Non-uniform Stress Distribution Research Articles

Microstructures and mechanical properties of Ti-55511 alloy subjected to rolling in the α+β dual-phase region

In this study, dual-phase region rolling was conducted on a Ti-55511 alloy with different initial rolling reductions in the single-phase region. The mechanical properties and microstructural characteristics of the alloy with different deformation conditions were investigated. Microstructure observations show the formation of a heterogeneous structure with a gradient size distribution of the α phase at the recrystallized grain boundaries, induced by the non-uniform stress distribution. The α phase and the β matrix exhibit the Burgers orientation relationship in the recrystallized region with the gradient structure. However, in the unrecrystallized region of the partially recrystallized specimens and in the grain interiors of the fully recrystallized specimens, the α phase and the β phase exhibit Pitsch-Schrader orientation relationship (P–S OR). A large number of the nano-sized α" martensite bands were observed after the dual-phase region rolling. These bands originated from the α/β interfaces and grew towards the interiors of the α phase. As the deformation increased, these nano-bands underwent a transformation into the {10 1‾ 1}α deformation twins, resulting in the fragmentation of the α phase. Mechanical testing results show that the mechanical properties of the alloy can be improved by the dislocation strengthening, the generation of profuse α phase and other microstructures including the heterogeneous distribution of the α phase, the nano-sized α" martensite and the {10 1‾ 1}α deformation twins.

Investigation of the Shear Mechanism at Sand-Concrete Interface under the Influence of the Concave Groove Angle of the Contact Surface

A “random-type” sand–concrete interface shear test was developed based on the sand cone method, with a focus on the most commonly encountered triangular contact surface morphology. A “regular-type” triangular interface, matched in roughness to the “random-type”, was meticulously designed. This “regular-type” interface features five distinct triangular groove inclinations: 18°, 33°, 50°, 70°, and 90°. A series of sand–concrete interface direct shear tests were conducted under consistent compaction conditions to investigate the impact of varying compaction densities and triangular groove inclinations on the shear strength at the interface. Particle flow simulations were utilized to examine the morphology of the shear band and the characteristics of particle migration influenced by the triangular contact surface. This analysis is aimed at elucidating the influence of the inclination of the triangular groove on the shear failure mechanism at the sand–concrete interface. The findings indicate that: (1) The morphology of the interface significantly impacts the shear strength of the sand–concrete interface, while the shape of the stress-displacement curve experiences minimal alteration. (2) At smaller inclination angles, particle contact forces are arranged in a wave-like configuration around the sawtooth tip, resulting in a non-uniform stress distribution along the sawtooth slope. However, as the inclination angle grows, the stress concentration at the sawtooth tip diminishes, and the stress distribution across the sawtooth slope becomes more consistent. (3) Particle migration is significantly influenced by the sawtooth’s inclination angle. At lower angles, particles climb the structure’s tip through sliding and rolling. As the angle increases, particle motion shifts to shear, accompanied by a transition in friction from surface friction to internal shear friction. This leads to the formation of a wider shear band and an increase in shear strength.

Spatial reconstruction, microstructure-based modeling of compressive deformation behavior, and prediction of mechanical properties in lightweight Al-based entropy alloys

Lightweight Al-based entropy alloys are newly emerged materials with promising potential for structural applications; however, their modeling and strengthening prediction require further exploration. In this study, the spatial distributions of various phases in three Al-based entropy alloys were investigated. A closely interconnected intermetallic compound (IC) network comprising Al2Cu and Al45Cr7 phases was identified. Finite element (FE) modeling was conducted based on the reconstructed three-dimensional microstructure to simulate compressive deformation behavior. The IC network served as the main stress bearer during deformation. Thin sections in the Al2Cu network were the weak sites where stress concentration and damage first occurred. However, the breakage of this limited region contributes to relatively coordinated deformation and extended plasticity. The breakage of large particles accounts for the final alloy failure. The results of the FE model were compared with the experimentally measured stress–strain behavior and mechanical properties, showing very good agreement. Given the non-uniform distribution of strain and stress during deformation, a strengthening model, merging the Voigt and Reuss models, was also developed to predict the mechanical properties of Al-based entropy alloys with the aim of facilitating Al-based entropy alloy development.

