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A non-uniform static floor field model was proposed to improve the limitations of existing floor field models in setting static field values and scene dimensions. Taking the overlapping area / volume of a single circular / spherical sphere (the evacuation exits as the center/ spherical center, and the width of the cell at the exit as the radius) and cell space as the setting benchmark of the static floor field value, the setting methods of the static floor field value in four different evacuation scenarios were determined. The MATLAB software was used to simulate the small evacuation scene. The results show that in the model, the static floor field has a significant effect on the evacuation step length, while the guide has a “reverse guidance” effect, and the interaction between the static and dynamic floor field inhibits the evacuation efficiency. The influence of guidance on the information entropy of cell evolution and the length of evacuation step is similar. Compared with the conventional static floor model, the non-uniform static floor model is more effective in showing the change of guiding function, and it can provide reference for making guidance strategy accurately. [ABSTRACT FROM AUTHOR]

Powders can exhibit different flow behaviour resulting from a combination of physical properties of the material and equipment design. Problems with powder flow are ubiquitous in process industry and become prominent when dealing with fine and cohesive powders. It is therefore of great importance to characterise the flowability of cohesive materials for better process control. Powder flowability is commonly assessed under relatively high preconsolidation loads using shear cell and uniaxial compression methods by which the unconfined yield strength (Y) is evaluated as a function of the applied load. However, these techniques are typically limited to applied stresses greater than 1 kPa and require a relatively large quantity of powder. To overcome these limitations, the recently developed Ball Indentation Method (BIM) is used in this work for assessing powder flow behaviour at low stress levels. The unconfined yield strength (Y) is inferred from the resistance to ball penetration into the surface of a powder bed, based on the method for measurement of hardness (H). This requires the flow resistance, represented by hardness, to be related to the unconfined yield strength by a proportionality factor termed the constraint factor, C , following the analogy with yield stress measurement in continuum solids, i.e. Y=H/C. The constraint factor for silanised glass ballotini, calcium carbonate, α-lactose monohydrate, Avicel and limestone is evaluated and reported here. It is shown that the unconfined yield strength inferred by this method correlates well with those from the uniaxial compression and shear cell measurement. The characterisation of the constraint factor makes it possible to use BIM for powder flowability testing at low stress levels and using a very small powder quantity. This is highly desirable for applications such as capsule filling, tableting and dry powder inhaler devices. [Display omitted] • We evaluate a method to infer powder flowability by ball indentation. • The technique can be applied at very low loads using small sample quantity. • Constraint factor, from unconfined yield strength and hardness measurement is reported. [ABSTRACT FROM AUTHOR]

This paper presents a feature modeling approach to address the 3D structural topology design optimization with feature constraints. In the proposed algorithm, various features are formed into searchable shape features by the feature modeling technology, and the models of feature elements are established. The feature elements that meet the design requirements are found by employing a feature matching technology, and the constraint factors combined with the pseudo density of elements are initialized according to the optimized feature elements. Then, through controlling the constraint factors and utilizing the optimization criterion method along with the filtering technology of independentmesh, the structural design optimization is implemented. The present feature modeling approach is applied to the feature-based structural topology optimization using empirical data. Meanwhile, the improved mathematical model based on the density method with the constraint factors and the corresponding solution processes are also presented. Compared with the traditional methodwhich requires complicated constraint processing, the present approach is flexibly applied to the 3D structural design optimization with added holes by changing the constraint factors, thus it can design a structure with predetermined features more directly and easily. Numerical examples show effectiveness of the proposed feature modeling approach, which is suitable for the practical engineering design. [ABSTRACT FROM AUTHOR]

