Development, Characterization of Mechanical Properties, Wear behaviour and Machining Analysis of Ceramic Composites for Bio-Medical Applications

Abstract

Ceramic composites incorporating synthetic hydroxyapatite (HAp) particulate and thermoplastic polymer matrices are finding wide spread applications in bio-medical field. The fractured or damaged bone can be repaired or replaced by artificial bone materials. HAp has been tested many times as an artificial bone, especially as augmentation material in surgery work or as a coating material on bio-inert implants materials. It has shown excellent biocompatibility and bonding characteristics. Many implant materials used for last three decades are basically metals, alloys, ceramics and polymers etc. Most metals and ceramics are much stiffer than bone tissue resulting in mechanical mismatch (i.e. “stress shielding”) between the implant and the adjacent bone tissue. Metals are too stiff and pose other biocompatibility problems whereas ceramics are too brittle but polymers are too flexible and weak to meet the mechanical strength. However, polymers are popular due to their low density, good mechanical strength and easy formability. Therefore, polymeric bone implants are widely used. HAp particulates are mixed with polymer matrix through a series of processing stages involving melt compounding, granulating and micro-injection moulding. HAp is a suitable ceramic material for hard tissue replacement. In the present work, HAp is synthesized by wet chemical precipitation route. The mechanical properties such as tensile, compressive, flexural, impact and hardness are assessed for the composites varying HAp volume percentage in polycarbonate (PC) and polysulfone (PSU) polymers. The wear resistance of composites in abrasion, erosion, sliding and fretting mode is assessed in dry environment. Adaptive neuro-fuzzy inference system (ANFIS) model is proposed for prediction of wear behaviour of composites. The effect of drilling parameters on surface integrity of internal holes made on composite is assessed to provide insight into machinability (i.e. drilling) aspects of composites. The aim of this study is to develop material that has similar mechanical properties to that of human bone in order to achieve mechanical compatibility in the body, examine the various mechanical properties of ceramic composites, assess the performance of the ceramic composites under different wear modes and evaluate the performance of the composites in drilling operation. The samples were characterized by x-ray diffraction (XRD), fourier transform infrared test (FTIR), and scanning electron microscopy (SEM). Two-body abrasion wear behaviour of the composite is evaluated using pin-on-disc friction and wear test rig (ASTM G99). The experiment is conducted using three different water proof silicon carbide (SiC) abrasive papers of 400, 600 and 1000 grit size. Taguchi’s L27 orthogonal array is used to evaluate the tribological property with four control variables such as HAp volume percentage, load applied, sliding speed and track radius, each at three levels. The highest abrasive wear loss is noticed in the specimens worn with 400 grit size SiC paper. Erosion wear of ceramic composites is performed on air jet erosion test rig (ASTM G76). In this study, dry silica sand (spherical) of different particle size of 300μm, 400μm and 500μm are used as erodent. Taguchi’s L27 design is used to evaluate the tribological property with three control variables such as pressure, HAp volume, and impingement angle, each at three levels. The higher erosive wear loss is noticed in the specimens worn with 500μm erodent particle size as compared to both 300μm and 400μm erodent particle size. The sliding wear test of ceramic composites is performed on ball on plate wear tester (ASTM G194). Taguchi’s L27 design is designed to evaluate the tribological properties with three control variables such as HAp volume percentage, load applied and sliding speed, each at three levels. The fretting wear test of ceramic composites is performed on high frequency reciprocating rig (HFRR) testing machine (ASTM D6079). Taguchi’s L27 orthogonal array is used to evaluate the tribological properties with three control variables such as HAp volume, load applied and frequency, each at three levels. Since drilling is used to join the composite material with adjacent bone tissue in orthopaedic surgery, it is important to study drilling performance of the composite. Experiments have been conducted on a CNC milling machine using Taguchi’s L27 design with four control variables such as HAp volume percentage, drilling speed, feed rate and drill bit diameter, each at three levels. The responses considered are circularity at entry and exit, torque and thrust force. The circularity at both entry and exit is measured using the ratio of minimum diameter (Dmin) to maximum diameter (Dmax) of the drilled hole. The torque and thrust force are measured using drill dynamometer.
Best parametric setting for simultaneous optimization of multiple performance measures such as circularity at entry, circularity at exit, torque and thrust in drilling operation is suggested using principal component analysis.