Effect Of External Load Research Articles

Examining the effects of a weighted pack on functional movements in smokejumpers.

Smokejumpers are required to parachute from planes, carry gear weighing more than 50 kg, and hike on steep terrain. With a majority of injuries sustained to the lower extremity, it is imperative to understand the influence a weighted pack may have on functional performance. To examine the effects of external load on functional movements in Smokejumpers. Using repeated measures design, ten Smokejumpers completed two trials consisting of 3 movements in weighted (50 kg) and unweighted conditions. Nine males and one female (age of 40.1±8.4 years, mass 81.1±8.3 kg) performed overhead squat, hurdle step and anterior reach. Movements were scored based on established guidelines. The mean of three trials was recorded for anterior reach on both limbs. Differences between weighted and unweighted scores in the overhead squat (p = 0.001), ND hurdle step (p = 0.005), D hurdle step (p = 0.000) and overall composite scores (p = 0.006) were found to be significantly different. Differences were also noted in D (p = 0.035) and ND (p = 0.045) anterior reach. The addition of a weighted pack negatively influences functional movements in Smokejumpers, which may lead to greater injury risk. Implementation of injury prevention strategies to reduce occupational injury risk should be explored.

Effect of External Load on Stress Distribution of a Pipeline Subjected to Indentation

Pipelines are widely used in industry for transporting oil and gas. Dents are one of the most common mechanical damage to pipelines due to external factors and significantly affect the performance of the pipelines. A dent is a permanent deformation of the circular cross-section of the pipelines. In this paper, numerical simulation using finite element analysis on API 5L X52 pipelines subjected to denting by a spherical indenter was carried out to determine the distribution of Von-Mises stress and permanent deformation. The given load was between the yield strength and ultimate strength of API 5L X52. The effect of indenter diameter and indenter displacement was studied. The results show that the indenter diameter and indenter displacement affect the value and area distribution of Von-Mises stress and permanent deformation.

The effect of external load on ultrasonic wave attenuation in steel bars under bending stresses

The stress state in deformed solids has a significant impact on the attenuation of an ultrasonic wave propagating through the medium. Measuring a signal with certain attenuation characteristics can therefore provide useful diagnostic information about the stress state in the structure. In this work, basic principles behind a novel attenuation-based diagnostic framework are introduced. An experimental study on steel bars under three-point bending was carried out, and finite element analyses were used to numerically model the experiments. Obtained test results showed a strong correlation between the external load and the ultrasonic signal energy, which decreases with increasing load. A similar but positive correlation appeared between the level of attenuation of longitudinal ultrasonic wave signals and the external load, which allowed for efficient estimation of the mid-span bending moment. Upon proper calibration of testing equipment, the change in ultrasonic signal energy can therefore be used as an indicator of the external load level. As a result, this effect has potential applications in non-destructive structural health monitoring frameworks.

Multiphase modeling of the effect of external loading on the shrinkage of concrete and its consequences for modeling tensile creep

Multiphase modeling is a powerful framework for the simulation of the early-age and long-term behavior of concrete. Nevertheless, state-of-the-art multiphase models do not capture the experimentally observed instantaneous change in internal relative humidity upon external loading, which also manifests in the lack of predicting load-induced shrinkage. The approach presented in this publication is a step to overcome this deficiency. It is based on a poromechanical multiphase model for coupled creep and shrinkage of concrete, which is enhanced by a strong hygro-mechanical coupling, introduced via a load-dependent desorption isotherm. The enhanced model is evaluated for sealed and drying uniaxial compressive and tensile creep tests. Instantaneous changes in internal relative humidity upon loading are recovered by the enhanced model. In compression, the influence on the mechanical response is small. In contrast, the representation of tensile creep is significantly improved by considering load-induced shrinkage.

