Focal chondral defects of the knee develop in hyaline cartilage when subjected to repetitive overloading or impact trauma. The degeneration of the articular surface results in joint pain and stiffness during daily activities such as walking. In most cases palliative non-invasive treatments can be used to alleviate pain; however, more severe lesions require restorative or replacement surgical interventions to repair the damaged cartilage. The use of a novel pyrolytic carbon knee trochlear implant aims to eliminate the aforementioned orthopedic pain by providing a focal replacement of lesions in the patellar sulcus. Pyrolytic carbon was the selected material due to its superior wear properties, mechanical strength, and biocompatibility. The purpose of this study was to develop a verified computational simulation in Abaqus to evaluate the experienced tensile stress of six different pyrolytic carbon trochlear implants undergoing two different physiologically relevant load conditions. This data was compared to an experimental conjugate study to provide insight into the implants strength. Regions of peak maximum principal stress were observed to be at the medial fillet and sulcus groove when undergoing a single- or two-point loading condition, respectively. The magnitude of tensile stress in the medial fillet was 2-3 times of that experienced at the sulcus groove. These findings reflected experimental data in which trochlear implants failed at either the medial fillet or sulcus groove during their respective loading conditions. Verified simulations allowed for computational testing of a modified implant and calculations of expected critical fracture loads. / acase@tulane.edu

In the field of maxillofacial surgery, the treatment for the recovery of the fracture at condyle region of the mandible has been carried out using Bio-metals such as Titanium, Cobalt, Stainless-Steel because they were considered the standard materials for Implant plate devices for fracture fixation. Using these materials have led to undesired disturbances where the patient must undergo secondary surgery after recovery leading to exposure of the fracture site to the surrounding, metal-ion release into the human system, stress-shielding and interruption during imaging i.e. (Computerized tomography scans). The healing of the mandible requires a delicate and stable fixation procedure for the bone structure to heal. Bio-resorbable materials are the renovation for substituting metals for recovery of the fracture. The main dis-advantage using resorbable plates is absence of mechanical strength and stability. Bio-composites are the innovation for the treatment of the fractures the main study for this thesis is comparing the combination bio-ceramic and bio-resorbable materials using Finite Element Analysis software.

A primary motivation for this research comes from the need to improve the ability of polymer-matrix composites to withstand lightning strikes. In particular, we are concerned with lightning strike damage in composite wind turbine blades. The direct effects of lightning strike on polymer-matrix composites often include rapid temperature rise, melting or burning at the lightning attachment points, and mechanical damage due to lightning-induced magnetic force and acoustic shock wave. The lightning strike damage accumulation problem is essentially multiphysic. The lightning plasma channel discharges an electric current up to 200 kA, inducing a severe heat flux at the surface of the composite structure, as well as generating Joule heating through the composite structure. The resulting electro-thermo-mechanical response of the composite structure may include matrix degradation and decomposition, delamination, and fiber breakage and sublimation, thus leading to catastrophic failure. The existing studies related to the lightning strike damage in composites ignored the lightning channel radius expansion during the initial lightning discharge and lacked adequate treatment of material phase transitions. These assumptions significantly simplify the mathematical treatment of the problem and affect the predictive capabilities of the models. Another common feature of these limited studies is that they all focused on carbon-fiber-reinforced polymer-matrix (CFRP) composites, which are electrically conductive. In the present thesis, the thermal responses and thermal ablations in a non-conductive glass-fiber-reinforced polymer-matrix (GFRP) composite wind turbine blade and in a conductive CFRP composite wind turbine blade are studied, respectively. In the case of non-conductive GFRP composite wind turbine blade, prior to the thermal response and thermal ablation analysis, a finite element analysis is performed to calculate the electric field due to lightning stepped leader to estimate the dielectric breakdown of the non-conductive composite wind turbine blade. The estimation of dielectric breakdown is used to determine whether Joule heating needs to be included in the problem formulation. To predict the thermal response and thermal ablation in the composite structure due to lightning strike, a physics-based model describing surface interaction between the lightning channel and the composite structure has been developed. The model consists of: (i) spatial and temporal evolution of the lightning channel as a function of the electric current waveform; (ii) temporary and spatially non-uniform heat flux and current density (in the case of electrically conductive CFRP composite or if dielectric breakdown occurs in the case of non-conductive GFRP composite) generated at the composite structure; and (iii) nonlinear transient heat transfer problem formulation for layered anisotropic composites that includes the moving boundary of the expanding lightning channel and the phase transition moving boundary associated with instantaneous material removal due to sublimation. The model has been employed to investigate the thermal responses and thermal ablations in a GFRP composite laminated panel used in a Sandia 100-meter all-glass baseline wind turbine blade (SNL 100-00) and a typical CFRP composite laminated panel subjected to lightning strike. The temperature-dependent directional material properties for both the GFRP and CFRP composites have been determined in this thesis using a micromechanics approach based on the experimental data for fibers and resin. An integrated Matlab-ABAQUS numerical procedure features the aforementioned aspects (i), (ii), and (iii) of the developed model. The obtained results include the evolution of temperature fields in the composite laminated panel and the progressive shape change of the composite laminated panel due to thermal ablation. The predictions of thermal ablation in the CFRP composite laminated panel are validated by reported experimental results.

