Yield Stress Of Material Research Articles

Copper Wire Multi-Pass Drawing: Process Modeling and Optimization

During cold wire drawing process, the drawing stress applied to the wire at the exit of the die must be lower than the material yield stress (including strain-hardening) to avoid wire necking and fracture. Several studies have been developed to investigate and model the stress acting on the wire in the single pass drawing and its dependence on the main process parameters. The aim of this work is to apply an analytical model for the calculation of the drawing stresses during the whole complex multi-pass manufacturing process in industrial environment, considering not only the forces acting in the die but also the driving forces of the rotating capstans (drawing tension and back tension). The drawing of ETP Pure Copper (99.9% in weight), using two industrial multi-pass machines with different reduction ratio sequences, is analysed and then discussed in order to understand the different failure rates. Finally, the study compared step by step, the evolution of the drawing stresses respect to material yield stress when different processing conditions (i.e. change of capstan windings, change of friction conditions in the die and in the capstan) are applied.

Volume-shear coupling in a mesoscopic model of amorphous materials.

We present a two-dimensional mesoscopic model of a yield stress material that includes the possibility of local volume fluctuations coupled to shear in such a way that the shear strength of the material decreases as the local density decreases. The model reproduces a number of effects well known in the phenomenology of this kind of material. In particular, we find that the volume of the sample increases as the deformation rate increases; shear bands are no longer oriented at 45^{∘} with respect to the principal axis of the applied stress (as in the absence of volume-shear coupling); and homogeneous deformation becomes unstable at low enough deformation rates if volume-shear coupling is strong enough. We also discuss the effect of this coupling on some out-of-equilibrium configurations, which can be relevant to the study of the shear bands observed in metallic glasses.

Viscoelastoplastic classification of cementitious suspensions: transient and non-linear flow analysis in rotational and oscillatory shear flows

Rheological modeling of special concretes such as ultra-high performance concretes (UHPCs), self-compacting concretes (SCCs), or environmentally friendly concretes with low clinker contents but containing many fine particles increases model complexity because high amounts of colloidal and fine particles and complex chemistry result in strongly non-Newtonian rheological behavior. Straight-forward viscoplastic rheological models such as the well-known Bingham- or Herschel-Bulkley approach do not fit the flow behavior on a large scale at and lead to boundary value problems in numerical flow simulations. Increased viscoelastic properties due to chemical admixtures are not described by pure viscoplasticity analysis methods. To fill this gap, our research presents viscoplastic and viscoelastic linear and non-linear rheological characterization methods for common and strongly non-Newtonian cement pastes and combines the methods for a comprehensive viscoelastoplastic modeling of cementitious building materials. We illustrate and discuss the benefits and boundaries of each measurement technique in dependence of cementitious paste complexity. Three solid volume fractions from phi = 0.45 to 0.55 and three different flowability ranges, adjusted through varying superplasticizer amounts, were investigated in respect of steady-state and transient yield stress, viscosity, and non-linear viscoelastic material properties. Our results reveal that with increasing solid volume fraction and polymer amount, viscoelastoplastic modeling describes rheological flow on a large flow scale more appropriately than common viscoplastic methods. The results show a new approach for a full quantitative and qualitative rheological classification of cementitious building materials and thus improve the understanding of densely packed colloidal cementitious suspensions. The findings serve as prospective guideline to model complex cementitious building materials both at low and high shear rates, and to find an appropriate rheological description at the boundaries of flow.Graphical abstract

Inter-laboratory study on the influence of 3D concrete printing set-ups on the bond behaviour of various reinforcements

This study investigates the influence of different printing set-ups and materials on the bond strength of reinforcement manually placed between 3D printed concrete layers. An identical experimental campaign was performed at two institutes in Switzerland and Italy. Each institute used its own printing process, which consisted either of a set on-demand mix or a high yield stress material. Two types of reinforcement (reinforcing bar Ø8 mm and a high strength steel wire Ø1 mm) and three production configurations (casting and printing with the reinforcement parallel or perpendicular to the printing direction) were investigated. The results showed high bond strength with only a limited influence of the fabrication method for the reinforcing bars. An increased bond was observed for the set on-demand approach compared to the high yield strength material. The comparison with existing models showed that the reinforcing bar bond strength of printed concrete varies slightly from conventional concrete. The high strength wires exhibited poor bond. Based on the gathered experiences, insights into the standardisation of testing for 3D concrete printing are discussed.

