Non-uniform Loading Research Articles

Experimental investigation of microchannel heat sink performance under non-uniform heat load conditions with different flow configurations

Cooling methods for multiple hotspots with high heat flux pose a reliability threat to electronic devices. This study investigates the microchannel-based heat sink performance under various non-uniform heat load conditions for different geometry with three different flow configurations (I, U and Z). An in-house designed Heater Array Unit (HAU) facilitates the generation of both uniform and non-uniform heat loads using a heater power supply. Two different microchannel geometries were employed, namely, microchannel-1 (MC-1) with channel and fin widths of 0.6 mm and 0.33 mm, respectively, and MC-2 with dimensions of 0.64 mm and 0.572 mm. Each microchannel incorporates three manifold configurations (I, U, and Z). Each flow configuration is regulated by flow control valves. Various non-uniform heat load patterns were considered, including streamline, non-streamline, and across-streamline conditions. To assess the thermal performance of the heat sinks the parameters used are thermal resistance (Rth), Nusselt number (Nu), and temperature non-uniformity (Ѱ). Experimental findings indicate that the MC-2 design with an I flow configuration is more suitable for uniform heat load conditions. On the contrary, for some non-uniform heat load cases MC-1 also showed up as a suitable design over MC-2.

Nonlinear Stability of Curved Multiphase Composite Panels: Influence of Agglomeration in Randomly Distributed Carbon Nanotubes with Nonuniform In-Plane Loads

Nonlinear Stability of Curved Multiphase Composite Panels: Influence of Agglomeration in Randomly Distributed Carbon Nanotubes with Nonuniform In-Plane Loads

The influence of different load distribution considering geometric error on the fatigue life of ball screw

The ball screw pair is a precision drive component that converts rotary motion into linear motion. In practical applications, because the feed system usually has rotational torque and geometric errors, it may increase the contact load of the ball screw pair and reduce the fatigue life. In order to study the influence of different loads and geometric errors on the maximum contact load and fatigue life of ball screw pairs, the following research work was carried out. Firstly, based on the composite load and rotational torque, the ball load distribution model is established, and the accuracy of the model is verified by finite element modeling analysis. Then, the influence of different composite loads, rotation times and geometric errors (including ball size error, lead error and raceway tooth profile error) on the ball load distribution is analyzed. Finally, the influence of compound load, rotating torque and geometric error on the fatigue life of ball screw pairs is studied. The results show that the rotational torque and lead error have a great influence on the load distribution and fatigue life of the ball, and the influence of lead error on load distribution is greater than that of dimension error and tooth profile error. The fatigue life of the ball screw pair with non-uniform load distribution is shorter than that of the ball screw pair with uniform load distribution.

Seismic response analysis of subway station under obliquely incident SV waves

This paper aims to investigate the dynamic response characteristics of subway station under earthquakes. To this end, seismic waves are transformed into equivalent nodal loads on viscoelastic artificial boundaries using theories and methods of wave motion. The calculation formulas for equivalent nodal loads of SV waves incident at any angle are established, and ANSYS' APDL program compiles to automatically generate the viscoelastic artificial boundary and input the seismic loads. A finite element model of soil-subway station interaction was established, and the seismic response characteristics of a two-story three-span subway station under different incidence angles of SV waves were investigated using the above seismic input method. The results indicate that the incidence angle of seismic waves has a significant impact on the seismic response of subway station. Inclined incidence of seismic waves causes non-uniform loading and deformation of the subway station. Specifically, a small angle leads to predominantly transverse shear deformation, while a large angle causes mainly vertical shear deformation. The inclined incidence of seismic waves significantly increases the vertical acceleration of the subway station, with the effect becoming more pronounced as the angle increases. Additionally, special attention should be given to the joints between the structural slab and the side wall, slab and center column, as well as the two ends of the center column as they are vulnerable areas during earthquakes and require careful consideration in seismic design.

