Principles and approaches for the machining simulation of ceramic matrix composites at microscale: a review and outlook

Ceramic Matrix Composites (CMC) are advanced materials composed of ceramic fibers embedded in a ceramic matrix, resulting in a highly durable and lightweight composite structure offering exceptional high-temperature performance, excellent mechanical properties, and superior resistance to wear and corrosion. CMC find applications in industries such as aerospace, automotive, energy, and defense, where high strength and thermal stability are crucial. Despite their numerous advantages, machining CMC presents unique challenges. The hardness and brittleness of ceramics make them difficult to machine using conventional methods. The abrasive nature of ceramic particles can rapidly wear down cutting tools, leading to decreased tool life and increased costs. Numeric simulations for the machining of CMC are therefore particularly interesting due to their ability to provide insights into tool-material interactions and optimize machining parameters without the need for expensive and time-consuming physical trials. This paper discusses existing methods and approaches from different materials like Carbon Fiber Reinforced Plastics (CFRP) and monolithic ceramics and puts forward an outlook for the numerical simulation of the machining process of CMC

Investigation of cutting mechanics in single point diamond turning of silicon

As a kind of brittle material, silicon will undergo brittle fracture at atmospheric pressure in conventional scale machining. Studies in the last two decades on hard and brittle materials including silicon, germanium, silicon nitride and silicon carbide have demonstrated ductile regime machining using single point diamond turning (SPDT) process. The mirror-like surface finish can be achieved in SPDT provided appropriate tool geometry and cutting parameters including feed rate, depth of cut and cutting speed are adopted.The research work in this thesis is based on combined experimental and numerical smoothed particle hydrodynamics (SPH) studies to provide an inclusive understanding of SPDT of silicon. A global perspective of tool and workpiece condition using experimental studies along with localized chip formation and stress distribution analysis using distinctive SPH approach offer a comprehensive insight of cutting mechanics of silicon and diamond tool wear. In SPH modelling of SPDT of silicon, the distribution of von Mises and hydrostatic stress at incipient and steady-state was found to provide the conditions pertinent to material failure, phase transformation, and ductile mode machining. The pressure-sensitive Drucker Prager (DP) material constitutive model was adopted to predict the machining response behaviour of silicon during SPDT. Inverse parametric analysis based on indentation test was carried out to determine the unknown DP parameters of silicon by analysing the loading-unloading curve for different DP parameters. A very first experimental study was conducted to determine Johnson-Cook (J-C) model constants for silicon. High strain rate compression tests using split Hopkinson pressure bar (SHPB) test as well as quasi-static tests using Instron fatigue testing machine were conducted to determine J-C model constants.The capability of diamond tools to maintain expedient conditions for high-pressure phase transformation (HPPT) as a function of rake angle and tool wear were investigated experimentally as well as using SPH approach. The proportional relationship of cutting forces magnitude and tool wear was found to differ owing to wear contour with different rake angles that influence the distribution of stresses and uniform hydrostatic pressure under the tool cutting edge. A new quantitative evaluation parameter for the tool wear resistance performance based on the cutting distance was also proposed. It was also found that the machinability of silicon could be improved by adopting novel surface defect machining (SDM) method.The ductile to brittle transition (DBT) with the progressive tool wear was found to initiate with the formation of lateral cracks at low tool wear volume which transform into brittle pitting damage at higher tool edge degradation. A significant variation in resistance to shear deformation as well as position shift of the maximum stress values was observed with the progressive tool wear. The magnitude and distribution of hydrostatic stress were also found to change significantly along the cutting edge of the new and worn diamond tools.As a kind of brittle material, silicon will undergo brittle fracture at atmospheric pressure in conventional scale machining. Studies in the last two decades on hard and brittle materials including silicon, germanium, silicon nitride and silicon carbide have demonstrated ductile regime machining using single point diamond turning (SPDT) process. The mirror-like surface finish can be achieved in SPDT provided appropriate tool geometry and cutting parameters including feed rate, depth of cut and cutting speed are adopted.The research work in this thesis is based on combined experimental and numerical smoothed particle hydrodynamics (SPH) studies to provide an inclusive understanding of SPDT of silicon. A global perspective of tool and workpiece condition using experimental studies along with localized chip formation and stress distribution analysis using distinctive SPH approach offer a comprehensive insight of cutting mechanics of silicon and diamond tool wear. In SPH modelling of SPDT of silicon, the distribution of von Mises and hydrostatic stress at incipient and steady-state was found to provide the conditions pertinent to material failure, phase transformation, and ductile mode machining. The pressure-sensitive Drucker Prager (DP) material constitutive model was adopted to predict the machining response behaviour of silicon during SPDT. Inverse parametric analysis based on indentation test was carried out to determine the unknown DP parameters of silicon by analysing the loading-unloading curve for different DP parameters. A very first experimental study was conducted to determine Johnson-Cook (J-C) model constants for silicon. High strain rate compression tests using split Hopkinson pressure bar (SHPB) test as well as quasi-static tests using Instron fatigue testing machine were conducted to determine J-C model constants.The capability of diamond tools to maintain expedient conditions for high-pressure phase transformation (HPPT) as a function of rake angle and tool wear were investigated experimentally as well as using SPH approach. The proportional relationship of cutting forces magnitude and tool wear was found to differ owing to wear contour with different rake angles that influence the distribution of stresses and uniform hydrostatic pressure under the tool cutting edge. A new quantitative evaluation parameter for the tool wear resistance performance based on the cutting distance was also proposed. It was also found that the machinability of silicon could be improved by adopting novel surface defect machining (SDM) method.The ductile to brittle transition (DBT) with the progressive tool wear was found to initiate with the formation of lateral cracks at low tool wear volume which transform into brittle pitting damage at higher tool edge degradation. A significant variation in resistance to shear deformation as well as position shift of the maximum stress values was observed with the progressive tool wear. The magnitude and distribution of hydrostatic stress were also found to change significantly along the cutting edge of the new and worn diamond tools