Aseptic loosening due to wear-induced osteolysis remains a leading cause of failure in total hip arthroplasty (THA), particularly in revision cases beyond the second decade of use. Historically, there have been large amounts of variability of wear within individual THA patient cohorts. Evidence indicates that femoral head damage can be a cause of this variability. While femoral head damage as a result of third body particles and subluxation and dislocation events has been well documented, direct quantifiable linkage between femoral head damage and wear acceleration remains to be established. Due to large ranges of observed retrieval damage, wear testing protocols for simulating third body and other damage effects have been subject to a wide range of variability, making it difficult to know where the clinical reality lies. To study the effect of retrieval femoral head damage on total hip implant wear, a damage-feature-based finite element (FE) formulation which allowed for wear prediction due to individual damage features developed. A multi-scale imaging procedure was also developed to globally map and quantify micron-level damage features appearing on retrieval femoral heads. This allowed for wear simulations of damage patterns observed on specific retrieval femoral heads. Retrieval damage was shown to be highly variable among patients, and capable of producing up to order-of-magnitude wear increases when compared to undamaged head wear rates. Damage following dislocation and subsequent closed reduction maneuvers was particularly detrimental, with average wear rate increases equal to half an order of magnitude. These data were used to develop wear testing protocols for simulating clinically-occurring third body and other damage effects.

The use and implementation of adhesive joints for space structures is necessary for incorporating fiber-reinforced composite materials. Correct modeling and design of cylindrical adhesive joints can increase the dimensional stability of space structures. The few analytical models for cylindrical adhesive joints do not fully describe the displacement or stress field of the joint. A two-dimensional axisymmetric finite element model for the design and analysis of adhesive joints was developed. The model was developed solely for the analysis of cylindrical adhesive joints, but the energy techniques used to develop the model can be applied to other types of joints as well. A numerical program was written to solve the system of equations [K]{d}={R} for the unknown displacements {d}. The displacements found from the program are used to design cylindrical adhesive joints based on dimensional stability. Stresses were calculated from the displacements for comparison with analytical models. The cylindrical joints were assumed to remain within the linear elastic region and no failure criteria was taken into account. The design process for cylindrical joints was developed based on dimensional stability. The nodal displacements found from the finite element model were used in the optimization of geometric parameters of cylindrical joints. The stacking sequence of the composite, the bond length, and the bond thickness were found to have the greatest impact on dimensional stability. Other factors that were found to further reduce the maximum displacements are the implementation of 0° and 90° laminas, the isotropic cylinder thickness, tapering of the isotropic cylinder, and the inside radius of the cylindrical joint. This axisymmetric finite element model is beneficial in that a cylindrical joint can be designed before any testing is performed. The results and cases in this thesis are generalized in order to show how the design process works. The model can be used in conjunction with design requirements for a specific joint to reduce the maximum displacements below any specified operating requirements. The joint is dimensionally stable if the overall displacements meet specific design requirements.

