Literatura académica sobre el tema "Fasteners modelling"

Les effets de la foudre sur les lignes d'assemblage des avions peuvent s'avérer catastrophiques. L'un des phénomènes redoutés est l'étincelage au niveau d'une fixation bien souvent associé à un défaut sur les résistances de contact. Au vu des contraintes normatives, du manque de connaissance de cette problématique multi-physiques et de l'incapacité structurelle à avoir une approche uniquement expérimentale, les avionneurs se sont notamment tournés vers la modélisation. Dans ce manuscrit, on s'intéresse particulièrement à la modélisation des lignes d'assemblage pour le dimensionnement de la contrainte locale sur celles-ci. La méthode des différences finies dans le domaine temporel (FDTD), couramment utilisée pour la problématique foudre en aéronautique, nous sert de méthode de résolution. De multiples modèles de fixations allant de modèles simplifiés, représentant par exemple la fixation par un fil résistif, à des modèles plus complexes, représentant l'ensemble des résistances de contact, sont développés et validés. Par ailleurs, pour répondre aux incertitudes associées aux résistances de contact des fixations, des modèles statistiques sont appliqués aux paramètres résistifs des modèles de fixation. Ces mêmes modèles statistiques découlent de l'étude d'une base de données issue d’une campagne de mesures menée par Dassault Aviation sur un ensemble d’éprouvettes tests. A l'aide de ces modèles, la contrainte sur les fixations d'un caisson représentant un réservoir de carburant d'un avion est étudiée de manière stochastique<br>The lightning effects on the fastening assemblies of an airplane may be critical. One of the most critical phenomenon is the sparking effect around the fasteners. This effect is usually associated to the contact resistances. Due to the standards, the lack of knowledge about this multiphysics issue and the inability to follow only an experimental approach, the aircraft manufacturers have chosen a modelling way. In this manuscript, we model the fastening assemblies in order to understand the local constraint on these assemblies. The finite difference time domain (FDTD) method mostly used for the lightning issue in the aircraft industry is chosen as the solving method. Several fastener models are developed and validated. We present simplified models, as the resistive wire model for instance, up to complex one with all the contact resistance of the fastener. Furthermore, due to the large uncertainties from one fastener to the other one in the same family, the fastener models are supplemented with statistical models. Thanks to a data base measurement created from several measurement campaigns made by Dassault Aviation, distribution laws are established to characterize the lightning injection effects or the state after lightning injection on the fasteners. Using this statistical models, a stochastic study is presented in order to evaluate the uncertainties in a fuel tank modelling

<p>This report investigates the feasibility and accuracy of determining fastener flexibility with 3D FE and representing fasteners in FE load distribution models with simple elements such as springs or beams. A detailed study of 3D models compared to experimental data is followed by a parametric study of different shell modelling techniques. These are evaluated and compared with industry semi-empirical equations.</p><p>The evaluated 3D models were found to match the experimental values with good precision. Simulations based on these types of 3D models may replace experimental tests. Two different modelling techniques were also evaluated for use in load distribution models. Both were verified to work very well with representing fastener installations in lap-joints using the ABAQUS/Standard solver. Further improvement of one of the models was made through a modification scale factor. Finally, the same modelling technique was verified using the NASTRAN solver.</p><p>To summarize, it is concluded that:</p><p>• Detailed 3D-models with material properties defined from stress-strain curves correspond well to experiments and simulations may replace actual flexibility tests.</p><p>• At mid-surface modelling of the connecting parts, beam elements with a circular cross section as a connector between shell elements is an easy and accurate modelling technique, with the only data input of bolt material and dimension.</p><p>• Using connector elements is accurate only if the connecting parts are modelled in the same plane, i.e. with no offset. Secondary bending due to offset should only be accounted for once and only once throughout the analysis, and it is already included in the flexibility input.</p>

Two failure mechanisms in a double lap joint are investigated. Analytical models of net-section and gross-section failure modes are proposed to describe these mechanisms. The effects of lamping force, interference fit, maximum axial load and WDCP on fatigue performance of the joint are included in the models. The effect of WDCP is assumed to give a reduction in friction coefficient. Three types of stress reduction factors are proposed in the net-section failure model to account for these parameters. The stress reduction factors modify stress range that is used in crack growth calculation. If there are no effects of these parameters, the stress reduction factors are equal to one. Two types of fretting stress are introduced in gross-section failure model to describe either sliding contact or incipient sliding contact on faying surface. The fretting stress is combined with body stress to modify stress range. The net-section failure model predicts that fatigue life is increasing as interference fit, clamping force and friction coefficient increase. The gross-section failure model predicts that fatigue life is decreasing as clamping force and friction coefficient increase. Both models predict that fatigue life is decreasing as maximum axial load increases. Transition of the failure mode occurs earlier as friction coefficient and interference fit increase, while it is delayed as maximum axial load increases. A transition parameter is proposed to establish a relationship between the four main parameters. The transition parameter is expressed in a polynomial equation. It gives an optimum combination of the four main parameters in order to achieve relatively higher fatigue life by having gross-section failure mode. Finite element analysis and fatigue testing are performed to validate the models. The finite element and the analytical models show that stress concentration factor at the edge of the hole is decreasing as clamping force increases. The rate of decrease of stress concentration factor is increasing as friction coefficient increases. While stress concentration factor on the faying surface is increasing as clamping force and friction coefficient increase. Fatigue testing reveals that the fatigue life of the joint is in good agreement with the predicted fatigue life of the proposed models.

碩士<br>國立高雄大學<br>土木與環境工程學系碩士班<br>100<br>The existing sandwich panel with quick-handed hooks can provide fast and economic shelter for the need during natural disasters. The hook system takes the responsibility to carry the loads between panels and becomes one of the key components in this kind of buildings. A roof made of the same kind of panels is a patented new way for a faster construction but the connectors between the roof panel and the wall panel or between one roof panel and another roof panel are still in default. For wider applications of this kind of construction material in the future, it is necessary to fill up the gap and complete the integrity of the building. The present study is to improve the quick-handed hook, design two types of new connectors, and simplify the sandwich panel numerical model. Through component numerical analyses and lab test evaluations, the results show that new design of hook and connectors can provide required strength and the simplified shell model is able to reasonable simulate the actual sandwich panel. The mechanical behavior of the equivalent shell elements is found to be in good agreement with that of solid elements. The needed CPU resources are dramatically reduced and this will achieve the feasibility of the numerical analysis of a full house model in the future.