Global buckling and post-buckling of web-core sandwich and stiffened panels: sensitivity to general corrosion

Corrosion can lead to reduction of structural stiffness and strength. This paper investigates the influence of a reduction in the thickness of the plates as a result of general corrosion on sandwich panel buckling load and onset of plasticity. The results are compared to the stiffened panel of the same in-plane and bending stiffness. Current guidelines for corrosion protection threat these two structures equally. Load-shortening curves are obtained 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, modeled using shell and connector elements. The former is also used to identify the influence of corrosion on the stiffness coefficients and, consequently, the buckling load, also via analytical equation. The decrease of the buckling load is found higher in sandwich panel than in stiffened panel. The reduction is especially high in the case of the diffusion of moisture (water) into the core. The reason for the higher sensitivity of sandwich panel is a larger reduction of transverse shear stiffness opposite to the stiffener direction due to corrosion.Peer reviewe

Load-carrying behaviour of web-core sandwich plates in compression

This paper investigates theoretically the compressive load-carrying behaviour of geometrically imperfect web-core sandwich plates. Slender plates, which first buckle globally, are considered. The study is carried out using two approaches, both solved with the finite element method. The first is the equivalent single-layer theory approach. First-order shear deformation theory is used. The second approach is a three-dimensional shell model of a sandwich plate. Plates are loaded in the web plate direction. Simply supported and clamped boundary conditions are considered with a different level of in-plane restraint on the unloaded edge. The results show that the behaviour of the sandwich plate is qualitatively equal to the isotropic plate of the same bending stiffness for deflections lower than the plate thickness. As the deflections increase, the lower in-plane stiffness of the sandwich plate results in lower post-buckling stiffness. Local buckling of face plates in the post-buckling range of the sandwich plate further reduces the structural stiffness.Peer reviewe

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

Abaqus UGENS subroutine for nonlinear analysis of periodic panels

This report describes an Abaqus UGENS subroutine for geometric and material nonlinear analysis of periodic panels using the first-order shear deformation theory. The structure is modelled with shell elements, as one layer of equivalent mechanical properties. The subroutine modifies the stiffness matrix of each shell element of the mesh separately based on its strain state. It relies on pre-computed stiffness curves that define the ABCD stiffness matrix of a unit cell. By looking at combinations of force and strain, the code interpolates the stiffness curves to calculate equivalent nonlinear stiffness. Complex stress states with different types of nonlinearity occurring simultaneously in the structure can be described. The examples show that the subroutine can deal with nonlinearities such as global buckling, local buckling and post-yield response with good accuracy and low computational cost compared to conventional FEM. The report includes the necessary information to set up the subroutine, including selection and compatibility of software and packages and input file preparation. Web-core sandwich panels are used as example throughout the report; the same principles are valid for any periodic structure. The full implementation is given in Appendix

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 weld stiffness on buckling strength of laser-welded web-core sandwich plates

This paper investigates the influence of weld rotation stiffness on the global bifurcation buckling strength of laser-welded web-core sandwich plates. The study is carried out using two methods, the first is the equivalent single-layer theory approach solved analytically for simply supported plates and numerically for clamped plates. First-order shear deformation theory is used. The second method is the three-dimensional model of a sandwich plate solved with finite element method. Both approaches consider the weld through its rotation stiffness. The weld rotation stiffness affects the transverse shear stiffness. Plates are loaded in the web plate direction. Four different cross-sections are considered. Weld stiffness is taken from experimental results presented in the literature. The results show a maximum of 24% decrease in buckling strength. The strength was affected more in plates with high reduction of transverse shear stiffness and high bending stiffness. Furthermore, clamped plates were influenced more than simply supported. The intersection between buckling modes shifted towards higher aspect ratios, in the maximum case by 24%. The results show the importance of considering the deforming weld in buckling analysis.Peer reviewe