| Popis: |
The study residual stresses due to machining is a very important facet industrial applications such as in aircraft of the components. End milling tests were performed on free machining brass plates. Compressive residual stresses were left within the machined surfaces. Assessments of the distribution of resisdual stresses underneath the machined surface have been given via a post removal technique. Microstructural examinations were made utilizing an optical microscope. Nitric acid of 32.5% concentration was used as etchant for the sides of the plates to reveal the proper grain boundaries. The change in the average grain size with the sub-surface depth, after milling was determined. The milled sides of the free machining brass specimens were subjected, as well, to micro-hardness examinations via a 100 gram load starting from the specimen surface till no change in micro-hardness were noted. Relationships between the knop micro-hardness values and the sub-surface depth were, then, obtained. All the test results indicated that maxima for residual stresses and micro-hardness together with minima for average grain size occurred near the surface of the plates . Moreover, it was found that starting off such locations values of residual stresses and micro-hardness decreased while grain size increased inter-relations among these three variables under such conditions were, then, deduced. |
