Experimental characterization and finite element modelling of strain-rate dependent hyperelastic properties of PVB interlayers

Laminated glass provides safety in an impact or explosion event by way of a polymer interlayer to which glass fragments adhere upon fracture. The mechanical deformation of the interlayer defines how the impact energy can be absorbed to prevent calamities by flying glass debris, penetration of a blast wave, lacerations, etc. The PVB interlayer used in safety glass shows highly nonlinear viscoelastic material behaviour, with a great sensitivity to temperature and deformation rate. Although various material models for PVB can be found in literature, few publications discuss the full range of its mechanical behaviour and none are found to describe a material model that is valid in a wide range of deformation rates and up to high elongations. Such material model is necessary for the numerical study of the post-fracture response in a dynamic event. The article describes the mechanical behaviour of PVB interlayer and the constitutive models by which the polymer can be represented under different load cases. Tensile experiments of Saflex® PVB are presented for a wide range of deformation rates and up to tearing of the specimens. Subsequently, a method to calibrate a hyper-viscoelastic material model for the interlayer by numerically simulating the tensile tests is developed. The resulting material models are valid up to the tearing strain of the interlayer and are accurate within a specified range of deformation rates and temperatures

Fused-core HPLC method development implemented in a short-term stability study of Triple IT solution

For the majority of children with acute lymphoblastic leukemia (ALL), treatment consists in part of a triple intrathecal (Triple IT) therapy, i.e. a combination of cytarabine (CB), methotrexate (MTX) and methylprednisolone sodium succinate (MPSS) [1]. This combination product is prepared ex-tempore. However, no in-use shelf-life under defined storage conditions has yet been established. During stability studies, a large number of samples are generated, thus creating the need for a fast, accurate and selective analytical method. In this study, a fused-core HPLC method was developed. This hybrid technology, consisting of a 0.5 µm thick porous shell fused to a 1.7 µm inert core, enables faster chromatographic separation with sufficiently high resolution. During method development, both stressed and unstressed solutions containing both single Triple IT components and the mixture thereof, were analyzed using different linear gradient times, ranging from 5 to 30 min. The mobile phase composition was fixed (A: 0.1% glacial acid in H2O; B: 0.1% glacial acid in ACN), starting with A:B (90:10, V/V) and ending with A:B (10:90, V/V). Method selectivity was evaluated based on the observed peaks in stressed CB, MTX and MPSS solutions, i.e. incubation at 40°C and 80°C. A balance between fast separation and sufficient resolution between the Triple IT components and related degradants, was found by setting the gradient time at 15 min. The Triple IT related degradation peaks were chromatographically separated from the remaining Triple IT components. Moreover, selectivity was supported by a peak purity analysis on the observed peaks. Linearity was demonstrated (R² > 0.999) for the three Triple IT components. Repeatability was evaluated by triplicate injections of 100% reference assay: relative standard deviation varied between 0.155% (MPSS), 0.464% (CB) and 1.352% (MTX) [2]. References [1] A. Ruggiero, V. Conter, M. Milani, E. Biagi, I. Lazzareschi, P. Sparano, R. Riccardi. Intrathecal chemotherapy with antineoplastic agents in children. Paediatric drugs 3(4) (2001) 237-246. [2] M. D’Hondt, E. Vangheluwe, S. Van Dorpe, J. Boonen, T. Bauters, B. Pelfrene, J. Vandenbroucke, H. Robays, B. De Spiegeleer. Stability of ex-tempore prepared Triple intrathecal solution consisting of cytarabine, methotrexate and methylprednisolone sodium succinate. American Journal of Health-System Pharmacy, submitted for publication

A theoretical study on the P-I diagram of framed monolithic glass window subjected to blast loading

In this paper, an analytical model for determining the iso-damage curves for framed monolithic glass panels subjected to blast loading is proposed. Two typical damage levels corresponding to different conditions in GSA/ISC are classified, namely (a) the glass crack limit and (b) glass fragments invading with a certain velocity. The nonlinear dynamic responses and failure modes of framed monolithic glass under different blast loadings are firstly analysed numerically. Then critical states of glass panel in both impulsive region and quasi-static region of the pressure-impulse (P-I) diagram are defined. Based on the energy balance approach, an analytical method is proposed for determining the pressure asymptote and the impulse asymptote of framed monolithic glass for different damage levels. The proposed method is verified through comparison with published experimental data and numerical results. The method can be applied for any framed monolithic glazing with different dimension and thickness and provides a practical approach for engineering design and hazard level estimation of framed monolithic glass against blast loading

