Effects Of Loading Parameters Research Articles

Fatigue characteristics of concrete subjected to indirect cyclic tensile loading: Insights from deformation behavior, acoustic emissions and ultrasonic wave propagation

This work aims to investigate the fatigue behaviour of concrete subjected to indirect cyclic tensile loading. A series of laboratory tests were performed based on Brazilian disk-shaped (BD) concrete samples. Two schemes of cyclic loading tests were designed by considering complex variations of maximum and minimum stresses. The effect of loading parameters, such as loading method, maximum and minimum stress, on sample deformation, acoustic emission (AE) characteristics, P-wave speed evolution and failure patterns were analysed. The features of AE behaviour and P-wave speed were compared between monotonic loading and indirect cyclic loading. Insight on the specific fatigue behaviour was obtained from AE hit counts, AE energy and P-wave speed degradation. The failure patterns of BD concrete samples are governed by the loading method as well as the stress paths. The stress paths have a direct and pronounced impact on the distribution of main and sub cracks on the surface of BD sample at failure.

Effect of time–temperature, strain level and cyclic loading on the complex Poisson’s ratio of asphalt mixtures

Complex modulus and complex Poisson’s ratio are two parameters which characterise the 3D linear viscoelastic properties of asphalt mixtures. Compared to the complex modulus, the complex Poisson’s ratio is more difficult to be measured because of the great accuracy needed for the experimental device. This investigation focuses on the complex Poisson’s ratio of asphalt mixtures and the effect of loading parameters on its values. The three loading parameters considered in the paper include the time–temperature, the strain level and the number of cyclic loadings. To fulfil the objective of study, complex modulus tests, fatigue tests combined with the rest time, large amplitude cyclic loading tests and cyclic permanent deformation tests are performed. The complex modulus tests are conducted at different temperatures, frequencies and strain amplitudes. Thanks to the fatigue tests, the large amplitude cyclic loading tests and the cyclic permanent deformation tests, the change in complex Poisson’s ratio with the number of cycle, the pre-deformation strain level of specimen and the accumulated permanent deformation (up to some %) respectively is also investigated. The obtained results show that the time–temperature and the number of cyclic loading have a clear effect on the complex Poisson’s ratio of asphalt mixtures. No significant change in the complex Poisson’s ratio is observed when varying the strain cyclic loading amplitude within the small strain domain. The change in the complex Poisson’s ratio becomes more important and is observed to be proportional with the norm of the strain deviator tensor when the axial strain is accumulated or pre-loaded up to some percent.

In vitro release kinetics of drugs from silica aerogels loaded by different modes and conditions using supercritical CO2

The present work aims to investigate release kinetics of a model drug (benzoic acid) loaded on silica aerogels from supercritical carbon dioxide (scCO2). Effects of loading parameters on release kinetics have been analysed for two modes of drug loading: (i) only adsorption (mode I) at varying contact times and initial concentrations in scCO2 and (ii) adsorption followed by precipitation (mode II) at varying initial concentrations and depressurization times. It is observed that drug loaded by mode II releases faster than mode I, both much faster than neat BA, though releases faster for both modes at lower initial concentration. Drug precipitated during fast depressurization releases faster than that during slow depressurization. Storage does not affect release kinetics for mode I at lower initial concentration, whereas storage slows down release for mode II. It is inferred that release is significantly enhanced and can be altered by varying the mode and loading conditions.

Active Control of Plates Made of Functionally Graded Piezoelectric Material Subjected to Thermo-Electro-Mechanical Loads

The present paper concentrates on the active control of the static bending and dynamic response of a functionally graded piezoelectric material (FGPM) plate subjected to thermo-electro-mechanical loads. Using the first-order shear deformation theory and Hamilton’s principle, the equation of motion for the FGPM plate is deduced. Based on the smart properties of piezoelectric ceramic, the active control of the static bending and vibration of the FGPM plate is studied by the mechanical load feedback, velocity feedback and LQR control methods in thermal environment. The effects of load parameter, temperature, volume fraction index and feedback control gain on the static bending and dynamic response of the FGPM plate are examined in detail. The simulation results show that the present control method can largely improve both the static and dynamic stability of the FGPM plate.

Investigations on fatigue behavior and surface damage of Cu film by nano impact and molecular dynamics simulation

The fracture resistance of nanoscale MEMS films under high frequency impact seriously influences its service life. Nano impact test is a reliable technique to evaluate the fatigue fracture resistance of films by simulating the dynamic cyclic loading conditions. In this paper, a kind of Cu film was prepared by magnetron sputtering. The effects of loading parameters and indenter size on the fatigue damage behavior were studied for the Cu films during by nano impact test technique. The dislocation propagation and crack initiation during the nano impact process were also analyzed by molecular dynamics simulation. The results show that: Nano impact failure of Cu film can be divided into three stages and the main failure forms are cracks and delamination. The increase of the indenter radius leads to the increase of fatigue indentation size. The deformation range and damage accumulation degree of thin film material also increased correspondingly. With the increase of nano impact loading rate, the film material suffered more momentum from the indenter. The fatigue damage energy accumulation accelerates the damage.

