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Article

Sam Joshy, Jayadevan K.R., Ramesh A. and Mahipal D.

In hot forging, a significant amount of forging force is used for overcoming frictional force at the die-billet interface. The high frictional force along with…

Abstract

Purpose

In hot forging, a significant amount of forging force is used for overcoming frictional force at the die-billet interface. The high frictional force along with thermomechanical stress lead to wear, plastic deformation, mechanical fatigue and cracks, which reduce the service life of hot forging dies. Of all these different types of issues, wear is the predominant mode of failure in hot forging dies. This paper aims to describe mechanisms of wear transition in different loads at near forging temperature, occurring during sliding of chromium-based H11 tool steel specimens.

Design/methodology/approach

High temperature pin-on-disc tests are performed with pin specimens machined from bars of X38CrMoV5 steel, heat treated to surface hardness of 40-42 HRc. The disc is made of EN 31 steel with hardness of 60-62 HRc. Tests are performed at constant temperature of 500°C, and the normal load was varied from 20 to 70 N.

Findings

Scanning electron microscopy investigations on worn surface have revealed that wear is primarily due to abrasion and plastic deformation. The test results show an increasing trend in wear rate with increase in load up to 30 N, followed by a reversal in trend until 50 N. This transition in wear rate is caused by development of wear resistant layers, which are formed by compaction of wear debris particles on to the worn surfaces. These compact layers are found to be stable during load range from 40 and 50 N. However, with further increase in load, abrasive wear tracks are observed without any evidence of protective layers. As a result, there is an increase in wear rate with increase in loads above 50 N. In addition, plastic shearing was dominant over abrasive wear at this load regime.

Originality/value

The study on wear behaviour of H11 hot forging steel at 20 to 70 N will be an input to the research in hot forming industries.

Details

World Journal of Engineering, vol. 16 no. 5
Type: Research Article
ISSN: 1708-5284

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Article

Sam Joshy, Jayadevan K.R., Ramesh A. and Mahipal D.

The prime task of research in hot forging industry is to improve the service life of forging dies. The in-service microstructural changes that may occur in a die during…

Abstract

Purpose

The prime task of research in hot forging industry is to improve the service life of forging dies. The in-service microstructural changes that may occur in a die during hot forging is expected to significantly affect the service life. The purpose of this work is to analyse the microstructural evolution of double tempered hot forging dies in a real industrial environment, and the correlation of microstructural and microhardness evolution to the in-service wear and plastic deformation.

Design/methodology/approach

Specific hot forging tests were carried out on double tempered AISI H11 chromium tool steel for 100, 500 and 1,000 forging strokes. Macro analysis was conducted on die cross section to analyse the wear and plastic deformation at different stages of forging cycles. Microhardness and microstructural analyses were performed on the die surface after these forging tests.

Findings

The macro analysis on the transverse section of dies shows that wear is predominant during initial forging strokes, whereas plastic deformation is observed in later stages. Microstructural analyses demonstrate that during first 500 forging cycles, carbide population decreases at 63 per cent higher rate as compared to corresponding drop during 501 to 1,000 forging cycles. Additionally, the carbide size increases at all stages of forging cycle. Further, microstructural images from dies after 1,000 forging strokes show clustering and spherodisation of carbides by which the “blocky”-shaped carbides in pre-forging samples had spherodised to form “elongated spherical” structures.

Practical implications

The findings of this work can be used in hot forging industries to predict amount of wear and plastic deformation at different stages of service. From the results of this work, the service life of double tempered H11 hot forging dies used in forging without lubrication is within 501 to 1,000 forgings.

Originality/value

Most of the literatures are focussed on the cyclic softening of material at constant temperature. This work analyses the microstructural evolution of double tempered hot forging dies in a real industrial environment and correlates the microstructural and microhardness evolution to the in-service wear and plastic deformation.