Leading edge cracking observed in WEST

One of the missions of the WEST tokamak is to test in a realistic tokamak environment, the ITER-like divertor plasma facing components made with tungsten. On exposed leading edges of monoblocks, poloidally-distributed cracks having an average spacing of 0.4 mm, running perpendicular to the cooling tube axis, were observed following the experimental campaigns in 2018. Damage may be induced by different processes which can lead to: brittle fracture below the Ductile to Brittle Transition temperature or ductile failure for which softening (recovery/recrystallization) process plays a major role. To improve our understanding about the leading edge damage process, numerical simulations were run here. The following results are specially studied: (i) the thermal gradients; (ii) the softening fraction gradient and (iii) the stress and strain distributions taking into account the mechanical properties of tungsten (elastic-viscoplastic) and the softening phenomenon. This paper describes the results obtained for a range of WEST steady state parallel heat flux (from 45 MW/ m2 to 70 MW/ m2 ) and disruption (600 MW/ m2 ) heat loading on the leading edge. Estimated results related to the plastic strain accumulation, give an interpretation of the premature cracking of the monoblock leading edge but do not explain the poloidal distribution. According to the numerical results, brittle fracture are expected under disruption as estimated normal stresses are beyond the material yield stress, along 88% of the leading edge.

Tool Design for Reducing Excessive Transportation in a Textile Industry: Case Study in a Textile Company in Indonesia

This research aimed to design a tool that can reduce one type of waste on the production floor, namely excessive transportation in the form of a waste of transportation time. The design of the tool was carried out by inspecting to the details of the failures that occurred in the previous means of transportation. This development research implemented stopwatch time study method and failure mode and effect analysis to find out the value of the loss of transportation time and the types of failures that cause it. The sample of the transportation process time was taken by simple random sampling method from the intensity of the transportation process per month, based on the type of transportation process on the production floor of a textile company. Then the design of the tool was carried out using the morphological matrix method and weighted objectives table to create the design that fits the needs. The results show that the prediction of the amount of excessive transportation in the form of a waste of time can be minimized by 8,11 hours. Moreover, the new design tool also has a safe structure due to its attained maximum equivalent stress was 17.4 MPa which was smaller than the maximum yield stress of the ST37 material.

Recent developments on yield stress materials

<h2>Abstract</h2> Several gels, suspensions, emulsions and foams found both in nature and industrial processes and products are complex yield stress materials that exhibit a rich variety of mechanical responses, like elasticity and time-dependence, in addition to yielding. A rigorous definition and physical interpretation of the related material functions are challenging. In this talk we discuss how this complexity affects fundamental concepts and measurements of these materials. Our discussion covers different related topics, such as (i) the need for the introduction of a yield stress tensor, (ii) thixotropy modeling---including the choice of the microstructure destruction agent, (iii) rheological characterization with quasilinear large amplitude oscillatory shear, and (iv) transient and steady-state shear banding.

Analysis of Sealing Performance of Metal B-ring Self-Tightening Structure

Process industries often use B-ring self-tightening sealing structures and rely on interference assembly to meet the initial sealing requirements. Therefore, determining reasonable B-ring material, size and interference is crucial to ensure the sealing performance of the structure. In this paper, based on elastic deformation analysis, the deformation co-ordination equation of a B-ring sealing structure was established, and a sealing contact pressure calculation formula was obtained, with discussion of the main factors affecting sealing performance. With the finite element method, transient temperature field analysis was carried out for startup and shutdown load cases, and contact analysis was carried out for interference assembly, startup and shutdown. Based on the evaluation criteria of sealing performance with proposed sealing rate and leakage parameters, the effects of material properties, interference, B-ring size, etc., on sealing performance were investigated, revealing that although a B-ring with high material yield stress can meet the sealing requirements, both the B-ring and the sealing surface of a reactor body will yield plastic deformation. B-rings with a low material yield stress exhibit obvious plastic deformation during startup and leak during shutdown. However, leakage parameters can be minimized by smaller interference and moderate wave radius.

