Mechanical performance of binder yarn composites

This investigation concerns the mechanical response of binder coated carbon tow preforms and laminates. The main focus is on evaluating and modelling the robustness of preforms whilst the methodologies developed are also applied to cured laminates produced using the binder coated preforms. Conventional manufacturing techniques were altered to address the differences in behaviour due to the presence of the binder with the development of infusion schedules. These involve lower temperatures, which eliminate the possibility of binder reactivation during processing. Different development versions of the material in the form of an inhomogeneously or homogeneously bindered tow were characterised in terms of their mechanical response in the preform state. It was observed that the inhomogeneously bindered material had higher modulus and strength in both tension in the fibre direction and shear, while the behaviour of the homogeneous preform is significantly more robust in the transverse to the fibre direction. Laminates produced, using the homogeneously bindered material, were compared to a reference unbindered laminate system, using an aerospace epoxy as a matrix. The out-of-plane properties of the material with binder were superior to the reference laminate, whereas in-plane properties were similar or inferior. The development of models of the mechanical response built around continuum damage mechanics models allowed the simulation of the behaviour of preforms under loading. The implementation of these constitutive models necessitated the development of appropriate parameter estimation techniques capable of solving the inverse problem of identifying the values of 27 material constants that minimise the error between experimental and modelling results. Two novel methodologies were developed and compared to a conventional technique following simplified laminate analysis. The first method performed a gradient-based error minimisation and the second uses the Markov Chain Monte Carlo technique. The gradient-based technique results in a close fit, while this method requires proper definition of the constraints to yield an appropriate solution set. Markov Chain Monte Carlo yields satisfactory results with the additional advantages of overcoming the ill-posedness of the inverse problem without regularisation and providing an output in the form of multivariate probability distributions that can be used directly instochastic simulations. The material parameters obtained and the corresponding constitutive models were used in finite element models of the mechanical response of preforms and laminates. The models were based on the concept of a combination of shell elements representing sub-laminates and cohesive elements simulating the delamination behaviour of interfaces between them. The performance of the models was evaluated using the case of impact of a spar section for preforms and three point bending for the laminates. The agreement between experimental and simulation results was satisfactory. The validated model was used in the context of a design case study based on a helicopter pitch horn component. The aim was to use the results of a draping analysis in the finite element model to evaluate the effects of the assumption of nominal fibre orientations on design and to combine the results of drape optimisation in respect to fibre shear angle with finite element analysis incorporating damage. The results showed that the use of nominal fibre orientation predicts a good performance of the component, whereas the influence of optimising draping on the mechanical performance was inferior

Engineering students\u27 preferred roles: Are they stable, are there gender differences?

Being able to situate oneself in an engineering role is a developmental process. Students may initially have idealized perceptions of a professional role and over time, they make this role more congruent with their own values and goals [1]. In light of this, Higher Education Institutions are being challenged to offer learning experiences and career exploration activities to enable students to clarify their interests, values and competencies in relation to a professional role [2]. This study compared the professional role preferences of more than 700 engineering students at TU Dublin (Ireland) and KU Leuven (Belgium). Professional role preference was measured with PREFER Explore, a personal preference test for engineers. The test aligns students to three professional roles for early career engineers: Product leadership (focus on radical innovation), Operational excellence (focus on process optimization) and Customer intimacy (focus on tailored solutions and customer satisfaction). A comparison was drawn between the role preference of first year students at TU Dublin and KU Leuven to establish if there were significant differences in preference across both universities. The results suggest that the role preference of engineering students does not shift from first to third year. There is also evidence that the PREFER Explore is sensitive to gender differences, with female students showing a greater preference for customer intimacy than males and males showing a greater preference for operational excellence than females at TU Dublin. The data have a number of implications for the labor market in Ireland and Belgium