Crystal-plasticity modelling of machining

A machining process is one of the most common techniques used to remove material in order to create a final product. Most studies on mechanisms of cutting are performed under the assumption that the studied material is isotropic, homogeneous and continuous. One important feature of material- its anisotropyis linked to its crystallographic nature, which is usually ignored in machining studies. A crystallographic orientation of a workpiece material exerts a great influence on the chip-formation mechanism. Thus, there is a need for developing fundamental understanding of material’s behaviour and material removal processes. While the effect of crystallographic orientation on cutting-force variation is extensively reported in the literature, the development of the single crystal machining models is somewhat limited. [Continues.

Microstructural Evaluation of Aluminium Alloy A365 T6 in Machining Operation

The optimum cutting parameters such as cutting depth, feed rate, cutting speed and magnitude of the cutting force for A356 T6 was determined concerning the microstructural detail of the material. Novel test analyses were carried out, which include mechanical evaluation of the materials for density, glass transition temperature, tensile and compression stress, frequency analysis and optimisation as well as the functional analytic behaviour of the samples. The further analytical structure of the particle was performed, evaluating the surface luminance structure and the profile structure. The cross-sectional filter profile of the sample was extracted, and analyses of Firestone curve for the Gaussian filter checking the roughness and waviness profile of the structure on aluminium alloy A356T6 is proposed. A load cell dynamometer was used to measure different parameters with the combination of a conditioning signal system, a data acquisition system and a computer with visualised software. This allowed recording the variations of the main cutting force throughout the mechanised pieces under different cutting parameters. A carbide inserted tool with triangular geometry was used. The result shows that the lowest optimum cutting force is 71.123 N at 75 m/min cutting speed, 0.08 mm/rev feed rate and a 1.0 mm depth of cut. The maximum optimum cutting force for good surface finishing is 274.87 N which must be at a cutting speed of 40 m/min, 0.325 mm/rev feed rate and the same 1.0 mm depth of cut

