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methods for composite bolted joints,
using both closed-form analytical methods
and numerical techniques such as
the finite element method. However, the
majority of models to date have been
overly simplistic in nature, and have
had limited success in predicting joint
behaviour. Consequently, the current
design methods used in industry are
largely empirical and heavily reliant on
expensive and time-consuming testing.
Many of the methods have advanced little
from those developed during an
intense period of testing in the USA in
the 70s and 80s. Their application to
new, primary structures of commercial
aircraft, with increased uncertainties
due to new materials and thicker laminates,
and increased quantities of material
used in each test, is likely to lead to
expensive design cycles and overweight
joint designs. With recent developments
in computational mechanics and continued
increase in processing power, there
is the potential to develop more
advanced analysis tools which could be
used to optimise joint design, reduce the
quantity of experimental tests required
in development, and improve fundamental
understanding of joint behaviour,
hence ensuring continued safety.
Project objectives
The overall objectives are:
• reliable and user-friendly analysisbased
design methods, with improved
predictive capability which will
enable:
(a) a significant reduction in testing,
and hence time and cost of development,
and
BOJCAS: Bolted Joints in Composite Aircraft
Structures
Michael McCARTHY
The objective of BOJCAS is to develop advanced numerical design methods for bolted
joints in composite aircraft structures. This is a critical technology supporting the introduction
of composites into the primary structure of large commercial aircraft. The methods
developed have the potential to significantly reduce testing, and hence time/cost
of development, as well as aircraft weight with consequent increase in efficiency. They will
also help to ensure continued safety. This article provides an overview of activities within
the project.
Aircraft Technologies STRUCTURES
2
(b) the incorporation of composites
into the primary structure with
optimal weight savings.
• a fundamental improvement in understanding
of composite bolted joint
behaviour, especially in primary
structures, thus contributing to continued
safety.
The partnership
The consortium consists of three aircraft
manufacturers, four national aerospace
laboratories, two universities, and two
research companies. Eight countries are
represented as shown in table I.
The start date was February 2000 and
the duration of the project is 36 months.
Programme content
The programme structure is illustrated
in figure 1. Bearing in mind the needs of
industry for preliminary and detailed
design tools, the following outputs are
planned:
• global design methods, for preliminary
design of complex, multi-fastener
joints;
• detailed design methods for final
design of critical joints;
• methods to couple global and detailed
design methods, i.e. to streamline
the process of producing a detailed
analysis from a preliminary analysis;
• design guidelines for primary composite
bolted joints based on analyses
and tests.
The project is divided into a global
strand (WP 1, 2 and 3) and a local strand
(WP 4 and 5) with the coupled globallocal
methods bridging the two strands.
Interaction takes place between the
strands by using the knowledge gained
from the detailed local methods to
improve the global methods. Each
strand contains major testing and analysis
components.
At the global level, a series of ‘benchmark’
structures representative of complex,
primary, multi-fastener joint configurations,
will be designed and tested.
Global design techniques will be used to
design and predict the performance of
these benchmarks. Initially, existing inhouse
methods will be used to provide
a baseline (Tasks 2.1 and 2.2). These
methods include handbook/design
chart methods and two-dimensional
finite element methods. Then new global
methods will be developed mostly
based on two-dimensional finite element
methods with specialised techniques
to model bolt-hole interaction,
and validated on the benchmarks
(Task 2.3). Figure 2 illustrates one of the
benchmark structures. This benchmark
structure will consist of several variations
　
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