O fenômeno de impacto mecânico entre corpos sólidos está presente em diversas áreas da engenharia. Exemplos atuais deste tipo de problema podem ser encontrados no projeto de elementos de máquinas, sistemas de transporte como containers com material nuclear, tubulações em indústrias químicas, autoveículos e várias outras estruturas que devem obedecer à códigos de segurança estabelecidos por legislações governamentais. Na maioria destes casos, o conhecimento das tensões oriundas do impacto entre os corpos é fundamental para evitarem-se fa-lhas nas estruturas projetadas, predizer danos indesejáveis, diminuir coeficientes de segurança, etc. Neste contexto, é proposta neste trabalho uma metodologia de projeto contra impacto em sistemas mecânicos elásticos baseada nas equações de superfície de tensão máxima, que representam diferentes situações de impacto em uma determinada geometria. O Método dos Elementos Finitos com a integração explícita no tempo é aplicado para resolver o problema dinâmico associado ao impacto. Como exemplos de aplicações são estudados um suporte e um eixo chavetado. / Impact between solid bodies is present in many areas of engineering. Relevant examples of this sort of problem can be found in machine element design, transport systems such as containers for nuclear material, pipes in chemical plants, vehicles and many others structures that should comply with safety codes issued by govern agencies. In the majority of these cases, the knowledge of the stresses due to the impact between the bodies is fundamental to avoid failures on the designed structures, to predict undesired damages, and to decrease safety factors. Therefore, in this work a design methodology for linear mechanical systems submitted to impact is proposed. It is based on the surface of maximum stress which represents different crash situations for a given elastic model. The Finite Element Method with the explicit time integration algorithm is used to solve the associated dynamic problem. Examples are presented such as a bracket and a shaft.

O fenômeno de impacto mecânico entre corpos sólidos está presente em diversas áreas da engenharia. Exemplos atuais deste tipo de problema podem ser encontrados no projeto de elementos de máquinas, sistemas de transporte como containers com material nuclear, tubulações em indústrias químicas, autoveículos e várias outras estruturas que devem obedecer à códigos de segurança estabelecidos por legislações governamentais. Na maioria destes casos, o conhecimento das tensões oriundas do impacto entre os corpos é fundamental para evitarem-se fa-lhas nas estruturas projetadas, predizer danos indesejáveis, diminuir coeficientes de segurança, etc. Neste contexto, é proposta neste trabalho uma metodologia de projeto contra impacto em sistemas mecânicos elásticos baseada nas equações de superfície de tensão máxima, que representam diferentes situações de impacto em uma determinada geometria. O Método dos Elementos Finitos com a integração explícita no tempo é aplicado para resolver o problema dinâmico associado ao impacto. Como exemplos de aplicações são estudados um suporte e um eixo chavetado. / Impact between solid bodies is present in many areas of engineering. Relevant examples of this sort of problem can be found in machine element design, transport systems such as containers for nuclear material, pipes in chemical plants, vehicles and many others structures that should comply with safety codes issued by govern agencies. In the majority of these cases, the knowledge of the stresses due to the impact between the bodies is fundamental to avoid failures on the designed structures, to predict undesired damages, and to decrease safety factors. Therefore, in this work a design methodology for linear mechanical systems submitted to impact is proposed. It is based on the surface of maximum stress which represents different crash situations for a given elastic model. The Finite Element Method with the explicit time integration algorithm is used to solve the associated dynamic problem. Examples are presented such as a bracket and a shaft.

The goal of the present doctoral research is to create a theoretical framework and develop a numerical implementation for a shell finite element that can potentially achieve higher performance (i.e. combination of speed and accuracy) than current Continuum-based (CB) shell finite elements (FE), in particular in applications related to soft biological tissue dynamics. Specifically, this means complex and irregular geometries, large distortions and large bending deformations, and anisotropic incompressible hyperelastic material properties. The critical review of the underlying theories, formulations, and capabilities of the existing CB shell FE revealed that a general nonlinear CB shell FE with the abovementioned capabilities needs to be developed. Herein, we propose the theoretical framework of a new such CB shell FE for dynamic analysis using the total and the incremental updated Lagrangian (UL) formulations and explicit time integration. Specifically, we introduce the geometry and the kinematics of the proposed CB shell FE, as well as the matrices and constitutive relations which need to be evaluated for the total and the incremental UL formulations of the dynamic equilibrium equation. To verify the accuracy and efficiency of the proposed CB shell element, its large bending and distortion capabilities, as well as the accuracy of three different techniques presented for large strain analysis, we implemented the element in Matlab and tested its application in various geometries, with different material properties and loading conditions. The new high performance and accuracy element is shown to be insensitive to shear and membrane locking, and to initially irregular elements.

Indiana University-Purdue University Indianapolis (IUPUI) / In this thesis, an explicit time integration code which integrates multibody dynamics and the discrete element method is used for modelling the excavation and moving operation of cohesive soft soil (such as mud and snow) by bulldozers. A soft cohesive soil material model (that includes normal and tangential inter-particle force models) is used that can account for soil compressibility, plasticity, fracture, friction, viscosity and gain in cohesive strength due to compression. In addition, a time relaxation sub-model for the soil plastic deformation and cohesive strength is added in order to account for loss in soil cohesive strength and reduced bulk density due to tension or removal of the compression. This is essential in earth moving applications since the soil that is dug typically becomes loose soil that has lower shear strength and lower bulk density (larger volume) than compacted soil. If the model does not account for loss of soil shear strength then the dug soil pile in front of the blade of a bulldozer will have an artificially high shear strength. A penalty technique is used to impose joint and normal contact constraints. An asperity-based friction model is used to model contact and joint friction. A Cartesian Eulerian grid contact search algorithm is used to allow fast contact detection between particles. A recursive bounding box contact search algorithm is used to allow fast contact detection between the particles and polygonal contact surfaces. A multibody dynamics bulldozer model is created which includes the chassis/body, C-frame, blade, wheels and hydraulic actuators. The components are modelled as rigid bodies and are connected using revolute and prismatic joints. Rotary actuators along with PD (Proportional-Derivative) controllers are used to drive the wheels. Linear actuators along with PD controllers are used to drive the hydraulic actuators. Polygonal contact surfaces are defined for the tires and blade to model the interaction between the soil and the bulldozer. Simulations of a bulldozer performing typical shallow digging operations in a cohesive soil are presented. The simulation of a rear wheel drive bulldozer shows that, it has a limited digging capacity compared to the 4-wheel drive bulldozer. The effect of the relaxation parameter can be easily observed from the variation in the Bulldozer's velocity. The higher the relaxation parameter, the higher is the bulldozer's velocity while it is crossing over the soil patch. For the low penetration depth run the bulldozer takes less time compared to high penetration depth. Also higher magnitudes of torques at front and rear wheels can be observed in case of high penetration depth. The model is used to predict the wheel torque, wheel speed, vehicle speed and actuator forces during shallow digging operations on three types of soils and at two blade penetration depths. The model presented can be used to predict the motion, loads and required actuators forces and to improve the design of the various bulldozer components such as the blade, tires, engine and hydraulic actuators.