External Compressive Load Research Articles

Effect of Applied Stress on the Interfacial Kinetics, Ionic Conductivity, and Other Phenomena in Thin-Film Solid-State Batteries

Controlled stress is critical to both fabrication and operation of solid-state batteries to ensure pristine, low-impedance interfaces. The effects of externally applied stresses on overall cell performance and degradation due to altered thermodynamics, interfacial kinetics, and bulk transport of the active species have been studied in several prior works. In addition to the applied stack pressure which can vary up to 100s MPa, internal and localized stresses up to a few ~1 GPa can be generated from volume changes during charge and discharge. Electrode volume changes can result in cracking and delamination, causing loss of conductive pathways and active electrode-electrolyte area, and electrolyte fracture in the case of dendrite growth. The extent of these stress-electrochemistry couplings depends on the material and geometry of interfaces that affects the local stress distribution. To decouple some of these stress-potential, stress-kinetics, and stress-transport coupling phenomena, we use a nanoindenter platform to apply controlled uniaxial compressive forces to a thin-film electrochemical devices and batteries1. Interfaces in a thin-film sample can be uniform and planar over large areas, helping us study the effect of stress on the interfacial electrochemistry more directly and with greater quantitative accuracy. In this work we present our observations and analysis on the direct electrochemical-mechanical coupling in thin-film TiO2 and V2O5 metal oxide thin films as the working electrode with the single-ion Li+ conductor solid electrolyte LiPON. Preliminary results show that external uniaxial compressive load affects the electrochemistry observed through cyclic voltammetry and electrochemical impedance spectroscopy (EIS) measurements on thin-film batteries with TiO2 and V2O5 electrodes.

NUMERICAL INVESTIGATIONS ON COMBINED EFFECT OF WELDING RESIDUAL STRESS AND AXIAL COMPRESSIVE LOAD ON BUCKLING CAPACITY OF THIN LOW CARBON STEEL PLATES

Arc welding is the most commonly used metal joining process and its broad range of applications from large structural fabrications such as bridges to delicate satellite and aerospace components. Welding Residual Stress (WRS) and cracks developed during welding, reduce the quality of welds. Aerospace structures are normally fabricated using thin metal sheets to reduce mass and are always susceptible to buckling. Many researchers have published WRS numerical models and experimental validations, but the impact of WRS on the buckling of thin low carbon steel plates is yet to be studied. The main objective of this study is to analyse the influence of external compressive load and tendon force generated by welding residual stress on buckling strength of the TIG welded low-carbon steel plates. Linear buckling of welded plates under the combined effect of external compressive load and WRS generated due to various weld lengths were numerically modelled and its critical buckling loads are computed. The numerical simulation findings show that the critical buckling strength decreases by 80% when the weld length to plate width ratio (w/wl) is equal to unity and it reduces to minimum when the w/wl ratio is 0.5. After w/wl ratio is 0.5, buckling strength increases and this behavior is caused by the stress field interaction that arises from both the applied axial compressive load and the WRS on the plate.

Impact of external biaxial compressive loading on the fire spalling behavior of normal-strength concrete

Explosive spalling of concrete exposed to fire consists in the expulsion of shards from the heated face during rapid heating. The phenomenon can seriously jeopardize the integrity of reinforced concrete structures due to the reduction of the cross-sectional area of the structural elements and even lead to the direct exposure of reinforcing bars to flames. The literature shows that various parameters influence the occurrence of fire spalling, such as heating rate, specimen geometry and boundary conditions, concrete grade, and external loads. In this regard, the present study aims at highlighting the role of external loading in combination with the effects of pore pressure and thermo-mechanical stresses in triggering spalling in normal-strength concrete (fc28days ≈ 45 MPa). Unreinforced concrete slabs (size: 800 × 800 × 100 mm3) were subjected to a standard (ISO 834–1) fire curve under seven different levels of external membrane biaxial compressive load. The experimental results clearly show that compressive loading significantly increases spalling propensity and severity.

Compressive Strength Analysis of a Steel Bolted Connection under Bolt Loss Conditions

The aim of the study is the numerical analysis of a bolted connection under the conditions of loss of bearing capacity of some fasteners in this connection. The joined plates in the connection were made of the 3D finite elements, while the fasteners were treated as hybrid models consisting of rigid heads and nuts and flexible beams between them. A model of unilateral contact with friction was used between the joined plates. The bolted connection was first preloaded according to three different tensioning sequences and with a normalised force. After all the bolts were tensioned, the selected bolts were removed, simulating bolt damage under connection loading conditions. The connection was tested for external compressive loads up to 210 kN. The effect of the loosening of the connection on the load in the remaining bolts at the stage of the connection operation was investigated.

