Meshfree formulation for modelling of orthogonal cutting of composites

The Element-Free Galerkin method (EFG) is a prominent member of the meshfree methods family. In this work, EFG is utilised to simulate the orthogonal cutting process of unidirectional composites. The mathematical model is derived from the weak form of the momentum conservation equation with frictional contact constraints based on penalty method. Spatial discretisation using moving least squares shape functions are used. The onset and progression of damage are predicted by two stress-based failure criteria. Full Newton Raphson solver is used to solve the non-linear system equations iteratively. Numerical experiments investigating the effect of rake angle and fibre orientation are conducted. Cutting forces are compared against experiments and finite element simulations available in literature. Simulations show that the meshfree model is capable of predicting cutting forces as a function of the fibre orientation. Sensitivity analysis is conducted to investigate the effect of important meshfree parameters such as the domain of influence and weight function on forces. One of the strongest advantages of the proposed model is the simple and automatic set up process, as meshing for domain discretisation is not required

Modelling of cutting fibrous composite materials: current practice

Using fibre reinforced polymers (FRP) is increasing across many industries. Although FRP are laid-up in the near-net shape, several cutting operations are necessary to meet quality and dimensional requirements. Modelling of cutting is essential to understand the physics of the cutting phenomena and to predict quality and cost of products. This paper aims at reviewing the current practice in modelling of cutting FRP including analytical, numerical, mechanistic and empirical approaches, with emphasis on analytical models of cutting forces and delamination. Processes detailed include orthogonal cutting, drilling, milling and turning. Finally, advances in machining of metal-composite stacks are presented

Optimising Electrical Power Supply Sustainability Using a Grid-Connected Hybrid Renewable Energy System—An NHS Hospital Case Study

This study focuses on improving the sustainability of electrical supply in the healthcare system in the UK, to contribute to current efforts made towards the 2050 net-zero carbon target. As a case study, we propose a grid-connected hybrid renewable energy system (HRES) for a hospital in the south-east of England. Electrical consumption data were gathered from five wards in the hospital for a period of one year. PV-battery-grid system architecture was selected to ensure practical execution through the installation of PV arrays on the roof of the facility. Selection of the optimal system was conducted through a novel methodology combining multi-objective optimisation and data forecasting. The optimisation was conducted using a genetic algorithm with two objectives (1) minimisation of the levelised cost of energy and (2) CO2 emissions. Advanced data forecasting was used to forecast grid emissions and other cost parameters at two year intervals (2023 and 2025). Several optimisation simulations were carried out using the actual and forecasted parameters to improve decision making. The results show that incorporating forecasted parameters into the optimisation allows to identify the subset of optimal solutions that will become sub-optimal in the future and, therefore, should be avoided. Finally, a framework for choosing the most suitable subset of optimal solutions was presented

Element-free galerkin modelling for cutting of fibre reinforced plastics

The utilisation of composite materials is increasing across many industries, spurred by the need for weight reduction and improved mechanical properties. This has led to an increase in their machining requirements. Although composites are laid in near-net shape, machining processes such as drilling and edge trimming are required to give the composites parts their final geometry and functionality. Machining of composites is challenging due to their low machinability and high cost. Numerical modelling presents a valuable tool for cost reduction and better understanding of the machining processes. Most modelling of machining is carried out using the Finite Element Method, which requires significant time in generating the mesh. Meshfree methods present an attractive choice for machining simulations due to their capabilities in modelling large deformations without the need to construct a mesh. This work aims at developing an efficient meshfree model to simulate orthogonal cutting of unidirectional composites. The Element-Free Galerkin (EFG), which is a prominent meshfree method, is used to construct the model using MATLAB. Steady-state and dynamic models are developed and validated against experimental evidence. The models include several novel features in constitutive relations, composites failure and contact modelling. The main outputs of the simulations are cutting forces and chip formation. Good agreement with experiments is achieved in predicting cutting force. However, thrust force is significantly under-estimated, which is noticed in most of the relevant literature. Three phases of orthogonal cutting experiments are carried out to gain better understanding of the cutting process and generate model validation data. Statistical significance of fibre orientation angle, depth of cut, rake angle and cutting speed on cutting forces and surface integrity is established. Furthermore, the effect of fibre volume fraction on cutting forces is investigated. This work showed that the EFG is a viable numerical method to simulate orthogonal cutting. The simple and automated preprocessing and high quality of approximation are the most advantageous features of the developed model

Novel Twin-Screw Stirling Cycle Machine for Cryogenic and Refrigeration Applications

This paper describes design and principles of operation of a novel rotary type Stirling cycle machines based on rotary positive displacement mechanisms such as twin-screw, gate rotor screw, scroll, and conical screw compressors and expanders. When these mechanisms are used as separate expanding or compressing machines, the flow of the gas is one-directional with volumes of chambers varying in accordance with a saw-tooth type function. The proposed design solution combines at least two units of gas-coupled compressor and expander arrangements with a required shift in the shaft angle. Every unit has a series of gas channels for timing the connection of its compressor and expander parts. Units are connected to each other via a set of heat exchangers, which are conventional for Stirling cycle machines: recuperative cooling and warm heat exchangers with a regenerator, built between them. The operational capability is demonstrated using three-dimensional CFD simulations. Computational results demonstrate reciprocating flow of the gas between units, as in conventional Stirling machines, and functioning of the proposed design as a multi-cylinder, double acting Stirling machine. The suggested design makes it possible to achieve full dynamic balancing, especially in the case of twin-screw and gate rotor mechanisms, due to the rotation of screws around their axes. It also eliminates a number of problems, which are specific to Stirling machines with reciprocating pistons and their kinematic drive mechanisms

An Investigation into the Dependency of Cutting Forces on the Volume Fraction and Fibre Orientation during Machining Composite Materials

This paper presents an empirical force model quantifying the effect of fibre volume fraction and fibre orientation on the cutting forces during orthogonal cutting of unidirectional composites. Glass fibre plates and high speed steel cutting tools are used to perform orthogonal cutting on shaping machine whereas cutting forces are measured using platform force dynamometer. The analysis of forces shows almost linear dependency of cutting forces on the fibre content for both cutting and thrust forces. High dependency of cutting forces is also observed on fibre orientation with high percentage contribution ratio (up to 95.31\%). Lowest forces corresponded to 30o and highest to 90o fibre orientation. Multivariate regression technique is used to construct the empirical model

Dynamic simulation of machining composites using the explicit element-free Galerkin method

Machining operations are performed on composite parts to obtain the final geometry. However, machining composites is challenging due to their low machinability and high cost. Numerical modelling of machining presents a valuable tool for cost reduction and a better understanding of the cutting process. Meshfree methods are an attractive choice to model machining problems due to their capability in modelling large deformations. This work presents an explicit meshfree model for orthogonal cutting of unidirectional composites based on the element-free Galerkin (EFG) Method. Advantages of the proposed model include: simple and automated preprocessing, advanced material modelling and ability to model high-speed machining. Workpiece material is modelled as orthotropic Kirchhoff material with a choice of three failure criteria: maximum stress, Hashin and LaRC02. Frictional contact calculations are performed based on central differencing, therefore avoiding the use of penalty parameters. Validation of the EFG model is conducted by comparing cutting forces against orthogonal cutting experiments on GFRP samples using a vertical milling machine. It is found that while the numerical cutting forces are in good agreement with experimental ones, the numerical thrust forces are significantly under-estimated. Analysis of failure showed that chip is formed along the fibre direction in the studied range