Issue 48

S. E. Oliveira et alii, Frattura ed Integrità Strutturale, 48 (2019Y) 249-256; DOI: 10.3221/IGF-ESIS.48.26 253 R ESULTS AND DISCUSSION urface roughness was analyzed to verify the adequacy of the machined processing under development. Fig. 6 shows the results obtained for both material batches: length fiber 0.5mm and 6mm, presenting the average values and the dispersion range of the experimental tests. The analysis of the figure shows that the experimental results are in good agreement with the usual values in the manufacturing industry, particularly to metallic materials. These results indicate that the parameter Rz increases slightly with the drilling speed, in spite of the natural dispersion of the results. Composites with lower fiber length and content exhibit much higher roughness Rz, probably a consequence of the lower glass transition temperature, Tg, of the polymer resin, and consequently in this case it is easier for the temperature on the surface of the tool to reach a value close to or greater than Tg during the cutting operation. The analysis of the data indicated that the speed cutting up to 2250 rpm and feed 150 mm per minute presents smaller values of surface roughness. The temperature on the surface of the carbide tool during the cutting of the SCFC plates was measured with an infrared thermograph camera, as shown in Fig. 4. The values of the maximum observed temperature in the cutting tool during face machining are plotted against the rotation speed for both composites in Fig. 7. In both cases, a significant increase of the temperature with the increase of cutting speed was observed. The temperature profile reveals that in some cases (above 3000 rpm) its values reach the glass transition temperature, Tg, of the polymer matrices. For the 6mm fibers composites the Tg of the resin (113 ºC [9]), while for Biresin® CR83 resin, Tg 84 ºC, according the manufacturer. Figure 5 : SEM low magnification characteristic micrograph of the fracture surface. Figure 6 : Surface roughness, Rz, against drilling speed. The results of the tensile tests are summarized in Figs. 8 and 9, which present the tensile strength and the Young’s modulus, respectively, against drilling speed. Tensile strength is the axial stress for the load peak of the load versus S