Abstract
This article presents a comprehensive thermomechanical analysis and failure assessment in the drilling of glass fiber-reinforced polymer (GFRP) composites with different thicknesses using a CNC machine and cemented carbide drill with a diameter of 6 mm and point angles of ϕ = 118°. The temperature distribution through drilling was measured using two techniques. The first technique was based on contactless measurements using an IR Fluke camera. The second was based on contact measurements using two thermocouples inserted inside the drill bit. A Kistler dynamometer was used to measure the cutting forces. The delamination factors at the hole exit and hole entry were quantified by using the image processing technique. Multi-variable regression analysis and surface plots were performed to illustrate the significant coefficients and contribution of the machining variables (i.e., feed, speed, and laminate thickness) on machinability parameters (i.e., the thrust force, torque, temperatures, and delamination). It is concluded that the cutting time, as a function of machining variables, has significant control over the induced temperature and, thus, the force, torque, and delamination factor in drilling GFRP composites. The maximum temperature recorded by the IR camera is lower than that of the instrumented drill because the IR camera cannot directly measure the tool–work interaction zone during the drilling process. At the same cutting condition, it is observed that by increasing the thickness of the specimen, the temperature increased. Increasing the thickness from 2.6 to 7.7 had a significant effect on the heat distribution of the HAZ. At a smaller thickness, increasing the cutting speed from 400 to 1600 rpm decreased the maximum thrust force by 15%. The push-out delaminations of the GFRP laminate were accompanied by edge chipping, spalling, and uncut fibers, which were higher than those of the peel-up delaminations.
Highlights
Fiber-reinforced polymer (FRP) composites have desirable features such as design flexibility, low weight, high strength, and a high stiffness-to-weight ratio
It is shown that the thrust force and delamination have the same behaviors, rather than the temperature, as the variation in the drilling time, which assures that the delamination is proportionally dependent on the thrust force and inversely dependent on the temperature, which may lead to softening
The significant effect of the machining parameters on the machinability of the glass fiber-reinforced polymer (GFRP) composite can be measured by the p-value
Summary
Fiber-reinforced polymer (FRP) composites have desirable features such as design flexibility, low weight, high strength, and a high stiffness-to-weight ratio. Khashaba and El-Keran [20] experimentally and analytically investigated the impact of machining parameters on the thrust force and delamination during drilling of a thin woven GFRP. Khashaba et al [26] experimentally explored the thrust force, torque, and delamination of GFRP composites during drilling processes with different machining parameters. Erturk et al [33] studied the effects of the cutting temperature and drilling parameters (drill bits, feed rate, and spindle speed) on the delamination of GFRP composites. Zhang et al [35,36] predicted novel fiber fracture criteria in the machining process of CFRP by analyzing the effects of the axial force and hole exit temperature on the formation of hole exit surface damage. Where Vf is the fiber volume fraction, n is the number of layers, Aw is the areal weight of the fabric, t is the thickness of the product, and ρ f is the fiber density
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