A Numerical Method for Simulating Viscoelastic Plates Based on Fractional Order Model

In this study, an efficacious method for solving viscoelastic dynamic plates in the time domain is proposed for the first time. The differential operator matrices of different orders of Bernstein polynomials algorithm are adopted to approximate the ternary displacement function. The approximate results are simulated by code. In addition, it is proved that the proposed method is feasible and effective through error analysis and mathematical examples. Finally, the effects of external load, side length of plate, thickness of plate and boundary condition on the dynamic response of square plate are studied. The numerical results illustrate that displacement and stress of the plate change with the change of various parameters. It is further verified that the Bernstein polynomials algorithm can be used as a powerful tool for numerical solution and dynamic analysis of viscoelastic plates.

Investigation of Various Parameters in Magneto-Rheological Dampers

Automobile industry and magneto-rheological dampers are now a new area of research. Magneto-rheological mufflers utilize the energy generated by magnetic fields, and scientists have initiated a re-consideration of new damping systems. The suspension system based on magneto-rheological fluid in modern era is becoming an intelligent system with superior properties such as strength, controllability, range, response time, energy utilization, structure etc. In magneto-rheological dampers number of required components are too less which leads to cost effective suspension. In this exploration, a magneto-rheological damper was fabricated, and experimental study had been performed. The magneto-rheological damper's construction cost is not as much since it doesn’t have intricate components. The modern enquiries the consequences of magnetic field/current on applied load, yield stress, and stress developed in suggested magneto-rheological dampers. The experimental results illustrate the effect of external load, yield stress, & stress generated in suggested dampers depends on magnitude of current/magnetic field. The experimental investigation also demonstrates that magneto-rheological dampers work at a specific threshold magnetic field substandard to critical value of a magnetic field, magneto-rheological fluid reposes in a liquid phase. The threshold magnetic field and mechanical properties are inter-related with each other in magneto-rheological based dampers.

Theoretical analysis on stress distribution characteristics around a shallow buried spherical Karst cave containing fill materials in limestone strata

The chief objective of the article is to learn the spatial characteristics of stress distribution around a shallow buried spherical Karst cave containing fill materials in limestone strata. First, considering the effect of external load, stress field in the Earth’s crust, internal filling and Karst geomorphology characteristics in China, a spatial axisymmetrical model was established. Concurrently, combing available work and the concept of elasticity, the boundary conditions are determined. Subsequently, the Love displacement method was introduced, and stress component expressions were obtained. The diagram characteristics of each stress component are summarized, which are affected by various influencing factors. Finally, to prove the rationality of the general solution, a numerical simulation was carried out based on practical engineering, and the maximum error is less than 5%. Thus, the analytical solution could represent the spatial characteristics of stress distribution around a shallow buried spherical karst cave containing fill materials in limestone strata.

A novel model for prediction of burst capacity of corroded pipelines subjected to combined loads of bending moment and axial compression

Most of the commonly used standards and codes for burst pressure prediction at a corrosion defect of steel pipelines generally just consider internal pressure alone. However, an actual oil/gas pipeline is usally subjected to external loads, such as axial compression/tension and bending moment, which may affect the burst capacity of the pipeline. In this study, a three-dimensional (3D) nonlinear finite element (FE) model validated by burst tests was developed to investigate the effect of bending moment and axial force on the burst capacity of corroded pipelines. Subsequently, the effects of external loads (i.e., bending moment, and axial force) and corrosion geometry features (involving corrosion depth, width, length, and clock position) on the pipe burst pressure were determined. Then, based on a series of FE cases, a new burst prediction model for corroded pipelines subjected to the combination loads of bending load and axial compressive force was fitted and developed. Finally, the effectiveness and reliability of the new proposed model were verified by extensive parametric FE analysis and burst test data. The results show that the prediction errors for the failure pressures between the proposed-model and the FEM were less than 10% for most 92.793% of the 222 cases. Moreover, the proposed model can also be applied to the condition that the pipeline is under single internal pressure, and its prediction accuracy is better than that of other seven well-known models of ASME B31G, Mod B31G (0.85 d L), Z662, DNV, PCORRC, CUP, and Shell-92.

