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Nuclear magnetic resonance (NMR) spectral analysis of biofluids can be a time‐consuming process, requiring the expertise of a trained operator. With NMR becoming increasingly popular in the field of metabolomics, there is a growing need to change this paradigm and to automate the process. Here we introduce MagMet, an online web server, that automates the processing and quantification of 1D 1H NMR spectra from biofluids—specifically, human serum/plasma metabolites, including those associated with inborn errors of metabolism (IEM). MagMet uses a highly efficient data processing procedure that performs automatic Fourier Transformation, phase correction, baseline optimization, chemical shift referencing, water signal removal, and peak picking/peak alignment. MagMet then uses the peak positions, linewidth information, and J‐couplings from its own specially prepared standard metabolite reference spectral NMR library of 85 serum/plasma compounds to identify and quantify compounds from experimentally acquired NMR spectra of serum/plasma. MagMet employs linewidth adjustment for more consistent quantification of metabolites from higher field instruments and incorporates a highly efficient data processing procedure for more rapid and accurate detection and quantification of metabolites. This optimized algorithm allows the MagMet webserver to quickly detect and quantify 58 serum/plasma metabolites in 2.6 min per spectrum (when processing a dataset of 50–100 spectra). MagMet's performance was also assessed using spectra collected from defined mixtures (simulating other biofluids), with >100 previously measured plasma spectra, and from spiked serum/plasma samples simulating known IEMs. In all cases, MagMet performed with precision and accuracy matching the performance of human spectral profiling experts. MagMet is available at http://magmet.ca. [ABSTRACT FROM AUTHOR]

In this study, the effects of the microstructural features on the mechanical behavior of the spheroidal steel sheets are investigated. The crystal plasticity finite element method is used for simulations. For this purpose, a 2D preprocessing and grain generator software was developed. A series of representative volume elements (RVEs) with different microstructures and boundary conditions were produced. The hardening parameters in the simulations are calibrated according to the available experimental data in the literature. Then, the flow behaviors of the steel sheets under uniaxial tensile load and pure shear were extracted, and the effects of cementite particle fraction and size on steel sheet behavior were investigated. When the cementite particle fraction and size increase, the uniform elongation decreases. Also, the effects of boundary conditions and cementite particle distribution in the steel sheet were studied. It was also shown that symmetric boundary conditions impose more constraints on the material, making the steel sheets stiffer and damage starts earlier. Three RVEs with different particle distributions were modeled. The simulation results showed that by increasing the fraction of particles in the banding structure, the damage starts sooner, and the uniform deformation decreases. [ABSTRACT FROM AUTHOR]

In this research, we investigate the effects of various microstructural features on the behavior of spherical steel sheets, using the crystal plasticity finite element method. The cementite phase ratio, the grain sizes of ferrite and cementite, and the percentage of residual pearlite in the steel structure due to incomplete annealing are the major microstructural parameters studied in this work. A grain generator software has been developed to generate hexagonal ferrite grains as well as circular cementite particles distributed in the ferrite matrix. We use a hard coating with special properties as an intermediate layer around the cementite grains to simulate the contact between ferrite grains and cementite particles. This software can also assist with the preprocessing including boundary condition and load producing and introducing constitutive modeling relations. We use representative volume elements (RVEs) to simulate the microstructure of the steel sheet. The hardening parameters in the simulations are calibrated according to the available experimental data in the literature. Several RVEs were prepared and solved to investigate the effect of the thickness of this layer on material behavior. We can replicate the experimental results by setting the ratio of this thickness to the cementite particles' diameter to be 0.25. Moreover, by reducing the size of ferrite grains and cementite particles, the strength of steel increases. On the other hand, increasing the ratio of the cementite phase increases the strength of steel but the uniform plastic deformation of the material is reduced. We also model and discuss the remaining pearlite content and its effect on the flow behavior of the material. Finally, the effect of the cementite precipitation location and its bimodal size distribution were discussed in this study. [ABSTRACT FROM AUTHOR]

