Modeling the progressive damage in biomimetic composite sandwich T-joints


Ali A. Saeid

Date of Award


Degree Name

Ph.D. in Mechanical Engineering


Department of Mechanical and Aerospace Engineering


Advisor: Steven L. Donaldson


Composite sandwich structures are used extensively in aerospace, marine and other industrial applications. This is primarily due to the ability to fabricate lightweight structures with high bending stiffness and strength. A common joint between sandwich panels is a T-Joint, wherein the sandwich panels connect at 90° to each other. Current composite T-joint designs are prone to complex failure modes, including delamination and shear core failure, which significantly reduce the strength of the joints. This dissertation presents a methodology for the design and analysis of composite sandwich T-joints using a biomimetic design approach. It offers unique attributes to optimize the continuous fiber paths for minimum stress concentrations and multi sandwich layers to increase the bending strength. The major attention was to investigate the progressive failure modes in the joints numerically and verify by experiments. Experimental studies were conducted on three different designs of biomimetic composite sandwich T-joints under tension and bending loads. The results show significant improvements to the ultimate load: up to 68% improvement in bending and 40% in pull-off in the biomimetic sandwich T-joints compared to the reference conventional design. Two failure modes were predominant: the initiation and propagation of delamination and core kinking cracks. The finite element models provided important insights into the core failure and delamination. Key parameters of the cohesive zone method for traction-separation laws of multi-interface materials were developed and used to track the crack growth. The results predicted the onset, propagation, and ultimate failure consistent with the experimental observations.


Joints (Engineering) Design and construction, Bending stresses, Biomimetic materials Mechanical properties, Composite materials Mechanical properties, Mechanical Engineering, Industrial Engineering, Design, Engineering, composite sandwich T-joints, biomimetic approach, multiple delamination, fracture modes, cohesive zone method, finite element analysis

Rights Statement

Copyright 2016, author