Thermo-Electric Detection of Early Fatigue Damage in Metals

There are numerous nondestructive inspection methods which can be used to detect and quantitatively characterize advanced fatigue damage following crack initiation. However, crack nucleation occurs at a much smaller microstructural scale following a more or less extended period of gradual material degradation which remains beyond the reach of known eddy current, ultrasonic, and other inspection methods. Before crack initiation, fatigue degradation remains an elusive process leading to distributed crystal defects on the scale of individual grains and grain boundary imperfections. This gradual evolution of early fatigue damage first results in increasing dislocation density, formation of slip bands, microplasticity, cold work, etc., then leads to crack nucleation at multiple sites. Following crack nucleation the growing microcracks ultimately coalesce into larger detectable fatigue cracks, but current NDE methods cannot detect the often quite serious preexisting fatigue damage in the material before this point

An experimental study into the effect of micro-textures on the performance of cutting tool

Micro-textures on cutting tool surface have been reported for their benefits in terms of reduction of adhesion, wear, force and friction during the cutting process. However, these benefits are dependent on the micro-texture parameters. This paper presents an experimental study on the effect of micro-textures during orthogonal cutting of aluminium, aiming to determine a suitable parameter combination. Micro-textures were fabricated on the rake face of tungsten carbide (WC) cutting tools by a picosecond laser. Circular dimples were selected as the texture unit cell, and the parameters included diameter, depth, pitch and distance from the cutting edge. Experiments were conducted by varying these parameters using the Taguchi method. Signal-to-noise (S/N) ratio and analysis of variance (ANOVA) were used to find the optimal levels of the selected parameters and to study the effect of the micro-textures on cutting forces, shear angle, contact area as well as adhesion of aluminium. It is found that diameter was the most influential parameter based on the factors taken into consideration. Then, a confirmation test using the derived levels of texture parameters was carried out to demonstrate the effectiveness of the micro-texture. The best combination of texture parameters was identified considering all the responses and the range of parameters