Influence of general corrosion on buckling strength of laser-welded web-core sandwich plates

The strength of a web-core steel sandwich plate is potentially reduced in a corrosive environment. This study is dedicated to the influence of a reduction in the thickness of the plates as a result of general corrosion on sandwich plate buckling strength and first-fibre failure. Two scenarios are investigated in which corrosion reduces the thickness of (a) the outer sides of the face plates and (b) all surfaces, including the core. The laser weld between the face sheets and the core is assumed to be intact. The assumptions are made on the basis of earlier experimental findings. Critical buckling and geometric non-linear analysis are carried out with the finite element method, with the kinematics being represented using two approaches: (1) equivalent single-layer with first-order shear deformation theory, and (2) a three-dimensional model of the actual geometry of the structure, modelled using shell and connector elements. The former is used to identify the effect of corrosion on the stiffness coefficients and, consequently, the buckling strength. The later is used for verification and for stress prediction during post-buckling. A rapid decrease in the buckling strength was found for corrosion affecting the outer sides of the sandwich plate. The decrease in the buckling strength doubled in the case of the diffusion of moisture (water) into the core. The shear-induced secondary bending of the faces was found to affect the first-fibre yield.Peer reviewe

Improvement of Teaching and Learning Experience by Online Course Diary Tool : Qualitative Exploration of Teachers’ Perspective

Due to the rapid shift to online learning, it has become increasingly difficult for teachers to monitor students’ learning experiences. This paper analyzes teachers’ experiences with an online tool for monitoring students’ metacognitive states during the learning process. Through an open-ended questionnaire, we collected teachers’ aims for starting to use the tool and experienced benefits. Our results show that teachers use this tool to understand the learning status of students in greater depth and to adjust their teaching according to feedback collected during the course. Moreover, teachers reported receiving better quality summative course feedback after starting to use the tool.Peer reviewe

Benefits of Online Course Diary Tool on Teaching and Learning Experience

Recently it has become increasingly difficult for teachers to get a grip on student’s learning experience, especially in the ear of distance-learning. This study analyzes teachers’ experiences in using an online monitoring tool of students’ metacognitive states. Through the open-ended questionnaire, we collected teachers’ reasoning to start using this new tool. We elaborated on the effect of this on teaching and learning and compared the official static course feedback with the dynamic provided by the tool. Our results show that teachers use this tool to understand student learning status more deeply and adjust the course according to the feedback. Moreover, teachers reported that they have been getting better quality summative course feedback after starting to use the tool.Non peer reviewe

Influence of grain size distribution on the Hall–Petch relationship of welded structural steel

The strength of polycrystalline metals increases with a decrease in grain size according to the Hall-Petch relationship. However, heterogeneous microstructures deviate from this relationship dependingon the distribution of grain sizes. This paper introduces a rule of mixtures based approach fordetermining the characteristic length of the microstructure for heterogeneous weld metal. Theproposed grain size parameter, the volume-weighted average grain size, is measured experimentallyfor nine structural steel weld metals and two base materials. The weld metals are found to have alarge variety of grain size distributions that are noticeably broader than those of the base material dueto differences in phase contents. The results show that the volume-weighted average grain size is ableto capture the influence of grain size distribution on the strength of welded structural steel. Based onthe experimental results, a modified Hall-Petch relationship is formulated for the strength predictionof heterogeneous microstructures. The modified relationship is also found to be applicable to datafrom the literature.Peer reviewe

Curricular Concept Maps as Structured Learning Diaries : Collecting Data on Self-Regulated Learning and Conceptual Thinking for Learning Analytics Applications

The collection and selection of the data used in learning analytics applications deserve more attention. Optimally, selection of data should be guided by pedagogical purposes instead of data availability. Using design science research methodology, we designed an artifact to collect time-series data on students’ self-regulated learning and conceptual thinking. Our artifact combines curriculum data, concept mapping, and structured learning diaries. We evaluated the artifact in a case study, verifying that it provides relevant data, requires a limited amount of effort from students, and works in different educational contexts. Combined with learning analytics applications and interventions, our artifact provides possibilities to add value for students, teachers, and academic leaders.The collection and selection of the data used in learning analytics applications deserve more attention. Optimally, selection of data should be guided by pedagogical purposes instead of data availability. Using design science research methodology, we designed an artifact to collect time-series data on students’ self-regulated learning and conceptual thinking. Our artifact combines curriculum data, concept mapping, and structured learning diaries. We evaluated the artifact in a case study, verifying that it provides relevant data, requires a limited amount of effort from students, and works in different educational contexts. Combined with learning analytics applications and interventions, our artifact provides possibilities to add value for students, teachers, and academic leaders.Peer reviewe