Design and parameter study of a thermoelectric generator for waste heat recycling in flexible micro-light-emitting diodes

• A 3D model is proposed for studying heat recycling in micro-light-emitting diode. • An annular thermocouple design is preferred under a heat source array. • Effect of external load can be mitigated through thermocouple parameter study. • A relatively high specific power output density of 40 µW/cm 2 .K 2 is predicted. Flexible thermoelectric generators have attracted a tremendous amount of attention as they enable waste heat recovery in a wide range of applications ranging from flexible displays to biomedical devices. However, design limitations still exist in flexible micro thermoelectric generators, in particular for applications with a heat source array such as in flexible micro-light-emitting diodes. Hence, this paper proposes a thin film flexible annular thermoelectric generator design that specifically aims for heat recycling in flexible micro-light-emitting diodes for the first time. In order to evaluate the generator performance, a three-dimensional steady-state model is constructed and a systematic study on design parameters is carried out based on the finite element method. The model first takes into account the heat transfer from a heat source array to the thermocouples. Seebeck, Peltier, as well as Joule heating effects, are then considered to evaluate the specific power density of the generator. Additionally, critical design parameters including thermocouple structural dimensions, thermocouple numbers, and substrate thickness have been thoroughly investigated. After model validation using experimental data from the literature, the results show that the relationship between the thermocouple design parameters and the output power is nonmonotonic and for each parameter, a certain optimum range can be found, in which the obtained output power does not vary significantly (within 95% of the maximum output power P max ). The thickness of the flexible substrate is inversely correlated to the output power. Moreover, the metallic thermocouples serve as a heat sink that helps to lower the temperature of the active region by ∼ 3 °C. Overall, the model predicts an impressive specific power density of ∼ 40 µW/cm 2 .K 2 , thus demonstrating the potential applicability of using flexible thermoelectric generators to recycle heat from micro-light-emitting diodes while providing a path to further improve the performance of flexible thermoelectric generators.

Farklı Yaş Gruplarındaki Aerobik Cimnastikçilerin Kalça Eklemlerinde Kuvvet ve Eklem Pozisyon Duyularının İncelenmesi ve Dış Yükün Eklem Pozisyon Duyusuna Etkisinin Karşılaştırılması

Objective: This study aimed to investigate the development of target joint position sense (JPS) and force sense (FS) in young gymnasts at different age groups and compare the effect of external load on position sense. Material and Methods: A total of 38 gymnasts were divided into three age groups: 12-14, 15-17, and 18 and over age groups. The maximum voluntary isometric contraction (MVIC) forces of the participants at a 90-degree hip angle were measured with an isokinetic dynamometer. For the isometric FS test, the target of 50% MVIC was used. Two active JPS tests were performed with and without a load. For the JPS test under load, 50% of MVIC was isotonically applied. The error scores were acquired from the absolute difference between the reproduced and targeted values in all conditions. Results: Results of repeated measures indicated the significant main effect of loads [F(1,37)=7.41, p=0.010, η2 =0.17]. Significant differences were found between no-load and under load JPS error values [t(37)=2.72, p=0.010]. Under load (2.05 ±1.86-degree), absolute error scores were statistically less than no-load (3.50 ±3.02-degree). A significant negative correlation was found between age groups and FS error scores. Conclusion: The hip JPS improves with the external load. Testing gymnasts' joint position sense acuity under external loads, such as the nature of the sport, may be a more appropriate test criterion. This is especially important in determining the criteria for returning to sports after injury. Those in the higher age group make fewer FS errors. This indicates that strength acuity improves as the age of athletes improves and reveals the contribution of aerobic gymnastics to the development of the sense of force.

