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Arterial bifurcations loaded by internal pressure represent significant stress concentrators. Increased mechanical stress inside arterial wall probably accelerates pathogenic processes at these places. Stress concentration factor (SCF) depends mainly on geometry, loading and material. This work presents a map of SCFs calculated by FEM at aortic bifurcation (AB) loaded by static internal pressure. Influence of geometry (aortic diameter, wall thickness, bifurcation angle, "non-planarity" angle and radius of apex), material properties and internal pressure were evaluated statistically by regression of FEM results. Two variants of materials were used (linear Hook and hyper elastic Ogden). Viscoelastic behaviour, anisotropy and prestrain were neglected. Results indicate that the highest Mises stress appears in the inner side of AB apex and that the SCF is negatively correlated with bifurcation angle and with internal pressure. The SCF varies from 4,5 to 7,5 (Hook) and from 7 to 21 (Ogden).

The U.S. Army needs a Heavy Dry Support Bridge (HDSB) that can support the Military Load Class (MLC) 96 Heavy Equipment Transporter (HET) tractor trailer carrying an M-I Tank. An existing Axial Folding Bridge (AFB), which was originally designed for MLC 70 loading, has been proposed for load upgrade to demonstrate the feasibility of achieving MLC 96 capacity. This report reviews the upgrade, a finite element model of the bridge, and the actual testing of the bridge to verify the model. The bridge was modeled using the Structural Analysis and Design/Integrated Structural Design System (STAAD-III/ISDS) finite element analysis software. The analysis demonstrated that the existing bridge could be upgraded by simply bolting flat, thin plate elen1ents to the bottom chord of the structure using existing pin plate connector bolt holes and longer bolts. These plates effectively stiffen the bridge structure and maintain a stress level for all elements of the bridge that is no higher for the MLC 96 loading than was experienced for the unreinforced MLC 70 base structure. The modification added 208.7 kg per center section, or an increase in weight of 4.6%, for an increase in load capacity of 37%. A working load static test was conducted on a modified bridge. Four hydraulic actuators applied incremental loading on the bridge. Strain gauge and deflection data were recorded and compared to the analytical model. The model proved to be more flexible than the bridge, but the data showed good correlation in terms of stress ratios between various members. Stress levels were acceptable for the given loading, demonstrating that MLC 96 had successfully been achieved on the bridge. ; Master of Science

This paper presents the design principles and structure of the object-oriented finite element software OOFEM, which has been under active development for several years. The main advantages of the presented framework include modular design, extensibility, and robustness. The code itself is freely available and is distributed under GNU public license. It provides tools for linear and nonlinear analysis of mechanical and transport problems on sequential and parallel computers.

The majority of car crash deaths occur in the front seats because the majority of occupants sit in the front seats. Traditionally, the rear seats were safer than the front seats because a front seated occupant would be closer to rigid structures such as the steering wheel, and they would be closer to the location of the impact. Therefore, government crash test regulations as well as academic and industry testing up to this point have principally focused on the front seats. Since the beginning of efforts to make cars safer, innovations were applied to the front seats first. Only some of these safety innovations have transitioned into the rear seats. Over the years, the front seats have gotten much safer due to advanced seatbelts with pretentioners and load limiters, airbags surrounding the driver, and structural changes to the vehicle frame to prevent intrusion into the occupant compartment. At the same time, occupant safety in the rear seats has also improved, however at only a fraction of the improvement of the front seats. With modern vehicles, the front seats have actually become safer than the rear seats for certain occupants and specific crash types (e.g., adult occupants in frontal crash). The lagging performance of the rear seats represents a problem because thousands of rear-seated occupants are injured or killed each year. With the rise in autonomous driving systems, the amount of occupants sitting in the rear seats, and therefore sustaining injury, could increase dramatically. In this dissertation, rear seats of a range of current vehicles were reconstructed to examine injury risk with the finite element models of two anthropomorphic test devices. These models showed a wide range of injury risks in the reconstructed seats. They were also able to show results similar to sled impact tests with the same vehicles. Knowledge gained from these reconstructions was then used to perform parametric studies on key variables that influence injury risk in the rear seats. From the parametric studies, it was found that the seat back angle, the width of the seatbelt anchors, and the presence of a seatbelt pretensioner had the largest influences on the injury risk. One of the injury mechanisms prevalent in the rear seats is submarining. Submarining likelihood and injury probability is difficult to predict with anthropomorphic test devices; however, human body models can help to improve injury prediction in these cases. To improve the injury prediction capability of human body models, several additions to the models are necessary. This dissertation outlines the investigation of spleen and kidney shapes through statistical shape analysis. This type of analysis allows more customizable human body models which could better capture the injury probability to these organs for a wider range of the population. Finally, subject-specific models of ribs were created to investigate factors affecting the predictive capability of finite element models. The findings and methodology from this body of work have the ability to add critical contributions to the understanding of injury risk and injury mechanisms in the rear seats. ; Doctor of Philosophy ; The majority of car crash deaths occur in the front seats because the majority of occupants sit in the front seats. Traditionally, the rear seats were safer than the front seats because a front seated occupant would be closer to hard objects such as the steering wheel, and they would be closer to the location of the impact. Therefore, government crash test regulations as well as academic and industry testing up to this point have principally focused on the front seats. Since the beginning of efforts to make cars safer, technology such as seatbelts and airbags were applied to the front seats first. Only some of this technology has been added into the rear seats. Over the years, the front seats have gotten much safer due to all the work focused on the front seats. At the same time, the rear seats have also improved, however at only a fraction of the improvement of the front seats. With modern vehicles, the front seats have actually become safer than the rear seats in some cases. The lagging performance of the rear seats represents a problem because thousands of rear-seated occupants are injured or killed each year. With the rise in self driving cars, the amount of occupants sitting in the rear seats, and therefore sustaining injury, could increase dramatically. In this dissertation, rear seats of a range of current vehicles were reconstructed to examine injury risk with the models of two crash test dummies. These models showed a wide range of injury risks in the reconstructed seats. They were also able to show results similar to physical tests with the same vehicles. Knowledge gained from this work was then used to help look at key variables that influence injury risk in the rear seats. It was found that the angle of the seat back, the width of the seatbelt anchors, and the presence of advanced seatbelts had the largest influences on the injury risk. One of the injury mechanisms prevalent in the rear seats is submarining, where the seatbelt slides up off the hips. Submarining likelihood and injury probability is difficult to predict with crash test dummies; however, human body models can help to improve injury prediction in these cases. To improve the injury prediction capability of human body models, several additions to the models are necessary. This dissertation outlines the investigation of spleen and kidney shapes to allow more customizable human body models which could better capture the injury probability to these organs for a wider range of the population. Finally, subject-specific models of ribs were created to investigate factors affecting the predictive capability of rib models. The findings and methodology from this body of work have the ability to add critical contributions to the understanding of injury risk and injury mechanisms in the rear seats.