Interrelations between Printing Patterns and Residual Stress in Fused Deposition Modelling for the 4D Printing of Acrylonitrile Butadiene Styrene and Wood–Plastic Composites

Four dimensional printing enables the advanced manufacturing of smart objects that can morph and adapt shape over time in response to stimuli such as heat. This study presents a single-material 4D printing workflow which explores the residual stress and anisotropy arising from the fused deposition modelling (FDM) printing process to create heat-triggered self-morphing objects. In particular, the study first investigates the effect of printing patterns on the residual stress of FDM-printed acrylonitrile butadiene styrene (ABS) products. Through finite element analysis, the raster angle of printing patterns was identified as the key parameter influencing the distribution of residual stresses. Experimental investigations further reveal that the non-uniform distribution of residual stress results in the anisotropic thermal deformation of printed materials. Thus, through the design of printing patterns, FDM-printed materials can be programmed with desired built-in residual stresses and anisotropic behaviours for initiating and controlling the transformation of 4D-printed objects. Using the proposed approach, any desktop FDM printers can be turned into 4D printers to create smart objects that can self-morph into target geometries. A series of 4D printing prototypes manufactured from conventional ABS 3D printing feedstock are tested to illustrate the use and reliability of this new workflow. Additionally, the custom-made wood–plastic composite (WPC) feedstocks are explored in this study to demonstrate the transposability of the 4D printing approach.

Micromechanism of strength and damage trade-off in second-phase reinforced alloy by strain gradient plasticity theory

The strength and damage are mutually exclusive in most alloys. It is still a challenge to understand the role of microstructural features in affecting strength and damage tolerance simultaneously. In this study, we provide a general approach to unveil the micromechanism of strength and damage trade-off in second-phase reinforced alloy. Concretely, a microstructure-based constitutive model incorporating the strain gradient plasticity theory is developed to evaluate the overall mechanical behavior and local deformation behavior of particle-reinforced alloys by finite element simulations. The strain gradient effect exacerbates the non-uniform stress distribution, particularly enhancing the local stress level around the particle-matrix interface, thereby improving the total strain hardening of the alloys. Importantly, the strain gradient effect can significantly expand regions with local stress levels surpassing the critical stress for microcrack nucleation, ultimately leading to damage initiation and failure. This elucidates the micromechanism underpinning the trade-off between strength and damage. By revealing the competitive relationship between local stress concentration and microcrack nucleation stress, the comprehensive effects of particle size and volume fraction on the strength, strain hardening and damage tolerance are quantitatively predicted. It is recommended to adjust the particle volume fraction based on reducing the particle size to obtain the desired properties. The present work discerns the inherent origin of the strength-damage trade-off in particle-reinforced alloy and sheds light on the role of the particle size and volume fraction on the strength and damage tolerance, which can offer valuable guidance for developing high-performance particle-reinforced materials.

Investigating the Effects of Adhesive on the Shear Capacity of Bolted Steel Connections

Recently, there has been a particular emphasis on the use of structural adhesives in steel connection systems. Applying adhesives that possess both high strength and flexibility would be highly advantageous for structural purposes. In this study, experimental tests are conducted on two main different types of steel-plate connections; namely, bolted connections and bolted connections with glue. The number of bolts ranged from one to eight for each connection type, such that a total of seven specimens of each type are tested. Additionally, one specimen with only glue is also tested for comparison. The findings indicated that the inclusion of up to four bolts with glue along the connection does not significantly increase the ultimate stress. This can be attributed to the non-uniform distribution of normal stresses, induced by the tightening of the small number of bolts that are not arranged across the entire connection region, on the capacity of the connection in the perpendicular direction. Thus, the connection could have been adequately established the same capacity through the use of adhesive alone. In contrast, the capacity is increased up to 60% and 100% when six or eight bolts are added, respectively, compared to the use of the connection with glue only. A three-dimensional finite-element analysis is developed based on the tested connections using ABAQUS/Explicit software. The glued interface between two steel plates is modelled using cohesive and damage criteria. The results are demonstrated to be consistent with the experimental findings. Keywords: ABAQUS, Adhesive, Bolts, Finite-element analysis, Shear, Steel connections

