Investigation of a methodological approach to modelling sandwich structures using cohesive elements

Lightweight multi-material architectures like sandwich structures can contribute to reaching environmental targets regarding the reduction of emissions from vehicles. In modern development processes, modelling sandwich structures' mechanical behaviour in finite-element simulations is essential. In the Next Generation Car (NGC) research project, a novel vehicle concept is being developed that makes extensive use of sandwich materials - the Safe Light Regional Vehicle (SLRV). Particularly, crash load cases are considered in the development of this sandwich structure. The investigated sandwich material consists of two metallic layers and a polyurethane foam core. For the derivation of an appropriate mechanical surrogate model, the damage mechanisms during loading have to be analysed and evaluated. Preliminary studies show potentials for the investigated approach that uses cohesive elements to model the sandwich core

Mechanical behavior and microstructural analysis of extruded AZ31B magnesium alloy processed by backward extrusion

This study investigates the mechanical behavior of an extruded AZ31B magnesium alloy profile at various strain rates from 0.001 to 375/s. The electron backscatter diffraction analysis revealed that the profile has {0001}⟨101 ¯ ¯ ¯ 0⟩ {0001}⟨101¯0⟩ and {101 ¯ ¯ ¯ 0}⟨112 ¯ ¯ ¯ 0⟩ {101¯0}⟨112¯0⟩ textures. Due to the textures, the profile exhibits pronounced anisotropy in mechanical properties. In the extrusion direction (ED), the profile shows the highest yield strength (YS) but the lowest total elongation at fracture (TE) due to a hard activation of non-basal slip and {101 ¯ ¯ ¯ 1}⟨101 ¯ ¯ ¯ 2 ¯ ¯ ¯ ⟩ {101¯1}⟨101¯2¯⟩ twinning; in the diagonal direction (DD), it shows the lowest ultimate tensile strength (UTS) but the highest TE due to an easy activation of basal slip; in the transverse direction (TD), it shows the lowest YS due to an easy activation of {101 ¯ ¯ ¯ 2}⟨101 ¯ ¯ ¯ 1 ¯ ¯ ¯ ⟩ {101¯2}⟨101¯1¯⟩ twinning. Moreover, the number of twins increases with the increasing strain rate. This indicates that deformation twinning becomes prevalent to accommodate high-rate deformation. Due to the different deformation mechanisms, the profile exhibits an orientation-dependent effect of strain rate on the mechanical properties. A positive effect of strain rate on the YS and UTS was found in the ED, while the effect of strain rate on the YS is negligible in the DD and TD. The TE in the ED, DD, and TD decreases in general as the strain rate increases. Fractographic analysis under a scanning electron microscope revealed that the fracture is a mixed mode of ductile and brittle fracture, and the magnesium oxide inclusions could be the origins of the fracture

Crash Absorbing Structures for Different Vehicle Concepts

Two different crash energy absorbing concepts for road and railway vehicles are introduced, which were developed during research activities at the German Aerospace Center (DLR) – Institute of Vehicle Concepts. The crash concept for road vehicles uses AZ31B magnesium, a material with a tension-compression asymmetry. Crash-related structures under bending can be significantly improved by filling hollow thin-walled beams with a stabilizing polyurethane core. To evaluate the crashworthiness of hollow and foam filled magnesium beams, quasi-static and dynamic three-point bending tests were performed. The crash concept for railway vehicles uses structurally load bearing tapering tubes with different sizes and energy levels. Results given in the paper present the smallest energy absorbers with tubes made of HSD®-steel, a material which combines a high strength with a high ductility, and a die made of tempered steel. Quasi-static and dynamic tests in longitudinal and transverse directions relative to the tube axis were performed, to evaluate the energy absorbing and load bearing capabilities of the absorbers

Novel concepts for the application of Magnesium Sheets and profiles in Crash loaded vehicle areas

