PEER REVIEW
20
th
Australian International Aerospace Congress, 27-28 February 2023, Melbourne
Potential Uses for the Fatigue Damage Spectrum (FDS)
in Test Specification and
Health and Usage Monitoring Systems (HUMS)
Mark F. Warren
1
, Peter Woodward
1
, William Granger
1
,
1
Softwire Systems Pty Ltd,
Level 6, 111 Macquarie St, Hobart, Tasmania, 7000
Abstract
The Fatigue Damage Spectrum (FDS) is a frequency domain representation of fatigue damage,
calculated using an acceleration time-waveform which accounts for both the magnitude and
duration of the signal. The FDS can be generated using either time-domain based methods or
can be calculated directly from frequency domain signal representations, such as Power
Spectral Density (PSD) plots. The FDS’s primary use case is in specifying and comparing
vibration tests for mechanical vibration testing; however, it also has potential in comparing the
damage potential of various signals, as well as edge processing and data reduction at the source,
where storing time-domain data is impractical or unfeasible. The main barrier to the adoption
of FDS based practices comes from both resistance to change in the industry, and the
complexity of adoption of these methods. This submission presents a literature review on the
rationale of adopting the FDS, as well as an overview of a newly developed software package
that seeks to overcome some of the obstacles to adoption. The literature clearly shows that FDS
methods are superior in developing test profiles from mixed-terrain input data. Combined with
well-designed software, the FDS offers potential benefits to industries relying on vibration
testing, by way of an increase in accuracy and reduction in conservatism compared with default
severities listed in defence standards.
Keywords: Fatigue Damage Spectrum, FDS, Shock Response Spectrum, SRS, Vibration
Testing, HUMS, Aquila.
Introduction
The use of mechanical vibration testing is commonplace in both defence and civilian
applications, and is primarily used to reduce the risk of in-service failures due to vibration. A
robust test profile is derived from measured data collected from environments representative of
those which the test article will be exposed to in service. To achieve this, a wide range of
vibration data is required across both platform types and mission terrains. A repeatable and
accurate method for data conversion is also required, to allow for appropriate vibration profiles
to be developed for programming into mechanical vibration test equipment. The challenge in
achieving these aims, means that test specifiers often turn to default severities (for example
those listed in defence standards), which can be unsuitable due to their generic nature. To
challenge these existing practices, both an efficient method of data acquisition and a repeatable
method of converting this data into test profiles is needed. Software which leverages the FDS,
both as a method to create damage equivalent tests, and as a method of data reduction, would
allow for organizations to adopt more robust test strategies developed from a wider range of
platforms.