Details

World Journal of Engineering, vol. 16 no. 5
Type: Research Article
ISSN: 1708-5284

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Book part

Dirk Baur

Existing multivariate generalized autoregressive conditional heteroskedasticity (GARCH) models either impose strong restrictions on the parameters or do not guarantee a…

Abstract

Existing multivariate generalized autoregressive conditional heteroskedasticity (GARCH) models either impose strong restrictions on the parameters or do not guarantee a well-defined (positive-definite) covariance matrix. I discuss the main multivariate GARCH models and focus on the BEKK model for which it is shown that the covariance and correlation is not adequately specified under certain conditions. This implies that any analysis of the persistence and the asymmetry of the correlation is potentially inaccurate. I therefore propose a new Flexible Dynamic Correlation (FDC) model that parameterizes the conditional correlation directly and eliminates various shortcomings. Most importantly, the number of exogenous variables in the correlation equation can be flexibly augmented without risking an indefinite covariance matrix. Empirical results of daily and monthly returns of four international stock market indices reveal that correlations exhibit different degrees of persistence and different asymmetric reactions to shocks than variances. In addition, I find that correlations do not always increase with jointly negative shocks implying a justification for international portfolio diversification.

Details

Econometric Analysis of Financial and Economic Time Series
Type: Book
ISBN: 978-0-76231-274-0

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Book part

Dekar Urumsah

The concept and practice of e-services has become essential in business transactions. Yet there are still many organizations that have not developed e-services optimally…

Abstract

The concept and practice of e-services has become essential in business transactions. Yet there are still many organizations that have not developed e-services optimally. This is especially relevant in the context of Indonesian Airline companies. Therefore, many airline customers in Indonesia are still in doubt about it, or even do not use it. To fill this gap, this study attempts to develop a model for e-services adoption and empirically examines the factors influencing the airlines customers in Indonesia in using e-services offered by the Indonesian airline companies. Taking six Indonesian airline companies as a case example, the study investigated the antecedents of e-services usage of Indonesian airlines. This study further examined the impacts of motivation on customers in using e-services in the Indonesian context. Another important aim of this study was to investigate how ages, experiences and geographical areas moderate effects of e-services usage.

The study adopts a positivist research paradigm with a two-phase sequential mixed method design involving qualitative and quantitative approaches. An initial research model was first developed based on an extensive literature review, by combining acceptance and use of information technology theories, expectancy theory and the inter-organizational system motivation models. A qualitative field study via semi-structured interviews was then conducted to explore the present state among 15 respondents. The results of the interviews were analysed using content analysis yielding the final model of e-services usage. Eighteen antecedent factors hypotheses and three moderating factors hypotheses and 52-item questionnaire were developed. A focus group discussion of five respondents and a pilot study of 59 respondents resulted in final version of the questionnaire.

In the second phase, the main survey was conducted nationally to collect the research data among Indonesian airline customers who had already used Indonesian airline e-services. A total of 819 valid questionnaires were obtained. The data was then analysed using a partial least square (PLS) based structural equation modelling (SEM) technique to produce the contributions of links in the e-services model (22% of all the variances in e-services usage, 37.8% in intention to use, 46.6% in motivation, 39.2% in outcome expectancy, and 37.7% in effort expectancy). Meanwhile, path coefficients and t-values demonstrated various different influences of antecedent factors towards e-services usage. Additionally, a multi-group analysis based on PLS is employed with mixed results. In the final findings, 14 hypotheses were supported and 7 hypotheses were not supported.

The major findings of this study have confirmed that motivation has the strongest contribution in e-services usage. In addition, motivation affects e-services usage both directly and indirectly through intention-to-use. This study provides contributions to the existing knowledge of e-services models, and practical applications of IT usage. Most importantly, an understanding of antecedents of e-services adoption will provide guidelines for stakeholders in developing better e-services and strategies in order to promote and encourage more customers to use e-services. Finally, the accomplishment of this study can be expanded through possible adaptations in other industries and other geographical contexts.