Using cracked pipes design standards and finite element analysis, the limit load analysis for pipes containing surface cracks was determined. The study was performed on five pipes of different diameters with a constant crack length and depth. The crack geometry is a semi-elliptical surface crack. The cracked pipes are subjected to internal pressures which are obtained from formulas of cracked pipes design standards. Due to the ductile behavior of polyethylene pipes, the failure occurs when the critical stress reaches a value equal to the ultimate tensile strength multiplied by a constraint factor. In this work, the constraint factor was calculated and its evolution with the pipe diameter was analyzed. Three different definitions of a constraint factor based on global or local approaches were also compared, so that a new failure criterion can be obtained. The new failure criterion makes the prediction of the pipe residual life possible which, in turn, facilitates a systematic approach to maintenance and replacement of pipes. • Limit load analysis for pipes containing surface cracks was determined. • constraint factor was calculated and the pipe diameter was analyzed. • The results of the standards in terms of critical failure pressures, critical stresses and constraint factors are close to each other. • The constraint factor L∗ are always smaller than the values of factor L for all diameters and for all standards. • The deduced failure criterion based upon L∗enables the prediction of the remaining life of the studied pipes so that the maintenance and replacement works of drinking water pipes can be estimated [ABSTRACT FROM AUTHOR]

Medical image segmentation has been widely used in clinical practice. It is an important basis for medical experts to diagnose the disease. However, weak edges and intensity inhomogeneity (Niu et al. in 2nd IEEE international conference on computational intelligence and applications (ICCIA). 10.1109/ciapp.2017.816722, 2017) in medical images may hinder the accuracy of any traditional active contour segmentation methods. In this paper, we propose an improved active contour method by embedding a boundary constraint factor and adding the local information of images to the energy function of Chan–Vese model. Then graph cuts method is used to optimize the new energy function of the improved active contour method in this paper. There are several salient features: (1) we can obtain more accurate boundaries by embedding a constraint factor and adding local information of images. (2) The energy function is not easily to fall into local optimum. (3) Finally, our method only need to adjust one parameter. The evaluation results on Magnetic Resonance Imaging and Computed Tomography, blood vessel images, and mammograms masses show that the proposed method leads to more accurate boundary detection results than the state-of-the-art edge-based and region-based active contour segmentation methods. [ABSTRACT FROM AUTHOR]

Temperature dependence of ball indentation behaviour of Armox500T and IN718 in terms of Meyer's hardness, constraint factor (CF) and pile-up around indentation as a function of average strain at ambient temperature and elevated temperature (673 K) has been analysed using FEA. Subsequently, FE model has been validated by experimental data for IN718 and Armox500T. The value of CF for Armox500T and IN718 at RT is found to be 2.80 and 2.75, respectively. The CF value is increased to 3.66 and 3.41, respectively, at 673 K indicating the dependence of temperature. It is also observed that pile-up at a given strain for Armox500T is higher (low strain hardening) compared to IN718 (high strain hardening) under static indentation conditions. The FEA results are in good agreement with expansion cavity model and fully plastic model. [ABSTRACT FROM AUTHOR]

Measuring the uniaxial stress-strain response from indentation testing has been of great interest to the materials community ever since the seminal work on spherical indentation by David Tabor. In this regard, spherical indentation is the primary choice due to the ability to access a wide range of strains in a single test. While indentation testing is fairly simple to perform, the conversion factors required to calculate the uniaxial flow stress from hardness, which is commonly referred to as constraint factor and uniaxial strain from indentation contact radius and ball radius, which is called the Tabor coefficient, are not necessarily constant and most of the prior work involves assumptions about one of these conversion factors to calculate the other. In this work, we present a finite element analysis-based approach to independently determine the constraint factor and Tabor coefficient in the fully plastic indentation regime which is a pre-requisite for this analysis. The criteria to determine whether fully plastic indentation regime is satisfied has also been presented. The proposed approach has been validated by comparing the uniaxial stress-strain response from spherical indentation tests on OFHC copper and the data obtained by conventional uniaxial testing. Excellent agreement has been found between the two approaches which can be readily applied for measuring the uniaxial stress-strain response of coatings which is otherwise difficult to determine. [ABSTRACT FROM AUTHOR]

