OPTIMAL DESIGN OF A COMPOSITE SCARF REPAIR PATCH UNDER TENSILE LOADING

ABSTRACT Mechanics of the composite scarf repair under tensile loading with and without overlay plies was examined for nontraditional patch ply orientations. Three-dimensional nonlinear analysis was performed for repair failure prediction and good baseline comparison for open-hole scarfed panels and panels repaired by using standard ply-by-ply replacement patch composition was achieved. Multidimensional optimization was performed to calculate the repair patch ply orientations which minimize the von Mises stresses in the adhesive. These optimal stacking sequences achieved significant reduction of the stress levels and resulted in predicted up to 75% and 85% strength restoration for flush and single ply thickness over-ply repair. These results are intended to illustrate additional design variables available for efficient composite repair design, namely the composition of the repair patch

Temperature Effects on Mechanical Properties of Woven Thermoplastic Composites for Secondary Aircraft Structure Applications

The effect of temperature on the mechanical behavior of 8-H satin woven glass fabric/polyethylene sulfide (GF/PPS) was investigated in this paper. Static-tensile tests were both conducted on notched and unnotched specimens at typical temperatures (ambient, 95°C and 125°C) based on the glass transition temperatures (Tg) of the neat resin and composite, their strength and moduli were obtained and compared. The damage patterns of failed specimens of notched and unnotched were examined with the aid of high-definition camera and stereomicroscope. The results of stress-strain relationships showed that the slight nonlinearity of the curves were observed for these two specimens, which was associated with the plastic deformation of localized resin. The damage patterns of notched and unnotched specimens at different temperatures proved that damage and plastic deformation were two simultaneous mechanisms and it was prominent in the notched. It was the overstress accommodation mechanism that led to a relative high strength rentention for the notched and a reduction of the hole sensitivity. The results obtained in this paper indicated that GF/PPS can be used as secondary aircraft structures at elevated temperatures higher than its Tg