Modelling and analysis of internally BFRP reinforced beams at elevated temperatures

The aim of the work is to conduct a finite element model analysis on a small – size concrete beam and on a full size concrete beam internally reinforced with BFRP exposed at elevated temperatures. Experimental tests performed at Kingston University have been used to compare the results from the numerical analysis for the small – size concrete beam. Once the behavior of the small – size beam at room temperature is investigated and switching to the heating phase reinforced beams are tested at 100°C, 200°C and 300°C in loaded condition. The aim of the finite element analysis is to reflect the three – point bending test adopted into the oven during the exposure of the beam at room temperature and at elevated temperatures. Performance and deformability of reinforced beams are straightly correlated to the material properties and a wide analysis on elastic modulus and coefficient of thermal expansion is given in this work. Develop a good correlation between the numerical model and the experimental test is the main objective of the analysis on the small – size concrete beam, for both modelling the aim is also to estimate which is the deterioration of the material properties due to the heating process and the influence of different parameters on the final result. The focus of the full – size modelling which involved the last part of this work is to evaluate the effect of elevated temperatures, the material deterioration and the deflection trend on a reinforced beam characterized by a different size. A comparison between the results from different modelling has been developed.

FEM and experimental analysis of a wind turbine blade

This paperwork compares the a numerical validation of the finite element model (FEM) with respect the experimental tests of a new generation wind turbine blade designed by TPI Composites Inc. called BSDS (Blade System Design Study). The research is focused on the analysis by finite element (FE) of the BSDS blade and its comparison with respect the experimental data from static and dynamic investigations. The goal of the research is to create a general procedure which is based on a finite element model and will be used to create an accurate digital copy for any kind of blade. The blade prototype was created in SolidWorks and the blade of Sandia National Laboratories Blade System Design Study was accurately reproduced. At a later stage the SolidWorks model was imported in Ansys Mechanical APDL where the shell geometry was created and modal, static and fatigue analysis were carried out. The outcomes of the FEM analysis were compared with the real test on the BSDS blade at Clarkson University laboratory carried out by a new procedures called Blade Test Facility that includes different methods for both the static and dynamic test of the wind turbine blade. The outcomes from the FEM analysis reproduce the real behavior of the blade subjected to static loads in a very satisfying way. A most detailed study about the material properties could improve the accuracy of the analysis.

Influence of adhesive thickness on adhesively bonded joints under fatigue loading

Research on adhesive joints is arousing increasing interest in aerospace industry. Incomplete knowledge of fatigue in adhesively bonded joints is a major obstacle to their application. The prediction of the disbonding growth is yet an open question. This thesis researches the influence of the adhesive thickness on fatigue disbond growth. Experimental testing on specimens with different thickness has been performed. Both a conventional approach based on the strain energy release rate and an approach based on cyclic strain energy are provided. The inadequacy of the former approach is discussed. Outcomes from tests support the idea of correlating the crack growth rate to the cyclic strain energy. In order to push further the study, a 2D finite element model for the prediction of disbond growth under quasi-static loading has been developed and implemented in Abaqus. Numerical simulations have been conducted with different values of the adhesive thickness. The results from tests and simulations are in accordance with each other. According to them, no dependence of disbonding on the adhesive thickness has been evidenced.

Global Fatigue Assessment of a Decommissioned Jacket Platform for a Sustainable Reuse as an Offshore Wind Turbine

When the offshore oil and gas supplies exhaust, offshore platforms must be decommissioned and removed. The present thesis highlights the importance of evaluating the possibility of reuse of decommissioned offshore jacket platforms for offshore wind energy. In order to shift to the new structure, the topside must be removed from the substructure and a wind turbine can be installed in its place. The feasibility of this project was investigated using a finite element analysis software called Sesam. To study fatigue life in offshore structures, an exhaustive review of the background and state of the art was done. A finite element model was created by the means of Sesam and two different fatigue analysis approaches were applied and compared. In the end, an analysis methodology is suggested for the structural fatigue analysis of offshore wind turbine structures based on international standards, addressing the industry’s need to account for the combined effect of wind and hydrodynamic loads in these type of structures.

Shear behaviour of reinforced cconcrete slab under concentrated load: an investigation through non-linear and sequentially linear analysis

English: The assessment of safety in existing bridges and viaducts led the Ministry of Public Works of the Netherlands to finance a specific campaing aimed at the study of the response of the elements of these infrastructures. Therefore, this activity is focused on the investigation of the behaviour of reinforced concrete slabs under concentrated loads, adopting finite element modeling and comparison with experimental results. These elements are characterized by shear behaviour and crisi, whose modeling is, from a computational point of view, a hard challeng, due to the brittle behavior combined with three-dimensional effects. The numerical modeling of the failure is studied through Sequentially Linear Analysis (SLA), an alternative Finite Element method, with respect to traditional incremental and iterative approaches. The comparison between the two different numerical techniques represents one of the first works and comparisons in a three-dimensional environment. It's carried out adopting one of the experimental test executed on reinforced concrete slabs as well. The advantage of the SLA is to avoid the well known problems of convergence of typical non-linear analysis, by directly specifying a damage increment, in terms of reduction of stiffness and resistance in particular finite element, instead of load or displacement increasing on the whole structure . For the first time, particular attention has been paid to specific aspects of the slabs, like an accurate constraints modeling and sensitivity of the solution with respect to the mesh density. This detailed analysis with respect to the main parameters proofed a strong influence of the tensile fracture energy, mesh density and chosen model on the solution in terms of force-displacement diagram, distribution of the crack patterns and shear failure mode. The SLA showed a great potential, but it requires a further developments for what regards two aspects of modeling: load conditions (constant and proportional loads) and softening behaviour of brittle materials (like concrete) in the three-dimensional field, in order to widen its horizons in these new contexts of study.

