Uneven Stress Distribution Research Articles

Numerical investigation of ice pigging isothermal flow in water-supply pipelines cleaning

Ice pigging, which is a trenchless technology in pipeline cleaning, is novel and efficient to remove the sediment in water-supply pipelines. The numerical model was built in this work to simulate the ice pigging isothermal flow for the first time. Due to the complexity of the solid-liquid two-phase physical properties in the ice pigging flow, the numerical model adopted the kinetic theory of granular flow in the Eulerian-Eulerian multiphase model which was validated by the experimental data reported in literature. The numerical model results showed that the ice volume fraction distribution varied in different pipe section locations and revealed the uneven shear stress distribution in the pipe. Moreover, the ice particles in the ice pig had little effect on the bottom of the pipe during the pipe cleaning process due to the inevitable inhomogeneity of the ice slurry. Besides, with ice melting the uneven distribution of ice particles reduced.

Optimization of Stress Distribution in Tendon-Driven Continuum Robots Using Fish-Tail-Inspired Method

Tendon-driven continuum robots are widely used in different engineering disciplines due to their simple structure and high flexibility. The typical structure of a tendon-driven continuum robot usually contains a series of identical compliant joints in its backbone to achieve large-deflection bending movements. However, with compliant joints of the same geometry, the real bending shape of the robot backbone is an arc with variable curvature, which results in uneven stress distribution along the robot backbone. In the long term, higher stresses in the compliant joints near the fixation base could lead to fatigue or fracture of the entire robot structure. To cope with this problem, we propose a fish-tail-inspired method in this letter to optimize the stress distribution along the serial compliant joints. Several optimization examples were presented to show the performance of the proposed method. Simulation and experimental results have demonstrated that the developed method can effectively reduce the stress differences in serial compliant joints during large-deflection bending movements.

Experimental and numerical study of thermoforming of Al/CFRP hybrid composites

Composite materials are more and more widely used in the automotive industry with the increasing requirements of lightweight design. In order to obtain automotive parts with excellent comprehensive mechanical properties, the 7075-T6 aluminum alloy was integrated with Carbon Fiber Reinforced Plastic (CFRP) by using thermoforming process. The influence of four forming methods on the forming process, forming accuracy, and interface bonding strength was studied in this work. A finite element model based on cohesion and forming was established to study the integrated thermoforming and properties prediction of Al/CFRP hybrid composites. The results showed that forming CFRP and unformed 7075 Al aluminum alloy sheet together required higher forming energy and the formed parts had higher Mises stresses. When the CFRP was located below 7075 aluminum alloy sheet, the uneven stress distribution due to the severe deformation of the resin resulted in the worst forming accuracy. For all four processes, the thickness of the formed parts decreased at the round corners and side wall area, increased at the flange area, and changed little at bottom surface. The thickness distribution of the formed part depends on the deformation process and the contact pressure between the tools and the blank. Greater contact pressure resulted in greater thinning rate. For the processes of preformed 7075 aluminum alloy, although less forming force was needed, the interface debonding risk between 7075 aluminum alloy and CFRP might arise due to the small contact pressure.

Eccentric punching tests on column bases ‐ Influence of column geometry

AbstractExperimental investigations on centrically loaded column bases provide the basis for current punching shear design provisions. However, this symmetric loading condition represents an exception in daily engineering practice since usually load eccentricities occur leading to uneven shear stress distributions along the control perimeter. To account for this effect, design approaches define different factors to either increase the acting shear force or to decrease the punching shear resistance in design. New punching test results of 14 eccentrically loaded and four centrically loaded column bases now allow the evaluation of design approaches depending on different geometric boundary conditions. In this new test series, the load eccentricities were systematically graded to analyze their influence on the punching behavior. Strain measurements in the multiaxial compression zone of the concrete in the column‐footing connection reveal new insights on the punching failure of column bases. As a result, a correlation between tangential concrete strains and the reduction of punching shear strength can be recognized for increasing load eccentricities. The comparison of experimentally determined load increase factors with the design results according to Eurocode 2, Model Code 2010 and the stable version of the next generation of Eurocode 2 reveals optimization potential for deriving more advanced design provisions in the future.

