MSc. Thesis Defense:Saher Gul28-11-2019




Saher Gul

Manufacturing Engineering, MSc. Thesis, 2019


Thesis Jury

Assoc. Prof. Dr. Burcu Saner Okan (Thesis Advisor)

Asst. Prof. Dr. Adnan Kefal (Thesis co-advisor)

Prof. Dr. Mehmet Yildiz

Asst. Prof. Dr. Eralp Demir

Asst. Prof. Dr. Bertan Beylergil



Date & Time: 05-December-2019 & 10:00 am to 12:00 pm

Place: KTMM, Teknopark Istanbul, 3rd Floor

Keywords: Thick hybrid laminate composites, Digital Image Correlation, Finite Element Method, Flexural Property, Thick hybrid laminate


There is a growing interest in the use of thick hybrid composite laminates in the structural elements of aeronautical and aerospace structures, and the study of their mechanical properties and failure behavior are gaining attention. In the present work, the influence of weak external layers of carbon and glass fibers on the flexural behavior of thick carbon/glass fiber reinforced hybrid composite laminates was examined to monitor their failure mechanisms. In the first part, four types of symmetric laminate structures were designed by tailoring stacking sequence of glass (G) and carbon (C) fiber reinforced prepregs and their fabrication was achieved by hot-press technique. In each composite structure, 48 prepreg plies were used and their configurations were adjusted as (8C/8G/8G)s, (8G/8C/8G)s, (8G/8G/8C)s, and (8C/8G/8C)s. Flexural tests showed that the highest flexural strength (1310 MPa) was exhibited by the laminate with the configuration of (8G/8G/8C)s, and the highest flexural modulus (79.64 GPa) was shown by the laminate with configuration of (8C/8G/8C). In addition, Digital Image Correlation (DIC) technique was used for the full-field in-plane strain and displacement registration, and for the study of failure mode development during the bending tests. The results indicated that the type of fiber placed along the horizontal midplane of the laminate controlled the failure mode, and the behavior of stress-strain curve was governed by the type of fiber available on the faces. The fracture surface characterization performed by optical and scanning electron microscopy techniques indicated that the compressive failures in the form of kink band formation along with interlaminar delamination were the two most prevalent forms of failure in thick hybrid laminates. In parallel to the experimental study, numerical study was carried out by Finite Element Method (FEM) to investigate the displacement values in the direction parallel and transverse to the loading axis, and for obtaining the longitudinal and shear strain values. Both experimental and numerical studies emphasized the importance of using stacking sequence of a thick hybrid laminate as a practical approach in controlling the flexural properties of the composites. To conclude, this work brings about a new insight in the design and fabrication of thick-section hybrid laminates by the adjustment of stacking sequence.