Influence Of Loading Effect Research Articles

The Evaluation of Axial Stress in Continuous Welded Rails via Three-Dimensional Bridge–Track Interaction

The crucial differences between conventional rail with split-type connectors and continuous welded rails are axial stress in the longitudinal direction and stability, as well as other issues generated under the influence of loading effects. Longitudinal stresses generated in continuously welded rails on railway bridges are strongly influenced by the nonlinear behavior of the supporting system comprising sleepers and ballasts. Thus, the track structure interaction cannot be neglected. The rail-support system mentioned above has properties of non-uniform material distribution and uncertainty of construction quality. The linear elastic hypothesis therefore cannot correctly evaluate the stress distribution within the rails. The aim of this study is to apply the nonlinear finite element method using the nonlinear coupling interface between the track and structural model and to illustrate the welded rail behavior under the loading effect and uncertain factors of the ballast. Numerical results of nonlinear finite analysis with a three-dimensional solid and frame element model are presented for a typical track–bridge system. A composite plate girder, modeled by solid and shell elements, is also analyzed to consider the behavior of the welded rail. The analysis result showed buckling under the independent calculations of load cases, including ‘temperature change’, ‘bending of the supporting structure’, and ‘braking’ of the railway vehicle. A parametric study of the load combination method and the loading sequence is also included in this analysis.

The Wear of Glass Fiber Reinforced Polyester Composite Materials at Different Loads and Speeds

Glass fiber reinforced polyester (GFRP) materials which are polymer matrix composites have some properties such as high specific strength, excellent elasticity, low weight, high corrosion resistance, high chemical resistance and high thermal stability. One of most important causes of failure of mechanical parts is wear. It is a surface property that can be reduced by changing the surface chemistries of the materials and microstructures. For this reason GFRP materials should be investigated not only for their mechanical properties but also for their tribological behaviours. The aim of this study is investigation of effects of different fillers and resins materials on adhesive wear properties of GFRP at different loads and speeds. In the sample production, different resins (reactive orthophtalic polyesters), reinforcing materials and fillers (glass beads, alumina) are used. . Initially, the samples were subjected to adhesive wear tests on two different loads (F=10N, F=20N) and two different speeds (n=100rpm, n=200rpm) at 150m sliding distance. The friction force and friction coefficient were measured during the test on tribometer. The densities of samples were measured. In the next step, the wear trace thicknesses were measured and the wear rates were calculated. In results, the addition of glass beads to plain orthophtalic polyester resin reduced wear rate. The influence of load effect on wear behavior of samples is more the influence of speed.

An estimate of the influence of loading effects on tectonic velocities in the Pyrenees

Surface displacements due to temporal changes in environmental mass redistributions are observable in the coordinate time series of many Global Navigation Satellite System (GNSS) sites. In this study, we investigated the effect of loading on estimates of tectonic velocity computed from campaign-style GNSS observations. The study region is in the Pyrenees mountain range between France and Spain (ResPyr campaigns). In this area, seismic activity is continuous and moderate and the expected amplitude of the horizontal tectonic velocity is less than 0.5 mm/yr. In order to determine the velocity, 4 sparse GNSS campaigns were carried out from 1995 to 2010. Considering this small rate of deformation, loading phenomena can contribute a non-negligible artifact to the velocity computation that could affect our geodynamical interpretation. In this investigation, we specifically considered the atmospheric, hydrological, and non-tidal ocean loading phenomena. The computed loading deformations for this region show the horizontal displacements are dominated by the non-tidal ocean loading (maximum 4 mm for the North and 3.1 mm for the East components); the main vertical contributions are due to the atmospheric and continental water storage loading (maximum 14.3 for the atmosphere and 8.1 mm for the hydrology, respectively). We have found that the dominant loading effect on the horizontal velocity is the non-tidal ocean loading (mean of 0.11 mm/yr), whereas the vertical component is dominated by the hydrological loading (mean of 0.21 mm/yr). Since the study area is in a mountainous region, we also analyzed the difference between the atmospheric and the topography dependent atmospheric loading models at our GNSS campaign sites. We did not find any significant difference between the two atmospheric loading models in terms of horizontal velocity. Finally, we performed simulations to identify the optimum timing and frequency of future GNSS campaigns in this area that would minimize the loading effects on tectonic velocity estimates.

Laser wakefield acceleration of supershort electron bunches in guiding structures

High gradient acceleration of electrons by plasma waves generated in plasma channels by short intense laser pulses is analyzed. The influence of loading effect and initial emittance on the quality of accelerated electron bunches is studied for the proposed scheme of bunch injection in front of a laser pulse, which opens an opportunity for monoenergetic acceleration of ultra-short electron bunches of submicrometer sizes to high energies.