An efficient isogeometric-based framework is presented to integrate optimum design and formability analysis of sheet metal forming processes. To assess the quality of the formed parts, several objective functions such as fracture, wrinkling, thickness variation, and stretching are studied. In this framework, geometric parameters of addendum surfaces and middle tools are considered as design variables, the objective functions are calculated using the recently developed one-step and multi-step inverse isogeometric methods, and the optimum design variables are obtained using the genetic global optimization algorithm. The major advantage of employing the inverse methods is to analyze the formability of the parts with a low computation time. In this research, the effects of altering addendum surfaces and/or middle tools on the quality of the formed parts are simultaneously observed since modeling, formability analysis, and optimization stages of sheet metal forming simulation are integrated using the NURBS functions. To evaluate the performance of the inverse isogeometric models in calculation of the studied objective functions, the results obtained by these models are compared to those of experiment and forward FEM. Comparisons of the results indicate that these models predict the objective functions with acceptable accuracy at a low computation time. For instance, in sheet metal forming analysis of a rectangular box with three different addendum surfaces, the maximum error in prediction of minimum thickness using the one-step inverse model is approximately 4.65% more than forward FEM, while the solution time of forward FEM is around 40 times greater. Finally, the presented optimization procedure is applied to design addendum surfaces in forming of a rectangular box and the middle tools in a two-stage drawing of a square box. The results of these problems confirm the credibility of the present approach in rapid optimum design of addendum surfaces and intermediate tools with acceptable accuracy. [ABSTRACT FROM AUTHOR]

The capability to standardize the fracture strength of solder joints is an effective tool to investigate the reliability of electronic devices. To achieve this purpose, in this research, the influences of joint arrangement (loading arm and load sharing) on the level of constraint imposed on joint deformation, fracture energy, and generally, fracture behavior of solder joints were investigated. Fracture behavior of solder joints using double-cantilever-beam (DCB) specimens as a function of loading arm and load sharing (i.e., the distance between two solder joints) was studied under mode I loading conditions at a strain rate of 0.03 s−1. By increasing the loading arm, the fracture force, Fci, decreased linearly, while the critical strain energy release rate for crack initiation, Jci, increased from a loading arm of 12.7 mm to 38.1 mm and then remained almost unchanged for loading arms of 38.1 mm to 71.1 mm. Plastic deformation in the solder layer and criteria such as opening stress (i.e., the predominant stress component in DCB specimen) and stress triaxiality factor were calculated. It was shown that for the larger loading arms (from 38.1 mm to 71.1 mm), the fracture behavior was as a normal DCB specimen (i.e., the normal stress caused by bending was predominant and normal stress caused by tensile loading could be ignored). For the loading arm of less than 38.1 mm, the fracture behavior was similar to that of tensile-type specimens (i.e., the normal stress caused by bending decreased significantly by decreasing the loading arm and normal stress caused by tensile loading became considerable). Variations in the distance between two solder joints did not affect the Jci value, while Fci was influenced by the joint arrangement. This behavior was attributed to stress distribution in the solder layer. [ABSTRACT FROM AUTHOR]

This paper attempts to predict how the microstructural features and mechanical properties of the individual constituents affect the deformation behavior and formability of ferrite-pearlite steels under quasi-static loading at room temperature. For this purpose, finite element simulations using representative volume elements (RVEs) based on the real microstructures were implemented to model the flow behavior of the ferrite-pearlite steels with various microstructural morphologies (non-banded and banded). The homogenized flow curves obtained from the RVEs subjected to periodic boundary conditions together with displacement boundary conditions were validated with the experimental results of the uniaxial tensile tests. Then, the initial microstructural inhomogeneity and Johnson–Cook damage criteria were employed for both non-banded and banded RVEs to estimate the onset of plastic instability under different loading paths ranging from uniaxial tension to equi-biaxial tension. Finally, the forming limit diagrams of both ferritic-pearlitic microstructures were predicted, which show a good agreement with the experimental results of the Nakazima stretch-forming tests (less than 13 pct error). It implies that the initial microstructural inhomogeneity criterion adequately enables to predict the plastic instability in the ferritic-pearlitic steel sheets without using any damage or failure criterion. The most commonly observed damage mechanism is the severe plastic deformation of the ferrite grains near the pearlite colonies due to the strength contrast between ferrite and pearlite. Another significant finding is that the microstructural morphology has a crucial influence on the strain partitioning, strain localization, and formability of the ferritic-pearlitic steels. [ABSTRACT FROM AUTHOR]

