Parâmetros de influência no cálculo do fator fab, em eventos produzidos via esclerometria retilínea

Abstract

Several authors have been writting that the abrasive wear characterization through the material removal factor (fab) is a difficult task, in many practical applications. It was observed that the fab values, under certain experimental conditions, showed a significant low repeatability, leading in some cases to result invalidation. To overcome this problem, in this work, a robust and efficient methodology of easy implementation was proposed and validated. An extensive study to identify the error sources that can affect the fab assessment was made through mechanical profilometry with contact and optical profilometry without contact. Protocols for sample preparation, for scratch performing and for measuring areas of interest were developed and adopted. The measurement uncertainty associated with all measurands was estimated by applying the method proposed in the GUM-JCGM 100. The results showed that the proposed methodology is robust, efficient and easy to apply. Testing a gauge block of grade 0 manufactured of high carbon and chrome steel alloy, results showed that, in contact measurement the repeatability associated with the fab obtained from five measurements was good, since the standard deviation represented in the worst case, 8 % and 12 %, for scratches performed using the Rockwell-C and Vickers indenters, respectively. The highest variability observed in the values of fab for the Vickers indenter can be attributed to the combination of smaller events with massive pile up and chip formation. Standard deviation values of the order of 2 % fab were obtained through non-contact measurement by adopting an average profile resulting from 2000 profile measurement. This work showed that the sample test surface must be carefully prepared, since Ra values of the order of 0.07 ± 0.08 μm and 0.04 ± 0.08 μm did not guarantee the achievement of fab values with adequate repeatability. Obtaining traceable and low repeatability fab values may increase the use of this parameter in researches aimed at improving materials wear resistance, as well as optimize decisions related to selecting and classifying these materials in order to increase the lifespan and efficiency of machines, equipments and pieces.