Investigation on effect of geometric, material and load parameters on strength of composites with cutouts

Composite applications require presence of multiple holes for mechanical fasteners or cutouts in laminates. Unlike isotropic materials, composite materials experience change in stress values due to different parameters such as geometric, material and loading parameters. The present study is devoted to primarily determine whether geometric or material parameters have dominant influence on strength of composite laminates. Computational study using ABAQUS CAE software is employed for the analyses. Results reveal that geometric parameters have much significant influence on stress concentration factor and thereby the strength of composite laminates, when compared to material parameters. An elliptical cutout is seen to have comparatively more adverse effect on strength of laminate, when compared with other cutout shapes. Further, effect of load parameters - in-plane tension, compression and shear, is also studied. However, no significant effect was evidenced in stress concentration factor due to load parameters.

Investigation on effect of geometric, material and load parameters on strength of composites with cutouts

Composite applications require presence of multiple holes for mechanical fasteners or cutouts in laminates. Unlike isotropic materials, composite materials experience change in stress values due to different parameters such as geometric, material and loading parameters. The present study is devoted to primarily determine whether geometric or material parameters have dominant influence on strength of composite laminates. Computational study using ABAQUS CAE software is employed for the analyses. Results reveal that geometric parameters have much significant influence on stress concentration factor and thereby the strength of composite laminates, when compared to material parameters. An elliptical cutout is seen to have comparatively more adverse effect on strength of laminate, when compared with other cutout shapes. Further, effect of load parameters - in-plane tension, compression and shear, is also studied. However, no significant effect was evidenced in stress concentration factor due to load parameters.

Influence of selective reinforcement in dynamic performance of glass-epoxy composites

Polymer composites are in the growing trend of replacing the metallic materials because of their ability toenhance the properties. Property enhancement in composites can be achieved by selective positioning of reinforcement in the matrix and it is termed as selective reinforcement. The reliability of a component in dynamic application depends on the effect of loading parameters. The flexural modulus of glass epoxy composite laminate exposed to dynamic loadingis experimentally investigated. This study isan experimental simulation for a leaf spring application. Two different unidirectional (UD)laminate configurations, 0/R/0/0/0 and 0/0/0/0 are fabricated with and without selective reinforcementby hand lay-up technique. The Taguchi’s DOE and L9 orthogonal array with two loading parameters (frequency and load cycle) are used to plan the experiments. The specimens are exposed to cyclic load using a disc camwith a rise of 6 mm at 2.6 Hz, 4.6 Hz and 8.6 Hz frequencies for 11X103, 22X103 and 33X103 cycles. The flexural modulus of the cyclic loaded laminates is measured by three point bent test (ASTM D 790). Experimental results are statistically analyzed by ANOVA, S/N ratio and Regression analysis. There exists a proportional raise in the flexural modulus of the cyclic loaded laminate and a shift in the effect of the loading parameters on composite flexural modulus attributed to selective reinforcement.

ВЛИЯНИЕ СКОРОСТИ И РЕЖИМА НАГРУЖЕНИЯ НА ПРОЧНОСТЬ И ЖЕСТКОСТЬ АРМИРОВАННЫХ УГЛЕПЛАСТИКОВ

This paper presents a method for evaluating the effect of loading parameters on the strength of ani-sotropic unidirectional carbon-fiber composite material under tension in the plane of orientation of the fibers. Experimentally studied mechanisms of deformation and fracture of the samples shows the dependence of the mechanical properties of reinforced carbon fiber reinforced plastics. The objective of the study is to determine the applicability of CFRP for strengthening by external reinforcement has lost the strength of the stretched zones of concrete elements, as well as analysis of the degree of influence of parameters of loading of the structures on their strength after amplification.

A numerical analysis of the mechanisms behind plasticity induced crack closure: Application to variable amplitude loadings

The effect of loading parameters on fatigue crack growth has been explained using the concept of crack closure. Plasticity induced crack closure (PICC) is linked to the crack tip plastic deformation, which becomes residual with crack propagation. The objective here is to identify the main mechanisms behind PICC, and for that different loading cases were considered namely overloads and load blocks. An analytical model was used to isolate the effect of residual plastic deformation on PICC, however significant differences were obtained relatively to finite element results. A second mechanism, which is crack tip blunting, was used to explain the transient behaviour observed after overloads and load blocks. For overloads and low–high load sequences there is a sudden increase of crack tip blunting with load increase which explains the sudden decrease of crack opening level. For high–low load sequences there is a sudden decrease of crack tip blunting which enhances the effect of residual plastic wake. Finally, the partial closure concept was tested looking to non-linear crack tip parameters but no evidences of Donald’s effect were found for the material studied.

