Search results

The purpose of this study is to evaluate the capability and performance of analytical models to predict the structural mechanical behaviour of parts fabricated by fused deposition modelling (FDM).

A total of eight existing and newly proposed analytical models, tailored to satisfy the structural behaviour of FDM parts, are evaluated in terms of their capability to predict the ultimate tensile stress (UTS) and the elastic modulus (E) of parts made of polylactic acid (PLA) by the FDM process. This evaluation is made by comparing the structural properties predicted by these models with the experimental results obtained from tensile tests on FDM specimens fabricated with variable infill percentage, perimeter layers and build orientation.

Some analytical models are able to predict with high accuracy (prediction errors smaller than 5%) the structural behaviour of FDM and categories of similar additive manufactured parts. The most accurate model is Gibson’s and Ashby, followed by the efficiency model and the two new proposed exponential and variant Duckworth models.

The study has been limited to uniaxial loading conditions along three different build orientations.

The structural properties of FDM parts can be predicted by analytical models based on the process parameters and material properties. Product engineers can use these models during the design for the additive manufacturing process.

Existing methods to estimate the structural properties of FDM parts are based on experimental tests; however, such methods are time-consuming and costly. In this work, the use of analytical models to predict the structural properties of FDM parts is proposed and evaluated.

This paper aims to investigate the structural behaviour of polylactic acid (PLA) parts fabricated by fused deposition modelling (FDM) to support the development of analytical and numerical models to predict the structural performance of FDM components and categories of similar additive manufactured parts.

A new methodology based on uniaxial tensile tests of filaments and FDM specimens, infill measurement and normalization of the results is proposed and implemented. A total of 396 specimens made of PLA were evaluated by using variable process parameters.

The infill and the build orientation have a large influence on the elastic modulus and ultimate tensile stress, whereas the layer thickness and the infill pattern have a low influence on these properties. The elongation at break is not influenced by the process parameters except by the build orientation. Furthermore, the infill values measured on the test specimens differ from the nominal values provided by the system.

The analysis of the structural properties of FDM samples is limited to uniaxial loading conditions.

The obtained results are valuable for the structural analysis and numerical simulation of FDM components and for potential studies using machine learning techniques to predict the structural response of FDM parts.

A new experimental methodology that considers the measurement of the real infill percentage and the normalization of the results for inter-comparison with other studies is proposed. Moreover, a new set of experimental results of FDM-PLA parts is presented and extends the existing results in the literature.

This paper aims to report the development and key features of a novel virtual reality system for assembly planning and evaluation called Haptic Assembly and Manufacturing System (HAMS). The system is intended to be used as a tool for training, design analysis and path planning.

The proposed system uses the physics-based modelling (PBM) to perform assemblies in virtual environments. Moreover, dynamic assembly constrains have been considered to reduce the degrees of freedom of virtual objects and enhance the virtual assembly performance.

To evaluate the effectiveness and performance of HAMS, the assembly of various mechanical components has been carried out, and the results have shown that it can be effectively used to simulate, evaluate, plan and automatically formalise the assembly of complex models in a more natural and intuitive way.

The collision detection performance is the bottleneck in any virtual assembly system. New methods of collision shape representation and collision detection algorithms must be considered.

HAMS introduces the use of dynamic assembly constraints to enhance the virtual assembly performance. HAMS also uses features not yet reported by similar systems in the literature. These features include: automatic or manual definition of assembly constraints within the virtual assembly system; the implementation of control panels and widgets to modify simulation parameters during running time to evaluate its influence on simulation performance; assembly data logging such as trajectories, forces and update rates for post-processing, further analysis or its presentation in the form of chronocyclegraphs to graphically analyse the assembly process.

In this study, a new methodology to evaluate the performance of physics simulation engines (PSEs) when used in haptic virtual assembly applications is proposed. This methodology can be used to assess the performance of any physics engine. To prove the feasibility of the proposed methodology, two-third party PSEs – Bullet and PhysXtm – were evaluated. The paper aims to discuss these issues.

Eight assembly tests comprising variable geometric and dynamic complexity were conducted. The strengths and weaknesses of each simulation engine for haptic virtual assembly were identified by measuring different parameters such as task completion time, influence of weight perception and force feedback.

The proposed tests have led to the development of a standard methodology by which physics engines can be compared and evaluated. The results have shown that when the assembly comprises complex shapes, Bullet has better performance than PhysX. It was also observed that the assembly time is directly affected by the weight of virtual objects.

A more comprehensive study must be carried out in order to evaluate and compare the performance of more PSEs. The influence of collision shape representation algorithms on the performance of haptic assembly must be considered in future analysis.

The performance of PSEs in haptic-enabled VR applications had been remained as an unknown issue. The main parameters of physics engines that affect the haptic virtual assembly process have been identified. All the tests performed in this study were carried out with the haptic rendering loop active and the objects manipulated through the haptic device.

This paper aims to investigate automatic assembly planning for robot and manual assembly.

The octree decomposition technique is applied to approximate a computer‐aided design model with an octree representation which is then used to generate robot and manual assembly plans. An assembly planning system able to generate assembly plans was developed to build these prototype models.

Octree decomposition is an effective assembly planning tool. Assembly plans can automatically be generated for robot and manual assembly using octree models.