Thermal Mechanical Numerical Modeling of Friction Element Welding

With the objective of minimizing carbon footprint of vehicles, different organizations across the world are increasingly enforcing higher fuel efficiency targets for the automobile manufacturers. To improve the fuel economy while retaining or further improving the structural integrity, the automobile industry is vigorously shifting towards substituting conventional heavy materials like cast iron with new age materials such as aluminum alloys, steel alloys, etc. which are not only much lighter but also offer superior strength-to-weight ratio. Engineers use a mix of these new age materials with the aim of maximizing the benefits from each material. However, the utilization of such materials is currently limited in the industry as welding them using conventional methods such as resistance spot welding or fusion welding process, is plagued with inherent difficulties such as formation of brittle inter-metallic compounds, irreversible and adverse changes in the thermal and mechanical properties of the materials. Dissimilar material joining is of critical importance in aiding the manufacturers realize the crucial objective of a safer and more fuel efficient vehicle. Friction element welding (FEW), a friction based joining process, has been proposed for joining highly dissimilar materials in minimal time and with low input energy. FEW process can join a variety of materials which differ significantly in their mechanical, thermal, and metallurgical properties without inducing any of the defects associated with conventional welding methods. The fundamental governing mechanisms that characterize the FEW process needs to be investigated to help optimize the process for specific applications. Conducting experimental investigation is undesirable and infeasible due to the highly complex thermal-mechanical procedures occurring simultaneously in a very short period of time of about one second. As such, the utilization of a finite element model to simulate and analyze the FEW process is warranted which would help understand the underlying mechanisms of the process in detail and provide an efficient yet effective tool to observe the effect of different process parameters on the weld quality. A coupled thermal-mechanical finite element model (FEM) is developed in this work to simulate the FEW process and gain an understanding of the physical mechanisms involved in the process and help predict the influence of variation of process parameters on the evolution of temperature, material flow, and their effect on weld quality. The primary difficulty in simulating a highly transient process like FEW, wherein not only the workpiece is subjected to deformation but also the auxiliary joining element i.e. friction element undergoes extensive deformation, is that the mesh elements are prone to distortion failure while trying to capture such high amount of deformation. The presence and importance of temperature effect on material properties further complicate the FEM. To help eliminate the distortion issue while simultaneously achieving an accurate simulation of the FEW process, the coupled Eulerian-Lagrangian (CEL) approach is adopted. The novelty of the current approach employed lies in using a Eulerian definition for the tool as against the more traditional convention of adopting a purely Lagrangian definition. The Eulerian definition enables to simulate the extreme deformation of friction element and capture the material flow without any computational issues. To inspect for the accuracy of the FEM results, mechanical deformation for different parts observed in the FEM is compared against the experimental results. To further validate the FEM, experimental measurements of temperature at different locations at the interface of two layers of workpiece are compared against the FEM results at same locations in the model. With respect to, both, thermal and mechanical measurements comparisons good agreement is shown between the simulation results and the experimental data. The simulation results for sets with varying process parameters show that the rotational speed of the friction element has the highest influence on the amount of frictional heat generated followed by the time period for different steps. Higher amount of heat is generated and conducted into the top aluminum layer for longer Penetration time, whereas for more heat concentration into the friction element to achieve the required deformation, longer Welding step with higher rotational speed is desired

A Study of the Abrasive Waterjet Machining Process for Carbon Fibre-Reinforced Polymers

