International Journal of Mechanical Sciences 163 (2019) 105115 Contents lists available at ScienceDirect International Journal of Mechanical Sciences journal homepage: www.elsevier.com/locate/ijmecsci Design and numerical evaluation of recycled-carbon-fiber-reinforced polymer/metal hybrid engine cradle concepts João Henrique Fonseca a , Giyeol Han a , Luca Quagliato a , Yonghee Kim a , Joeun Choi a , Taeyeon Keum b , Sungeun Kim b , Do Suck Han a , Naksoo Kim a , Hyungyil Lee a,∗ a Department of Mechanical Engineering, Sogang University, 35 Baekbeom-ro, Mapo-gu, Seoul 04107, Republic of Korea b Research and Development Center, Donghee Industrial Company, Ulsan 44784, Republic of Korea a r t i c l e i n f o Keywords: Multi-material design Engine cradle Recycled carbon fiber Polymer-metal hybrid structures Weight reduction a b s t r a c t The design and evaluation of polymer-metal hybrid (PMH) engine cradles are realized via the design of con- cept models and finite element (FE) analyses. The structures consider a low-cost recycled carbon fiber (rCF) and PMH technologies. The initial conceptual design consists of creating C-type/hollow-type inserts and modifying the plastic components by considering the dimensions and thickness of insert and inclusion of plastic ribs as the design parameters. The PMH engine cradles are then evaluated by performance criteria, including weight reduc- tion, stiffness, natural frequency and strength. The integration of rCF with injection-molding over metal inserts promoted weight reduction. The hollow-type and C-type PMH engine cradles achieved the weight reduction of 19 and 16% compared to the reference steel engine cradle, respectively, while they fulfilled the evaluation cri- teria. The results contribute to the advance of lightweight engine cradles with improved structural performance, fabricated with low-cost carbon fiber and fast manufacturing processes. 1. Introduction The automotive industry has faced numerous challenges in the past decades regarding the emission of greenhouse gases from its automo- biles. With the increasing awareness of global warming, especially in the last decade, governmental agencies have tightened regulations in order to bring CO 2 emissions to a minimum level. Weight reduction of vehicles have been achieved with lightweighting materials and com- putational optimization techniques [1–3]. Lightweighting improves the fuel efficiency up to 7% for each 10% reduction in vehicle weight [4]. Advanced materials emerged as important materials for automotive lightweighting, and they have been applied to numerous automotive parts, such as front ends, body structures and engine cradles [5]. The engine cradle (Fig. 1) is one of the key components of the engine sub- system and has as its main functions: (i) support the engine, transmis- sion and suspension; (ii) distribute high chassis loads; (iii) reduce vibra- tion and shocks; and (iv) contribute to rigidity and crash management. A regular engine cradle is commonly manufactured with welded steel stampings, having about 48 parts and 28 kg [6]. GM introduced the first all-wrought aluminum engine cradle in the 1999 Chevy Impala, weigh- ing 18 kg with a total of 17 parts [6]. A thin-wall-casted magnesium engine cradle was first used on the Chevrolet Corvette Z06 from model year 2006 through 2013, in which weight was reduced to 10.5 kg with ∗ Corresponding author. E-mail address: hylee@sogang.ac.kr (H. Lee). components integrated into a single-piece. Although polymers are ex- pected to vastly compose newly developed vehicles, including electric ones [7], high costs of precursors and heat treatment [5,8–11] and long processing times [6] are the main barriers for a wider use of carbon- fiber-reinforced polymer (CFRP) composites in engine cradles and other automotive parts. More recently, solutions like the use of rCF materials have been thought to overcome the high costs of CF materials [12–14]. The chassis component for the Zenos E10 sports car is an example of its recent com- mercial utilization. PMH manufacturing technologies allow to promote additional weight reduction by integrating metal and polymer materi- als in a single structure by means of faster-capability molding processes [15,16]. Such molding processes are efficient ways to produce polymer components [17] and process rCF into CFRP materials [18]. The PMH front-end of Audi A6, fabricated by injection overmolding, is the first reported case of the application of PMH technology into the automotive industry [19]. Thus, the integration of rCF materials and PMH technolo- gies has the potential to reduce the total costs and manufacturing time to produce CFRP composite components. Although several efforts have been made to achieve lightweighting of engine cradles through the replacement of steel by lightweighting materials, high cost, limited processing technology and incompatibil- ity with existing infrastructure have restrained their further application https://doi.org/10.1016/j.ijmecsci.2019.105115 Received 17 July 2019; Accepted 26 August 2019 Available online 31 August 2019 0020-7403/© 2019 Elsevier Ltd. All rights reserved.