abstract: Shock loading is a complex phenomenon that can lead to failure mechanisms such as strain localization, void nucleation and growth, and eventually spall fracture. Studying incipient stages of spall damage is of paramount importance to accurately determine initiation sites in the material microstructure where damage will nucleate and grow and to formulate continuum models that account for the variability of the damage process due to microstructural heterogeneity. The length scale of damage with respect to that of the surrounding microstructure has proven to be a key aspect in determining sites of failure initiation. Correlations have been found between the damage sites and the surrounding microstructure to determine the preferred sites of spall damage, since it tends to localize at and around the regions of intrinsic defects such as grain boundaries and triple points. However, considerable amount of work still has to be done in this regard to determine the physics driving the damage at these intrinsic weak sites in the microstructure. The main focus of this research work is to understand the physical mechanisms behind the damage localization at these preferred sites. A crystal plasticity constitutive model is implemented with different damage criteria to study the effects of stress concentration and strain localization at the grain boundaries. A cohesive zone modeling technique is used to include the intrinsic strength of the grain boundaries in the simulations. The constitutive model is verified using single elements tests, calibrated using single crystal impact experiments and validated using bicrystal and multicrystal impact experiments. The results indicate that strain localization is the predominant driving force for damage initiation and evolution. The microstructural effects on theses damage sites are studied to attribute the extent of damage to microstructural features such as grain orientation, misorientation, Taylor factor and the grain boundary planes. The finite element simulations show good correlation with the experimental results and can be used as the preliminary step in developing accurate probabilistic models for damage nucleation. / Dissertation/Thesis / Ph.D. Mechanical Engineering 2013

Orientador: Felippe Bevilacqua Prado / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba / Made available in DSpace on 2018-08-26T08:09:14Z (GMT). No. of bitstreams: 1 Rolfini_ElisaCamilaSantos_M.pdf: 3102623 bytes, checksum: 79d2050326b963a716ef989bc26acf67 (MD5) Previous issue date: 2014 / Resumo: O esqueleto facial é formado por uma estrutura ideal para resistir às forças mastigatórias. O pilar pterigoideo suporta as tensões provenientes da mastigação posterior. O objetivo deste estudo foi avaliar a distribuição das tensões mecânicas simuladas no pilar pterigoideo, baseado em sua geometria, por meio da análise de elementos finitos. Foi selecionada uma tomografia computadorizada de um crânio humano seco do Laboratório de Elementos Finitos, Departamento de Morfologia, Área Anatomia, FOP / UNICAMP. No laboratório de Elementos Finitos foi utilizado o software InVesalius 3.0 (Brasil) para a realização da segmentação das imagens da tomografia computadorizada e, assim, selecionou-se o conjunto de imagens referentes à estrutura óssea e aos dentes de interesse na análise. As estruturas segmentadas foram reconstruídas tridimensionalmente e exportadas em formato estereolitográfico (STL). Este arquivo foi importado para o software Rhinoceros 5.0 (McNeil, Assoc USA), no qual foi realizada a modelagem Bio-CAD para obtenção da geometria. O modelo geométrico (CAD) obtido foi importado ao software ANSYS v14 (USA) para realização da análise de elementos finitos. Neste software, como configuração da análise foram aplicadas as seguintes condições: simetria na superfície de corte do plano sagital mediano, simulando a presença do lado oposto do modelo e restrições nos planos de corte superior e posterior. No segundo e no terceiro molares superiores foi adicionado um suporte fixo em sua face oclusal. As forças dos músculos elevadores da mandíbula foram aplicadas em cada área correspondente às suas respectivas origens no crânio humano. A ação das forças musculares juntamente com o suporte na face oclusal dos segundo e terceiro molares superiores resultaram na simulação de uma condição de oclusão molar. Foram avaliadas Tensões de Von-Mises. A partir do processo alveolar na altura do segundo e terceiro molares superiores, as tensões se concentraram na tuberosidade da maxila, se estendendo até o processo piramidal do osso palatino, e se distribuíram para o processo pterigoide, o qual apresentou menores valores de tensão. No terço superior deste processo, as tensões foram menores do que em outras regiões. Concluiu-se que as estruturas anatômicas que compõem o pilar pterigoideo atuaram como regiões de transferência de tensões à base do crânio / Abstract: The facial skeleton is formed by an ideal structure to resist masticatory forces. The pterygoid pillar supports the tensions arising from the posterior chewing. The aim was to evaluate the stresses distribution simulated in the pterygoid pillar, based on its geometry, by FEA. Was used selected a CT scan files a dry human skull of Finite Element Laboratory, Department of Morphology, Anatomy area, FOP / UNICAMP. In the Laboratory Finite Element (Piracicaba, Brazil) was used was used InVesalius 3.0 (Brazil) software to perform the segmentation of images computed tomography and, thus, was selected the set of pictures related to bone structure and teeth of interest in the analysis. The segmented structures were reconstructed three-dimensionally and exported in estereolitographic format (STL). This file was imported into Rhinoceros 5.0 (McNeil, Assoc USA) software, in which the modeling Bio-CAD was performed to obtain the geometry. The geometric model (CAD) obtained was imported to ANSYS v14 (USA) software to perform the finite element analysis. On this software as configuration analysis the following conditions were applied: symmetry on the cut surface of the median sagittal plane, simulating the presence of the opposite side of the model and restrictions in the plans of superior and posterior cut. In the second and third molars superiors was added a fixed support at its occlusal surface. The forces of the elevator muscles of the mandible were applied in each corresponding area their respective origins in the human skull. The action of muscle strength along with support on the occlusal surface of the second and third molars superiors resulted in the simulation in a condition of molar occlusion. Tensions Von-Mises were evaluated. From the alveolar process at the time of the second and third molars, tensions concentrated on the maxillary tuberosity, extending into the pyramidal process of the palatine bone, and distributed to the pterygoid process, which presented lower stress values. In the upper third of the process, the stresses were lower than in other regions. It was concluded that the anatomical structures that compose the pterygoid pillar regions acted as transfer of stresses to the skull base / Mestrado / Anatomia / Mestra em Biologia Buco-Dental