Functionally varied negative-stiffness metamaterial core sandwich structures with three-phase bending deformation

Abstract This paper introduces a novel class of negative-stiffness (NS) core sandwich composite structures that exhibit unique mechanical performance, including shape recovery, superelasticity, and energy absorption (EA) in bending and shear mode. The core of these structures consists of a periodic cellular arrangement of double-curved beams that undergo consecutive local snap-buckling transitions between multiple equilibrium states, enabling the structures to change shape reversibly between their initial and deformed configurations. To characterize the force-displacement relationship of the core, a comprehensive analysis was conducted using a combination of 3D printed models and finite-element simulations. The metamaterial core with gradient-thickness negative-stiffness beams were examined under uniform compression, demonstrating that the snap-through behavior of the curved beams was intricately controlled by the beam thickness in each row. The numerical simulations accurately predicted the deformation characteristics of the graded cellular core, supporting the design of a metamaterial core with functionally varied beam thickness for nonuniform transverse loading. This led to spatially controlled NS core material with specific EA of around 50 J kg−1 and an apparent core shear strength of 0.1 MPa, all mainly within the reusable elastic regime. The resulting sandwich structures efficiently mitigated the localized effect from concentrated compressive forces and achieved complete snap-through buckling in all curve beams. Three-point bending response revealed three distinct phases of flexural deformation: the local facial bending phase, the sequential core-snapping superelastic phase, and the global bending phase.

Dynamic screening by plasticity in amorphous solids.

In recent work it was shown that elasticity theory can break down in amorphous solids subjected to nonuniform static loads. The elastic fields are screened by geometric dipoles; these stem from gradients of the quadrupole field associated with plastic responses. Here we study the dynamical responses induced by oscillatory loads. The required modification to classical elasticity is described. Exact solutions for the displacement field in circular geometry are presented, demonstrating that dipole screening results in essential departures from the expected predictions of classical elasticity theory. Numerical simulations are conducted to validate the theoretical predictions and to delineate their range of validity.

Experimental and simulation research on rupture behavior of coal-based solid waste material backfilling column under non-uniformly distributed load with different loading ratios

Artificial construction backfilling columns underground based on coal-based solid waste materials is an important method to slow down surface subsidence and reduce the environmental pollution caused by coal gangue hills and fly ash. Taking the Xinyang coal mine as an example, based on a self-developed non-uniform load application device, acoustic emission (AE) and digital image correlation (DIC) monitoring technology, the evolution law of rupture behavior of coal-based solid waste material backfilling columns under different loading ratios was revealed. When the loading ratios are 1, 1.1319, 1.3585, 1.6371, and 2.0631, the average compression strength with the same material ratio is 3.96 MPa, 4.05 MPa, 4.22 MPa, 4.57 MPa, and 3.94 MPa, respectively. It is indicated that an increase in the loading ratio within the critical range is beneficial for stimulating the collaborative bearing of different parts inside the backfilling columns. From the perspective of the internal rupture behavior of the backfilling columns, the increase in loading ratio promotes a significant increase in the proportion of shear cracks, which has increased from 17.07% to 37.02%, resulting in the shear failure of backfilling columns. Meanwhile, as the loading ratio increases, the crack initiation position gathers from the left and right sides to the middle, and the final crack shape gradually transitions from two inclined and parallel main cracks to an inverted "V" shaped intersecting main cracks. The research is of great significance for improving the understanding of the failure law of backfilling columns and the safety evaluation of engineering-bearing structures under non-uniform loads.

Regional shear wave speeds track regional axial stress in nonuniformly loaded fibrous soft tissues

Ligaments and tendons undergo nonuniform deformation during movement. While deformations can be imaged, it remains challenging to use such information to infer regional tissue loading. Shear wave tensiometry is a promising noninvasive technique to gauge axial stress and is premised on a tensioned beam model. However, it is unknown whether tensiometry can predict regional stress in a nonuniformly loaded structure. The objectives of this study were to (1) determine whether regional shear wave speed tracks regional axial stress in nonuniformly loaded fibrous soft tissues, and (2) determine the sensitivity of regional axial stress and shear wave speed to nonuniform load distribution and fiber alignment. We created a representative set of 12,000 dynamic finite element models of a fibrous soft tissue with probabilistic variations in fiber alignment, stiffness, and aspect ratio. In each model, we applied a randomly selected nonuniform load distribution, and then excited a shear wave and tracked its regional propagation. We found that regional shear wave speed was an excellent predictor of the regional axial stress (RMSE = 0.57 MPa) and that the nature of the regional shear wave speed-stress relationship was consistent with a tensioned beam model (R2 = 0.99). Variations in nonuniform load distribution and fiber alignment did not substantially alter the wave speed-stress relationship, particularly at higher loads. Thus, these findings suggests that shear wave tensiometry could provide a quantitative estimate of regional tissue stress in ligaments and tendons.

