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The ability of microwave radiation to penetrate and interact directly with materials has led to its extensive use in food and drug industries, and more recently in composites manufacturing. Microwave heating of composites allows rapid heat transfer throughout the material thickness with reduced thermal gradients and processing times as well as energy efficiency. Design of microwave systems to process composite parts with various geometries and sizes demands improved understanding of electromagnetic energy distribution and factors influencing it. Finite-element (FE) models can be efficient design tools in such cases, as physical experimentation can be impractical. In this study, a fully-coupled FE model of a carbon fibre composite in an industrial microwave environment is developed using COMSOL Multiphysics®. The effects of the heating process parameters including the number of active magnetrons, specimen thickness and the variation in the frequency of radiation on the electromagnetic field distribution are studied. The FE model showed that a substantial difference in the electromagnetic field distribution exists for the frequencies above 1 GHz compared to the lower frequencies in the microwave regime, resulting in non-uniform heating.

Finite elements (FE) provide an excellent and low-cost approach in the assessment of composite machining induced damage. This article is focused on the evaluation of the damage underlying the machined surface through the development of a novel 3D FE model in composite machining. Sub-surface damage of UD-CFRP with fibre orientations from 0o to 90o is evaluated. An algorithm to assess composite damage evolution and chip formation is inserted via user-defined subroutine. Damage initiation is determined using Hashin’s failure criteria for fibre damage modes, while matrix damage modes are assessed via Puck’s failure criteria. Subsequent damage evolution is modelled using an energy-based linear damage degradation law. Numerical results reveal relevant advances in the prediction of the damage induced underlying the machined surface for fibre orientations from 60o to 90o obtained in previous investigations.

This article presents a finite-element analysis (FEA) based study to understand the influence of cutting parameters (rake angle, relief angle and cutter edge radius) on the machining-induced damage of unidirectional (UD) composites. Carbon/epoxy (CFRP) and glass/epoxy (GFRP) composites are considered. Onset of damage in composites is modelled using a combination of maximum stress and Puck's fracture criteria, while a novel damage propagation algorithm is proposed to account for the post-damage material softening behaviour. A spring-back phenomenon (partial elastic recovery of workpiece material after tool passed a cutting surface) often observed in composites machining, is considered in the FE model to allow a better prediction of the thrust force and induced damage. A validated FE model predicts that with increasing relief angle, the extent of sub-surface damage is reduced. Rake angle or tool edge radius are not found to have a great influence on the induced damage. A large dependence is observed between the fibre angle and the induced damage, as the severity of damage increase when fibre orientations varies from 30° to 90°.

Nowadays, the development of robust finite element models is vital to research cost-effectively the optimal cutting parameters of a composite machining process. However, various factors, such as the high computational cost or the complicated nature of the interaction between the workpiece and the cutting tool significantly hinder the modelling of these types of processes. For these reasons, the numerical study of common machining operations, especially in composite machining, is still minimal. This paper presents a novel approach comprising a mixed multidirectional composite damage mode with composite edge trimming operation. An ingenious finite element framework which infer the cutting edge tool wear assessing the incremental change of the machining forces is developed. This information is essential to replace tool inserts before the tool wear could cause severe damage in the machined parts. Two unidirectional carbon fibre specimens with fibre orientations of 45° and 90° manufactured by pre-preg layup and cured in an autoclave were tested. Excellent machining force predictions were obtained with errors below 10% from the experimental trials. A consistent 2D FE composite damage model previously performed in composite machining was implemented to mimic the material failure during the machining process. The simulation of the spring back effect was shown to notably increase the accuracy of the numerical predictions in comparison to similar investigations. Global cutting forces simulated were analysed together with the cutting tool tooth forces to extract interesting conclusions regarding the forces received by the spindle axis and the cutting tool tooth, respectively. In general terms, vertical and normal forces steadily increase with tool wear, while tangential to the cutting tool, tooth and horizontal machining forces do not undergo a notable variation.

