<p>As we know that nature made the things optimized in all point of views, also it is supposed that nature works under some evolutionary process.</p><p>Since there was no such Evolutionary Structural Optimization (ESO) method having strong mathematical background, that’s why these are not much reliable. The purpose of this thesis work is a little effort to introduce such an ESO method having a strong mathematical background.</p><p>In this thesis work Optimization as a thermodynamic system, we are introducing a new method for topology optimization by using concept of Free Energy and Dissipation Potential from non-smooth thermodynamics system. For better understanding we may call it as Evolutionary Structural Topology Optimization (ESTO), and this project work is done in the following steps.</p><p>An evolution problem is formulated in terms of free energy and dissipation potential for a non-smooth thermodynamical system. Free energy is taken as an objective function for a general structural optimization problem. Derivation of a well posed evolution problem for which evolution is such that objective function always decreases. An optimality criteria method is derived for given evolution problem and it is implemented in a FEM program TRINITAS. And the behaviour of the so called evolutionary parameters such as Forward and Backward plastic constants is analyzed.</p>

As we know that nature made the things optimized in all point of views, also it is supposed that nature works under some evolutionary process. Since there was no such Evolutionary Structural Optimization (ESO) method having strong mathematical background, that’s why these are not much reliable. The purpose of this thesis work is a little effort to introduce such an ESO method having a strong mathematical background. In this thesis work Optimization as a thermodynamic system, we are introducing a new method for topology optimization by using concept of Free Energy and Dissipation Potential from non-smooth thermodynamics system. For better understanding we may call it as Evolutionary Structural Topology Optimization (ESTO), and this project work is done in the following steps. An evolution problem is formulated in terms of free energy and dissipation potential for a non-smooth thermodynamical system. Free energy is taken as an objective function for a general structural optimization problem. Derivation of a well posed evolution problem for which evolution is such that objective function always decreases. An optimality criteria method is derived for given evolution problem and it is implemented in a FEM program TRINITAS. And the behaviour of the so called evolutionary parameters such as Forward and Backward plastic constants is analyzed.

This work aims at providing a numerical tool for the efficient design of the multidirectional carbon fiber reinforced composite material by means of finite element simulations. Abaqus/ CAE v 6.9-1 software has been used to establish a 3D model for simulation of the tensile test on the composite specimen. The aim of this analysis of multidirectional carbon fiber reinforced composite is to predict the strain and stress distribution in different plies through thickness. Tensile test experiment was carried out and the result was analyzed by ARAMIS to calculate the young’s modulus, stress, loads and strain of the composite specimen. The numerical model was compared against the result obtained from tensile test experiment to arrive at meaningful results for validation. This is done in order to understand the mechanical strength and strain at failure of the composite material. In this work three types of CFRP composite specimens are used, all have same 15 no. of ply but stacked in different orientation. It is found out that mechanical strength, failure load and strain differ slightly depending on this different ply orientation. A series of different modeling technique has also been done to verify the best modeling technique. The micromechanics of composite material is complex and the experimental predictions are time consuming and expensive. Though using FEM frequently solves the problem.

The design and analysis of drop test to investigate the behaviour of adhesive joints in automotive structures is performed. The drop test is simulated by FE software. The specimen geometry is based on Volvo Car Corp. drop test standard. In the drop test machine, a general beam structure is supporting all the parts. The machine includes a lifting system. The test is applied to a pre designed specimen, which will provide the information about adhesive joint strength.

<p>The design and analysis of drop test to investigate the behaviour of adhesive joints in automotive structures is performed. The drop test is simulated by FE software. The specimen geometry is based on Volvo Car Corp. drop test standard.</p><p>In the drop test machine, a general beam structure is supporting all the parts. The machine includes a lifting system. The test is applied to a pre designed specimen, which will provide the information about adhesive joint strength.</p>

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Tube hydroforming is a forming method which has several advantages. By using pressure in combination with material feeding it is possible to manufacture products with high structural integration and tight dimensional tolerances. The forming method is especially suited for aluminium alloys which have a relatively low ductility. Finite Element simulations are used extensively in the sheet metal stamping industry, where the methodology has contributed to a better understanding of the process and the new prediction capability has significantly reduced costly die tryouts. Similarly, the tube hydroforming industry can benefit from Finite Element simulations, and this simulation methodology is the topic of this dissertation. Deep drawing and tube hydroforming have a basic difference, namely that the latter process essentially is a force controlled process. This fact, in combination with the anisotropic behaviour of aluminium tubes, enforces a need for accurate constitutive descriptions. Furthermore, the material testing needs to account for the specifics of tube hydroforming. The importance of proper material modelling is in this work shown for hydrobulging and hydroforming in a die with extensive feeding. The process parameters in hydroforming are the inner pressure and the material feeding, where a correct combination of these parameters is crucial for the success of the process. It is here shown, that Finite Element simulations together with an optimisation routine are powerful tools for estimating the process parameters in an automated procedure. Finally, the reliability and quality of the simulation results depend on how failure is evaluated, which in the case of hydroforming mainly oncerns wrinkling and strain localisation. Since tube hydroforming often is preceded by bending operations this fact also demands the criteria to be strain path independent. In this work, it is shown that the prediction of strain localisation depends on the ability to predict diffuse necking, which in turn is strongly related to the chosen constitutive model.

