Surface integrity is of great significance in grinding performance since grinding process is often used as a finishing step. For metallic materials, residual stresses play an important role in surface integrity for its strong effect on fatigue life, corrosion resistance, and part distortion. For ceramic materials, the surface damage induced by grinding process could greatly affect the mechanical strength and surface finish of the component. The functional behavior of machined components can be enhanced or impaired by the grinding process. Because of this, understanding the surface integrity imparted by grinding is very important. The use of fluid is common in grinding process, however, the high cost and environmental impact of the conventional flood cooling is very undesirable. The minimum quantity lubrication (MQL) have been introduced in industry for about two decades as a promising alternative to conventional flood cooling for economical and environmental advantages. A comprehensive understanding of the MQL effect on the process performances and surface integrity is of great value to the implementation of MQL technique in industrial situation. Grinding-induced residual stress prediction has been a topic of research since the 1970’s while the studies of MQL grinding is still on the early stage with experimental investigations. A comprehensive study and quantitative description of MQL effect on the residual stress generation in grinding is highly demanded. On the other hand, although there has been significant research in the area of surface damage in ceramic grinding, there are still opportunities for advancing predictive methods. Therefore, the objectives of the current research are set as follows: (1) develop a method of predicting residual stress based on an analytical description of the grinding process under MQL condition, (2) develop a method of predicting surface finish and damage in ceramic grinding, and (3) validate the model with experimental data. The research will first focus on predicting residual stresses in MQL grinding based on first principles. This includes predictive models of grinding forces, and grinding temperature stemmed from grinding kinematics and dynamics principles as part of the overall modeling effort. The effect of MQL on both lubrication and cooling aspects has been integrated into these models. The mechanical and thermal output parameters will serve as the basis for determining the loading history which generate residual stresses. The research will also aim at surface roughness modeling in ceramic grinding. A ductile-brittle mixed surface generation is predicted based on the nature of ceramic materials and grinding kinematics. The crack system developed from indentation fracture mechanics approach will be utilized in evaluating the brittle mode surface generation. The modeling techniques will be applied to a range of grinding conditions and materials. This research would aid in evaluating various surface integrities in grinding of metallic and ceramic materials with little experimental efforts. The output could be used to machine these materials effectively to order to improve the functionality of the component.

This thesis concerns residual stress modeling in soft living tissues. The word living means that the tissue interacts with surrounding organs and that it can change its internal properties to optimize its function. From the first day all tissues are under pressure, due, for example, to gravity, other surrounding organs that utilize pressure on the specific tissue, and the pressure from the blood that circulates within the body. This means that all organs grow and change properties under load, and an unloaded configuration is never present within the body. When a tissue is removed from the body, the obtained unloaded state is not naturally stress free. This stress within an unloaded body is called residual stress. It is believed that the residual stress helps the tissue to optimize its function by homogenizing the transmural stress distribution. The thesis is composed of two parts: in the first part an introduction to soft tissues and basic modeling is given and the second part consist of a collection of five manuscripts. The first four papers show how residual stress can be modeled. We also derive evolution equation for growth and remodeling and show how residual stress develops under constant pressure. The fifth paper deals with damage and viscosity in soft tissues.

