Yield Stress Of Material Research Articles

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.

Displacement flow of yield stress materials in annular spaces of variable cross section

We conducted an experimental study of a yield stress material being displaced upwardly at controlled flow rate by a Newtonian fluid in an annular space whose external wall consists of a sudden expansion–contraction. This system is a simplified representation of the primary cementing process of an oil well, whose bore diameter may present variations. In the experiments, different pairs of fluids were employed. The yield stress materials were Carbopol aqueous solutions at three different weight concentrations, with Herschel–Bulkley viscosity behavior. The Newtonian liquid was a glycerin/water mixture. A wide range of flow rates were explored, varying the dimensionless cavity depth and cavity axial length. A non-monotonic behavior is observed for the dimensionless volume of yield stress material displaced from the cavity by the Newtonian fluid flow. In addition, the rheological properties and geometrical parameters were seen to have a strong influence on the displaced volume.

Analysis of Factors Affecting the Rheological Properties of Muddy Flow and Their Measurement Method

Abnormal weather phenomena debris damage has recently been increasing worldwide. As primary rheological properties, the yield stress and plastic viscosity of muddy materials affect the flow distance and velocity. Therefore, in this study, direct and indirect measurement test methods for rheological properties and factors affecting the these properties were analyzed. Measurement methods utilize rheometers, shear creep, fall cones, inclined planes, direct shear, and ring shear, with each method having its respective advantages and disadvantages. Factors that affect rheological properties are water content, liquidity index, and the size of soil particles. This study enables determination of the best test and rheological properties suitable for the selected range and selected object.

Comparative Multi-Modal, Multi-Scale Residual Stress Evaluation in SLM 3D-Printed Al-Si-Mg Alloy (RS-300) Parts

SLM additive manufacturing has demonstrated great potential for aerospace applications when structural elements of individual design and/or complex shape need to be promptly supplied. 3D-printable AlSi10Mg (RS-300) alloy is widely used for the fabrication of different structures in the aerospace industry. The importance of the evaluation of residual stresses that arise as a result of the 3D-printing process’ complex thermal history is widely discussed in literature, but systematic assessment remains lacking for their magnitude, spatial distribution, and comparative analysis of different evaluation techniques. In this study, we report the results of a systematic study of residual stresses in 3D-printed double tower shaped samples using several approaches: the contour method, blind hole drilling laser speckle interferometry, X-ray diffraction, and Xe pFIB-DIC micro-ring-core milling analysis. We show that a high level of tensile and compressive residual stresses is inherited from SLM 3D-printing and retained for longer than 6 months. The stresses vary (from −80 to +180 MPa) over a significant proportion of the material yield stress (from −⅓ to ¾). All residual stress evaluation techniques considered returned comparable values of residual stresses, regardless of dramatically different dimensional scales, which ranged from millimeters for the contour method, laser speckle interferometry, and XRD down to small fractions of a mm (70 μm) for Xe pFIB-DIC ring-core drilling. The use of residual stress evaluation is discussed in the context of optimizing printing strategies to enhance mechanical performance and long-term durability.

Defining developable ship surfaces considering material properties

This paper presents a practical method to define a quasi-developable surface that leans on two boundary curves or directrices. As a main difference with the rest of literature that works with quasi-developable surfaces assuming the fact that most of practical materials allow for a little bit of stretching, this paper presents how to quantify this developability in terms of a geometrical factor, the limit warp angle.The limit warp angle has been calculated numerically for steel and aluminum, applying a bending moment to plates of different geometries until a given percentage of the material's yield stress is surpassed. It has been demonstrated that developability depends on the material properties, thickness and aspect ratio of the plates that will be used to construct the real surface. The presented approach considers both physics and geometry and links them together.By considering the limit warp angle, a quasi-developable surface can be obtained without altering the directrices shape, unless the directrix curves present a very different shape between each other. This is very useful in engineering applications that produce designs based on curves and ease the use of parametric design techniques into the object definition. The constrained or parametric definition of ship hulls is beneficial during the initial phases of the ship design because it speeds up the creation process, provides more clarity about the influence of various parameters, and allows for the development of a range of concept hull surfaces.All the designs and calculations in this paper have been developed with a single, affordable and non specialized CAD software, indicating the capabilities of CAD products currently available for any designer.

