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Title: Analysis and design of composite panels with Stringer run-outs
Author: Cosentino, Enzo
ISNI:       0000 0004 2706 2367
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2010
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Despite their high level of performance in specific areas, such as weight, durability and through-life costs, composites are often used at relatively low strain levels in primary structures, due in part, to poor through-thickness failure characteristics. This has lead to relatively slow take-up within primary flight structures. This delay is mostly due to a reduced understanding of the failure causes and mechanisms and of their behaviour when damaged. The widespread lack of knowledge and know-how often leads to over sized structures, which are in contrast with the lightweight philosophy characterizing new design solutions. The present study focuses on particular joints, the so called "Stringer Run-outs". The vulnerability of composite structures to through-thickness stresses is particularly exacerbated in these special joints where the necessity to terminate stiffeners generates eccentric structural sub-components. When undergoing normal in-flight inplane loading conditions, the eccentricity produces significant transverse displacements, which trigger premature localized skin-stringer disbond and/or delamination. Such crack initiations may then develop and grow following unpredictable path patterns that jeopardize the integrity of the primary structure and often lead to catastrophic failure of the sub-component. The somewhat high nonlinearity of these phenomena in conjunction with an extensive lack of analytical tools have been causes of major concerns for the aerospace industries over the past decade, following the introduction of "total carbon design" philosophy. The present work was conducted with the main purpose of developing fast and reliable analytical methods for predicting crack initiation loads for stringer run-outs. Nevertheless, the complexity of the modelled structure and need for novel modelling strategies have led to the development of analysis methods, which are extensively exploitable for calculation of analytical solutions to a variety of problems. A deep fundamental insight to the behaviour of eccentric structures is presented, which mostly represent the new and unique aspect of the present research. Analytical models are developed to predict structural behaviour in the moderately large displacement regime. Furthermore, analytical methods to calculate buckling loads of composite stiffened panels with discontinuous stringer are developedTo predict crack initiation, the analysis methods are used in conjunction with local linear elastic fracture mechanics based sub-models. All the proposed analysis methods are experimentally validated by means of coupon level tests. Advanced non-linear finite element method is used to validate analytical predictions on composite panels. Finally, a novel design principle (compound joint) based on decoupling failure subcauses is presented and experimentally validated
Supervisor: Weaver, Paul Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available