PhD Oral Exam - Alireza Gorjipoor, Mechanical Engineering
When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.
Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.
This research study introduces a numerical model to predict failure in thick glass/epoxy laminated beams subjected to flexural bending moment and bolt joint loads. The accuracy of the proposed model was verified by experiments using strain gages and Digital Image Correlation (DIC) methods. During last decades, aluminum and steel have been substituted by composite materials specially in the aerospace industry where higher specific strength and stiffness are the main criteria for material selection. The yoke of the helicopter is one of the recent applications of thick composite structures. The yoke connects the main rotor blade to the hub using bolt joints and it is manufactured as a thick glass/epoxy beam. Performing the experimental tests during the design process of the yoke is highly expensive and time-consuming.
In this study, a numerical model is introduced to perform stress and failure analysis for a simplified model of the yoke. This simplified model consists of a thick composite laminate subjected to flexural bending moment and bolt joint connections. At first, a finite element model was developed to predict the structural behavior of the beam in the presence of flexural bending which is the main load in the real application. In the next step, Progressive damage modeling was added to the stress analysis code, to provide a package for failure prediction for this case study.
This model can be utilized in the design process of the yoke to reduce the number of the required iterative experiments. The results showed the agreement between strain distribution obtained from the finite element model and the experimental results from strain gages and Digital Image Correlation (DIC). Also, a good correlation was observed between experimental tests and failure prediction performed through simulation.