The Concrete Effective Width of a Composite I Girder with Numerous Contact Points as Shear Connectors

Due to the shear strain in the plane of the slab, the parts of the slab remote from the steel beam lag behind the part of the slab located in its proximity. This shear lag effect causes a non-uniform stress distribution across the width of the slab. As a result, several standards have introduced the concept of an effective flange width to simplify the analysis of stress distribution across the width of composite beams. Both the computed ultimate moment and serviceability limit states are directly impacted by the effective width. The effect of using a large number of contact points as shear connectors on the effective width of a steel beam flange has not been investigated. A three-dimensional finite element analysis is carried out in this paper. The ABAQUS software (version 6.14) is used for this purpose, where several variables are considered, including the surface area connecting the steel beam and concrete slab, the transverse space, and the number of shear connectors. It was discovered that the number of shear connectors on the steel beam flange has a major impact on the effective width. The many connectors work together to provide a shear surface that improves the effective width by lowering the value of the shear lag.

The influence of the geometric characteristics on the behavior of braces with restrained buckling - case study of perforated steel core.

Buckling restrained braces are elements that equip the building with additional capacity for resistance and stability when subjected to earthquakes. As an answer to the problem of the possible loss of stability of the buckling-preventing component, the “perforated-core buckling restrained braces” (PCBRB) is a concept that involves the introduction of gaps, in the core of the bracing, to control the plasticizing mechanism of the dissipative element. The research addresses the behavior of PCBRB groups where all the elements belonging to the same group have the same area and length of the section considered active dissipative. A numerical analysis environment was developed that simulates the support conditions and material behavior. Based on the results of the numerical analyses, the influence of the geometry (b/t ratio) of the section of the dissipative zone on the behavior and the mechanism of stress strain distribution in the bracing core. It can be noticed the development of over-resistance to the compressive stress and non-uniform distribution of stresses on the surface of the elements whose b/t ratio exceeds the value of 5.5; for the elements whose b/t ratio has a value lower than 1.75 local instability problems in the dissipative zone occurred.

Residual stress effects on short crack propagation behavior in friction stir welded 7075-T6 aluminum alloy panel under biaxial loading: An experimental and numerical study

The effects of residual stress on short crack propagation behavior of friction stir welded (FSWed) 7075-T6 aluminum alloy panel was investigated under biaxial loading. The biaxial fatigue tests were carried out on three kinds of cruciform samples, including base material (BM) cruciform sample and FSWed cruciform sample with crack perpendicular or parallel to the weld. Scanning electron microscope (SEM) fractography was conducted to identify and relate fracture surface features to governing fatigue damage mechanisms. Finite element method combined with stress intensity factor (SIF) analysis was used to simulate the biaxial fatigue propagation. In a comparison of the crack path in BM and FSWed cruciform samples, experimental and numerical results showed that residual stress can change the nominal biaxiality ratio, leading to crack path changes in FSWed cruciform sample with crack parallel to the weld, and the curved fatigue crack front formed on the fracture surface due to the non-uniform distribution of the residual stress through the thickness. The fatigue damage mechanisms are different depending upon the biaxiality ratio as well as the weld direction.

Improved strain transfer model for flexible sensors based on non-uniform distribution of shear stress in each layer

The assumption of linear stress distribution for flexible sensors results in inaccurate strain transfer assessment because of low elastic moduli and thick layers, and the coating further constrains the deformation of the sensitive layer. A novel strain transfer model based on non-uniform distribution of shear stress is proposed to accurately characterize the strain of sensitive layer. The quadratic shear stress distribution is derived to calculate the strain transfer coefficient of each layer, replacing the linear attenuation of the shear stress. The average relative displacement of the sensitive layer was obtained through Hooke's law, thereby introducing the shear stress at the contact interface between the coating and the sensitive layer. Numerical simulations and experiments demonstrate that the substrate of the sensors is the primary factor causing strain transfer loss and the proposed model can accurately reflect the strain of the sensitive layer.