Details

E-services Adoption: Processes by Firms in Developing Nations
Type: Book
ISBN: 978-1-78560-709-7

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Article

Carmen Medrea, Antonios Kalfopoulos, Dimitrios Papageorgiou and Ionel Chicinas

A local company producing aluminum profile encounters frequent failures to bridge dies. In total, 22 dies failed within a year, entailing production disruptions and…

Abstract

Purpose

A local company producing aluminum profile encounters frequent failures to bridge dies. In total, 22 dies failed within a year, entailing production disruptions and extensive downtimes. Bridges usually exhibit cracks on the ribs. The failure analysis of the failed parts has been performed in order to propose solution for correct and economical process. The paper aims to discuss these issues.

Design/methodology/approach

Recorded history was collected regarding tool’s material selection, manufacturing conditions, usage and service. A representative failed bridge was in depth analyzed. The piece was optically inspected. Rockwell hardness measurements and chemical analysis were performed. The paper is focussed on the microscopic examination of the failed parts. Specimens were cut from bridge’s ribs. Areas including cracks were analyzed on the cross section of the samples by optical and scanning electron microscopy. Local chemical analysis was made by X-ray microanalysis.

Findings

Design, deficiency and improper maintenance are considered to be responsible for the systematic die damage. Prolonged preheating duration and poor quality surfaces before nitriding render dies premature unusable. The preheating duration should be controlled and protective atmosphere should be used. Furthermore, it is suggested to protect the ribs during nitriding as a preventive measure against crack initiation. The bridge’s geometry can be improved by fabricating ribs with larger radii. A finer polishing is recommended.

Originality/value

The present analysis resolved a serious deficiency in extrusion production. Extended research has been conducted in the field of aluminum extrusion dies, nevertheless, the present work presents new metallographic aspects as well as some interesting notes regarding the repetitive nitriding of bridge dies.

Details

International Journal of Structural Integrity, vol. 6 no. 5
Type: Research Article
ISSN: 1757-9864

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Article

Maja Konecnik

The paper points out the image of a destination as a possible source of competitive advantage of the destination. A review of the literature is included showing the rising…

Abstract

The paper points out the image of a destination as a possible source of competitive advantage of the destination. A review of the literature is included showing the rising importance of the image of a destination. Slovenia's image as a tourist destination perceived by foreign tourist experts is analysed. Interesting mountains and lakes, beautiful natural attractions and interesting and friendly people were identified as the most typical attributes of Slovenia's image from the foreign tourist experts' point of view. The significant differences in Slovenia's image between those experts familiar with Slovenia compared to those experts who are only just aware of Slovenia are presented. The research shows that familiarity with Slovenia increases a tourist expert's image of Slovenia, especially the perceptual/cognitive component. According to the results of discriminant analysis, the discriminant attributes of Slovenia's image for each group are emphasised. Slovenia's appealing food and modern health resorts were the discriminant attributes for the group of tourist experts that is familiar with Slovenia, while traditional events were the distinguish attribute for the group of experts that is only just aware of Slovenia. Suggestions as organising familiarisation tours that include tour operators, travel agents and travel writers seemed to be a proper way of boosting Slovenia's image compared to other competitive tourist destinations.

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Article

D.D. Bainov and I.M. Stamova

Investigates the global stability of the zero solution of an impulsive system of differential‐difference equations with variable impulsive perturbations. By means of…

Abstract

Investigates the global stability of the zero solution of an impulsive system of differential‐difference equations with variable impulsive perturbations. By means of piecewise continuous functions which are analogues of Lyapunov’s functions, and of the comparison principle, sufficient conditions for global stability of the zero solution of the systems considered are found.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 16 no. 1
Type: Research Article
ISSN: 0332-1649

Keywords

Content available
Article

Hina Amin and Munawar Sultana Mirza

This paper intended to explore the knowledge and use of the digital verbs and tools by the students and teachers for conceptual understanding in the virtual and…

Abstract

Purpose

This paper intended to explore the knowledge and use of the digital verbs and tools by the students and teachers for conceptual understanding in the virtual and conventional learning environment. The study also explored the use of such digital tools for lower- and higher-order thinking.