Influence of Non-Uniform Rail Loads on the Rotation of Railway Sleepers

This article presents an innovative, two-stage railway track model, which takes into consideration the rotation of railway sleepers due to non-uniform loads on rails. Examples of determining the dynamic response of the railway track are provided. The calculations were performed for a curve, in which non-uniform loads on rails result from the distribution of vertical loads at different train speeds. The analysis was performed using a variable moment of inertia of a sleeper.

Experiments and simulations for dynamic yarn pull-out response of Kevlar® fabrics

This work presents a novel experimental method for performing dynamic yarn pull-out using a modified tensile split Hopkinson pressure bar. The pull yarn is fixed to a piezoelectric load cell, while the woven fabric specimen is displaced at pull-out velocities ranging from 22 to 32 m/s. Pull-out force, displacement, and energy absorption over time are quantified for commercially available Kevlar® KM2+ woven fabric with pull lengths L = 5 mm and 27 mm in both quasi-static (QS) and dynamic loading. Dynamic peak pull-out force increases over QS by as much as 290–460% and 170–220% for L = 5 mm and L = 27 mm, respectively, and overall energy absorption increases by 140–420% and 40–140% for L = 5 mm and L = 27 mm, respectively. In QS loading, stick–slip interactions result in forces dropping by approximately 70–80% between oscillating peaks for L = 5 mm and 30–40% between peaks for L = 27 mm, and displacements between peaks are typically 1.5 mm, corresponding to two yarn crossings or two spans. However, at dynamic rates, stick–slip stage force drops by 100% after the first and all subsequent peaks due to the dynamic release of the pull yarn from the fabric, resulting in the pull yarn passing through multiple yarn crossings. To better understand the underlying mechanisms for these observations, finite element simulations of the experiments are performed. Strain rate dependent longitudinal shear stiffness of the yarn is found to significantly affect the dynamic yarn pull-out response and explain the enhanced dynamic yarn pull-out peak force and energy absorption. While the shorter yarn of L = 5 mm experiences a more uniform loading along the entire length, non-uniform loading via progressive uncrimping is observed in the longer yarn of L = 27 mm along the length.

Buckling analysis of nonuniformly compressed rectangular FG-CNT reinforced laminated composite plate resting on elastic foundation: An analytical solution

The present study is focused on the development of an analytical solution for the buckling analysis of carbon nanotube reinforced functionally graded (FG-CNTRC) laminated plates resting on Pasternak elastic foundation and subjected to different nonuniform edge loads. The analytical solution is formulated using a two-step procedure: First, an accurate in-plane stress solution is developed by superimposing three suitable Airy’s stress functions; second, the stress solution is utilized to compute the critical buckling loads using the Galerkin’s procedure. Results from parametric studies show that the buckling behavior of FG-CNTRC plates greatly depends on the type of nonuniform loads, plate configurations, and support parameters.

Changes in filtration and capacitance properties of highly porous reservoir in underground gas storage: CT-based and geomechanical modeling

The paper presents the results of comprehensive studies of filtration and capacitance properties of highly porous reservoir rocks of the aquifer of an underground gas storage facility. The geomechanical part of the research included studying the dependence of rock permeability on the stress-strain state in the vicinity of the wells, and physical modeling of the implementation of the method of increasing the permeability of the wellbore zone - the method of directional unloading of the reservoir. The digital part of the research included computed tomography (CT)-based computer analysis of the internal structure, pore space characteristics, and filtration properties before and after the tests. According to the results of physical modeling of deformation and filtration processes, it is found that the permeability of rocks before fracture depends on the stress-strain state insignificantly, and this influence is reversible. However, when downhole pressure reaches 7-8 MPa, macrocracks in the rock begin to grow, accompanied by irreversible permeability increase. Porosity, geodesic tortuosity and permeability values were obtained based on digital studies and numerical modeling. A weak degree of transversal anisotropy of the filtration properties of rocks was detected. Based on the analysis of pore size distribution, pressure field and flow velocities, high homogeneity and connectivity of the rock pore space is shown. The absence of pronounced changes in pore space characteristics and pore permeability after non-uniform triaxial loading rocks was shown. On the basis of geometrical analysis of pore space, the reasons for weak permeability anisotropy were identified. The filtration-capacitance properties obtained from the digital analysis showed very good agreement with the results of field and laboratory measurements. The physical modeling has confirmed the efficiency of application of the directional unloading method for the reservoir under study. The necessary parameters of its application were calculated: bottomhole geometry, stage of operation, stresses and pressure drawdown value.

