342 research outputs found
Metal cutting modelling SPH approach
Get PDFThe purpose of this work is to evaluate the use of the smoothed particle hydrodynamics (SPH) method within the framework of high speed cutting modelling. First, a 2D SPH based model is carried out using the LS-DYNA® software. The developed SPH model proves its ability to account for continuous and shear localised chip formation and also correctly estimates the cutting forces, as illustrated in some orthogonal cutting examples. Then, the SPH model is used in order to improve the general understanding of machining with worn tools. At last, a hybrid milling model allowing the calculation of the 3D cutting forces is presented. The interest of the suggested approach is to be
freed from classically needed machining tests: Those are replaced by 2D numerical tests using the SPH model. The developed approach proved its ability to model the 3D cutting forces in ball end milling
Development of a total Lagrangian SPH code for the simulation of solids under dynamioc loading
Get PDFThis thesis makes use of an alternative SPH formulation, the Total
Lagrangianf ormulation, to characterised ynamic eventsi n solids and to achieve
the proposed objectives outlined in Chapter 1. The structure is as follows:
Chapter 1, Introduction, describes the motivation for this research and
outlines the objectives and the structure of this thesis.
Chapter 2, SPH fundamentals, supplies the standard procedure to
generate particle equations and provides a comprehensive summary of gradient
approximation formulae in SPH. The discretised SPH form of the conservation
laws is included here.
Chapter 3, SPH drawbacks: describes the limitations of SPH such as
particle deficiency, consistency, zero energy modes, treatment of boundaries
and the tensile instability problem. A rigorous stability analysis of continua and
SPH particle equations is also presented in this chapter.
Chapter 4, Total Lagrangian SPH. Continuum Mechanics considerations
are discussed here; detailed derivations of SPH equations in a total Lagrangian
framework are given together with potential corrections to the total Lagrangian
SPH equations.
Chapter 5, Total Lagrangian SPH algorithms and their implementation
using FORTRAN. This chapter gives a brief introduction to explicit codes. It
also provides flow charts describing the Total Lagrangian algorithms and their
integration into the MCM code.
Chapter 6, Total Lagrangian SPH code validation. This chapter includes
problems of varying degrees of complexity. Examples are provided to illustrate
how the Total Lagrangian SPH code compares to a conventional collocational
SPH code. Cases are supplied for which the analytical solution is known, and
the results compared with the SPH approximations in order to show the accuracy of the approximation. Some examples are supplied which provide a
direct comparison between SPH and non linear FE results and SPH and
experimental results.
Chapter 7, Alternative formulation of SPH equations and improvements
to the standard MCM code: Various modifications to the standard SPH code are
presented. These modifications include the implementation of subroutines that
make use of an alternative approach to ensure the conservation of mass law is
met locally at every particle. The introduction of XSPH to achieve further
stabilisation of the code was also carried out and some examples are provided.
The theory behind an alternative form of the conservation of mass equation as
proposed by Belytschko [4] is explained and its implementation into the SPH
code is assessed through examples. Also, an alternative formulation of SPH
equations based on the general theory of mixed Lagrangian-Eulerian
formulations [35] is presented: these equations could serve as the foundation for
future research in this field.
Chapter 8, Conclusions are presented in this chapter.
