Numerical and experimental characterization of a railroad switch machine

This contribution deals with the numerical and experimental characterization of the structural behavior of a railroad switch machine. Railroad switch machines must meet a number of safety-related conditions such as, for instance, exhibiting the appropriate resistance against any undesired movements of the points due to the extreme forces exerted by a passing train. This occurrence can produce very high stress on the components, which has to be predicted by designers. In order to assist them in the development of new machines and in defining what the critical components are, FEA models have been built and stresses have been calculated on the internal components of the switch machine. The results have been validated by means of an ad-hoc designed experimental apparatus, now installed at the facilities of the Department of Industrial Engineering of the University of Bologna. This apparatus is particularly novel and original, as no Standards are available that provide recommendations for its design, and no previous studies have dealt with the development of similar rigs. Moreover, it has wide potential applications for lab tests aimed at assessing the safety of railroad switch machines and the fulfilment of the specifications by many railway companies

On Hirth Ring Couplings: Design Principles Including the Effect of Friction

Rings with Hirth couplings are primarily used for the accurate positioning of axial-symmetric components in the machine tool industry and, generally, in mechanical components. It is also possible to use Hirth rings as connection tools. Specific industries with special milling and grinding machines are able to manufacture both tailor made and standard Hirth rings available on stock. Unfortunately, no international standard (for instance ISO, DIN or AGMA) is available for the production and the design of such components. In the best-case scenario, it is possible to find simplified design formulae in the catalogue of the suppliers. The aim of this work is to provide some accurate formulae and computational methods for design to provide better awareness on the limitations and the potential of this type of connection. The work consists of five parts: (i) a review of the base calculation derived mainly from the catalogues of manufacturers; (ii) an improved calculation based on a new analytical method including the friction phenomenon; (iii) an experimentation run for validating the method; (iv) a case study applied to a machine tool; and, (v) a closed form formulation to determine an upper threshold for friction, thus ensuring the Hirth coupling regular performance

INFLUENCE OF THE STIFFNESS AND FRICTIONAL CHARACTERISTICS ON THE SHANK TORQUE OF SCREWS IN BOLTED JOINTS

This work aims at determining the influence of tribological and stiffness characteristics of a bolted joint on the residual shank torque of the screw. Even if it is commonly accepted to consider such a residual torque equal to half the torque at the thread, the literature lacks experimental data about the topic. The residual shank torque combines with the axial preload and the external loads to bring about the overall stress on the screw. Hence, the higher the residual torque, the lower the admissible external load for given size and class of the screw. From there stems the need for an analytical tool allowing the designer to calculate the residual torque as a function of the key parameters of the joint

A methodology for the lightweight design of modern transfer machine tools

This paper deals with a modern design approach via finite elements in the definition of the main structural elements (rotary table and working unit) of an innovative family of transfer machine tools. Using the concepts of green design and manufacture, as well as sustainable development thinking, the paper highlights the advantages derived from their application in this specific field (i.e., the clever use of lightweight materials to allow ruling out high-consumption hydraulic pump systems). The design is conceived in a modular way, so that the final solution can cover transfers from four to 15 working stations. Two versions of the machines are examined. The first one has a rotary table with nine divisions, which can be considered as a prototype: this machine has been studied in order to set up the numerical predictive model, then validated by experimental tests. The second one, equipped with a rotary table with 15 divisions, is the biggest of the range: this machine has been entirely designed with the aid of the previously developed numerical model. The loading input forces for the analyses have been evaluated experimentally via drilling operations carried out on a three-axis CNC unit. The definition of the design force made it possible to accurately assess both the rotary table and the working units installed in the machine

