Composite structural joints, as observed throughout the natural world, have been systematically altered and proven via lengthy evolutionary processes. Biological fixed joints tend to exhibit unique attributes, including highly optimized fiber paths to minimize stress concentrations. In addition, since the joints consist of continuous, uncut fiber flow patterns, the joint does not inhibit the biological organism in the transportation of information, chemicals and food from one part of the body to the other.
To the contrary, large sections of man-made composite material structures are often joined using bolted or bonded joints, which involve low strength and high stress concentrations. These methods are also expensive to achieve. Additional functions such as fluid transport, electrical signal delivery, and electrical and thermal conductivity across the joints typically require parasitic tubes, wires, and clips. By using the biomimetic methods, we seek to overcome the limitations which are present in the conventional methods.
In the present work, biomimetic co-cured composite sandwich T-joints were constructed using unidirectional glass fiber, epoxy resin, and structural foam. The joints were fabricated using the wet lay-up vacuum bag resin infusion method. Foam sandwich T-joints with multiple continuous fiber architectures and sandwich foam thickness were prepared. The various joint designs were tested quasi-statically in bending of the T in a calibrated screw-driven load frame. Custom, purpose-designed fixtures were required to support the base of the joint during the bending load. The weight savings using the biomimetic approaches is discussed, as well as a comparison of failure modes versus fiber/core architectures is given.
In addition to developing structurally optimized, weight-efficient joints, a tremendous ancillary benefit to the approach is the ability to easily embed wires and micro tubes contiguous across the joined elements. This approach is key to achieving true robust structural multi-functionality.