High-temperature axial tensile property and fire resisting performance of CFRP strand cable

High-temperature tensile tests and fire resisting performance tests were conducted on carbon fiber reinforced polymer (CFRP) strand cable, respectively, to identify axial tensile property deterioration of CFRP strand tendon (i.e., cable without initial tensile load) under 100–600℃ temperature range and determine fire resisting duration and ultimate temperature of CFRP strand cable with initial tensile load ratio from 0.2 to 0.8. High-temperature axial tensile property and fire resisting performance of different cables including CFRP and steel cables were compared to identify influence of non-uniform load distribution. The obtained results demonstrated that the dominate failure modes of specimen in both high-temperature tensile test and fire resisting performance test are tensile failure. Due to the degradation of mechanical property of resin matrix and bonding performance for resin matrix-fiber bundle interface exposed to elevated temperature, axial tensile strength of CFRP strand tendon degraded by 33.4% and 80.8% under 210℃ (glass transition temperature) and 600℃, respectively, compared to that under ambient temperature. Fire resisting duration of CFRP strand cables varied from 1.3 to 16.4 mins, indicating poor fire resisting performance. Reduction coefficient of bearing capacity for CFRP strand tendon decreased from 0.96 to 0.74 as temperature varied from 25 to 400℃, and then increased to 1.54 at 600℃. Compared to ribbed CFRP cable, CFRP strand cables with initial tensile load ratios ranging of 0.4 ∼ 0.8 (low ultimate temperatures) display worse fire resisting performance due to the prominent non-uniform load distribution among seven wires. Axial tensile strength and reduction coefficient of bearing capacity for CFRP strand tendon exposed to elevated temperature and fire resisting duration of CFRP strand cable and ribbed CFRP cable can be accurately predicted by the developed practical models.

Behavior of piled rafts in sand under nonuniform and eccentric loads

Behavior of piled rafts in sand under nonuniform and eccentric loads

The Simulation Analysis and Experimental Study on the Temperature Field of Four Row Rolling Bearings of Rolling Mill under Non-Uniform Load Conditions

As a key component of the rolling mill, the four-row cylindrical roller bearing (FCRB) operates under complex working conditions of high speed, high temperature, and heavy load. Due to the lack of an effective temperature test scheme for rolling mill bearings, a too high temperature can easily lead to bearing failure or damage under unsteady conditions. To reveal the internal temperature distribution law of four-row roller bearings of rolling mills and solve the common problem of difficult temperature monitoring of rolling mill bearings, in this paper, a four-row cylindrical roller bearing of 1140 mm cold rolling six-high mill is taken as the research object, and the temperature field calculation model for four-row cylindrical roller bearings is established. Firstly, the mechanical analysis model of FCRB is established on the basis of single row bearing by slice method. Secondly, the mechanical calculation model of FCRB is established by the Newton–Raphson method (NRM) and the finite element method (FEM). Thirdly, based on the mechanical calculation model, the finite element method is used to establish the temperature field model of FCRB under uniform load distribution and non-uniform load distribution. Finally, the temperature test experiment is carried out with the FCRB in the rolling mill fault diagnosis test bench. The results show that the error between the FCRB temperature calculation model and the experimental results is less than 10%. It can be seen that the uneven temperature distribution of FCRB is mainly caused by the uneven load distribution. The temperature distribution along the axial direction of the bearing is related to the load distribution of each column, while the circumferential temperature distribution is related to the azimuth angle.

A new elastic T-shape joint of longitudinally connected slab ballastless track structure for releasing thermal stress caused by non-uniform temperature loads

In a longitudinally connected slab ballastless track structure (LCSBTS), the T-shape joint is the critical section where severe damage is often found due to the extremely high-temperature effect, mainly concerned with routine high-speed railway maintenance. This paper proposes a new elastic T-shape joint that replaces a section of the original C55 concrete joint with elastic material. A numerical model of LCSBTS with a new elastic T-shape joint is established to simulate the development of the interfacial bond failure and joint compressive damage under temporally and spatially non-uniform temperature loads. The influence of the size, material properties and replacement position of the elastic material with the new elastic T-shape joint on the damage, deformation, and stress of LCSBTS subjected to the temperature loads is investigated. Results show that, by adopting the new elastic T-shape joint, the joint compressive damage and the longitudinal thermal stress of LCSBTS are reduced significantly. The lower the elastic modulus of the elastic material, the greater the longitudinal thermal stress release of the track structure. As the elastic modulus of the elastic material decreases, the vertical displacement of the track slab, interfacial damage of LCSBTS and joint compressive damage increase while the vertical displacement of the joint improves. The best new elastic T-shape joint is to replace the middle of the wide joint made of C55 concrete with 50 mm-width elastic material, where the elastic modulus is 17324 MPa. Compared to the original designation of C55 concrete joint, LCSBTS with a new elastic T-shape joint achieves 11.2% maximum thermal stress reduction ratio and reduces the joint compressive damage by 23.5% and interfacial damage by 4.2%.