Recently, eliminating the gap between design and formability analysis of sheet metal parts has been studied to simulate sheet metal stamping processes. In this regard, a transfer-based inverse isogeometric formulation has been proposed. This method has various advantages such as solving the governing equations in two-dimensional networks without any concern about the convergence; however, it neglects the bending effect which is a major contributor in die/punch profile radii. The present work aims to consider the bending effects by introducing a bending-dependent inverse isogeometric formulation. The developed model deals with the minimization of potential energy, deformation theory of plasticity, classical plate theory, and considering a yield criterion in stress-resultant space. In addition to all advantages of the transfer-based inverse isogeometric formulation, one major benefit of this study is that the bending effects are included with a slight increase in the computation time. This methodology allows for accurately predicting the effects of changing die/punch profile radii and initial sheet thickness on the formability of the final part by presenting a new material updating process. To assess the credibility of this approach, an experimental setup and forward FEM software have been utilized to form a rectangular box. The results acquired by the developed method and those achieved by experiment and forward FEM reveal acceptable accuracy in the presented model. Also, strains and thicknesses predicted by the developed method, membrane inverse isogeometric model, and forward FEM for nine different values of punch radius to the sheet thickness ratio have been compared. Considering forward FEM as a reference method, the average of calculated error in the presented model for prediction of thickness at the middle of punch radius zone is around half of that in the membrane model. In solving the studied problems, the presented model requires only slightly more computation time (around 2%) than the membrane inverse isogeometric model and much less computation time than forward FEM. Therefore, the presented method is a valuable inverse forming solver especially when the bending effects are significant. [ABSTRACT FROM AUTHOR]

Recently, eliminating the gap between design and formability analysis of sheet metal parts has been studied to simulate sheet metal stamping processes. In this regard, a transfer-based inverse isogeometric formulation has been proposed. This method has various advantages such as solving the governing equations in two-dimensional networks without any concern about the convergence; however, it neglects the bending effect which is a major contributor in die/punch profile radii. The present work aims to consider the bending effects by introducing a bending-dependent inverse isogeometric formulation. The developed model deals with the minimization of potential energy, deformation theory of plasticity, classical plate theory, and considering a yield criterion in stress-resultant space. In addition to all advantages of the transfer-based inverse isogeometric formulation, one major benefit of this study is that the bending effects are included with a slight increase in the computation time. This methodology allows for accurately predicting the effects of changing die/punch profile radii and initial sheet thickness on the formability of the final part by presenting a new material updating process. To assess the credibility of this approach, an experimental setup and forward FEM software have been utilized to form a rectangular box. The results acquired by the developed method and those achieved by experiment and forward FEM reveal acceptable accuracy in the presented model. Also, strains and thicknesses predicted by the developed method, membrane inverse isogeometric model, and forward FEM for nine different values of punch radius to the sheet thickness ratio have been compared. Considering forward FEM as a reference method, the average of calculated error in the presented model for prediction of thickness at the middle of punch radius zone is around half of that in the membrane model. In solving the studied problems, the presented model requires only slightly more computation time (around 2%) than the membrane inverse isogeometric model and much less computation time than forward FEM. Therefore, the presented method is a valuable inverse forming solver especially when the bending effects are significant. [ABSTRACT FROM AUTHOR]