Suitability of subsequently installed vibrating wire sensors for direct stress measurement in concrete and mortar

Over the past decades, a major part of the building infrastructure has aged and is now in need of repair. In order to ease the repair backlog and to be able to distinguish between urgent and long-term repair needs, it is advisable to install a monitoring system to the structure. This monitoring is, among others, often based on periodical strain or deformation measurements, as they provide a direct indication of the effect of external loads on the structure (crack opening or heavy deformations). Still, most of the available monitoring systems cannot be installed subsequently or they are limited to measurements on the surface. For monitoring the structural behaviour inside specific components, the use of a sensor system based on the vibrating wire measuring principle appears promising. This sensor system has proven itself in geotechnical engineering. However, there is no profound experience of using this system in concrete structures. Therefore, the aim of the work presented in this paper was to investigate the suitability of these sensors for stress measurement in concrete and mortar. We will furthermore give an outlook on a possible application for monitoring reinforced concrete structures.

Analysis of Non-Uniform Accreted Ice in Overhead Power Lines Using SAP2000

The design principles of overhead power lines cover the effect of external loads in the atmosphere (ice load and wind load) on the layout of power transmission systems. These additional loads are closely related to the geographical and meteorological characteristics of the land, so each country projects the additional loads on the power line design by considering its conditions. The ice load, which should be especially considered in mechanical calculations of power lines, causes forces on the conductor in the vertical direction. However, these vertical forces affect only one part of the conductor in the presence of partial ice, which generally occurs due to falling some ice in the power line to the ground for any reason or directly because of meteorological events and geographical features. The analysis of partial ice load is defined as the non-uniform accreted ice problem in the related studies. This study investigates the effect of non-uniform accreted ice on the conductor curve using data from Turkey. The results obtained from the non-linear model created using SAP2000 (Structural Analysis Program) are verified with the equations in the literature. The proposed model can be used to solve other problems by changing the parameters for cases in different countries.

Determination of Thermomechanical Stresses in Elements of Vehicles' Braking Systems

The main objective of the study was to develop a model and analyze the thermomechanical behavior of the hub material of the vehicle brake disk. The simulation strategy was based on the solution of the three-dimensional problem of the theory of elasticity for the case of effect of external loads and temperature fields on the metal structure element of the vehicle brakes. To solve this type of task of the theory of elasticity, the differential equations of the second order were used for the first time. Adaptation of the proposed model, completed in the article, has proved the correctness of use of these equations in modeling the thermomechanical processes with determination of stresses and displacements in unevenly heated rotary cylinders of the final length. The proposed method can be applied with high efficiency in stress strain state simulation of individual parts of vehicles.

Modeling of contact load distribution of planetary threaded roller bearing based on deformation coordination

Planetary threaded roller bearing (PTRB) mainly consists of an outer ring, an inner ring, and rollers and all these parts have multiple annular threads. The PTRB is used in heavy loading linear transmission mechanisms because of its high-power density. It has been designed mainly to bear the axial load, and its load carrying capacity is determined by the contact load distribution characteristics of the threads in the axial direction. In this study, axial static stiffness model of the PTRB was developed to obtain the deformation of threaded teeth, threaded contact zone, and shaft sections. Based on the coordination of the above-mentioned deformations, contact load distribution of PTRB was calculated. Moreover, the contact load distribution coefficient was proposed to evaluate the distribution regularity of contact load. The validity of the proposed mathematical model was verified by the results of finite element simulation. Finally, the effects of external load, pitch, and number of threaded teeth on the contact load distribution regularity were analyzed.