Finite-element (FE) method offers a low cost virtual alternative to assist in optimisation of critical process parameters in machining of composites. This study is focussed on understanding the mechanics of chip formation in orthogonal cutting of unidirectional (UD) carbon-fibre-reinforced polymer (CFRP) laminates through development of FE models. Machining responses of UD CRFP laminates with fibre orientation of 45° (measured with respect to the cutting direction) are assessed. Modelling of material removal in the form of fragmented chips is considered. Damage initiation is determined using the Hashin stress criterion for the fibre component, while matrix failure predicted using Puck criteria. Subsequent damage evolution events are modelled using a strain-based softening approach to degrade relevant material properties linearly. Primary numerical results compared with experimental data revealed that developed FE models are able to predict global machining responses (i.e. cutting forces) and characterise various discrete damage modes associated with machining response of quasi-brittle CFRP laminates successfully. The models also provide a valuable insight into variation in chip morphology.

Adoption of greener machining techniques shall offer Indian industry a cost-effective route to improve its economic, environmental, and social footprint when it comes to cutting aerospace-grade intractable materials. Cryogenic machining is one such technique which uses an advanced method to deliver liquid nitrogen (LN2) (at -321° F) directly to the cutting edge enabling substantially faster processing speeds and increased tool life compared to conventional cooling methods. This results in higher throughput and reduced process energy demand, thus improving the efficiency of the cutting process. Further, the retrofitting ability of cryogenic systems mean they can be paired-up with in-house machining centers, making them an easy to use low-cost solution. This study presents the comparison of process energy consumption in the dry and cryogenic turning of Ti-6Al-4V. A hybrid design of experiments (DoE) is considered for the machining trials - this consists of a combination of full factorial DoE and Taguchi method to identify the influence of cutting process parameters on the process energy consumption in dry and cryogenic machining. Results show that cryogenic machining is more effective in achieving higher material-removal-rate when compared to dry machining.

FE models offer a promising virtual alternative to study machining responses of composites, thereby allowing an informed selection of favorable cutting parameters. Appropriate mathematical schemes are needed to predict damage initiation in fibrous composites; Hashin and Puck failure criteria are the most commonly used for this purpose. This work focusses on the assessment of these criteria to predict ply-level damage in orthogonal cutting of unidirectional composites. A novel algorithm accounting for strain-softening after damage initiation is also proposed. Efficacy of the developed FE model is shown by simulating effects of the cutter tool on the damage of underlying workpiece.

The virtual assessment of a composite machining process using finite element (FE) models constitutes a cost-effective solution to study the surface quality of machined parts. Thus, the correct simulation of the chip fracture becomes essential to obtain consistent numerical results. This work develops an original FE approach to emulate the chip formation in the machining of carbon fibre reinforced polymer (CFRP) laminates. Composite damage initiation modes are evaluated via hybrid Puck-Hashin composite failure criteria. Subsequently, mechanical properties of the damaged elements are linearly degraded. Finally, a novel strain-based element deletion criterion is applied to reliably simulate the chip release process. Five different cutting configurations are successfully modelled. The influence of relevant fibre orientations and cutter rake angles on chip formation are analysed in detail. The shape of the simulated chips reaches a high similarity with the chips obtained in relevant experimental trials presented in the literature. Useful insights about the modelling of sub-surface damage in composite machining are also produced in this investigation. For instance, the modelling of the fibre bending damage which take place in the machining of 90° laminates is modelled with great precision.

2D and 3D finite element models were developed to simulate the machining of CFRP with different levels of tool wear. Models were validated by edge trimming experiments on a uni-directional laminate at different fibre orientations using a three flute PCD milling tool. MSC Marc was used to develop the model and in conjunction with a Hashin damage material model. Modelling results are validated according to measured cutting forces at different cutting speeds and feed rates. A percentage difference of +10% and +5% was calculated for the 3D model for Fx and Fy respectively, while a percentage difference of -9% and -50% was found for the 2D model. Tool wear was found to have a significant effect on measured cutting forces.

This manuscript offers a comprehensive review of the state of art on the machining induced damage modelling of long fibre reinforced polymers (LFRP), focusing on the two most common simulated machining operations, orthogonal cutting and drilling. A novel and critical discussion of composite damage modelling techniques used in machining works is offered, yielding numerous insights; advantages and disadvantages of current numerical techniques as well as possible improvements are included. Additionally, computational findings achieved so far in the literature are analysed in detail to allow remark of the current scope in the machining of LFRP laminates. Despite ingenious numerical solutions having been generated by previous authors to face the complex problems involve with the simulation of composite machining, the numerical capabilities to model the machining induced damage are still limited. Hence, different numerical strategies should be considered in future computational studies to enhance the reliability of current finite element models. The use of advanced continuum damage mechanics (CDM) approaches inserted via user-defined subroutines or the use of other computationally advanced methods such as eXtended Finite Element Method (XFEM) or phase field methods (PFM) to model composite fracture are recommended to improve the quality of numerical predictions.