Yielding and buckling behavior of aluminium and steel shear panels with different slenderness ratios

The present study investigates the effects of material mechanical properties and plate slenderness ratios on the nonlinear and cyclic behavior characteristics of metal shear panels (including carbon steel (CS), low yield point steel (LYP160) and aluminium (AL)), using the finite element method. The plates are first qualitatively and quantitatively classified into the five groups of very slender, slender, moderate, stocky and very stocky, regarding their slenderness ratios. Very slender plates have negligible buckling capacity and thus, they buckle at the initial stages of loading. Slender plates buckle in the elastic range of behavior. Moderate plates buckle in the inelastic range of stresses before material yielding occurs in the plates. Stocky plates buckle in the plastic (post-yield) range of stresses. The behavior of very stocky plates is only dominated by yielding phenomenon and they do not buckle during loading. Based on the statistical analysis of results, new relationships for estimation of inelastic and plastic buckling loads are also proposed. The cyclic analysis results show that the energy dissipation capability of very stocky/stocky/moderate plates is solely dependent on the material yield stress and elastic modulus of elasticity, whereas for the slender plates, the effectiveness of material yield stress in the energy dissipation of plates is decreased and the role of the material elastic modulus of elasticity becomes more important. In the case of very slender shear plates, the energy dissipation capability seems to be dependent on the initial and secondary modulus of material only.

A layer of yield-stress material on a flat plate that moves suddenly

The flow of an unbounded Newtonian fluid above a flat solid plate, set into motion suddenly with uniform velocity, is a canonical problem investigated by Stokes (On the effect of the internal friction of fluids on the motion of pendulums, Trans. Camb. Phil. Soc., vol. 9, 1851) and Rayleigh (Lond. Edinb. Dubl. Philos. Mag. J. Sci., vol. 21, issue 126, 1911, pp. 697–711). We tackle the same problem but with the fluid replaced by a yield-stress material of finite height with a free surface; the latter ensures both yielded (fluid-like) and rigid behaviour. The interface between the yielded and rigid regions – the so-called ‘yield surface’ – always emerges from the plate at a rate faster than that for momentum diffusion. The rigid region, adjacent to the free surface, is accelerated by the constant yield stress acting at this yield surface. As the velocity of this region increases following start-up, its acceleration climaxes and subsequently diminishes. In this latter period, the thickness of the rigid region increases owing to relaxation of the velocity gradients and the stress. The yield surface eventually collides with the plate in finite time, after which the entire material moves in concert with the plate as a rigid body. Analytical and numerical results are presented that can form the basis for practical applications. This includes the development of a ‘rheological microscope’ to directly detect and measure the yield stress. The analysis focuses on exploring the flow physics of a Bingham material. This is shown to be similar to that of a general Herschel–Bulkley material with shear-thinning or shear-thickening rheology.

Physico–mechanical properties of poly(ethylene‐co‐vinyl acetate)/acrylonitrile‐butadiene rubber/multi‐walled carbon nanotubes nanocomposites

AbstractThe influence of multi‐walled carbon nanotubes (MWCNTs) on thermal, mechanical and wetting properties as well as rheological behavior of poly(ethylene‐co‐vinyl acetate) (EVA)/acrylonitrile‐butadiene rubber nanocomposites were studied. The solid surface free energy (), work of adhesion (), interfacial free energy (), spreading coefficient () and Girifalco‐Good's interaction parameter () were calculated for the materials fabricated. The results showed that the contact angle and decreased; however, , , , and increased with the increase in MWCNTs content. The maximum tensile strength and toughness were obtained for the nanocomposite containing 1 wt% nanofillers. It was also found that both of the relaxation ratio (Rr) and relaxation rate index (n) decreased with increasing in the carbon nanotubes (CNTs) concentration. The results designated that the values of Rr and n for the nanocomposite containing 7 wt% MWCNTs were 19% and 60% smaller than those of the unfilled blend, respectively. The Casson plot analysis indicated that the yield stress of the molten materials incremented with the increase in MWCNTs loading according to a quadratic equation. The analysis of crystallization exotherms and melting endotherms revealed that CNTs triggered the crystallization process at slightly higher temperature, however, melting point slightly and the rate of nucleation noticeably reduced with the increase in the nanofillers content.

The dynamic ultimate strength of stiffened panels under axial impact loading

ABSTRACT The dynamic ultimate compressive strength of stiffened panels under longitudinal compressive impact is studied based on the non-linear finite element method (FEM), and an empirical formula was derived based on the results. Three types of initial deflections are considered in numerical simulation. The FE procedure was validated by comparing with existing formulas and published pieces of literature. The influences of parameters, such as material yield stress, impact duration, impact shape, plate thickness ratio, plate aspect ratio, web height ratio and web thickness ratio, were investigated. The results indicate the impact duration has a significant influence on the non-dimensional dynamic ultimate strength; the geometrical parameters and material yield strength also have a certain effect. While with the same duration, amplitude and impulse, different impact shapes have little influence. The fitting accuracy of the formula was proved by a comparison between the proposed formula and FE results. And its applicability was validated by applying to real ship panels.

