In this work, a methodology to quantify the effect of the drilling operation, during the application of the incremental hole-drilling technique (IHD) for measuring residual stresses in laminate composites, in particular, the polymer matrix composites (PMC), is presented. This technique will allow the optimization of the drilling procedures and its parameters, enabling the quantification of the drilling effect. This quantification is obtained by using an experimental calibration procedure followed by a numerical simulation of the whole process. The direct comparison of the experimental and numerical results will allow quantifying the effect of the drilling operation. As example, the methodology was applied to the case of carbon/epoxy cross-ply laminate [0°/90°]5s. The holes have been made by using two different drilling procedures, but the same tool geometry. High speed milling powered by air compression, a process usually employed in the case of the application of hole-drilling technique to metal alloys and a conventional computer numerically controlled (CNC) milling machine, were used. The results seem to show that incremental hole-drilling could be a reliable technique to determine residual stresses in fibre-reinforced polymers.
Residual strains induced by drilling of glass-fibre reinforced polymers (GFRP) were determined using a hybrid experimental-numerical methodology. Experimentally, a set of GFRP specimens were drilled under well-defined tensile (calibration) stresses, using an especially designed tensile test device. To remove the effect of the initial residual stresses, this methodology considers differential stress values instead of absolute ones. Numerically, the experimental procedure was simulated using the finite element method. The induced drilling strains were determined by comparing the experimental measured strains with those calculated numerically. Clear differences between the selected drilling operations could be observed and evaluated.
Tool wear during hard machining leads to unfavourable changes in the workpiece surface and subsurface layers. Due to increasing flank wear, thermal and mechanical loads affect the microstructure and the residual stress state of the workpiece subsurface. These effects cause a reduction in the lifetime of the machined components during operation. This article presents an approach of modified corner radii of cutting tools for hard turning processes to change the tool wear progression and the influence on the machined subsurface layers. Hereby the size and direction of the contact length of the cutting edge is adjusted as well as the specific load during machining. The results show the potential of controlling the tool wear and the workpiece subsurface properties by the contact conditions of the tool-workpiece interface during hard turning.
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