Na construção de cascos resistentes de submarinos são utilizados, frequentemente, os processos de conformação a frio e de soldagem. Estes processos produzem na estrutura deformações plásticas permanentes originando tensões residuais. A presença das tensões residuais é equivalente a introduzir uma pré-carga inicial na estrutura, o que acelera o processo de plastificação, reduzindo à capacidade de resistência da estrutura à pressão hidrostática. Para quantificar esta redução foi realizado, inicialmente, um estudo considerando a presença das tensões residuais devido à conformação a frio das chapas do casco e do flange das cavernas, para submarinos com 6, 8 e 10 m de diâmetro, em aço HY100. Para isso, um modelo não-linear foi produzido considerando não-linearidades geométricas e de material. Complementarmente, também foi estudada a influência de perfis de tensões residuais definidos a partir de resultados experimentais na redução da pressão de colapso do casco resistente do submarino espanhol S-80. Estes perfis consideram a presença simultânea de tensões residuais de conformação e de soldagem. Em todos os modelos estudados, as tensões residuais foram introduzidas no modelo numérico utilizando o comando INISTATE disponível no software comercial Ansys. Este comando é frequentemente utilizado na literatura em modelos numéricos envolvendo tensões residuais e foi validado utilizando três modelos de referência disponíveis na literatura. Ao final, pôde-se verificar que a presença das tensões residuais acelera a plastificação do casco resistente e reduz a pressão de colapso em até 5%, sendo a tensão residual de conformação a que mais contribuí nesta redução. De qualquer forma, pôde-se concluir que a influência das tensões residuais é pequena quando comparada com a pressão de colapso obtida para cada casco resistente analisado. / During the manufacturing of submarine pressure hull are often applied processes like cold forming and welding. Those processes lead to permanent plastic deformations which are associated with residual stresses. The presence of residual stresses is equivalent to the introduction of an initial pre-load in the structure, which accelerates the plastification process, decreasing hull pressure resistance. To quantify this reduction, a case study that considers residual stresses due to cold forming on hull and flange plates has been performed. The study encompasses hull diameters of 6, 8 and 10 m, made of HY100 steel. A nonlinear model has been done, considering material and geometric non-linearity. Complementarily, the influence of experimental residual stresses profiles on the reduction of collapse pressure of the Spanish S-80 submarine has been studied. These profiles consider the simultaneous presence of residual stresses due to cold forming and welding. In all studied models, the residual stresses have been introduced in the numerical models through INISTATE Ansys software command. This command has been validated using three reference models available in open source literature. In the end, it has been possible to verify that the presence of residual stresses increase the hull plastification and reduces the collapse pressure up to 5%, being the cold forming induced stress which most contributes to this reduction. Finally, it could be concluded, in the end of the study, that the influence of the residual stresses is small when compared with the collapse pressure obtained for the analyzed pressure hulls.

The finite difference method was used to calculate the variable heat transfer coefficient required to maximize mechanical properties of heat treated wrought 7075 aluminum alloy without causing residual stress. Quench simulation enabled determination of maximum surface heat flux bordering on inducing plastic flow in the work piece. Quench Factor Analysis was used to correlate cylinder diameter to yield strength in the T73 condition. It was found that the maximum bar diameter capable of being quenched without residual stress while meeting military mechanical design minimums is 2". It was also found that the cooling rate must increase exponentially and that the maximum cooling rate needed to achieve minimum mechanical properties is well within the capability of metals heat treatment industry.

The research presented in this thesis covers two critical problems regarding lined pipes: dynamic impact and welding. A lined pipe consists of an inner layer (the liner) made of corrosion resistant alloy (CRA), e.g. AISI304 stainless steel, and an outer layer made of low carbon steel, e.g. carbon-manganese steel, C-Mn. To manufacture the lined pipe, a special heat treatment, known as tight fit pipe (TFP), based on cooling the liner to -200°C, heating the backing pipe to +500°C and inserting the liner inside the outer pipe, was used in this work. Both welding and impact with external objects are responsible for accumulating high levels of plastic strains and residual stresses which could lead to failure in the pipe sometime after the impact or the welding. The special welding process used in lined pipes typically consists of the overlay welding (inner welding) of the liner with the C-Mn steel pipe for each segment and the girth welding (outer welding) of the two segments. To simulate this welding process using the ABAQUS code, nonlinear heat-transfer and mechanical finite-element (FE) analyses have been conducted. A distributed power density of the moving welding torch and a non-linear heat transfer coefficient accounting for both radiation and convection have been used in the analysis and implemented in ABAQUS user-subroutines. The modelling procedure has been validated first against previously published experimental results for stainless steel and carbon steel pipe welding separately. The model has been then used to determine the isotherms induced by the one-pass weld overlay and the one-pass girth welding and to clarify their influence on the transient temperature field and residual stress in the lined pipe. Furthermore, the influence of the cooling time between weld overlay and girth welding and of the welding speed have been examined thermally and mechanically as they are key factors that can affect the quality of lined pipe welding. The same FE numerical procedure to analyse line pipe welding is then applied to simulate six cases experimentally tested in the lab within this project. Furthermore, two cases have been analysed first, namely a reference case, in which the effect of the TFP pre-heat treatment is neglected, and a second one where the pre-heat treatment has been taken into consideration. During welding, the FE thermal history and mechanical strain results for both cases correlate well with the experimental ones in the region with the highest residual stresses, because the effect of initial residual stresses is cancelled in the regions subject to very high temperatures. After welding, the numerical and experimental results have proved that the initial residual stresses due to the TFP pre-heat treatment are reasonably important in the liner whereas they are practically negligible in the C-Mn pipe. The same reference case is then compared numerically and experimentally with further five parametric cases to study the effect of welding properties (weld overlay and girth welding materials), geometric parameters (using weld overlay and liner) and welding process parameters (heat input). The numerical temperature fields and residual stresses are in good agreement with their experimental counterparts for all cases. The dynamic impact problem is a crucial one for lined pipes because of the reduction in the thickness of the outer pipe ensured by the internal protection from corrosion given by a thinner liner. In this case, the lined pipe is more affected by potential impact with external objects (so-called 'third party interference' in the Oil and Gas industry). In general, a dent produced by a freely dropped weight is responsible to a large extent of catastrophic failure in pipelines. Therefore, in this work, 3D FE models have been developed to simulate the mechanism of vertical free drop of a weight from different heights resulting in damage in the pipe. Models have been executed using a three-dimensional non-linear explicit-dynamics FE code, ABAQUS/EXPLICIT. In order to precisely simulate the response of the pipe to subsequent impacts and spring back, an elastic-plastic constitutive law is adopted using the isotropic Hooke's law and a Von Mises yield criterion, with work hardening based on an isotropic hardening rule associated with the equivalent plastic strain rate. Strain-rate dependent properties are specified for both materials, C-Mn and AISI304, to take into account the change in velocities during impact. The numerical strain results are reasonably consistent with the experimental ones recorded by four strain gauge rosettes positioned symmetrically around the dent centre. Numerical and experimental results are comprehensively analysed and discussed also in terms of practical implications in the industry.