As the lightest structural metal, magnesium alloys have been attractive to reduce vehicle weight and emissions by lightweight design in the automotive industry. Crashworthiness is not a physical property itself, but correlates with the material’s ductility and structural design. Magnesium is known to be a material with lower failure strain than other metallic structural materials. Therefore the use of magnesium in crash-related areas is more challenging compared to steel and aluminum. In structures with a bending load, like e. g. the bumper or the sill, crash properties can be significant improved by filling profiles with a stabilizing core. In order to evaluate the crashworthiness of this hybrid structure under bending loads, both empty and polyurethane foam-filled rectangular section beams were constructed and tested by using the quasi-static/dynamic three-point bending facilities at German Aerospace Centre (DLR) – Institute of Vehicle Concepts. For structures with axial crash loads the normal buckling mode will lead to a very early fracture of the magnesium part. In collaboration with researchers from the University of Windsor and the University of Waterloo, novel technologies for energy absorption which are based on cutting or peeling mechanisms have been developed and investigated, which allow the use of magnesium in these challenging applications. Results of the joint research will be presented

'Wissen über die Welt'? - Bildung für alle als Verlernen eines hierarchisierenden Blicks

Flores Rojas C, Streicher NP. 'Wissen über die Welt'? - Bildung für alle als Verlernen eines hierarchisierenden Blicks. In: Grünheid I, Nikolenko A, Schmidt B, Landesarbeitsgemeinschaft politisch-kulturelle Bildung Sachsen e. V., eds. Bildung - für alle? Kritische Impulse für eine inklusive Schule in der Migrationsgesellschaft. Ein Dossier im Auftrag der Landesarbeitsgemeinschaft politisch-kulturelle Bildung Sachsen e. V., Dresden. Dresden; In Press

Orbital volume changes during growth and development in human children assessed using cone beam computed tomography

Abstract Objectives To measure growth-related changes in orbital volume from childhood to the late teenage years using cone-beam computed tomography (CBCT) scans. Methods This retrospective cohort study involved 65 (24 male, 41 female) healthy Caucasian children (ages 6–18 years) with existing serial craniofacial CBCT scans. CBCT scans were available for 292 orbits. Each orbit was transformed into a closed space with well-defined boundaries, and orbital volume was measured using manual segmentation. A novel statistical analysis was applied to extract the maximum amount of longitudinal information from the data. Intra- and inter-operator correlation coefficients were calculated from replications performed on a random subset of 10% of the sample. Results Orbital volume increased at a rate of 1–2% annually until the late teenage years. Intra- and inter-operator agreement between repeated measurements were >90%. Conclusions Orbital volume increases by 1–2% per year throughout childhood continuing until the late teenage years. This annual increase is large enough to be clinically relevant as it may lead to less-than-optimal long term surgical outcomes when reconstructive surgery for the pediatric anophthalmic socket is required

Playing a musical instrument is associated with slower cognitive decline in community-dwelling older adults

Background: Elucidating behavioral protective factors for cognitive decline and dementia can have a far-reaching impact. Aims: To describe the association of present and past musical instrument playing with cognitive function in cognitively intact older adults. Method: A post hoc observational analysis of the Zurich Disability Prevention Trial. Past and present musical instrument playing was correlated with Mini-Mental State Examination (MMSE) and EuroQol-Visual Analogue Scale (EQ-VAS) using linear regression at baseline and mixed-model linear regression over 1 year. Results: Two hundred community dwelling adults age 70 and older (mean age 77.7) were included. There were 48.5% (97/200) participants, who ever played a musical instrument; 35% (70/200) played in the past and 13.5% (27/200) played at present. At baseline, present players had a suggestively higher adjusted-MMSE than never players (28.9 vs. 28.5, p value 0.059). Over 12 months, compared to never players, ever players showed a significantly better improvement from baseline in adjusted-MMSE (0.29 vs. - 0.12, p value 0.007). The association remained significant even after restricting to participants without higher education (p value 0.03). Over time, no differences were observed for EQ-VAS (p value 0.45). However, past players had the largest decline in health-related quality of life at 12 months. Discussion: The support for a protective association in our observational study suggests the need for clinical trials to examine the effect of playing a musical instrument on cognitive function and decline. Both returning to play after an interruption and learning to play from the beginning should be examined. Conclusions: Present and past musical instrument playing may assist in preserving cognitive function in community-dwelling older adults