Drilling-induced Damage Research Articles

Experimental thrust forces and delamination analysis of GFRP laminates using candlestick drills

ABSTRACTDrilling is usually performed using twist drills while assembling the composite components. However, it is necessary to adopt appropriate tool as the risk of delamination damage is high. Many researchers have performed experimental and theoretical study concerning drilling-induced delamination damage in composites utilizing special drills. The article performed drilling experiments of glass fiber reinforced plastic laminates utilizing candlestick drills. Ten candlestick drills with different drill tip geometries were compared in thrust forces and push down delamination. The results revealed the drilling behavior of the outer cutting edges and the outer drill tips for candlestick drill, and also indicated that the push down delamination depended on exit thrust force instead of maximum thrust force. What is more, thrust forces and push down delamination were significantly reduced when holes were produced using reasonable candlestick drill tip geometry. Finally, the analysis was useful for selecting appropriate candlestick drill tip geometry and conducting candlestick drill tip geometry optimization.

Drilling of pultruded and liquid composite moulded glass/epoxy thick composites: Experimental and statistical investigation

Composites are often one of the foremost difficult-to-machine materials. Out of many defects due to hole making process, the prime concern is delamination. This investigation aims to reveal the best drill geometry and corresponding optimal process parameter levels for making defect tolerance holes in thick pultruded and liquid composite moulded (LCM) composites. The novelty in this work are carrying out drilling operations with special geometry drills in thick composites, considering the entire depth of hole for assessing the damage and studying the influence of self-excited vibration of the work material. Minimization of drilling forces, drilling-induced damage and tri-axial self-excited vibration of the work material have been executed simultaneously to reveal the optimum process parameter levels for drilling the tested composite materials with each of the selected drill tools. It has been found that three flute and four-facet WC twist drills are more suitable for pultruded and LCM composites, respectively.

Comparisons of the use of twist, pilot-hole and step-drill on influence of carbon fiber-reinforced polymer drilling hole quality

Understanding the drilling-induced damage to carbon fiber-reinforced polymer composites remains the most active research being undertaken in the composite materials world of today. Despite the vast amounts of literature available, the relationship between drilling and damage to the composites has not been fully understood. In this research, a comparative study of different drilling methods including the use of a twist drill, the use of a pilot hole/pre-drilled hole and the use of a step drill on the influence of the hole quality has been accomplished. In order to achieve this comparison, thrust forces have been monitored during drilling experiments where four different feed rates and one spindle speed have been considered. A finite element model has also been included to study delamination damage on the laminates and validate the experimental results. Results show that thrust forces increase with increasing feed rates and that drilling by step drill is the most appropriate method as it records low forces hence minimal delamination damage.

Analytical and experimental investigation of the delamination during drilling of composite structures with core drill made of diamond grits: X-ray tomography analysis

Among the various forms of material damage, exit-ply delamination has been identified as one of the most deleterious damage processes associated with drilling fibre-reinforced plastics. The thrust force has been cited as the primary cause for drilling-induced exit-ply delamination. Only one analytical model for the prediction of the critical thrust force responsible for delamination using core drills can be found in the literature. In this study, a realistic model to predict critical thrust force responsible for drilling-induced exit-ply delamination in a multi-directional carbon fibre-reinforced plastic laminate with core drill has been proposed. A comparison between the proposed model, literature model as well as the experimental tests conducted during punching tests is presented. The proposed model is found to correlate well with experimental punching tests. In fact, the maximum relative errors recorded between the experimental values of the critical thrust force and the measured values are around 15%. Micro-tomography experiments have also been conducted that capture the drilling-induced damage in multi-directional carbon fibre-reinforced plastics in great detail. The X-ray images highlight the difficulty in controlling the thickness of the uncut plies located under the core drill during punching tests that can be attributed to some deviations in predictions of critical thrust force. Postmortem examination of the blind holes after punching tests also confirms the presence of a net delamination near the vicinity of the nominal diameter of the core drill, which correlates well to the hypothesis of the analytical model.