"Influence of lower-limb joint models on subject-specific musculoskeletal model predictions during gait" ( "modelli muscoloscheletrici personalizzati dell'arto inferiore: Analisi dell'effetto della modellazione dei giunti sulla predizione dei carichi agenti sul sistema scheletrico durante il cammino").

The aim of the present thesis was to investigate the influence of lower-limb joint models on musculoskeletal model predictions during gait. We started our analysis by using a baseline model, i.e., the state-of-the-art lower-limb model (spherical joint at the hip and hinge joints at the knee and ankle) created from MRI of a healthy subject in the Medical Technology Laboratory of the Rizzoli Orthopaedic Institute. We varied the models of knee and ankle joints, including: knee- and ankle joints with mean instantaneous axis of rotation, universal joint at the ankle, scaled-generic-derived planar knee, subject-specific planar knee model, subject-specific planar ankle model, spherical knee, spherical ankle. The joint model combinations corresponding to 10 musculoskeletal models were implemented into a typical inverse dynamics problem, including inverse kinematics, inverse dynamics, static optimization and joint reaction analysis algorithms solved using the OpenSim software to calculate joint angles, joint moments, muscle forces and activations, joint reaction forces during 5 walking trials. The predicted muscle activations were qualitatively compared to experimental EMG, to evaluate the accuracy of model predictions. Planar joint at the knee, universal joint at the ankle and spherical joints at the knee and at the ankle produced appreciable variations in model predictions during gait trials. The planar knee joint model reduced the discrepancy between the predicted activation of the Rectus Femoris and the EMG (with respect to the baseline model), and the reduced peak knee reaction force was considered more accurate. The use of the universal joint, with the introduction of the subtalar joint, worsened the muscle activation agreement with the EMG, and increased ankle and knee reaction forces were predicted. The spherical joints, in particular at the knee, worsened the muscle activation agreement with the EMG. A substantial increase of joint reaction forces at all joints was predicted despite of the good agreement in joint kinematics with those of the baseline model. The introduction of the universal joint had a negative effect on the model predictions. The cause of this discrepancy is likely to be found in the definition of the subtalar joint and thus, in the particular subject’s anthropometry, used to create the model and define the joint pose. We concluded that the implementation of complex joint models do not have marked effects on the joint reaction forces during gait. Computed results were similar in magnitude and in pattern to those reported in literature. Nonetheless, the introduction of planar joint model at the knee had positive effect upon the predictions, while the use of spherical joint at the knee and/or at the ankle is absolutely unadvisable, because it predicted unrealistic joint reaction forces.

The behaviour of osteocyte dendritic processes in bone under cyclic load (il comportamento dei processi dendritici degli osteociti nel tessuto osseo sottoposti a carico ciclico)

Bone is continually being removed and replaced through the actions of basic multicellular units (BMU). This constant upkeep is necessary to remove microdamage formed naturally due to fatigue and thus maintain the integrity of the bone. The repair process in bone is targeted, meaning that a BMU travels directly to the site of damage and repairs it. It is still unclear how targeted remodelling is stimulated and directed but it is highly likely that osteocytes play a role. A number of theories have been advanced to explain the microcrack osteocyte interaction but no complete mechanism has been demonstrated. Osteocytes are connected to each other by dendritic processes. The “scissors model" proposed that the rupture of these processes where they cross microcracks signals the degree of damage and the urgency of the necessary repair. In its original form it was proposed that under applied compressive loading, microcrack faces will be pressed together and undergo relative shear movement. If this movement is greater than the width of an osteocyte process, then the process will be cut in a “scissors like" motion, releasing RANKL, a cytokine known to be essential in the formation of osteoclasts from pre-osteoclasts. The main aim of this thesis was to investigate this theoretical model with a specific focus on microscopy and finite element modelling. Previous studies had proved that cyclic stress was necessary for osteocyte process rupture to occur. This was a divergence from the original “scissors model" which had proposed that the cutting of cell material occurred in one single action. The present thesis is the first study to show fatigue failure in cellular processes spanning naturally occurring cracks and it's the first study to estimate the cyclic strain range and relate it to the number of cycles to failure, for any type of cell. Rupture due to shear movement was ruled out as microcrack closing never occurred, as a result of plastic deformation of the bone. Fatigue failure was found to occur due to cyclic tensile stress in the locality of the damage. The strain range necessary for osteocyte process rupture was quantified. It was found that the lower the process strain range the greater the number of cycles to cell process failure. FEM modelling allowed to predict stress in the vicinity of an osteocyte process and to analyse its interaction with the bone surrounding it: simulations revealed evident creep effects in bone during cyclic loading. This thesis confirms and dismisses aspects of the “scissors model". The observations support the model as a viable mechanism of microcrack detection by the osteocyte network, albeit in a slightly modified form where cyclic loading is necessary and the method of rupture is fatigue failure due to cyclic tensile motion. An in depth study was performed focusing on microscopy analysis of naturally occurring cracks in bone and FEM simulation analysis of an osteocyte process spanning a microcrack in bone under cyclic load.