Search results

Fused deposition modeling enables multiscale structure control. However, most of this structural space is unexplored. Specifically, the impact of biomimetic porous structures on the mechanical behavior and reliability of common thermoplastics are unclear. In this work, porous structures inspired by the multifunctional crab exoskeleton were 3D-printed with different raster orientations, including fully rotating rasters similar to Bouligand structures found in biological materials. Tensile tests and simulations were performed to observe the stochastic behavior of fracture properties and to reveal the underlying origins of mechanical reliability in biomimetic porous systems.

Tensile tests were performed on 3D-printed porous structures with four different rasters. These rasters were biomimetic Bouligand, semi-Bouligand, 00 raster and 45°/−45° raster. In addition, two different sets were manufactured to observe the impact of contours on the mechanical behavior. A total of 137 tensile tests were performed. A total of 88 finite element simulations were executed using Abaqus built-in Hashin damage initiation criterion and energy-based damage evolution law. Weibull analyses were performed to quantify the stochastic properties.

Biomimetic Bouligand structure is effective in increasing fracture strength. Average fracture strength of the Bouligand structure was 33% higher compared to the default 45°/−45° and 10% higher compared to 00 rasters. Variations in strength were lower in Bouligand structure compared to the default 45°/−45° raster. However, 00 raster had the highest Weibull modulus m = 54 compared to Bouligand m = 25 and 45°/−45° m = 17. Simulations showed that Bouligand structure is effective in increasing the mechanical reliability through local damage accumulation around the holes. The simulated Weibull modulus of the Bouligand structure was 40 compared to the moduli of other rasters that ranged from 18 to 25.

The mechanical reliability of porous Bouligand structures is higher compared to other rasters, which makes the biomimetic structure a better choice for industrial applications. Contours decrease the strength and strain at failure for 3D-printed porous structures. Bouligand structures with rotating raster orientations increased strength and strain at failure when contours are present in the porous structure.

To the best of the authors’ knowledge, this is the first study showing the effects of biomimetic raster orientations on the mechanical behavior and the effects of contours on the tensile fracture properties of 3D-printed porous acrylonitrile butadiene styrene using tensile tests and fracture simulations. This is the first study applying composite fracture model to anisotropic porous 3D-printed polymers.

Mechanical reliability (variations in mechanical properties) of fused deposition modeled (FDMed) short-fiber-reinforced composites are unknown, which limits wider and safer use of these composites. Accordingly, this paper aims to investigate the mechanical reliability of FDMed model material short-carbon-fiber-reinforced acrylonitrile butadiene styrene (SCFR-ABS). A new vibration-assisted FDM (VA-FDM) process was used to reduce porosity.

Tensile tests were performed on FDMed SCFR-ABS produced with and without vibrations. Weibull analysis was performed to quantify the variation in fracture strength, tensile strength, strain at break and strain at tensile strength.

Introduction of vibrations to the extrusion head during FDM decreased the inter-bead porosity in SCFR-ABS and thus improved elastic modulus, toughness, fracture strength, tensile strength and strain at break. Weibull modulus of fracture strength increased from 25 to 57 with vibrations.

The reported Weibull analysis offers a practical design guideline to predict failure rates at specific service stresses.

A detailed Weibull analysis of the variations in the mechanical properties of FDMed SCFR-ABS was performed for the first time. A new vibration-assisted FDM process was reported to reduce inter-bead porosity in FDMed composites.

Increasing use of 3D printing techniques to manufacture consumer products and open-source designs raises the question of “What is the mechanical reliability of 3D printed parts?” Therefore, the purpose of this paper is to investigate the impacts of build orientation on the mechanical reliability of acrylonitrile butadiene styrene (ABS) produced using 3D printing.

Tensile tests on ABS specimens were performed with and without a hole in the center, which were produced by fused deposition modeling (FDM). Seven sets of approximately 30 specimens were printed in XY, XZ and C+45 orientations to obtain reliable fracture statistics. Weibull analysis was performed to quantify the variation in the tensile strength.

The Weibull analysis showed that the reliability of FDM produced ABS can be as low as advanced ceramics. Weibull moduli of specimens without a hole were between 26 and 69, and specimens with a hole had Weibull moduli between 30 and 41. P-type deviations from the Weibull statistics were observed. The XZ orientation resulted in the highest average fracture strength for specimens with and without a hole, and C+45 orientation resulted in the lowest strength.

As the Weibull distribution relates the applied stress to probability of failure, the Weibull analysis provides a practical design criterion to achieve specific reliability levels for additively manufactured parts.

This study, for the first time, provides Weibull statistics for FDM-produced ABS parts, which can be used to predict mechanical reliability.

