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Title: Fatigue of composite truss structures
Author: Harper, Paul
ISNI:       0000 0004 2672 9836
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2009
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Truss assemblies offer a high stiffness, light-weight option for the construction of aerospace and civil structures. Their more widespread use is currently limited by significant design challenges associated with the nodal joints between struts, particularly in relation to fatigue. The initial focus of this research degree was the multi-partner, DTI funded `Nodal Optimisation of Truss Structures (NOTS)' project, which explored the potential of replacing a conventional metallic panel aircraft rib with a composite truss structure. The role of the author's work within NOTS was to aid the design of the adhesively bonded nodal joint through the implementation of a fatigue test programme. The NOTS project highlighted the need for improved analysis techniques in relation to both bond-line failure and delamination. To address this requirement, a numerical fatigue crack propagation law was developed within the explicit finite element code 'LS-Dyna. ' The law can be used to evaluate whether the crack tip strain energy release rate is sufficient for crack growth to occur and if so, to simulate the rate and direction of growth. The novelty of this work lies in the detailed analysis of the numerical cohesive zone which forms ahead of the crack tip and is critical to the accurate implementation of the fatigue degradation law. The extraction of strain energy release rate from the cohesive zone enables a direct link with the Paris Law for crack growth and experimental parameters obtained from standard fracture toughness specimens. The analysis technique has been validated using models of standard mode I, mode II and mixed mode specimens. It has then been applied to analyse fatigue crack propagation in both an adhesively bonded single-lap joint and the nodal joint developed within the NOTS project. Recommendations have been provided to guide further development of the analysis technique and to enable its integration within the design process
Supervisor: Hallett, Stephen Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available