Mixed Mode I/II Interlaminar Fracture Toughness of Carbon Fiber/RTM-6 Laminates Manufactured by VARTM Rita de C  assia Mendonc¸a Sales , 1,2 Fernando Guimar ~ aes, 2 Ricardo Francisco Gouv ^ ea, 2 Geraldo Maurı ´cio C ^ andido, 1 Maurı´cio Vicente Donadon 1 1 Department of Aeronautics, Instituto Tecnol  ogico de Aeron  autica, Prac¸a Marechal Eduardo Gomes, 50, Vila das Ac  acias, 12228-900, S ~ ao Jos  e dos Campos, S ~ ao Paulo, Brazil 2 Faculdade de Tecnologia de S ~ ao Jos  e dos Campos - Prof. Jessen Vidal, Cesare Mansueto Giulio Lattes Avenue, 1350, Eug ^ enio de Melo,12247-014, S ~ ao Jos  e dos Campos, S ~ ao Paulo, Brazil This work investigates and compares the interlaminar fracture behavior of composites manufactured by vacuum-assisted resin transfer molding subjected to three different temperatures (–54, 25, and 808C) and mode ratios (25, 50, and 75%). The results indicate ductility enhancement with increasing temperature, which were confirmed by fractographic analyses. In tested specimens with 25% mode ratio, the G I and G II values were not greatly affected by the temperature. As the temperature and the mode ratio increases, the specimens exhibited higher G I and G II values compared with those measured at 2548C. In the tested speci- mens with 75% mode ratio, an unstable crack propa- gation was observed at 2548C due to brittle behavior of matrix, which is promoted by the decrease of the adhesion represented by cusps and broken fibers in SEM images. The cusps formation is less pronounced for specimens tested at 808C and the fracture surface is flatter compared with those tested at 254 and 258C. POLYM. COMPOS., 00:000–000, 2018. V C 2018 Society of Plas- tics Engineers INTRODUCTION In recent years, the use of laminated composite materi- als in aerospace applications has considerably increased, due, among other factors, to their specific stiffness and strength. However, these materials are susceptible to internal defects and/or damage that can be produced dur- ing fabrication or by inappropriate or hazardous service loads [1]. The most predominant and life-limiting failure mechanisms in composite structures are the delamination, which is almost impossible to avoid in service. Delamina- tion failure depends not only upon the external loading conditions, but also on the intrinsic fiber and resin proper- ties. It may develop due to non-optimum curing or the introduction of foreign bodies or voids during the manufacturing process [2–4]. Improvements in the resin infusion based manufacturing processes have been one of the main research areas in the aeronautical industry in the last two decades. In recent years there is a clear need for developing low cost manufacturing processes to replace conventional lamina- tion processes with cure in autoclave. Infusion techniques, such as VARTM (Vacuum-Assisted Resin Transfer Mold- ing), have been recently employed to manufacture some secondary parts of the aircraft. The main disadvantages of the vacuum-assisted resin infusion processes are the low layer compaction (low fiber volume fraction) and the high void content in the final product [5]. The low compaction levels may result in internal defects in the final product that are not easily detectable which can compromise the structural integrity of the final composite component. In most real applications, transverse cracks and delamination in the matrix are intrinsically linked and constitute a typical mechanism of damage in composites, especially when the structures are submitted to bending loads [4, 6, 7]. The development of high fidelity predictive techniques to model delamination induced failure require a better understanding of the interlaminar failure mechanisms of laminated composite materials and the evaluation of inter- laminar fracture toughness properties under mixed mode loading conditions in different environmental conditions. Several approaches have been proposed in the literature in order to develop testing specimens and setups for com- bined loading conditions. However, most of the research Correspondence to: Rita de C assia Mendonc ¸a Sales; e-mail: rita.sales@ fatec.sp.gov.br Contract grant sponsor: National Research Council CNPq; contract grant numbers: 103671/2014-5, 155963/2014-7, 300990/2013-8. DOI 10.1002/pc.24810 Published online in Wiley Online Library (wileyonlinelibrary.com). V C 2018 Society of Plastics Engineers POLYMER COMPOSITES—2018