A review on nondestructive testing of bonding interface using nonlinear ultrasonic technique

<p indent="0mm">As an important complement to traditional mechanical connections, bonded structures are widely used in industry. Under the combined effect of external loads and environmental factors, the performance of the bonding interface will deteriorate, which seriously affects the safe use of bonding structures. Therefore, the performance evaluation of bonding interfaces has always been a hot and difficult issue in the field of non-destructive testing. Traditional linear ultrasonic technology can effectively detect damage such as delamination and debonding in the bonding interface, but it is difficult to detect and quantitatively evaluate the early degradation of the bonding interface (such as closed defects and weak bonding). However, the nonlinear ultrasonic technology can overcome the low sensitivity of the traditional linear ultrasonic technology and is expected to be an effective means for nondestructive testing of early deterioration of bonding interface performance. In this paper, we review the recent development of nonlinear ultrasonic technology for bonding interface detection from theoretical models and testing experiments. From the perspectives of contact nonlinearity of the interface and material nonlinearity of the interlayer, we introduce relevant theoretical models for nonlinear ultrasonic inspection of bonded interfaces, such as nonlinear spring model, interface contact model and contact model considering the thickness of the interlayer. These models can be used for the description of various acoustic nonlinear effects (such as second harmonic generation, wave mixing and nonlinear resonance) generated by ultrasonic waves at weak bonding interfaces, but the ability of different models to characterize the nonlinear propagation behavior of ultrasonic waves at weak bonding interfaces needs to be further investigated. Meanwhile, we review the progress of three nonlinear techniques of nonlinear ultrasonic resonance, wave mixing and second harmonic generation in the experimental testing of bonding interface properties. The nondestructive testing of bonding interface using nonlinear ultrasonic resonance technique remains relatively limited. Mixing technology is of great interest because of its flexibility and selectability of excitation frequency, mode and area of action, and its ability to effectively avoid the effects of system nonlinearity. Among the nonlinear ultrasonic methods, harmonic techniques are the most widely used, and have been used for damage detection and performance evaluation of bonding interfaces, such as bonding thickness measurement, debonding detection, bond strength and fatigue life evaluation. The harmonic technique is considered as a possible solution for the quantitative detection of the interface properties of multilayer bonded structures. However, how to distinguish the harmonics generated by weakly bonded interfaces from those generated by detection systems has been a challenge for its application. Finally, we provide an outlook for the development of nonlinear ultrasonic detection technology for early degradation of bonding interfaces.

DEM modeling of the effects of external loads and material properties on the stability of nickel ore in a cargo hold

Cargo liquefaction leading to the serious loss of ship stability is attracting more attention from the international community. However, due to the complexity of external loads and the properties of the cargo, the mechanism of cargo liquefaction has not been revealed for every situation. In this study, considering the effects of the moisture content, particle size grading, initial porosity and motions of a typical cargo hold, a three-dimensional full-scale numerical model based on the discrete element method is established, and numerical investigations are carried out. To better ensure that the full-scale model conditions are consistent with the reality and the rationality of particle amplification, a static incline test and a cargo loading test are also simulated and verified. The results show that the effect of the moisture content on the cargo stability can be estimated using the friction coefficients between particles. Additionally, the moisture content is the key factor that affects the stability of the cargo and promotes its liquefaction. Furthermore, there are critical values for fine particle content, at which cargo fluidity is greatly enhanced. For external loads, the cargo stability is greatly weakened with the increase of the motion amplitude. Furthermore, there is a critical frequency, beyond which the cargo stability will be further damaged.

Effects of Carriage Flexibility on Friction Force in Linear Ball Guides

Abstract This article presents the effects of carriage flexibility on the friction force in linear ball guides, which includes hydrodynamic rolling friction, elastic hysteresis friction, slip friction, and drag friction. To this end, we developed a computational model for the friction force in linear ball guides that accounts for the carriage flexibility. The model was validated through experiments, and the results prove that it provides more accurate friction-force estimates than the conventional model under the assumption of a rigid carriage. Subsequently, we examined the effects of external load, preload, and speed on the friction force. Among several friction components, hydrodynamic rolling friction makes a major contribution to the total friction force. Ball contact loads, which significantly vary with carriage flexibility, were found to influence the hydrodynamic rolling, elastic hysteresis, and slip friction forces. The proposed model considering carriage flexibility in linear ball guides is expected to find use in the design and operation of linear-ball-guide systems.

