Investigation on some factors affecting crack formation in high resistance aluminum alloys

Aluminum alloys having good mechanical properties are Al-Zn-Mg alloys (7xxx) and Al-Cu-Li alloys (Weldalite®). These alloys may be subjected to stress corrosion cracking. In order to overcome this problem the Al 7050 alloy has been developed and it is widely used for aerospace applications. Despite that, some components made of this alloy cracked during the manufacturing process including machining and chemical anodization. In a previous work cracked Al 7050 components have been analyzed in order to identify possible causes of crack formation. In this work the susceptibility of this alloy to intergranular corrosion has been analysed and compared with that of other high resistance aluminum alloys

Effect of surface modification on the stability of oxide scales formed on TiAl intermetallic alloys at high temperature

TiAl intermetallic alloys have many interesting potential application in the automitive and aerospace industry due to their low density and good mechanical properties. Unfortunately they have a low oxidation resistance at temperature higher than 700 °C and the improvement of their oxidation behavior is still an open issue. In this work the surface of a TiAlCrNB alloy has been modified by means of their anodic coating or cerium converison coating. Afterwards the stability of the oxide scale formed at 900 °C has been studied by analyzing crack formation and porpagatin, which is the phenomenon that con produce scale spallation during the alloy cooling

Analysis of the fracture criticality of biphasic brass

Some hydraulic brass components were subjected to in service structural failures. In the present work some case histories were analyzed and revealed that such failures were determined by the material microstructural characteristics dependent not only on the alloy composition, but also on the adopted production techniques. The study highlighted that the β phase orientation significantly affects the fracture behavior of the studied biphasic brass. Moreover the effect of different applied stresses that caused component failure was analyzed

Study of defect formation in Al 7050 alloys

The Al 7050 alloy is an Al-Zn-Mg-Cu-Zr alloy having good mechanical properties. This alloy has been developed in order to overcome stress corrosion cracking problems that characterise 7xxx Al alloys. Despite Al 7050 is widely used for aerospace applications, it can be subjected to crack initiation and propagation during the manufacturing process. In this work cracked Al 7050 components have been analysed in order to identify possible causes of crack formation such as coarse intermetallic phase presence, voids or wrong mechanical machining processes

Fracture behaviour of alloys for a new laser ranged satellite

A new laser-ranged satellite called LARES 2 (Laser Relativity Satellite 2) has been recently designed for accurate tests of Einsten's theory of General Relativity and space geodesy. Some high density alloys (8.6-9.3 g/dm3) have been studied and characterised for producing the LARES 2 passive satellite. The considered materials were Copper and Nickel based alloys that have been produced and characterised. Aim of this work was to analyse their fracture behaviour that is a requirement for materials to be used for space applications. Fracture tests have been carried out on several specimens and fracture surfaces have been analysed

The Waste Management Of Large-Scale Recirculating Aquaculture Systems And Potential Value-Added Products From The Waste Stream

Recirculating Aquaculture Systems (RAS) is an emerging technology that is capturing the attention of many in aquaculture due to its ability to produce high-quality seafood using sustainable models. This study explored the waste management of RAS, specifically further treatment technologies, and the potential value-added products from the RAS waste stream that can be reused. Advanced, tertiary, or down-stream treatment technologies available for RAS were investigated through a literature review. Utilizing the constant comparative method and semistructured interviews with stakeholders in RAS, opinions and attitudes were collected about advanced treatment of RAS waste and reuse opportunities presented from value-added products generated from the waste stream. Collected data provided insight on the current state of waste management of RAS and how RAS waste management may develop over time. This study confirmed that all RAS users intend to expand their waste management methods to incorporate reutilization of waste, whether by assimilating nutrients back into their respective system or by producing value-added products for other markets. RAS waste is a resource, holds economic value, and will be reutilized. Enhanced RAS waste management must be cost effective to the farmer or publicly subsidized if the public demands the result. The motivations behind further reuse of generated waste, typically, stems from the scale of the farm. Large-scale RAS will reutilize their waste in an effort to reduce costs of getting rid of the waste, whereas smaller scale farms will reutilize their waste to reincorporate valuable resources back into the farm. The major recommendation from this study is for RAS farms to work directly with agricultural and energy management groups to develop efficient waste management strategies and utilize useful synergies. With better defined best practices and increased co-management between aquaculture, energy, and agriculture, RAS will continue to increase its contribution to the seafood supply chain

Risk management and land use planning for environmental and asset protection purposes