Machining experiments were conducted to evaluate the impact of cutting parameters on the hole quality and cutting forces in drilling Al2024-T3 aerospace alloy. Al2024-T3 specimen were drilled using Φ6-mm TiAlN-coated carbide twist drills under dry cutting conditions. The hole quality was inspected in terms of its surface roughness, burr and chip formations, hole size, circularity error and post-machining microhardness of the subsurface of the holes. An analysis of variance (ANOVA) was carried out to determine the percentage contribution of cutting parameters on cutting forces and the inspected hole quality parameters. A three-dimensional (3D) finite element (FE) model of drilling Al2024-T3 is developed using Abaqus/Explicit to predict thrust force and torque. The FE model was validated using experimental results and found to be in good agreement. The results of the study showed that the cutting parameters have a significant impact on cutting forces and inspected hole quality parameters. Drilling at feed rates of 100 and 300 mm/min and spindle speeds of 1000, 3000, and 6000 rpm are recommended for producing holes with smaller surface roughness, deviation from nominal hole size, circularity error and burrs.

The use of fiber-reinforced polymer composites (FRPs) in aerospace, automotive, and military applications as well as in energy and naval structures is ever expanding, mainly, due to the weight-saving benefits. To manufacture durable composites parts, understanding their structural behavior under severe loading conditions is critical to designers and end-users. FRPs usually demonstrate a multiplicity of damage mechanisms under varying impact conditions due to their heterogeneous microstructure. A wealth of knowledge is available on a low-velocity impact response of composites, though with continuously emerging advanced materials and structures, established structure–property–performance relationships that could provide guidelines on dynamic impact behavior of composites are rare. A compulsory compliance with extensive testing standards and affirmation to the personnel health and safety makes real-time dynamic impact experiments rather expensive. Repeatability and reliability of their results may also suffer due to the rapid time frame in the absence of a suitable data-acquisition system. Finite-element (FE) models, in such cases, can be used as a virtual simulation tool to help engineers improving design of composite structures exposed to dynamic loading.

This research focuses on the effect of ultrasonically-assisted drilling (UAD) on carbon fibre-reinforced plastics. High-frequency vibration was used to excite a drill bit during its standard operation. An extensive experimental study of drilling forces, temperature, chip formation, surface finish, circularity, delamination and tool wear was conducted using ∅3 mm drill and presented here. UAD showed a significant improvement in drill quality when compared to conventional drilling processes. A finite-element study was also conducted to understand the nature of drilling-force reduction in UAD.

Conventional-drilling (CD) methods often initiate discrete damage phenomena such as micro-cracking, matrix burning; delamination and fibre pull-out in difficult-to-machine heterogeneous materials such as carbon fibre-reinforced polymer (CFRP) composites. Ultrasonically assisted drilling (UAD) is a promising machining technique suitable for drilling holes in CFRP composites. UAD has been shown to possess several advantages over CD, including reduction in a thrust force and torque, diminished burr formation at drill exit in ductile materials and an overall improvement in roundness and surface finish of the drilled hole. Recently, our in-house experiments of UAD in CFRP composites demonstrated remarkable reductions in levels of thrust force and torque (average force reductions in excess of 60%) when compared to CD with the same machining parameters. 3D Finite Element (FE) models of CD and UAD techniques for a CFRP laminate were developed using a general-purpose FE software ABAQUS/Explicit and validated using experimental results. The magnitudes of thrust force and torque obtained with FE analysis of UAD are compared with those for CD. The numerical results obtained with the developed FE model were found to be in a good agreement with the experimental data.

Experimental and numerical studies wereconducted to understand the effect of plate curvature on the blast response ofcarbon/epoxy composite panels. A shock-tube system was utilized to impartcontrolled shock loading to quasi-isotropic composite panels with varying radiiof curvature. A 3D digital image correlation (DIC) technique coupled withhigh-speed photography was used to assess the out-of-plane deflection ofcomposite panels. A finite element (FE) model integrating fluid-structureinteraction to represent coupling between the air surrounding composite panels,shock wave and panels, was developed using a general-purpose FE softwareABAQUS/Explicit. The numerical results were compared to the experimental dataand showed a good correlation.

