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Article
Publication date: 31 May 2011

T. Ghidini, C. Dalle Donne and U. Alfaro Mercado

Friction stir welding (FSW) is simple, clean and cost effective joining technology which allows high‐quality joining of materials that have been traditionally troublesome…

Abstract

Purpose

Friction stir welding (FSW) is simple, clean and cost effective joining technology which allows high‐quality joining of materials that have been traditionally troublesome to weld conventionally without distortion, cracks or voids such as high‐strength aluminium alloys. Since FSW has been identified as “key technology” for primary aerospace structures, the recent FAR regulations for damage tolerance and fatigue evaluations of aircraft structures require fatigue life predictions for this specific joint type also in the presence of corrosion. The purpose of this paper is to give an overview of the prediction of small coupon fatigue lives of thin section friction stir welded butt and T‐joints.

Design/methodology/approach

Particularly, as a special application, widespread fracture mechanics software will be used to predict the fatigue life of FSW joints and to obtain SN curves. The engineering approach will start from an easy definition of the damage affecting the fatigue life of any of the previously mentioned cases (inclusions, tool markings, corrosion pits) and will move through affordable fracture mechanics solutions. Particularly, a first step in predicting the fatigue life of complex friction stir welded structures will be taken by combining the FEM code with the fracture mechanics software in the prediction of the FSW T‐joints.

Findings

The calculations are in very good agreement with the experimental results once the following basic assumptions are done: the welded material is treated as base material; particle inclusions and welding imperfections are treated as initial flaws while predicting the life of polished and un‐polished (including the T‐joints) FSW material, respectively, and the entire fatigue life was comprised of crack propagation; pitting and inter‐granular corrosion are treated as a single corrosion damage source and the model surface crack comprehends this damage; and the several corrosion‐damaged areas of the specimen surface are simulated with a single semi elliptical surface crack having the dimensions of the deepest and the widest corrosion damage area.

Originality/value

A simple engineering approach which is based on a relatively solid background and which is checked against fatigue test data for various FSW test specimens was developed: it may provide a practical and reliable basis for the analysis of fatigue tests of integral structures in the presence of corrosion attack, by using widespread fracture mechanics principles.

Details

International Journal of Structural Integrity, vol. 2 no. 2
Type: Research Article
ISSN: 1757-9864

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Article
Publication date: 12 August 2019

Dmytro Babich, Volodymir Bastun and Tatiana Dorodnykh

The purpose of this paper is to consider an approximate model of accumulation of microdefects in a material under repeated loading which makes it possible to define…

Abstract

Purpose

The purpose of this paper is to consider an approximate model of accumulation of microdefects in a material under repeated loading which makes it possible to define theoretical parameters of the fatigue failure (durability, fatigue limit, etc.). The model is involving the relevant law of distribution of ultimate (yield) stresses in the material of these members in combination with the basic characteristics of main mechanical properties of a material (ultimate and yield stresses and associated standard deviations).

Design/methodology/approach

The model of fatigue failure of brittle and elastoplastic materials based on the use of the structural-probabilistic approach and up-to-date ideas on the mechanism of material fracture is proposed. The model combines statistical fracture criteria, which are expressed in terms of damage concentrations, with the approximate model of microcrack accumulation under repeating loading of the same level. According to these criteria, the fatigue failure begins with the accumulation of separation- or shear-type microdefects up to the level of critical values of their density.

Findings

The failure mechanism is associated with the accumulation of dispersed microdamages under repeated loading. The critical value of the density of the microdamages, which are identified with those formed either by separation or shear under static loading in consequence of simple tension, compression or shear, is accepted as the criterion of the onset of fatigue failure. The fatigue being low-cycle or high-cycle is attributed to accumulation of shear microdamages in the region of plastic deformation in the former case and microdamages produced by separation under elastic deformation in the latter one.

Originality/value

The originality of the paper consists in the following. The authors theoretically define parameters of the fatigue failure (durability, fatigue limit, etc.) using the model in combination with the statistical failure (yield) criteria appearing in the damage measures. The constructed fatigue diagram has discontinuities on the conditional boundary dividing domains with the shear-type and separation-type fractures of structural elements. Such results are supported by the experimental results.

Details

International Journal of Structural Integrity, vol. 10 no. 4
Type: Research Article
ISSN: 1757-9864

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Article
Publication date: 27 January 2021

Amin S. Azar, Magnus Reiersen, Even W. Hovig, Mohammed M’hamdi, Spyros Diplas and Mikkel M. Pedersen

This study aims to introduce a novel approach in form of a comprehensive software suite to help understanding and optimizing the build orientation toward maximizing the…

Abstract

Purpose

This study aims to introduce a novel approach in form of a comprehensive software suite to help understanding and optimizing the build orientation toward maximizing the fatigue lifetime of complex geometries. The objective is to find an optimized build orientation under a given in-service loading state, which brings on smoother surfaces in stressed regions, mitigated roughness-induced stress concentration and deferred crack initiation stage. The solution addresses scenarios that no post-build surface treatment can be applied.