Numerical simulation of the EN 12600 Pendulum Test for Structural Glass

In modern-day architecture, transparent glass units are omnipresent as large façades, windows, floors and balustrades. To ensure safety in an accident, glass panels must successfully pass the 'human impact' test, described by the international standard EN 12600. This test setup consists of a steel frame in which the test plate is clamped with prescribed force; and the pendulum impactor, hanging from a steel cable. The impactor weighs a total 50 kg and is built up from a rigid steel core to which two small tyres are mounted. The window panels are assigned a qualification number as they remain intact, fracture without losing integrity or fragment completely in impacts from different drop heights. As experimental testing is expensive and time-consuming, there is an interest in numerical modelling to predict a qualifying glass panel, which is already allowed by the German standard DIN 18008-4. Several modelling approaches allow the impact simulation for intact glass panels. This paper presents a detailed numerical model for the pendulum impact which enables realistic simulation of impactor, frame and test plate, to be valid also for the post-breakage safety assessment of laminated glass. The model shows good correspondence for static compression of the tyres and for impact against a pressure plate. Further comparison is made for the impact on a laminated glass panel that remains intact. Although less suited for structural design qualification, the detailed model can be used for future simulation of the post-breakage response of laminated glass panels

Local ageing patterns in Flanders

Résumé L’article analyse la variation géographique du vieillissement démographique en Flan­dre. Nous examinons les évolutions combinées de la population âgée de plus de 65 ans et de celle des 20 à 49 ans, ainsi que leur lien avec la croissance naturelle et la migration. Les séries temporelles utilisées concernent la période 2001-2015 et proviennent du Registre National de Population publiées par l’office belge de statistique (Statbel). Elles sont complétées par les Projections démographiques pour les municipalités flamandes 2015-2030, préparées par le Gouvernement flamand. Les municipalités sont regroupées sur la base d’une analyse typologique des séries temporelles sur la composition de la population, l’évolution de la population de 65 ans et plus et de la population de 20-49 ans ainsi que sur les changements dans la migration nette et la croissance naturelle. La typologie issue de cette analyse discerne six modèles de vieillissement dont les plus proéminents sont : un important et ancien vieillissement à la côte ; un futur vieillissement dans le Limbourg oriental et dans le nord de la province d’Anvers et, finalement, une croissance démographique et un vieillissement limité dans le centre de la Région flamande. Abstract The paper analyses the geographic variation in demographic ageing patterns in Flanders. We examine the combined evolutions of the elderly population aged over 65, and the young adult population aged 20-49, in relation to natural growth and migration. The data concern time-series on the period 2001-2015 from the National Population Register as published by the Belgian statistical office (Statbel). We complemented the time series with the Population Projections for the Flemish Municipalities, 2015-2030, prepared by the Flemish Government. A Finite Mixture Model is applied to cluster municipalities on the basis of population composition, change in the population aged 20-49 and over 65, and change in net migration and natural growth. We discern six ageing patterns. The most prominent ones are: first, a strong ageing in the past along the coast; second, a strong future ageing in Eastern Limburg and the North of the province of Antwerp; and third, population growth and limited ageing in the center of the Flemish Region. &nbsp

Added value of micro-tomography measurements in mechanical characterization of materials: some case studies in engineering applications

The research group Mechanics of Materials and Structures at Ghent University in Belgium is doing research on the experimental and computational mechanics of (composite) materials. Micro-tomography is used as a measurement tool to improve insight in mechanical testing and to provide input for finite element simulations. In this contribution, several case studies in engineering applications will be discussed: • Laminated glass is widely used in all building applications. The EN12600 standard is a testing standard to assess the resistance of laminated glass against "human impact", as it frequently happens that people accidently walk into a glass door or tumble into a large glass window or glass fence. As the "human impact" should be replaced by a standardized impactor, an inflated rubber tyre is used to that purpose. In modelling the EN12600 standard, the interaction of the tyre with the laminated glass is important. Micro-CT imaging has been used to reconstruct the tyre model (Figure 1), • All large OEM companies in automotive industry are actively doing research on weight reduction of cars. One of the considered options is (partially) replacing metallic components by composite components. However, cycle times in automotive industry are extremely short (about 1 minute per part) and 50,000 to 100,000 parts per year are target numbers that should be reached. Therefore, novel composite material combinations have to be designed that can be processed very fast. Figure 2 shows a dry 3D woven fabric with commingled glass/polyester yarns that can be consolidated very fast in a heated press. The Micro-CT images are used to characterize the fabrics and reconstruct the "as-woven" geometry, • Figure 3 shows a CT-scan of a 3D printed PA12 (polyamide-12) material. In this research, relations are sought between the internal microstructure of the 3D printed material, the sequence of layer-by-layer deposition and the resulting mechanical properties of the 3D printed material