Man or Boy? Probleme der Rekursion in Compilern

Eingegangen am 20.03.1996, in überarbeiteter Form am 17.02.1997     

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.     

Processing and characterization of chemically modified wood sawdust reinforced (diospyros,dialium) epoxy composites

Polymer composite materials based on natural fiber such as wood had been widely used for research purposes and engineering interests. The interest in wood reinforced polymer composites had grown quickly due to their better performance in aspects of mechanical properties compared to pure wood. In this study, wood sawdust of diospyros (kayu malam) and dialium (keranji) were chosen to be incorporated into an epoxy-based polymer composite. The wood is made into sawdust, which was treated with boric acid and hydrogen peroxide. Surface treatment with these reagents was used to improve the mechanical properties of the polymer composite compared to untreated wood polymer composite. Sawdust reinforced epoxy composite that was fabricated are with different weight percentages from 0 % (no wood), 5 %, 10 %, 15 % to 20 % wt % for comparison on their tensile, flexural, and impact strength properties. Tensile, flexural, and impact tests were performed to determine the changes in mechanical properties where it was found that tensile strength had increased by 34 percent with an optimum keranji and kayu malam fiber weight of 15 wt % for both boric acid and hydrogen peroxide treatments. For flexural strength, in both wood fibers, the optimum fiber weight was found to 15 wt %, and the addition of wood had increased the strength by 57 percent. As for impact strength, it decreased as the weight of fiber increased, where it was assumed that the addition of wood might have increased the crack initiation. Adhesive bonding between hydrophilic wood sawdust and the hydrophobic epoxy polymer was the phenomenon that was focused on this research. The range of optimum weight percentage of sawdust would be determined from the experiment result.