Experimental failure strengths of composite single-lap joints reinforced with I-Fiber stitching process

Abstract

Composite lap joints have been extensively used due to their excellent properties and the demand for light structures. However, composites exhibit weak mechanical properties in their thickness, which may cause failure in composite lap joints. Various reinforcement methods that delay fracture by dispersing stress concentration have been discussed to overcome this problem, such as z-pinning and conventional stitching. After several studies and publications, the I-Fiber stitching process is a promising technology that combines the advantages of both z-pinning and the conventional stitching process. In this paper, the reinforcing effect of the I-Fiber stitching process was verified by fabricating composite single-lap joint specimens with different thicknesses, number of I-Fibers, and stitching angles to evaluate the lap shear strengths. Experimental results showed an improvement of up to 52.1% using the I-Fiber stitched process compared with the unstitched specimens. In addition, a better ratio of improvement in the reinforcement was observed with thinner composite adherends, and a higher failure load was achieved using a 45 degrees stitching angle compared with 0 degrees. Finally, through finite element analysis, it was possible to study the behavior and predict the interface failure of the single-lap joint. The results obtained showed good agreement with the experimental data and supported the failure mechanism's understanding using the I-Fiber stitching process.