Show/Hide Menu
Hide/Show Apps
Logout
Türkçe
Türkçe
Search
Search
Login
Login
OpenMETU
OpenMETU
About
About
Open Science Policy
Open Science Policy
Open Access Guideline
Open Access Guideline
Postgraduate Thesis Guideline
Postgraduate Thesis Guideline
Communities & Collections
Communities & Collections
Help
Help
Frequently Asked Questions
Frequently Asked Questions
Guides
Guides
Thesis submission
Thesis submission
MS without thesis term project submission
MS without thesis term project submission
Publication submission with DOI
Publication submission with DOI
Publication submission
Publication submission
Supporting Information
Supporting Information
General Information
General Information
Copyright, Embargo and License
Copyright, Embargo and License
Contact us
Contact us
Fatigue and static behavior of curved composite laminates
Download
index.pdf
Date
2018
Author
Taşdemir, Burcu
Metadata
Show full item record
Item Usage Stats
334
views
237
downloads
Cite This
By virtue of the fact that curved composite laminates which are utilized as load carrying subcomponents in aircraft and wind turbine structures are subjected to cyclic loading during their operating time, it is crucial to understand fatigue failure mechanisms at least as much as static failure mechanisms. With the intention of understanding fatigue failure mechanisms and thus improving fatigue life of structures, these curved laminates are investigated experimentally under static and fatigue loadings. The failure mechanisms observed in the tests are supported by analytical and numerical methods. CFRP laminates with four different ply architectures (UD, cross-ply with two different thicknesses and fabric) are examined. A new test fixture is designed to apply moment/axial combined loading to curved specimens properly. Static and fatigue experiments are conducted using servo-hydraulic testing machine and in-situ photographs are taken. In addition, DIC method is used to obtain strain distribution in the curved region just before the failure. The stress state at the curved region for each specimen configuration is analytically calculated using the multilayer curved beam solution. In the experimental results of UD and fabric laminates, it is observed that both static and fatigue failures initiate at roughly the maximum radial stress location (approximately 35% of the thickness from inner radius). For UD laminates, there is no visible difference between the failure mechanisms under static and fatigue loadings. For fabric laminates, fatigue failure is observed to occur as a single major crack at the maximum radial stress location just as in UD laminates, whereas static failure is observed to occur as multiple diffusive cracks at the maximum radial stress location. In contrast to UD and fabric laminates, different failure locations and mechanisms are observed in the fatigue and static experiments of cross-ply specimens. Fatigue failure is observed to form at the maximum radial stress location whereas the static failure is observed to form in the region where the combined radial, tangential and shear stresses attain a maximum value, in the form of Tsai-Wu failure criterion. For fatigue failure, micro-cracks existing in the maximum radial stress location grow more rapidly under cyclic loading compared to cracks in other regions and coalesce into one major matrix crack which reaches the 0/90 interface gradually and continues to propagate as a delamination. As for the static failure, failure initiates as a matrix crack in the group of 90° layers and jumps to the upper 0/90 interface by an abrupt 40-50° angle and propagates as a delamination. Against the common belief in the literature, according to our observations, we conclude that static and fatigue failure mechanisms are not always the same.
Subject Keywords
Composite materials.
,
Materials
,
Fracture mechanics.
,
Strength of materials.
URI
http://etd.lib.metu.edu.tr/upload/12622118/index.pdf
https://hdl.handle.net/11511/27316
Collections
Graduate School of Natural and Applied Sciences, Thesis
Suggestions
OpenMETU
Core
Experimental and numerical investigation of damage process in composite laminates under low-velocity impact
Topaç, Ömer Tanay; Çöker, Demirkan; Gürses, Ercan; Department of Aerospace Engineering (2016)
Damage sensitivity of composites under out-of-plane dynamic loading, and its limited detectability on a structure has long remained a prominent problem in industry. In this study, simulations are compared with the real-time damage formation scheme, with the aim of increasing confidence in failure predictions. Drop-weight impact experiments are carried out on a [0/90]_s CFRP beam laminate. Initiation and progression of damage, consisting of matrix cracks and delamination, are visualized via ultra-high-speed ...
Modeling of intersonic delamination in curved and thick composite laminates under quasi-static loading
Gözlüklü, Burak; Çöker, Demirkan; Department of Aerospace Engineering (2014)
One of the widely used geometrically complex parts in advanced commercial aircraft is L-shaped composite laminates in which mixed-mode delamination failure is reported. Dynamic delamination under quasi-static loading is studied using explicit finite element method in conjunction with Cohesive Zone Modeling (CZM). A 4-noded interface element working with Bilinear (BL), Xu-Needleman (XN) and ratedependent bilinear (RD) CZMs are implemented in ABAQUS/Explicit. The interface elements are validated with benchmar...
Failure analysis of advanced composites under impact by cohesive zone method
Doğan, Oğuz; Parnas, Kemal Levend; Department of Mechanical Engineering (2013)
The main objective of this study is to investigate the delamination damage of laminated composites subjected to low velocity impact. Three-dimensional finite element analyses are conducted to determine delamination area, shape and location. The impact analysis is performed by using the explicit finite element method which uses the central difference rule to integrate the equations of motion through the time. The composite structures are modeled using eight-node solid elements. The critical interfaces betwee...
Design optimization of a laser path length controller through numerical analysis and experimental validation
Fenercioglu, Tevfik Ozan; Yalçınkaya, Tuncay (IOS Press, 2019-01-01)
As an integral part of Strapdown Inertial Navigation Systems, ring laser gyroscopes (RLG) are exposed to joint loading conditions where thermal, static and dynamic loads occur simultaneously. The effects of different loading conditions on overall RLG performance should be addressed in parallel for an optimum design. A crucial aspect in this process is the development of the path length controller (PLC), consisting of a mirror, a composite piezo electric bending actuator and other motion transfer elements. T...
ANALYTICAL INVESTIGATION OF AERO-ELASTIC BEHAVIOR OF AIRCRAFT COMPOSITE BOX WINGS IN UNSTEADY COMPRESSIBLE FLOW
Farsadi, T.; Haddadpour, H.; Yuceoglu, U. (2011-11-17)
In this study, an anisotropic thin-walled "Composite Box Beam" as the "Wing System" is used to consider the effects of the fiber orientation and the lay-up configuration on the aeroelastic stability and the dynamic response of an aircraft wing. The present "Circumferentially Asymmetric Stiffness Model (CAS)" takes into account a group of non-classical effects; such as the transverse shear, the material anisotropy, warping inhibition, etc. The "Aerodynamic Strip Method" based on "Wagner Functions" in unstead...
Citation Formats
IEEE
ACM
APA
CHICAGO
MLA
BibTeX
B. Taşdemir, “Fatigue and static behavior of curved composite laminates,” M.S. - Master of Science, Middle East Technical University, 2018.