Mechanical braking systems for trains: A study of temperatures, fatigue and wear by experiments and simulations

Increased demand for shorter travel times, higher axle loads, increased volumes and increased punctuality of railway traffic calls for a better design and management of the railway subsystems. The present thesis deals with aspects of mechanical friction brakes, in the form of tread brakes and disc brakes. These are critical for reliable, safe and economical operation of trains. The thesis establishes models and simulation tools for frictional braking systems that may operate in parallel with an electrodynamic braking system.A main focus is the influence of thermal loading on rolling contact fatigue fromtread brakes at stop braking. A simulation methodology for thermomechanicalcracking of railway wheel treads due to rolling contact and repeated stop braking by tread brakes, is established based on full-scale brake rig experiments. Building on the same approach, plastic deformation of the tread is also investigated. The results indicate that tread damage increases drastically for frictional temperatures above some 450 \ubaC.Another focus is temperatures and wear of tread brakes and disc brakes under operational loading. In two field test campaigns, detailed instrumentation and continuous measurements of relevant temperatures and braking parameters are combined with intermittent measurement of wear of friction brake components. Wear of brake blocks and wheel treads is quantified. It is found that the tread wear introduced by the block contact dominates for trailing wheelsets, whereas for powered wheelsets wear from tractive forces in the wheel–rail contact can be of equal importance.\ua0In a study on disc brakes, temperatures and wear performance are compared for two friction pairs: one new segmented disc with sintered pads and a traditional disc with an undivided friction ring combined with organic pads.It is found that the discs have similar braking temperatures, but that the wear of disc and pads is substantially lower for the segmented disc. A numerical investigation of thermomechanical fatigue damage of the two disc types indicates that the segmented disc also has a substantially longer fatigue life

Periodic Noise Removal in Strain and Natural Images Using 2-D Fast Fourier Transform

This paper presents a 2-D FFT removal algorithm for reducing the periodic noise in natural and strain images. For the periodic pattern of the artifacts, we apply the 2-D FFT on the strain and natural images to extract and remove the peaks which are corresponding to periodic noise in the frequency domain. Further the mean filter applied to get more effective results. The performance of the proposed method is tested on both natural and strain images. The results of proposed method is compared with the mean filter based periodic noise removal and found that the proposed method significantly improved for the noise removal

Towards enhanced mechanical braking systems for trains. Thermomechanical capacity of wheel treads at stop braking

Modern trains are equipped with different braking systems, between which the braking effort can be distributed. Among these, tread braking is still the most common system\ua0for friction braking. Tread brake systems are cheap and robust. However, extensive usage of tread brakes demands knowledge of operational limits to ensure safety and decrease life cycle costs (LCC) of the running gear.In the present work, a state-of-the-art literature survey has been compiled which covers topics related to establishing operational limits such as: brake control and blended braking, braking temperatures, brake block materials, wear and rolling contact fatigue of wheels due to tread braking, and capacity of tread brakes and brake discs.A methodology to simulate full-scale brake rig tests, including wheel-rail contact, has been further developed. It includes an axisymmetric thermal analysis, a 3D mechanical wheel-rail contact analysis, and a 3D thermomechanical analysis of the braked wheel. The behaviour of ER7 grade railway wheel material is mimicked by use of a plasticity model calibrated against results from cyclic experiments on test specimens. The results from the simulations in terms of predicted fatigue lives show good agreement with full-scale test rig results for three combinations of initial velocity and brake block material.The developed methodology is employed in parametric studies. These consist of braking load cases characterised by operational parameters such as axle load, maximum vehicle speed, deceleration, block material, and initial wheel temperature. Damage evolution in the wheel tread is studied. A strong infuence of high temperatures on rolling contact fatigue formation in the wheel tread was observed. In particular, braking temperatures over 450 \ub0C can result in a very short life up to crack initiation. However, for braking temperatures in the range of 300 - 350 \ub0C, wheel tread material is more resistant to fatigue due to strain hardening

Mapping the Brake Energy in Articulated Haulers

An energy recovery analysis method was developed for the F generation articulated haulers in the form of a MATLAB script. The method is based on the mapping of the peak brake power, brake energy and engine energy. The method was developed using adequate signals collected on haulers at customer sites and test tracks. A conceptual study was also carried out concerning the brake energy that may be stored in the Energy storage systems (ESS) and the results shows the actual amount of brake energy that can be accumulated in the ESS along with the accurate selection of the ESS for a particular work site. The developed method was implemented in a measurement system (M-LOG) and two test runs were made. Results revealed that the energy recovery analysis method was implemented successfully with minor issues. The method developed in this thesis was welcomed by Volvo CE after test run and is in use presently

