Initial Loading Conditions Research Articles

One-Dimensional Consolidation of Unsaturated Soil Subjected to Time-Dependent Loading with Various Initial and Boundary Conditions

This study assesses the one-dimensional (1D) consolidation of unsaturated soil subjected to time-dependent loading based on the 1D consolidation theories of unsaturated soil. The differential quadrature method (DQM) is used to produce a general solution that considers various boundary conditions, various initial pore-water and pore-air distributions, and complex time-dependent loading. A special case in which the analytical solution is available in the literature is used for verification and accuracy analysis. It is found that the DQM solution can deliver more accurate results compared with the finite-difference method with a small number of sampling points. The general solution can avoid cumbersome computations in solving eigenequations encountered with the analytical solution. In addition, the proposed solution is more suitable for practical engineering because of its generality in complex initial, boundary, and loading conditions. Finally, the characteristics of the 1D consolidation of unsaturated soils under various initial pore pressure distributions, boundary conditions, and complex time-dependent loading conditions are investigated, and it is found that the initial and boundary conditions have a significant influence on the consolidation of unsaturated soils.

A two-surface plasticity model for clay

This paper presents a two-surface plasticity constitutive model for clays based on critical-state soil mechanics. The model reproduces the mechanical response of clays under multi-axial loading conditions and predicts both drained and undrained behavior at small and large strains. The constitutive model also captures both the strain-rate-dependent behavior of clays and the drop in strength towards a residual value at very large shear strains using novel approaches. The paper also describes a hierarchical process for the determination of the model parameters relying more on simple curve fitting of model equations to experimental data points corresponding to specific soil states instead of trial-and-error simulations of entire experiments. Model parameter values are determined for London Clay, San Francisco Bay Mud, Boston Blue Clay and Lower Cromer Till, and the performance of the model in simulating mechanical response of clays is demonstrated for a variety of initial states and loading conditions.

메카노 규제 이론에 기초한 복합재료 IM-rod가 적용된 골절부의 세포분화과정의 유한요소해석

본 논문에서는 복합재료 IM rod가 적용된 골절부의 세포 분화과정을 모사하기 위해 유한요소해석을 실시하였다. 세포의 골화과정을 해석하기 위해 편향 변형률을 이용한 메카노 규제 이론을 사용하였으며, 반복 계산을 위해 Python 코드를 이용하여 서브루틴을 구현하였다. 치료에 가장 적절한 복합재료 IM rod의 강성을 찾기 위해 직물 탄소섬유/에폭시 복합재료 (WSN3k)의 적층각도를 바꾸어 해석을 실시하였다. 골절부에 가해지는 기계적 자극에 따른 치료효율을 비교하기 위해 두 가지 초기 하중 조건을 적용하였다. 그 결과 치료효율은 강성의 차이보다 하중에 의해 큰 영향을 받았으며, 초기 하중이 몸무게의 10%이고, 적층순서가 <TEX>$[{\pm}45]_{nT}$</TEX>일 때 치료효율이 가장 높았다. This paper describes the bone healing process of fractured long bones such as a tibia applied by composite IM rods using finite element analysis. To simulated tissue differentiation process mechano-regulation theory with a deviatoric strain was implemented and a user's subroutine programmed by a Python code for an iterative calculation was used. To broadly find the appropriate rod modulus for healing bone fractures, composite IM rods were analyzed considering the stacking sequence. To compare mechanical stimulation at fracture gap, two kinds of initial loading conditions were applied. As a result, it was found that the initial loading condition was the most sensitive factor for the healing performance. In case a composite IM rod made of a plain weave carbon fiber/epoxy (WSN3k) had a stacking sequence of <TEX>$[{\pm}45]_{nT}$</TEX>, the healing efficiency was the most effective under a initial load of 10%BW.

Combination of Newmark method and natural element method for elastodynamics

The natural element method (NEM) is a meshless method. The trial and test functions of the NEM are constructed using natural neighbor interpolations which are based on the Voronoi tessellation of a set of nodes. The NEM interpolation is linear between adjacent nodes on the boundary of the convex hull, which makes imposition of essential boundary conditions easy to implement. We investigate the performance of the NEM combined with the Newmark method for problems of elastodynamics in this article. Applications are considered for a cantilever beam with different initial load conditions. The NEM numerical results are compared with the finite element method. NEM shows promise for these applications.