Investigation of microstructure and mechanical properties evolution in 7050 aluminum alloy and 316L stainless steel treated by laser shock peening

Laser shock peening (LSP) has been widely applied to enhance the mechanical properties of metallic materials by modifying their sub-surface microstructures. However, controversies still exist on whether grain refinement can be obtained after the LSP process. To investigate the effect caused by LSP in metallic materials, a 7050 aluminum alloy and 316L stainless steel, which are typically high and low stacking fault energy (SFE) materials, respectively, were selected for this study. The microstructure modified by different LSP cycles and energy densities in both materials was illustrated by Electron Backscatter Diffraction (EBSD). The result shows that no grain refinement was observed regardless of the laser cycles and energy density. The most evident change was the increase of dislocation density, and higher dislocation density was observed with the increase of LSP cycles and energy density. The hardness and residual stress measurements around the LSPed areas show that LSP can effectively introduce a plastic deformation layer ranging from 600~1300 μm. It was revealed from the tensile tests that the yield strength of both materials was improved after the LSP process with the scarification of their elongations. Moreover, a potential method to calculate the dynamic yield stress of metallic materials was put forward with the help of the LSP process.

Experimental and analytical studies of mechanical properties of additively manufactured lattice structure based on octagonal bipyramid cubic unit cell

In this study, analytical relationships were developed to calculate the mechanical properties including elastic modulus, Poisson's ratio, and yield stress of a new porous material based on the regular polygonal transversely isotropic micro-architecture called octagonal bipyramid. Stiffness matrix of the lattice structure was extracted based on superposition principle method using Euler-Bernoulli beam theory equations. The octagonal bipyramid unit cell has a higher stiffness than other shapes due to its triangular faces, vertical, horizontal, and inclined trusses, as well as having eight node connections in the lattice configuration. Analytical results were validated by utilizing the finite element modeling of the structure in Abaqus software. Also, additively manufactured porous lattice structure was fabricated by FDM method and compressive test experiments were performed to determine its mechanical properties. Then, digital image correlation (DIC) method was used to calculate the Poisson's ratio during compression test. The analytical results are in good agreement with the numerical and experimental results. Finally, the effect of changes in the geometric parameters of the unit cell was evaluated on the mechanical behavior of the structure including elastic modulus, Poisson's ratio, and yield stress in the X and Y directions.

Slump Test: A New Empirical Model for High Yield Stress Materials

Abstract In order to decrease the fitting deviation between rheometrical measurements and empirical parameters using slump test, this paper proposes a new analytical method to evaluate the high yield stress of materials (cement pastes).In doing so, an experimental study was performed for measuring the empirical characteristics by cylindrical mold with different water to binder ratios (w/b) by aiming to increase the yield stress. Parallelly, experimental observations showed clearly the unyielded zone at flow stoppage of high yield stress samples. Based on these results, an idea was formed to applied metallic element at inlet of mold in order to push the spreading of paste. The obtained results of the model proposed in this paper were compared with the yield stress evaluated from shear flow curves using AR2000-rheometer with plate-plate geometry at rate-controlled. In fact, this study demonstrates the applicability and novelty of the present model in the process of relating the empirical parameters to yield stress.

FINITE ELEMENT ANALYSIS FOR DESIGN OF PLATE FOR FRACTURED FEMUR

In this paper, finite element analysis for design of plate for fractured femur is presented. The plates with different hole types are simulated. The types of hole are duo, flower and sloted forms and paired with a screw of 4.5 mm diameter. The plate and screw is made of SUS316L. A maximum load of 550 N is applied for each variation of plate design. The results are presented in terms of deformation and stress for both plate and screw. Numerical results show that the sloted plate is the best among the considered designs, from which the produced stress is below the material yield stress for almost all configurations.