INHERITED HEARING LOSS: FROM GENE VARIANTS TO MECHANISMS OF DISEASE

Nonsyndromic Sensorineural Hearing Loss (NSHL) is the most common sensory disorder worldwide, affecting at least 1 in 500 newborns and more than half individuals older than 80 years. It is estimated that about 60-70% of cases are due to genetic factors [Raviv et al., 2010]. More than 70 genes have been associated with NSHL so far, but many others are still to be discovered. In this thesis, we investigated the genetic and molecular bases of NSHL by a double approach, consisting in: a) investigating the pathogenic mechanisms of mutations within the MIR96 gene, and b) searching for new genes/mutations by Whole-Exome Sequencing (WES) in selected NSHL families. As far as MIR96 is concerned, we identified and characterized a novel mutation (the third described) within the MIR96 gene, miR-96 (+57T>C), in an Italian family with autosomal dominant NSHL. MiR-96 is part of the conserved miR-183 microRNA (miRNA) family, which plays essential functions in the vertebrate inner ear. Point mutations within the seed region of miR-96 (miR-96-5p) cause autosomal dominant NSHL (AD-NSHL). The novel identified mutation replaces a highly conserved nucleotide and is predicted to reduce the stability of the pre-miRNA hairpin. Ex vivo assays in mammalian cells confirmed that both miR-96 and miR-96*(miR-96-3p) mature species were significantly reduced in the mutant, whereas the precursor level was unaffected. Moreover, miR-96 and miR-96* expression could be restored to normal levels by reconstituting the secondary structure of the pre-miR-96 hairpin, thus demonstrating that the mutation hinders the precursor processing. Finally, even though the mature miR-96 sequence is not altered, we demonstrated that the identified mutation significantly impacts on miR-96 regulation of selected targets. Taken together, these data provide further evidence of the involvement of miR-96 in human deafness and demonstrate that a quantitative defect of this miRNA may contribute to NSHL. As far as WES is concerned, the application of NGS to the identification of novel genes/mutations in 6 genetically undiagnosed Italian families (NSHL1-4 and 6, 7), with recessive NSHL and at least two affected individuals, has enabled the molecular diagnosis in two families (NSHL4 and NSHL6), and highlighted a putative novel deafness-associated gene in another family (NSHL3). In particular, a novel missense mutation within the PRPS1 gene was found in family NSHL4 and functionally characterized, together with other two mutations identified by candidate-gene screening in a larger X-linked NSHL cohort. In the NSHL3 family, WES pointed out a novel missense variant in DIAPH2, a gene not directly linked to NSHL but belonging to a family of proteins already involved in hearing loss. Studies aimed at the functional characterization of this mutation and at the clarification of the possible involvement of the gene in the pathogenesis of the disease are now being performed. For the other three families (NSHL1, 2 and NSHL7), the search for pathogenic variations is still ongoing

Fatigue response of as built DMLS processed Maraging Steel and effects of machining and heat and surface treatments

The main motivations for this study arise from the need for an assessment of the fatigue performance of DMLS produced Maraging Steel MS1, when it is used in the \u201cas fabricated\u201d state. The literature indicates a lack of knowledge from this point of view, moreover the great potentials of the additive process may be more and more incremented, if an easier and cheaper procedure could be used after the building stage. The topic has been tackled experimentally, investigating the impact of heat treatment, machining and micro-shot-peening on the fatigue strength with respect to the \u201cas built state\u201d. The results indicate that heat treatment significantly enhances the fatigue response, probably due to the relaxation of the post-process tensile residual stresses. Machining can also be effective, but it must be followed (not preceded) by micro-shot-peening, to benefit from the compressive residual stress state generated by the latter

Chapter Measuring content validity of academic psychological capital and locus of control in fresh graduates

Positive psychological capital (PsyCap; hope, resilience, self-efficacy, and optimism) and locus of control (LoC; internal and external) denote psychological dimensions which have been identified as crucial resources for occupational satisfaction and success. These dimensions could impact fresh graduates’ ability to stand the labour market in times of crisis. Two instruments, called Academic PsyCap and Academic LoC, have been specifically developed to evaluate these dimensions among fresh graduates. The two instruments consist of 34 and 10 items respectively, which have been selected, through factor analyses, from a large initial pool of items administered to fresh graduated at the University of Padova. Results suggested adequate psychometric properties for both Academic PsyCap and Academic LoC. The factor structure of the two instruments was confirmed (CFI = .92, RMSEA = .07, SRMR = .07 for Academic PsyCap; CFI = .96, RMSEA = .05, SRMR = .05 for Academic LoC), and internal consistency was satisfactory for all the subscales. The two instruments are presented, and their psychometric properties are described

Chapter Psychometric properties of a new scale for measuring academic positive psychological capital

Positive psychological capital (PsyCap) is the name given to a set of psychological dimensions (hope, resilience, self-efficacy, and optimism) that may support students in their effort to achieve better academic results and even improve the employability of graduates. These dimensions could help students to achieve better academic results and impact fresh graduates’ ability to stand the labour market in times of crisis. A scale, called Academic PsyCap, was specifically developed to evaluate the four PsyCap dimensions among students and fresh graduates. To deeply investigate the structural validity of the scale, three alternative models (one-factor model, correlated four-factor model, bifactor model) were run on the responses provided by about 1,600 fresh graduates at the University of Padua. The results indicated that the bifactor model fit the data better than the other two models. In this model, all items significantly loaded on both their own domain specific factor and on the general factor. The values of Percentage of Uncontaminated Correlations (PUC), Explained Common Variance (ECV), and Hierarchical Omega suggested that multidimensionality in the scale was not severe enough to disqualify the use of a total PsyCap score. The scale was found to be invariant across gender and academic degree (bachelor’s and master’s degree). Internal consistency indices were satisfactory for the four dimensions and the total scale