Developmental dysplasia of the hip (DDH) refers to some hip disorders, from mildly dysplastic to hip joint dislocation. The main feature of DDH is the deficient acetabular coverage, which is related to a small contact area in the hip joint, and causes an increase in contact pressure. Ganz periacetabular osteotomy (PAO) is a surgical procedure to correct acetabular orientation in DDH. It changes the position of the acetabulum to increase the femoral head coverage and distribute the contact pressure over the cartilage surface. The procedure of Ganz PAO is technically demanding and its success depends significantly on the surgeon’s experience. The aim of this research is to investigate whether it is possible to optimize the position of the acetabular fragment in patients suffering DDH before a Ganz PAO by using finite element (FE) analysis. Using computed tomography (CT) data from patients with DDH, five three-dimensional (3D) hip models were developed. A virtual Ganz PAO was then performed on the hip models. FE analyses were carried out on the hip models before and after virtual Ganz PAO. Contact area, contact pressure and Von Mises stress in the hip cartilage were checked and analysed in order to find an optimal acetabular position. The first virtual surgery performed was only to rotate the acetabular fragment in the lateral direction to improve the acetabular coverage. Analyses were conducted under loading conditions associated with four commonly daily activities: one leg stance, normal walking, descending stairs and knee bend. Second virtual surgery performed was to rotate the fragment in both the lateral and anterior directions and FE analysis conducted for one leg stance loading condition. Contact area, contact pressure and Von Mises stress in the cartilage all varied according to the change of the acetabular fragment position through virtual Ganz PAO. The optimal lateral position of the acetabular fragment occurs close to the inferior border of its normal range. Large anterior position of the acetabular fragment results in large contact area, low contact pressure and Von Mises stress. However, an overcorrection of the acetabular fragment, especially in the anterior correction, leads to problems in performing normal hip movements. The optimal anterior position of the acetabular fragment is therefore close to the superior limit of the normal range. In conclusion, the present analysis shows that an optimal position of the acetabular fragment for patients suffering DDH which improves the acetabular femoral head coverage in the normal range, maximizes the contact area and minimizes the contact pressure and Von Mises stress can be established using 3D models and FE analysis. This information will be useful to the surgeons for the planning of PAO.

