Optimization of process variables in drilling of carbon fiber reinforced plastics using various multi criteria decision making approaches

Carbon fiber-reinforced polymers are one of the lightweight materials used in structural design due to their exceptional mechanical performances. The drilling operation is indispensable as it facilitates the assembling of various manufactured components. However, drilling of fibrous laminates is deemed difficult in comparison to the traditional metals because of the anisotropic and non-homogeneous nature. The present work addresses the parametric effect on the drilled hole delamination and further reduces it with an optimal combination of parameters for multi-objectives using different multi-criterion decision-making techniques. Initially, the response surface-based regression model of delamination as a function of three static inputs has been developed, further revised with induced thrust as well as mean torque for the improvisation of the prediction capability. Finally, for the overall improvement, a decision-making model has been used that includes grey relation analysis, technique for order performance by similarity to ideal solution, and VIšekriterijumsko Kompromisno Rangiranje method. The delamination was found to be minimum at a low drill point angle (100°), high spindle rotation (2150 min⁻¹ ), and low feed rate (0.025 mm/rev) due to reduced thrust force. The mean absolute prediction error was significantly improved considering root mean square torque rather than axial thrust with process variables.     

Effect of the structural reinforcement of composite adherends on the mechanical strength of adhesive joints

This study proposes a novel method to strengthen fiber reinforced plastic (FRP) adherends in a single lap joint (SLJ) by using Kevlar threads. The adherend reinforcement procedure consists of applying a zigzag thread in the fiber glass layers that comprise the adherend in order to subsequently manufacture the adherends using the vacuum infusion method. For this study, three single lap joint configurations were used: Adherends without Kevlar reinforcement (SLJ₁), adherends with Kevlar reinforcement with a medium step zigzag (SLJ₂) and adherends with Kevlar reinforcement with a small step zigzag (SLJ₃). Mechanical tensile tests were carried out to determine the ultimate strength and displacement of the single lap joint configurations studied. Adherends reinforced by Kevlar threads increase the strength and displacement of the single lap joint. However, the influence of the step size of zigzag threads on the adherend does not significantly influence the strength, but significantly affects the maximum displacement of the single lap joint.     

Brücken mit Fahrbahnen aus glasfaserverstärktem Kunststoff (GFK) – Neue Straßenbrücke in Friedberg (Hessen)

In Friedberg (Hessen) wurde im Juli 2008 erstmals in Deutschland eine Straßenbrücke unter Verwendung von glasfaserverstärktem Kunststoff (GFK) fertig gestellt. Das Bauwerk überspannt mit 27 m die Bundesstraße B 3a bei der Stadt Friedberg (Hessen) und wurde in Stahl‐GFK‐Verbundbauweise realisiert. Die hohe Dauerhaftigkeit des neuen Werkstoffs und die zügige Montage der Brücke waren die entscheidenden Gründe pro GFK. In den letzten Jahren wurden in den USA, Japan und auch in Europa einige Leichtbaubrücken mit faserverstärkten Kunststoffen realisiert. Dabei konnten wertvolle Erfahrungen zum Bau und Betrieb gesammelt und die Leistungsfähigkeit von Verbundwerkstoffen unter Beweis gestellt werden. Die Brücke in Friedberg geht über diese Vorbilder hinaus, indem hier erstmals die Verbundwirkung zwischen der GFK‐Fahrbahn und dem Haupttragwerk aus Stahl berücksichtigt wird. Außerdem wurde konsequent der Ansatz eines wartungsarmen und langlebigen Bauwerks verfolgt, indem auf Lager und Fahrbahnübergänge verzichtet wurde. Bridges with Glass Fibre Reinforced Polymers (GFRP) decks – The new Road Bridge in Friedberg (Hessen, Germany). In July 2008 the first road bridge in Germany using glass fibre reinforced polymers (GFRP) was finished in Friedberg (Hessen). The structure has a span of 27 m and acts as overfly of the federal road B 3 near Friedberg (Hessen). The high durability of the new construction material and the fast assembly of the bridge were decisive factors in favour of GFRP. Within the last years several light weight bridges using FRP were realised in USA, Japan and also in Europe. Through this valuable experiences could be gathered regarding construction, the use and performance of composites could be demonstrated. The bridge in Friedberg extends this experience with the approach of considering the composite action of the FRP deck and the steel girders. It also follows consequently the approach of durable bridge construction by omitting any bearings or expansion joints.     

Metall‐Kunststoff‐Verbunde: Untersuchungen zur Wirkungsweise einer Adhäsionsschicht aus Uretdionpulverlacksystemen

Metal plastic hybrids combines the properties of the components: the high strength and rigidity of the metal, as well as the excellent possibilities of the lightweight thermoplastic in moulding processes. This allows the production of new parts with integration of different functions. Assembly injection moulding is a very effective and low‐cost technology for the metal plastic hybrid manufacture. We investigate three layer hybrids of steel plate, low module polyurethane and an adhesion layer. A new developed low temperature uretdione polyurethane powder coating material in two different curing grades is used as the adhesion layer. This curing grades are the allophanate‐ and the urethane group grades. The aim of our work consist in the investigation of the influence of the two curing grades on the three layer hybrid bond strength. The results of the model tests as well as of the analytical investigations are in good correlation to the bond strength level. This allowed us to make two thesis: on the one hand the fusing thesis and on the other hand the reaction thesis.     

Über die Verwendung und Bedeutung von Kerbformzahlen bei der Auslegung von Faser‐Kunststoff‐Verbunden

On the application and meaning of stress concentration factors in the design process of fibre reinforced composites Translation: The application of stress concentration factors is a common method to rate stress concentrations in the design process. Even in the case of layered composites stress concentration factors, which do not only depend on the form but also on the elastic properties of the composite, are applied. In many cases the application of such stress concentration factors lead to a misinterpretation of the stress state at the cut‐out. Based on concrete examples the failing of an analysis based on common stress concentration factors and the resulting misinterpretation is shown. In order to remove these deficiencies a new layer‐wise stress concentration factor is established. The definition of this new stress concentration factor corrects the deficiencies of common factors. A given example helps to understand the new definition. Criteria are derived to distinguish in which cases common stress concentration factors are applicable to layered composites.