Fused filament fabrication of continuous-fiber-reinforced polymers is a promising technique to achieve customized high-performance composites. However, the off-axis tensile strength (TS) and Mode I fracture toughness of fused filament fabricated (FFFed) continuous-glass-fiber-reinforced (CGFR) nylon are unknown. The purpose of this paper is to investigate the mechanical and fracture behavior of FFFed CGFR nylon with various fiber content and off-axis fiber alignment.

Tensile tests were performed on FFFed CGFR-nylon with 9.5, 18.9 and 28.4 fiber vol. %. TS was tested with fiber orientations between 0^∘ and 90^∘ at 15^∘ intervals. Double cantilever beam tests were performed to reveal the Mode I fracture toughness of FFFed composites.

TS increased with increasing fiber vol. % from 122 MPa at 9.5 vol. % to 291 MPa at 28 vol. %. FFFed nylon with a triangular infill resulted in 37 vol. % porosity and a TS of 12 MPa. Composite samples had 11–12 vol. % porosity. TS decreased by 78% from 291 MPa to 64 MPa for a change in fiber angle θ from 0^∘ (parallel to the tensile stress) to 15^∘. TS was between 27 and 17 MPa for 300 < θ < 900. Mode I fracture toughness of all the composites were lower than ∼332 J/m2.

Practical applications of FFFed continuous-fiber-reinforced (CFR) nylon should be limited to designs where tensile stresses align within 15^∘ of the fiber orientation. Interlayer fracture toughness of FFFed CFR composites should be confirmed for product designs that operate under Mode I loading.

To the best of the authors’ knowledge, this is the first study showing the effects of fiber orientation on the mechanical behavior and effects of the fiber content on the Mode I fracture toughness of FFFed CGFR nylon.

With the irresistible growth in digitization, data backup policies become essential more than ever for organizations seeking to improve reliability and availability of organizations' information systems. However, since backup operations do not come free, there is a need for a data-informed policy to decide how often and which type of backups should be taken. In this paper, the authors present a comprehensive mathematical framework to explore the design space for backup policies and to optimize backup type and interval in a given system. In the authors' framework, three separate cost factors related to the backup process are identified: backup cost, recovery cost and data loss cost. The objective function has a multi-criteria structure leading to a backup policy minimizing a weighed function of these factors. To formalize the cost and objective functions, the authors get help from renewal theory in reliability modeling. The authors' optimization framework also formulates mixed policies involving both full and incremental backups. Through numerical examples, the authors show how the authors' optimization framework could facilitate cost-saving backup policies.

The methodology starts with designing different backup policies based on system parameters. Each constructed policy is optimized in terms of backup period using renewal theory. After selecting the best back-up policy, the results are demonstrated through numerical studies.

Data backup polices that are tailored to system parameters can result in significant gains for IT (Information Technology) systems. Collecting the necessary parameters to design intelligent backup policies can also help managers understand managers' systems better. Designed policies not only provides the frequency of back up operations, but also the type of backups.

The original contribution of this study is the explicit construction and determination of the best backup policies for IT systems that are prone to failure. By applying renewal theory in reliability, the authors present a mathematical framework for the joint optimization of backup cost factors, i.e. backup cost, recovery time cost and data loss cost.