Na construção de cascos resistentes de submarinos são utilizados, frequentemente, os processos de conformação a frio e de soldagem. Estes processos produzem na estrutura deformações plásticas permanentes originando tensões residuais. A presença das tensões residuais é equivalente a introduzir uma pré-carga inicial na estrutura, o que acelera o processo de plastificação, reduzindo à capacidade de resistência da estrutura à pressão hidrostática. Para quantificar esta redução foi realizado, inicialmente, um estudo considerando a presença das tensões residuais devido à conformação a frio das chapas do casco e do flange das cavernas, para submarinos com 6, 8 e 10 m de diâmetro, em aço HY100. Para isso, um modelo não-linear foi produzido considerando não-linearidades geométricas e de material. Complementarmente, também foi estudada a influência de perfis de tensões residuais definidos a partir de resultados experimentais na redução da pressão de colapso do casco resistente do submarino espanhol S-80. Estes perfis consideram a presença simultânea de tensões residuais de conformação e de soldagem. Em todos os modelos estudados, as tensões residuais foram introduzidas no modelo numérico utilizando o comando INISTATE disponível no software comercial Ansys. Este comando é frequentemente utilizado na literatura em modelos numéricos envolvendo tensões residuais e foi validado utilizando três modelos de referência disponíveis na literatura. Ao final, pôde-se verificar que a presença das tensões residuais acelera a plastificação do casco resistente e reduz a pressão de colapso em até 5%, sendo a tensão residual de conformação a que mais contribuí nesta redução. De qualquer forma, pôde-se concluir que a influência das tensões residuais é pequena quando comparada com a pressão de colapso obtida para cada casco resistente analisado. / During the manufacturing of submarine pressure hull are often applied processes like cold forming and welding. Those processes lead to permanent plastic deformations which are associated with residual stresses. The presence of residual stresses is equivalent to the introduction of an initial pre-load in the structure, which accelerates the plastification process, decreasing hull pressure resistance. To quantify this reduction, a case study that considers residual stresses due to cold forming on hull and flange plates has been performed. The study encompasses hull diameters of 6, 8 and 10 m, made of HY100 steel. A nonlinear model has been done, considering material and geometric non-linearity. Complementarily, the influence of experimental residual stresses profiles on the reduction of collapse pressure of the Spanish S-80 submarine has been studied. These profiles consider the simultaneous presence of residual stresses due to cold forming and welding. In all studied models, the residual stresses have been introduced in the numerical models through INISTATE Ansys software command. This command has been validated using three reference models available in open source literature. In the end, it has been possible to verify that the presence of residual stresses increase the hull plastification and reduces the collapse pressure up to 5%, being the cold forming induced stress which most contributes to this reduction. Finally, it could be concluded, in the end of the study, that the influence of the residual stresses is small when compared with the collapse pressure obtained for the analyzed pressure hulls.