One disadvantage of the octree decomposition technique is that it approximates a part model with cubes instead of using the actual model. This limits its use and applications when complex assemblies must be planned, but in the context of prototyping can allow a rough component to be formed which can later be finished by hand.

Assembly plans can be generated using octree decomposition, however, new algorithms must be developed to overcome its limitations.

This paper has proved that the octree decomposition technique is an effective assembly planning tool. As a result, an assembly planning system has been developed. Assembly plans for automatic and manual assembly can be generated automatically by the proposed system, which is a novelty since there are no fully automatic assembly planning systems for manual assembly reported in the literature.

The purpose of this paper is to prove that the abolition of state monopoly in the provision of educational services in Continental Europe will result in members of the educational community spending less time towards rent protection and more time towards educational activities, something that should also benefit the consumers of these services. It also aims to prove that once deregulation reform is introduced, those that now fiercely resist to it will, rationally, accept the new status quo and adapt to it.

The paper presents a model in which externalities affect the decision of the community of educational services providers to allocate time among their profession and towards opposing reform and protecting rents that follow from laws that establish state monopolies in the market for education services. The model proposed shows that, in the presence of such externalities, the introduction of reforms that remove the state monopoly will make the educational community adapt to the new status quo by allocating less time to protect monopoly rents and oppose reform, and more time and effort towards educational‐related activities like research and publications, high‐quality teaching and tutorials, etc.

The prediction of the assumed model that no internal forces can lead to a departure from the unfavorable equilibrium that exists before reform, underlines the need of society to press ahead with reforms regardless of the objections raised by the affected interest communities.

The paper provides for the first time in the relevant literature, an analysis of the harms and drawbacks of the higher education state monopoly in Continental Western Europe.

In the future, library applications related to traditional functions may increasingly assume some of the roles and characteristics of archives and museums. In this article, the author describes fundamental archival concepts and theories and their evolution in recent times. Basic archival functions—appraisal, arrangement, description, reference, preservation, and publication—are also introduced. Finally, early applications of automation to archives (including SPINDEX, NARS‐5, NARS‐A‐1, MARC AMC, presNET, CTRACK, PHOTO, and DIARY) and automation trends for the future are discussed. The article presents a cogent introduction to archival operations, thereby providing 1) a basis for understanding distinctions between current archival and library practices and 2) insight concerning the possible convergence of selected roles and functions.

Aim of the present monograph is the economic analysis of the role of MNEs regarding globalisation and digital economy and in parallel there is a reference and examination of some legal aspects concerning MNEs, cyberspace and e‐commerce as the means of expression of the digital economy. The whole effort of the author is focused on the examination of various aspects of MNEs and their impact upon globalisation and vice versa and how and if we are moving towards a global digital economy.

This paper seeks to contribute to an understanding of the organizational culture of the spin‐off knowledge‐based enterprises, which operate within the science and technology parks in Greece. In this context, a critical number of questionnaires have been distributed to the spin‐offs to examine whether firms born within the parks have developed a functional organizational culture, one that provides a solid foundation for organizational effectiveness and business excellence.

The Organizational Culture Assessment Questionnaire (OCAQ) was developed by Sashkin to help people identify and understand the nature of the culture in their own organization, as a first step in identifying problems and defining the sort of culture they want (and the sort of culture that will help deal with organizational problems). The data for the present study were obtained by the OCAQ mailed to a sample of 33 spin‐off companies that operate within the aforementioned science and technological parks. The mailing consisted of the questionnaire itself, a cover letter, and a stamped pre‐addressed return envelope. Of the 90 questionnaires mailed after phone contact, 33 were received, representing a 37 percent response rate.

There seems to have been ascertained serious organizational culture weaknesses regarding management of change practices, goal and customer orientation, cultural strength and efficient team working. It is of critical importance for policy makers to set general principles, guidelines as well as organizational reform measures and priorities to achieve better efficiency and effectiveness of spin‐offs in Greece and approach business excellence. Finally, implications for theory, managers and future research are presented.

This paper provides useful information on organizational culture assessment.

The purpose of this paper is to illustrate how a systematic application of middle-range theorizing, which pays particular attention to contexts and mechanisms, can be used to extend current knowledge on logistics customer service (LCS) in a number of critical areas.

The paper applies Stank et al.’s (2017) framework for middle-ranging theorizing in logistics to develop a research framework and agenda that can guide future LCS research. Results are generated through a review of the LCS literature and an application of the main concepts of middle-range theorizing.

The paper outlines opportunities for middle-range research that would extend LCS knowledge in the areas of human and behavioral factors, time-based competition, supply chain complexity, and digitization and technological innovation.

Describing the main characteristics of middle-range theorizing and how middle-range theorizing can be fruitfully applied to LCS research should help to stimulate new knowledge creation in this important area of supply chain logistics management.

By focusing on why and when questions, middle-range theorizing engages with the practical realities of LCS that interest managers and students. Middle-range theorizing moves researchers toward developing a detailed understanding of what actually has to change in order for desired LCS-related outcomes to occur and the contextual factors likely impacting the change process. The paper should, therefore, allow managers to better translate LCS theory into action.

Middle-range theorizing remains new to the supply chain logistics field. The application of middle-range theorizing to LCS research, and logistics research more generally, demands new perspectives on established relationships with the potential to drive original research in areas most relevant to managers.