Multinational companies whose importance has increased or improved depending on global capitalisation and travelling around the world without knowing borders have activities in developing countries due to suitable conditions (e.g. cheap workers costs, flexible legal arrangements). In this study, the precautions set forth to prevent environmental troubles, to obliterate or to minimise it, are the activities undertaken by the multinational companies which are considered. In the study, Turkey as a case country in which this subject was studied. Globalisation is the last step of economical sovereignty set up by means of multinational companies all over the world by capitalism which affects our age deeply. Unlimited capital stocks of capitalism and its economical development aim “whatever the result is” fastens the problems internationally as a result of not recognizing the social developments and justice, inequality, poverty and unsocializing people in developing countries. As a result of this, we're having environmental problems, the speed of nature's being consumed has been increased and there have been troubles almost every field of the social lives. However there is no one else who accepts the responsibilities of cost and social policies in the global economies in which international capital and global corporations decide on the rules; there is also no one else who accepts the responsibilities of environmental pollution and natural possessions' destruction as the result of the activities of international capital and global companies. The reason for this is that it is assumed that the government must take the responsibility “to protect and to development the environment”. According to this idea, protecting and developing the environment has been supplying public use and public service. Thus public service is the duty of the state. Environmental rights subject, known as third generation rights or corporation rights, is to protect the environment and to development it. People who have the environmental rights are those actors who will make use of these rights and who will have the responsibilities of these rights. The people who will make use of these rights and who will have the responsibilities are generally the same actors. These are not only the people but also public and special institutions including communities; states and public; and the next generation. In this case, all the right owners who have the rights to live in a healthy and well balanced environment are obliged to protect and to development the environment at the same time, including the multinational companies. Every economic activity has an effect on the environment. Multinational companies have activities in the fields like gold mining, petrol, chemicals and food industry which have high potential effects on the environment in developing countries like Malaysia, Indonesia and Nigeria. On this point the question why multinational companies choose these countries should be answered. The answer doesn't only help to explain the issue's political sides but also it could show that the most dirtying foreign capital activities take place in developing countries. Why multinational companies have chosen these developing countries was studied under two titles. (1) Dirtying industries are choosing the countries which don't have severe legal arrangements, (2) The public opinion in developing countries is unconscious of the harms that economical activities give to the environment. If the first finding hadn't been true, the activities in most polluting sectors wouldn't have been directed to the countries where environmental laws are flexible/flexibly practised. Besides, the public opinion in these low educational level countries doesn't have enough knowledge about the environmental problems and importance of environment. This information also gives assurance to the multinational companies that they don't face with the opposing activities of the public there. Nevertheless, foreign capital is wanted by these countries to supply new technologies, to supply the political and economical support of the countries which export development and capital, to open their economy to other countries and to protect the environment of the country. But, in practice, these countries which are under pressure to pay their debts don't pay attention to the ecological defects of the activities let the multinational companies to settle in the country, import the wastes which supply currency entrance, to be stored in the national borders and to be reused without evaluation. Foreign capital entrance in gold mining fields is a small example about being served and defended as a gold opportunity to pay Turkey's foreign debts. As a result, multinational companies are unsuccessful in sharing environmental responsibilities in the developing countries. Multinational companies have been making use of the opportunities that the environment presents but they don't do their duties to environmental rights. The efforts by multinational companies have been improving as prevention of increasing the environmental standards. Related to this, in the countries mentioned and also in Turkey, where economical activity fields like ecological sensitivity isn't assured enough by law and isn't protected wholly is a kind of great danger for Turkey.

In this study, industrialisation has been evaluated in the context of social change theory. Industrialisation as a period of social change is the source of public library development. The public library has emerged as a result of the changes in educational and cultural structure caused by industrialisation. Public libraries emerged as supporting elements of basic and adult diffused education effort. The change in thoughts, attitudes and values by the effect of urbanisation made public libraries a part of the new culture that is social life. The public library is a product of social change.

Along with accounting scandals in the past, academics, researchers, and legislators have focused on fraud. The purpose of this study is to examine postgraduate and doctoral studies, articles, and books about forensic accounting and fraud audit published between the years 2008 and 2018 in Turkey. For this purpose, a total of 96 studies have been examined and 35 of these are master’s theses, 10 of them are PhD theses, 45 of them are articles, and six of them are books. These studies were presented in tables as classified. The studies examined in our research are summarized as year they were published, the author, and the scope of the topic and in terms of results. The conclusions of this study can be summarized as follows: (a) the majority of thesis published about forensic accounting and fraud audit are in 2011 and following years. In addition, most of the theses are focused on forensic accounting review rather than fraud audit. (b) Results in the articles reviewed are in the same direction with theses. (c) There are very few books about fraud audit and forensic accounting. One of them is related to fraud audit, while the rest of them are related to forensic accounting and forensic accounting profession. We suggest extending the scope of the study and making to other countries.

This paper aims to explore Turkey’s current energy status with a on renewable energy sources (RES) cooperation mechanisms, within the framework of RES Directive 2009/28/EC. The study uses the SWOT (strengths, weaknesses, opportunities, threats) analysis for drawing results about perspectives of RES cooperation between Turkey and European Union (EU) Member States. In particular, the SWOT analysis provides a clearer view of expanding RES in Turkey, as well as the level of utilization and potential of cooperation mechanisms and renewable energy in the country.

The approach followed incorporates desktop analysis, stakeholders’ mapping and involvement, key factors’ identification and results analysis and validation. The adopted approach is based on research conducted within the context of the “Bringing Europe and Third countries closer together through renewable Energies (BETTER)” (project number: IEE/11/845/SI2.616378) project, co-financed by the Intelligent Energy Europe Programme.

Based on the SWOT analysis conducted for Turkey, there are huge opportunities for RES deployment and cooperation in the country, because of its large unexploited RES potential. Turkey is a country with strategic importance, e.g. regarding energy security. Substantial savings can occur for the EU28 Member States through this cooperation, whereas Turkey will also benefit through income and investments, as well as technology transfers and further synergies associated with the cooperation. For the above potentials to be reached, nevertheless, national policies for RES development would have to be strengthened substantially, and non-economic barriers mitigated.

The potential of Turkey to utilise cooperation mechanisms provides opportunities for RES exporting between the country and EU countries. An analysis of these opportunities for cooperation will allow drawing clearer conclusions on cooperation potentials and business cases for Turkey.