Full-depth, precast panel deck systems are becoming more common in bridge installation and repair. The objective of these systems is to achieve the performance of cast-in-place systems while simultaneously saving time and money. The structural behavior of these systems has been the subject of scrutiny in recent research. The Utah Department of Transportation demolished a steel I-girder bridge containing a precast panel deck system and provided two full-scale specimens for this project. Destructive testing was performed at Utah State University on the specimens to investigate three failure modes: flexural, beam shear, and punching shear. Finite-element models were created using ANSYS software to replicate experimental behavior. Overall, it was found that the elastic, post-elastic, and ultimate behavior of the full-scale bridge sections containing precast panel deck systems can be accurately predicted in analytical models. Another aspect of this project was to investigate changes in dynamic behavior as the system was subjected to flexural yield and failure. Point loads were applied and removed in increments, and dynamic testing was conducted at each load level. It was found that significant damage is somewhat noticeable by monitoring the changes in natural frequencies.

During the late 70's and early 80's, several precast deck panel bridges were constructed in Florida. These utilize prestressed precast panels as stay-in-place forms and are designed to act compositely with a cast-in-place deck which is poured subsequently. Such bridges offer advantages of quicker construction and lower costs. However, several such bridges built in Florida developed extensive cracking and spalling. Following localized failures, the Florida Department of Transportation has decided to replace all 127 precast panel deck bridges in Districts 1 and 7. Since deck replacement is contingent on funding, it is necessary to develop a rational procedure to decide the order in which they are replaced. This requires a better understanding of the deterioration process and failure mechanism in such bridge decks. The methodology used in this study was to first analyze in detail 5 cases of sudden localized deck failures to identify the causes of the failures and any common factors in the failed bridges. Also, forensic studies were conducted on eight bridges scheduled for deck replacements during 2003 and 2004. In these studies it was possible to investigate in detail the condition of the deck at different stages of deterioration. Based on the information collected, a deck failure model was developed.

Orientador: Eduardo Piza Pellizzer / Coorientador: Fellippo Ramos Verri / Banca: Aldiéris Alves Pesqueira / Banca: Leonardo Perez Faverani / Banca: Estevão Tomomitsu Kimpara / Banca: Eduardo Miyashita / Resumo: Este projeto teve como objetivo analisar as tensões geradas em próteses implantossuportadas fixa unitária variando o sistema de conexão implante/prótese, o sistema de retenção, material restaurador, tipo ósseo, e o nível de tecido ósseo ao redor do implante através do método dos elementos finitos tridimensionais, e realizar uma revisão sistemática com meta-análise sobre o tema osteoporose em relação a taxa de sobrevivência e perda óssea marginal ao redor dos implantes dentários. Em relação à metodologia experimental, foram simulados 24 modelos tridimensionais com ajuda dos programas de desenho assistido Rhinoceros 3D 4.0 (NURBS Modeling for Windows, USA) e SolidWorks 2011 (SolidWorks Corp, USA), e para confecção da porção óssea será utilizado o programa InVesalius (CTI, São Paulo, Brasil). Cada modelo representou uma secção de osso da região posterior maxilar, na forma de um bloco ósseo tipo IV (normal e osteoporótico), variando o nível de reabsorção do tecido ósseo (a nível do pescoço do implante; perda de 1,5 mm; perda de 3,0 mm; e perda de 4,5 mm) com a presença de um implante de 4,0 mm de diâmetro e 10 mm de comprimento com diferentes tipos de conexão (hexágono externo e cone morse), restaurado com coroas (metalocerâmicas e/ou metal free) com diferentes sistemas de retenção (cimentada e/ou parafusada). Os desenhos tridimensionais foram exportados ao programa de pré e pós processamento FEMAP v.11.2 (Siemens Product Lifecycle Management Software Inc. USA) para geração da ma... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The aim of this thesis was to perform the analysis on the stress distribution for implant-supported fixed prostheses varying the implant-abutment connection system, the fixation system, restorative material, bone type, and the level of bone tissue around the dental implant using the finite element method. Furthermore, the aim was to perform a systematic review and meta-analysis about the effect of osteoporosis in terms of implants survival rate and marginal bone loss. In relation to the experimental methodology, 24 three-dimensional models were simulated with the aid of the Rhinoceros 3D 4.0 (NURBS Modeling for Windows, USA), SolidWorks 2011, and InVesalius (CTI, São Paulo, Brazil) softwares. Each model represented a bone section of the maxillary posterior area (bone type IV) (normal and osteoporotic), varying the level of bone resorption (at the level of the implant, loss of bone tissue in 1.5 mm, loss of bone tissue in 3.0 mm and loss of bone tissue in 4.5 mm). All models containing the presence of a dental implant with 4.0 mm in diameter and 10 mm in length with two different abutment-implant connection (external hexagon and Morse taper), restored with crowns (metaloceramic and/or monolithic) with different fixation system (cemented and/or screwed). The designs were exported to FEMAP v.11.2 pre-and postprocessing software (Siemens Product Lifecycle Management Software Inc. USA) for mesh generation and loading application of 200N axial and 100N oblique (45° in the long axis... (Complete abstract click electronic access below) / Doutor