Design/methodology/approach

To account for the surface topography, the staircase induced surface roughness is registered as a function of build angle using the white light interferometry characterization, based on which the stress concentration factor (kt) is calculated. Thereafter, the developed module in “Fatlab toolbox” is used to find the optimum build angle, considering the integrated surface orientations and stress analysis under a given loading condition.

Findings

Surface topography creates local stress concentrations upon loading, directly influencing the fatigue lifetime. It is a well-established fact that the conditions of the staircase geometry and surface roughness affect the magnitude of the stress concentration upon loading, which is influenced by the build orientation of the component. The proposed solution suggests the best build orientation that mitigates staircase-related surface roughness.

Originality/value

The suggested numerical approach assists the designers with positioning of the part on the build plate to minimize the build orientation-induced surface roughness and improve the as-built fatigue lifetime of the component.

Details

Rapid Prototyping Journal, vol. 27 no. 2
Type: Research Article
ISSN: 1355-2546

Keywords

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Article
Publication date: 6 January 2020

Shijie Jiang, Yannick Siyajeu, Yinfang Shi, Shengbo Zhu and He Li

The purpose of this study is to investigate the efficiency of applied vibration in improving the forming quality (mechanical property and dynamics characteristics) of…

Abstract

Purpose

The purpose of this study is to investigate the efficiency of applied vibration in improving the forming quality (mechanical property and dynamics characteristics) of fused filament fabrication (FFF) parts.

Design/methodology/approach

A vibrating FFF three-dimensional printer was set up, with which the samples fabricated in different directions were manufactured separately without and with vibration applied. A series of experimental tests, including tensile tests, dynamics tests and scanning electron microscopy (SEM) tests, were performed on these samples to experimentally quantify the effect of applied vibration on their forming quality.

Findings

It has been found that the applied vibration can significantly increase the tensile strength and plasticity of the samples built in Z-direction, and obviously decrease the orthogonal anisotropy. It can also significantly change the sample’s natural frequency, decrease the resonant response and increase the modal damping ratio, thus improve the anti-vibration capability of FFF samples. In addition, the SEM analysis confirmed that applying vibration into FFF process could improve the forming quality of the fabricated part.

Research limitations/implications

Future research may be focused on investigating the efficiency of applied vibration in improving the forming quality of parts fabricated by the other additive manufacturing techniques.

Practical implications

This study helps to improve the reliability of FFF parts and extend the application range of FFF technology.

Originality/value

A novel method to improve the forming quality of FFF parts is provided and the available information about the performance of dynamics characteristics.

Details

Rapid Prototyping Journal, vol. 26 no. 1
Type: Research Article
ISSN: 1355-2546

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Article
Publication date: 3 February 2021

Ali Alperen Bakır, Resul Atik and Sezer Özerinç

This paper aims to provide an overview of the recent findings of the mechanical properties of parts manufactured by fused deposition modeling (FDM). FDM has become a…

Abstract

Purpose

This paper aims to provide an overview of the recent findings of the mechanical properties of parts manufactured by fused deposition modeling (FDM). FDM has become a widely used technique for the manufacturing of thermoplastic parts. The mechanical performance of these parts under service conditions is difficult to predict due to the large number of process parameters involved. The review summarizes the current knowledge about the process-property relationships for FDM-based three-dimensional printing.

Design/methodology/approach

The review first discusses the effect of material selection, including pure thermoplastics and polymer-matrix composites. Second, process parameters such as nozzle temperature, raster orientation and infill ratio are discussed. Mechanisms that these parameters affect the specimen morphology are explained, and the effect of each parameter on the strength of printed parts are systematically presented.

Findings

Mechanical properties of FDM-produced parts strongly depend on process parameters and are usually lower than injection-molded counterparts. There is a need to understand the effect of each parameter and any synergistic effects involved better.

Practical implications

Through the optimization of process parameters, FDM has the potential to produce parts with strength values matching those produced by conventional methods. Further work in the field will make the FDM process more suitable for the manufacturing of load-bearing components.

Originality/value

This paper presents a critical assessment of the current knowledge about the mechanical properties of FDM-produced parts and suggests future research directions.

Details

Rapid Prototyping Journal, vol. ahead-of-print no. ahead-of-print
Type: Research Article
ISSN: 1355-2546

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Article
Publication date: 20 July 2020

Lukas Englert, Stefan Dietrich and Pascal Pinter

The purpose of this paper is to understand the relationship between defect properties and the tool path used for generating additively manufactured parts. The correlation…

Abstract

Purpose

The purpose of this paper is to understand the relationship between defect properties and the tool path used for generating additively manufactured parts. The correlation between processing strategy and porosity architecture is one of the key aspects for a precise understanding of defect formation and possibilities for defect reduction.

Design/methodology/approach

The authors present a new combined geometry, processing path and porosity analysis procedure based on the use of x-ray computed micro tomography image data and numerical control programming code. The procedure allows for a covisualisation of the track of the respective processing head with the three-dimensional microstructure data.

Findings

The presented method yields statistical results about defect distribution and morphologies introduced by the respective process characteristics in parts. The functionality of the proposed procedure is demonstrated on an aluminum (AlSi10Mg) and a polylactide test sample to show the additional insight found for both additive manufacturing processes and the resulting microstructural properties.