Forming limit diagram is often used as a criterion to predict necking initiation in sheet metal forming processes. In this study, the forming limit diagram was obtained through the inclusion of the Marciniak–Kaczynski model in the Nakazima out-of-plane test finite element model and also a flat model. The effect of bending on the forming limit diagram was investigated numerically and experimentally. Data required for this simulation were determined through a simple tension test in three directions. After comparing the results of the flat and Nakazima finite element models with the experimental results, the forming limit diagram computed by the Nakazima finite element model was more convenient with less than 10% at the lower level of the experimental forming limit diagram. [ABSTRACT FROM AUTHOR]

The continuum theory of dislocations is applied to formulate the problem of a double ended dislocation pileup under quadratic applied stress. Accordingly, a second order stress gradient plasticity model is presented to address the contribution of the first and the second stress gradients in the effect interpretation. The model is employed to predict the initial strengthening and subsequent hardening in curved and straight thin foils under pure bending within the continuum framework. It is shown that the so-called stress gradient plasticity model that ignores the second stress gradient may not give sound interpretations of the size effects. The plastic response of thin foils is affected by both the first and second stress gradients, yet their interaction strongly depends upon the length scale parameter. The larger the length scale parameter, the quadratic term contribution would be important and the predictions of the first and second order models deviate significantly from each other. [ABSTRACT FROM AUTHOR]

This article presents a crystal plasticity methodology to evaluate the AA1050 sheet formability. In order to determine the orientation distribution of the crystals, initial texture of the material is measured through X-ray diffraction technique. Also, the stress–strain behavior of the material is determined by performing tensile test. In order to simulate the path-dependent crystal plasticity behavior of body-centered cubic crystal structures, a UMAT subroutine that employs the rate-dependent crystal plasticity model along with the power law hardening was developed previously by the authors and linked to the finite element software ABAQUS. This subroutine was further developed to simulate face-centered cubic crystal structures. The second-order derivative of sheet thickness variations with respect to time is considered as the instability factor, and forming limit diagram of the material is predicted. In order to assess the validity of formability prediction results for face-centered cubic materials, forming limit diagram of AA1050 sheet is also experimentally extracted by conducting hemi-spherical punch test. It is observed that the predicted forming limit diagram is in agreement with the experimental results. Finally, the prediction accuracy in different regions of forming limit diagram is discussed and some suggestions for further improving the accuracy are made. [ABSTRACT FROM AUTHOR]

This paper focuses on the determination of the complete set of ideal orientations of FCC materials in the equibiaxial tension mode of deformation. The simulations are based on the numerical procedure developed by the authors in which, a rate-sensitive crystal plasticity model with Secant hardening law was employed. The resulting nonlinear system of equations is solved by the modified Newton–Raphson method. An Euler space scanning method is used to obtain the ideal orientations of a deformation mode. In this method some initial orientations which are evenly spaced in the Euler space are selected and their evolutions into the ideal orientations are tracked. To verify the accuracy of the presented Euler space scanning method for FCC crystal structures, the ideal orientations of plane strain compression loading are calculated and compared with the existing experimental results. It is observed that this method can predict all of the reported ideal orientations of this deformation mode accurately. Afterward, by applying this method to the equibiaxial tension mode of deformation, eight lines of ideal orientations E1–E8 are resulted. Finally, the major characteristics of the obtained ideal orientations along with the crystal evolution patterns are thoroughly discussed. [ABSTRACT FROM AUTHOR]

Ideal orientations are one of the material characteristics of the applied mode of deformation. The transfer of material texture to orientations near specific ideal orientations can improve the mechanical properties of the material. In this paper, we focus on the determination of ideal orientations of BCC crystals under the equibiaxial tension mode of deformation. To do this, an Euler space scanning method based on a crystal plasticity approach is presented. In this method some initial orientations which are evenly spaced in the Euler space are selected and their evolutions into the ideal orientations are tracked. The loading is applied incrementally until all of the lattice spin components become permanently zero. The rate sensitive crystal plasticity model with power law hardening is employed and the resulting nonlinear system of equations is solved by the modified Newton–Raphson method. In order to verify the simulation results, the ideal orientations of rolling textures are calculated. A comparison of the obtained results with the existing experimental data demonstrates that all of the reported ideal orientations are satisfactorily predicted. Afterward, preferred orientations for equibiaxial tension mode of deformation which have not been reported previously in the literature are calculated. This analysis resulted in eight fibers EF1–EF8 together with a plane of ideal orientations for equibiaxial tension loading. The effects of symmetry of the crystal structure and loading on the obtained ideal orientations are finally discussed. [ABSTRACT FROM AUTHOR]