Design of Microfabricated Mechanically Interlocking Metamaterials for Reworkable Heterogeneous Integration

Abstract Next-generation interconnects utilizing mechanically interlocking structures enable permanent and reworkable joints between micro-electronic devices. Mechanical metamaterials, specifically dry adhesives, are an active area of research which allows for the joining of objects without traditional fasteners or adhesives, and in the case of chip integration, without solder. This paper focuses on reworkable joints that enable chips to be removed from their substrates to support reusable device prototyping and packaging, creating the possibility for eventual pick-and-place mechanical bonding of chips with no additional bonding steps required. Analytical models are presented and are verified through finite element analysis (FEA) assuming pure elastic behavior. Sliding contact conditions in FEA simplify consideration of several design variations but contribute ∼10% uncertainty relative to experiment, analysis, and point-loaded FEA. Two designs are presented; arrays of flat cantilevers have a bond strength of 6.3 kPa, and nonflat cantilevers have a strength of 29 kPa. Interlocking designs present self-aligning in-plane forces that emerge from translational perturbation from perfect alignment. Stresses exceeding the material yield stress during adhesion operations present a greater concern for repeatable operation of compliant interlocking joints and will require further study quantifying and accommodating plastic deformation. Designs joining a rigid array with a complementary compliant cantilever array preserve the condition of reworkability for the surface presenting the rigid array. Eventual realization of interconnect technology based on this study will provide a great improvement of functionality and adaptability in heterogeneous integration and microdevice packaging.

The concept of elasto-visco-plasticity and its application to a bubble rising in yield stress fluids

• New simulations are presented that include the elasticity of yield stress materials, as oldroyd first suggested. • The inverted teardrop bubble shape and the negative wake are predicted. • Numerical results indicate the importance of elasticity in yield stress materials. • A satisfactory agreement is found between experiments and simulations for the bubble shape and rising velocity. • The critical yield stress value for bubble entrapment increases by elastic forces. Based on the original ideas by Oldroyd in 1947, Saramito in 2007 introduced a generally acceptable model for yield stress fluids that also accounts for their elasticity. We use this model to examine the buoyancy-driven rise of a bubble through Carbopol and predict the inverted teardrop shape that bubbles often attain when they translate through an elastoviscoplastic material. Such shapes are common in viscoelastic materials, but it is impossible to predict them using viscoplastic models without elasticity. Our results also show that generally, the fore-aft symmetry is lost and the negative wake is formed in the trailing edge of the bubble, even when creeping flow conditions are approached. We show that elastic and plastic forces are dominant in the smaller bubbles, whereas significant shear and extensional thinning occurs in the larger ones, making inertia forces dominant. The agreement of our predicted bubble shapes and rise velocities with their experimental counterparts is very satisfactory either for the smaller or the larger bubbles from those we examined. The former have an inverted teardrop shape and the latter have either an oblate or spherical cap shape. A deviation is found in the bubble radius for which the transition from the inverted teardrop shape to the oblate shape occurs. This deviation is attributed primarily to insufficient rheological characterization of the materials, particularly in terms of their nonlinear elasticity and their extensional properties.

On a plastic instability criterion for ultra-large radial-axial ring rolling process with four guide rolls

A dynamic mechanical model is proposed to describe the complexing actions of all the rolls on the ring during the ultra-large radial-axial ring rolling (RARR) process with four guide rolls. Based on the model, the calculation models for bending moment and normal stress at any section of the ring are deduced by force method. If the maximum section bending normal stress exceeds the yield stress of the ring materials, the ring will be distorted thus leading to the instability of the RARR process. According to this, a plastic instability criterion for the ultra-large RARR process with four guide rolls is developed, based on which a mathematical model to calculate the critical guide force for avoiding plastic instability of ring is obtained. The influence rule of the position of guide roll on the dangerous ring section of plastic instability is revealed, from which it is found the dangerous ring section mainly appears at the radial and axial deformation regions and the contact positions of the guide rolls and ring. The optimized layout of guide roll around the ring in favor of stability is determined to be about α1 = 61° and α2 = 119°. The plastic instability criterion is proven to be reliable from the aspects of the critical guide force, the section bending moment and normal stress and the dangerous ring section of plastic instability. Intelligent simulation case studies for the RARR process of ultra-large aluminum alloy ring indicate that the stable forming of the process can be effectively realized by regulating the guide force based on the plastic instability criterion. This work could provide a valuable guidance for the control of guide rolls and the optimization of the ultra-large RARR process with four guide rolls.

