Effects of Transverse Stitching and Hygrothermal Environment on Composite Wing T-Joints

The present paper deals with the effects of transverse stitching and hygrothermal environment at the web-skin interface of composite wing T-joints that are made of carbon fibre composite (CFC) materials. The T300 carbon fibres are considered for the transverse stitching. The statistical bundle strength based on the Weibull distribution function is used for the estimation of the joint strength. A thick composite shell finite element is specially developed taking into account the hygrothermal effects and is used for a detailed finite element analysis of composite T-joints. T-joints may be exposed to moisture and temperature during their service life. Under such circumstances moisture and temperature diffuse into T-joints. As a consequence, the stiffness and strength properties of the laminates are degraded. Moreover, since the laminas in the laminate cannot deform freely, residual stresses are introduced. All the normal and shear stresses are computed and the failure loads are also computed using various failure criteria to get better insight into the behaviour of laminated T-joints. Additional stresses due to hyghrothermal forces are also computed. The T-joint is supported along the length and a pull-out force is applied on the top of the web. It is found that the web-skin interface where load transfer is out of plane, is the critical zone for failure due to high transverse normal and shear stresses. Also, higher temperature and moisture levels introduce additional transverse normal and shear stresses that make the zone more critical. The present study also shows how the transverse stitching at the web-skin interface zone adds to the transverse strengthening of the interface laminates and helps the T-joints to sustain higher loads.