Hosseinpour Dashatan, Saeid
In some applications of composite laminates, thickness variation is necessary to fulfill specific design requirements. One way of accomplishing the intentional thickness variation in composite structures is terminating some plies within a layup. Introducing ply drop-offs causes geometrical and material discontinuities, which lead to high localized stresses around drop-off locations. Despite all the progress made in damage analyses of tapered composite laminates, estimating their load-carrying capacity and strength remains a significant challenge.In this study, damage in tapered composite laminates under tensile loading is investigated. The cohesive zone method is used to simulate the delamination failure.For simulation of intralaminar damages, a 3-D continuum damage mechanics-based model with Hashin criteria for damage initiation and bi-linear damage propagation softening is employed. Finite element analyses are implemented in Abaqus/Explicit.Computational results are compared to an experimental study.No significant fiber or matrix damage is detected before and during delaminations. In addition to loads corresponding to delamination onset, both delamination locations and propagation characteristics are also utilized for making comparisons between computational results and experimental observations. Dynamic characteristic of delamination is employed to validate numerical analyses, further. For this purpose, the delamination predictions are compared to images taken by a high-speed camera. Results show that the ply drop-off type influences laminates’ strength and governs the delamination growth to be either dynamic (unstable) or static (stable). A good correlation between experimental and finite element results is observed in terms of delamination onset location, propagation patterns, and stability of delamination growth. For some specimen types, a modified cohesive strength pair is required to enhance these correlations. To further investigate the local delamination behavior around the resin pocket, combinations of unidirectional plies with 0 ◦ and 45◦ orientations for a laminate with a single, double, and three drop-offs are considered as well. In addition to delamination patterns, the load transfer mechanism, especially in the drop-off region, is also studied. A different delamination behavior is detected for each case, which shows the significance of the effect of orientation of each sublaminate on the load transfer mechanism. Also, results show that the progression of delaminations within various interfaces to be similar for both 2-D and 3-D models in laminates with 0 ◦ plies. However, there are some differences in laminates, including 0◦ . Also, the 3-D model clarifies the significance of ply orientation in delamination propagation patterns, which is not detectable in the 2-D model..


Gozluklu, B.; Uyar, I; Çöker, Demirkan (2014-07-25)
In wind energy and aerospace industries, new advances in composite manufacturing technology enable to produce primary load carrying elements as composite materials in wide variety of shapes large such as an L-shape. However, due to the geometry, Interlaminar Normal Stresses (ILNS) are induced once a moderately thick laminate takes highly curved shape. In the curved part of the L-shaped structure, the development of ILNS promotes mode-I type of delamination propagation which is the weakest fracture mode. Thi...
Investigation of crack growth along curved interfaces in L-shaped composite and polymers
Yavas, D.; Gozluklu, B.; Çöker, Demirkan (2014-01-01)
Delamination in unidirectional L-shaped composite laminates is modeled with two L-shaped polycarbonate plates bonded to each other where the effect of pre-crack length on the stability of the crack growth is investigated experimentally and computationally. In the experimental study, a unique testing fixture with a sliding platform is designed to create a pure vertical displacement to one of the arms. The full-field technique of photoelasticity is used in order to visualize isochromatic fringe pattern around...
3D Simulation of Dynamic Delamination in Curved Composite Laminates
Ata, Tamer Tahir; Çöker, Demirkan (Elsevier BV; 2019-01-01)
In this study, dynamic fracture of curved carbon fiber reinforced plastic (CFRP) laminates under quasi-static loading is investigated using explicit three dimensional (3D) finite element method in conjunction with Cohesive Zone Modelling (CZM). The simulations are based on the experimental studies conducted by Tasdemir (2018). Three dimensional finite element models of two different ply architectures (unidirectional and fabric laminate) are generated corresponding to the experimental configurations. The com...
Design of a high precision hybrid AM machine
Yılmaz, Yunus Emre; Dölen, Melik; Department of Mechanical Engineering (2019)
Precision requirements in fused deposition modelling (FDM) processes have been increasing in recent years, especially after recognizing the potential of FDM process to produce complex and functional components. In order to increase precision of FDM process, 6-axis hybrid manufacturing system, which can carry out additive- and subtractive manufacturing processes in one manufacturing system platform, is designed. During design, kinematic analysis of the machine is done, axial- and angular errors are estimated...
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 ...
Citation Formats
S. Hosseinpour Dashatan, “INVESTIGATION OF DAMAGE IN GFRP TAPERED COMPOSITE LAMINATES,” Ph.D. - Doctoral Program, Middle East Technical University, 2021.