In this study, the effect of a compressive normal stress has been considered in the determination of forming limit diagrams and forming limit stress diagrams to predict neck initiation failure in tube hydroforming of T-shaped parts. Computation of the forming limit diagrams and FLSDs is based on the generalized Marciniak and Kuczynski method to consider the existence of through-thickness compressive normal stress. The proposed forming limit diagrams and FLSDs were used in conjunction with ABAQUS/EXPLICIT finite element simulations to predict the onset of necking in tube hydroforming of T-shaped part. The amount of calibration pressure and axial feeding required to produce an acceptable part in finite element method was compared to published experimental data, and a satisfactory agreement between the FEM and test results has been achieved. Therefore, the present approach can be used as a reliable criterion to design tube hydroforming processes and reduce the number of costly trials. [ABSTRACT FROM AUTHOR]

Crystallographic texture considerably affects the formability of crystalline materials. In this paper, the effects of BCC ideal rolling fibers-including α, 휖, η, γ, and ξ fibers-on the sheet formability are numerically studied. The simulations are based on the numerical procedure developed by the authors in [] in which a rate dependent crystal plasticity model along with the power law hardening are employed in a user material subroutine to model the behavior of crystalline materials. In order to determine FLD-in a M-K type approach-second-order derivative of sheet thickness variations with respect to time is used as necking criterion. The calculated FLDs of the fibers are compared with each other and with the FLD of isotropic condition. It was observed that in the case of γ fiber a higher formability with respect to other fibers can be achieved in all regions of the curve. Also, α fiber, although weaker than other fibers at at right-hand side of FLD, shows higher formability at left. Finally, some suggestions are made based on FLD comparisons to improve sheet formability by controlling the texture produced in the manufacturing process. [ABSTRACT FROM AUTHOR]

The behaviour of a dislocation pileup with a finite-strength source is investigated in the presence of various stress gradients within a continuum model where a free-dislocation region exists around the source. Expressions for dislocation density and stress field within the pileup are derived for the situation where there are first and second spatial gradients in applied stress. For a pileup configuration under an applied stress, yielding occurs when the force acting on the leading dislocations at the pileup tips reaches the obstacle strength, and at the same time, it is required that the source be at the threshold stress for dislocation production. A numerical methodology is presented to solve the underlying equations that represent the yielding conditions. The yield stress calculated for a pileup configuration is found to depend on stress gradients, obstacle spacing and source/obstacle strengths. It increases with increasing the first stress gradient, yet dependent on the second stress gradient. Furthermore, while the dependency of yield stress on the obstacle spacing intensifies with increasing the first stress gradient, it diminishes with an increase of second stress gradient. Therefore, the second stress gradient, as a newly introduced parameter, can provide a new physical insight into the size-dependent plasticity phenomena at small length scales. [ABSTRACT FROM AUTHOR]

An enhanced unfolding inverse finite element method (IFEM) has been used together with an extended strain-based forming limit diagram (FLD) to develop a fast approach to predict the feasibility of tube hydroforming process of concept part and determine where the failure or defects can occur. In tube hydroforming, the inverse IFEM has been used for estimating the initial length of tube, axial feeding and fluid pressure. The already developed IFEM algorithm used in this study is based on the total deformation theory of plasticity. Although the nature of tube hydroforming is three-dimensional deformation, in this article a modeling technique has been used to perform the computations in two-dimensional space. Therefore, compared with conventional forward finite element methods, the present computations are quite fast with no trial and error process. In addition, the solution provides all the components of strain. Using the extended strain-based forming limit diagram, the components of strain can lead us to measure the potentials for failures during the deformation. The extended strain-based FLD based on the Marciniak and Kuczynski (M-K) model has been computed and used to predict the onset of necking during tube hydroforming. The extended strain-based FLD is built based on equivalent plastic strains and material flow direction at the end of forming. This new forming limit diagram is much less strain path dependent than the conventional forming limit diagram. Furthermore, the use and interpretation of this new diagram is easier than the stress-based forming limit diagram. The results of analysis for free bulging and square bulging have been compared with some published experimental data and the results obtained by conventional commercial software. The results indicate that the fluid pressure estimated by this method is 2.7 % greater than the results obtained by the experiment in the square bulging sample. In addition, the fluid pressure estimated in the free bulge sample is 5.6 % greater than the experimental results. [ABSTRACT FROM AUTHOR]

