Laser machining of Kevlar fiber reinforced laminates e Effect of polyetherimide versus polypropylene matrix Hemant Chouhan a, d, 1 , Dilpreet Singh b, 1 , Vinod Parmar c , Dinesh Kalyanasundaram b, e, * , Naresh Bhatnagar a a Department of Mechanical Engineering, Indian Institute of Technology Delhi, India b Centre for Biomedical Engineering, Indian Institute of Technology Delhi, India c Department of Physics, Indian Institute of Technology Delhi, India d Department of Mechanical Engineering, Amity University Uttar Pradesh, India e Department of Biomedical Engineering, All India Institute of Medical Sciences, New Delhi, India article info Article history: Received 7 April 2016 Received in revised form 27 August 2016 Accepted 30 August 2016 Available online 3 September 2016 Keywords: Kevlar fiber reinforced plastics (KFRP) Fiber laser machining Polyetherimide Polypropylene Scanning acoustic microscopy abstract Kevlar ® fabric reinforced plastics (KFRPs) are specialized composites with multiple layers of fabrics (~ranging from 20 to 50 layers) designed for high impact applications. In this work, Kevlar-129 fiber was reinforced with polyetherimide (PEI) and polypropylene (PP) to obtain two groups of laminates in three configurations i.e. 16, 24 and 30 layers. Holes of diameter 11.6 mm were profile cut using fiber laser machining system operating at 1070 nm wavelength. Effects of polymeric matrix on the failure of the Kevlar e polyetherimide (K-PEI) and Kevlar e polypropylene (K-PP) laminates were characterized by studying the following: (i) threshold laser power required to make the holes (ii) surface morphology using scanning electron microscopy (iii) damage zone along the laser cut path using scanning acoustic microscopy and optical microscopy. K-PEI laminates underwent material separation at much lesser line energy (ratio of laser power to velocity) than K-PP laminates during laser machining. Scanning electron microscopy (SEM) was used to further analyze the laser cut surfaces. A prominent observation on the laser-irradiated surface was: less recast/resolidified polymer covered the Kevlar fabric in K-PEI as compared to a thicker polymeric layer in K-PP. Heat affected zone and damage factors were evaluated using scanning acoustic microscopy (SAM). Surface roughness and kerf width were also analyzed to understand the effect of laser machining of Kevlar laminates. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction Kevlar fiber reinforced plastics (KFRPs) are materials with high specific strength, and high specific stiffness. The long molecular chains produced from poly paraphenylene terephthalamide is termed as Kevlar and is highly oriented with strong inter-chain covalent bonding in the fiber direction and weak hydrogen bonding in the transverse direction, resulting in anisotropic prop- erties. Kevlar fiber is five times better than steel in terms of strength per unit weight with reasonably high temperature resistance and corrosion resistance [1]. Kevlar is considered one of lightweight and high strength engineering composite and hence finds applications in aerospace, military and automotive industry. Several grades of Kevlar fibers are available such as K-29, K-49, K-100, K-129, AP, XP and KM2 [2]. Amongst these, K-129 is very versatile fiber and has been used for industrial applications ranging from interior panels to structural aircraft parts. The first four varieties are used for low and high velocity impact application such as stab resistance as well as for personal body armors. Though polymer based composites are made to near net shape, but machining becomes a necessity, either because of dimensional accuracy requirements or for generating holes needed for fastening purposes [3,4]. Therefore, there is a strong need of optimizing machining process parameters for composites [5,6]. Traditional machining processes like turning, milling, drilling, and shaping have been used on polymer composites. Owing to inherent heterogeneity and anisotropy, conventional machining results in damage of composites due to matrix cracking, fiber * Corresponding author. E-mail addresses: dineshk.iitdelhi@gmail.com, dineshk@cbme.iitd.ac.in (D. Kalyanasundaram). 1 First authors, equal contribution. Contents lists available at ScienceDirect Composites Science and Technology journal homepage: http://www.elsevier.com/locate/compscitech http://dx.doi.org/10.1016/j.compscitech.2016.08.026 0266-3538/© 2016 Elsevier Ltd. All rights reserved. Composites Science and Technology 134 (2016) 267e274