Void growth based inter-granular ductile fracture in strain gradient polycrystalline plasticity

The precipitation hardened, high strength aerospace alloys (e.g. Al 7000 alloy series) suffer from loss of fracture toughness due to the heat treatment leading to intergranular ductile fracture. Depending on the quenching and aging processes, large precipitates at the grain boundaries with wide precipitate free zones might develop. Therefore the grain boundaries constitute a potential location for micro void formation and evolution under the effect of external loads. This is a common problem of such materials where there is considerable ductile intergranular fracture, which is normally attributed to the embrittlement effects of the environment in other type of alloys. In this context, for the modeling of such a degradation process, the current paper develops a physics based intergranular cracking model of polycrystalline materials where a strain gradient crystal plasticity model is combined with cohesive zone elements whose traction separation relation is based on the evolution of micro-voids at the grain boundaries. The framework successfully predicts the intergranular crack formation and propagation, taking into account different microstructural features, such as porosity, pore shape, grain orientation distribution, and grain boundary conditions.

A Flexible Robotics-Inspired Computational Model of Compressive Loading on the Human Spine

The use of powerful robotics tools in modeling and analysis of complex biomechanical systems has led to the development of computationally effective and scalable human models. Our early work in this regard focused on a humanoids-based rigid-body modeling of human kinodynamics to monitor instantaneous and accumulating effects of external loads on body joints. Nevertheless, despite their high-computational efficiency, the flexible nature of the spine and its characteristic were not taken into account, resulting in less accurate estimations of the spinal compressive forces. Accordingly, in this work, we propose a flexible model of the human spine mechanics for assessing compressive loading, and integrate it in our robotics-based whole-body model. Such a model can quantify the compressive force distribution along the spine and the muscles' activity for a measured back configuration and known external forces, which both contribute to increasing the ergonomic risk level. The muscles' activity predictions are validated through an experimental analysis on six human subjects. Three different tests are conducted considering different loading conditions. Results demonstrate the potential of the proposed approach in monitoring the spine compressive loading and predicting a muscles activity with an average relative error of 10% against experimental data. Minimizing the required number of sensors and the amount of computational resources, the presented approach is particularly suitable for online risk evaluation in a real working scenario.

RESEARCH OF TRANSIENT PROCESSES OF PRESSURE CHANGE WHEN OPERATING A HYDRAULIC SYSTEM WITH FOUR CONNECTED HYDRAULIC MOTORS

The publication is devoted to the study of the quality of the hydraulic system with four series-connected hydraulic motors. These hydraulic systems can be used to drive the working bodies of agricultural machines, have significant advantages in their layout, but at the same time and disadvantages, the elimination of which requires a detailed study of the processes occurring during the operation of this type of system. The analysis of the previous works of scientists in this area allows us to conclude that it is possible to conduct theoretical research in this direction. A mathematical model of the proposed hydraulic system has been developed, which takes into account the effect of external load on the shafts of hydraulic motors, the inertia of the system, the effect of leaks from the connections of the elements of the hydraulic system and possible overflows of the working fluid from the high-pressure zone to the low-pressure zone. At this stage, wave processes occurring in the cavities of the hydraulic system were not taken into account. The solution of the resulting system of differential equations was carried out using the Runge-Kutta-Feldberg method with automatic change of the integration step in the mathematical package MathCad. The resulting transient processes were analyzed for the amplitude of pressure surges and the frequency of its change. Carrying out this analysis allows you to obtain comprehensive information about the nature of transient processes in the hydraulic system in order to find such a ratio of design and technological parameters, in which the system under study met the requirements regarding the quality of work as part of a technological machine. During the research, special attention was paid to the processes occurring at the moment of starting the hydraulic system, and the moment of application of the technological load.