Effect of Transverse Restraint on Welding Residual Stress in V-Groove Butt Welding

When evaluating the safety of steel structures, welding residual stress is used as the secondary load and if there is any restraint, the yield stress of the base material is used for secondary load, regardless of the size of the restraint. Of late, as the yield stress of members is increasing with the increase in the use of high-strength steels, the proportion of the residual welding stress in the total load during the evaluation of the safety of structures is increasing. Therefore, it is necessary to investigate the effect of the size of the restraint on the residual welding stress, determine reasonable residual stress according to the size of the restraint, and apply the residual stress as a secondary load. To investigate the effect of constraint conditions on residual welding stress, thermoelastic–plastic analysis was performed for different member thicknesses, yield stresses, and constraint sizes. The restraint did not affect the residual stress in the direction of the weld line but did affect the residual stress in the direction perpendicular to the weld line. The restraint moved the tensile stress to the compression stress in the direction perpendicular to the weld line at the first layer of the weld and moved the compression stress to the tensile stress at the middle and final layers of the weld. The change in residual stress was the largest in the middle of the weld.

Machine learning-based sensitivity of steel frames with highly imbalanced and high-dimensional data

The machine learning-based feature selection approach is presented to estimate the effect of uncertainties and identify failure modes of structures that incorporate a low failure probability and high-dimensional uncertainties. As structures are designed to have few failures, a dataset classified based on the failure status becomes imbalanced, which poses a challenge for the predictive modeling of machine learning classifiers. Moreover, in order to improve the accuracy and efficiency of the model performance, it is necessary to determine the critical factors and redundant factors, especially for a large feature set. This study benchmarks the novel method for sensitivity analysis by using datasets that exacerbate the problems involved in class imbalance and large number of input features. This study investigates two planar steel frames with spatially uncorrelated properties between structural members. Geometric and material properties are considered as uncertainties, such as material yield stress, Young’s modulus, frame sway, and residual stress. Six feature importance techniques including ANOVA, mRMR, Spearman’s rank, impurity-based, permutation, and SHAP are employed to measure the feature importance and identify parameters germane to the prediction of structural failures. Logistic regression and decision tree models are trained on the important feature set, and the predictive performance is evaluated. The use of the feature importance approach for structures with a low probability of failure and a large number of uncertain parameters is validated by showing identical results with the reliability-based sensitivity study and appropriate predictive accuracy.

Multi-level arch characteristics and flow enhancement regulation of nano powders discharged from silo

Nanoparticles have broad application prospects, but their poor flowability poses a challenge to the handling and transportation. Here, we experimentally demonstrate that modulated pulsed aeration can destroy the consolidation of nano powder and achieve a breakthrough in silo discharge from clogging to flow. We confirm the multi-level arch structure in the silo discharge of nano powders: free-fall arch and cohesive arch. And the location of multi-level arch can be determined by the yield stress of material. Furthermore, the method of combined pulsed aeration was proposed to enhance the discharge flow. Specifically, the influence of modulation of pulsed airflow including frequency and duty cycle and aeration location configuration on nanoparticles silo discharge flow was explored. And the optimal combination method of double pulsed aeration was determined to eliminate the cohesive arch and greatly increase the discharge rate, which is close to the hypothesis liquid-like flow rate.

Residual stress indentation model based on material equivalence

A novel residual stress indentation model for conical indentation loading is proposed to describe the relationship between the residual stress, material constitutive parameters, load, and displacement for materials with a uniaxial constitutive relationship that obeys Hollomon’s power law (H-law). The novel model was established based on the principle that the equivalent material without residual stress corresponds to the original material with residual stress, conical indentation theoretical model based on energy density equivalence, and an assumed power-law relationship between the dimensionless residual stress and relative difference of the yield stresses of the equivalent material and original material. Sixty imaginary H-law materials with ten equibiaxial and ten uniaxial residual stresses were investigated by Finite Element Analysis (FEA). The residual stresses predicted by the novel model from the indentation load–displacement curves simulated for the imaginary materials are in close agreement with those applied by the FEA. Finally, indentation tests for Cr12MoV steel, 45 steel, and 6061-T6511 aluminum alloy were carried out on their specimens without residual stress and their bending specimens with equibiaxial and uniaxial residual stresses. The residual stresses predicted by the novel model according to the indentation load–displacement test curves are in good agreement with those applied by the tests.

