1. Comparison of three methods of measuring residual stresses in welded joints of high-strength steel S960QLMirza Manjgo, Gorazd Lojen, Nenad Gubeljak, Blaž Karpe, Tomaž Vuherer, 2025, original scientific article Abstract: The influence of residual stresses as a result of the welding process in the overall stress state of the weld joint is of great importance because they significantly affect the creation and growth of cracks, the occurrence of brittle fracture, and material fatigue. Previous experiences indicate that it would be necessary to provide an assessment of the deformation and stress state in the critical zones of the weld joints using a suitable test method, which will not endanger the structural integrity of the tested places. There are different methods for measurement of residual stress in welded constructions: destructive, semi-destructive and non-destructive. To choose one method over another, it is necessary to take into account the advantages and limitations of these techniques for practical application. This paper considers and analyzes the residual stresses in the welded joint of high-strength steel S960QL. MAG welding was performed by a robot. Three methods were used to measure the residual stresses: the magnetic method (MAS), the X-ray diffraction method (XRD), and the hole drilling method (HD). By all three methods, the highest residual stresses were measured in the weld metal and in the heat-affected zones. Nevertheless, the measured values differed considerably. The differences can be contributed to (a) the kind of stress that the individual method measures, (b) to the volume of material from which each method captures the signal and averages it, and (c) to the different sensitivities of the applied methods to coarse-grained microstructure and microstructural gradients. Keywords: welded joints, high-strength steel, residual stress, magnetic method, X-ray diffraction method, hole drilling method Published in DKUM: 11.06.2025; Views: 0; Downloads: 4
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2. Copper sulfate elicitation effect on biomass production, phenolic compounds accumulation, and antioxidant activity of Morus nigra L. stem node cultureJan Senekovič, Špela Jelen, Andreja Urbanek Krajnc, 2025, original scientific article Abstract: Phenolic compounds are strong antioxidant and antibacterial agents with great pharmacological, medicinal, nutritional, and industrial value. The potential of Morus nigra in stem node culture was investigated for the production of phenolic compounds and their elicitation with CuSO4. Individual phenolic compounds in the samples were identified and quantified by using HPLC-PDA and HPLC-MS methods, while the content of total phenolic compounds, the content of total flavonoids, and the antioxidant activity of methanolic extracts were evaluated spectrophotometrically. The highest fresh and dry weights were obtained in plantlets treated with 0.5 mM CuSO4 for 42 days. The highest total phenolic content, total flavonoid content, and antioxidant activity of the extracts were determined in stem node cultures treated with 3 mM CuSO4 for 42 days. Under the latter conditions, the predominant representatives of the caffeoylquinic acids, p-coumaric acid derivatives, kaempferol derivatives, and quercetin derivatives also achieved the highest content. The most abundant phenolic compound in all samples was the chlorogenic acid. The nodal culture of M. nigra elicited with CuSO4 could potentially be used for the industrial production of phenolic compounds, especially caffeoylquinic acids. Moreover, considering the biochemical response to CuSO4 treatment and the ability to tolerate and accumulate copper, the potential application of M. nigra in phytoremediation is also highlighted. Keywords: antioxidative potential, black mulberry, copper stress, elicitation of phenolics, flavonoids, in vitro culture, nodal culture, phenolic acids Published in DKUM: 25.03.2025; Views: 0; Downloads: 10
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3. Structural integrity and life assessment of Ti-6Al-4V orthopaedic implantsKatarina Čolić, Svetlana M. Kostić, Simon Sedmak, Nenad Gubeljak, Aleksandar Grbović, 2024, original scientific article Abstract: This paper presents an experimental and numerical analysis of the mechanical behaviour of orthopaedic implants with crack-type defects, considering the principles and advantages of the modern X-FEM method, which was used due to limitations of traditional FEM in terms of crack growth simulation, especially for complex geometries. In X-FEM, the finite element space is enriched with discontinuity functions and asymptotic functions at the crack tip, which are integrated into the standard finite element approximation using the unity division property. Though rare, femoral component failures are well-documented complications that can occur after hip prosthetic implantation. Most stem fractures happen in the first third of the implant due to the loosening of the proximal stem and fixation of the distal stem, leading to bending and eventual fatigue failure. The main goal of this paper was to obtain accurate and representative models of such failures. Experimental analyses of the mechanical behaviour of implants subjected to physiological loads, according to relevant standards, using a new combined approach, including both experiments and numerical simulations was presented. The goal was to verify the numerical results and obtain a novel, effective methodology for assessing the remaining fatigue life of hip implants. For this purpose, the analysis of the influence of Paris coefficients on the total number of cycles was also considered. Hence, this simulation involved defining loads to closely mimic real-life scenarios, including a combination of activities such as ascending stairs, stumbling, and descending stairs. The