Strain rate dependency of the properties of a unidirectional thermoplastic composite material

This research work established the strain rate dependency of the the mechanical properties of a highly orientated glass fibre/thermoplastic composite lamina and validated a model for Computer Aided Engi­neering (CAE). The mechanical properties examined for strain rate dependency were elasticity, strength and damage evolution at a ply level. A rigourous statistical methodology were established and implemented through mechanical testing to­gether with processing of the results for the development of semi-empirical strain rate models. Two different methods of data acquisition were considered, specifically strain measurement using videoex- tensometry and contacting extensometry. The resulting strain measurements were then computed. Video extensometry appeared to have clear advantages, however, scatter in the response was appreciably higher compared to the contacting extensometry. This was due to the much smaller scale of gauge length for strain measurement. A rigourous validation methodology was further complemented through a statistical procedure and tool kit (utilising statistical tools and procedures like density distributions plot, hypothesis testing, analysis of variance). The statistical tool kit was developed to enable objective assessment of strain rate dependency and to establish the quality of a relationship (model) should one exist for the range of mechanical properties tested. Using this validation methodology, a semi empirical strain rate dependent model was validated for elasticity strength and damage evolution. The effect of strain rate on the above mechanical properties was investigated for Plytron1 Ai. The Plytron™material was supplied by Borealis as a lOOmm-wide, 0.22[mm]-deep tape, comprising aligned continuous glass fibres in a polypropylene matrix. To manufacture a laminate, the tape was laid-up ply-by-ply into an unconsolidated stack. This stack was then consolidated using under pressure and heat according to a Warwick Manufacturing Group’s proprietary membrane-forming process [!]. For the purposes of this study, specimens were machined in accordance with ISO-527-4 from 4 different layup sequences: [0°]4, [±45°]2,, [+45°]s and [±67.5°]2„. The specimens were tested at 5, 50 and 500[min/min] crosshead displacement rates using monotonic and cyclic loading. FYom this investigation, over the examined strain rate range, the longitudinal tensile modulus increased with strain rate, while the shear modulus and Poisson’s ratio decreased. The transverse tensile modulus did not exhibit any statistically significant difference. The shear failure stress and the longitudinal tensile failure strain and stress appeared to increase for increasing strain rate, while the shear failure strain were not strain rate dependent. The transverse tensile failure stress and strain did not exhibit any statistically significant strain rate dependency. The characterisation parameters of the damage evolution were based on the global composite ply model for composites in the framework of continuum damage mechanics (CDM). This model was developed by Ladeveze et al. (.’), [It], for thermosetting composites. It was established that shear damage evolution of the thermoplastic materials exhibits different behaviour compared to thermosets. It also was established that the rate of shear damage evolution decreases with increasing strain rate and that the point that shear damage initiates increases with increasing strain rate. All testing was conducted with INSTRON 4505 universal testing machine instrumented with a 100[kN] load cell. Contacting extensometry and videoextensometry has been examined as data acquisition meth­ods. It was established in this work that contacting extensometry provided data with less scatter, however the videoextensometry exhibited significant advantages. Having established and validated semi-empirical rate dependent models, for the characterisation parame­ters to service the CDM models, CAE models were established and validated using a well known explicit FE numerical simulation. To maintain rigour, the validation methodology employed new metrics to en­able objective comparison between FE and experimental results. These metrics are Pearson correlation coefficient and correlation range ratio. The comparison of experimental to FEM results revealed that the available models predict adequately well the stiffness of laminates as expected. The onset of failure is predicted at significantly lower strains compared to the experimental results (depended on layup - usually 30% of the total failure strain). The premature failure is attributed to the failure criterion implementation at ply level and/or the definition of the boundary conditions

Investigation of Submergence Depth and Wave-Induced Effects on the Performance of a Fully Passive Energy Harvesting Flapping Foil Operating Beneath the Free Surface

This paper investigates the performance of a fully passive flapping foil device for energy harvesting in a free surface flow. The study uses numerical simulations to examine the effects of varying submergence depths and the impact of monochromatic waves on the foil's performance. The results show that the fully passive flapping foil device can achieve high efficiency for submergence depths between 4 and 9 chords, with an "optimum" submergence depth where the flapping foil performance is maximised. The performance was found to be correlated with the resonant frequency of the heaving motion and its proximity to the damped natural frequency. The effects of regular waves on the foil's performance were also investigated, showing that waves with a frequency close to that of the natural frequency of the flapping foil aided energy harvesting. Overall, this study provides insights that could be useful for future design improvements for fully passive flapping foil devices for energy harvesting operating near the free surface

'The Degree of Despair': The Disjointed Labour Market, the Impact of the Pandemics, the Expansion of Precarious Work among Youth and Its Effects on Young People's Life Trajectories, Life Chances and Political Mentalities - Public Trust; The Case of Greece