The simulation of bone healing process of fractured tibia applied with composite bone plates according to the diaphyseal oblique angle and plate modulus

This paper presents the simulation of the bone healing process of a fractured tibia with oblique angles according to plate modulus and initial loading condition by FE analysis. To simulate tissue differentiation and the pathway of development of the curing cells during the healing process, a mechano-regulation theory on deviatoric strain is introduced. For the iterative calculation to determine cell phenotype during the healing period, a user subroutine was programmed by Python code. The analysis result revealed that the healing efficiency was strongly affected by the initial loading condition and the coupling of the plate’s modulus with the oblique angle. By FE analysis, the most appropriate plate modulus for each initial load condition and oblique angle was suggested.

Collapse and coalescence of spherical voids subject to intense shearing: studied in full 3D

Micro-mechanical 2D cell model studies have revealed ductile failure during intense shearing to be governed by the interaction of neighbouring voids, which collapse to micro-cracks and continuously rotate and elongate until coalescence occurs. For a three-dimensional void structure, this implies significant straining of the matrix material located on the axis of rotation. In particular, the void surface material is severely deformed during shearing and void surface contact is established early in the deformation process. This 3D effect intensifies with decreasing stress triaxiality and complicates the numerical analysis, which is also reflected in published literature. Rather than moving towards very low triaxiality shearing, work has focused on extracting wide-ranging results for moderate stress triaxiality (T ~ 1), in order to achieve sufficient understanding of the influence of initial porosity, void shape, void orientation etc. The objective of this work is to expand the range of stress triaxiality usually faced in 3D cell model studies, such that intense shearing is covered, and to bring forward details on the porosity and void shape evolution. The overall material response is presented for a range of initial material configurations and loading conditions. In addition, a direct comparison to corresponding 2D cell model predictions for circular cylindrical voids under plane strain shearing is presented. A quantitatively good agreement of the two model configurations (2D vs. 3D) is obtained and similar trends are predicted. However, the additional layer of matrix material, connecting voids in the transverse direction, is concluded to significantly influence the void shape evolution and to give rise to higher overall ductility. This 3D effect is demonstrated for various periodic distributions of voids.

Effect of Contact Conditions on Void Coalescence at Low Stress Triaxiality Shearing

Recent numerical cell-model studies have revealed the ductile failure mechanism in shear to be governed by the interaction between neighboring voids, which collapse to micro-cracks and continuously rotate and elongate until coalescence occurs. Modeling this failure mechanism is by no means trivial as contact comes into play during the void collapse. In the early studies of this shear failure mechanism, Tvergaard (2009, “Behaviour of Voids in a Shear Field,” Int. J. Fract., 158, pp. 41-49) suggested a pseudo-contact algorithm, using an internal pressure inside the void to resemble frictionless contact and to avoid unphysical material overlap of the void surface. This simplification is clearly an approximation, which is improved in the present study. The objective of this paper is threefold: (i) to analyze the effect of fully accounting for contact as voids collapse to micro-cracks during intense shear deformation, (ii) to quantify the accuracy of the pseudo-contact approach used in previous studies, and (iii) to analyze the effect of including friction at the void surface with the main focus on its effect on the critical strain at coalescence. When accounting for full contact at the void surface, the deformed voids develop into shapes that closely resemble micro-cracks. It is found that the predictions using the frictionless pseudo-contact approach are in rather good agreement with corresponding simulations that fully account for frictionless contact. In particular, good agreement is found at close to zero stress triaxiality. Furthermore, it is shown that accounting for friction at the void surface strongly postpones the onset of coalescence, hence, increasing the overall material ductility. The changes in overall material behavior are here presented for a wide range of initial material and loading conditions, such as various stress triaxialities, void sizes, and friction coefficients.