Many different hub assembly procedures have been utilized over the years in bascule bridge construction. The first assembly procedure (AP1) involves shrink fitting a trunnion component into a hub, followed by the shrink fitting of the entire trunnion-hub (TH) assembly into the girder of the bridge. The second assembly procedure (AP2) involves shrink fitting the hub component first into the girder, then shrink fitting the trunnion component into the hub-girder (HG) assembly. The final assembly procedure uses a warm shrink fitting process whereby induction coils are placed on the girder of the bridge and heat is applied until sufficient thermal expansion of the girder hole allows for insertion of the hub component. All three assembly procedures use a cooling method at some stage of the assembly procedure to contract components to allow the insertion of one part into the next. Occasionally, during these cooling and heating procedures, cracks can develop in the material due to the large thermal shock and subsequent thermal stresses. Previous works conducted a formal design of experiments analysis on AP1 to determine the overall effect of various factors on the critical design parameters, overall minimum stress ratio (OMSR) and overall minimum critical crack length (OMCCL). This work focuses on conducting a formal design of experiments analysis on AP1, AP2 and AP3 using the same cooling methods and parameters as in previous studies with the addition of the bridge size as a factor in the experiment. The use of the medium bridge size in AP1 yields the largest OMCCL values of any bridge and the second largest OMSR values. The large bridge size has the largest OMSR values versus all factors for AP1. The OMCCL and OMSR increases for every bridge size with an increase in the alpha ratio for AP1. The smallest bridge showed the largest OMCCL and OMSR values for every cooling method and every alpha ratio for AP2 and AP3. The OMCCL and OMSR decrease for every bridge size with an increase in the alpha ratio for AP2 and AP3.

This thesis investigates the capacity and failure mode of suction caissons under inclined loading. Parametric finite element analyses have been carried out to investigate the effects of caisson geometry, loading angle, padeye depth (i.e. load attachment point), soil profile and caisson-soil interface condition. Displacement-controlled analyses were carried out to determine the ultimate limit state of the suction caissons under inclined load and the results presented as interaction diagrams in VH load space. VH failure interaction diagrams are presented for both cases where the caisson-soil interface is fully-bonded and where a crack is allowed to form along the side of the caisson. An elliptical equation is fitted to the normalised VH failure interaction diagram to describe the general trend in the case where the caisson-soil interface is fully-bonded. Parametric study reveals that the failure envelope in the fully-bonded case could be scaled down (contracted failure envelope) to represent the holding capacity when a crack is allowed to form. A stronger effect of crack on the capacity was observed in the lightly overconsolidated soil, compared to the normally consolidated soil. The sensitivity of caisson capacity to the changes in load attachment position or loading angle was quantified based on the load-controlled analyses. It was found that, for caisson length to diameter ratios of up to 5, the optimal centreline loading depth (i.e. where the caisson translates with no rotation) is in the range 0.65L to 0.7L in normally consolidated soil, but becomes shallower for the lightly overconsolidated soil profile where the shear strength profile is more uniform. The reduction of holding capacity when the padeye position is shifted from the optimal location was also quantified for normally consolidated and lightly overconsolidated soil profiles at loading angle of 30 [degrees]. Upper bound analyses were carried out to augment the finite element study. Comparison of holding capacity and accompanying failure mechanisms obtained from the finite element and upper bound methods are made. It was found that the upper bound generally overpredicted the inclined load capacity obtained from the finite element analyses especially for the shorter caisson considered in this study. A correction factor is introduced to adjust the upper bound results for the optimal condition. Comparisons of non-optimal capacity were also made and showed that the agreement between the upper bound and finite element analyses are sensitive to the change in the centreline loading depth when the caisson-soil interface is fully bonded, but less so when a crack forms.