Experimental characterization and finite element modeling of critical thrust force in cfrp drilling

ABSTRACTComposite laminates are used in many applications in ae-rospace/defense industries due to their high strength-to-weight ratio and corrosion resistance properties. In general, composite materials are hard-to-machine materials which exhibit low drilling efficiency and drilling-induced delamination damage at exit. Hence, it is important to understand the drilling processes for composite materials. This article presents a comprehensive study involving experimental characterization of drilling process to understand the cutting mechanism and relative effect of cutting parameters on delamination during drilling of carbon fiber reinforced plastic (CFRP). Thrust force and torque data are acquired for analyzing the cutting mechanism, initiation and propagation of delamination, and identification of critical thrust force below which no damage occurs. An FE model for prediction of critical thrust force has been developed and validated with experimental results. A [0/90] composite laminate is modeled simulating the last two plies in exit condition and a thin interface layer is inserted in between the plies to capture delamination extent. The tool geometry is modeled as “rigid body” with geometric features of twist drill used in experiments. The tool is indented on the workpiece to simulated tool feeding action into the workpiece. The FE model predicts the critical thrust force within 5% of the experimentally determined mean value.

Microstructural investigation of drilling induced damage in fibre metal laminates constituents

Fibre metal laminates (FMLs) are used in the upper fuselage of the Airbus A380 aircraft. Machining FMLs might cause various forms of damage around the hole either in the composite layers or the metallic sheets, all of which are known as drilling-induced damage which deteriorates the surface quality of the metal/composite. The current study investigates the effects of cutting parameters on the drilling-induced damage during drilling of GLARE FMLs at a microstructural level. This study extends the previous investigation of our study on dry drilling of GLARE laminates by incorporating two modern cooling technologies namely cryogenic liquid nitrogen (LN2) and minimum quantity lubrication (MQL) to investigate their impact on drilling-induced damage in FMLs. The results showed that both cutting parameters had an impact on the drilling induced damage in the borehole, while using MQL and cryogenic coolants showed the ability to eliminate waste formation on the machined borehole surface.

Multiphase flow in oil and gas reservoirs

The porous rocks that make up oil and gas reservoirs are composed of complex combinations of pores, pore throats, and fractures. Pore networks are groups of these void spaces that are connected by pathways that have the same fluid entry pressures. Any fluid movement in pore networks will be along the pathways that require the minimum energy expenditure. After emplacement of hydrocarbons in a reservoir, fluid saturations, capillary pressure, and energy are in equilibrium, a significant amount of the reservoir energy is stored at the interface between the fluids. Any mechanism that changes the pressure, volume, chemistry, or temperature of the fluids in the reservoir results in a state of energy non-equilibrium. Existing reservoir engineering equations do not address this non-equilibrium condition, but rather assume that all reservoirs are in equilibrium. The assumption of equilibrium results in incorrect descriptions of fluid flow in energy non-equilibrium reservoirs. This, coupled with the fact that drilling-induced permeability damage is common in these reservoirs, often results in incorrect conclusions regarding the potential producibility of the well. Relative permeability damage, damage that can change which fluids are produced from a hydrocarbon reservoir, can occur even in very permeable reservoirs. Use of dependent variables in reservoir analysis does not correctly describe the physics of fluid flow in the reservoir and will lead to potentially incorrect answers regarding producibility of the reservoir.

Thermo-mechanical modelling of FRP cross-ply composite laminates drilling: Delamination damage analysis

Abstract Among other factors, thrust force, feed rate, twist drill bit chisel edge and point angle are the principal factors responsible for delamination drilling-induced damage during thermo-mechanical deformation. Hence, in this paper, an analytical thermo-mechanical model is proposed to predict critical feed rate and critical thrust force at the onset of delamination crack on CFRP composite cross-ply laminates, using the principle of linear elastic fracture mechanics (LEFM), classical plate theory, cutting mechanics and energy conservation theory. The delamination zone (crack opening Mode I) is modelled as an elliptical plate. The advantages of this proposed model over the existing models in literature are that the influence of drill geometry (chisel edge and point angle) on push-out delamination are incorporated, and mix loads condition are considered. The forces on chisel edges and cutting lips are modelled as a concentrated (point) and uniformly distributed loads, resulting into a better prediction. The model is validated with models in the literature and the results obtained show the flexibility of the proposed model to imitate the results of existing models.

