Original Article Feasibility study of delamination in rotary ultrasonic-assisted drilling of glass fiber reinforced plastics Mohammad Baraheni and Saeid Amini Abstract Glass fiber reinforced plastics are used in variety of industrial and constructional applications for their superb mechanical and physical properties. Delamination is one of the most important and prevalent damages in machining of glass fiber reinforced plastics. Diamond core drills have the capability of simultaneously drilling and grinding of fiber reinforced plastics, which results in hole quality improvement. Rotary ultrasonic-assisted drilling is the new machining process to drill holes on fiber reinforced plastics and has attracted increasing attention in recent years. In this paper, thrust force and delamination in rotary ultrasonic-assisted drilling of glass fiber reinforced plastics using diamond core drill have been investigated. A proper ultrasonic system for a core drill in ABAQUS was designed and fabricated. Influence of ultrasonic vibration and then tool grain size, fiber-volume fraction and machining parameters including spindle speed and feed rate on thrust force and delamination was investigated. Higher thrust force induces more delamination. As a result of the study, less delamination was achieved in ultrasonic-assisted mode by using a tool with larger grain size onto lower fiber- volume fraction composites. Additionally, experiments showed that lower spindle speed and higher feed rate induce more delamination. Keywords Glass, fiber, reinforced, plastic, rotary, ultrasonic, assisted, drilling, diamond, core, drill, thrust, force, delamination Introduction Glass fiber reinforced plastics (GFRPs) due to high physical and mechanical properties are being widely used in construction, aerospace, military and transpor- tation applications. 1,2 On the other hand, in machining area, chipping mechanism of GFRPs differs from homogeneous materials and special attention must be taken into account. 3 Precise hole size achievement through assembling of fiber reinforced composites is a challenging problem in aviation industry. 4 Main diffi- culties in machining of fiber reinforced composites are owing to different properties of fiber and resin seg- ments. Based on the experiments, composites tolerate a little plastic deformation and their elongation at break is less than steels’. 5 General problems in drilling of composites are delamination at entry and exit, tearing, chipping, roughness of hole wall. 6 Fiber reinforced composites drilling is affected by material tendency to delamination under different machining forces or moments. 7,8 Delamination is a dominant problem in machining of GFRPs, which rapidly deteriorates mechanical proper- ties of the workpiece. 9,10 Due to importance of this issue, numerous attempts have been made to determine delamination and develop the relationship between machining parameters and delamination. 5,11 Figure 1 demonstrates the delamination in core drilling process. Typically, delamination damage occurs at entry and exit of the hole. 13 Delamination also happens in inner layers for which advanced instruments are needed to determine the damage area. 14 According to previous University of Kashan, Kashan, Islamic Republic of Iran Corresponding author: Saeid Amini, University of Kashan, Kashan 4741636763, Islamic Republic of Iran. Email: amini.s@kashanu.ac.ir Journal of Reinforced Plastics and Composites 0(0) 1–10 ! The Author(s) 2017 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0731684417729565 journals.sagepub.com/home/jrp