Investigation of loading features effects on resilient modulus of asphalt mixtures using Adaptive Neuro-Fuzzy Inference System

The aim of this study is to explore the effects of loading features on resilient modulus (Mr) of asphalt mixtures using Adaptive Neuro-Fuzzy Inference System (ANFIS). The resilient modulus of asphalt mixture samples were determined using indirect tensile test (IDT) under haversine and square waveforms at four temperatures (5, 15, 25, and 40°C). Applied loading times were 50, 100, 300, 600, and 1000ms with the ratio of rest period to loading time (R/L) equal to 4, 9, and 30. Two ANFIS models were developed for two loading waveforms. In ANFIS modeling, temperature, loading time and R/L are the parameters for the input layer and the resilient modulus is the parameter for the output layer. With application of developed models, the effects of loading parameters on Mr were examined. The results showed that Mr increased by reduction of temperature, decrease of loading time and slightly by reduction of R/L. Besides, it is realized that predicted resilient modulus is closely relevant to the measured one and prediction capability of the ANFIS models was satisfactory that can be prevented from expensive and time-consuming laboratory tests.

Effect of loading parameters on motor performance during a dynamic weight-shift task

Controlling weight shift (WS) is essential to performing motions safely and smoothly during daily and athletic activities. This study investigated the impact of loading parameters on the motor performance and difficulty level of a dynamic WS task performed while standing. Twelve healthy young adults (21.2±0.9 years, 53.5±7.4kg) were asked to match the target and their weight loads using visual feedback displayed on a computer monitor. Motor performance was estimated by assessment of loading accuracy and pace of motor skill acquisition, measured as a proxy of difficulty level, was estimated by assessment of learning rate. As predicted, both loading accuracy values decreased with increasing target frequency. Notably, the interaction of loading size and frequency had a significant effect on loading accuracy, which was increasingly impaired as the weight load increased at frequencies greater than 0.5Hz. Moreover, the pace of motor skill acquisition in a dynamic WS task while standing was affected by the weight-load speed independently of the weight-load size. These results indicate that loading accuracy is affected by both the weight-load size and frequency and that 0.5Hz is a critical frequency at which the difficulty level increases during dynamic WS tasks while standing in healthy youths. These findings suggest that the adequacy of the initial settings used regarding loading size and frequency is an important consideration in rehabilitative and athletic training aimed at evaluating and improving WS while standing.

Microscopic modelling of ignition and burning for well-arranged energetic crystals in response to drop-weight impact

To probe into impact sensitivity of energetic crystals, a theoretical approach was developed for modelling a single layer of energetic particles between upper striker and below base. Considering the particle plasticity, frictional heating, melting, fracture, and chemical reaction at particle level, effects of loading parameters and sample characteristics on time-to-ignition and burning rate were compared. Finite element numerical simulations were simultaneously performed to provide supporting evidence for thermo-mechanical interactions among energetic particles. Once hot- spots ignition occurred during impact, the macrokinetics of chemical reactions were formulated by hot-spots density, combustion wave velocity and geometric factor. The resulting reaction may or may not develop into a violent event, may be sustained or be extinguished, which can be revealed from the subsequent burn reaction rate.

CFD simulation and parameter analysis on launch performance of two-stage light-gas propulsion

This work presents numerical simulation and parameter studies on a two-stage light-gas launcher with a piston-compressor type. An adaptive grid generation algorithm is developed to consider the changes of the computational domain due to the motion of the piston and projectile after diaphragms are opened. A computational fluid dynamics (CFD) code is utilised to simulate the interaction of the gas dynamics with piston and projectile motion, and lots of data, such as the pressure on compression tube, the piston velocity, the diaphragm failure pressure, etc. are obtained under given geometry parameters and loading conditions. The effects of loading parameters on the launching performance are discussed. According to the numerical results, it is concluded that the developed CFD model can provide theoretical references for structure dimension design and loading parameter configuration of light-gas launcher.

Mechanical performance and parameter sensitivity analysis of 3D braided composites joints.

3D braided composite joints are the important components in CFRP truss, which have significant influence on the reliability and lightweight of structures. To investigate the mechanical performance of 3D braided composite joints, a numerical method based on the microscopic mechanics is put forward, the modeling technologies, including the material constants selection, element type, grid size, and the boundary conditions, are discussed in detail. Secondly, a method for determination of ultimate bearing capacity is established, which can consider the strength failure. Finally, the effect of load parameters, geometric parameters, and process parameters on the ultimate bearing capacity of joints is analyzed by the global sensitivity analysis method. The results show that the main pipe diameter thickness ratio γ, the main pipe diameter D, and the braided angle α are sensitive to the ultimate bearing capacity N.

