Jan Belis

Guidance for European Structural Design of Glass Components

Keywords: structural glass Reference EPFL-REPORT-196634 Record created on 2014-02-13, modified on 2016-08-09

Plasticity as a Lifesaver in the Design of Cardiovascular Stents

A common treatment to restore normal blood flow in an obstructed artery is the deployment of a stent (i.e. small tube-like structure). The vast majority of stents are crimped on a folded balloon and laser cut from 316L stainless steel tubes. Although, several numerical studies (exploiting the Finite Element Method) are dedicated to the mechanical behaviour of balloon expandable stents, there seems to be no consensus regarding the mechanical properties to describe the inelastic material behaviour of SS316L. Moreover, as the typical dimensions of stent struts (e.g. 100 μm for coronary stents) are of a similar order of magnitude as the average grain size in stainless steel (i.e. 25 μm), continuum approaches relying on macroscopic material properties may be questionable. In addition, an experimental study on stainless steel stent strut specimens showed a size-dependency of the failure strain. In this study the impact of the magnitude of the yield stress on the stent expansion behavior is examined. An increase in the yield stress (from 205 N/mm² to 375 N/mm²) results in an increase of the pressure (from about 0.3 N/mm² to approximately 0.4 N/mm²) which the clinician needs to exert for the balloon to unfold and to reach its cylindrical expanded shape. Furthermore, the effect of the size dependency behavior of the material is studied by monitoring the nominal strain during stent expansion. The maximum value of the nominal strain in the expanded stent (e.g. εn = 23 %) does not exceed the critical value of the failure strain, (i.e. εn = 33 %), moreover the critical values are nowhere exceeded in the whole stent during the expansion. Our numerical results - accounting for the presence of the balloon in its actual folded shape - correspond very well with pressure/diameter data supplied by the manufacturer. Consequently, this study shows that the free expansion of new generation balloon-expandable stents can be studied accurately with computational analysis based on the Finite Element Method (FEM) and relying on macroscopic material properties. In this context, there is no need to implement a size-based constitutive material model, but before accepting the results of the study, one should check in any case the maximum strain against the limit as shown above.

Experimental investigation of unconventional canopy prototypes, suspended by adhesive bonds

In this contribution the performance of an adhesively bonded glass to metal connection with a carefully selected epoxy adhesive is investigated experimentally. Deliberately pushing the limits of conventional safety concepts for the sake of the experiment, laminated glass canopies were suspended on stainless steel local point-fixings, adhesively bonded to the upper glass sheet only. Subsequently, the suspended system was subjected to a ball-drop test, a uniform load and a hammer impact. Different glass types and canopy arrangements have been tested in this way. Depending on the design parameters, several compositions demonstrated surprisingly good residual structural safety: even after 24 hours of full loading in broken conditions, the heat-strengthened canopy configurations did not collopse.

Experimental investigation of the influence of temperature on local bridging behaviour in laminated glass elements in post-breakage state

The assessment of the post-breakage performances of laminated safety glass elements used in construction needs to take into account the sensitivity to the temperature of the mechanical behaviour and properties of the product, in particular of the interlayer material. After a general problem statement, an overview is given of tests at different scales, with typical observations and results for two different interlayer materials. Through the different presented experimental scales, the mechanisms ruling the bridging behaviour in cracked laminated safety glass are explained, highlighting the difficulty of assessing the mechanical properties to be used in practical design calculations.

Glass Structures and Plasticity: Contradiction or Future?

Under normal serviceability temperatures, glass behaves like a linear elastic material, which will break suddenly when tensile stresses exceed a critical value. This does not necessarily mean that fracture occurs without any visual warnings. Especially when appropriate tempered glass is used, glass beams show a considerable deformation capacity. Still, there is no plasticity involved since all deformations are linear. The main safety concept is to create an overall structural “plasticity” for the glass beam as a whole, rather than for the individual material. This is usually done by building laminates: individual glass leafs alternated with soft transparent interlayers are composed as one coherent structural element. Currently, polyvinyl butyral is the most used interlayer material. Experiments with other transparent interlay materials have been carried out at different research institutes, in order to introduce more plasticity in the structural behaviour of glass beams. Not all attempts are as successful, but some results are promising. It is the authors’ opinion that the ability to create an overall structural plasticity will strongly influence the breakthrough of load bearing glass constructions. In the available literature however, the authors lack an overall picture of the current state of the art. For this reason, an attempt is made to present the actual research and different aspects of “plasticity in glass constructions” in this paper.