This thesis concerns the simulation of locomotion in vertebrates. The state-of-the-art uses genetic algorithms together with solid body kinematics to generate possible solutions for stable gaits. In recent work, this methodology led to a hopping gait in a dinosaur and the researchers wondered if this was realistic. The purpose of the research carried out in this thesis was to examine whether quick and simple finite-element analyses could be added to the simulator, to evaluate a simple ―break or―not break failure criterion. A break would rule out gaits that might damage theowner‘s skeleton. Linear elastic analysis was considered as a possible approach as it would add little overhead to the simulations. The author used X-ray computed tomography and the finite element method to examine the axial loading of a barnacle goose femur. The study considered four levels of detail for a linear elastic simulation, finding that all the analyses carried out overestimated the strength of the bone, when considering safety factors. The conclusion is that to incorporate stress-strain analysis into the gait simulation requires more realistic models of bone behaviour that incorporate the nonlinear response of bone to applied loading. A new study focusing on the use of novel techniques such as model order reduction is recommended for future work. The outputs of this research include chapters written up as journal papers covering a 4D tomography experiment; a level of detail study; an analysis of a purported tendon avulsion injury in Tyrannosaurus rex and a review of the elastic properties of bone.

Doctor of Philosophy / Department of Grain Science and Industry / X. Susan Sun / With continued population growth, more food production will be required with lower resource inputs. A significant drain on resources is post-harvest loss due to insects, which results in loss of product, quality and market access, and increased grain spoilage. Aeration and fumigation are key tools to control insect growth in stored grains and grain foods. The implementation of aeration strategies in Australia is made difficult by the warm subtropical climate, meanwhile the success of fumigation is being threatened by the spread of insect resistance to the fumigant phosphine. This dissertation project seeks to improve the understanding of aeration and fumigation by modifying the Maier-Lawrence (M-L) 3D ecosystem model by adding insect growth equations and quantifying fumigant loss from sealed bulk grain silos. The improved model was used to examine aeration under Australian conditions, validate its capability to accurately describe fumigant concentrations during silo fumigation, determine the extent to which fumigations are influenced by operational variables and environmental conditions, and validate its capability to describe fumigant concentrations post-fumigation in order to investigate the time needed to clear a grain storage silo of fumigant in order to assure worker safety. Six aeration strategies were evaluated under Australian conditions. Of these strategies, two were found to be effective in lowering temperatures, i.e., fans were turned on when ambient temperature was less than 20oC, and less than internal grain temperature. The strategy based on temperature differential was the most effective because it cooled the interior of the grain mass with the least amount of energy (using the fewest fan run hours, and reaching 15oC an average of 11 days after than the fastest strategy). Using a 0oC temperature differential was the most effective strategy in terms of reducing insect growth. The expanded (M-L-P) model was then validated based on experimental fumigant concentrations. The model was effective in reproducing average fumigant concentrations and fumigant trends vertically through the grain mass, but was not able to reproduce lateral fumigant variations. Verifications of the model with two different periods of phosphine release (i.e., 24h and 30h) were tested. Based on a 24h phosphine release period the predicted Ct-product differed from the experimental value by 0.9%. A 30h release period predicted a Ct-product that differed by 4.3% from the experimental value but it was more accurate during the times of highest concentration. Increases in leakage reduced fumigant concentrations, but the size of the effect decreased as leakage grew. Increasing temperature and wind speed in the model led to decreased phosphine concentrations, with temperature changes having a more significant impact overall than wind speed changes for the conditions investigated. Decreasing silo surface area to volume ratio dampened the impact of changing weather conditions on phosphine concentrations. A fumigant venting experiment was conducted in a silo at Lake Grace, Australia, to investigate full scale desorption. Two equations estimating fumigant desorption were tested, with an average of 65.5% and -86.3% error. The length of venting periods was simulated to quantify hours needed to mitigate hazardous conditions. For the scenarios investigated 10 to 24 h of venting were needed to reduce residual fumigant concentration below 0.3 ppm depending on simulation assumptions.

