Mechanical performance and machinability of hybrid FRP composite via abrasive water-jet machining using Response Surface methodology and Numerical model

Driven by the need for light-weight and high-strength materials for parts and components in the aviation and automotive sectors, research activities in attaining these requirements have been exponentially increased. This research describes an experimental investigation on the machinability of hybrid fibre reinforcement polymer (FRP) composites under abrasive water-jet machining (AWJM). Prior to machining, hybrid FRP composites of different architectures or arrangements were initially fabricated using resin transfer moulding for screening purposes. Mechanical properties such as tensile strength, flexural strength and volume fraction of the hybrid composites were determined per ASTM standards. Material screening experimentation indicates that the [CW2]6 arrangement, where C and W are weaved carbon fibre and glass fibre respectively, were superior in terms of mechanical properties. The machinability of [CW2]6 hybrid composites was then further investigated due to their excellent mechanical performance. However, it is well known that machining of FRP composites without any defect is extremely challenging when using conventional machining processes. This is mainly due to their inherent anisotropic, heterogeneous, thermal sensitivity, and highly abrasive of nature of fibre reinforcements. This research attempted to comprehensively evaluate the significant and optimal combination of AWJ machining parameters with respect to the kerf ratio, surface roughness and delamination (entrance and exit) on the hybrid FRP composite by the response surface methodology and statistical analysis of variance. A 2k factorial design that follows a face-centred composite design (FCD) with a total of 30 experimental runs (16 factorial points—24, eight axial points—2 × 4, and six centre points) were outlined using Design Expert software. It is worth to note here that previous attempts in the trimming of composites has been challenging due to the presence of poor kerf taper, rough surface and severe delamination on top and bottom surface of trimmed surface. Experimental results revealed that the kerf ratio was influenced by the stand-off distance and traverse rate. On the other hand, both side of delamination were only influenced by abrasive flow rate, traverse rate, and hydraulic pressure. Lastly, surface quality was highly affected by the abrasive flow rate, stand-off distance, and traverse rate rather than the hydraulic pressure. In short, minimum kerf ratio, surface roughness, and delamination can be achieved by increasing the kinetic energy of abrasive water-jet stream when impinging into the composite under a lower speed. The optimum process parameters setting in achieving high-quality composites after the machining process were at abrasive flow rate of 600 g/min, hydraulic pressure of 262.6 MPa, stand-off distance of 2 mm and low traverse speed of 1000 mm/min. Further work on understanding the mechanism of surface damage under high velocity condition of AWJM has been developed using finite element method coupled with smooth-particle hydrodynamics. Results of this numerical model indicated that stagnation of abrasive particles at impact point generated delamination (crack initiation and propagation) and subsequently shear-out mechanisms. A good agreement was evident (qualitatively and quantitatively) between the simulation and experimental results in this particular study.