International Science Index


The Effect of Nylon and Kevlar Stitching on the Mode I Fracture of Carbon/Epoxy Composites


Composite materials are widely used in aviation industry due to their superior properties; however, they are susceptible to delamination. Through-thickness stitching is one of the techniques to alleviate delamination. Kevlar is one of the most common stitching materials; in contrast, it is expensive and presents stitching fabrication challenges. Therefore, this study compares the performance of Kevlar with an inexpensive and easy-to-use nylon fiber in stitching to alleviate delamination. Three laminates of unidirectional carbon fiber-epoxy composites were manufactured using vacuum assisted resin transfer molding process. One panel was stitched with Kevlar, one with nylon, and one unstitched. Mode I interlaminar fracture tests were carried out on specimens from the three composite laminates, and the results were compared. Fractographic analysis using optical and scanning electron microscope were conducted to reveal the differences between stitching with Kevlar and nylon on the internal microstructure of the composite with respect to the interlaminar fracture toughness values.

[1] D. D. L. Chung, Carbon Fiber Composites, 1994. doi:10.1016/B978-0-08-050073-7.50010-5.
[2] L. Tong, A. Mouritz, M. Bannister, 3D Fibre Reinforced Polymer Composites, Elsevier Science, 2002.
[3] A. Yudhanto, G. Lubineau, I. A. Ventura, N. Watanabe, Y. Iwahori, H. Hoshi, Damage characteristics in 3D stitched composites with various stitch parameters under in-plane tension, Compos. Part A Appl. Sci. Manuf. 71 (2015) 17–31. doi:10.1016/j.compositesa.2014.12.012.
[4] A. Yudhanto, N. Watanabe, Y. Iwahori, H. Hoshi, Effect of stitch density on fatigue characteristics and damage mechanisms of stitched carbon/epoxy composites, Compos. Part A Appl. Sci. Manuf. 60 (2014) 52–65. doi:10.1016/j.compositesa.2014.01.013.
[5] U. Beier, J. K. W. Sandler, V. Altstädt, H. Spanner, C. Weimer, Mechanical performance of carbon fibre-reinforced composites based on stitched and bindered preforms, Compos. Part A Appl. Sci. Manuf. 40 (2009) 1756–1763. doi:10.1016/j.compositesa.2009.08.012.
[6] N. Ghafari-Namini, H. Ghasemnejad, Effect of natural stitched composites on the crashworthiness of box structures, Mater. Des. 39 (2012) 484–494. doi:10.1016/j.matdes.2012.03.025.
[7] M. Ravandi, W.S. Teo, L.Q.N. Tran, M.S. Yong, T.E. Tay, The effects of through-the-thickness stitching on the mode I interlaminar fracture toughness of flax/epoxy composite laminates, Jmade. 109 (2016) 659–669. doi:10.1016/j.matdes.2016.07.093.
[8] A. P. Mouritz, C. Baini, I. Herszberg, Mode I interlaminar fracture toughness properties of advanced textile fibreglass composites, Compos. Part A Appl. Sci. Manuf. 30 (1999) 859–870. doi:10.1016/S1359-835X(98)00197-3.
[9] H. P. Zhao, R. K. Y. Li, X. Q. Feng, Experimental Investigation of Interlaminar Fracture Toughness of CFRP Composites with Different Stitching Patterns, Key Eng. Mater. 297–300 (2005) 189–194. doi:10.4028/
[10] L. K. Jain, Y. W. Mai, Analysis of stitched laminated ENF specimens for interlaminar mode II fracture toughness, Int. J. Fract. 68 (1994) 219–244. doi:10.1007/BF00013069.
[11] K. Tan, N. Watanabe, Y. Iwahori, Stitch fiber comparison for improvement of interlaminar fracture toughness in stitched composites, J. Reinf. Plast. Compos. 30 (2011) 99–109. doi:10.1177/0731684410383065.
[12] H. Ghasemnejad, Interlaminar Fracture Toughness of Stitched FRP Composites, Comput. Math. Autom. Mater. Sci. (n.d.) 93–96.
[13] L. K. Jain, K. A. Dransfield, Y.-W. Mai, On the effects of stitching in CFRPs—II. Mode II delamination toughness, Compos. Sci. Technol. 58 (1998) 829–837. doi:10.1016/S0266-3538(97)00186-3.
[14] K. A. Dransfield, L. K. Jain, Y.-W. Mai, On the effects of stitching in CFRPs—I. mode I delamination toughness, Compos. Sci. Technol. 58 (1998) 815–827. doi:10.1016/S0266-3538(97)00229-7.
[15] A. D.- ModeI, D5528-01 2001. Standard Test Method for Mode I Interlaminar Fracture Toughness of Unidirectional Fiber-Reinforced Polymer Matrix Composites, Am. Soc. Test. Mater. (2014) 1–13. doi:10.1520/D5528-13.2.
[16] T. Rys, B. V Sankar, P.G. Ifju, Investigation of Fracture Toughness of Laminated Stitched Composites Subjected to Mixed Mode Loading, J. Reinf. Plast. Compos. 29 (2009) 422–430. doi:10.1177/0731684408099407.