Static indentation and uniaxial compression tests have been conducted on Armox500T steel and its weldments to predict the constraint factor (CF), i.e., ratio of Meyer’s hardness to uniaxial flow stress. Series of dynamic indentation experiments were carried out at impact velocities ranging from 5 to 300 m/s to estimate dynamic hardness as a function of average strain. Subsequently, dynamic indentation (DI) test data and CF determined under static indentation conditions have been used to study the high strain rate plastic flow behavior of Armox500T weldments in comparison with the base metal. It was observed that flow stress for Armox500T and its weldments under dynamic loading conditions (104 s−1) are significantly higher than flow stress measured under static loading conditions (10−3 s−1). The plastic flow behavior computed from DI is in good agreement with the data evaluated through conventional split Hopkinson pressure bar technique. Further, the study of the microstructure of base metal and weldments by optical microscopy and SEM revealed a considerable variation in the microstructure. [ABSTRACT FROM AUTHOR]

In this paper, plasticity effects at the tip of an edge through-the-thickness crack are investigated by invoking the strip-yield model and the first order plate theory. The latter theory is the simplest extension of the classical plane theories of elasticity, which is capable of accounting for three-dimensional effects and, in particular, the plate thickness effect. By utilising the distributed dislocation technique, new results are obtained on the interaction of the free boundaries (free edge and free plate planes) with the crack tip plasticity region. Numerical results for the crack tip opening displacement and global constraint factor are first presented at various crack length to plate thickness and applied stress to yield stress ratios. The results are validated against past 3D solutions for an embedded crack as well as analytical solutions obtained under the plane stress or plane strain assumption. The new model and results can be utilised in advanced fracture and fatigue analyses of cracks emanating from a free surface. [ABSTRACT FROM AUTHOR]

The relation between the fatigue crack growth rate and stress state is significant for fatigue life estimation, especially for thick-welded structures with complex stress states. This paper proposes a hybrid Experimental-Finite Element Method aimed to obtain the fatigue crack growth rate corresponding to plane stress and plane strain states. A static load marking method is proposed to mark a series of crack fronts in a single edge notched bending specimen at known numbers of cycles, which is analysed by nonlinear finite element method to evaluate the stress state by a local constraint factor. Stress intensity factor at the center of the thickness and the surface position where plane strain and plane stress states approximately exist and remain unchanged with crack propagation, is calculated by the 1/4-node displacement method with consideration of non-orthogonal mesh influence. The J -integral method and the virtual crack closure technique are also applied to check the performance of the methods in dealing with the actual cracked body problem. Crack length increments are determined based on the crack front profiles. The da/dN-ΔK curves of plane strain and plane stress states are determined and compared with the results from normal fatigue crack growth rate tests according to Chinese standard: GB/T 6398-2000. The fatigue crack growth behavior of a semi-elliptical surface crack located at the weld toe of a T-plate welded joint subjected to cyclic tension loading is assessed based on the curves and the analytical results are compared with the experimental results. The asymptotic crack shape observed in experiments is successfully predicted by using the curves determined by the hybrid method. [ABSTRACT FROM AUTHOR]

Temperature dependence of constraint factor i.e. the ratio of static indentation hardness to uniaxial flow stress was studied for Ti-6Al-4V from RT to 673 K using FEA. Surface-to-surface contact with finite sliding, which was used to model the interaction between spherical indenter/test specimen and the constitutive equations were then applied in axi-symmetric FE model. The results obtained from numerical analysis were in good agreement with the modified Expanding Cavity Model. Meyer's hardness increased with average strain and strain hardening index increased from 0.19 to 0.21 with rise in temperature. [ABSTRACT FROM AUTHOR]

