithm

Slab analysis of asymmetrical sheet rolling is presented by considering non-uniform normal and shear stress profiles across the section of product. An important phenomenon considered in this paper is the deflection of plate at entry to the deformation zone and the amount of which is predicted by using a genetic algorithm (GA). In the utilized GA, the elimination/replacement operator and a new operator called “the adaptive mutation” are developed in order to increase the efficiency of the search. Shear stresses are taken into account in applying the Von-Mises yield criterion, and it is shown that this improves the accuracy of the model. Rolling force and pressure distribution predicted by the present model are shown to be in good agreements with the experimental and theoretical results of other investigators.     

Kinematic and dynamic modeling of viscoelastic robotic manipulators using Timoshenko beam theory: theory and experiment

This paper presents an investigation into the development of modeling of n-viscoelastic robotic manipulators. The dynamic model of the system is derived using Gibbs-Appell formulation and assumed mode method. When the beam is short in length direction, shear deformation is a factor that may have significant effects on system dynamic. So, in modeling, the assumption of Timoshenko beam theory and associated mode shapes has been considered. Although including the effect of damping in continuous systems makes the formulations more complicated, two important damping mechanisms, namely, Kelvin-Voigt damping as internal damping and the viscous air damping as external damping have been considered. Based on derived formulation, a non-linear recursive algorithm is developed for deriving the inverse dynamic equation of motion, systematically. The performance of the proposed algorithm was assessed in terms of the required mathematical operations for deriving the kinematic and dynamic equations of the mechanical system. Finally, to validate the proposed formulation, a comparative assessment between the results achieved from experiment and simulation is presented in time and frequency domains.     

Analysing the life index of diamond cutting tools for marble building stones based on laboratory and field investigations

Bulletin of Engineering Geology and the Environment - Cutting tool wear constitutes one of the principal parameters in the processing cost of building stone. The life index of the cutting tool is...     

An Investigation into the Simple Tensile Test of SMA Wires Considering Stress Concentration of Grippers

To simulate the behaviors of shape memory alloy (SMA) wires, several 1-D constitutive models have been proposed most of which assume a homogeneous behavior for the material. However, stress concentration caused by the grippers would lead to inhomogeneous behavior of an SMA during the tensile test. In this paper, effect of stress concentration caused by the grippers is studied on the stress-strain response of an SMA wire during tension. At first, a relation for minimum required gripping force is provided. Then the extent of influence of stress concentration is estimated, and a minimum length is proposed for the test sample of ordinary materials. Using this result and by finite element simulating the effect of stress concentration caused by grippers, a minimum length for an SMA tensile test sample is proposed. By considering this minimum length, it is possible to simulate the material behaviors neglecting the stress concentration caused by grippers and to determine material parameters with a reasonable precision using a constitutive model in which inhomogeneous behaviors are not taken into account. A simple tensile test is performed on an SMA wire whose length is more than the recommended number, and a good agreement is seen between predicted stress-strain curve based on uniform stress distribution throughout the wire and the obtained experimental results.