Two-Level Weight Optimization of Composite Laminates Using Integer Programming

Optimization of composite laminates requires the satisfaction of constraints where the design ply thicknesses and orientations can only take discrete values prescribed by the manufacturers. Heuristics such as particle swarm or genetic algorithms are inefficient in such cases because they provide suboptimal solutions when the number of design variables is large. They also are computationally expensive in handling the combinatorial nature of the problem. In contrast, with the help of binary decision variables, mixed integer programming can be adopted to optimize such laminates efficiently. This paper presents an approach to reformulate lamination parameters and failure constraints as functions of binary decision variables. The buckling load maximization for a simply supported laminated plate is initially demonstrated using integer linear programming. Next, the laminate weight is minimized by varying the number of plies for a given external bi-axial compressive load and subjected to buckling and material failure constraints. A variation of laminate weight minimization is demonstrated by fixing the number of plies and assuming discrete changes in ply thicknesses. This is achieved using a sequential two-level optimization for laminates having uniform ply thickness. Finally, a scalability study is performed to evaluate the performance of mixed integer programming for different problem sizes. It is demonstrated that all three formulations with integer programming achieve significant performance gain and robustness over standard heuristic solvers.

Effect of Compressive Stress in Tumor Microenvironment on Malignant Tumor Spheroid Invasion Process.

In this study, we proposed an in vitro tumor model to simulate the mechanical microenvironment and investigate the effect of compressive stress on the invasion process of malignant tumors. It has been pointed out that the biomechanical environment, as well as the biochemical environment, could affect the transformation of cancer cell migration, invasion, and metastasis. We hypothesized that the solid stress caused by the exclusion of surrounding tissue could transform tumor cells from noninvasive to invasive phenotypes. Colorectal cell spheroids were embedded and cultured in agarose gels of varying concentrations to simulate the earliest stages of tumor formation and invasion. The spheroids embedded in gels at higher concentrations showed peculiar growth after 72 h of culture, and the external compressive loading imposed on them caused peculiar growth even in the gels at lower concentrations. In conclusion, the mechanical microenvironment caused the transformation of tumor cell phenotypes, promoting the growth and invasion of tumor cell spheroids.

Nonlinear thermo-mechanical analysis of ES double curved shallow auxetic honeycomb sandwich shells with temperature-dependent properties

It is the first time the nonlinear thermo-mechanical analysis (buckling and postbuckling) of imperfect eccentrically stiffened (ES) double curved shallow shells made of auxetic material under uniform external pressure, axial compressive and thermal loads has been studied by adopting analytical method. The double curved shallow sandwich shell is constructed by an auxetic honeycomb core layer with negative Poisson’s ratio and two isotropic homogeneous skin layers. In the present study, the outer surface of the structure is reinforced by a system of FGM stiffeners and taking the influence of pores in the stiffeners into account to increase the load capacity of the structure. Besides, the material properties of the shells and stiffeners are both temperature-dependent. The first-order shear deformation theory is applied to derive equilibrium and compatibility equations of double curved shallow auxetic shell, considering both the geometrical nonlinearity in the Von Karman sense and initial geometrical imperfections and shells placed on the Winkler – Pasternak foundation. The Galerkin and stress function methods are proposed to determine the critical load value and the deflection– load curve by taking the root form of the two-term rotation angles to give the Galerkin integral an equilibrium equation. Several comparisons with results in other literature are made to examine the reliability and accuracy of the method used in the present study. Finally, the effects of thermal environment, reinforced stiffeners, elastic foundation, pores and parameters of auxetic core layer on the buckling and postbuckling loads are evaluated in this paper. The numerical and graphical results show that the reinforced stiffeners, auxetic core, temperature and porous distribution have significantly influenced on the buckling and postbuckling loads of ES double curved shallow auxetic honeycomb sandwich shells.

The influence of the rigidity of mining security structures on the stability of side rocks in the coal-rock massif

