Innovative tailored fiber placement technique for enhanced damage resistance in notched composite laminate Ermias G. Koricho a,⇑ , Anton Khomenko a , Tommy Fristedt b , Mahmoodul Haq a,c a Composite Vehicle Research Center (CVRC), Michigan State University, 2727 Alliance Drive, Lansing, MI 48910, USA b LayStitch Technologies LLC, 2210 N Tipsico Lake Road, MI 48357, USA c Department of Civil Engineering, Michigan State University, 3546 Engineering Building, East Lansing, MI 48824, USA article info Article history: Available online 25 October 2014 Keywords: Tailored fiber placement Glass fiber reinforced plastic Notched composite Tensile strength FEM abstract Composites have recently gained considerable acceptance in the transportation sector such as the aero- space and automotive industries, as these materials offer the ability to reduce weight, greenhouse gas emissions and associated fuel cost. Conversely, problems related to material behavior, cost, manufactur- ing process, assembly and choice of joining technique pose challenges that limit the wide acceptance and implementation of the composite materials. Specifically, a major problem related to joining is the use of mechanical/fastener joints with drilled holes that can damage the continuous fibers and cause consider- able reduction in the load carrying capacity of resulting composite structures. To address this issue, an innovative solution that manufactures fabric laminates using ‘tailored place- ment’ of fibers around the holes/notch was proposed. This eliminates the need for drilling and machining of holes thereby eliminating the sources of delamination. The tensile performance of notched composites from the novel tailored fiber placement (TFP) approach was compared to conventional notched compos- ites. Additionally, the effect of various fiber placement patterns and machining processes on the strength, damage initiation and fracture mode of notched composite laminates were studied. Specifically, the stress and strain fields around the notch were thoroughly evaluated. The experimental results for notched specimens were compared with the damage initiation and strength predictions obtained from the Hashin failure criteria as available in commercially available FEA package (ABAQUS Ò ). A good agree- ment between experimental results and numerical predictions was observed. Overall, the proposed approach shows great promise in the use of tailored fiber placement technique to eliminate delamina- tions, maintain continuous fiber alignments and reduce associated stress concentrations in a wide range of composite applications including but not limited to mechanical fastening. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Recent advancements in novel materials, design for manufac- turing (DFM), and computer-aided design (CAD) have enabled composite structural designs that offer more than 50% weight sav- ings versus lightweight metals, as well as a threefold increase in specific strength and stiffness. However, joining of composites to other existing lightweight materials, such as magnesium, steel, aluminum, plastics, or glass fiber composites, to produce multi- material components has not fully advanced far enough to be used extensively in high volumes. Both simple and complex composite structures utilize different joining techniques, such as mechanical fastening, adhesive joining, and combination of both mechanical and adhesive joining (hybrid joint). In applications with high level of safety requirements, e.g. in aerospace and ground vehicles, hybrid joint is the most commonly used joining technique, to achieve the desired performance requirements of high load carrying capacity and evenly distributed stress within the structure. Generally, mechanical fastening is not a preferred joining method, as drilling holes reduces the strength of composite structure through fiber breakage and delamination. However, it is inevitable, since some structural integrity cannot be obtained by other connection/joining technique. Therefore, in order to have firm structural integrity within the structural parts, appropriate safety factor is used to compensate the loss of strength caused by cutout and notches or holes [1]. Presently, a number of advanced hole making processes such as machining of composites using high performance tools, water jet cutting, laser cutting, electric discharge machining (EDM) and http://dx.doi.org/10.1016/j.compstruct.2014.10.016 0263-8223/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: koricho@msu.edu (E.G. Koricho). Composite Structures 120 (2015) 378–385 Contents lists available at ScienceDirect Composite Structures journal homepage: www.elsevier.com/locate/compstruct