Analysis of Pressure Pulsation and Structural Characteristics of Vertical Shaft Cross-Flow Pumps

In order to study the pressure pulsation characteristics and structural dynamic response characteristics of a vertical shaft cross-flow pump, this study used a computational fluid dynamics (CFD) numerical simulation method to analyze the pressure pulsation characteristics of the inlet passage, impeller, and guide vane positions of the vertical shaft cross-flow pump device. At the same time, this study analyzed the equivalent stress–strain characteristics of the impeller and guide vane of a vertical shaft cross-flow pump based on fluid structure coupling technology and comprehensively analyzed the deformation modes of the impeller blades and guide vanes under dynamic water flow. This research shows that due to the influence of rotor–stator interaction, the amplitude of pressure pulsation at the interface between the impeller and guide vane of the pump device is the largest and that the main frequency distribution at this position is relatively complex. The non-uniformity of stress distribution at the impeller position gradually decreases with an increase in the radial distance. The high stress and strain zones of the impeller and guide vane are concentrated at the root of the blade. This study can provide reference for hydraulic optimization design and stable operation of similar pump devices.

4D hydrogels: fabrication strategies, stimulation mechanisms, and biomedical applications.

Shape-morphing hydrogels have emerged as a promising biomaterial due to their ability to mimic the anisotropic tissue composition by creating a gradient in local swelling behavior. In this case, shape deformations occur due to the non-uniform distribution of internal stresses, asymmetrical swelling, and shrinking of different parts of the same hydrogel. Herein, we discuss the four-dimensional (4D) fabrication techniques (extrusion-based printing, dynamic light processing, and solvent casting) employed to prepare shape-shifting hydrogels. The important distinction between mono- and dual-component hydrogel systems, the capabilities of 3D constructs to undergo uni- and bi-directional shape changes, and the advantages of composite hydrogels compared to their pristine counterparts are presented. Subsequently, various types of actuators such as moisture, light, temperature, pH, and magnetic field and their role in achieving the desired and pre-determined shapes are discussed. These 4D gels have shown remarkable potential as programmable scaffolds for tissue regeneration and drug-delivery systems. Finally, we present futuristic insights into integrating piezoelectric biopolymers and sensors to harvest mechanical energy from motions during shape transformations to develop self-powered biodevices.

Investigation of the effect of non-uniform stress distribution on the transient electromagnetic behavior of a no-insulation REBCO racetrack coil

Racetrack superconducting coils are widely used in magnetic levitation (maglev), generators, and accelerators, showing very important application prospects in many fields. However, due to the special geometry, the straight part and the arc part of the coil are given different radial stresses during the winding, cooling, and excitation, which will cause a difference in their transient performance during charging/discharging. In this paper, we investigated the transient electromagnetic behavior of the no-insulation (NI) REBCO racetrack coil during charging/discharging. First, an equivalent circuit model of a NI racetrack pancake (RP) coil was established. The stress distribution calculated by the analytical and finite element methods was used to consider the difference in contact resistance, the model can predict the current distribution of the straight and arc parts of different turns of the coil during charging/discharging. Afterward, A small-scale NI RP coil was successfully wound to validate the model, and the calculation results show good consistency with the experimental results. Finally, we investigated the transient behavior of the NI RP coil under different stress distributions. A targeted charging protection strategy for the coil was proposed and its effectiveness was verified experimentally. The work in this paper can help us to better understand the transient behavior of different parts of the NI RP coil during charging/discharging and provide guidance for its future construction.

Coupled fluid-thermal-structural analysis during the air cooling for glass tempering

The tempering process of plate glass involves rapidly cooling the high-temperature glass using an array of impinging air jets, inducing desired stress during cooling. Consequently, the formation of tempering stress results from the coupled interaction among flow, heat transfer, and stress. However, most previous studies have commonly neglected the influence of the flow field by assuming a uniform and constant distribution of heat transfer coefficients at different positions on the glass plate, which deviates from actual situations. This study employed a fluid-thermal-structural coupled simulation approach to predict the non-uniform residual stress distribution in tempered glass and investigate the interaction mechanisms among flow, heat transfer, and stress. Simultaneously, to validate the reliability of the method and model, this study experimentally investigated the single-nozzle jet impingement cooling for glass tempering. The study concluded that the simulation results were consistent with the experiment. Subsequently, a comparative analysis was performed between the fluid-thermal-structural coupled simulation results based on real boundary conditions and the thermal-structural coupled simulation results based on ideal uniform heat transfer coefficient boundary conditions. The results revealed non-uniform distributions of both heat transfer coefficient and temperature due to varying localized flow characteristics. Consequently, the ratio of surface compressive stress to internal tensile stress along the width direction of the glass was not a fixed value but ranged from 1.63 to 2.38. Furthermore, significant differences were observed in the stress distribution under the simulations of fluid-thermal-structural coupling and thermal-structural coupling. Therefore, it is recommended to employ the fluid-thermal-structural coupling method when predicting localized stress distribution.

