Study of Nanocomposite Laminates and Failure Analysis of Pin Joints

Abstract

Fiber reinforced composites have high demand as a structural material, often in load bearing applications. This is because of their light weight with high strength, environment resistance and high durability. Fiber reinforced composites are required to be joined in the different applications for the efficient design and assembly of the structures. These joints exhibit poor performance and unexpected failure due to the stress concentration around or vicinity of the holes. The main objective of the present work is to increase the performance of the joints prepared from glass fiber reinforced composites with the addition of the nanofiller, with different fiber orientations and with different geometric parameters. The effect of the different ply orientations and nanofiller on the bearing strength and failure mode of the pin joints were investigated both experimentally and numerically. Glass-epoxy composite laminates were prepared with [0°/45°/90°], [0°/45°/0°] and [0°/90°/0°] ply orientations. Nanoclay filler with 1, 2, 3, 4 and 5 wt.% were added in epoxy for the said orientations to prepare the single hole pin joints. Results show that the strength of the pin joints is significantly dependent on both the ply orientations and nanofiller wt.%. The joint geometry i.e., distance from the free edge of specimen to the diameter of the hole (E/D) ratio and width of the specimen to the diameter of the hole (W/D) ratio were also investigated in single hole configuration. The E/D and W/D ratios were varied from 2 to 5. Results show that the bearing strength and failure mode were significantly affected by the geometric parameters. Taguchi method was used to optimize the geometric parameters for double holes pin joint configurations. The orthogonal array, the signal-to-noise ratio, and analysis of variance were employed to study the effect of geometric parameters on the bearing strength of the joints. Geometric parameters, i.e., distance from the free edge of the specimen to the diameter of the first hole (E/D) ratio, width of the specimen to the diameter of the hole (W/D) ratio, distance between the two holes to the diameter of the hole (P/D) ratio and side width to the diameter of the hole (K/D) ratio, were investigated for the serial and parallel hole configurations. The results demonstrate that the E/D ratio is the most significant parameter to increase the bearing strength in both serial and parallel double pin joint configurations. Its percentage contribution is about 84.5% and 64.23% in serial and parallel pin joint configurations, respectively. For multi holes pin joint configurations, the geometric parameters i.e., distance from the free edge of the specimen to the diameter of the first two holes (E/D) ratio, distance between two holes along the length of the specimen to the diameter of the hole (F/D) ratio, distance between the two holes along the width of the specimen to the diameter of the hole (P/D) ratio and side width to diameter (S/D) ratio, were studied for their effect on strength and failure modes of the joint. Design of experiments along with Taguchi method was used for the optimization of different geometric parameters. ANOVA was applied to determine the influence of individual geometric parameter on the strength of joint. The results demonstrate that E/D and F/D ratios are the most significant parameters to increase the strength of multi holes pin joint configurations. Their percentage contributions were about 62% to 65% and 23% to 26%, respectively. The characteristic curve method along with Tsai-Wu failure criteria was used to compare the numerical and the experimental results. A good agreement was obtained between the numerical and experimental predictions.