Design/methodology/approach

A survey research method was used for the study. All the students and teachers of the faculty of education from one virtual and one conventional university were the population of this study. Teachers were selected through census sampling. Student enrollment in the faculty of education of the virtual university during Spring 2019 was 1,139 while the conventional university had 1,809 students. In total, 20% of the students from each of the two universities were sampled by using a convenient proportionate sampling technique. A questionnaire was developed by the researchers and validated by three experts before administration. The reliability of the instrument was a = 0.934. Mean, SD, parametric and nonparametric statistics were applied for data analysis.

Findings

The study reveals that the students of ODL are far better in using digital tools and activities that is, googling, collaborating and Skyping. They are good at understanding and application levels and are involved in higher-order thinking tasks, that is, publishing and podcasting as well. Unlike the students, the teachers of the virtual university are using digital tools of lower-order thinking. The authors infer that the students and teachers of the online universities are using these tools regularly because of the demands of the ODL environment. These findings suggest further research to explore the factors that hinder the use of higher-order thinking skills by the teachers in the online environment.

Originality/value

The study suggests the adoption of Bloom's digital taxonomy in teaching–learning processes, that is, curriculum, instructions and assessment for the millennials. The findings may motivate the online and conventional higher education institutions to adopt digital pedagogy for instructional purposes as the students of the digital age are already extensively involved with digital tools.

Details

Asian Association of Open Universities Journal, vol. 15 no. 2
Type: Research Article
ISSN: 1858-3431

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Book part

Yushi Yoshida

We investigate whether or not the effects of the subprime financial crisis on 12 Asian economies are similar to those of the Asian financial crisis by examining volatility…

Abstract

We investigate whether or not the effects of the subprime financial crisis on 12 Asian economies are similar to those of the Asian financial crisis by examining volatility spillovers and time-varying correlation between the US and Asian stock markets. After pretesting volatility causality and constancy of correlation, we estimate an appropriate smooth-transition correlation VAR-GARCH model for each Asian stock market. First, the empirical evidence indicates stark differences in stock market linkages between the two crises. The volatility causality comes from the crises-originating country. Volatility in Asian stock markets Granger-caused volatility in the US market during the Asian crisis, whereas volatility in the US stock market Granger-caused volatility in Asian stock markets during the subprime crisis. Second, decreased correlations during the period of financial turmoil were observed, especially during the Asian financial crisis. Third, the estimated points of transition in the correlation are indicative of market participants’ awareness of the ensuing stock market crashes in July 1997 and in September 2008.

Details

The Evolving Role of Asia in Global Finance
Type: Book
ISBN: 978-0-85724-745-2

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Article

Tanti Handriana, Praptini Yulianti, Masmira Kurniawati, Nidya Ayu Arina, Ratri Amelia Aisyah, Made Gitanadya Ayu Aryani and Raras Kirana Wandira

The purpose of this study is to analyze millennial generation purchase behavior on halal cosmetic products in Indonesia.

Abstract

Purpose

The purpose of this study is to analyze millennial generation purchase behavior on halal cosmetic products in Indonesia.

Design/methodology/approach

The research approach used is a quantitative approach with the research method in the form of a survey and the sampling technique using purposive sampling. The respondents in this study are 206 Muslim females of the millennial generation. Structural equation modeling (SEM) with AMOS software is used for analyzing the data of this study.

Findings

This study found that of the 11 hypotheses tested, 10 of them were accepted: H1, H2, H3, H4, H6, H7, H8, H9, H10 and H11. The accepted hypotheses are the influence of perceived value on trust, brand image on trust, brand image on attitude, religious belief on attitude, halal certification on halal awareness, trust on attitude and halal awareness on attitude. As for trust, attitude toward product, halal awareness affects the intention to purchase halal cosmetics. Moreover, H5 was not accepted, namely, the influence of religious belief on halal awareness. The findings of this study are expected to contribute to the development of marketing theory, specifically related to consumer behavior of halal cosmetic products, as well as the development of the concept of consumer behavior based on demographics, namely, the millennial generation.

Originality/value

This study is more comprehensive than previous studies, and this study is focused on the millennial generation.

Details

Journal of Islamic Marketing, vol. ahead-of-print no. ahead-of-print
Type: Research Article
ISSN: 1759-0833

Keywords

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