A brief literature review is provided at the beginning of each chapter as a
means of introduction to the topic and a concise summary outlines the main
points discussed
Modelling High Speed Machining with the SPH Method
Get PDFThe purpose of this work is to evaluate the use of the Smoothed Particle Hydrodynamics (SPH) method within the framework of high speed cutting modelling. First, a 2D SPH based model is carried out using the LS-DYNA® software. SPH is a meshless method, thus large material distortions that occur in the cutting problem are easily managed and SPH contact control allows a “natural” workpiece/chip separation. The developed SPH model proves its ability to account for continuous and shear localized chip formation and also correctly estimates the cutting forces, as illustrated in some orthogonal cutting examples. Then, The SPH model is used in order to improve the general understanding of machining with worn tools. At last, a milling model allowing the calculation of the 3D cutting forces is presented. The interest of the suggested approach is to be freed from classically needed machining tests: Those are replaced by 2D numerical tests using the SPH model. The developed approach proved its ability to model the 3D cutting forces in ball end milling
SPH method applied to high speed cutting modelling
Get PDFThe purpose of this study is to introduce a new approach of high speed cutting numerical modelling. A Lagrangian smoothed particle hydrodynamics (SPH)- based model is arried out using the Ls-Dyna software. SPH is a meshless method, thus large material distortions that occur in the cutting problem are easily managed and SPH contact control permits a "natural" workpiece/chip separation. The developed approach is compared to machining dedicated code results and experimental data. The SPH cutting model has proved is ability to account for continuous to shear localized chip formation and also correctly estimates the cutting forces, as illustrated in some orthogonal cutting examples. Thus, comparable results to machining dedicated codes are obtained without introducing any adjusting numerical parameters (friction coefficient, fracture control parameter)
Investigations of smoothed particle hydrodynamics method for fluid-rigid body interactions
No full textThe aim of this project is to investigate the capability of smoothed particle hydrodynamics (SPH) method for fluid-rigid body interactions. SPH is one of the most widely used meshless methods which use particles to represent the system. The fluid is assumed either slightly compressible so weakly compressible SPH (WCSPH) is applied or truly incompressible so incompressible SPH method (ISPH) is adopted. The performance of SPH method is affected by a number of modelling parameters including the choice of kernel functions, smoothing length, total number of particles and time step size. Investigations of the effect of these parameters were conducted using one dimensional cases and the results show that smoothing length and the total number of particles can influence the accuracy significantly but other parameters are less important. In order to generate the model efficiently and maintain accuracy an appropriate boundary treatment is important. Two boundary treatments are investigated for ISPH method. Although these two boundary treatments have been used in WCSPH, they have not been used in ISPH method in the literature. They are easier to use for complicated engineering situations related to fluid structure interaction problems compared with the traditionally used ghost particles. Two approaches for solving Poisson’s equation of ISPH method are studied including the implicit solution approach and explicit solution approach. A new method is developed for multi-phase flow by combining WCSPH method and truly ISPH method to study the effect from air pressure. Within this method the compressibility of air and incompressibility of water can be retained. Based on these studies, algorithms for fluid rigid-body interaction in 2 dimensional and 3 dimensional cases have been developed to simulate the general engineering problems related to fluid rigid body interactions
Toward a better understanding of tool wear effect through a comparison between experiments and SPH numerical modelling of machining hard materials
Get PDFThe aim of this study is to improve the general understanding of tungsten carbide (WC–Co) tool wear under dry machining of the hard-to-cut titanium alloy Ti6Al4V. The chosen approach includes experimental and numerical tests. The experimental part is designed to identify wear mechanisms using cutting force measurements, scanning electron microscope observations and optical profilometer analysis. Machining tests were conducted in the orthogonal cutting framework and showed a strong evolution of the cutting forces and the chip profiles with tool wear. Then, a numerical method has been used in order to model the machining process with both new and worn tools. The use of smoothed particle hydrodynamics model (SPH model) as a numerical tool for a better understanding of the chip formation with worn tools is a key aspect of this work. The redicted chip morphology and the cutting force evolution with respect to the tool wear are qualitatively compared with experimental trends. The chip formation mechanisms during dry cutting process are shown to be quite dependent from the worn tool geometry. These mechanisms explain the high variation of the experimental and numerical feed force between new and worn tools
Assessment and investigation of SPH modelling for nano-scratching