Drilling carbon fibre reinforced plastics (CFRPs) is typically cumbersome due to high structural stiffness of the composite and low thermal conductivity of plastics. Resin-rich areas between neighbouring plies in a laminate are prone to drilling-induced delamination that compromises structural integrity. Appropriate selection of drilling parameters is believed to mitigate damage in CFRPs. In this context, we study the effect of cutting parameters on drilling thrust force and torque during the machining process both experimentally and numerically. A unique three-dimensional (3D) finite element model of drilling in a composite laminate, accounting for complex kinematics at the drill-workpiece interface is developed. Cohesive zone elements are used to simulate interply delamination in a composite. Experimental quantification of drilling-induced damage is performed by means of X-ray micro computed tomography. The developed numerical model is shown to agree reasonably well with the experiments. The model is used to predict optimal drilling parameters in carbon/epoxy composites.

Machining Glass fibre aluminium reinforced epoxy (GLARE) is cumbersome due to distinctively different mechanical and thermal properties of its constituents, which makes it challenging to achieve damage-free holes with the acceptable surface quality. The proposed work focuses on the study of the machinability of thin (~2.5 mm) GLARE laminate. Drilling trials were conducted to analyse the effect of feed rate and spindle speed on the cutting forces and hole quality. The resulting hole quality metrics (surface roughness, hole size, circularity error, burr formation and delamination) were assessed using surface profilometry and optical scanning techniques. A three dimensional (3D) finite-element (FE) model of drilling GLARE laminate was also developed using ABAQUS/Explicit to help understand the mechanism of drilling GLARE. The homogenised ply-level response of GLARE laminate was considered in the FE model to predict cutting forces in the drilling process.

Ultrasonically assisted drilling (UAD) is a novel machining technique suitable for drilling difficult-to-machine materials such as carbon/epoxy composites, where ultrasonic vibrations are superimposed on the tip of the revolving drill bit. Recently, UAD has been shown to possess several advantages in comparison to conventional drilling, including a reduced thrust force and torque, reduced drilling-induced damage and overall improvement in roundness and surface finish of the drilled hole. Here, a finite element model of UAD in carbon/epoxy composite is presented. This model accounts for volumetric and thermal softening phenomena in the workpiece material under the influence of localized vibro-impacts, which is a characteristic feature of UAD. The model was implemented in Abaqus/Explicit and validated with results from experiments, demonstrating a reasonable correlation between them. A parametric study was also carried out to examine the effect of variation in intensity of ultrasonic energy on the extent of softening in the carbon/epoxy composite for UAD.

The use of composite materials such as carbon fiber-reinforced plastic (CFRP) has grown considerably in recent years, especially in aerospace, automotive, sports and construction industries. The properties such as high strength and stiffness, low weight, excellent fatigue and corrosion resistance have made them a useful material for light-weight applications. Though parts made from CFRP are often manufactured to a near-net shape, various machining processes such as drilling, can be used to facilitate assembly of structures. Drilling CFRPs involve penetrating through several plies of laminate, which causes high stresses and strains in the vicinity of the drilled hole. Thus, the machining process not only affects the overall hole quality but also initiates discrete damage phenomena such as micro-cracking, matrix burning; delamination and fiber pull out in the specimen. Moreover, the cutting edges of a drill wear dramatically out due to presence of highly abrasive fibers in the matrix, resulting in increased thrust forces that can cause interply delamination.

Carbon fiber-reinforced plastic (CFRP) composites are attractive for many industrial applications due to their superior properties. The parts made from CFRP are usually manufactured to a near-net shape; however, various machining processes, such as drilling, are often required to facilitate component assemblies. Conventional Drilling (CD) of CFRP induces high stresses in the vicinity of the drilled hole; along with high thrust forces on a drilling tool. An advanced drilling technique known as Ultrasonically Assisted Drilling (UAD) has been used to demonstrate its several advantages over CD including a reduced thrust force. A 3D finite element (FE) models simulating CD and UAD techniques for drilling in CFRP laminates were developed using the general-purpose FE software ABAQUS/Explicit. The numerical results obtained with the FE model were found to be in a good agreement with the experimental data.