In the recent years, it has been shown that the Pathak–Kalidindi (P–K) spherical indentation protocol and its accompanying definition of the indentation strain has many advantages over the classical definition. In the present work, an improved methodology to obtain the uniaxial stress–strain curve from the spherical indentation stress–strain curve is proposed based on the P–K protocol. The classical definitions of the representative strain, ϵ r u n i , which relates the indentation strain to an equivalent uniaxial strain, and the non-dimensional strain, ϵ N D , which relates the indentation strain to the uniaxial stress, are revised in this work. These revisions are made such that they are consistent with the P–K protocol, and are shown to have the similar relationships as the classical equations. Using non-dimensional analysis, a closed form expression is obtained for the uniaxial stress as a function of the elastic–plastic properties of the material and the indentation strain. Based on this expression, an inverse approach is then utilized using results of finite element simulations to develop a methodology to predict uniaxial stress–strain curves from spherical indentation data for a large range of elastic–plastic mechanical properties. This methodology is demonstrated on spherical indentation stress–strain curves obtained from a set of finite element simulations for materials with mechanical properties spanning those of widely used structural alloys. Finally, this method is shown to provide good estimates of the uniaxial stress–strain curves from experimental spherical microindentation tests. • An improved way to estimate stress–strain curves from indentation data is presented. • The method is consistent with the Pathak–Kalidindi (P–K) spherical indentation protocol. • One key feature of the method is a better estimate of the constraint factor. • The constraint factor depends on a new definition of the non-dimensional strain. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) opening mode stress intensity factors (SIFs) for structural steel-welded 'T' details were investigated by the finite element method. A 3D shape-dependent correction factor is proposed for semi-elliptical surface cracks. The aspect ratio (a/c) of a semi-elliptical crack plays a key role in the approximation of 3D-SIF values, and in the present study, it was estimated for a 3D crack analysis. The estimated 3D-SIF was determined through a correlation between the a/c ratio and the two-dimensional SIF for semi-elliptical cracks in the thickness direction adjacent to the web-flange junction of a welded 'T'. The resulting equation can be used to estimate the 3D-SIF values from the two-dimensional SIF without much ambiguity. [ABSTRACT FROM AUTHOR]

Functionally graded cemented carbides (FGCCs) have an excellent combination of high hardness and high toughness. But the appearance of residual stresses, resulting from cobalt gradient and mismatch between mechanical properties and material constituents, influences the lifetime of FGCCs. To get the thermal stress field distribution, a constitutive equation for WC-Co FGCCs was developed by redefinition of elastic constraint factor and introduction of plastic constraint factor. The constitutive model was applied to thermal stress analysis of WC-Co composites. The distribution of thermal stresses in WC-Co specimen was obtained by the finite element numerical method. Simultaneously, the surface compressive stress of FGCCs alloy was measured by X-ray diffraction (sinψ) 2 . Numerical results show the thermal stresses of WC-Co composites mainly concentrate in the cobalt gradient zone and the maximum value of principal compressive stress is 380 MPa in the surface zone. This result is in good agreement with X-ray diffraction measurement. [ABSTRACT FROM AUTHOR]

The stress-strain fields realized in spherical indentation tests are highly heterogeneous, and present a significant challenge to the recovery of bulk stress-strain responses such as those measured in simple compression tests performed on samples with a uniform cross section in the gauge section. In this paper, we critically explore the correlations between indentation stress-strain curves and the simple compression stress-strain curves using the finite element model of indentation as a surrogate for the actual experiment. The central advantage of using a finite element model is that it allows us to critically explore the sensitivity of various assumptions or values of parameters or other choices made in the analyses protocols on the extracted results. Based on this study, a general protocol has been established to reliably recover the uniaxial stress-strain response directly from the indentation stress-strain curve for isotropic elastic-plastic materials. The protocols developed are validated for a range of hardening behaviors. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to avoid traditional particle swarm optimization algorithm converges too fast and easy to fall into local optimal value, on the basis of particle swarm algorithm with global-local optimal value, this paper proposed a hybrid particle swarm algorithm with improved learning factor and constraint factor. It added the neighborhood optimal value to the updating formula of speed, the speed updated by the role of global optimal value and neighborhood optimal value together, and improved the search ability of particles. It improved the learning factor and constraint factor, balance global search capability and local development capacity of particles. Compared several classical test functions, the algorithm can greatly improve the search ability of the particles. [ABSTRACT FROM AUTHOR]