No full textThe computational modelling of nano-machining using Smooth Particles Hydrodynamics (SPH) method is a research area of recent interest. Among the papers which focus on SPH simulation of nano-machining on copper workpieces, Johnson-Cook model parameters obtained at macro-scale have been used previously [1]–[3] for describing constitutive properties of copper. This paper establishes a SPH model for nano-scratching on copper workpiece with the aim of evaluating the feasibility of using these macro-scale Johnson-Cook parameters in SPH simulation of nano-scale machining. The geometrical parameters for tool tip and workpiece for SPH modelling of nano-scratching is adopted from Islam et al. [4] and simulation results are compared with the experimental work of these authors which was reported in [4] and [5]. The analysis of machining forces shows that the cutting and normal forces slightly increase as the cutting speed increases, and that these are close to experimental results. Simulation results also show that ploughing is the main mode of surface deformation and that the cross-sectional profile of a machined nano-groove matches well with experimental results. This paper contributes towards further elaborating the suitability of employing macro-scale Johnson-Cook parameters in the SPH simulation of nano-machining to predict material responses
Characterizing flow in oil reservoir rock using SPH: absolute permeability
No full textIn this paper, a three-dimensional smooth particle hydrodynamics (SPH) simulator for modeling grain scale fluid flow in porous rock is presented. The versatility of the SPH method has driven its use in increasingly complex areas of flow analysis, including flows related to permeable rock for both groundwater and petroleum reservoir research. While previous approaches to such problems using SPH have involved the use of idealized pore geometries (cylinder/sphere packs etc), in this paper we detail the characterization of flow in models with geometries taken from 3D X-ray microtomographic imaging of actual porous rock; specifically 25.12 % porosity dolomite. This particular rock type has been well characterized experimentally and described in the literature, thus providing a practical 'real world' means of verification of SPH that will be key to its acceptance by industry as a viable alternative to traditional reservoir modeling tools. The true advantages of SPH are realized when adding the complexity of multiple fluid phases, however, the accuracy of SPH for single phase flow is, as yet, under developed in the literature and will be the primary focus of this paper. Flow in reservoir rock will typically occur in the range of low Reynolds numbers, making the enforcement of no-slip boundary conditions an important factor in simulation. To this end, we detail the development of a new, robust, and numerically efficient method for implementing no-slip boundary conditions in SPH that can handle the degree of complexity of boundary surfaces, characteristic of an actual permeable rock sample. A study of the effect of particle density is carried out and simulation results for absolute permeability are presented and compared to those from experimentation showing good agreement and validating the method for such applications
On the SPH Orthogonal Cutting Simulation of A2024-T351 Alloy
No full textAbstractSmoothed Particle Hydrodynamics (SPH) is known for its ability to simulate a natural flow of material without mesh distortion problems related to the Finite Element Method (FEM) frequently. Therefore it can be used to simulate material flow around the tooltip in machining simulations.This paper presents some results of the SPH orthogonal cutting simulations of A2024-T351 aluminium alloy compared to the experimental and FEM simulation results published by Mabrouki et al. recently. Simulations were performed with the ANSYS LS- DYNA solver. To simulate the workpiece behavior during cutting, the Johnson-Cook constitutive material model was used. In this work, an influence of the Johnson-Cook failure parameters D1-D5 and SPH density on a saw-toothed chip formation was observed. Chip shapes, von Mises stress, plastic strains, strain rates and cutting forces were compared to published results, confirming that the SPH method is able to predict the cutting and feed forces and the chip shape correctly. For experimental verification, a CNC machine, dry cutting, uncoated cemented carbide inserts ISO N10-20, cutting speeds in the range of 200-800 m/min, feed 0.4mm and depth of cut 4.0mm were used. Regarding the SPH particles density it was found that the model with smaller space among particles tended to form a highly segmented chip. However, for a good correlation with experimental results the Johnson-Cook failure parameters together with minimum required strain for failure should be set
A new kernel function for SPH with applications to free surface flows
No full textSmoothed particle hydrodynamics (SPH) is a popular meshfree Lagrangian particle method, which uses a kernel function for numerical approximations. The kernel function is closely related to the computational accuracy and stability of the SPH method. In this paper, a new kernel function is proposed, which consists of two cosine functions and is referred to as double cosine kernel function. The newly proposed double cosine kernel function is sufficiently smooth, and is associated with an adjustable support domain. It also has smaller second order momentum, and therefore it can have better accuracy in terms of kernel approximation. SPH method with this double cosine kernel function is applied to simulate a dam-break flow and water entry of a horizontal circular cylinder. The obtained SPH results agree very well with the experimental results. The double cosine kernel function is also comparatively studied with two frequently used SPH kernel functions, Gaussian and cubic spline kernel functions. (C) 2014 Elsevier Inc. All rights reserved
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