Assessment of rail grinding maintenance surface quality and damage propagation in subsequent loading cycles for premium rail grades

Rail samples were tested under various scenarios as part of a complete analysis of the rail grinding process. Two main group of tests were performed which assessed the following: 1) preventive and corrective maintenance on fresh rail samples and 2) post-grinding tribological performance of the ground samples. The results allowed further knowledge to be acquired with regards to the performance and effectiveness of the grinding process and its effect on the surface quality of the rail samples. Results indicated a correlation between White Etching Layer and the formation of cracks and defects. Additionally, the harder grades were found to retain larger quantities of White Etching Layer upon completion of the rolling/sliding testing due to the hardness gradient between the White Etching Layer and bulk material, promoting the formation of cracks

Post-field grinding evaluation of different rail grades in full-scale wheel/rail laboratory tests

Rail grinding is a maintenance task performed in the field to return it to profile and/or remove damage, however, it can affect the surface integrity of the rail. In this paper, the damage resistance of three different ground rails (R260, R350HT and R400HT) was evaluated. Rail samples were ground using the same parameters in a low-traffic line in the field. The rail metallurgy was then examined, and white etching layer (WEL) formation was evaluated. The resistance to wear and rolling contact fatigue (RCF) was studied in a Full-Scale Rig (FSR). Cracking was detected and, in some cases, WEL was found pressed into the pearlitic microstructure whereas in others the bonding between the WEL and the pearlite failed leading to delamination

A laboratory demonstration of rail grinding and analysis of running roughness and wear

Rail grinding has been widely used for rail maintenance to keep the performance of the rail track at satisfactory levels. However, there is a lack of knowledge on the relationship between different grinding parameters and the effect on the rails and the post-grinding evolution of roughness and wear. Rail undergoes significant levels of stress during grinding to remove any defects that appear during its life-cycle which can cause significant microstructural change. By developing a method of demonstrating rail grinding it will allow further investigation of the process and potentially the exploration of different grinding patterns. Moreover, an analysis of the roughness of wheel and rail is an input parameter in most modern simulation tools that could be associated with the coefficient of friction. This paper reports a laboratory demonstration of rail grinding followed by a series of tests to determine the wear of the rail and if there is a relationship between friction coefficient and roughness. The rail specimens that were ground have undergone a phase transformation and showed White Etching Layer (WEL) on the contact surface. This was found to initially act protectively for the rail disc reducing the wear rates, but then contributed to crack formation. No clear long-term correlation was identified between the coefficient of friction and roughness during the testing, however a relationship could be drawn when test periods were studied individually

Rail Surface Quality Improvements from Utilising a Novel High Speed Superabrasive Grinding Approach

Throughout the content of this PhD project the current technology utilised for rail grinding is reviewed and a novel, more efficient grinding technique for the railway industry is proposed. The current conventional method comprises resin bonded grinding stones along with low speeds and low material removal rates. Testing under laboratory conditions was performed on rail specimens to aid in the research of the technique. Several aspects of the ground specimens were analysed such as roughness, microstructure, and post-grinding performance. This verified the undesirable effect of conventional grinding on the rail material, as it was revealed that White Etching Layer (WEL) can be formed out of the grinding process which can eventually lead to the initiation of cracks and negatively affect the rail performance. Additional analysis of field ground specimens was done on a Full-Scale Testing Facility that simulates the rolling/sliding mechanisms between wheel and rail to validate the scaled post-grinding results. This further aided in identifying the problems and weaknesses of the conventional technique. Hence, upon a broader literature research, a high speed grinding technique which utilizes superabrasive material was defined as the most appropriate for the railway industry. By utilising the superabrasive material, elevated rotational speeds can be used on the grinding wheel along with higher feed rates. This will reduce maintenance times, improve the surface properties, and the overall efficiency of the process will drastically increase. Upon assessment, the most appropriate design was selected for a test rig that is able to simulate operating conditions of the grinding process as well as perform experiments at higher grinding speeds. Experiments were performed on full scale rail specimens to assess the technique and establish the methodology. Testing on full scale rails allowed the validation of the method under near real-life conditions. The ultimate goal is the implementation of the technique in the railway industry resulting in the reduction of rail damage as a consequence of the grinding process, the elimination of undesirable grinding by-products such as WEL, the decrease of the downtime for rail networks and maximising the overall efficiency and performance of the industry

Hf Incorporation in (Ti,Zr)NiSn Half Heusler Solid Solutions via Mechanical Alloying

Half Heusler materials are promising thermoelectric materials with potential application in generators at medium range temperatures. Solid solutions are typically prepared by arc melting, presenting interesting properties. In this work, the effect of Hf incorporation and the formation of solid solutions is discussed. More specifically, Ti1−xHfxNiSn and (Ti0.4Zr0.6)1−yHfyNiSn half Heusler materials were synthesized via mechanical alloying and consolidated via hot press sintering. Hf incorportation in the lattice strongly affected the lattice thermal conductivity due to the large mass fluctuation. The power factor and thermoelectric figure of merit was optimized via Sb doping the values of 34 μW/cmK2 and 38 μW/cmK2; 0.72 and 0.76 at 762 K for Ti0.4Hf0.6NiSn0.985Sb0.015 and (Ti0.4Zr0.6)0.7Hf0.3NiSn0.98Sb0.02, respectively, were reached

Hf Incorporation in (Ti,Zr)NiSn Half Heusler Solid Solutions via Mechanical Alloying