In this study, a methodology has been presented for radial positioning of the die holes in multi-hole extrusion of non-symmetric sections. The objective of radial positioning is to minimize exit profile curvature. For this purpose, a two-hole die with non-symmetric T-shaped holes has been investigated. A kinematically admissible velocity field at deformation zone has been developed. The deformation region includes the dead metal zone (DMZ) which is assumed to be linear. The DMZ length was obtained by energy minimization through the upper bound method. To predict the exit profile curvature a deviation function has been suggested. Using the proposed function, the velocity field has been used for prediction of the exit profile curvature and thereby positioning of the die holes. The predictions of the proposed methodology were validated with physical modeling. With little development, this methodology could be applied to dies, which have more holes and/or generate profiles that are more complex. This will help die designers enhance the quality of extrusion process. [ABSTRACT FROM AUTHOR]

The axial turbine is one of the most challenging components of gas turbines for industrial and aerospace applications. With the ever-increasing requirement for high-aerodynamic performance blades, three-dimensional aerodynamic shape optimization is of great importance. In this research, the rear part of a gas turbine consisting of a one-stage axial turbine is optimized numerically. A useful optimization algorithm is presented to improve the efficiency and/or pressure ratio of the axial turbine with two different objective functions. The three-dimensional blade-shape optimization is employed to study the effects of the turbine stator and rotor lean and sweep angles on the turbine performance. The investigation is carried out at the turbine design speed. By coupling a verified computational fluid dynamics simulation code with the genetic algorithm, an automated design procedure is prepared. Geometry candidates for the optimization algorithm are generated by re-stacking of the two-dimensional airfoil sections. Three-dimensional, turbulent, and compressible flow field is numerically investigated via a Navier–Stokes solver to calculate various objective functions. Experimental results of the gas turbine are used for specifying the boundary conditions and validation of the simulation results. The proposed method results in 1.3% and 1.5% improvements in the turbine stage efficiency in design speed and reduced mass parameter at choke condition, respectively. [ABSTRACT FROM PUBLISHER]

Prediction of stable orientations is a key subject in the crystal plasticity literature. This work deals with the effects of deformation mode on the resulted stable orientations and texture evolution of FCC materials. The simulations are based on the numerical procedure developed by the authors in previous works in which, a rate-sensitive crystal plasticity model with Secant hardening law was employed. The resulting non-linear system of equations is solved by the modified Newton–Raphson method. In order to obtain the stable orientations for a deformation mode, initial orientations evenly spaced in the Euler space are selected and their evolution into the stable orientations is tracked. The deformation is applied incrementally until all of the lattice spin components become permanently zero. In this way, all preferred orientations for different ratios of strain-rate components= 0, 0.1, 0.25, 0.5 and 1 (from plane strain compression to equibiaxial tension) are calculated. It is observed that, by increasing this ratio, rolling texture components are gradually replaced by stable orientations of equibiaxial tension loading. In other words, the stable orientations of intermediate strain modes can be extracted from summation of stable orientations of plane strain compression and equibiaxial tension. This suggests that, it is not needed to search other intermediate strain modes for new stable orientations. The presented stable orientations can be evaluated by crystal plasticity-based simulation tools to determine which ones have superior characteristics to be used for texture improvement of material. [ABSTRACT FROM PUBLISHER]