Mapping the Brake Energy in Articulated Haulers

An energy recovery analysis method was developed for the F generation articulated haulers in the form of a MATLAB script. The method is based on the mapping of the peak brake power, brake energy and engine energy. The method was developed using adequate signals collected on haulers at customer sites and test tracks. A conceptual study was also carried out concerning the brake energy that may be stored in the Energy storage systems (ESS) and the results shows the actual amount of brake energy that can be accumulated in the ESS along with the accurate selection of the ESS for a particular work site. The developed method was implemented in a measurement system (M-LOG) and two test runs were made. Results revealed that the energy recovery analysis method was implemented successfully with minor issues. The method developed in this thesis was welcomed by Volvo CE after test run and is in use presently

Selectable Fractional-order Controller for Industrial Control Designs

Differential Equation (DE) of fractional-order specifically gives clear view of fractional-order systems. Since genuine processes are typically or most anticipated to be fractional, employing fractional-order’s concept might be results to take us closer to the actual world. A lot of recent publications concentrate on employing fractional-order dynamics is to describe actual physical processes. In this paper, fractional calculus is applied in the field of control systems. Fractional-order controller also known as FOC has been proposed in numerous studies. The fundamental benefit of a FOC is that it gives the control mechanism of greater flexibility of time and frequency responses, enabling better and more reliable functioning of the system. The industrialization of fractional-order control has practical benefits of better solutions for control problems. The industrial controller has the requirement of different gains and orders of fractionalorder controllers. The selectable improved design is proposed, and an optimal and efficient controller is suggested with fractional-order approach. The results show that the best controller is selected from different controllers for water tank and bio-reactor systems. It is found in the results that the Mod FPID controller has the least overshoot of 4.31% and the fastest settling time of 76.5 s for water tank system and fractional-order controller (PID)n is selected for bio-reactor control systems

Thermomechanical capacity of wheel treads at stop braking: A parametric study

During tread braking, the treads of railway wheels are subjected to a complex loading due to combined rolling contact and thermally induced stresses. In revenue traffic the running mode of the train varies and the operational parameters will influence the life of the wheels. To prevent excessive damage, it is therefore important to understand at which operational conditions wheel damage becomes unacceptable. The current study aims to find limits for tread braking with respect to the influence of thermal stresses on rolling contact fatigue (RCF) of the wheel tread when subjected to repeated stop braking. A parametric study, using 3D FE simulations and involving operational parameters such as axle load, maximum vehicle speed, deceleration, brake block material and initial wheel temperature, is carried out for a new wheel with an S-shaped web. Additional analyses investigate impact from wheel geometry by studying a wheel with a straight web and a wheel with a thin (worn) rim. The effects of simultaneous thermal loading from wheel–block frictional contact during braking and mechanical loading, due to the traversing wheel–rail rolling contact, are studied in an uncoupled thermomechanical analysis. In the wheel–rail contact simulations, frictional rolling contact stress distributions induced by braking are accounted for. Interfacial shear stresses and partial slip are also included in the model. A temperature-dependent elastoplastic model is utilised to characterise changes in material behaviour during braking. In the vicinity of the wheel tread, damage evolutions for the studied brake load cases are evaluated. The results show that high tread temperatures, in particular temperatures above 450 \ub0C, have a strong detrimental influence on the RCF formation and, hence, also on the thermomechanical capacity of the wheel. On the other hand, it is found that for braking temperatures between 300 \ub0C and 375 \ub0C, the fatigue resistance is increased due to strain hardening effects. In addition, the parametric study points towards actual braking load cases that can give such temperatures in terms of initial speeds, axle loads, etcetera. Specifically, the study shows that the train axle load, that controls the normal wheel–rail contact force, has a substantial impact on the life of the wheel treads. Wheels having straight webs and S-shaped wheel web exhibit the same fatigue life of their treads, whereas a reduction in wheel rim thickness promotes ratchetting due to increased flexural stresses from the mechanical wheel–rail contact loading