This paper focuses on the expansion of precarious forms of employment (temporary, seasonal, part-time jobs etc.) and on the impact this expansion has on young peoples' key determinants of life course. Based on both secondary quantitative-data analysis and primary qualitative research, the paper analyzes the state of play regarding precarious work among youth both in the EU and (mainly) in Greece, while it highlights the impact of the pandemic and the subsequent Recession in the abovementioned. The paper also explores the various aspects and facets of the impact of precarious employment in young peoples' life trajectories. Key findings include: a) the strong correlation between precarious employment, social vulnerability and risk of poverty, b) the fact that, during the pandemic, the "labour market slack" in Greece hit young people aged 15-24 more than people aged 25-54, further widening their precariousness, c) that there is a wider tendency to expand and "normalize" the forms of precarious employment among youth, concerning, especially, the combination of declared and undeclared work, d) that a new labour market dualization is formed, e) that both the pandemic and the subsequent restrictive measures have had a significant impact on the majority of precarious young people, effectively causing a rupture in their already precarious life course and f) that all the abovementioned have a severe impact on key determinants of political behavior - mentalities as well as on public trust among young people. The paper is based on an ongoing Research Project, co-financed by Greece and the European Union (European Social Fund- ESF) through the Operational Programme "Human Resources Development, Education and Lifelong Learning 2014-2020" in the context of the project "Precarious Work and Youth in today's Greece: secondary quantitative analysis, qualitative filed research and research-based policy proposals" (MIS 5048510)

Shoulder Arthroscopy After a Proximal Humeral Fracture Malunion: Athlete Care and Clinical Medicine in Middle-Aged Athletes

Malunion of the proximal humerus is operationally defined as healing of the fractured bone in a non-anatomical position, resulting in a painful and disabling deformity (e.g., a bone being shorter than normal, twisted or rotated in a bad position, or bent), which affects the range of motion (ROM) and functional movement. A correction and functional restoration are often needed in athletes, since their profession requires superior physical functioning. Shoulder arthroscopy has evolved dramatically over the past 15 years and has been used in cases of malunion of the humerus in athletes. However, there is a scarcity of evidence concerning middle-aged athletes. PURPOSE: To examine the benefits of shoulder arthroscopy after a proximal humeral fracture unified in malposition in middle-aged athletes. METHODS: Physical examination and imaging evaluation using 3D Computed Tomography(3D-CT), Magnetic Resonance Imaging (MRI), and shoulder radiographs (anteroposterior, internal rotation, and lateral scapular view) were used to evaluate shoulder dysfunction after proximal humeral fracture in malposition. Fourteen athletes (9 males, 5 females; Mage = 43.1, SD = 3.5) were included in this research. According to Neer classification before surgery, 11 (78%) had one part displaced and the rest three (22%) had two parts displaced. Post-operative clinical results were evaluated with self-reported pain score (1-10), UCLA scores, and shoulder abduction ROM measured with a goniometer. RESULTS: There was significant difference in pain scores (Mbefore = 8, Range: 6-9; Mafter = 4, Range: 2-6; p \u3c .001), in UCLA scores (Mbefore = 12, Range: 9-16; Mafter = 28, Range: 20-31; p \u3c .01), and in shoulder abduction ROM (Mbefore = 80, Range: 70-100; Mafter = 135, Range: 120-150; p \u3c .05). CONCLUSION: Our research provides evidence for clinical translation in improving health outcomes in middle-aged athletes with a history of proximal humeral fracture union in malposition: shoulder arthroscopy can be simultaneously beneficial in terms of decreasing pain level, increasing ROM, and restoring limb function

Fulminant Aeromonas hydrophila infection during acute lymphoblastic leukemia treatment

Aeromonas hydrophila septicemia has a fulminant course and it has been usually reported in immunocompromised hosts and rarely among children with leukemia. High morbidity and mortality is associated with A hydrophila infections. We describe the case of a child with acute lymphoblastic leukemia who presented with septicemia due to A hydrophila. The patient presented with fever and skin discoloration during a febrile neutropenia episode, which rapidly evolved into bacteremia and extensive thigh suppuration, fasciitis, and myonecrosis. Apart from antibiotic treatment, surgical debridement to relieve compartment pressure and prevent further lower extremity compromise was promptly performed. Despite long delays in chemotherapy and an extensive tissue gap, primary closure of the involved area was possible with full cosmetic and functional limb recovery, and the patient has remained in clinical remission for more than 7 years

Translation and cross-cultural adaptation methodology for soundscape attributes – A study with independent translation groups from English to Greek

The use of questionnaires for soundscape evaluation is a key aspect of soundscape research. Since standards and protocols mainly exist in English, using an appropriate translation and cross-cultural adaptation (CCA) methodology is necessary to maintain content equivalence between source and target language. However, many examples can be found in the literature where no appropriate methodology was applied. This study addresses the neglected aspect of the translation and CCA process in soundscape research by selecting, applying and evaluating an appropriate methodology. After a survey of the relevant literature, an approach based on a combined technique of the forward translation, synthesis, back translation, pre-test and a committee approach was selected. Additional translation guidelines drawn from the literature are suggested and implemented. For the case study of the Greek translation of ISO/TS 12913–2:2018 attributes (Method A), the steps of the methodology were applied by four independent translation groups with different compositions according to the biculturalism and bilingualism of the group members. A method for categorization of bilinguals according to the literature is proposed. In order to compare and validate the results, translated and original attributes were used in listening tests with Greek and English participants respectively, and principal component analysis (PCA) was applied. The most important findings of this research are: the results of the bicultural translation group were closer to the PCA results of the English participants for every attribute, translation of bilingual groups may not be always sufficient, translation errors may be misinterpreted for cross-cultural differences without proper application of a translation methodology and the process of back translation can be effective, especially in cases where there are not corresponding words in the target language. Finally, PCA can be used as a validation methodology for comparison of different translations