The simulation of tissue differentiation at a fracture gap using a mechano-regulation theory dealing with deviatoric strains in the presence of a composite bone plate

The endochondral ossification process of fractured long bones was simulated using a three-dimensional finite element model when various composite bone plates were applied to the fracture site. To simulate time-varying cell phenotypes and the corresponding deviatoric strains in the calluses, a user’s subroutine was programmed for iterative calculations. Three representative initial loading conditions were investigated to find a relationship between the initial loading condition and tissue differentiation. Through finite element analysis, the trends in tissue differentiation and healing efficiency in the calluses were evaluated according to the plate modulus and loading conditions; further, the most appropriate plate modulus under each initial loading condition was suggested.

Experimental and Numerical Study of Transient Distortion in Titanium Alloy Tig Welding

In this paper, the convex distortion and transient distortion characteristics of TIG welding for a titanium alloy with finite dimensional thin plate were investigated experimentally and numerically. A three dimensional thermal-mechanical finite element method (FEM) was adopted to predict the characteristics of Transient distortion by taking the initial shape, gravity loading and restriction conditions into account. The simulation results were validated by the experimental results. The results show that the numerical simulations could provide accurate prediction on the Transient temperature and distortion processing. The temperature gradient through thickness, the dimension of plate and the clamping were main factors governing the distortion during welding.

Effect of Crushed Clay Brick as Coarse Aggregate on Creep Behavior of Concrete

Difference between creep behaviors of concrete made from stone chips and crushed clay bricks, i.e. brick chips as coarse aggregate are examined by means of creep testing on their representative samples. Two different grades of concrete 17.2 and 27.5 N/mm2 are prepared from brick chips and stone chips using appropriate mix design and are tested for creep for up to 50 days. Stone chips and brick chips aggregates used are selected in a way so that their gradation and fineness modulus remains as close as possible. Results from creep testing shows that concrete made from brick chips as coarse aggregate having same strength as that of concrete made from stone chips shows higher creep strain. As concrete strength increases, the difference in creep strain becomes more pronounced. Also, at initial loading condition, concrete made from brick chips shows higher rate of creep strain than that of concrete made from stone chips.

Gear Defect Modeling of a Multiple‐Stage Gear Train

This study demonstrates the transient and steady state dynamic loading on teeth within a two‐stage gear transmission arising from backlash and geometric manufacturing errors by utilizing a nonlinear multibody dynamics software model. Backlash between gear teeth which is essential to provide better lubrication on tooth surfaces and to eliminate interference is included as a defect and a necessary part of transmission design. Torsional vibration is shown to cause teeth separation and double‐sided impacts in unloaded and lightly loaded gearing drives. Vibration and impact force distinctions between backlash and combinations of transmission errors are demonstrated under different initial velocities and load conditions. The backlash and manufacturing errors in the first stage of the gear train are distinct from those of the second stage. By analyzing the signal at a location between the two stages, the mutually affected impact forces are observed from different gear pairs, a phenomenon not observed from single pair of gears. Frequency analysis shows the appearance of side band modulations as well as harmonics of the gear mesh frequency. A joint time‐frequency response analysis during startup illustrates the manner in which contact forces increase during acceleration.

Plasticity in Confined Dimensions

This review examines the size effects observed in the mechanical strength of thin metal films and small samples such as single-crystalline pillars, whiskers, and wires. Experimental results from mechanical testing and electron microscopy studies, as well as recent insights from discrete dislocation dynamics simulations, are presented. The size dependency of deformation may be separated into three regimes: the nanometer regime of roughly 100 nm and below, an intermediate regime between 100 nm and approximately 1 μm, and a bulk-like regime. We argue that there is no scaling law with one universal power-law exponent encompassing the entire range. Instead, there are a number of different mechanisms and underlying effects, e.g., the initial dislocation microstructure or loading conditions. The complex interaction of these mechanisms leads to the typically observed scaling behavior.

Fuzzy modeling of fuel cell based on mutual information between variables

This paper discusses estimation analysis study of fuel cell using Kalman filter and modeling of the output variables using fuzzy technique based on Gastofan-Kessel (GK) clustering algorithm. The objective of fuzzy model is to represent the dynamics of output variable as a function of most relevant set of input variables. The choice between most relevant and non-redundant input variables is based on mutual information theory. The fuel cell stack system is considered to have important interacting modules. The analytical equations are used to generate data to develop fuzzy model which closely flows the variations of output variables. The dynamic characteristics are predicted taking into account the reactant pressures, their mass flow etc. The performance of identified fuzzy model is tested at different initial load conditions. An analysis of the results based on the computation of the relative errors and on graphical representations is discussed.