Exploiting the flow maldistribution characteristics in parallel microchannel heat sinks of I, U, and Z configurations to tackle the nonuniform heat loads

This study aims to analyze the cooling performance of parallel microchannel heat sinks (PMCHS) under uneven heat flux distributions, taking into account different flow configurations including I, U, and Z. The objective is to demonstrate the potential of utilizing the flow maldistribution inherent in each configuration to effectively manage and mitigate the effects of uneven heat flux distributions. Four different heating arrangements have been considered, namely uniform, non-streamline, streamline, and across-streamline to generate the uneven heat flux distributions. A three-dimensional numerical simulation has been performed to analyze the combined effect of uneven heat flux distributions and flow maldistribution characteristics on the thermal performance of PMCHS. To assess the thermal performances; thermal resistance (Rth), Nusselt number (Nu), temperature nonuniformity (Ψ), and fin efficiency (ηfin) have been employed. The results show that all three flow configurations exhibit similar thermal performances for uniform heat load conditions (0.1 K/W for Rth, 5.5 kW for Nu, 0.3 for Ψ, and 0.98 for ηfin). However, in the case of uneven heat flux distributions, the thermal performance of each configuration is observed to be varying with respect to hotspot positions. This study reveals that each configuration has a huge discrepancy in terms of thermal performance with respect to uneven heat flux distributions. Also, the study concludes that a single flow configuration alone is insufficient to address the cooling challenges that arise due to uneven heat flux distributions. The cooling capability of any configuration to handle uneven heat distributions mainly depends upon the flow maldistribution characteristics of the respective configurations.

Fracture Disaster Assessment of Model Concrete Piles in Loess Slope Engineering under Non-Uniform Lateral Loading

Existing model tests for reinforcing loess slopes with stabilizing piles are often challenged by simulation inaccuracies in lateral loading modes and scaling. Addressing these concerns, this study conducts model tests and numerical simulations to scrutinize the damage characteristics of concrete piles in two varying loess slope conditions under non-uniform lateral loading. The tests were designed to strictly maintain the similarity ratio of the concrete piles. The results reveal a no table 20% reduction in lateral bearing capacity due to the penetration of a potential sliding surface, exacerbating the stress on the piles. Furthermore, compared to uniform loess slopes, the presence of a sliding surface leads to a 38.4% increase in the height of the stress concentration point, resulting in earlier crack formation in the piles. These findings offer substantial theoretical and practical insights, highlighting the critical need for accurate model simulation in slope stabilization research and providing a basis for improving engineering practices.

New insights into the mechanism of load transfer in steel-encased CFST connections

Extensive numerical studies and analysis are presented to gain insights into the mechanism of load transfer in T- and K-type concrete-filled steel tube (CFST) connections. The new mechanism of load transfer investigated in this paper manifests that the shear load is transferred non-uniformly in the CFST column. Using validated finite element (FE) models, contact pressure stresses of the concrete-tube and angle-concrete interfaces are investigated to examine the interfacial interaction between each component. It indicates that the friction resistances between three components occur almost throughout the loading process, which is non-uniformly distributed along the column length. In addition, stress in each component is evaluated to determine the region of non-uniform load transfer in the column. For T-type connection, non-uniform load transfer shall only be considered for concrete-tube interface. For K-type connection, non-uniform load transfer should be considered for both concrete-tube and angle-concrete interfaces. Non-uniform load transfer mainly occurs in the connecting region and one time diameter of column above the connecting region for theses connections. Finally, the uneven transferred load of each component for the connections is analysed, whilst different force allocation schemes are compared. Based on the shear stresses at the tube-concrete and concrete-angle interfaces, non-uniform load transfer factor of each interface is calculated to quantitatively evaluate the non-uniformity of load transfer for the T- and K-type CFST connections.

Influence of stiffeners on the buckling behaviour of composite panels subjected to non-uniform edge loads

Influence of stiffeners on the buckling behaviour of composite panels subjected to non-uniform edge loads