The object of research is the processes of controlling the state of side rocks to prevent the collapse of the stratified rock strata in the coal-rock massif containing the workings. The studies carried out made it possible to establish the influence of the rigidity of the guard structures of mine workings on the stability of side rocks in the coal-rock massif. It is proved that as a result of the action of an external compressive load on the supporting lateral rocks, the structure, in the form of a model of bunches made of wooden posts, increases its rigidity until the destruction of the security structure. After that, there is an increase in the convergence of side rocks and their destruction. The change in the stiffness of the crushed rock in the filling massif model, which is used to support the lateral rocks, occurs as a result of the compaction of the original material. This is due to repackaging of crushed rock fractions of different sizes and its additional grinding. As a result of this interaction of the side rocks with the filling massif, the integrity of the roof and soil is ensured and convergence is limited. To assess the stability of side rocks, it is proposed to use a dimensionless stress concentration factor k. This coefficient takes into account the rigidity of the guard structures of the mine workings and the flexural rigidity of the side rocks. It was found that when the values of the coefficient k are close to zero (k→0), there is a loss of stability of the guard structures of mine workings and the destruction of side rocks in the coal-rock massif. The preservation of the integrity of the side rocks and the stability of security structures is ensured at values of k>0.1, which corresponds to the parameters of the pliable supporting structures. Most favorably on the condition of side rocks in the coal-rock massif is influenced by the method of backing up the mined-out space of crushed rock. The use of this method excludes the collapse of side rocks. When solving the problem of stability of mine workings at the stage of making technical decisions, it is necessary to predetermine the issues of rigidity of security structures with deformation characteristics of side rocks.

On the effect of the boundary conditions of plain concrete exposed to high temperatures under uniaxial compression

AbstractThe effect of the boundary conditions, defined as the thermal expansion restraint imposed by the external uniaxial compressive load in plain concrete subjected to high temperatures, is discussed. A numerical mesoscopic investigation uncoupled the load induced thermal strain (LITS) into three main components (aggregates and matrix strain contributions and the effect of the thermal expansion restraint). The analyses demonstrate that LITS depends on the materials properties (viscous‐plastic behavior) and also on the boundary conditions, which is function of the test setup and seems to be not related to the material properties. In this paper, the role of the boundary conditions on 1‐phase (homogeneous) and 2‐phase (matrix + aggregates) numerical analyses are investigated. A LITS semi‐empirical model is incorporated in the numerical modeling to account for the stiffness degradation. It is demonstrated that in 1‐phase models, the effect of the boundary conditions is absent, which is not true for mesoscale analyses. In this case, the effect of the boundary conditions should be taken into account and subtracted from the results to avoid an overestimation of the material response. It is important mentioning that the analyses of concrete behavior at elevated temperatures and transient creep experimental procedures completely neglect the role of the boundary conditions.

Uniaxial Strain-Induced Grain Boundary Migration in Titanium

The mechanical response of a bi-crystal model with a 90° grain boundary under external compressive and tensile loading parallel to the boundary plane normal was investigated with molecular dynamics simulations. The grain boundary was found to migrate along two opposite directions upon compressive and tensile straining, with the formation of inter-connected coherent twin boundary and basal/prismatic boundary. The atomic details of such grain boundary migration were unraveled, which indicated the role of interface dislocations. The temperature effect was also discussed.

Effective strut-based design approach of multi-shaped lattices using equivalent material properties

We propose an effective approach for designing a multi-lattice structure (MLS) that simultaneously considers local densities and the fillet-joint shape of struts to express practical equivalent material properties. The density of each cell is optimized by changing the strut diameter and fillet-joint radius according to loading conditions. The equivalent material properties of MLS, such as elastic modulus and shear modulus, are calculated based on a computational homogenization method. Finite element analyses of the full-shape and homogenized lattice model under external compressive load are conducted to evaluate the equivalent material properties. We also designed an optimized three-point bending structure using the proposed method. Based on the results of the topology optimization, three types of lattices with different relative densities are designed in a local zone considering local deformation modes. The result of this work shows that multi-lattice bending structure has about 86.9 % higher strength than that of a uniform BCC lattice structure with the same weight.

Buckling of lattice columns made from three-dimensional chiral mechanical metamaterials

The three-dimensional (3D) chiral mechanical metamaterials were found to exhibit unique compression-twisting coupling effect. The metamaterial will twist in addition to axial shortening when subjected to the external compressive load. For a slender structure made from 3D chiral mechanical metamaterial, global buckling may occur if the compressive load exceeds the critical value. In this work we investigated the buckling strength of the chiral lattice columns which were constructed by periodically placing the inclined straight beams in a chiral manner. Based on the Cosserat rod theory, a novel constitutive model with a new parameter governing the compression-twisting coupling was built to describe the deformation of 3D chiral metamaterial. A semi-analytical homogenization method was proposed to connect the stiffness parameters of arbitrary sized lattice column to the properties of the unit cell. The constitutive model together with the homogenization method well interpreted and quantified the size dependency of the chirality. The fourth-order governing equations of buckling were developed and solved analytically to predict the critical buckling load of 3D chiral metamaterial. The effects of chirality on the buckling strength and buckling mode were revealed.

