Influence of suspension parameter for derailment analysis of a full railway vehicle model cruising on a curved track

The main intention of this research work is to study the derailment response of high speed railway vehicle (HSRV) cruising on a curved track. In previous research work, lower degree of freedom (DOF) has been considered for the derailment analysis which may not give more accurate results. Hence, a 31 DOF bondgraph model of HSRV has been developed which consist of carbody, two truck frames and two selfsame wheelsets for each truck frame. Vertical, lateral, roll, yaw and pitch motion are considered for carbody and bogie and except pitch motion all the other motion are considered for wheelsets. Non-linearities in terms of heuristic nonlinear creep model and flange contact has been employed to simulate the derailment response at high speed. The effect of vehicle speed running on a curved track was investigated for derailment quotient. The main aim of present research work to evaluate derailment quotient at the speed range of 150 kmph to 600 kmph for hard and soft suspension parameter. Derailment quotient has been calculated for both linear and nonlinear creep models and it is seen that DQ for linear model has a lower value compare to non linear creep. The major advantages of the proposed model are that, the presented model can actively predict the derailment of a railway vehicle, and also precisely determine the nonlinear critical hunting speeds.

An Improved Mechanistic-Empirical Creep Model for Unsaturated Soft and Stabilized Soils

Soft soils are usually treated to mitigate their engineering problems, such as excessive deformation, and stabilization is one of most popular treatments. Although there are many creep models to characterize the deformation behaviors of soil, there still exist demands for a balance between model accuracy and practical application. Therefore, this paper aims at developing a Mechanistic-Empirical creep model (MEC) for unsaturated soft and stabilized soils. The model considers the stress dependence and incorporates moisture sensitivity using matric suction and shear strength parameters. This formulation is intended to predict the soil creep deformation under arbitrary water content and arbitrary stress conditions. The results show that the MEC model is in good agreement with the experimental data with very high R-squared values. In addition, the model is compared with the other classical creep models for unsaturated soils. While the classical creep models require a different set of parameters when the water content is changed, the MEC model only needs one set of parameters for different stress levels and moisture conditions, which provides significant facilitation for implementation. Finally, a finite element simulation analysis of subgrade soil foundation is performed for different loading levels and moisture conditions. The MEC model is utilized to predict the creep behavior of subgrade soils. Under the same load and moisture level, the deformation of soft soil is largest, followed by lime soil and RHA–lime-stabilized soil, respectively.

Developing an Implicit Creep Model From Open Literature Data

As pressure ratios and firing temperatures continue to rise, creep becomes of greater concern everywhere within a gas turbine engine. As a rule of thumb, just a 14°C increase in metal temperature can halve the expected rupture life of a part. In the past, companies might be satisfied with conservative creep estimates based on Larson-Miller-Parameter curves and 1D calculations. Now companies need functional implicit-creep models with finite element analysis for an ever-increasing number of materials. Obtaining adequate test data to create a good creep prediction model is an expensive and time-consuming proposition. Test costs depend on temperature, material, and location, but a single, 10,000hr, rupture test may reasonably be expected to cost > $20,000. Other than large OEMs, small companies and individuals lack the resources to create creep models from their own data. This paper will lead the reader through the creation of a modified theta projection creep model of Haynes 282, a high-temperature, combustion alloy, using only literature data. First, literature data is collected and reviewed. Data consists of very few complete curves, estimated stresses for rupture and 1% strain, and discrete times to individual strains for individual tests. When adequate data exists, individual tests are fit to theta projection model curves. These “local” theta fits of different test conditions are used as input for the global model. Global fits of theta parameters, as a function of stress and temperature, are made from the full data set. As the global creep model is improved, correction factors introduced to account for true stress and strain effects. A statistical analysis is made of actual rupture time versus predicted onset of failure time, theta5=1. A time-based scatter factor is determined to evaluate temperature margin required to ensure reliability. After the creep model was completed, Haynes International, the material inventor, provided specific test conditions (stress and temperature) of 5 tests that had already been run. Creep predictions were generated for these test conditions, before viewing the actual results. The creep model predicted strain curves matched actual tests very well, both in shape and time to rupture. Continued refinement is possible as more data is acquired.

On the nonsmooth dynamics of towed wheels

In this paper, a nonsmooth model of towed wheels is analysed; this mechanism can be a part of different kind of vehicles. We focus on the transitions between slipping and rolling in the presence of dry friction. The model leads to a three-dimensional dynamical system with a codimension-2 discontinuity. The systems can be analysed by means of the tools of extended Filippov systems. The essence of the calculation is to find the so-called limit directions, which show the possible directions of slipping-rolling transitions and their properties. By this method, four different scenarios are found. The results are compared to those from the creep models.

Simulation of the Stress-Strain State of Diesel Engine Pistons Taking into Account Inelastic Deformations

The failure of aluminum pistons of diesel engines is often associated with formation of cracks originating at the bowl rim. The appearance of cracks is a consequence of thermal fatigue of the material due to low-frequency cycles of heating and cooling of the piston during the engine start-up, operation at various speed and load conditions, and subsequent shutdown. To assess the lifetime of the bowl rim, it is necessary to simulate non-isothermal elastoplastic deformation of the alloy using material plasticity and creep models available in finite element analysis software (e.g. ANSYS). This paper presents the results of uniaxial tensile and creep tests of proportional specimens made from piston blanks of the V-type diesel engines YaMZ-658. The piston material is AlSi12CuNiMg silumin alloy. The article describes methods for determining constants in plasticity and creep models. The results of numerical simulation of the piston’s stress-strain state for the start — nominal power mode — stop cycle using the finite element method are presented. Conclusions about the presence of plastic and creep strains at the piston edge are drawn.