Anjali De Silva

Electrochemical Machining (ECM) is a metal removal process that operates on the principle of anodic dissolution. ECM has the ability to produce complex shapes in difficult-to-machine alloys with precision and excellent surface finish. However, since most of these alloys contain chromium, one of the major challenges to ECM’s wider utilisation in industry is how to eliminate the resulting hexavalent chromium (Cr⁺⁶) from the spent electrolyte. This paper presents methods for controlling the Cr⁺⁶ level to within the permitted guidelines for an industry application of ECM, and reducing it to trivalent chromium (Cr⁺³), to then precipitating it from the electrolyte solution, The workpiece material – Triboloy (Co; Mo; Cr alloy) has hitherto not been machined by ECM and hence no literature exists on how to treat the by-products generated. This research involves experimental analysis of various Cr⁺⁶ to Cr⁺³ chemical reduction methods for ECM of Tribaloy in sodium nitrate electrolyte, using spent electrolyte samples. The reduction in Cr⁺⁶ is assessed over time. It was observed that the concentration of Cr⁺⁶ decreased within a span of two minutes. Subsequently, the solution pH level was increased by the addition of an alkali to precipitate the Cr⁺³ ions, which then can be filtered out from the solution. The optimum solution for hexavalent chromium is thus implemented in the industrial electrolyte system for successfully machining the Tribaloy component.

Carbon fiber reinforced polymer (CFRP) offers the highest potential for lightweight applications due to its excellent weight to strength ratio in comparison to other materials. However, it is cost-intensive and therefore rarely used monolithically. This makes pretreatment and joining processes so important. Hybrid connections of CFRP and metals can be made by riveting, bolting, stir joining and by adhesive. For adhesive bonding, a pretreatment of the materials is necessary. A laser pretreatment has the advantage, that it is automatable and contactless. This paper deals with the pretreatment of CFRP with different laser wavelengths in near-infrared (NIR, 1030 and 1064 nm) and ultraviolet (UV, 355 nm) range. The influence of the processing direction relative to the fiber layer and the influence of the energy density was investigated with a short pulsed NIR infrared laser. In addition, the influence of different surface structures on the mechanical strength was investigated. The treated CFRP surfaces were examined with a light microscope and a scanning electron microscope. The tensile shear strengths were determined using CFRP and aluminum substrates, joined with a 2-part epoxy adhesive. As a comparison, UV laser treated specimens were also mechanically tested. An ultra-short pulsed NIR laser system was used to generate periodic structures on the CFRP to maximize the surface area without fiber damage and breakage. The investigations on the influence of the machining direction with NIR relative to the fiber layer showed insignificant differences in shear strengths. The variation of the energy density showed an influence on the ablation behavior of the CFRP matrix and the mechanical strength. The maximum strength with a cohesive failure in the adhesive was achieved with optimized short pulsed NIR laser parameter.

One of the main global engineering challenges for wind energy sector is to develop efficient wind turbine blades with high fatigue life. Large wind turbine blades made out of polymer composites to delivering high specific stiffness and strength, and good fatigue performance. The arbitrary nature of wind flow and extreme weather conditions render wind turbine blades as fatigue critical elements. Therefore, reliable fatigue damage models need to be developed. Numerous studies were carried out in the past to identify the effect of various materials and loading conditions for fatigue life of wind turbine blades. However, these models do not consider the effect of manufacturing defects and in-service damages for fatigue life of wind turbine blades. This paper discusses the available fatigue life estimation models for wind turbine blades and their limitations. The paper, propose a framework for developing fatigue life estimation technique for wind turbine blades based on finite element analysis (FEM) stress and strain data.