The advancement of the structural steel manufacturing industry has led to the recent emergence of steel members with Elliptical Hollow Sections (EHS) and Semi Elliptical Hollow Sections (SEHS). Although these sections are gaining popularity among architects, the lack of design guidelines specifically tailored towards these sections inhibits their efficient structural use. Within this context, this thesis provides several steps towards the development of such guidelines. A review of the manufacturing process of hot-rolled steel sections is conducted with emphasis on hollow structural sections. The main factors affecting the formation of residual stresses during cooling of the sections are discussed. Lower bound plastic interaction relations for EHS subjected to combinations of axial force, bi-axial bending moments and torsion are then derived. The formulation is based on the lower bound theorem of plasticity and the maximum distortional energy density yield criterion. Its applicability for conducting the cross-sectional interaction check in structural steel design problems is illustrated through a practical example. A simplified and conservative interaction equation is then proposed based on curve fitting of the results of the lower bound solution. Upper bound interaction relations are next developed for EHS subjected to combinations of axial force, bi-axial bending moments, torsion and bimoments. The formulation is based on kinematically admissible strain fields within the context of the upper bound theorem of plasticity. The interaction relations derived successfully capture the effect of confining radial strains present at welded end sections, as well as sections that are free to deform in the radial direction away from end welded sections. An iterative solution technique is developed to solve the resulting highly non-linear system of interaction relations. The effects of residual stresses and initial imperfections on axial compressive resistance of hot-rolled EHS are then incorporated into the lower bound interaction relations. Towards that goal, the thermo-mechanical properties of steel were extracted from the literature. A thermo-mechanical finite element model was developed for prediction of residual stresses in rolled sections. The validity of the model was assessed by comparison against residual stress measurements available in the literature. The model is then applied to predict the residual stresses in hot-rolled EHS. A series of geometric and material nonlinear finite element analyses is conducted on columns of EHS sections. The analyses include predicted residual stresses and initial out-of-straightness imperfections in order to determine the inelastic buckling capacity of EHS members and generate column curves for EHS sections. The column curves are subsequently compared to those based on Canadian, American and European design codes. Two column curve equations are proposed in a format similar to that of the Canadian Standards for buckling about major and minor axes. The column curves were subsequently combined with the interaction relations developed to provide design rules for EHS members under combined loads. The last contribution of the thesis provides a formulation of lower bound interaction relations for SEHS subject to combinations of axial force, bi-axial bending moments and torsion. An iterative scheme for solving the parametric form of the interaction relations is developed and a grid of admissible stress resultant combinations is generated. A series of trial functions are fitted to the grid of internal force combinations and two simplified and conservative interaction equations are proposed.

Inverse spectral techniques are developed in this dissertation for recovering the shear modulus and residual stress of soft tissues. Shear modulus is one of several quantities for measuring the stiffness of a material, and hence estimating it accurately is an important factor in tissue characterization. Residual stress is a stress that can exist in a body in the absence of externally applied loads, and beneficial for biological growth and remodeling. It is a challenge to recover the two quantities in soft tissues both theoretically and experimentally. The current inverse spectral techniques recover the two unknowns invasively, and are theoretically based on a novel use of the intravascular ultrasound technology (IVUS) by obtaining several natural frequencies of the vessel wall material. As the IVUS is interrogating inside the artery, it produces small amplitude, high frequency time harmonic vibrations superimposed on the quasistatic deformation of the blood pressure pre-stressed and residually stressed artery. The arterial wall is idealized as a nonlinear isotropic cylindrical hyperelastic body for computational convenience. A boundary value problem is formulated for the response of the arterial wall within a specific class of quasistatic deformations reflexive of the response due to imposed blood pressures. Subsequently, a boundary value problem is developed from intravascular ultrasound interrogation generating small amplitude, high frequency time harmonic vibrations superimposed on the quasistatic finite deformations via an asymptotic construction of the solutions. This leads to a system of second order ordinary Sturm-Liouville problems (SLP) with the natural eigenfrequencies from IVUS implementation as eigenvalues of the SLP. They are then employed to reconstruct the shear modulus and residual stress in a nonlinear approach by inverse spectral techniques. The shear modulus is recovered by a multidimensional secant method (MSM). The MSM avoids computing the Jacobian matrix of the equations and is shown to be convenient for manipulation. Residual stress is recovered via an optimization approach (OA) instead of the traditional equation-solving method. The OA increases the robustness of the algorithms by overdetermination of the problem, and comprehensive tests are performed to guarantee the accuracy of the solution. Numerical examples are displayed to show the viability of these techniques.