Lumbar intervertebral disc disorder is a spinal condition that affects the normal function of the intervertebral discs mainly due to the natural aging process. This condition can manifest itself in pain and limited motion in the legs, amongst others. Posterolateral Fusion (PLF) and Posterior Lumbar Interbody Fusion (PLIF) are two of the most used surgical procedures for treating lumbar intervertebral disc disease. Although these procedures are commonly used and performed successfully the impact in terms of the stresses developed in the posterior implants employed and in the spinal components adjacent to the surgical site has not been exhaustively investigated. In addition, the consequences of the procedure on the reduction of the Range of Motion of the lumbar spine is not clearly understood. The objective of this research is to investigate the effect of one-level spinal fusion of lumbar segment L4-L5 on the stresses and the range of motion at the remaining, adjacent lumbar levels. Four 3 dimensional finite element models of a lumbosacral spine were created from Computer Tomography data (CT scan). The models were used to investigate four surgical scenarios, including the use of 0o and 4o interbody cages, in addition to the un-instrumented spine for flexion, extension, torsion and lateral bending motions. The predictions obtained from the models enabled the mechanical behaviour of the lumbar spine following fusion surgery using 0 o and 4o cages to be investigated and compared. In addition, a clinical study was performed to quantify the reduction in the range of motion for subjects who had undergone L4/5 posterior lumbar interbody fusion surgery. The clinical results were compared to those of subjects who had not undergone surgery and to the range of motion predictions from the computational model. The results from this research demonstrate that the insertion of posterior instrumentation does not have an impact on the spinal structures above the L3/4 intervertebral disc. However, the pedicle screws and the insertion of the interbody cages causes stress levels in the area adjacent to the surgical site to rise which could promote accelerated degeneration of the discs. Additionally, this study demonstrates how the pedicle screws are affected by the surgical spinal fusion techniques. Furthermore, the investigation demonstrates how posterior lumbar interbody fusion causes the range of motion of patients that had undergone this surgery to decrease. The results from the comparison of the behaviour of the use of 0º and 4º interbody cages in L4-5 posterolateral fusion demonstrates that the stress levels in the adjacent vertebrae, intervertebral discs and pedicle screw fixation system increase when 4º are used cages than when 0º cages were employed. The results from the in-vitro study show a decrease in the range of motion of the subjects who had undergone L4/5 posterior lumbar interbody fusion surgery when compared with the subjects with no low back pain history. This indicates that the PLIF surgery combined with the normal disc degeneration is subjected to higher stresses than the healthy spine.

Doctor of Philosophy / Department of Industrial & Manufacturing Systems Engineering / Zhijian Pei / Grinding is one of the important operations employed in modern manufacturing industry to remove materials and achieve desired geometry and surface finish. Simultaneous double side grinding (SDSG) and ultrasonic vibration assisted grinding (UVAG) are two typical cost-effective grinding processes which are utilized to grind semiconductor materials and high performance ceramic materials, respectively. The objectives of this research are to investigate several technical issues in modern grinding processes by using theoretical, numerical, and experimental research approaches. Those technical issues are related to SDSG and UVAG, which have been chosen as two typical grinding processes for this research. This thesis reviews the literature on SDSG (covering process applications, modeling of grinding marks, and modeling of wafer shapes) and UVAG (covering process applications, edge chipping, and coolant effects, etc). The theoretical research work of this thesis is conducted by developing mathematical models for grinding marks and wafers shapes in SDSG of silicon wafers. These developed models are then used to study the effects of SDSG parameters on the curvature of the grinding marks, the distance between adjacent grinding marks, and the wafer shapes. The numerical research work of this thesis is done by conducting a three dimensional (3-D) finite element analysis (FEA) of UVAG process. A 3-D FEA model is developed to study the edge chipping commonly observed in UVAG of ceramics. Edge chippings not only compromises geometric accuracy but also possibly causes an increase in machining cost. A solution to reduce the edge chipping is proposed based upon the FEA simulations and validated by pilot experiments. Several experimental studies are conducted to provide new knowledge for the UVAG process. Firstly, a novel coolant delivery system is explored for UVAG machine system. Secondly, UVAG is introduced into machining of fiber-reinforced ceramic matrix composites (CMC). Results of a feasibility study and a designed experimental investigation show that UVAG is a promising process for CMC machining. Finally, an experimental study on cutting forces during UVAG of zirconia/alumina composites is conducted. The feasibility to machine different zirconia/alumina composites using UVAG is also investigated and discussed. The findings in this thesis will provide theoretical and practical guidance for modern grinding processes especially for SDSG and UVAG.

