Fatigue failure of metallic structures operating under dynamic loading is a
common occurrence in engineering applications. It is difficult to estimate the
response of complicated systems analytically, due to structure& / #8217 / s dynamic
characteristics and varying loadings. Therefore, experimental, numerical or a
combination of both methods are used for fatigue evaluations. Fatigue failure can
occur on systems and platforms as well as components to be mounted on the
platform.
In this thesis, a helicopter& / #8217 / s Missile Warning Sensor - Cowling assembly is
analyzed. Analytical, numerical and experimental approaches are used wherever
necessary to perform stress and fatigue analyses. Operational flight tests are used
for obtaining the loading history at the analyzed location by using sensors.
Operational vibration profiles are created by synthesizing the data (LMS Mission
Synthesis). Numerical fatigue analysis of the assembly is done for determining the
natural modes and the critical locations on the assembly by using a finite element
model (MSC Fatigue). In addition, numerical multiaxial PSD analysis is
performed for relating the experimental results (Ansys). Residual stresses due to
riveting are determined (MSC Marc) and included in experimental analysis as
mean stresses. Bolt analysis is performed analytically (Hexagon) for keeping the
v
assembly stresses in safe levels while mounting the experimental prototype to the
test fixture.
Fatigue tests for determining the accelerated life parameters are done by an
electromagnetic shaker and stress data is collected. Afterwards, fatigue test is
performed for determining whether the assembly satisfies the required operational
life. Resonance test is performed at the frequency in which the critical location is
at resonance, since there was no failure observed after fatigue testing. A failure is
obtained during resonance test. At the end of the study, an analytical equation is
brought up which relates accelerated life test durations with equivalent alternating
stresses. Therefore, optimization of the accelerated life test duration can be done,
especially in military applications, by avoiding the maximum stress level to reach
or exceed the yield limit.
| Identifer | oai:union.ndltd.org:METU/oai:etd.lib.metu.edu.tr:http://etd.lib.metu.edu.tr/upload/2/12606966/index.pdf |
| Date | 01 February 2006 |
| Creators | Ozsoy, Serhan |
| Contributors | Kadioglu, Suat |
| Publisher | METU |
| Source Sets | Middle East Technical Univ. |
| Language | English |
| Detected Language | English |
| Type | M.S. Thesis |
| Format | text/pdf |
| Rights | To liberate the content for METU campus |
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