Lateral-Torsional Buckling Resistance of Castellated Beams

AbstractThe existing design expressions for the lateral-torsional buckling behavior of castellated beams conflict. Furthermore, they do not take into account the detrimental effect of the residual stress modification attributable to the fabrication process, which was only recently demonstrated by the authors. This makes these design rules possibly unsafe. In this paper, the lateral-torsional buckling behavior of doubly symmetric castellated beams loaded by a constant bending moment is investigated numerically. The numerical model, including the modified residual stresses, was validated by comparing its results with experimental results. A preliminary design approach is proposed based on the current European guidelines for the calculation of the lateral-torsional buckling resistance of I-section beams. According to the proposed approach, the lateral-torsional buckling resistance of castellated beams can be determined using the cross-sectional properties calculated at the center of the web opening. The modi...

Technical improvements in 19th-century Belgian window glass production

Glass was used since the Roman age in the building envelope, but it became widely applied together with iron since the 19th century. Belgium was a major producer of window glass during the nineteenth century and the majority of the produced window glass was exported all over the world. Investigating the literature on the development of 19th century Belgian window glass production is therefore internationally relevant. In the 17th century, wood was replaced as a fuel by coal. In the 19th century, the regenerative tank furnace applied gas as a fuel in a continuous glass production process. The advantages were a clean production, a more constant and higher temperature in the furnace and a fuel saving. The French chemist Nicolas Leblanc (1787-1793) and later the Belgian chemist Ernest Solvay (1863) invented processes to produce alkali out of common salt. The artificial soda ash improved the quality and aesthetics of the glass plates. During the 19th century, the glass production was industrialized, influencing the operation of furnaces, the improvement of raw materials as well as the applied energy sources. Although the production process was industrialized, glassblowing was still the work of an individual. By improving his work tools, he was able to create larger glass plates. The developments in the annealing process followed this evolution. The industry had to wait until the invention of the drawn glass in the beginning of the 20th century to fully industrialise the window glass manufacture process.

TORSIONAL STIFFNESS OF LAMINATED GLASS ELEMENTS IN STRUCTURAL APPLICATIONS — INFLUENCE OF A ELASTO-VISCOPLASTIC IONOMER INTERLAYER ON THE PRE-BREAKAGE BEHAVIOUR

To investigate the mechanical behaviour of laminated glass with the elasto-viscoplastic ionomer interlayer SentryGlas® by DuPont, an experimental program was executed on full-scale glass laminates. The results of this research improved the insight in the complex mechanical behaviour of this stiff interlayer. More specifically, a clear influence of load duration and temperature could be observed for both creep and relaxation setups during bending experiments. The stiffness reduction due to the load duration and the temperature raise was most significant for the smaller specimens - with a span of 1 m - while for the largest specimen - with a span of almost 3 meter - the reduction remained less than 25 % of the monolithic bending stiffness, even after a load duration of 48 hours at 65 °C.

Design Curve to Use for Lateral Torsional Buckling of Tapered Cantilever Beams

Beams with tapered webs are used to adapt the bending resistance of a beam to the moment distribution. In this study, tapered cantilevers are loaded at their free end with a point load at the upper flange. A large number of beams with different tapers, lengths and cross section classes are simulated with the finite element code Abaqus. Welding stresses and geometrical imperfections are included in the model and the use of geometrical and material nonlinearities result in a realistic behaviour up to failure. The results are presented in a buckling diagram and confronted with existing buckling curves of Eurocode 3. The results indicate that the “General method for lateral torsional buckling of frames” can safely be used as a design rule. Introduction For large span frames, the weight of the beams is often the dominating load. Weight can be saved by adapting every cross section to the internal forces. Adapting the cross section in a continuous way can only be achieved when beams are welded from strips with a varying width, resulting in so called tapered beams. Practical realisations indicate that the additional fabrication cost can be compensated by the achieved weight reduction. The I-beams studied here have a linearly varying height and two equal flanges. The use of tapered beams results in slender constructions that are more susceptible to instability phenomena such as lateral torsional buckling (LTB). Unfortunately, there are no general and simple design rules as for prismatic beams yet available for tapered beams. The draft version of Eurocode 3 [1] describes in section 6.3.3. a method that may be used for the verification of frames with non uniform cross sections. In this contribution, the results of finite element simulations are used to verify the applicability of this method for the case of tapered cantilever beams which are loaded with a concentrated force which is applied at the upper flange of the tip section.

Influence of the Load History on the Edge Strength of Glass with Cut Edge Finishing

Keywords: Structural glass ; Edge strength ; Load history ; Load duration ; Load type ; Edge finishing ; Fracture mechanics ; Stress corrosion Reference EPFL-CONF-176264 URL: http://www.challengingglass.com/ Record created on 2012-04-18, modified on 2016-08-09