A phenomenological constitutive model for semicrystalline two-way shape memory polymers

Recently, two-way shape memory effect (2W-SME) has been demonstrated in several types of shape memory polymers (SMPs). Unlike classical one-way shape memory effect (1W-SME), these polymers can switch back and forth repeatedly between two different shapes without subsequent programming procedure. The reversible actuation can be realized either under a constant external tensile load, which is referred to as quasi 2W-SME, or under zero load, which is referred to as true 2W-SME. Most recently, actuation under an external compressive load, which is referred to as advanced 2W-SME, has also been discovered. Test results have shown that semicrystalline 2W-SMPs exhibit 2W-SME in two distinct regions due to two different mechanisms: one is due to entropic elasticity above the crystallization temperature, and the other is due to melt/crystallization transition below the crystallization temperature. While several constitutive models have been developed over the years for semicrystalline 2W-SMPs, there is currently a lack of effort towards modeling the true and advanced 2W-SME within the two-mechanism framework. In this study, we developed a thermomechanical constitutive model which captured both the entropic elasticity and melt/crystallization events. The modeling results and test results show reasonable agreement. It is found that the model captured the three types of 2W-SMEs: quasi 2W-SME, true 2W-SME, and advanced 2W-SME. It is also found that proper tensile programming before the first thermomechanical cycle can make a semicrystalline SMP exhibit all the three types of 2W-SMEs. This study may serve as a design tool to enhance applications of semicrystalline 2W-SMPs in engineering structures and devices.

Mechanical Properties of Concrete Pipes with Pre-Existing Cracks

Concrete pipes are the most widely used municipal drainage pipes in China. When concrete pipes fall into years of disrepair, numerous problems appear. As one of the most common problems of concrete pipes, cracks impact on the deterioration of mechanical properties of pipes, which cannot be ignored. In the current work, normal concrete pipes and those with pre-existing cracks are tested on a full scale under an external compressive load. The effects of the length, depth, and location of cracks on the bearing capacity and mechanical properties of the concrete pipes are quantitatively analyzed. Based on the full-scale tests, three-dimensional finite element models of normal and cracked concrete pipes are developed, and the measured results are compared with the data of the finite element analysis. It is clear that the test measurements are in good agreement with the simulation results; the bearing capacity of a concrete pipe is inversely proportional to the length and depth of the crack, and the maximum circumferential strain of the pipe occurs at the location of the crack. The strain of the concrete pipe also reveals three stages of elasticity, plasticity, and failure as the external load rises. Finally, when the load series reaches the limit of the failure load of the concrete pipe with pre-existing cracks, the pipe breaks along the crack position.

Mechanical behavior of Silicon-Graphite pouch cells under external compressive load: Implications and opportunities for battery pack design

The mechanical behavior of high capacity (1.4Ah) multilayer Si alloy-Graphite/NMC622 pouch cells under an external compressive load is presented in this research. The results show that their mechanical behavior is more complex compared to traditional cells with graphite anodes. Three distinct mechanisms are identified in the pressure evolution: i) a reversible pressure variation related to the lithiation of the anode, ii) an irreversible relaxation that occurs during early cycles and iii) an irreversible pressure growth related to capacity degradation. All mechanisms are investigated separately and a root cause is proposed for each one. Cells are cycled at different conditions to study the effect of initial compressive load, ambient temperature, current rate and depth of discharge on the mechanical behavior. Finally, a modeling methodology is proposed to estimate cell capacity fade based on cell pressure measurements and to model the expected pressure evolution during cycling. Presumably, this pressure behavior will become a key factor in designing future battery modules and packs containing energy-dense, volume changing electrode materials such as Silicon.

Buckling of piezoelectric sandwich microplates with arbitrary in-plane BCs rested on foundation: effect of hygro-thermo-electro-elastic field

Buckling and post-buckling behaviors of simply supported microplates in complex environment are studied, where elastic foundation and hygro-thermal-electro-mechanical loads are considered. The first-order shear deformation theory is used to establish basic equations of the microplate considering the von Karman’s nonlinearity. The size-dependent effect is characterized by the modified couple stress theory. A unified boundary condition model is introduced to discuss various in-plane boundary conditions (BCs). Analytical solutions for critical mechanical/hygrothermal buckling loads and post-buckling paths of the microplate under different in-plane BCs are obtained by using the perturbation method and the Galerkin method, respectively. Results reveal that size-dependent effect and elastic foundation enhance the stiffness of the microplate. Transverse displacement of the microplate in the post-buckling stage increases with the external compressive load, temperature and moisture concentration, expressing a nonlinear curve. When the displacement constraint in the normal direction is applied on the microplate edge, the critical mechanical/hygrothermal buckling load decreases. These results can be utilized in the optimization design of the micro-electro-mechanical systems.