Following a comprehensive literature review on the progress of abrasive waterjet (AWJ) machining, an experimental study of the AWJ machining of carbon fibre-reinforced polymers (CFRPs) of various thicknesses was conducted, showing that clean cuts can be achieved with good processing rates. The effect of process parameters on the machined kerf and hole characteristics is amply discussed in the thesis. It was demonstrated that AWJ machining is a good process for thick CFRPs that other processes may be unable to cut. However, material delamination in the form of edge pop-up in the jet entry and push-out at the jet exit caused by the initial pure waterjet impact of an AWJ piercing operation was observed. It was experimentally shown that using a steel mask on top of the workpiece can eliminate pop-up delamination, while push-out delamination at the jet exit can be reduced or eliminated by proper process parameters. However, the mechanisms involved require further investigation. Mathematical models for predicting the major machining performance indicators were developed using dimensional and regression analysis. Experimental verification confirms that the predictive models are reasonable and reliable for assisting in the planning of AWJ machining processes. A computational model is developed and verified experimentally to study the interaction between a pure waterjet and CFRPs. The behaviour of the waterjet is modelled using the smoothed particle hydrodynamics method while the CFRP is modelled by finite element using a continuum damage material model and cohesive zone method. A computational study using the developed model reveals that the material pop-up delamination is initiated due to the material’s elastic response to a rapid release of shock pressure to stagnation pressure and the traverse shear stresses induced by the downward bending of the laminated layers. The pure waterjet impact causes flow divergence and a hydro wedging effect between the material plies, which propagates the delamination. The delamination magnitude is found to increase initially with waterjet pressure up to a threshold after which a change in pressure does not affect the pop-up delamination significantly. The smallest pop-up delamination area occurs on the [0]12 laminate, followed by the [0/45/90/-45/0/45]s and [0/90]3s laminate. It is also found that the push-out loading towards the jet exit and the hydro wedging effect act jointly to result in push-out delamination

Novel Simulation-Inspired Roller Spreading Strategies for Fine and Highly Cohesive Metal Powders

When fine powders are to be used in powder bed metal additive manufacturing (AM), a roller is typically utilized for spreading. However, the cohesive nature of fine metal powder still presents challenges, resulting in low density and/or inconsistent layers under sub-standard spreading conditions. Here, through computational parameter studies with an integrated discrete element-finite element (DEM-FEM) framework, we explore roller-based strategies that are predicted to achieve highly cohesive powder layers. The exemplary feedstock is a Ti-6Al-4V 0-20 um powder, that is emulated using a self-similarity approach based on experimental calibration. The computational studies explore novel roller kinematics including counter-rotation as well as angular and transverse oscillation applied to standard rigid rollers as well as coated rollers with compliant or non-adhesive surfaces. The results indicate that most of these approaches allow to successfully spread highly cohesive powders with high packing fraction (between 50%-60% in a single layer) and layer uniformity provided that the angular/oscillatory, relative to the transverse velocity, as well as the surface friction of the roller are sufficiently high. Critically, these spreading approaches are shown to be very robust with respect to varying substrate conditions (simulated by means of a decrease in surface energy), which are likely to occur in LBPF or BJ, where substrate characteristics are the result of a complex multi-physics (i.e., powder melting or binder infiltration) process. In particular, the combination of the identified roller kinematics with compliant surface coatings, which are known to reduce the risk of tool damage and particle streaking in the layers, is recommended for future experimental investigation

Numerical modeling of heat transfer and fluid flow in laser metal deposition by powder injection

Laser metal deposition is an additive manufacturing technique which allows quick fabrication of fully-dense metallic components directly from Computer Aided Design (CAD) solid models. A self-consistent three-dimensional model was developed for the laser metal deposition process by powder injection, which simulates heat transfer, phase changes, and fluid flow in the melt pool, The governing equations for solid, liquid and gas phases in the calculation domain have been formulated using the continuum model. The free surface in the melt pool has been tracked by the Volume of Fluid (VOF) method, while the VOF transport equation was solved using the Piecewise Linear Interface Calculation (PLIC) method. Surface tension was modeled by taking the Continuum Surface Force (CSF) model combined with a force-balance flow algorithm. Laser-powder interaction was modeled to account for the effects of laser power attenuation and powder temperature rise during the laser metal deposition process. The governing equations were discretized in the physical space using the finite volume method. The advection terms were approximated using the MUSCL flux limiter scheme. The fluid flow and energy equations were solved in a coupled manner. The incompressible flow equations were solved using a two-step projection method, which requires a solution of a Poisson equation for the pressure field. The discretized pressure Poisson equation was solved using the ICCG (Incomplete Cholesky Conjugate Gradient) solution technique. The energy equation was solved by an enthalpy-based method. Temperature-dependent thermal-physical material properties were considered in the numerical implementation. The numerical model was validated by comparing simulations with experimental measurements --Abstract, page iv

