This article was published in the journal, Composites Part A: Applied Science and Manufacturing [© Elsevier] and the definitive version is available at: http://dx.doi.org/10.1016/j.compositesa.2012.11.020Drilling carbon fibre reinforced plastics (CFRPs) is typically cumbersome due to high structural stiffness of the composite and low thermal conductivity of plastics. Resin-rich areas between neighbouring plies in a laminate are prone to drilling-induced delamination that compromises structural integrity. Appropriate selection of drilling parameters is believed to mitigate damage in CFRPs. In this context, we study the effect of cutting parameters on drilling thrust force and torque during the machining process both experimentally and numerically. A unique three-dimensional (3D) finite element model of drilling in a composite laminate, accounting for complex kinematics at the drill-workpiece interface is developed. Cohesive zone elements are used to simulate interply delamination in a composite. Experimental quantification of drilling-induced damage is performed by means of X-ray micro computed tomography. The developed numerical model is shown to agree reasonably well with the experiments. The model is used to predict optimal drilling parameters in carbon/epoxy composites

Bone drilling is widely used in orthopaedics and surgery; it is a technically demanding surgical procedure. Recent technological improvements in this area are focused on efforts to reduce forces in bone drilling. This study focuses on forces and a torque required for conventional and ultrasonically-assisted tool penetration into fresh bovine cortical bone. Drilling tests were performed with two drilling techniques, and the influence of drilling speed, feed rate and parameters of ultrasonic vibration on the forces and torque was studied. Ultrasonically-assisted drilling (UAD) was found to reduce a drilling thrust force and torque compared to conventional drilling (CD). The mechanism behind lower levels of forces and torque was explored, using high-speed filming of a drill-bone interaction zone, and was linked to the chip shape and character of its formation. It is expected that UAD will produce holes with minimal effort and avoid unnecessary damage and accompanying pain during the incision.

The mechanical properties of cortical bone vary not only from bone to bone; they demonstrate a spatial viability even within the same bone due to its changing microstructure. They also depend considerably on different loading modes and orientations. To understand the variability and anisotropic mechanical behavior of a cortical bone tissue, specimens cut from four anatomical quadrants of bovine femurs were investigated both in tension and compression tests. The obtained experimental results revealed a highly anisotropic mechanical behavior, depending also on the loading mode (tension and compression). A compressive longitudinal loading regime resulted in the best load-bearing capacity for cortical bone, while tensile transverse loading provided significantly poorer results. The distinctive stress-strain curves obtained for tension and compression demonstrated various damage mechanisms associated with different loading modes. The variability of mechanical properties for different cortices was evaluated with two-way ANOVA analyses. Statistical significances were found among different quadrants for the Young's modulus. The results of microstructure analysis of the entire transverse cross section of a cortical bone also confirmed variations of volume fractions of constituents at microscopic level between anatomic quadrants: microstructure of the anterior quadrant was dominated by plexiform bone, whereas secondary osteons were prominent in the posterior quadrant. The effective Young's modulus predicted using the modified Voigt-Reuss-Hill averaging scheme accurately reproduced our experimental results, corroborating additionally a strong effect of random and heterogeneous microstructure on variation of mechanical properties in cortical bone.