Browsing by Author "Goyder, Hugh"
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Item Open Access Experimental investigation of the nonlinear dynamic behaviour of bolted lap joints(2019-04) Lancereau, Damien Paul Thibaut; Goyder, Hugh; Purdy, David J.The physics behind the vibration of joints is currently unknown and therefore unpredictable. Consequently in sensitive structures, like aircraft or turbines, prototype testing is necessary to evaluate the dynamic behaviour and avoid catastrophic failures. The thesis objective is to reduce the unpredictability by identifying the dominant parameters linked to bolted lap joint nonlinear behaviour. This study has found that the size of the interface had the most impact. A large interface creates a receding contact which created an amplitude dependent damping and stiffness. In contrast, a small interface creates a complete contact, with limited nonlinear behaviour. In-between interface sizes involved a lock-up which was interpreted as amplitude dependent slip or bound regions in the lap joint interface. Accordingly, the bending moment dynamic loading at the joint location is correlated to the nonlinear behaviour, only if there is a receding contact. This correlation between bending and damping was interpreted as a rolling effect with a changing contact patch during a cycle of vibration, which creates a specific behaviour in different regions of the lap joint interface. An experimental approach was used to reach these conclusions. The use of shims allowed the comparison of seven sizes of interfaces on the same structure. Then, a novel method was developed to measure the effect of a receding contact at 18 joint locations, by placing or removing washer-size-shims in a beam with 18 identical lap joints. Hammer impact excitation allowed the 12 first bending modes to be measured with minimum interference. The decaying vibration time histories were filtered and fitted in the time domain, using novel signal processing methods, to extract the amplitude dependant damping ratio and natural frequencies. Also, a finite element simulation enabled the natural frequency to be predicted, using an approximated contact patch.Item Open Access Models for the Dynamic Simulation of Tank Track Components(Cranfield University, 2006-01) Allen, P.; Hameed, Amer; Goyder, HughThis project has been sponsored by QinetiQ Limited (QinetiQ); whose aim it is to model the dynamics of a prototype high-speed military tracked vehicle. Specifically their objective is to describe the mechanism by which force inputs are transmitted from the ground to the vehicle’s hull. Many track running gear components are steel and can be modelled as simple lumped masses or as linear springs without internal damping. These present no difficulty to the modeller. However tracked vehicle running gear also has nonlinear components that require more detailed descriptions. Models for two rubber components, the road wheel tyre and track link bush, and a model for the suspensions rotary damper, are developed here. These three components all have highly nonlinear dynamic responses. Rubber component nonlinearities are caused by the materials nonlinear elastic and viscoelastic characteristics. Stiffness is amplitude dependent and the material exhibits a significant amount of internal damping, which is predominantly Coulombic in nature but also relaxes overtime. In this work, a novel method for measuring the elastic and viscoelastic response of Carbon Black Filled Natural Rubber components has been devised and a ‘general purpose’ mathematical model developed that describes the materials response and is suited to use in multibody dynamic analysis software. The vehicle’s suspension rotary damper model describes three viscous flow regimes (laminar, turbulent and pressure relief), as a continuous curved response that relates angular velocity to damping torque. Hysteresis due to the compression of entrapped gas, compliance of the dampers structure and compression of damper oil is described by a single non-parametric equation. Friction is considered negligible and is omitted from the model. All components are modelled using MSC.ADAMS TM multibody dynamic analysis software. The models are shown to be easily implemented and computationally robust. QinetiQ’s requirement for ‘practical’ track running gear component models has been met.