On the effect of plastic model on simulation of adhesive bonded joints with FM94

The stress-strain relationship of adhesive material is important as an input for numerical simulation. In this paper, a series of quasi-static experiments to measure the stress-strain relationship of FM94 adhesive material is reported. The experiments include the bulk tension test to obtain the tensile property and the V-notched beam shear test to obtain the shear property. The FE simulation with the Drucker–Prager model shows good agreement with experimental results. Moreover, further numerical results of adhesive joints show it is not always proper to use the Von Mises model to simulate adhesive joints as some previous studies proposed. The experimental results clearly show that the effective yield stress of adhesive materials is different for tension and shear, which disagrees with the Von Mises model often adopted in simulation.

Simple shear flow of a Herschel-Bulkley fluid with wall slip above a threshold stress

The simple shear flow of Herschel-Bulkley fluids is analyzed, under the assumption that wall slip occurs at both plates above a characteristic wall shear stress, the slip yield stress. The latter critical value is usually lower than the yield stress of viscoplastic materials exhibiting wall slip. The effects of wall slip and the slip yield stress on the apparent flow curve, i.e. the plot of the shear stress vs the apparent shear rate, are investigated. With non-viscoplastic fluids, the flow curve is gap-independent below the slip yield stress. Above a critical apparent shear rate at which the slip yield stress is exceeded, a plateau zone is encountered, and then the flow curve becomes gap dependent. Viscoplastic materials remain at rest for stresses below the slip yield stress, slide unyielded for stresses between the slip yield stress and the yield stress, at half the velocity of the moving plate, and yield and slip for stresses above the yield stress. Hence, the apparent flow curve exhibits an initial plateau corresponding to slip yield stress, followed by a rapid-growth gap-dependent part and a second plateau corresponding to the yield stress, and then approaches asymptotically its zero-slip-yield-stress counterpart. This behavior describes well certain rheometric experiments on concentrated suspensions and pastes.

A comparative study of finite element analysis of single-particle impact on mild steel with and without strain rate considered

Many materials are strain rate sensitive. It is therefore the purpose of this study to conduct a comparative study of single-particle impact on mild steel with and without strain rate considered using Finite Element Analysis (FEA). The Cowper-Symonds material model was used to define the target material. The parameters influencing the strain rate in the material model were determined based on experimental data. We built two types of FE models, which are the FE model of type I with the particle in a lower impact velocity and a smaller size as well as the FE models of type IIi (i=1, 2) with the particles in higher impact velocities and larger sizes. The simulation results show that the craters on the target material without strain rate considered are larger than those with strain rate considered in both FE models, which is because that for the target material with strain rate considered, the yield stress of the target material is increased due to an instantaneous impact of the particle, restraining its further deformation. It is interesting that for the FE models of type II2, the morphologies of simulation craters with strain rate considered and without strain rate considered are similar to those of experimental craters on the annealed copper and work-hardened copper, respectively. Under an oblique impact angle, an elongated lip is created at the end of the crater without strain rate considered, whereas no such lip is created on the target material with strain rate considered. This work provides a guideline for the investigation of the effect of strain rate on target material during erosion.

