Hot Compression Tests Using Total Lagrangian SPH Formulation in Energy-Based Framework

Limitations of the finite element method (FEM) in some cases involving large deformations as in forging or high compression tests are overcome nowadays by meshless methods such as the smoothed particle hydrodynamic (SPH) method. This paper presents a corrected total Lagrangian SPH formulation for problems encountering large deformations in solid mechanics. The continuum is modeled as a Hamiltonian system of particles (energy-based framework). The total Lagrangian formulation proposed overcomes some problems faced by standard SPH in simulating solid mechanic problems such as tensile instability. Numerical applications compared with experimental results are presented to show the capabilities of this novel formulation

An implicit non-ordinary state-based peridynamics for large deformation solid mechanics problems

The numerical simulation of the cracking process remains one of the most significant challenges in solid mechanics. Compared classical approaches, peridynamics(PD) has some attractive features because the basic equations remain applicable even when singularities appear in the deformation. Numerical time-integration plays a big role in any computational framework and unlike explicit time-integration, implicit time-integration methods can be much more efficient because of the ability to adopt fairly large time increments, making it a suitable option for PD analyses of large deformation problems. The objective of this thesis is to propose an implicit non-ordinary state-based peridynamics (NOSB PD) approach focusing on quasistatic analyses with large deformation mechanics. Firstly, the use of the adaptive dynamic relaxation (ADR) method as a solution strategy for quasi-static analyses with large deformation mechanics is discussed. Next, an analytical expression of the Jacobian matrix based on the equation of motion of NOSB PD is formulated to ensure optimum convergence of the global residual force. To address some instability issues in the existing “corresponding material” model, caused by zero-energy modes instability, recent approaches proposed by Silling (2017) are used to control the spurious deformation modes. An additional stabilisation term with respect to displacement is included in the derivatives for Jacobian formulation. This allows a more accurate NOSB PD approach to model material behaviour where correspondence materials have previously failed due to instability. Finally, to validate the proposed methodology, several numerical examples of 2D damage problems model using a stabilised correspondence model are verified, and suggestions are made for future implementation. The novelty of this thesis lies in providing theoretical development and numerical implementation of an implicit non-linear NOSB PD focusing on quasi-static analyses with large deformation mechanics. Findings from this thesis will interest researchers working in numerical methods, along with those solving discontinuous solid mechanics problems

Smoothed particle hydrodynamics for root growth mechanics

International audienceA major challenge of plant developmental biology is to understand how cells grow during the formation of an organ. To date, it has proved dicult to develop computational models of entire organs at cellular resolution and, as a result, the testing of hypotheses on the biophysics of self-organisation is currently limited. Here, we formulate a model for plant tissue growth in an SPH framework. The framework identies the SPH particle with individual cells in a tissue , but the tissue growth is performed at the macroscopic level using SPH approximations. Plant tissue is represented as an anisotropic poro-elastic material where turgor pressure deforms the cell walls and biosynthesis and cell division control the density of the tissue. The performance of the model is evaluated through a series of tests and benchmarks. Results demonstrate good stability and convergence of simulations as well as readiness of the technique for more complex biological problems

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

Hybrid Thermo-Mechanical Contact Algorithm for 3D SPH-FEM Multi-Physics Simulations

Numerical simulation of complex industrial processes has become increasingly ommon in recent years. Depending on the nature of the industrial application, multiple types of physical phenomena may need to be considered as well as the interaction of multiple disjoint bodies. This paper is focused on industrial applications with large plastic deformation. Such processes are typically not well treated by finite element (FE) methods. For this reason, the smoothed particle hydrodynamics method (SPH) is used. In this work, we introduce a robust and straightforward thermo-mechanical contact algorithm for multi-physics SPH simulations in 3D

Hypervelocity impact induced disturbances on composite sandwich panel spacecraft structures

The next generation of European scientific satellites will carry extremely sensitive measurement devices that require platform stability orders of magnitude higher than current missions. It is considered that the meteoroid and space debris (M/SD) environment poses a risk to the success of these missions as disturbances induced by the impact of these particles at hypervelocity may degrade the platform stability below operational requirements. In this thesis, disturbances induced by the impact of M/SD particles at hypervelocity on a representative scientific satellite platform have been investigated. An extensive experimental impact test program has been performed, from which an empirical ballistic limit equation (BLE) which defines the conditions of structural perforation for composite sandwich panel structures with CFRP facesheets and aluminium honeycomb cores (CFRP/Al HC SP) has been defined. The BLE is used to predict impact conditions capable of inducing the different excitation modes relevant for a SP sandwich panel structure, enabling a significant reduction in the time and expense usually required for calibrating the protective capability of a new structural configuration. As experimental acceleration facilities are unable to cover the complete range of possible in-orbit impact conditions relevant for M/SD impact risk assessment, a Hydrocode model of the representative CFRP/Al HC SP has been constructed. A series of impact simulations have been performed during which the local impact-induced disturbance has been measured. The numerical disturbance signals have been validated via comparison with experimental disturbance measurements, and subsequently subject to a characterisation campaign to define the local elastic excitation of the SP structure equivalent to that induced by impact of a M/SD particle at hypervelocity. The disturbance characterisation is made such that it is applicable as an excitation force on a global satellite Finite Element (FE) model, allowing propagation of impact-induced disturbances throughout the complete satellite body to regions of critical stability (i.e. measurement devices). The disturbance induced upon measurement devices by M/SD impacts at both near- and far-body locations can then be made, allowing the threat to mission objectives to be assessed

Loads calculation, stress analysis and bird strike simulation of a composite wing leading edge

Tato diplomová práce se zaměřuje na stanovení geometrických a materiálových parametrů konstrukce slotu letadla B737-200. V této práci je vypracovaný návrh kompozitového slotu s ohledem na dané zatěžovací případy, včetně tzv. “bird strike”. Analytické výpočty jsou ověřené metodou konečných prvků (MKP) v programech MSC.Nastran/Patran, MSC.DytranThis thesis deals with design of slat geometrical and material parameters of the B737-200 aircraft. In this thesis there is created design of the composite slat with respect to a given load cases including bird strike. Analytical calculations are verified by FE analysis in MSC.Nastran/Patran, MSC.Dytran software