This thesis addresses normal axisymmetric contact of dissimilar elastic solids at finite interfacial friction. It is shown that in the case of smooth and convex but otherwise arbitrary contact profiles and monotonically increasing loading a single stick-slip contour evolves being independent of loading and profile geometry. This allows developing an incremental procedure based on a reduced problem corresponding to frictional rigid flat punch indentation of an elastic half-space. The reduced problem, being independent of loading and contact region, was solved by a finite element method based on a stationary contact contour and characterized by high accuracy. Subsequently, a tailored cumulative superposition procedure was developed to resolve the original problem to determine global and local field values for two practically important geometries: flat and conical profiles with rounded edges and apices. Results are given for relations between force, depth and contact contours together with surface stress distributions and maximum von Mises effective stress, in particular to predict initiation of fracture and plastic flow. It is also observed that the presence of friction radically reduces the magnitude of the maximum surface tensile stress, thus retarding brittle fracture initiation. Hertzian fracture through indentation of flat float glass specimens by steel balls has been examined experimentally for a full load cycle. It has been observed that if the specimen survived during loading to a maximum level it frequently failed at decreasing load. It has been proposed by Johnson et al. (1973) that the underlying physical cause of Hertzian fracture initiation during load removal is that at unloading frictional tractions reverse their sign over part of the contact region. Guided by these considerations a robust computational procedure has been developed to determine global and local field values in particular at unloading at finite friction. In contrast to the situation at monotonically increasing loading, at unloading invariance properties are lost and stick-slip regions proved to be severely history dependent and in particular with an opposed frictional shear stress at the contact boundary region. This causes an increase of the maximum tensile stress at the contour under progressive unloading. It is shown that the experimental observations concerning Hertzian fracture initiation at unloading are at least in qualitative correlation with the effect friction has on the maximum surface tensile stress. A contact cycle between two dissimilar elastic bodies at finite Coulomb friction has been further investigated analytically and numerically for a wider range of material parameters and contact geometries. With the issue of Hertzian fracture initiation in mind, results concerning the influence of the friction coefficient and compliance parameters on the absolute maximum surface tensile stress during a frictional contact cycle are reported along with the magnitudes of the relative increase of maximum tensile stresses at unloading. Based on a critical stress fracture criterion it is discussed how the predicted increases will influence the critical loads required for crack initiation. Fracture loads are measured with steel and tungsten carbide spherical indenters in contact with float glass specimens at monotonically increasing loading and during a load cycle. Computational predictions concerning the fracture loads are given based on Hertz and frictional contact theories combined with a critical stress fracture criterion. The computational results obtained for frictional contact are shown to be in better agreement with experimental findings as compared to the predictions based on the Hertz theory. The remaining quantitative discrepancy was attributed to the well-known fact that a Hertzian macro-crack initiates from pre-existing defects on the specimen’s surface. In order to account for the influence of the random distribution of these defects on the fracture loads at monotonic loading, Weibull statistics was introduced. The predicted critical loads corresponding to 50% failure probability were found to be in close agreement with experimentally observed ones. / QC 20100729

This thesis concerns optimization of structures considering various uncertainties. The overall objective is to find methods to create solutions that are optimal both in the sense of handling the typical load case and minimising the variability of the response, i.e. robust optimal designs. Traditionally optimized structures may show a tendency of being sensitive to small perturbations in the design or loading conditions, which of course are inevitable. To create robust designs, it is necessary to account for all conceivable variations (or at least the influencing ones) in the design process. The thesis is divided in two parts. The first part serves as a theoretical background to the second part, the two appended articles. This first part includes the concept of robust design, basic statistics, optimization theory and meta modelling. The first appended paper is an application of existing methods on a large industrial example problem. A sensitivity analysis is performed on a Scania truck cab subjected to impact loading in order to identify the most influencing variables on the crash responses. The second paper presents a new method that may be used in robust optimizations, that is, optimizations that account for variations and uncertainties. The method is demonstrated on both an analytical example and a Finite Element example of an aluminium extrusion subjected to axial crushing. / ROBDES

This dissertation concerns failure modelling with material imperfections and element erosion in finite element analyses. The aim has been to improve the element erosion technique, which is simple to use and implement and also computationally inexpensive. The first part of the dissertation serves as an introduction to the topic and as a summary of the methodologies presented in the following part. The second part consists of seven appended papers. In paper A the standard element erosion technique is used for projectile penetration. In papers B and C a methodology that accounts for size effects is developed and applied to crack initiation in armour steel and tungsten carbide. A methodology to better predict the stress state at crack tips with coarse meshes is presented and applied to armour steel in paper D. Papers E and F concern the development of selective mass scaling which allows for larger time steps in explicit methods. Finally, in paper G the previously presented methodologies are used in combination and validated against experimental results on tungsten carbide. The computations show good agreement with the experimental results on failure initiation for both materials, while the computational results on the propagation of cracks show better agreement for the armour steel than for the tungsten carbide. / On the day of the public defence of the doctoral thesis, the status of articles I, III and IV was Accepted and article VII was Submitted.