Effect of micro-cracks on mechanical and damping properties of double-layered Al/Al plate

To investigate the influence of micro-cracks (including formation and growing) on mechanical and damping capacity, the grooved (with two dimensions) and non-grooved Al plates were subjected to cold roll bonding (CRB). Microscopic morphology, tensile and damping test of the experimental materials were investigated. Due to uneven stress distribution, the edges of grooves were heavily inclined in the normal direction (ND), and the grooves were changed into micro-cracks with the sizes of a few to a dozen microns. Mechanical properties of the Al sheet with micro-cracks were decreased, which further lowered with micro-cracks growing. There were two internal friction peaks for the Al sheet with micro-cracks, which mainly attributed to the stronger local stress and local plastic deformation around the micro-cracks.

Failure analysis of pulse magnetic induction coil in electromagnetic riveting

Pulse magnetic induction coil is the core component of electromagnetic riveting (EMR) equipment. Due to the multi-field coupling working environment, it was easy to fail. In this paper, multi-field coupled simulation was carried out to analyze the failure of pulse magnetic induction coil. The current, riveting force and damaged condition in experiment results demonstrated that the model was accurate and reliable. The simulation results showed that the current density was higher at the middle turns because of the eddy current. The Lorentz force, whose radial components concentrated in inner turns and axial components in middle turns, were unevenly distributed. The Lorentz force led to uneven deformation and this nonuniformity of stress deteriorated with the increase of the discharging voltage. The first turn of the coil suffered from greater stress and is more prone to deformation. Besides the Lorentz force, the higher temperature in the center of the coil also accelerated the breakdown of the insulator. In respect of the issues above, a new type of tower coil was proposed to improve the uneven distribution of Lorentz forces and stresses. The simulation results showed that the maximum stress of the coil decreases obviously under the same riveting force.

Numerical Study of the Soil-Structure Interaction Considering the Dynamic Response of the Soil

Abstract This paper presents the process of modeling a structure using the finite element method. There are two approaches through which the seismic behavior of structures can be modeled. Generally, the analysis of seismic behavior assumes the structures have a fixed base. The second method to model and analyze the seismic behavior of structures involves considering the soil-structure interaction by modeling the soil underneath the building. This paper also presents a comparison of the results of two finite element simulations, one of them considering the structure has a fixed base and the other having a flexible base. The results have shown that the fixed base model leads to higher frequencies and uneven distribution of stresses compared with the results of the flexible base model.

A comparative study of applying backscattering and transmission Raman spectroscopy to quantify solid-state form conversion in pharmaceutical tablets

Selecting appropriate Raman measurement and data processing method are of importance to enable effective quantification of solid form conversions upon processing or storage. Therefore, a comparative evaluation is presented herein on using backscattering and transmission Raman spectroscopy to quantify salt disproportionation in tablet matrices. The second part focuses on different spectra processing approaches and calibration models for quantifications. Finally, samples under different mechanical stresses were comprehensively analyzed using different Raman measurements. Much as transmission Raman spectrometry may provide accuracy on bulk measurements by having large sampling volume, it has the drawback of signal attenuation and may overlook process-induced phase transitions occurring on local regions of tablet surface. To overcome this limitation, backscattering Raman with deliberate subsampling can be used as an orthogonal method to probe the existence of low-level form conversion distributed over a tablet’s surface. In the present case, different levels of the form conversions were found at the edge and the center of tablets due to the uneven shear stress distribution invoked during tablet compression. In such a scenario, it would be beneficial to apply deliberate-focused backscattering and transmission Raman spectrometry together as complementary techniques to capture chemical information both locally and within the bulk of the tablet.

Mechanistic influence on uniformity of sheet resistance of AlGaN/GaN HEMT grown on Si substrate with the graded AlGaN buffer layers

In this study, the relationship among the wafer bow, dislocations, and transport characteristics of aluminum gallium nitride/gallium nitride (AlGaN/GaN) high electron mobility transistor (HEMT) grown on the silicon substrate using conventional AlGaN buffer layers was comprehensively investigated. It is speculated herein that the mechanism that affects the uniformity of sheet resistance is the uneven distribution of stress in GaN-based HEMT and the wafer bow it generates. The bow can lead to the difference in mobility through affecting the threading dislocations, resulting in poor uniformity of resistance. This conjecture was supported by the results of high-resolution X-ray diffraction, non-contact Hall measurement, Raman spectroscopy, and sheet resistance measurements. To further investigate this problem, a model was proposed to explain it from the perspective of formation mechanism.

