Local damage to Ultra High Performance Concrete structures caused by an impact of aircraft engine missiles

The impact of an aircraft engine missile causes high stresses, deformations and a severe local damage to conventional reinforced concrete. As a consequence the design of R/C protective structural elements results in components with rather large dimensions.Fiber reinforced Ultra High Performance Concrete (UHPC) is a concrete based material which combines ultra high strength, high packing density and an improved ductility with a significantly increased energy dissipation capacity due to the addition of fiber reinforcement. With those attributes the material is potentially suitable for improved protective structural elements with a reduced need for material resources.The presented paper reports on an experimental series of scaled aircraft engine impact tests with reinforced UHPC panels. The investigations are focused on the material behavior and the damage intensity in comparison to conventional concrete. The fundamental work of [Sugano et al., 1993a] and [Sugano et al., 1993b] is taken as reference for the evaluation of the results. The impactor model of a Phantom F4 GE-J79 engine developed and validated by Sugano et al. is used as defined in the original work. In order to achieve best comparability, the experimental configuration and method are adapted for the UHPC experiments. With ‘penetration’, ‘scabbing’ and ‘perforation’ all relevant damage modes defined in [Sugano et al., 1993a] and [Sugano et al., 1993b] are investigated so that a full set of results are provided for a representative UHPC structural configuration.     

Fabrication of a potentiometric/amperometric bifunctional enzyme microbiosensor

We report the fabrication and functional characterization of a needle-type bifunctional enzyme microbiosensor that has, as technical novelty, simultaneously integrated a potentiometric and amperometric detection of an enzyme-catalyzed reaction at the tip of a pulled glass micropipet. The construction involved immobilizing an enzyme onto the platinized outer tip surface using the precipitation of electrodeposition paint with direct entrapment of the biocomponent in the slowly growing polymer film. Products of enzyme-substrate reaction could then be targeted in a dual-detection mode on one hand with the covered Pt layer at the tip region as amperometric detector and on the other hand with a proton-selective liquid membrane-based potentiometric sensor inside the open pipet tip. Completing and testing bifunctional glucose microsensors demonstrated the functionality of the proposed strategy. Synchronized amperometric and potentiometric detection of the addition of a glucose standard to a buffer solution became evident by observing stepwise increases in the amperometric H2O2 oxidation current and corresponding increases in the potential of the pH-selective sensor, which translates to a local pH decrease around the tip due to hydrolysis of enzymatically formed gluconic acid.     

Monte-Carlo simulation of multiple fracture in the transverse ply of cross-ply graphite-epoxy laminates

Graphite-epoxy cross-ply laminates generally show multiple fracture of the transverse ply at higher applied stress. This phenomenon is described by means of a Monte Carlo simulation method based on the assumption that the strength of the transverse ply obeys a two-parameter Weibull distribution function. The main results show that the smaller the scatter of strength of the 90°-ply (i.e. the larger the shape parameter at a constant mean strength of the Weibull distribution), the higher becomes the threshold for the multiple fracture to occur, and the more rapidly the length of 90°-ply segments decreases with increasing applied stress once multiple fracture takes place. The methods to determine the shape and scale parameters of the Weibull distribution for the strength of the 90°-ply proposed by Manderset al. and Peters are proved to be useful even for a small number of test specimens. When the interfacial bond strength between 0°- and 90°-plies is low, saturation of 90°-ply cracking occurs at higher applied stress. The stress-carrying capacity and stiffness of the composites as a whole are reduced by multiple fracture of the 90°-ply. This reduction is more pronounced at increasing applied stress or at a larger number of transverse cracks, especially when the interfacial bond strength is low.     

Influence of artificial pre-stressing during curing of CFRP laminates on interfibre transverse cracking

In this paper results are shown for a cross-ply laminate where the internal residual stresses in the 90° plies were influenced by mechanically pre-stressing the 0° plies during the curing process. After curing and cooling to room temperature the mechanical pre-stresses were released. The 90° plies were now under compressive stresses. This had the effect that under tensile loading the development of transverse cracks was delayed and shifted to higher strain and load values.     

Inelastic scattering on particles with inclusions

The investigation of particles with inclusions is of high interest in many parts of scientific research. Raman scattering is very good at yielding information on the internal composition of the particle. We use a geometrical-optics-based technique to determine the angle dependence of the inelastic scattering on particles with several spherical inclusions.     

Model Checking Grundlagen und Praxiserfahrungen

Die Gewährleistung der korrekten Funktionsweise von Hard- und Software ist ein entscheidender Faktor bei der heutigen Systementwicklung. Dies trifft ganz besonders auf das Gebiet der sog. sicherheitskritischen Systeme zu, bei dem ein Systemversagen Menschenleben gefährden kann.