Mechanical performance of binder yarn composites

This investigation concerns the mechanical response of binder coated carbon tow preforms and laminates. The main focus is on evaluating and modelling the robustness of preforms whilst the methodologies developed are also applied to cured laminates produced using the binder coated preforms. Conventional manufacturing techniques were altered to address the differences in behaviour due to the presence of the binder with the development of infusion schedules. These involve lower temperatures, which eliminate the possibility of binder reactivation during processing. Different development versions of the material in the form of an inhomogeneously or homogeneously bindered tow were characterised in terms of their mechanical response in the preform state. It was observed that the inhomogeneously bindered material had higher modulus and strength in both tension in the fibre direction and shear, while the behaviour of the homogeneous preform is significantly more robust in the transverse to the fibre direction. Laminates produced, using the homogeneously bindered material, were compared to a reference unbindered laminate system, using an aerospace epoxy as a matrix. The out-of-plane properties of the material with binder were superior to the reference laminate, whereas in-plane properties were similar or inferior. The development of models of the mechanical response built around continuum damage mechanics models allowed the simulation of the behaviour of preforms under loading. The implementation of these constitutive models necessitated the development of appropriate parameter estimation techniques capable of solving the inverse problem of identifying the values of 27 material constants that minimise the error between experimental and modelling results. Two novel methodologies were developed and compared to a conventional technique following simplified laminate analysis. The first method performed a gradient-based error minimisation and the second uses the Markov Chain Monte Carlo technique. The gradient-based technique results in a close fit, while this method requires proper definition of the constraints to yield an appropriate solution set. Markov Chain Monte Carlo yields satisfactory results with the additional advantages of overcoming the ill-posedness of the inverse problem without regularisation and providing an output in the form of multivariate probability distributions that can be used directly instochastic simulations. The material parameters obtained and the corresponding constitutive models were used in finite element models of the mechanical response of preforms and laminates. The models were based on the concept of a combination of shell elements representing sub-laminates and cohesive elements simulating the delamination behaviour of interfaces between them. The performance of the models was evaluated using the case of impact of a spar section for preforms and three point bending for the laminates. The agreement between experimental and simulation results was satisfactory. The validated model was used in the context of a design case study based on a helicopter pitch horn component. The aim was to use the results of a draping analysis in the finite element model to evaluate the effects of the assumption of nominal fibre orientations on design and to combine the results of drape optimisation in respect to fibre shear angle with finite element analysis incorporating damage. The results showed that the use of nominal fibre orientation predicts a good performance of the component, whereas the influence of optimising draping on the mechanical performance was inferior.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Integrated STEM in secondary education: A case study

Despite many opportunities to study STEM (Science, Technology, Engineering & Mathematics) in Flemish secondary education, only a minority of pupils are actually pursuing STEM fields in higher education and jobs. One reason could be that they do not see the relevance of science and mathematics. In order to draw their pupils’ interest in STEM, a Belgian school started a brand new initiative: the school set up and implemented a first year course that integrates various STEM disciplines, hoping to provide an answer to the question pupils often ask themselves about the need to study math and science. The integrated curriculum was developed by the school’s teachers and a STEM education research group of the University of Leuven. To examine the pupils’ attitude towards STEM and STEM professions and their notion of relevance of STEM at the end of this one-year course, a post-test was administered to the group of pupils who attended the integrated STEM course (the experimental group) and to a group of pupils that took traditional, non-integrated STEM courses (the control group). The results reveal that attending the integrated STEM course is significantly related to pupils’ interest in STEM and notion of relevance of STEM. Another post-test was administered only to the experimental group to investigate pupils’ understanding of math and physics concepts and their relation when taught in an integrated way. The results reveal that the pupils have some conceptual understanding and can, to a certain extent, make a transfer of concepts across different STEM disciplines. However, the test results did point out that some additional introductory training in pure math context is needed

Effects of a 16-Week Home-Based Strength Training Randomized Controlled Trial on Depression in Obese Latino Adolescent Boys

While the data has shown that the overall prevalence of depression is 6% in adolescents, these statistics are primarily based on white children. Latino children are more likely to suffer anxiety, depression and other mental health disorders compared to their non-Latino peers. While incidents are higher in Latino kids (22% suffer from depression), few receive treatment when compared to white children (8% vs 14% respectively). Given the prevailing burden and impact of mental health disorders in youth, it is essential that effective interventions are identified and implemented. PURPOSE: To assess the effects of a 16-week (2x/week) home-based strength training (HBST) program on the reduction of depression symptoms in obese Latino adolescent boys. METHODS: 32 Obese Latino boys aged 14-17 years, were recruited, and randomly assigned to one of two groups: 1) Control (n=16) or 2) Home-Based Strength Training (n=16). C – No intervention. HBST – Progressive program consisted of a 2X weekly program for 16 weeks. Body Mass Index (BMI) percentiles for age and gender were determined using CDC age-appropriate cut-offs. Height and weight were measured using a beam medical scale and wall-mounted stadiometer. Depression was assessed using the Center for Epidemiological Studies Depression scale (CES-D). All testing was performed before and after the 16-week intervention. RESULTS: A total of 30 boys (mean age = 15.5 + 0.9 years) completed the study. All thirty adolescents had a BMI in the 95% percentile. All participants attended \u3e85 % of the strength training sessions. Repeated Measures General Liner Model showed significant improvements in the intervention group only, with participants reporting an “increased happiness” (p=0.06) and increased “enjoyment in life” (p=0.009). In the intervention group, scores improved for questions such as “I felt depressed”, and “I felt sad”, although these improvements were not statistically significant (p=0.16, p=0.17 respectively). CONCLUSION: In a sample of obese male Latino adolescent males, small improvements were seen in feeling happy and enjoyment of life after a 16 week, 2x week home based strength training intervention. Future studies should consider strength training as an acceptable modality for improving mental health in obese Latino adolescent boys

Kinderen warm maken voor wetenschap en techniek vereist meer dan knutselen

status: publishe