Novel drill structure for damage reduction in drilling CFRP composites

Drilling holes on CFRP components is inevitable for assembling process in the aviation industry. The drilling-induced damages frequently occur and affect not only the load carrying capacity of components but also the reliability. Therefore, it is of great urgency to enhance drilling quality on CFRP components. The article aims to propose a novel drill structure to change the cutting conditions at the drill exit and effectively reduce damages in drilling CFRP. Considering the drilling-exit constraint condition, a unique two-dimensional cutting model is established to represent the axial cutting of the main cutting edge at the drill exit. Based on the model, the effects of point of action and cutting direction on material removal at the exit are investigated, and the result indicates that cutting CFRP in the upward direction has positive effects on deflection limitation and damage reduction. In order to perform the upward cutting, a novel intermittent-sawtooth drill structure is proposed on the one-shot drill. The theoretical and geometrical analyses of the drilling process reveal that the cutting lips of the structure could reverse the cutting direction from downward to upward and thereby, reduce the drill-exit damages. Furthermore, drilling experiments are conducted and the drill structure is proved to be effective to reduce drilling damages as expected.

Hole making in natural fiber-reinforced polylactic acid laminates

Natural fiber-reinforced composite materials are finding wide acceptability in various engineering applications. A substantial increase in the volume of production of these composites necessitates high-quality cost-effective manufacturing. Drilling of holes is an important machining operation required to ascertain the assembly operations of intricate composite products. In the present experimental investigation, natural fiber (sisal and Grewia optiva fiber)-reinforced polylactic acid-based green composite laminates were developed using hot compression through film stacking method. The drilling behavior of green composite laminates was evaluated in terms of drilling forces (thrust force and torque) and drilling-induced damage. The cutting speed, feed rate, and the drill geometry were taken as the input process parameters. It was concluded that all the three input process parameters affect the drilling behavior of green composite laminates. The drill geometry was established as an important input parameter that affects the drilling forces and subsequently the drilling-induced damage.

Effect of drilling parameters on specific cutting energy and delamination of a composite made of unsaturated polyester resin and chopped glass fibres

Composites have gained wide acceptance because of their unique properties. Drilling is a prerequisite operation for composite materials to form assemblies. Poor hole quality can affect tensile strength, structural integrity in long-term usages. The parameters to predict machinability of a good-quality hole are lower specific cutting energy, minimum drilling-induced damages like peel up at entrance and push out delamination. In this article, effect of different tool geometries, speeds and feeds are investigated during drilling on a composite plate having different chemical composition for specific cutting energy, peel up at entrance and push out delamination. A series of experiments was established based on the techniques of Taguchi. Statistical tools like signal-to-noise ratio, the analysis of variance and regression analysis are used to investigate effect on specific cutting energy and delamination. Conclusions show that proper selection of tool and cutting parameters influence specific cutting energy and delamination.

Experimental investigation of delamination and surface roughness in the drilling of GFRP composite material with different drills

This paper describes the experimental investigation in the drilling of glass fiber reinforced polymer (GFRP) composites with three dissimilar tools, having different materials and geometries (i.e. helical flute (HSS) drill, Carbide tipped straight shank (K20) drill, and Solid carbide eight-facet drill). Tool geometry and materials are considered to be major factor, which is responsible for drilling-induced damage. Cutting parameters also influence drilling-induced damage. These damages were measured by two delamination factors. Image processed technique was utilized to determine the damaged area and maximum damaged zone diameter. The results showed that qualities of drill holes significantly improved when solid carbide eight-facet drill was used.