Layer-dependent fracture strength of few-layer WS2 induced by interlayer sliding: a molecular dynamics study

Understanding the relationship between interlayer interactions and the mechanical properties and behaviors of two-dimensional layered materials is critical in the development of related nanodevices. Nevertheless, it is still challenging due to difficulties in experiments. In this work, nanoindentation simulations on few-layer WS2 were conducted by varying the tip radius, suspended membrane radius, and membrane size using a molecular dynamics simulation. Consistent with our previous experimental results, few-layer WS2 exhibited a layer-dependent reduction in fracture strength owing to the uneven stress distribution among individual layers induced by interlayer sliding under out-of-plane deformation. Furthermore, apparent curve hysteresis was observed due to interlayer sliding in the supported region when a large tip radius and membrane radius were employed. However, instead of the supported part, the interlayer sliding within the suspended part resulted in reduced fracture strength with the increase of layer number. These findings not only provide an in-depth comprehension of the influence of interlayer sliding on fracture strength of few-layer WS2, but also suggest that the role of interlayer interactions should be seriously considered during nanodevice design.

Screw flow in cylindrical coarse filter

This work discuss the screw type of liquid (irrigation water) motion in a cylindrical coarse filter of a sprinkler machine. A vortex helical flow arises due to the instability of a rectilinear longitudinally uniform flow and uneven distribution of tangential stresses along the wetted perimeter of the cross section of the flow and manifests itself in the form of secondary flows of transverse circulation. The solution of the equations of motion in the gap "mesh - housing" of the filter, expressed in terms of the Bessel function, is obtained. Profiles of longitudinal and rotational velocities in the gap and in the entire filter have been constructed.

DNA sequence and methylation prescribe the inside-out conformational dynamics and bending energetics of DNA minicircles.

Eukaryotic genome and methylome encode DNA fragments’ propensity to form nucleosome particles. Although the mechanical properties of DNA possibly orchestrate such encoding, the definite link between ‘omics’ and DNA energetics has remained elusive. Here, we bridge the divide by examining the sequence-dependent energetics of highly bent DNA. Molecular dynamics simulations of 42 intact DNA minicircles reveal that each DNA minicircle undergoes inside-out conformational transitions with the most likely configuration uniquely prescribed by the nucleotide sequence and methylation of DNA. The minicircles’ local geometry consists of straight segments connected by sharp bends compressing the DNA’s inward-facing major groove. Such an uneven distribution of the bending stress favors minimum free energy configurations that avoid stiff base pair sequences at inward-facing major grooves. Analysis of the minicircles’ inside-out free energy landscapes yields a discrete worm-like chain model of bent DNA energetics that accurately account for its nucleotide sequence and methylation. Experimentally measuring the dependence of the DNA looping time on the DNA sequence validates the model. When applied to a nucleosome-like DNA configuration, the model quantitatively reproduces yeast and human genomes’ nucleosome occupancy. Further analyses of the genome-wide chromatin structure data suggest that DNA bending energetics is a fundamental determinant of genome architecture.

The Effect of Phase Separation on the Mechanical Behavior of the Co-Cr-Cu-Fe-Ni High-Entropy Alloy.

Phase separation phenomena in high-entropy alloys (HEAs) have attracted much attention since their discovery, but little attention has been given to the dynamics of the deformation mechanism of this kind of HEA during uniaxial tension, which limits their widespread and practical utility. In this work, molecular dynamics simulation was used to study the effect of phase separation on the mechanical properties of an HEA under uniaxial tensile loading. Moreover, the associated deformation behavior of the Co–Cr–Cu–Fe–Ni HEA was investigated at the nanoscale. Models with Cu-rich grain boundaries or grains were constructed. The results showed that Cu-rich grain boundaries or grains lowered the strength of the Co–Cr–Cu–Fe–Ni HEA, and Cu-rich grain boundaries significantly reduced ductility. This change of mechanical properties was closely associated with a deformation behavior. Furthermore, the deformation behavior was affected by the critical resolved shear stress of Cu-rich and Cu-depleted regions and the uneven stress distribution caused by phase separation. In addition, dislocation slipping and grain boundary sliding were the main mechanisms of plastic deformation in the Co–Cr–Cu–Fe–Ni HEA.

Recent Advances in Loop Heat Pipes with Flat Evaporator.