Experimental and numerical analyses of an U-bend tube made of an output inter-heater tube after exploitation

One of the important tasks of evaluating the integrity of mechanical process elements and structures is to determine the local mechanical properties. In this paper, experimental and numerical analyses of the mechanical behavior of an output inter-heater tube, made of 12H1MF heat-resistant steel, was performed after 200,000 h of exploitation. During exploitation, the tube was exposed to various mechanisms of damage including gas corrosion. The tube was cut from a pipe system during reparations of a thermal power plant, and then cold-deformed by bending to obtain a U-bend tube, which was then used in the experiment. For this purpose, a specimen holder made of structural steel S235 was specifically designed to test such a sample. The U-bend tube was then exposed to the external compressive load during the experiment. Experimental research was based on the application of the 3D digital image correlation (DIC), while a finite element method (FEM) was applied in numerical simulation performed by using the Abaqus software package. The 3D DIC is an optical and contactless experimental method that allows measurements of displacement fields and deformations of geometrically complex structures. The Aramis system was used for the experimental analysis as well as for verification of the numerical model. During the experiment, the von Mises strain field was measured at the top of the U-bend tube, in the tightening zone, as it represents a critical place for crack initiation and propagation during the work of an inter-heater. Based on the obtained results and a comparative analysis of experimental and numerical values of the von Mises strain field at the U-bend tube, deviation of the model predictions of about 18 % was determined. The FEM predicted smaller values of the von Mises strain field compared to the DIC method. This is the result of an incomplete geometry applied in the model due to deformation that occurred in the bend zone of the U-bend tube, loss of material and the tube surface damage due to the influence of gas corrosion during 200,000 h of exploitation. Experimental analysis has confirmed that the U-bend tube, after 200,000 h of exploitation, can remain in service even if it is damaged due to the effect of gas corrosion.

Nonlinear post-buckling and vibration of 2D penta-graphene composite plates

The newly developed penta-graphene is a two-dimensional (2D) carbon allotrope with promising mechanical properties. This paper investigates the nonlinear post-buckling and vibration of imperfect three-dimensional penta-graphene composite plates resting on elastic foundations and subjected to uniform external pressure and axial compressive load. The elastic constants of the single-layer penta-graphene are fully determined by the density functional theory by fitting the equation of strain energy to the density functional theory energy. Specifically, the elastic constant $$C_{66}$$ which has not been considered by other authors is also determined. The motion and compatibility equations are derived based on the classical plate theory taking into account von Karman geometrical nonlinearity, initial geometrical imperfection and Pasternak type elastic foundations. For nonlinear post-buckling, the Bubnov–Galerkin method is applied to obtain the load–deflection amplitude curves while the Runge–Kutta method and harmonic balance method are used to obtain the deflection amplitude–time curves and the amplitude–frequency curves for nonlinear vibration. Numerical results show the effects of geometrical parameters, initial imperfection and elastic foundations on the nonlinear post-buckling and vibration of the imperfect 2D penta-graphene plates. The present results are also compared to others to validate the accuracy of the applied method and approach.

Stability of steel struts with externally anchored prestressed cables

Externally anchored prestressed cables can be employed to enhance the stability of steel truss compression elements significantly. To demonstrate this concept, a system comprising a tubular strut subjected to an external compressive load and a prestressed cable anchored independently of the strut is studied. Energy methods are utilized to define the elastic stability of the perfect and imperfect systems, after which the first yield and rigid–plastic responses are explored. The influence of the key controlling parameters, including the length of the strut, the axial stiffness of the cable and the initial prestressing force, on the elastic stability, the inelastic response and the ultimate strength of the system is demonstrated using analytical and finite element (FE) models. To illustrate the application of the studied structural concept, FE modelling is employed to simulate the structural response of a prestressed hangar roof truss. A nearly two-fold enhancement in the load-carrying capacity of the truss structure is shown to be achieved owing to the addition of the prestressed cable.

Buckling Delamination of a Rectangular Orthotropic Thick Plate with an Embedded Rectangular Crack Subjected to an Axial Compressive Force

A 3D buckling delamination problem for a simply supported rectangular orthotropic composite thick plate containing a rectangular crack and subjected to an axial compressive force is studied. In the initial state, crack faces have an infinitesimal imperfection. The development of this imperfection caused by an external compressive loading along the crack is investigated within the framework of the 3D geometrically nonlinear elasticity theory of anisotropic bodies. The corresponding boundary-value problems are solved numerically by the 3D FEM. The influence of material and geometrical parameters of the plate on its critical buckling force is evaluated and discussed.