Half Heusler materials are promising thermoelectric materials with potential application in generators at medium range temperatures. Solid solutions are typically prepared by arc melting, presenting interesting properties. In this work, the effect of Hf incorporation and the formation of solid solutions is discussed. More specifically, Ti1−xHfxNiSn and (Ti0.4Zr0.6)1−yHfyNiSn half Heusler materials were synthesized via mechanical alloying and consolidated via hot press sintering. Hf incorportation in the lattice strongly affected the lattice thermal conductivity due to the large mass fluctuation. The power factor and thermoelectric figure of merit was optimized via Sb doping the values of 34 μW/cmK2 and 38 μW/cmK2; 0.72 and 0.76 at 762 K for Ti0.4Hf0.6NiSn0.985Sb0.015 and (Ti0.4Zr0.6)0.7Hf0.3NiSn0.98Sb0.02, respectively, were reached

Synthesis, characterization and thermoelectric performance of Mg2 (Si, Sn, Ge) materials using Si-kerf waste from photovoltaic technology

The recycling acquisition of silicon waste from photovoltaic industry has gained an increasing attention nowadays, since more than 50% of high purity material ends up as kerf during the wafer cutting process. Currently, different Si-based applications are being exploited in terms of using such Si kerf, in order to lower cost and significantly increase environmental impact. Thermoelectric devices can efficiently contribute towards this recycling approach, via the preparation of highly efficient silicides for power generation. In this work, Bi doped Mg2(Si,Sn,Ge) materials were prepared using Si-kerf originated from photovoltaic (PV) cutting wastes. Different Bi concentrations were studied in terms of thermoelectric properties and performance and a high figure-of-merit of 1.1. was achieved at 800K. In addition, a thorough structural and mechanical property characterization, such as morphology, phase identification, hardness and indentation modulus has been conducted. These results, which were evaluated and compared to materials prepared with pure Si (>99.9%), are presented for the first time for Mg2(Si,Sn,Ge) materials

Τουρισμός συνέργειας: σχεδιάζοντας την εμπειρία του τόπου

Μη διαθέσιμη περίληψηNot available summarizatio

Ένα όμορφο χάος: τουρισμός και εμπειρία του τόπου στον ελληνικό χώρο

Περίληψη: Ο ρόλος και η συμμετοχή του Τουρισμού στην ελληνική οικονομία τον καθιστά αντικείμενο ιδιαίτερου ενδιαφέροντος. Οι ελληνικοί τουριστικοί πόροι που μπορούν να προκαλέσουν ενδιαφέρον και έλξη στους επισκέπτες καταγράφουν ιδιαίτερη δυναμική για την Ελλάδα. Το πλήθος, η ποιότητα, η ποικιλία, ο αιφνιδιασμός είναι χαρακτηριστικά αυτής της δυναμικής και ταυτόχρονα τα χαρακτηριστικά του Ελληνικού τόπου. Παρ΄ όλα αυτά η διαχείριση του Ελληνικού Τουρισμού ανέκαθεν παρουσιάζει προβλήματα και ελλείψεις στην προσέγγιση, τις στρατηγικές, την πολιτική της και χαρακτηρίζεται από δυσκαμψία και στασιμότητα. Εγείρεται λοιπόν, το ερώτημα κατά πόσο η τρέχουσες τουριστικές πρακτικές και εφαρμογές αξιοποιούν τις δυνάμεις ελληνικού τόπου. Το κυρίαρχο τουριστικό μοντέλο ανάπτυξης περιορίζεται στον ήλιο και τη θάλασσα ως τα βασικά προϊόντα στον ελληνικό χώρο. Με κίνδυνο να χαρακτηριστεί ως ξεπερασμένο, γίνονται αποσπασματικές προσπάθειες προσαρμογής του στα νέα τουριστικά δεδομένα. Παράλληλα, τα ολοένα και περισσότερα είδη εναλλακτικού τουρισμού που εμφανίζονται επιχειρούν να διεκδικήσουν μερίδιο της τουριστικής ζήτησης μέσω της εξειδίκευσης τους σε συγκεκριμένες θεματολογίες. Σαν γενικότερη παρατήρηση, κάποια από αυτά παρουσιάζουν ενδιαφέρον και προοπτικές όμως είναι έκδηλη η έλλειψη συντονισμού μεταξύ τους αλλά και με το κυρίαρχο τουριστικό μοντέλο. Αυτό που αρχίζει να διαφαίνεται είναι η ανάγκης νέας πολιτικής και η αναπροσαρμογή του τουριστικού μοντέλου ανάπτυξης. Η καινοτόμα προσέγγιση που προτείνει ο βιωματικός τουρισμός έχει τη δυναμική να επανακαθορίσει την σχέση τόπου και τουρισμού. Αντιλαμβάνεται την τουριστική ζήτηση ως σύνολο προσδοκώμενων εμπειριών και την τουριστική προσφορά ως σύνολο προσφερόμενων εμπειριών. Κοινός παρονομαστής τους, το βίωμα. Εντός αυτής της νέας προσέγγισης, η αρχιτεκτονική καλείται ως η μελέτη του χώρου να συντελέσει σε αυτό το έργο προσφέροντας εργαλεία ανάγνωσης, αντίληψης και ανάλυσης του τόπου. Σημαντικότερα όμως, ως μορφοποιός του τουριστικού και μη χώρου, κατέχει μερίδιο ευθύνης στον καθορισμό του βιώματος ως βασικού συντελεστή στην ανάπτυξη και διατήρηση της τουριστικής ταυτότητας του τόπου.Presented on