Damage-Free Hole Making in Fiber-Reinforced Composites: An Innovative Tool Design Approach

Drilling is an inevitable machining technique that facilitates the assembly of composite parts. Drilling with the traditional tools causes significant damage to the composite parts. The forces that are produced during drilling are mostly accountable for the damage or rejection of the parts. Therefore, the main aim of the present investigation is to reduce the forces and subsequent damage that is induced during drilling operation. Thus, new tool geometry has been conceptualized, designed, developed, and implemented to investigate the drilling behavior of sisal-epoxy and nettle-epoxy laminates. A comparative analysis has been made to compare the performance of the developed tool with the widely used twist drill. The performance has been compared based on the forces and associated drilling-induced damage. It was found that the developed tool geometry gives better results than the traditional twist drill in terms of minimization of forces and damage as well.

Transient thermo-poroelastic analysis of drilling-induced mechanical damage in nonfractured rocks

Permeability variations in reservoirs and around boreholes are of great interest in petroleum engineering due to the fact that they can significantly affect reserve estimates, reservoir development, well production or injection rate, and the likely success of remedial actions of near-wellbore damage. A fully coupled transient thermo-poroelastic concept with and without rock mechanical damage models is employed to evaluate stress distribution and permeability variation around the boreholes and breakouts. The anisotropy concept is applied to permeability, rock modulus, and uniaxial compressive strength using Weibull distribution. The Mogi–Coulomb failure criterion is employed to model breakout initiation and propagation around the borehole. Strain-based stress–permeability equation and stress–permeability models based on the experimental results and correlations are used to evaluate permeability changes near the borehole. Two cases of overbalanced and underbalanced drilling conditions are employed. The simulations for medium with isotropic and anisotropic physical properties result in varied effective stress distribution, breakout geometries, and consequently different distributions of tangential and radial permeability. Generally, in isotropic medium, permeability reduces to less than 70 % of its original value in the overbalanced condition and 80 % in underbalanced operations; however, there are differences between permeability along x and y directions. For anisotropic medium, permeability increases to more than 150 % all over the borehole periphery in the overbalanced operations; moreover, permeability enhancement is essentially larger along maximum in situ springline. In the underbalanced condition, permeability decreases to less than 70 % along minimum in situ stress direction and increases to more than 200 % in a limited area near the borehole along maximum in situ stress springline.

A study about hole making in woven jute fabric-reinforced polymer composites

The time has come for natural fibres to stand as potent substitutes for synthetic fibres in various industrial applications. Recently, jute fibre is being used as reinforcement material in the development of reinforced plastics for various engineering products. The production cycle of a composite product often necessitates certain degree of machining operations. Drilling is one of the most widely practised machining operation for making holes in composite laminates. Hole making is imperative to ascertain the assembly of intricate composite products. The literature available indicate that not much research work has been reported on the machining behaviour of jute fibre-reinforced polypropylene composites. Hence, in the present experimental endeavour, drilling of woven jute fabric-reinforced polypropylene composite has been performed. The effect of operating variables on thrust force and torque signals was investigated. Drilling-induced damage in the developed composite was quantified using stereo microscope. The experimental values indicate close relationship between the tool geometries and the delamination factor. SEM analysis was also conducted to understand the drilling behaviour and surface morphology of the drilled holes. Among the solid drills compared, parabolic drill reveals better cutting behaviour in terms of lower drilling forces and better quality of holes. This may be attributed to the better tool-work piece interaction in case of parabolic drill point geometry.

Analysis of damage mechanisms in drilling of composite materials by acoustic emission

Conventional methods for analysis of drilling of composite materials usually study the amount of damaged area and effective parameters. However, these methods do not provide investigators with sufficient information regarding drilling-induced damage. In this paper, a procedure for discrimination and identification of different damage mechanisms based on the analysis of acoustical signals emitted during the process is presented. Using principle component analysis for data reduction and unsupervised pattern recognition analysis, the drilling process was divided into three main stages, i.e. entry stage, cutting stage and exit stage. Different methods of signal processing were then used to identify and discriminate the most active damage mechanisms in each stage. As a result, matrix cracking, delamination, fiber pull out and friction were discriminated and the frequency distribution of each one was identified.