tensile properties of the titanium alloy were experimentally determined, along with the Paris law coefficients C and m. The finite element software ANSYS 2022R2 version was used to develop and calculate the three-dimensional model with a crack, and the resulting stresses, stress intensity factors, and the number of cycles presented in the figures, tables, and diagrams. The results for the fatigue life of a partial hip implant subjected to various load cases indicated significant differences in behaviour, and this underscores the importance of analysing each case individually, as these loads are heavily influenced by each patient’s specific activities. It was concluded that the use of numerical methods enabled the preliminary analyses of the mechanical behaviour of implants under fatigue loading for several different load cases, and these findings can be effectively used to predict the possibility of Ti-6Al-4V implant failure under variable cyclic loads. Keywords: structural integrity, fatigue fracture, extended finite element method (XFEM), experimental testing, DIC, numerical simulations, stress intensity factor, orthopaedic implants, crack-type defect Published in DKUM: 21.03.2025; Views: 0; Downloads: 8
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4. A comparative study using two SEM techniques on different samples sizes for determining factors of older employeeʹs motivation and satisfactionMaja Rožman, Polona Tominc, Borut Milfelner, 2020, original scientific article Abstract: The purpose of this article is to present the relationships among older employee stress, motivation, satisfaction, and relationships in the workplace using two different approaches and different sample sizes. Research was implemented on an initial sample of 1013 older employees. In the next step, six smaller samples were calculated using the random selection of cases, namely samples with 25, 50, 100, 250, 400, and 500 older employees. This way the possible impact of sample size on relationships between latent variables using the covariance-based structural equation modeling (CB-SEM) and the partial least squares structural equation modeling (PLS-SEM) methods was assessed. The results on the larger samples have proved to be quite robust since they were confirmed with both approaches. They indicate that stress has a strong and negative impact on employee relationships and also a negative impact on employee satisfaction. Furthermore, employee relationships have a strong and positive impact on satisfaction and a positive impact on employee motivation. In addition, satisfaction has a strong and positive impact on employee motivation. The present paper helps readers to better understand the difference between the CB-SEM and the PLS-SEM methods. Researchers should be encouraged to use both techniques, even though CB-SEM methods have had a long tradition in management and marketing research since both fields heavily rely on psychometric measurement. From the organizational point of view, conclusions highlight the importance of the impact the variables of older employee stress, motivation, satisfaction and employee relations have on each other in the workplace. Keywords: stress, employee motivation, employee satisfaction, employee relations Published in DKUM: 10.03.2025; Views: 0; Downloads: 8
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5. A comprehensive approach in medical nutrition therapy for adults' weight loss management in LebanonMarie Therese Khalil, Joseph Matta, Mateja Videmšek, Damir Karpljuk, Maja Meško, 2020, original scientific article Abstract: The objective of the research is to identify the different factors of Lebanese culture that interfere with weight loss therapy and assist the field of nutrition in homogenising in a standardised manner the protocol of Medical Nutrition Therapy (MNT). The first part of the study is based on a literature review, and, in the second part, quantitative analysis was used. The research was conducted on 514 Lebanese adults via questionnaire. The analysis was performed with the AMOS (Version 22, IBM®, Amonk, NY, USA) statistical tool. For the analysis of correlations, chi-square and non-parametric tests were used. Variables affecting weight loss management were identified with the aid of seven hypotheses using structural equation modelling (SEM). Body shape and Body Mass Index (BMI) were found to be inter-related to cognitive behaviours toward food, lifestyle practices, medical conditions, food and beverages. In parallel, and based on the research results, younger adults, in particular women, have better BMI and look better in terms of body shape. Ageing has a direct impact on weight gain. Older people have a lower activity level, which is more prevalent among women, and they also prefer to eat typical Lebanese food. Habits, such as smoking, drinking alcohol, are directly related to obesity and some medical conditions. Low physical activity influences the problems related to body shape. For further studies, one should also include types of physical activities in terms of intensity and number of hours. This would assist the study in being more specified and credible toward the effect of exercise on weight loss management. Keywords: medical nutrition therapy, weight loss management, cost-effectiveness, anthropometry, culture, stress, physical activity Published in DKUM: 24.01.2025; Views: 0; Downloads: 6
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6. Quality of life and health status in middle-aged presumed healthy Slovenian family practice attendeesMatic Tement, Polona Selič-Zupančič, 2021, original scientific article Abstract: Background: There is a gap in our knowledge of health-related quality of life (HRQoL) in a population presumed healthy, so this study aimed to assess the associations between HRQoL, demographics and clinical variables.
