Modeling of intersonic delamination in curved and thick composite laminates under quasi-static loading

Download
2014
Gözlüklü, Burak
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 benchmark tests from literature for each fracture mode subjected to static and dynamic loading. A 12-ply woven-fabric Graphite/Epoxy Lshaped composite laminate is modeled with BL cohesive layers placed in all interfaces. Macromechanical and micromechanical behaviors are compared to experiments and are found to be in good agreement. Single delamination initiates in mode-I and smoothly transitions to mode-II during propagation at intersonic crack tip speeds reaching 3500 m/s. Shear Mach waves fronts, follower reflecting waves, train of pulses in normal stresses and vortex like particle velocity patterns are observed. The analysis is repeated using XN and RD CZMs. XN CZM exhibited early slippage of plies due to low initial stiffness, whereas RD CZM provided the best agreement with experiments. This thesis reports the intersonic crack propagation in engineering parts for the first time, which was previously observed in earthquakes.

Suggestions

Modeling of the dynamic delamination of L-shaped unidirectional laminated composites
Gozluklu, Burak; Çöker, Demirkan (2012-03-01)
One of the widely used geometrically complex parts in advanced commercial aircraft is the L-shaped composite. Due to the sharp curved geometry, interlaminar opening stresses are induced and delamination occurs under considerable mode-mixities in L-shaped beams. Dynamic phenomena during delamination initiation and propagation of L-shaped beams are investigated using dynamic (explicit) finite element analysis in conjunction with cohesive zone methods. The 2-D model consists of 24 plies of unidirectional CFRP ...
Fatigue and static behavior of curved composite laminates
Taşdemir, Burcu; Çöker, Demirkan; Department of Aerospace Engineering (2018)
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 f...
Experimental investigation of dynamic delamination in curved composite laminates
Uyar, İmren; Çöker, Demirkan; Department of Aerospace Engineering (2014)
In the aerospace industry, high demand for lightweight structures is fostering the use of composite laminates in a wide variety of shapes, as primary load carrying elements. However, once a composite laminate takes a highly curved shape, such as an L-shape, high interlaminar stresses induced in the curved region causes dynamic delamination formation. This thesis discusses the experimental investigation of delamination in L-shaped CFRP composite laminates under quasi-static shear loading. An experimental set...
Numerical investigation of stiffened composite panel into buckling and post buckling under combined loading
Akay, Erkan; Yaman, Yavuz; Department of Aerospace Engineering (2015)
This thesis presents the investigation of buckling and post buckling behaviour of stiffened thin walled laminated composite aerospace structures subjected to combined in-plane axial and shear loadings. Due to the fact that the state of stress developing especially in the post-buckling stage is quite complicated under the combined loading, the necessary computational model is usually based on Finite Element Modelling (FEM). In this study, after verifying the FEM methodology and completing the sensitivity stu...
MODELING OF DYNAMIC DELAMINATION IN L-SHAPED COMPOSITE BRACKETS
Gozluklu, Burak; Çöker, Demirkan (2012-11-15)
One of the widely used geometrically complex parts in recent civil passenger aircrafts is the L-shaped composite brackets connecting ribs to skins. Due to the sharp curved geometry, interlaminar opening stresses are induced and delamination occurs under considerable mode-mixities at the corner. Dynamic phenomena during delamination initiation and propagation of L-shaped beams are investigated using dynamic (explicit) finite element analysis in conjunction with cohesive zone methods (CZM). In ABAQUS a sequen...
Citation Formats
B. Gözlüklü, “Modeling of intersonic delamination in curved and thick composite laminates under quasi-static loading,” Ph.D. - Doctoral Program, Middle East Technical University, 2014.