Effective width of steel-concrete composite box girder bridges: a review and method comparison

Steel-concrete composite girders have non-uniform stress distribution on the slab, presenting maximum stresses next to the webs of the girder. This phenomenon is known as shear lag effect. To understand this effect, there is the effective width concept, in which only a portion of the slab width is considered effective in contributing to the composite element’s resistant capacity. However, in the technical standards, there is no recommendation for calculating the effective width in steel-concrete composite box girder bridges. In view of this situation, the purpose of this paper is to carry out a systematic review on effective width and/or the shear lag effect in steel-concrete composite bridges, in order to raise the main existing recommendations and compare them. Through a bibliometric scan with carefully chosen keywords, it was found that of all research on shear lag or effective width in steel-concrete composite structures, only 31.19 are on bridges and 14.97% are on bridges with box girders. Among the papers, those that have a method for calculating the effective width of steel-concrete composite girder bridges have been compared quantitatively and qualitatively with the procedures of AASHTO and EN 1994-2-2. In these procedures were also identified that the, for the boundary conditions of the present paper, the parameters that most influencing the effective width are, in that order, the span length, the distance between girders, the concrete slab height, the longitudinal position and the type of load.

Meso-scale deformation and strength mobilization mechanisms of EPS composite soil

Expanded polystyrene (EPS) composite soil is composed of two solid constituents (cemented soil and EPS beads), which together with the inter-constituent interfaces form a unique mesoscopic structure. The macroscopic behavior of EPS composite soil has been widely investigated so far, but the focus has seldom been put on the meso-scale mechanisms behind the macroscopic deformation features and strength mobilization processes. In this study, systematic experiments and refined numerical simulations are utilized to examine the meso-scale mechanical responses of EPS composite soil under triaxial compression to reveal the associated mechanisms. Here, meso-scale is a scale smaller than a sample scale but larger than an EPS bead scale. First, the mechanical behavior of cemented soil, EPS material and their interface is obtained in experiments; their constitutive models are formulated, and the model parameters are calibrated based on experimental results. Then, experiments and refined numerical simulations of triaxial compression on EPS composite soil are performed. It is found that the rich macroscopic mechanical behavior of EPS composite soil has a mechanical source (contrast in mechanical behavior between EPS and cemented soil) and a geometric source (non-uniform distribution of EPS beads). The mechanical source leads to highly non-uniform stress and strain distributions within an EPS composite soil. The geometric source causes strain localization in zones with local concentration of EPS beads, leading to three macroscopic deformation modes, i.e., overall shear localization, local lateral expansion, and overall uniform expansion. In strength mobilization, cemented soil matrix first mobilizes its strength because it takes most of the load and contributes much to deformation at the early stage of triaxial compression. EPS beads are later progressively involved in the overall load bearing and deformation of the EPS composite soil sample. EPS beads make more contribution to stress than to strain due to its soft nature.

Electromechanical characteristic of stacked REBCO tapes under tension deformation

Stacking REBCO tapes is an effective way to increase the current-carrying capacity of the cable. Various loading conditions, including combined tension-bend, are applied to these tapes during fabrication and operation of the magnets. This paper investigates the degradation behaviors of critical current (Ic) in stacked rare earth–barium–copper–oxide (REBCO) coated conductor (CC) tapes under tension loading through experimental. Uniaxial tension experiments are conducted on single tapes and 4-tape cables with different stacking at 77 K. The critical current degrades rapidly when strain exceeds an irreversible threshold around 0.4-0.5%. A 3D finite element model analyzes the non-uniform stress distribution in the cable cross-section under tension, causing different degradation behaviors. An empirical model combining the Ekin law and Weibull distribution is proposed to relate Ic and axial strain. By fitting experimental data, the key parameters are determined. The Ic of a single tape reduces 20% at 0.4% strain. Face-to-face stacking decays at 0.45% irreversible strain, while back-to-back decays at 0.38%. The model provides an effective way to optimize the electromechanical performance of stacked REBCO cables.