The objective of this research was to better understand how impact angle influences headform dynamic response and brain tissue deformation. A bare headform was impacted using a pneumatic linear impactor at 5.5 m/s. The impacts were directed on the front and side location at angles of 0, 5, 10 and 15° rightward rotations as well as -5, -10 and -15° (leftward) rotations at the side to examine the characteristics of the head and neckform on the results. Peak resultant linear and rotational accelerations from the headform as well as peak maximum principal strain (MPS) and von Mises stress (VMS) estimated from a brain finite element model were used to measure the effect of impact angle. Significant results were dependent upon the impact angle and location as well as the dependent variable used for comparison (p <0.05). Impact angle produced significant differences in rotational acceleration and MPS at both the front and side; however angle only had an effect on VMS and linear acceleration at the front and side locations, respectively. These findings show that the effect of impact angle is asymmetrical and is specific to the dependent variable. This study suggests that varying impact angle alone may not be as influential on headform dynamic response and brain tissue deformation and that the severity of an impact may be more of a function of how both location and angle create high risk conditions.

As the most commonly diseased heart valve, the mitral valve (MV) has been the subject of extensive research for many years. Unfortunately, the only treatment options currently available are surgical repair and replacement. Although repair is almost always preferable to replacement, it is often underperformed due to the complexity of MV repair surgeries. Consequently, there is significant interest in generating patient-specific finite element models of the MV for the purpose of simulating mitral repairs. For practical purposes transesophageal echocardiographic (TEE) images are most commonly used to reconstruct the mitral apparatus. However, limitations in ultrasound technology have prevented the detection of leaflet thicknesses. In the current study, a method was developed to accurately model variations in leaflet thicknesses using TEE datasets. Nine healthy datasets were modeled and the leaflet thicknesses were found to closely match previously reported results. As anticipated, normal valve function was also observed over the entire cardiac cycle.

Reinforcement corrosion is the most common deterioration problem observed in reinforced concrete (RC) structures located at coastal or cold regions. The corrosion process can impact the performance of these structures by inducing damage on the bonding action between concrete and steel, either by the splitting of the concrete cover due to the volumetric expansion of corrosion products or the lubricant effect at the steel/concrete interface as the corrosion by-products accumulate. The current research aims at investigating corrosion-induced deterioration of bond between steel and concrete through finite element (FE) analysis of the flexural behaviour of corroded RC components. By treating the concrete cover as a thick-wall cylinder subjected to internal pressure, the analytical evaluation of impaired bond capacity is studied first and verified against published bonding tests. Then, the formulation of a numerical model is performed using ABAQUS, wherein a link element to simulate the bond behaviour is formulated and implemented through the ABAQUS user-subroutine (UEL) feature according to the validated analytical model. By introducing corrosion-induced damages, i.e., smaller cross-sectional area of reinforcement, splitting of concrete and bond deterioration, in the FE analyses, the results of the numerical model show good agreement with experimental observations. Upon validation of the analytical and FE models, a parametric investigation is conducted, wherein the effects of concrete strength, dimension of reinforcing bars, properties of oxide products, different corrosion damage mechanisms and the corrosion location along the longitudinal reinforcement on the flexural behaviour of RC beams are studied. The results show that the analytical evaluation for bond degradation is impacted by the selection of the post-cracking material model and the thickness of cover that determine the ‘holding capacity’ after cracking initiation. Also, the density of rust by-products affects the results of the analytical model at high corrosion levels. From the FE model results, it was observed that each damage mechanism due to corrosion contribute to different levels of flexural degradation, although the flexural strength degradation is mainly due to the loss of bonding action. The parametric study also demonstrates that flexural members which have reinforcement corrosion initiated near the supports suffer greater deterioration in flexural capacity than those with damages at mid span. Finally, based on these observations, suggestions for the application of both analytical and numerical models are made.