The nonlinear rheology of complex yield stress foods

Many foods have a yield stress that allows them to retain a desired shape at rest, but transition into a viscous fluid when being served or consumed. The determination of the yield stress of the food dictates how the foods are formed and packaged, how they are served, and how they are perceived when being eaten. Oscillatory shearing provides an ideal test protocol to map the rheology across a range of time and flow strength scales. We couple oscillatory shearing and an iterative recovery procedure to show that the yielding process is a continuous transition for two common yield stress foods. We show that unrecoverable processes from oscillatory tests are equivalent to the steady shear flow behavior. We show that this yielding behavior can be well approximated by a recently published model that treats yield stress materials as continuous viscoelastic fluids with a rate-dependent relaxation time and has parameters that can be obtained from the linear viscoelastic oscillatory frequency sweep and the steady shear flow curve.

A Cylindrical Grip Type of Tactile Device Using Magneto-Responsive Materials Integrated with Surgical Robot Console: Design and Analysis.

This paper proposes a cylindrical grip type of tactile device that is effectively integrated to a surgical robot console so that a surgeon can easily touch and feel the same stiffness as the operating organs. This is possible since the yield stress (or stiffness) of magnetic-responsive materials can be tuned or controlled by the magnetic field intensity. The proposed tactile device consists of two main parts: a magnetorheological elastomer (MRE) layer and a magnetorheological fluid (MRF) core. The grip shape of the device to be positioned on the handle part of the master of the surgical robot is configured and its operating principle is discussed. Then, a couple of equations to calculate the stiffness from the gripping force and the field-dependent yield stress of MRF are derived and integrated using the finite element analysis (FEA) model. After simulating the stiffness of the proposed tactile device as a function of the magnetic field intensity (or current), the stiffnesses of various human organs, including the liver and heart, are calculated from known data of an elastic modulus. It is demonstrated from comparative data between calculated stiffness from human tissues and simulated stiffness from FEA that the proposed tactile device can generate sufficient stiffness with a low current level to recognize various human organs which are significantly required in the surgical robot system.

Numerical calculation on the seismic performance of a steel frame beam-to-column joint with welding residual stress

ABSTRACT Residual stress has almost always been an essential issue associated with welded structural steel. In this paper, thermal elastic–plastic finite element method (FEM) is adopted to calculate the welding residual stress of a steel frame beam-to-column, and then the calculated residual stress is applied to the subject as an initial condition to calculate its mechanical behaviour. Both monotonic loading and cyclic loading are designed to simulate the seismic behaviour of the structure. Bonora damage model [41–44] is used to calculate the initiation and propagation of the crack. Finally, the hysteretic curve of the structure under cyclic loading is obtained. The results show that the main component of the welding residual stress along weld fillers of the steel frame beam-to-column is longitudinal tensile stress, and the magnitude of the residual tensile stress in welding stable zone is about 1.2 times of the material yield stress. Welding residual stress mainly affects the ductility and fracture behaviour of the steel frame beam-to-column. Under monotonic loading, the drift ratio of crack initiation with welding residual stress is reduced by 9% compared with that without welding residual stress. Under cyclic loading, when welding residual stress is taken into account, the crack initiates a little earlier than when welding residual stress is not considered. Compared with monotonic loading, crack initiates much easier when the structure is subjected to cyclic loading.

Analytical prediction of yield stress and strain hardening in a strain gradient plasticity material reinforced by small elastic particles

The influence on macroscopic work hardening of small, spherical, elastic particles dispersed within a matrix is studied using an isotropic strain gradient plasticity framework. An analytical solution for strain hardening, i.e. the flow stress as a function of plastic strain, based on a recently developed model for initial yield strength is proposed. The model accounts for random variations in particle size and elastic properties, and is numerically validated against FE solutions in 2D/3D unit cell models. Excellent agreement is found as long as the typical particle radius is much smaller than the material length scale, given that the particle volume fraction is not too large (<10%) and that the particle/matrix elastic mismatch is within a realistic range. Finally, the model is augmented to account for strengthening contribution from shearable particles using classic line tension models and successfully calibrated against experimental tensile data on an Al−2.8wt%Mg−0.16wt%Sc alloy.