CFD-XDEM coupling approach towards melt pool simulations of selective laser melting

Within the domain of metal Additive Manufacturing (AM), the challenge of qualification emerges prominently. This challenge encapsulates the endeavor to establish a set of process parameters that can reliably yield consistent and repeatable production outcomes. While additive manufacturing technologies like selective laser melting (SLM) have gained widespread usage for crafting metal parts boasting intricate geometries and high precision, they are not exempt from critical concerns. Defects, most notably porosities, persist as a substantial hurdle. The origin of these imperfections lies in microscale phenomena inherent to the melting and solidification processes occurring during layer-by-layer fabrication. This study presents a Computational Fluid Dynamics-eXtended Discrete Element Method (CFD-XDEM) coupling to model the dynamics and thermodynamic interplay between the powder bed and melt pool during SLM. The XDEM model simulates various aspects of powder behavior, including deposition, heating via laser radiation, melting, shrinkage, and the associated transfer of mass, momentum, and energy between the particles and the surrounding liquid and gas. The CFD model is based on the Volume Of Fluid (VOF) method and simulates the formation and evolution of the melt pool, taking into account surface tension force, Marangoni flow, buoyancy-driven flow inside the melt pool, phase change (solidification and melting), and the laser radiation on the melt surface. A direct coupling establishes a bidirectional transfer of source term data between the XDEM and the CFD. This involves the exchange of information such as the mass source of molten metal, convective heat transfer between particles and the fluid mixture, as well as the drag forces acting between the liquid and the particles in both directions. This direct coupling is achieved through the incorporation of source terms within the equations of the XDEM and CFD models. The present study is currently undertaking a comprehensive validation of the proposed method throughout each stage of development. This validation involves comparing model results with experimental data and benchmark problems. To initiate the process, the Marangoni model is being i validated against benchmark problems. Subsequently, the laser model is being implemented to predict the results of a laser melting experiment on a metal block. As the CFD model is finalized, the coupling is concurrently being developed. To validate the reliability of heat, mass, and momentum transfer within the coupling, an experiment involving the melting of ice is being replicated. This experiment serves as a method to affirm the performance of the melting model. The outcomes of this experiment are providing validation for the CFD-XDEM coupling's performance. Moving forward, the model is being utilized to predict outcomes for a low-power SLM experiment involving a single layer, considering various laser scanning velocities. Impressively, the simulation outcomes are demonstrating excellent agreement with experimental data. This alignment is underlining the model's capacity to accurately forecast melt pool dimensions. Furthermore, the model is being extended to simulate a larger powder bed, enabling an examination of melt pool characteristics as well as heat transfer interactions with the powder particles. The model presented in this study offers several distinctive features: The phase change of the particles is explicitly solved in the XDEM model, with particles undergoing melting at the melting temperature, shrinking, and disappearing when they are completely melted. The XDEM model solves for conduction and radiation between adjacent particles, providing an advantage over continuous powder bed models that require an estimate of effective thermal conductivity. Moreover, The particles are modeled as one-dimensional elements instead of 3-dimensional CFD spherical geometries, which is anticipated to be computationally more efficient. The CFD model incorporates all the relevant physical phenomena to the dynamics of melt pool, including Marangoni flow, buoyancy-driven flow, and surface tension forces. The volumetric heat source for the laser radiation is adaptive to the geometry of melt pool. The proposed model offers a reliable and efficient method for predicting the behavior of melt pool, and it is expected to facilitate the optimization of SLM process parameters to reduce the defects and improve the quality of manufactured parts.9. Industry, innovation and infrastructur

Impact Welding of Materials

Recent industrial criteria increasingly require the production of multi-material components. However, the manufacturing requirements of these components are not met by conventional welding techniques. Alternative solid-state technologies, such as impact-based processes, must be considered. The impact welding family is composed of several processes, such as explosion welding, magnetic pulse welding, vaporizing foil actuator welding, and laser impact welding. These processes present very different length scales, providing the impact welding family with a broad applicability range. A sample of the cutting-edge research that is being conducted on the multidisciplinary field of impact welding is presented in this book