Multiscale analysis of damage-tolerant composite sandwich structures
File(s)
Author(s)
Gigliotti, Luigi
Type
Thesis
Abstract
Composite sandwich structures are widely regarded as a cost/weight-effective alternative
to conventional composite stiffened panels and are extensively utilized for lightweight
applications in various sectors, including the aeronautical, marine and transport
industries. Nevertheless, their damage tolerance remains a critical issue.
This work aims to develop reliable analytical and numerical tools for the design of
damage-tolerant advanced foam-cored composite sandwich structures for aerospace
applications. It comprises of original experimental observations together with novel
numerical and analytical developments, as detailed below.
A novel analytical model for predicting the post-crushing response of crushable
sandwich foam cores is presented. The calibration of the model is performed using
experimental data obtained exclusively from standard monotonic compressive tests.
Hence, the need for performing time-consuming compressive tests including multiple
unloading-reloading cycles is avoided.
Subsequently, the translaminar initiation fracture toughness of a carbon-epoxy
Non-Crimp Fabric (NCF) composite laminate is measured. The translaminar fracture
toughness of the UD fibre tows is related to that of the NCF laminate and the concept
of an homogenised blanket-level translaminar fracture toughness was introduced.
A multiple length/time-scale framework for the virtual testing of large composite
structures is presented. Such framework hinges upon a novel Mesh Superposition
Technique (MST) and a novel set of Periodic Boundary Conditions named Multiscale
Periodic Boundary Conditions (MPBCs).
The MST is used for coupling different areas of the composite structure modelled
at different length-scales and whose discretizations consist of different element types.
Unlike using a sudden discretization-transition approach, the use of the MST eliminates
the undesirable stress disturbances at the interface between differently-discretized
subdomains and, as a result, it for instance correctly captures impact-induced damage
pattern at a lower computational cost.
The MPBCs apply to reduced Unit Cells (rUCs) and enable the two-scale (solid-to-
shell) numerical homogenization of periodic structures, including their bending and
twisting response. The MPBCs allow to correctly simulate the mechanical response
of periodic structures using rUCs (same results as if conventional UCs were used),
thus enabling a significant reduction of both modelling/meshing and analysis CPU
times.
The developments detailed above are finally brought together in a realistic engineering
application.
to conventional composite stiffened panels and are extensively utilized for lightweight
applications in various sectors, including the aeronautical, marine and transport
industries. Nevertheless, their damage tolerance remains a critical issue.
This work aims to develop reliable analytical and numerical tools for the design of
damage-tolerant advanced foam-cored composite sandwich structures for aerospace
applications. It comprises of original experimental observations together with novel
numerical and analytical developments, as detailed below.
A novel analytical model for predicting the post-crushing response of crushable
sandwich foam cores is presented. The calibration of the model is performed using
experimental data obtained exclusively from standard monotonic compressive tests.
Hence, the need for performing time-consuming compressive tests including multiple
unloading-reloading cycles is avoided.
Subsequently, the translaminar initiation fracture toughness of a carbon-epoxy
Non-Crimp Fabric (NCF) composite laminate is measured. The translaminar fracture
toughness of the UD fibre tows is related to that of the NCF laminate and the concept
of an homogenised blanket-level translaminar fracture toughness was introduced.
A multiple length/time-scale framework for the virtual testing of large composite
structures is presented. Such framework hinges upon a novel Mesh Superposition
Technique (MST) and a novel set of Periodic Boundary Conditions named Multiscale
Periodic Boundary Conditions (MPBCs).
The MST is used for coupling different areas of the composite structure modelled
at different length-scales and whose discretizations consist of different element types.
Unlike using a sudden discretization-transition approach, the use of the MST eliminates
the undesirable stress disturbances at the interface between differently-discretized
subdomains and, as a result, it for instance correctly captures impact-induced damage
pattern at a lower computational cost.
The MPBCs apply to reduced Unit Cells (rUCs) and enable the two-scale (solid-to-
shell) numerical homogenization of periodic structures, including their bending and
twisting response. The MPBCs allow to correctly simulate the mechanical response
of periodic structures using rUCs (same results as if conventional UCs were used),
thus enabling a significant reduction of both modelling/meshing and analysis CPU
times.
The developments detailed above are finally brought together in a realistic engineering
application.
Version
Open Access
Date Issued
2016-01
Date Awarded
2016-04
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Pinho, Silvestre Taveira
Sponsor
Airbus Group
Publisher Department
Aeronautics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)