The focus of this review is to present the current advances in Loop Heat Pipes (LHP) with flat evaporators, which address the current challenges to the wide implementation of the technology. A recent advance in LHP is the design of flat-shaped evaporators, which is better suited to the geometry of discretely mounted electronics components (microprocessors) and therefore negate the need for an additional transfer surface (saddle) between component and evaporator. However, various challenges exist in the implementation of flat-evaporator, including (1) deformation of the evaporator due to high internal pressure and uneven stress distribution in the non-circular casing; (2) heat leak from evaporator heating zone and sidewall into the compensation chamber; (3) poor performance at start-up; (4) reverse flow through the wick; or (5) difficulties in sealing, and hence frequent leakage. This paper presents and reviews state-of-the-art LHP technologies; this includes an (a) review of novel manufacturing methods; (b) LHP evaporator designs; (c) working fluids; and (d) construction materials. The work presents solutions that are used to develop or improve the LHP construction, overall thermal performance, heat transfer distance, start-up time (especially at low heat loads), manufacturing cost, weight, possibilities of miniaturization and how they affect the solution on the above-presented problems and challenges in flat shape LHP development to take advantage in the passive cooling systems for electronic devices in multiple applications.

Numerical modeling of thermal field during friction stir welding using tool with polygonal pin profile

Friction stir welding produces better joint strength comparing with other conventional fusion welding techniques as the complete metal joining operation is executed in solid state itself. Even though the quality of weld is comparatively good, this joining technique has its own disadvantages. Improper material flow along the weld line may result in weld defects. Usage of polygonal pin geometry in tool pin rather than using conventional cylindrical pin geometry enhances flow of plasticized metal under the tool shoulder in the stir zone. Major problem associated with polygonal shaped tool pin is poor tool life. Yield strength of material under the tool shoulder creates opposing force for the movement of tool pin, which is submerged inside the workpiece for the entire joining process. Uneven stress distribution along the outer surface of the polygonal tool pin shape leads to premature tool failure. As the strength of material is a temperature dependent property, the heat input during the process has to be optimised with respect to the geometrical shape of the tool pin to improve tool life without compromising the weld quality a lot. In this paper, the variation in thermal field based on the geometrical shape of the tool pin was analysed using MATLAB based on the moving coordinate system. Rosenthal equation was used to estimate variation the peak temperature and temperature distribution with respect to pin shape in the view of optimising thermal environment towards better weld quality.

Synergistic enhancement of Re/B4C on cobalt-based composite coatings: Evolution of microstructure, microhardness and tribological properties

In recent years, the application of laser cladded composite coatings remains a challenge due to the uneven distribution of residual stress and the formation of cracks resulting from high cooling rates and thermal gradient. Hence, we report on the elimination of cracks and softening in-situ composite coatings by doping 4.0 wt% of Rhenium(Re). The variation in transient temperature field, cladding geometry, microstructure, phase composition and tribological properties were also investigated with different laser energy input. Results indicated that B4C and Stellite-6 can significantly improve the microhardness of the TC4 substrate owing to the in-situ formation of hard phases (metallic carbides and borides), whereas accompanied with numerous cracks. More notably, the addition of Re can effectively inhibit the occurrence of cracks and soften the composite coatings, meanwhile excellent surface morphologies and wear resistance were obtained. The as-prepared composite coatings exhibit the highest microhardness with the value of 608.2HV0.2 and the minimum wear rate for 0.938 ∗ 10−7 mm2/N.

Innovative Joint for Cable Dome Structure Based on Topology Optimization and Additive Manufacturing.

Aiming at the problems of a low material utilization rate and uneven stress distribution of cast-steel support joints in cable dome structures, topology optimization and additive manufacturing methods are used for optimization design and integrated manufacturing. First, the basic principle and calculation process of topology optimization are briefly introduced. Then, the initial model of the support joint is calculated and analyzed by using the universal software ANSYS Workbench 2020R2 and Altair OptiStruct, and the optimized joint is imported into Discovery Live to smooth the surface. The static behaviors of three types of joints (topology-optimized joints, joints after the smoothing treatment, and joints from practical engineering) are compared and analyzed. Finally, the joints are printed by using fused deposition modeling (FDM) technology and laser-based powder bed fusion (LBPBF) technology in additive manufacturing. The results show that the new support joint in the cable dome structure obtained by the topology optimization method has the advantages of a novel shape, a high material utilization rate, and a uniform stress distribution. Additive manufacturing technology can allow the manufacture of complex shape components with high precision and high speed. The combination of topology optimization and additive manufacturing effectively realizes the advanced design and integrated manufacturing of support joints for cable dome structures.