The PhD thesis presents a semi-quantitative methodology, developed to increase the efficacy of Land Use Planning related to the Management of risks, in particular as far as it concerns multiple risks impinging on the same territory (Multi-risks). At the moment, each risk is managed through a dedicated sectorial plan, having its proper procedures and scale, and the only “meeting point” for these plans – at least in Italy - are the Municipal city plans. The Municipalities have to implement the contents related to the various risks and directly intervene on the territory, but the lack of linkage and coordination between the plans and the authorities in charge often makes the emergency management and LUP less effective towards the achievement of a real safety of territories. In addition, the actual legislative framework does not face the possible consequences of risk interactions. In this context, the objective of the thesis was to develop a simple risk pre-screening tool, expressly designed for local planners, able to point out the areas more exposed to risks and risks interactions, in order to better address the distribution of the municipal resources for further studies and interventions. The local planners that, especially in Italy, have a central role for the risk management of the territory, became the central point for the proposed framework, assuming the role of evaluators, and then decision-makers. The methodology was developed taking into account the existing experimental frameworks developed for Multi-risks and NaTech events. Both qualitative and quantitative methodologies were settled in the last years, however the scales and the complex approaches proposed collide with the objectives of this PhD thesis. In fact, few methodologies were elaborated for little scales, and frequently the application of quantitative multi-risk methodologies at a local scale encountered difficulties related to data availability; in addition, all the methodologies require the involvement of experts of several disciplines. These aspects, in particular considering the scarce financial resources of Municipalities, risk to limit the awareness of the importance of a multi-risk approach for LUP planners. Therefore, a semi-quantitative approach, based on an index scale from 0 to 3 onwards was developed for a direct use from Municipal technicians; the proposed scale is applied to measure both the impact of the risks and risk interaction. The methodology is composed by 4 steps: 1) characterization of the risks; 2) assignation of the ratings to the risks; 3) assessment of binary risk interactions; 4) assessment of the compatibility and planning phase. Each step is accompanied by GIS mapping. Steps 1 and 2) Risk characterization and rating. The users (local planners) are required to describe the main territorial risks according to 3 macro-categories: Historical Events, Protection Measures and Strengthening Effects. The macro-categories help in majorly focus on the different aspects of the risks, in particular those that could enhance its final impact, or that could have been neglected in the existing plans. Each macro-category is evaluated and rated on the basis of a dedicated guide, developed on the basis of literature data. Step 3) Risk interaction. The impact of one risk on another one (binary interaction) is assessed in the areas where risks overlay, thanks to a weighted average sum of the values of their macro-categories. An excel table for the application of the formula was developed. The calculation of the interaction vales can be also executed directly through GIS. Step 4) Compatibility. Territorial and environmental vulnerabilities are classified in compliance with E.R.I.R. national and regional regulations. Then, the compatibility is assessed on the basis of an “alarm threshold”; when highly vulnerable territorial or environmental elements fall down in areas where the risks macro-categories or risks interaction are above 2,5, a potential incompatibility is detected. The Municipalities will have to focus here further studies, and then possible interventions: a collection of the possible actions, extracted from existing Guidelines and Manuals was drafted to guide this process. An optional step for the compatibility assessment was added to provide the Municipalities with an indicative mapping of the spatial consequences of the interactions involving industrial plants. This is the only step of the methodology that could presents difficulties for not expert users, because it entails the use of two modelling software (ALOHA and HSSM), that simulates the consequences of the releases. The methodology was tested on two Italian case-studies, two Municipalities affected by multiple types of risks which could interact. Both the territories were connoted by low levels of risk, however the application of the methodology highlighted possible unforeseen problems deriving from the interactions, that currently are not described in any existing sectorial or local plan. Once that the areas more exposed are identified, ad-hoc investigations and actions can be settled to address the problem, on the basis of a guide-line. The proposed approach demonstrated to be able in identifying and bring multi-risks aspects to the attention of the decision makers; in this way, they have a simple guide to risk that can be integrated with the existing planning instruments to improve the quality of decisions related to risks. Furthermore, local administrators recover a more active role, increasing their awareness about the contents and information of the sectorial plans, but also exploiting their major direct knowledge of the territory. This approach tried to fill two different existing gaps: on one side, the absence of an official and recognized legislation on Multi-risks; on the other side, the difficulties for non-risk experts to effectively use the Multi-risk and NaTech experimental methodologies developed so far now. The framework developed for this PhD thesis can be easily adapted to LUP procedures of other countries, through a re-construction of the tables that guide the risk-rating; the simple index scale can be easily managed by different types of users. Being the methodology a risk pre-screening, it can be useful in every context in which it is necessary to acquire more information about multi-risks and their consequences, to better define future actions and drive the application of quantitative methodologies

Effect of wall microstructure and morphometric parameters on the crush behaviour of Al alloy foams

Three different aluminium foams, manufactured by compact powder technology starting from 7075, 6061 and AlSi7 alloys were studied by performing microstructural and morphometric analyses, with the aim of explaining their different behaviour during axial crushing. Void distribution coupled with material microstructure justifies the behaviour of load-displacement curves obtained during axial crushing of the foams. The results show that 7075 alloy seems to be the material having the best behaviour during crushing, at least when the foam is removed of the external walls. Despite that outer skin presence coupled with the intrinsic brittle behaviour of this alloy may cause instability, if it is used to fill hollow components like crashboxes. During deformation process 6061 and AlSi7 alloys that are more ductile, give in and maintain contact adapting to the encasement deformation. (c) 2007 Elsevier B.V. All rights reserved

Model of multiple metal electrodeposition in porous electrodes

An electrochemical process is being developed for recovering metals from shredded waste electrical and electronic equipment by leaching and electrowinning. In a membrane-divided electrochemical reactor, chlorine is generated at the anode and used as oxidant in an external leach reactor, in which the metals are dissolved in an acidic chloride solution. As the resulting metal ion concentrations are relatively low, a porous (e.g.,graphite felt) cathode with a large specific surface area and high mass-transport rates is required to achieve acceptable rates and efficiencies of electrodeposition, the counter reaction to the anodic evolution of chlorine. Hence, as a design tool, a mathematical model was developed to predict potential, concentration, current density, and current efficiency distributions for individual metals within the (flow-through) porous cathode, as well as cell voltages and specific electrical energy consumptions of the electrochemical reactor as functions of cathode feeder potential, cathode thickness, porosity, concentrations, and flow rate and direction. To maximize current efficiencies and productivities of the predominant metal, copper, simulations suggest using an initial cathodic feeder electrode potential of -0.5V (standard hydrogen electrode) to metallize the felt, followed by electrodeposition of the bulk of the metal at -0.3V (standard hydrogen electrode), optimal felt thicknesses depending on reactant concentrations. (c) 2006 The Electrochemical Society