Fibre-reinforced polymer composites (FRPs) are extensively used in protective elements and structures exposed to a wide range of impact loading. The range of application is comprehensive, with impact velocities (and, consequently, impact energies) ranging from low to high levels. As widely reported, damage mechanisms in FRPs are observed to change significantly with the nature of impact, and hence need better understanding and assessment. In this chapter, impact events are studied in some detail using a numerical approach in analysis of various experimental data. Finite-element models of FRPs, once accurately developed and validated, allow elucidation of various deformation and damage mechanisms underpinning composite failure across impact-velocity envelopes. In this regard, results are discussed that were obtained from the authors' work on air blast on FRPs and ballistic impact on woven composites using a numerically accurate and computationally efficient modelling framework.

Ballistic damage of hybrid woven-fabric composites made of plain-weave E-glass- fabric/epoxy and 8H satin-weave T300 carbon-fabric/epoxy is studied using a combination of experimental tests, microstructural studies and finite-element (FE) analysis. Ballistic tests were conducted with a single-stage gas gun. Fibre damage and delamination were observed to be dominating failure modes. A ply-level FE model was developed, with a fabric-reinforced ply modelled as a homogeneous orthotropic material with capacity to sustain progressive stiffness degradation due to fibre/matrix cracking, fibre breaking and plastic deformation under shear loading. Simulated damage patterns on the front and back faces of fabric-reinforced composite plates provided an insight into their damage mechanisms under ballistic loading.

The mechanical response of CFRP-Al/HC (carbon fibre-reinforced/epoxy composite face sheets with Al honeycomb core) sandwich panels to hyper-velocity impact (up to 1 km/s) is studied using a finite-element model developed in ABAQUS/Explicit. The intraply damage of CFRP face sheets is analysed by mean of a user-defined material model (VUMAT) employing a combination of Hashin and Puck criteria, delamination modelled using cohesive-zone elements. The damaged Al/HC core is assessed on the basis of a Johnson Cook dynamic failure model while its hydrodynamic response is captured using the Mie-Gruneisen equation of state. The results obtained with the developed finite-element model showed a reasonable correlation to experimental damage patterns. The surface peeling of both face sheets was evident, with a significant delamination around the impact location accompanied by crushing HC core.

Experimental and numerical studies were conducted to understand the effect of plate curvature on blast response of carbon/epoxy composite panels. A shock-tube system was utilized to impart controlled shock loading to quasi-isotropic composite panels with differing range of radii of curvatures. A 3D Digital Image Correlation (DIC) technique coupled with high-speed photography was used to obtain out-of-plane deflection and velocity, as well as in-plane strain on the back face of the panels. Macroscopic post-mortem analysis was performed to compare yielding and deformation in these panels. A dynamic computational simulation that integrates fluid-structure interaction was conducted to evaluate the panel response in general purpose finite-element software ABAQUS/Explicit. The obtained numerical results were compared to the experimental data and showed a good correlation.

Ultrasonically assisted drilling (UAD) is a novel machining technique suitable for drilling in hard-to-machine quasi-brittle materials such as carbon fibre reinforced polymer composites (CFRP). UAD has been shown to possess several advantages compared to conventional drilling (CD), including reduced thrust forces, diminished burr formation at drill exit and an overall improvement in roundness and surface finish of the drilled hole. Recently, our in-house experiments of UAD in CFRP composites demonstrated remarkable reductions in thrust-force and torque measurements (average force reductions in excess of 80%) when compared to CD with the same machining parameters. In this study, a 3D finite-element model of drilling in CFRP is developed. In order to model acoustic (ultrasonic) softening effects, a phenomenological model, which accounts for ultrasonically induced plastic strain, was implemented in ABAQUS/Explicit. The model also accounts for dynamic frictional effects, which also contribute to the overall improved machining characteristics in UAD. The model is validated with experimental findings, where an excellent correlation between the reduced thrust force and torque magnitude was achieved.

A mechanical behaviour of plain-weave E-glass fabric/epoxy laminate composite plate exposed to ballistic impact is studied using a finite-element (FE) code Abaqus/Explicit. A ply-level FE model is developed, where a fabric-reinforced ply is modelled as a homogeneous orthotropic elastic material with potential to sustain progressive stiffness degradation due to fiber/matrix cracking, and plastic deformation under shear loading. The model is implemented as a VUMAT user subroutine. Ballistic experiments were carried out to validate the FE model. A parametric study for varying panel thickness is performed to compare impact resistance of the studied composite.