Simplified model for static stress analysis of straight eccentric lug subjected to cosine distribution pressure

A simplified analytical method is presented for predicting static stress distribution of the straight eccentric lug subjected to cosine distribution pressure. The method of analysis is only suitable for the situation where the predicted peak stress in the straight eccentric lug remains at or below the yield stress of the steel material used for it. In this method, the Castigliano’s theorem is used to determine the internal force distribution of the straight eccentric lug, and the bipolar coordinate system is introduced to analyze the stress state of the straight eccentric lug under bending moment. By comparing with the FEM’s results, it is proved that the present method can give a good precision in predicting the stress distribution of the straight eccentric lug subjected to the cosine distribution pressure. And the peak circumferential tension stress of the straight eccentric lug is observed at the edge of lug hole above the pin. Moreover, the effects of inner radius/outer radius ratio, distance between the two circle centers, and lug thickness to the peak tension stress are investigated. Based on contrastive analysis, it is concluded that the peak tension stress can be reduced either by increasing the inner radius/outer radius ratio and lug thickness, or by decreasing the distance between the two circle centers.

Signatures of the spatial extent of plastic events in the yielding transition in amorphous solids.

Amorphous solids are yield stress materials that flow when a sufficient load is applied. Their flow consists of periods of elastic loading interrupted by rapid stress drops, or avalanches, coming from microscopic rearrangements known as shear transformations (STs). Here we show that the spatial extent of avalanches in a steadily sheared amorphous solid has a profound effect on the distribution of local residual stresses that in turn determines the stress drop statistics. As reported earlier, the most unstable sites are located in a flat "plateau" region that decreases with system size. While the entrance into the plateau is set by the lower cutoff of the mechanical noise produced by individual STs, the departure from the usually assumed power-law (pseudogap) form of the residual stress distribution comes from far field effects related to spatially extended rearrangements. Interestingly, we observe that the average residual stress of the weakest sites is located in an intermediate power-law regime between the pseudogap and the plateau regimes, whose exponent decreases with system size. Our findings imply a new scaling relation linking the exponents characterizing the avalanche size and residual stress distributions.

Bubble entrapment condition in Bingham materials

We investigate the entrapment condition of initially spherical and ellipsoidal Newtonian bubbles in viscoplastic materials using direct numerical simulations. For a spherical bubble, the entrapment condition depends on the balance between the buoyancy force and the force exerted by the yield stress of the viscoplastic material. For non-spherical bubbles, surface tension may yield the surrounding material to minimize the surface energy of the bubble. The yielding of the surrounding material by surface tension force facilitates the rising motion of bubbles. Although surface tension may yield the surrounding material and start the rising motion, the bubble may get entrapped later if the stress exerted by buoyancy force is less than the yield stress of the material. We evaluate the yield-stress parameter for different bubble shapes over a range of non-dimensional parameters to predict the critical yield-stress parameter for the entrapment of a bubble. • The critical yield stress parameter decreases at very high viscosity ratios. • The yield stress parameter is a constant at low viscosity ratios. • Yield stress resistive force depends on the maximum cross-sectional area normal to the buoyancy. • The critical yield stress parameter is independent of the initial shape of the bubble. • Non-spherical bubbles may be momentarily mobile due to surface tension effects.

Analytical predictions of yield stress of a strain gradient plasticity material reinforced by small elastic particles

Theories describing the important role of small particles for strengthening of metals have evolved since the pioneering work of Orowan. Here, this problem is analysed by a strain gradient plasticity (SGP) theory. The structure of the governing equations on non-dimensional form reveals that the plastic strain in the matrix material is to zeroth order approximation constant for a sufficiently small particle size a in comparison to material length scale ℓ. Based on this observation, a perturbation solution has been developed by expansions of all field variables in terms of a/ℓ and the volume fraction of particles f. The simple structure of the plastic strain field is also exploited to derive an upper bound solution from the principles of virtual work and maximum plastic dissipation. These analytical solutions are then used to derive expressions for the yield stress taking into account a random distribution of particles of various size and shape with elastic constants that differ from the matrix. The accuracy and range of validity of these solutions are demonstrated by comprehensive 2D and 3D finite element analyses of material volumes containing realistic distributions of particles of spherical and spheroidal shape of various elastic modulus. The results show that significant strengthening will arise provided that the representative particle size is smaller than the material length scale ℓ of the SGP material.