Methods: The participants were attendees, presumed healthy, at 40 pre-selected model family medicine practices (MFMPs), aged between 30 and 65 years and recruited during a preventive check-up in 2019. Each MFMP pragmatically invited 30 attendees to voluntarily participate. The EQ-5D questionnaire was administered as a measure of HRQoL; the independent variables were demographic characteristics, smoking, alcohol consumption, stress perception, physical activity, signs of depression, cardiovascular risk, body mass index, blood pressure values, and blood sugar and lipidogram laboratory test values. Ordinal logistic regression was used to calculate associations between self-assessed quality of life, demographics, and clinical variables, with P<0.05 set as statistically significant.
Results: Of 986 participants, 640 (64.9%) were women and 346 (35.1%) men, aged 42.7+-8.6 years. The average values for the EQ-5D-3L were 0.9+1-0.15. In the multivariate model, a positive association between adequate physical activity (p=0.003), and a negative association between higher age (p<0.001), female gender (p=0.009), signs of depression (p<0.001), stress (p=0.013), and EQ-5D score were identified.
Conclusion: Given that physical activity was shown to be positively associated with HRQoL, it is of the utmost importance for family physicians to motivate their middle-aged patients, especially women and those with signs of depression and excessive stress, to adopt a more rigorously physically active lifestyle. Keywords: health related quality of life, health status, family practice, middle-age, physical activity, depression, stress, coping Published in DKUM: 11.12.2024; Views: 0; Downloads: 8
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7. Building organisational sustainability during the COVID-19 pandemic with an inspiring work environmentMaja Rožman, Anita Radman Peša, Mladen Rajko, Tjaša Štrukelj, 2021, original scientific article Abstract: This article aims to analyse significant differences in four constructs: occupational stress, job satisfaction, work engagement, and work productivity among employees before and after the COVID-19 pandemic. The purpose of the paper is to develop a multidimensional model with these four constructs and analyse the differences in the strength of their effects on the model across two intersectional times: before the COVID-19 pandemic and during the COVID-19 pandemic. The research was implemented on a sample of 885 employees in Slovenian organisations. During COVID-19, Slovenia had one of the strictest lockdowns. Based on the research, we can confirm significant differences in the four analysed constructs among employees before COVID-19 and during COVID-19. Based on the results, we can confirm that occupational stress had a more negative effect on job satisfaction and work engagement during COVID-19 than before prior to it. Our research and conclusions highlight the measures with which organisations can reduce the problem of occupational stress and with which organisations can increase job satisfaction, work engagement and work productivity among employees during COVID-19. Based on this, organisations may be able to build a more supportive work environment during, and after, COVID-19. Keywords: organisational sustainability, work engagement, work environment, COVID-19, stress, satisfaction, productivity, wellbeing Published in DKUM: 06.12.2024; Views: 0; Downloads: 6
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8. Effect of residual stresses on the fatigue stress range of a pre-deformed stainless steel AISI 316L exposed to combined loadingDarko Jagarinec, Nenad Gubeljak, 2024, original scientific article Abstract: AISI 316L austenitic stainless steel is utilized in various processing industries, due to its abrasion resistance, corrosion resistance, and excellent properties over a wide temperature range. The physical and mechanical properties of a material change during the manufacturing process and plastic deformation, e.g., bending. During the combined tensile and bending loading of a structural component, the stress state changes due to the residual stresses and the loading range. To characterize the component’s stress state, the billet was bent to induce residual stress, but a phase transformation to martensite also occurred. The bent billet was subjected to combined tensile–bending and fatigue loading. The experimentally measured the load vs. displacement of the bent billet was compared with the numerical simulations. The results showed that during fatigue loading of the bent billet, both the