Fatigue Crack Growth in Austenitic and Martensitic NiTi: Modeling and Experiments

AbstractFatigue crack growth of austenitic and martensitic NiTi shape memory alloys was analyzed, with the purpose of capturing the effects of distinct stress-induced transformation mechanics in the two crystal structures. Mode I crack growth experiments were carried out, and near-crack-tip displacements were captured by in-situ digital image correlation (DIC). A special fitting procedure, based on the William's solution, was used to estimate the effective stress intensity factor (SIF). The SIF was also computed by linear elastic fracture mechanics (LEFM) as well as by a special analytical model that takes into account the unique thermomechanical response of SMAs. A significant difference in the crack growth rate for the two alloys was observed, and it has been attributed to dissimilar dissipative phenomena and different crack-tip stress–strain fields, as also directly observed by DIC. Finally, it was shown that the predictions of the analytical method are in good agreement with effective results obtained by DIC, whereas a very large mismatch was observed with LEFM. Therefore, the proposed analytical model can be actually used to analyze fatigue crack propagation in both martensitic and austenitic NiTi

multiaxial fatigue behavior of additive manufactured ti 6al 4v under in phase stresses

Abstract The development and application of additive manufacturing (AM) technologies is constantly increasing. However, in many applications, AM parts are subjected to multiaxial loads, arising from operating conditions and/or complex geometries. These make AM components serious candidates for crack initiation and propagation mechanisms. Therefore, a deep understanding of the multiaxial fatigue behavior of AM parts is essential in many applications where durability and reliability are core issues. In this study, multiaxial fatigue of Ti6Al4V thin-walled tubular specimens, made by Selective Laser Melting (SLM) process, was investigated by combined axial-torsional loads. Infrared thermography (IR) was also used to investigate the temperature evolution during fatigue tests. Results highlighted different damage mechanisms and failure modes in the low- and high-cycle fatigue regimes

Multiaxial fatigue behavior of additively manufactured Ti6Al4V alloy: Axial–torsional proportional loads

Additive manufacturing (AM) techniques are under constant development and selective laser melting (SLM) is among the most promising ones. However, widespread use of AM techniques in many industries is limited by the different/unusual mechanical properties of AM metallic parts, with respect to traditionally processed ones, especially when dealing with complex fatigue loading conditions. In fact, crack formation and propagation mechanisms are mainly affected by the development of internal defects, residual stresses, and microstructural changes. This is actually one of the major issues the materials engineering community is facing today. In many applications, AM components are subjected to multiaxial fatigue loads, arising from operating conditions and/or from complex geometries, that unavoidably generate crack initiation and propagation mechanisms. The aim of this study is to investigate the multiaxial fatigue behavior of additively manufactured Ti6Al4V samples, made by SLM. Fatigue tests, combining proportional axial and torsional loads, were performed on thin-walled tubular specimens. Full-field measurement techniques, such as the infrared thermography and digital image correlation, were also used to capture temperature and strain evolutions, at both local scales and global scales. Fatigue results highlighted damage mechanisms, and failure modes are strongly related to the applied stress level

Mechanical characterization of basalt woven fabric composites: numerical and experimental investigation

Basalt fabric composite, with different twill wave reinforcements, i.e. twill 2/2 and twill 1/3, have been studied in this work by means of experimental tests and numerical finite element (FE) simulations. As fabric reinforcements show repeating undulations of warp and fill yarn, simple mixtures law cannot be applied.As a consequence, the mesoscopic scale, lying between the microscopic and the macroscopic one, has to betaken into account to mechanically characterize a fabric reinforced composite. The aim of this work is toevaluate the stiffness of a fabric reinforced composite in warp and fill direction. In particular a numerical FEmodel, assuming elliptical sections and sinusoidal shape of the yarns, has been implemented and experimentaltests have been carried out in order to validate the proposed model. Finally, the strength and the failure modesof the composite material, for each analysed structure and textile orientation, have been experimentallyinvestigated

Surface Integrity enhancement of aerospace components produced by subtractive and additive manufacturing processes