Orienting apples for imaging using their inertial properties and random apple loading

The inability to control apple orientation during imaging has hindered the development of automated systems for sorting apples for defects such as bruises and for safety issues such as faecal contamination. Recently, a potential method for orienting apples based on their inertial properties was discovered. To test this method, apples were rolled down a track consisting of two parallel rails. As angular velocity increased, apples generally moved to an orientation where the stem/calyx axis was parallel to the plane of the track and perpendicular to the direction of travel. However, theoretical analyses and experimental results have demonstrated that select initial loading conditions could prevent or impede this orientation process. In this study, the practical importance of initial loading conditions was tested using two different methods to randomly load apples onto a track. Replicate tests indicated that successful orientation at rates of about 80% for Red and Golden Delicious cultivar apples was random, and that only 5% of the apples exhibited undesirable loading condition and orientation. Results suggest that a commercially viable orientation system could be developed by recycling apples that are not oriented during imaging, and that it should be possible to improve single-pass orientation rates by addressing track compliance and loading velocity issues.

Modeling sand response using two-surface plasticity

This paper presents a two-surface plasticity constitutive model based on critical-state soil mechanics and describes a practical process for the determination of its parameters. Determination of the constitutive model parameters can be done in a hierarchical manner, starting with the model parameters that have the most bearing on sand behavior and that can be determined using routine experimental procedures. Most parameters can be determined through simple curve fitting through experimental data points. The constitutive model is calibrated against experimental data for Toyoura sand, clean Ottawa sand and mixtures of Ottawa sand with non-plastic silt. The model simulates closely the mechanical response of sands under various loading conditions and predicts both drained and undrained behavior of sands at small and large strains using the actual small-strain shear modulus, as measured in resonant column or bender elements tests, along with realistic values of Poisson’s ratio. Performance of the model in simulating sand response is demonstrated for a variety of initial states and loading conditions.

Estimation of the distributions of anisotropic, elastic properties and wall stresses of saccular cerebral aneurysms by inverse analysis

A new method is proposed for estimating the elastic properties of the inhomogeneous and anisotropic structure of saccular cerebral aneurysms by inverse analysis. The aneurysm is modelled as a membrane and the constitutive response of each individual layer of the passive tissue is characterized by a transversely isotropic strain energy function of exponential type. The collagen fibres in the aneurysm wall are assumed to govern the mechanical response. Four parameters characterize the constitutive behaviour of the tissue: two initial stiffnesses of the collagen fabric in the two in-plane principal directions, one parameter describing the degree of nonlinearity that the collagen fibres exhibit and the other structural parameter, i.e. the angle which defines the orientation of the collagen fibres. The parameter describing the fibre nonlinearity is assumed to be constant, while all others are assumed to vary continuously over the aneurysm surface. Two model aneurysms, with the same initial geometry, boundary and loading conditions, constitutive behaviour and finite-element discretization, are defined: a ‘reference model’ with known distributions of material and structural properties and an ‘estimation model’ whose properties are to be estimated. An error function is defined quantifying the deviations between the deformations from the reference and the estimation models. The error function is minimized with respect to the unknown parameters in the estimation model, and in this way the reference parameter distributions are re-established. In order to achieve a robust parameter estimation, a novel element partition method is employed. The accordance between the estimated and the reference distributions is satisfactory. The deviations of the maximum stress distributions between the two models are below 1%. Consequently, the wall stresses in the cerebral aneurysm estimated by inverse analysis are accurate enough to facilitate the assessment of the risk of aneurysm rupture.