Optimization of Substrate Sizes for In Situ Stress Measurement in Electrodeposits Relying on Nonlinear Effects

In situ stress measurements have been widely used in various deposition processes for stress detection. The substrate size can affect the uniformity of curvature across the entire surface, which is a major cause of incorrect stress measurements. However, because of the inherent concept of measurement theory and the complexities of the influence of substrate size on measurement accuracy, the underlying nonlinear effects of the rectangular substrate are still not fully understood. We discovered that increasing the substrate size caused an increase in nonlinear effect (nonuniform distribution of curvature radii and stresses in the x and y directions) and surface defects on the rectangular substrate using in situ stress measurement. Furthermore, the bending stiffness of the substrate, which was influenced by the substrate size, was established to illustrate the effect of substrate size on the nonlinear effect. The total stress of the deposit was concentrated at the edge in both the x and y directions, and the deposit at the edge was prone to delamination and cracking. When the substrate size was reduced, the deposit surface did not show obvious defects, and the stress errors in the x and y directions were only 2.34% and 2.54%, respectively. These findings will be beneficial to improve the accuracy of in situ stress measurement and further understand the causes of nonlinear effects.

Cell-Based Modeling of Tissue Developing in the Scaffold Pores of Varying Cross-Sections.

In this work, we present a mathematical model of cell growth in the pores of a perfusion bioreactor through which a nutrient solution is pumped. We have developed a 2-D vertex model that allows us to reproduce the microscopic dynamics of the microenvironment of cells and describe the occupation of the pore space with cells. In this model, each cell is represented by a polygon; the number of vertices and shapes may change over time. The model includes mitotic cell division and intercalation. We study the impact of two factors on cell growth. On the one hand, we consider a channel of variable cross-section, which models a scaffold with a porosity gradient. On the other hand, a cluster of cells grows under the influence of a nutrient solution flow, which establishes a non-uniform distribution of shear stresses in the pore space. We present the results of numerical simulation of the tissue growth in a wavy channel. The model allows us to obtain complete microscopic information that includes the dynamics of intracellular pressure, the local elastic energy, and the characteristics of cell populations. As we showed, in a functional-graded scaffold, the distribution of the shear stresses in the pore space has a complicated structure, which implies the possibility of controlling the growth zones by varying the pore geometry.

Phase-field study of the solutes-interstitial loops interaction in Fe–Cr alloys

Interstitial dislocation loops are typically formed in post-irradiated materials, such as Ferritic-Martensitic Fe–Cr alloys. These loops demonstrate solute segregation along their perimeters, effectively pinning the dislocation climb and resulting in high-density, small-sized loops that cause embrittlement. Phase-field simulations were conducted to investigate the behavior of Cr segregation in the stress field of a<100> type and various a/2<111> type interstitial dislocation loops in post-irradiated Fe–10Cr alloy. The study considers the long-range elastic interaction of solute Cr within the stress field of dislocation loops in a cubic elastic anisotropic material. The findings reveal a nonuniform stress distribution along the loop's perimeter depending on the included angle of habit plane normal n and Burgers vector b; the nonuniformity becomes more pronounced as the Burgers vector deviates from the normal direction. Furthermore, this nonuniform stress induces Cr segregation within regions experiencing tensile stress and Cr depletion in compression stress regions. Furthermore, a comprehensive analytical solution has been developed to characterize the diverse stress fields and solute segregation induced by interstitial dislocation loops with varying habit planes and Burgers vectors. The proposed analytical model effectively depicts the stress distribution of various dislocation loops, resulting in a Cr segregation profile that closely approximates those obtained through phase-field simulations. A thorough analysis of solute segregation mechanisms also elucidates the dispersed fine-scale nature and high density observed in experimental investigations of dislocation loops.