Originality/value

The novelty of this paper is the analysis of the porosity with respect to the underlying additive process zone and the sample geometry.

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Article
Publication date: 1 May 2005

Francesco Bellomi, Matteo Cristani and Roberta Cuel

Purpose – Several systems for the management of digital libraries have evolved in the recent past from simple document repository to sophisticated applications that…

Abstract

Purpose – Several systems for the management of digital libraries have evolved in the recent past from simple document repository to sophisticated applications that provide the possibility of classifying and, in some cases, even rating the documents collected in the library itself. In a few of those systems members of the community of practice that uses and produces the library itself can also be active in assigning a reputation score to each other. This study aimed to explore the idea of using a collectively negotiated term taxonomy in order to develop a better model for the automated evaluation of users’ competence on different discussion topics. Design/methodology/approach – The study provides a formalization of the approach we propose, and the proposal of an architecture for implementing a system deploying the approach. Findings – The study analyses the issues related to the implementation of a digital library, and develops an architecture that aims to evaluate users’ competence about different discussion topics in an automated way. Research limitations/implications – The paper only describes an abstract architecture of a self‐balancing digital library. Further research should investigate the different possible choices for the implementation details that have been left out from this first explorative analysis. Originality/value – The novelty of the approach resides in the fact that we make use of a collectively negotiated taxonomy in order to automatically assign relevance scores to reviewers’ evaluations.

Details

Library Management, vol. 26 no. 4/5
Type: Research Article
ISSN: 0143-5124

Keywords

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Article
Publication date: 1 May 1987

Geraint G. Howells

The four sections to this article have distinct but inter‐related objectives. Part I introduces the concepts, problems and tensions central to an understanding of the…

Abstract

The four sections to this article have distinct but inter‐related objectives. Part I introduces the concepts, problems and tensions central to an understanding of the product liability debate. These issues recur throughout the article. Part II outlines the development of product liability law in Europe and assesses the impact of the European Directive on Product Liability. The “product liability crisis” in the United States is discussed in Part III, which looks at the law's development and proposals for reform. In Part IV the United States and European positions are compared and the case is made out for a global uniform product liability law which recognises the social responsibility of the producer towards those injured by his products.

Details

Managerial Law, vol. 29 no. 5/6
Type: Research Article
ISSN: 0309-0558

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Article
Publication date: 23 August 2013

Meriel Huggard and Ciarán Mc Goldrick

The purpose of this study is to evaluate a practical laboratory task where final year undergraduate students design, implement and validate an inferred security wireless…

Abstract

Purpose

The purpose of this study is to evaluate a practical laboratory task where final year undergraduate students design, implement and validate an inferred security wireless sensor access system.

Design/methodology/approach

The quality of the learning and technical environment was evaluated from a number of perspectives using a mixed methods approach where both quantitative and qualitative data was collected and analysed. Two‐tailed paired t‐tests were used to analyse data on student performance, while a targeted survey was used to assess the achievement of the learning outcomes. The students’ experience of working with the Sun Microsystems SunSPOTs was evaluated and the evolution of their perception of both ubiquity and security from inception to completion of the activity was explored.

Findings

The results of this study indicate that the students’ level of engagement with the assigned laboratory task was higher than with the two other forms of continuous assessment used on the module. Quantitative feedback gathered indicated that the learning outcomes were achieved, while the qualitative data indicated a high level of student satisfaction with the laboratory assignment.

Originality/value

A novel wireless sensor network laboratory that encourages students to engage with the concepts of ubiquity and security is presented and evaluated.

Details

Campus-Wide Information Systems, vol. 30 no. 4
Type: Research Article
ISSN: 1065-0741

Keywords

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Article
Publication date: 1 July 1987

Anna Pellanda

This article on Messedaglia might start with Schumpeter's words: “I have chosen him for mention because of the strategic position he holds in the history of Italian…

Abstract

This article on Messedaglia might start with Schumpeter's words: “I have chosen him for mention because of the strategic position he holds in the history of Italian economics and statistics”. In fact the Italian history of economics in the nineteenth century is populated by many authors who were rather famous during their lifetime but less and less appreciated later. Generally speaking it can be said, again with Schumpeter, that “the economic research which was done during this period in the various centres of national life … was not on the same level with the achievements of either the earlier times of Beccaria and Verri or the later times of Pantaleoni and Pareto…. And if it is true that “the political and administrative structure of every nation reflects itself in the organisation of its scientific work” (ibid.) the difficulties faced by Italy, trying first to get rid of foreign domination and, secondly, to build national unity, can explain the trouble Italian economists have had in disentangling themselves from foreign influence and in avoiding divisions into regional schools of thought. Angelo Messedaglia is one of the few able to be original and not provincial, as will be shown later; instead, at this point it would seem useful to give a brief account of the historical situation of Italy in the nineteenth century.

Details

International Journal of Social Economics, vol. 14 no. 7/8/9
Type: Research Article
ISSN: 0306-8293

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