Fatigue damage analysis in asphalt concrete mixtures using the dissipated energy approach

An asphalt concrete damage–energy fatigue approach based on the concept of change in dissipated energy is presented in this paper. The damage–energy based fatigue approach is simple and based on a sound theoretical background. The central concept of the energy approach is the energy fatigue curve, which is based on two key elements, namely the plateau value (PV) and the number of load cycles to true failure (Ntf). The plateau value represents the constant value of the percentage of dissipated energy that produces damage to the material under cyclic loading. Failure is defined as the number of load cycles at which this percentage of dissipated energy begins to increase rapidly, indicating instability. Flexural fatigue testing was used to test hundreds of asphalt concrete beams, mainly under controlled-strain testing conditions. It was found that PV is highly dependent on the initial loading conditions, stress, strain, and dissipated energy. As a result, it can be used conveniently in pavement design. The number of load cycles to 50% reduction in initial stiffness was found to be highly correlated with the new failure point (Ntf). Using the dissipated energy concepts in fatigue analysis makes it possible to account for damage accumulation in a straightforward manner.Key words: fatigue of asphalt concrete, dissipated energy, damage, energy ratio.

Granular flow and segregation in a four-bladed mixer

In this study, we experimentally examine flow and segregation of granular material in a cylindrical mixer geometry agitated by four 45 ∘ pitched blades, which is representative of equipment such as high-shear granulators and filter-dryers. We observe that the free surface of the granular bed deforms, rising where the blades are present and falling between blades passes. Using particle image velocimetry (PIV), we measure the instantaneous, average, and fluctuating velocity fields at exposed surfaces (top surface and near the wall), for both near-monodisperse and polydisperse granular materials. The radial and axial point-velocity profiles indicate three-dimensional recirculation patterns indicative of avalanching and bed penetration. For polydisperse mixtures, we find that depending on the shear rate, different segregation mechanisms can take place. Under low shear, complex lobe and striation segregation patterns occur through stretching and folding due to surface avalanching. This leads to enhanced initial mixing rates in a manner consistent with spontaneous chaotic granular mixing. At high-shear rates, segregation is controlled by the rotation of the blades. As a result, coarse particles have a tendency to migrate both to the free surface and the outer wall independently of initial bed loading conditions.

Retardation and repair of fatigue cracks in a microcapsule toughened epoxy composite – Part I: Manual infiltration

As a first step towards a new crack healing methodology for cyclic loading, this paper examines two promising crack-tip shielding mechanisms during fatigue of a microcapsule toughened epoxy. Artificial crack closure is achieved by injecting precatalyzed monomer into the crack plane to form a polymer wedge at the crack tip. The effect of wedge geometry is also considered, as dictated by crack loading conditions during infiltration. Crack-tip shielding by a polymer wedge formed with the crack held open under the maximum cyclic loading condition ( K max) yields temporary crack arrest and extends the fatigue life by more than 20 times. Hydrodynamic pressure and viscous damping as a mechanism of crack-tip shielding are also investigated by injecting mineral oil into the crack plane. Viscous fluid flow leads to retardation of crack growth independent of initial loading conditions. The success of these mechanisms for retarding fatigue crack growth demonstrates the potential for in situ self-healing of fatigue damage.

A Proteomic Analysis of Human Hemodialysis Fluid

The vascular compartment is an easily accessible compartment that provides an opportunity to measure analytes for diagnostic, prognostic, or therapeutic indications. Both serum and plasma have been analyzed extensively by proteomic approaches in an effort to catalog all proteins and polypeptides. Limitations of such approaches in obtaining a comprehensive catalog of proteins include the fact that a handful of proteins constitute over 90% of plasma protein content and that the renal glomeruli filter out proteins and polypeptides that are smaller than 66 kDa from blood. We chose to study hemodialysis fluid because it contains a higher concentration of small proteins and polypeptides and is also simultaneously depleted of the most abundant proteins present in blood. Using gel electrophoresis in combination with LC-MS/MS, we identified 292 proteins of which greater than 70% had not been previously identified from serum or plasma. More than half of the proteins identified from the hemodialysis fluid were smaller than 40 kDa. We also found 50 N-terminally acetylated peptides that allowed us to unambiguously map the N termini of mature forms of the corresponding proteins. Several identified proteins, including cytokines, were only present as predicted transcripts in data bases and thus represent novel proteins. The proteins identified in this study could serve as biomarkers in serum using more sensitive methods such as ELISA-specific antibodies.