A novel intelligent software-based approach to predict forces and delamination during drilling of fiber-reinforced plastics

Drilling of fiber-reinforced plastics (FRPs) results in drilling-induced damage which leads to reduced part life and extensive part rejection. Thus far, there exists no standard handbook or knowledge-based tool that can predict drilling-induced forces and damage. Therefore, the present research initiative is an attempt to develop a software tool based on artificial intelligence which can predict drilling-induced thrust force, torque and delamination factor during drilling of FRPs. The developed intelligent software has a friendly graphic user interface (GUI). The user just interacts through the GUI and fills the input choices, and upon execution, the software predicts the drilling forces and delamination factor. In order to generate the database for the software, drilling experiments have been performed in two different types of composite materials with four different types of drill point geometries of two distinct diameters. The drilling of composite laminate has been conducted at three different levels of spindle speed and feed rate. The software results are based on three different artificial intelligence techniques namely artificial neural network (ANN), fuzzy logic (FL) and adaptive neuro-fuzzy inference system (ANFIS). The values of thrust force, torque and delamination factor for given inputs predicted by the developed tool are in close agreement with the experimental values.

Prediction and control of drilling-induced damage in fibre-reinforced polymers using a new hybrid force and temperature modelling approach

Reliable force and temperature prediction in drilling of fibre-reinforced polymers (FRPs) is the key to controlling drilling-induced damage. A novel hybrid analytical-numerical model is developed to capture time-varying forces and temperatures during transient and steady-state drilling of FRPs. Although the generalized force model is calibrated using a unidirectional FRP material and a single tool type, it can apply to wide ranges of drilling conditions, tool geometries, and laminate configurations. A methodology to define the damage criteria is presented. Extensive experimental validation confirmed the accurate predictions of delamination and thermal damage; such performance cannot be achieved by any available model.

Rotary mode ultrasonic drilling of glass fiber-reinforced epoxy laminates

The use of polymer–matrix composites in structural applications necessitates certain degree of machining operations to meet the final product integrity. Drilling is an essential machining operation being used in composite industries for making of holes for bolted joints. The conventional drilling, which is frequently used for making holes in polymer–matrix composite parts, is not convenient anymore because of plethora of challenges encountered. The major drawback is the drilling-induced damage, which mainly occurs due to the direct interaction between the tool and composite laminate. Therefore, there exists a research opportunity to develop cost-effective high-quality machining methods for composite laminates. In the present research endeavor, rotary-mode ultrasonic drilling process has been conceptualized and developed for the drilling of fiber-reinforced polymer composites. The influence of various process parameters including power rating, slurry concentration, and abrasive size on material-removal rate, tool wear rate, and average surface roughness (Ra) has been experimentally investigated. It has been observed that the entry and exit delamination is prevented, and hole circumferential edge quality is improved when holes are produced through rotary-mode ultrasonic drilling as compared to the conventional drilling. It has also been found that with substantial modification in the conventional ultrasonic drilling process, the drilling performance in terms of material-removal rate of glass-epoxy laminates can be significantly improved. The major contribution of the present research endeavor is the development of a novel method of making clean-cut damage-free holes in fiber-reinforced composite laminates.

Modulation-Assisted Drilling of Glass-Fiber-Reinforced Plastics

During drilling, delamination around the holes in composite parts results into a significant rejection. In the current work, modulation-assisted drilling (MAD) of glass-fiber-reinforced composites was done, with an aim to investigate the effect of MAD on hole oversize and delamination around holes. Taguchi method was used to optimize the process parameters. Delamination factor and hole oversize were considered as output responses of the experimental design. Tool maker's microscope and ImageJ software were used for measuring damage around the hole. However, coordinate measuring machine was used for measuring the hole oversize. Mode of drilling, cutting speed, and feed were found to be significant parameters which affect the drilling-induced damage. In this regard, MAD is found to be a better option in comparison with conventional drilling (CD). However, only feed is observed to be an influential parameter for hole oversize during MAD as well as CD.