Dottorato di Ricerca in Ingegneria Civile e Industriale. Ciclo XXXUniversity of Calabri

Thermo‐Fluid Dynamics Study of Oxy‐MILD combustion of pulverized coal in furnaces and in a novel concept of boiler

Dottorato di Ricerca in Ingegneria Civile e Industriale. Ciclo XXIX SSDThe thermal power plant for the generation of electricity, which uses coal as a primary energy source, presents multiple issues linked to the emission of pollutants and greenhouse gas (CO2) into the atmosphere. Furthermore, the conventional boilers greatly contribute to the increase of these harmful substances. The aim of this work is to propose and analyze the possibility of combining two new combustion technologies: the so-called oxy and MILD combustion. The rst one, allows to capture the carbon dioxide, while the second one provides several advantages, not only because it reduces the emission of nitrogen oxides, but also because it is characterized by uniform ows in the combustion chamber. Therefore, the challenge is to combine the two technologies with applications in furnaces and a new concept of boiler. For the latter, the planned applications include the ultra-super critical plants. For this reason, numerical simulations have been carried out by means of technical CFD (Computational Fluid Dynamics) because it is hard to provide large-scale tests. The initial phase of the work involves the application of the two technologies in furnaces. The rst one focuses on the MILD combustion by analyzing di erent positions of the pulverized coal jet, while the second one focuses on the application of the combination of the two technologies in order to analyze their e ects in terms of temperature and species concentration distributions. The next phase of the work, instead, has a focus on an innovative boiler. The testing of di erent geometrical solutions and models of char combustion has also allowed to study their e ects in terms of temperature, combustion products concentrations, burnout and, above all, wall heat ux. These latter results have been compared with the ones of traditional boilers and the results reported in the literature. The nal aim of this work is to analyze the advantages deriving from the combination of two technologies into a new concept of boiler, in order to reduce pollutant emissions, greenhouse gases and obtain a better performance than the one at the current state of the art.Università della Calabri

Dynamic thermal and energetic characteristics of building walls containing sensible storage and phase change materials. New analytical and numerical models and experimental validation

Dottorato di Ricerca in Ingegneria Civile e Industriale. Ciclo XXIXUniversità della Calabria

Adeguamento antisismico di edifici in c.a. irregolari in pianta mediante l'utilizzo di controventi dissipativi: modellazione, progettazione ed analisi non lineare

Dottorato di Ricerca in Ingegneria Civile e Industriale. Ciclo XXIXUniversità della Calabria

Emergency preparedness in industrial plants: an industry 4.0 driven training solution

Dottorato di Ricerca in Ingegneria Civile ed Industriale, Ciclo XXXIMajor accident hazards industrial sites or high-risk industries lack of a dedicated training methodology and environment to enhance significantly the personnel rate of retention as well as emergency preparedness and response skills (both technical and non-technical, e.g. leadership, decision-making, team-working, stress management). The need for effective industrial emergency preparedness and response training systems is widely acknowledged also from academic communities that have invested a great deal of time and effort to detect methodologies to enhance emergency response staff performance (emergency manager and emergency team members). This study takes a step forward in current practice proposing a multiplayer industrial emergency preparedness and response training system, which leverages on Industry 4.0 enabling technologies – namely Simulation, Virtual Reality & Serious Games – and on a cooperative, experiential and differentiated training strategy. It also pushes for an increased attention on human factors in the Occupational Health and Safety 4.0 and proposes an approach to analyze the effects of human factors with the ultimate aim to include them in the design of industrial safety protocols and regulations and in the assessment of hazards. This way, after an experimental campaign and statistical analysis of the results, the proposed training system has been critically investigated to ascertain: § how the emergency response staff performance evolves along repeated training sessions; § to which extent the proposed solution is effective in delivering procedural knowledge to the emergency response staff; § whether it is realistic enough to think that the training experience produces psychological stress in those people that are trained with it and how they cope with stress over the repeated replications § whether and to which extent human factors, such as stress and perceived workload, are correlated to the capability of the emergency manager to coordinate and monitor the execution of all the measures and actions intended to deal with an industrial accident and its effects.Università della Calabri