Parametric vibration response of foam-filled sandwich plates under periodic loads

In this paper, the dynamic stability of foam-filled sandwich plates with stiff composite laminated faces subjected to an arbitrary periodic load is studied. The load is taken to be a combination of periodic bending and normal stresses. The governing equations are established by using the Galerkin method with a reduced eigenfunctions transformation. The equations of motion of Mathieu type are derived and used to determine the regions of dynamic instability based on Bolotin’s method. A numerical approach is developed to determine the dynamic stability of foam-filled sandwich plates. The effects of load parameters and core layer thickness on the excitation frequency, dynamic stability region and dynamic instability index are discussed.

Modelling and analysis of fretting wear in rough point contacts in partial slip conditions

A numerical model for the evaluation of fretting wear in rough point contact has been developed. The Ciavarella–Jäger principle was applied for solving the partial slip problem, wear was estimated with Archard’s wear model, and allowance is made for elastic–perfectly plastic material deformation. Surface profiles are updated with wear data in simulations. The effect of load parameters and different types of wavy surface profiles on wear behaviour are analysed and discussed. The tangential force divided by the product of the friction coefficient and the normal force dominates the wear process of surfaces, because, essentially, it controls the size of the slip and stick zones.

유체 충격압력 시계열의 모델링에 관한 기초 연구

AbstractTo consider effects of essential parameters of water impact pressure on dynamic structural responses of bow bottom structures, a parametric study for a ship bottom panel is carried out. The idealized pressure time history models were assumed by triangular and rectangular shapes in time domain. The main loading parameters are duration time and peak pressure value maintaining the same impulse value. The str uctural models for local bottom stiffened panels of a container ship are analysed. The n atural frequency analysis and transient dynamic response analysis are performed using MSC /NASTRAN. Added mass effects of contacting water are considered and the pressure dis tributions are assumed to be uniform in the whole water contacting surface. The effects of loading parameters on the structural responses, especially maximum displacements, are con sidered. Besides the peak pressure value, effects of duration time correlated with natural frequencies are thought to be the important parameters.

A Theoretical Study of Mechanical Stability of Arteries

This study proposes a mathematical model for studying stability of arteries subjected to a longitudinal extension and a periodic pressure. An artery was considered as a straight composite beam comprised of an external thick-walled tube and a fluid core. The dynamic criterion for stability was used, based on analyzing the small transverse vibrations superposed on the finite deformation of the vessel under static load. In contrast to the case of a static pressurization, in which buckling is only possible if the load produces a critical axial compressive force, a loss of stability of arteries under periodic pressure occurs under many combinations of load parameters. Instability occurs as a parametric resonance characterized by an exponential increase in the amplitude of transverse vibrations over several bands of pressure frequencies. The effects of load parameters were analyzed on the basis of the results for a dynamic and static stability of a rabbit thoracic aorta. Under normal physiological loads the artery is in a stable configuration. Static instability occurs under high distending pressures and low longitudinal stretch ratios. When the artery is subjected to periodic pressure, an independent increase in the mean pressure, amplitude of the periodic pressure, or frequency, most often, but not always, increases the risk of stability loss. In contrary, an increase in longitudinal stretch ratio most likely, but not certain, stabilizes the vessel. It was shown that adaptive geometrical remodeling due to an increase in mean pressure and flow does not affect artery stability.

Finite-deformation analysis of the crack-tip fields under cyclic loading

The plane-strain crack subjected to mode I cyclic loading under small scale yielding was analysed. The influence of the load range, load ratio and overload on the near-tip deformation-, stress- and strain-fields was studied. Although the near-tip zones of appreciable cyclic plastic flow for all loading regimes matched closely one another, when scaled with (Δ K/ σ Y ) 2, the activities of plastic flow within them manifested dependence on K max and K min, as well as on overload. Cyclic trajectories of the crack-tip opening displacement (CTOD) converged to stable self-similar loops of the sizes proportional to Δ K 2 and positions in CTOD- K plane dependent on the maximum K along the whole loading route, including an overload. Computed near-tip deformation evidenced plastic crack advance, this way visualising of the Laird–Smith concept of fatigue cracking. This crack growth by blunting-resharpening accelerated with rising Δ K and was halted by an overload. Crack closure upon unloading had no place. The affinities were revealed between computed near-tip stress–strain variables and the experimental trends of the fatigue crack growth rate, such as its dependence on K max and K min (or Δ K and K max), and retardation by overload. Thus, the effects of loading parameters on fatigue cracking, hitherto associated with crack closure, are attributable to the stress–strain fields in front of it as the direct drives of the key fatigue constituents – damage accumulation and bond breaking.