This paper focuses on the study of 1010 steel sheet formability from a crystal plasticity viewpoint. The study is divided into experimental and numerical parts. In the experimental section, the initial texture of the sheet is measured through x-ray diffraction technique. Also, the stress-strain behaviour and FLD of the material are determined by performing simple tension and hemi-spherical punch tests, respectively. The presented experimental data provides the complete set of required input data for crystal plasticity simulation of 1010 steel sheet behaviour. In the numerical section, the rate dependent crystal plasticity model along with the power law hardening are employed in a user material (UMAT) subroutine to model the material behaviour. In order to determine FLD, second-order derivative of sheet thickness variations with respect to time is used as necking criterion. It is observed that the predicted FLD is in good agreement with the experimental curve. Finally, some points to further improve FLD prediction accuracy are remarked. [ABSTRACT FROM AUTHOR]

The inverse solution is helpful to determine the drawability of a part and drawing parameters at the initial design stage. The usual inverse algorithms consider the drawing process that occurs in one step and therefore they are not able to analyze the processes which need more than one drawing step. Therefore, multistep inverse solution has been used for such problems. The multistep inverse solution deals with finding the initial guesses of nodal positions on intermediate stages and solving inverse equations between two consecutive steps. In this paper, a new mapping method has been developed to find the initial nodal positions on intermediate stages and the unfolding technique has been applied to find the final nodal positions on the blank sheet. The proposed method would obtain a system of equations without convergence problems. Two examples have been considered to demonstrate the capability of the proposed modeling technique. First, a two-stage drawing process of a circular cup has been analyzed and the results have been compared with the experiment results. Second, in order to apply the technique on a non-axisymmetric part, a multistage drawing of a square cup has been examined and the results have been reported. [ABSTRACT FROM AUTHOR]

The linear unfolding inverse finite element method (IFEM) has been modified and enhanced by implementing large deformation relations. The method is helpful to predict forming severity of the part that should be deep drawn as well as its blank shape and strain distribution in preliminary design stage. The approach deals with minimization of potential energy and large deformation relations with membrane elements. To reduce the computation time, the part is unfolded properly on the flat sheet and treated as 2D problem. Moreover, the nonlinear stress-strain relationship of plastic material properties has been considered to increase the accuracy of the results. An experiment set up has been prepared to form a rectangular cup. Then, the obtained cup has been analyzed by linear unfolding IFEM and the proposed method. Comparisons of the measured thickness strains and the blank shape show that the proposed method predicts the strain distribution more accurately than the linear method. [ABSTRACT FROM AUTHOR]

In spite of the fact that the experimental results indicate the significant effect of strain rate on forming limits of sheets, this effect is neglected in all theoretical methods of prediction of Forming Limit Diagrams (FLDs). The purpose of this paper is to modify the most renowned theoretical method of determination of FLDs (e.g., M- K model) so as to enable it to take into account the effect of strain rate. To achieve this aim, the traditional assumption of preexistence of an initial geometrical inhomogeneity in the sheet has been replaced with the assumption of a preexisting 'material' inhomogeneity. It has been shown that using this assumption, the strain rate would not be omitted from equations; thus, it is possible to demonstrate its effect on FLDs. To validate the results, they are compared with some published experimental data. The good agreement between the theoretical and experimental results shows capabilities of the proposed method in predicting the effect of the imposed rate at the boundary (which is physically the effect of the punch speed difference in sheet forming) on FLDs. [ABSTRACT FROM AUTHOR]

Abstract: A new design for a valveless micropumping device has been proposed that integrates two existing pumping technologies, namely, the wall induced traveling wave and the obstacle-type valveless micropump. The liquid in the microchannel is transported by generating a traveling wave on the channel, while the placing of two asymmetric trapezoid obstacles, along the centerline of the channel inlet and outlet, leads to a significant (up to seven times) increase of the net flow rate of the device. The effectiveness of this innovative design has been proved through a verified three-dimensional finite element model. Fluid–Structure Interaction (FSI) analysis is performed in the framework of an Arbitrary Lagrangian–Eulerian (ALE) method. [Copyright &y& Elsevier]

