Evaluating the role of damage in the mechanics of chip segmentation.

Sem ResumoThe mechanics of chip segmentation is still controversial with regards to its root cause. Whether by thermoplastic instability or damage, chip segmentation is caused by local loss of strength of the chip in the region of primary shear. This work is mainly focused on the discussion of the different theories and the root cause of the phenomenon both by numerical and experimental viewpoints. Numerical experiments deal with the constitutive models that describe softening and damage in finite element simulations, while the experimental part deals with the phenomenon of chip segmentation in a brittle material with anomalous yield behavior, namely an iron aluminide intermetallic. This work concludes that damage mechanics dominate the phenomenon of chip segmentation, at least in materials with limited ductility, and that thermal effects are to be used only as an extension of the theory. In materials with considerable ductility, the numerical models cannot predict chip segmentation without the consideration of thermal effects, where the variables of thermal softening and softening due to damage strongly contribute to the phenomenon

Use of ball-cratering wear test and nanoscratching test to compare the wear resistance of homogeneous and functionally graded titanium nitride thin films

Homogeneous (HM) and functionally graded (FG) TiN thin films were produced by the grid-assisted magnetron sputtering (GAMS) technique. The joint use of ball-cratering micro-abrasive wear test (BCMA) and nanoscratching (NN) test was proposed and carried out to evaluate the wear resistance of TiN films. The results showed an increase of 33.3% wear resistance in the FG TiN thin film, when compared with the HM TiN thin film. This result was justified by the higher resistance to nucleation and propagation of cracks and higher level of adhesion to the substrate by the FG TiN thin film, validated through the NN tests