initial stress state at the critical point and the stress state during the dynamic loading itself must be considered. Analysis was demonstrated only for one single critical point on the surface of the bent billet. The residual stresses due to the phase transformation of austenite to martensite affected the range and ratio of stress. The model for the stress–strain behaviour of the material was established by comparing the experimentally and numerically obtained load vs. displacement curves. Based on the description of the stress–strain behaviour of the pre-deformed material, guidelines have been provided for reducing residual tensile stresses in pre-deformed structural components. Keywords: metastable austenitic stainless steel, fatigue, residual stress, phase transformation Published in DKUM: 28.11.2024; Views: 0; Downloads: 8
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9. Model of socially responsible transfer of parent organization culture to the subsidiary organization in a foreign cultural environment concerning internal communication, stress, and work satisfactionDarja Kukovec, Borut Milfelner, Matjaž Mulej, Simona Šarotar Žižek, 2021, original scientific article Abstract: The organizational culture is a significant construct in a time of change during the organizational transition, and it plays an important role in achieving goals of social responsibilities, which is an important part of sustainability. The literature shows the gap of socially responsible transfer of organizational culture with the impact on employee’s well-being. The cultural changes of the organization during the transition are particularly in connection with the impact on internal communication where organizational culture presents a part of values, norms, and ethics, which influences successfully implemented changes and in such a way has an influence on the stress and work satisfaction. The main purpose of the presented study is the development of the model of socially responsible transfer of organizational culture to the foreign subsidiaries on a basis of adjusted internal communication, which reduces stress and increases work satisfaction. Impacts of organizational culture on internal communication, stress, and work satisfaction are clearly presented, as well as inter-related impacts of the constructs concerning national culture, leadership, and organizational knowledge. Thus, the new holistic model of socially responsible transfer of the parent organization culture to foreign subsidiaries clearly defines steps of organizational culture, internal communication, stress management, and work satisfaction. Managerial implications are discussed. Keywords: organizational culture, internal communication, work stress, work satisfaction, organizational change, organizational transfer, social responsibility, sustainability Published in DKUM: 16.09.2024; Views: 14; Downloads: 16
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10. Personalizing human–robot workplace parameters in human-centered manufacturingRobert Ojsteršek, Borut Buchmeister, Aljaž Javernik, 2024, original scientific article Abstract: This study investigates the relationship between collaborative robot (CR) parameters and worker utilization and system performance in human–robot collaboration (HRC) environments. We investigated whether optimized parameters increase workplace efficiency and whether adapting these parameters to the individual worker improves workplace outcomes. Three experimental scenarios with different CR parameters were analyzed in terms of the setup time, assembly time, finished products, work in process, and worker utilization. The main results show that personalized CR parameters significantly improve efficiency and productivity. The scenario in which CR parameters were tailored to individual workers, balanced the workload, and minimized worker stress, resulting in higher productivity compared to non-people-centric settings. The study shows that personalization reduces cognitive and physical stress, promotes worker well-being, and is consistent with the principles of human-centered manufacturing. Overall, our research supports the adoption of personalized, collaborative workplace parameters, supported by the mathematical model, to optimize employee efficiency and health, contributing to human-centered and efficient HRC environments. Keywords: human–robot workplace, collaborative workplace, human-centered manufacturing, stress index, modelling, efficiencxy Published in DKUM: 03.09.2024; Views: 38; Downloads: 20
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