Generalized Formulation for Fatigue Assessment of Laser Stake-welded T-joints Varying Thicknesses and Loading Conditions

The present work considers the evolution of the crack tip plasticity ahead of the crack-like notches with varying the loading condition and the thickness of laser stake-welded T-joints. A general procedure is described for the fatigue assessment of the joints under different loading conditions and made of different thicknesses. The new method is based on the analyses of the first order plastic radius (according to Irwin) for pure mode I, and it is generalized to mixed mode (I+II) by using the Minimum Plastic Zone Radius (MPZR) criterion. The method is validated, in the end, with a case study and explains why the fatigue slope m varies for joints loaded under bending/tension and when the thickness is reduced. The results prove that the procedure gives an excellent estimation of the fatigue life

Methacholine, cold air and exercise challenge tests in the diagnosis of bronchial responsiveness at school age: A follow-up study from birth to school age

ABSTRACTBackgroundThe aim of the present study was to compare three bronchial challenge tests for assessing bronchial hyperresponsiveness (BHR) in twin pairs followed up from birth to school age.MethodsWe studied three different bronchial challenge tests (methacholine inhalation challenge, cold air inhalation challenge and exercise-bronchodilation tests) at school age in 29 children born at or before 38 weeks gestation (median 35 weeks gestation) from multiple pregnancies. The children had been followed up from birth and were examined at the age of 7-15 years (median age 10 years).ResultsBronchial hyperresponsiveness was found in 28-34% of children when these tests were analyzed separately. Eight children (28%) were exercise responders; two of them and three additional children were bronchodilator responders. Thus, 11 children (38%) had a pathologic result in the exercise-bronchodilation test. Ten children (34%) responded to cold air and nine children (31%) responded to methacholine inhalation. At least one test was pathologic in 18 children (62%), but only two children (7%) responded in all three challenges. A positive result in the exercise-bronchodilation test was associated with cold air reactivity, but not with methacholine reactivity. The exercise and cold air tests detected predominantly the same children. No differences were found in bronchial challenge test results between children who, at birth, were appropriately grown and those who had intrauterine growth retardation.conclusionsBronchial hyperresponsiveness was common (up to 62%) at school age in children born as moderately preterm. The outdoor exercise-bronchodilation test found 61% of all BHR cases. Bronchial hyperresponsiveness was not associated with intrauterine growth status. The most sensitive test was the cold air inhalation challenge and a good agreement was seen between this test and the exercise challenge outdoors

Exercise intervention and health checks for middle-aged men with elevated cardiovascular risk : A randomized controlled trial

Peer reviewe

Cut-off values to evaluate exercise-induced asthma in eucapnic voluntary hyperventilation test for children

Background and Aim The eucapnic voluntary hyperventilation (EVH) testing is a diagnostic tool for diagnostics of exercise-induced bronchoconstriction; while the testing has become more common among children, data on the test's feasibility among children remain limited. Our aim was to investigate EVH testing feasibility among children, diagnostic testing cut-off values, and which factors affect testing outcomes. Methods We recruited 134 patients aged 10-16 years with a history of exercise-induced dyspnoea and 100 healthy control children to undergo 6-min EVH testing. Testing feasibility was assessed by the children's ability to achieve >= 70% of the target minute ventilation of 30 times forced expiratory volume in 1 s (FEV1). Bronchoconstriction was assessed as a minimum of 8%, 10%, 12%, 15% or 20% fall in FEV1. Patient characteristics were correlated with EVH outcomes. Results Overall, 98% of the children reached >= 70%, 88% reached >= 80%, 79% reached >= 90% and 62% reached >= 100% of target ventilation in EVH testing; of children with a history of exercise-induced dyspnoea, the decline percentages were as follows: 24% (>= 8% fall), 17% (>= 10% fall), 10% (>= 12% fall), 6% (>= 15% fall) and 5% (>= 20% fall) in FEV1, compared to 11%, 4%, 3%, 1% and 0% among the healthy controls, respectively. Healthy controls and boys performed testing at higher ventilation rates (p <.05). Conclusion Eucapnic voluntary hyperventilation testing is feasible among children aged 10-16 years and has diagnostic value in evaluating exercise-induced dyspnoea among children. A minimum 10% fall in FEV1 is a good diagnostic cut-off value. Disease status appears to be important covariates.Peer reviewe