A review of the concept of representative strain in Vickers hardness testing is provided and different values reported in the literature are summarized. A new criterion for the proper selection of the representative strain is introduced. By using this criterion, the stress–strain curves of 63 specimens excised from a 7010 aluminum alloy rectilinear forging, cooled differently from the solution treatment temperature have been analyzed. Regression analyses have been conducted between the Vickers hardness numbers and the true stress values corresponding to twenty eight true plastic strain levels. These results indicate that the representative strain associated with diamond indentation is between 0.0185 and 0.0301 with the most likely number of 0.0240. The value of the constraint factor changes with the assumed representative strain and is essentially equal to 3.00 when 0.0240 is chosen as the representative strain. [ABSTRACT FROM AUTHOR]

Highlights: [•] The representative strain, εR , for Vickers indentation is numerically studied. [•] A new methodology for determining εR is proposed. [•] There is no universal representative strain in Vickers indentation. [•] The mean pressure-based representative strain is in the range from 0.08 to 0.25. [•] The Martens hardness-based representative strain lies between 0.025 and 0.095. [Copyright &y& Elsevier]

Copyright of Matériaux et Techniques is the property of EDP Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract: Dynamic indentation (DI) tests using spherical projectile have been carried out on solution treated and aged (STA) Ti–6Al–4V alloy at ambient conditions in the velocity range of 32–186m/s. The DI behavior of the alloy, especially, dynamic hardness, lip height as a function of average strain and depth of the plastic-zone underneath the indentation have been analyzed. Dynamic flow stress–strain curve representing high strain rate flow behavior was also evaluated using constraint factor (CF) determined under static indentation conditions. [Copyright &y& Elsevier]

In this study, finite element method and X-ray diffraction measurement were used to determine the thermal stress distribution of functionally graded WC-Co composites. The calculated results show that high stress concentration occurs in the cobalt gradient zone, tensile stress pile-up occurs in the cobalt rich zone and compressive stress pile-up occurs in the surface zone. As the sintering time is increased, compressive residual stress in the surface zone has a tendency of decreasing. The maximum value of compressive stress in the surface zone is 250 MPa. The results are in good agreement with X-ray diffraction measurement results. For the purpose of this work, the material design method is achieved by changing the calculated parameters. [ABSTRACT FROM AUTHOR]

Abstract: Static indentation and compression tests have been carried out on IN718 in the temperature range of 300–1073K with a view to evaluate the effect of temperature on constraint factor (CF), that is the ratio of indentation hardness to flow stress. The value of CF is found to be below 3 at room temperature and above 3 at elevated temperatures. The experimental results are also compared with Expansion Cavity Model (ECM) and Fully Plastic Model (FPM). [ABSTRACT FROM AUTHOR]

Abstract: The fatigue of mechanical components can be explained by the growth of very small fatigue cracks, which lead to the final fracture of the component. It is, therefore, essential to try to describe the growth and the thresholds of small cracks. In this paper, the Strip-Yield model is used to analyse the fatigue thresholds of a mild-steel widely used for manufacturing railway axles. Furthermore, the need for a precise definition of the constraint factor, under cyclic, non-linear response of the material, is addressed, together with the choice of an appropriate constraint formulation. This results in good fatigue threshold predictions at R =−1 for long cracks (obtained from SE(B) specimens), whereas the description of the Kitagawa diagram (obtained by fatigue tests on specimens with artificial defects) is relatively poor. The analysis of the cyclic stress ahead of small cracks enables us to compare the results with the threshold models for small cracks by McEvily, Usami and Shida. [Copyright &y& Elsevier]