In this paper, the fluid flow and the diaphragm deflection are studied in the pneumatically actuated diaphragm microvalve by performing finite element and analytical fluid-structure interaction simulations. The results of these approaches are compared and their validity is discussed. An analytical relation is obtained for the critical diaphragm deflection which leads to unstable response of the microvalve. This relation shows that the critical deflection is only a function of the microvalve geometry, namely its inlet height and outlet radius. The phenomenon of the diaphragm deflection jump is justified in the microvalve behavior. The effect of different fluid flow and diaphragm parameters on the microvalve response is investigated that can be used to improve the microvalve design. [ABSTRACT FROM AUTHOR]

Photo-oxidative degradation of LLDPE films (~250 μm thick) containing varying amounts of galbanic acid (a type of coumarin derivatives) was investigated by exposing the films to an artificial sunlight (emitted by 300 W OSRAM Ultra-Vitalux lamps) at 40°C for extended time periods. Photo-oxidative degradation of the neat polymer film and the LLDPE films containing benzophenone (an active photo-initiator for PE) and coumarin alone were also studied under similar conditions for comparison. The rate of photo-oxidation was assessed by measuring tensile properties, gel content, carbonyl index, molecular weight and density. It was shown that galbanic acid was highly effective in accelerating photo-oxidation of LLDPE films and an outstanding acceleration of photo-oxidation was observed for the film containing 0.2 wt % of galbanic acid in comparison with the film containing the same amount of benzophenone. However, the film containing coumarin did not exhibit considerable difference in behaviour in photo-oxidation relative to the neat LLDPE film during the exposure time. On the basis of the obtained results, the pro-oxidant activity of galbanic acid was described in terms of activity of the functional groups existing in the substituted moiety of its molecules. [ABSTRACT FROM AUTHOR]

In this article, a robust algorithm for prediction of forming limit diagrams (FLD) has been presented. The presented model is based on the "Marciniak and Kuczynski" (M-K) theory. Solution to the system of equations has been obtained by applying the Newton's method. Since the Newton's method usually has nonconverging problem, a particular backtracking algorithm has been developed and applied. In this algorithm, a technique for step length selection in the frame of gradient descent method has been implemented. Also for the convergence criterion the so-called "Armijo" condition has been used. For verification of the results, BBC2000 yield function and Swift hardening law for AK steel metal have been used. To obtain the necking angle, the effect of groove orientation on the left- and right-hand sides of FLD has been considered. Finally, the predicted FLD has been compared with the published experimental results. [ABSTRACT FROM AUTHOR]

The parameters affecting the grafting reaction and side reactions in free‐radical melt grafting of maleic anhydride (MA) onto high‐density polyethylene with the aid of 2,5‐dimethyl‐2,5‐di(t‐butyl peroxy)hexane peroxide(DTBPH) have been studied using an internal mixer. MA grafting degree of the maleated samples was measured with titrometry and FTIR spectroscopy methods. The extent of chain‐branching/crosslinking side reactions was evaluated with gel content and MFI determination. The flow behavior and melt viscoelastic properties of the samples were measured using a rheometric mechanical spectrometer. DTBPH and MA concentrations, reaction temperature, rotor speed, the type and concentration of coagents were among the studied parameters. The results show that MA and DTBPH concentration has a major role on the grafting reaction, chain‐branching/crosslinking side reactions and also the grafts microstructure in the final product. The reaction temperature has a complex effect on the maleation reaction. Increasing the rotor speed causes an increase in MA grafting degree of the samples and reduces the competitive side reactions. By using Gaylord additives, gel formation reduces at the expense of a dramatic decrease in the grafting degree. MA grafting degree is increased by the use of comonomers in the reaction and this is accompanied with a decrease in crosslinking side reaction when the vinyl type styrene comonomer is used. The results of processing torque in combination with the measurements of the melt viscoelastic property and gel content of the samples provide a great insight into understanding the gel formation mechanism. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 [ABSTRACT FROM AUTHOR]