The advancement of the structural steel manufacturing industry has led to the recent emergence of steel members with Elliptical Hollow Sections (EHS) and Semi Elliptical Hollow Sections (SEHS). Although these sections are gaining popularity among architects, the lack of design guidelines specifically tailored towards these sections inhibits their efficient structural use. Within this context, this thesis provides several steps towards the development of such guidelines. A review of the manufacturing process of hot-rolled steel sections is conducted with emphasis on hollow structural sections. The main factors affecting the formation of residual stresses during cooling of the sections are discussed. Lower bound plastic interaction relations for EHS subjected to combinations of axial force, bi-axial bending moments and torsion are then derived. The formulation is based on the lower bound theorem of plasticity and the maximum distortional energy density yield criterion. Its applicability for conducting the cross-sectional interaction check in structural steel design problems is illustrated through a practical example. A simplified and conservative interaction equation is then proposed based on curve fitting of the results of the lower bound solution. Upper bound interaction relations are next developed for EHS subjected to combinations of axial force, bi-axial bending moments, torsion and bimoments. The formulation is based on kinematically admissible strain fields within the context of the upper bound theorem of plasticity. The interaction relations derived successfully capture the effect of confining radial strains present at welded end sections, as well as sections that are free to deform in the radial direction away from end welded sections. An iterative solution technique is developed to solve the resulting highly non-linear system of interaction relations. The effects of residual stresses and initial imperfections on axial compressive resistance of hot-rolled EHS are then incorporated into the lower bound interaction relations. Towards that goal, the thermo-mechanical properties of steel were extracted from the literature. A thermo-mechanical finite element model was developed for prediction of residual stresses in rolled sections. The validity of the model was assessed by comparison against residual stress measurements available in the literature. The model is then applied to predict the residual stresses in hot-rolled EHS. A series of geometric and material nonlinear finite element analyses is conducted on columns of EHS sections. The analyses include predicted residual stresses and initial out-of-straightness imperfections in order to determine the inelastic buckling capacity of EHS members and generate column curves for EHS sections. The column curves are subsequently compared to those based on Canadian, American and European design codes. Two column curve equations are proposed in a format similar to that of the Canadian Standards for buckling about major and minor axes. The column curves were subsequently combined with the interaction relations developed to provide design rules for EHS members under combined loads. The last contribution of the thesis provides a formulation of lower bound interaction relations for SEHS subject to combinations of axial force, bi-axial bending moments and torsion. An iterative scheme for solving the parametric form of the interaction relations is developed and a grid of admissible stress resultant combinations is generated. A series of trial functions are fitted to the grid of internal force combinations and two simplified and conservative interaction equations are proposed.

A volumetric heat source finite element model is proposed to simulate the key hole effect during the Nd:YAG pulse laser welding. The measured data has been used to correlate the volumetric model parameters and the laser parameters. The laser power distributed in the beam cross area is in a Gaussian type. Two heat transfer models are employed in the fusion area, i.e the surface absorption heat transfer model in the low power intensity region and the keyhole heat transfer model in the high power intensity region. An experimentally measured critical power intensity is introduced to identify the occurrence of keyhole effect. The value of critical power intensity is dependent on the welding material. A series of MARC finite element simulations based on the proposed single pulse model are performed to investigate the feasibility and accuracy of this proposed pulse laser welding model. Different power and welding duration pulse laser have used to weld the S304L specimens. The results indicate a good agreement between the simulated and measured shape and size of the weld pool with different laser energy intensities. The validity of the proposed model is confirmed for the S304L steel. The temperature and residual stress distributions around the welding pool in a continuous pulse welding and two sheet overlap welding have also been studied by using the proposal model. The numerical results indicate that the pulse energy, duration and dwell period may affect the residual stress distribution and post-weld deformation significantly. All these results reveal that the proposed volumetric heat source finite element model is a feasible model to analyze the welding phenomena during the pulse laser welding. The results indicate that the pulse dwell period increase in dual pulse laser welding the residual stress decrease on the top of the weld spot surface. The results also show the lower residual stress in multi spots pulse laser welding with smaller weld spots center pitch and weld spot dwell period.