Effect of fiber hybridization types on the mechanical properties of carbon/glass fiber reinforced polymer composite rod

In order to balance the cost performance of carbon and glass fibers, the unidirectional carbon/glass hybrid fiber reinforced polymer composite rods were developed through the pultrusion technology in the present paper. Two kinds of fiber hybridization types were proposed including intra-yarn hybrid (uniform dispersed hybrid, UDH) and inter-layer hybrid (core-shell hybrid, CSH). Furthermore, the effects of fiber hybridization types on the mechanical properties (interface/short beam shear strength, three-point bending strength and tensile strength) were investigated experimentally. The full-field strain was obtained through the digital image correlation method to reveal the hybrid mechanism. It was found that the effects of fiber hybridization types on mechanical properties were remarkable. Through uniformly dispersing the carbon fiber into the glass fiber, the maximum increase percentages of available strength were up to 10.9% for short beam shear, 60.3% for three-point bending and 58.7% for tensile strength, respectively. The results of full-field strain analysis revealed that the mechanical failure of CSH rods was dominant by the interface debonding of shell/core, which significantly decreased the mechanical properties. In comparison, UDH rods had the intact interface bonding of carbon/glass fiber/resin, the mechanical failure was derived from the fracture of carbon fiber. The tensile strength of carbon fiber was fully utilized, which contributed to the higher mechanical properties. The larger scale carbon fiber tow may form the weaker interface layer of carbon/glass fiber/resin, which led to uneven interface stress distribution under the external loading and the decrease of interface shear strength.

Electrical and mechanical properties of Au–Si bonds for 3D interconnect applications

Driven by high-density and high-reliability demands on three-dimensional (3D) interconnections, electrical and mechanical properties of interconnection structures have been paid more attention. Aiming at the novel enable-3D interconnections realized by Au–Si wafer bonding, this study demonstrates the design, fabrication and test results of testing structures for dimension-define parameters of Au–Si bonds. In order to measure closely-realistic ohmic contact resistances of Au–Si bonds after wafer bonding processes implemented under certain bonding pressures and temperatures, the convex Si structures formed by the local oxidation of silicon process have been designed. Therefrom the specific contact resistance values of Au–Si bonds have been measured as 3.9–8.1 × 10−10Ω m2 for different contact radii (3–20 μm), which indicates the low-resistance potentiality for Au–Si bonds applied on 3D interconnections. On the other hand, two findings on bonding strengths are summarized from finite element simulations and tensile experiments: (a) Au–Si bonding strengths of circular bonding patterns (35–75 MPa) are superior to the ones of square bonding patterns (18–30 MPa) due to the stress concentration phenomenon on four corners of square bonding patterns; (b) there is an inverse relationship between bonding strengths and bonding areas owing to uneven stress distributions in bonding structures. Overall, this study provides a basic optimization design strategy at electrical and mechanical levels for 3D interconnections actualized by Au–Si bonding. Incidentally, these introduced analysis methods are also feasible for homologous Si-based eutectic bonding techniques to extend the forms of 3D interconnections.

Effect of lead angle of hole expansion mandrel on surface integrity and fatigue performance of TC17 titanium alloy hole structure

For the TC17 titanium alloy, the influence of the leading end angle of the mandrel on the expansion strengthening effect of the hole structure was studied, the surface integrity of the hole expansion strengthened under different process parameters was characterized, the high temperature and low cycle of the original and strengthened samples were tested. Fatigue life and the morphological characteristics of fatigue fracture are analyzed. The results show that the lead angle of the mandrel has a significant effect on the surface roughness after expansion. The uneven plastic flow of the metal on the surface of the hole wall during the expansion process leads to uneven residual stress distribution on the hole wall after expansion, and the residual stress amplitude at the exit end of the expansion is the largest, and the hole wall has a certain depth of residual compressive stress gradient field after expansion. When the interference of the core rod is constant, the fatigue life increases with the increase of the rear lead end angle of the mandrel. When the rear lead end angle is 8°, the median fatigue life gain after strengthening can reach 1.74 times, and the strengthening effect is the best, its minimum cycle life is 16331 times, which is higher than the longest cycle life of the original sample (13965 cycles). After strengthening, the origin of the cracks is changed from the multi-source type in the middle of the hole wall to the single-source crack initiation at the inlet end of the expansion.