Polyester Composites Reinforced with Noncrimp Stitched Carbon Fabrics: Mechanical Characterization of Composites and Investigation on the Interaction between Polyester and Carbon Fiber Volkan Cecen, 1 Mehmet Sarikanat, 2 Yolda¸ s Seki, 3 Tugrul Govsa, 4 Hasan Yildiz, 2 Ismail H. Tavman 1 1 Department of Mechanical Engineering, Dokuz Eylul University, 35100 Bornova, Izmir, Turkey 2 Department of Mechanical Engineering, Ege University, 35100 Bornova, Izmir, Turkey 3 Department of Chemistry, Dokuz Eylu ¨ l University, 35160 Buca, _ Izmir, Turkey 4 Govsa Composites Ltd., 35060 Pinarbasi, Izmir, Turkey Received 12 February 2006; accepted 19 June 2006 DOI 10.1002/app.24983 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: The primary purpose of the study is to in- vestigate the anisotropic behavior of different noncrimp stitched fabric (NCF) reinforced polyester composites. Car- bon fiber composite laminates were manufactured by vac- uum infusion of polyester resin into two commonly used advanced noncrimp stitched carbon fabric types, unidirec- tional and biaxial carbon fabric. The effects of geometric var- iables on composite structural integrity and strength were illustrated. Hence, tensile and three-point bending flexural tests were conducted up to failure on specimens strength- ened with different layouts of fibrous plies in NCF. In this article an important practical problem in fibrous composites, interlaminar shear strength as measured in short beam shear tests, is discussed. The fabric composites were tested in three directions: at 08, 458, and 908. Extensive photomicrographs of multilayered composites resulting from a variety of uni- axial loading conditions were presented. It was observed that broken fibers recede within the matrix in composites with weak interfacial bond. Another aim of the present work was to investigate the interaction between carbon fiber and polyester matrix. The experiments, in conjunction with scan- ning electron photomicrographs of fractured surfaces of composites, were interpreted in an attempt to explain the instability of polyester-resin–carbon-fiber interfaces. Ó 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4554–4564, 2006 Key words: carbon fiber; anisotropy; scanning electron microscopy; vacuum-assisted resin transfer molding INTRODUCTION Carbon-fiber-reinforced epoxy resins are widely used in the aerospace applications and defense industries because of the superior combination of stiffness, strength, and fatigue resistance that these materials offer, whereas polyester resins that command the greatest attention in the field of glass reinforcement comprise a major part of the reinforced plastics mar- ket today. The combination of carbon fibers and poly- ester matrix is becoming more important as the cost of carbon fibers is decreasing, and because of the devel- opment of new composites manufacturing technolo- gies. 1 The vacuum-assisted resin transfer molding (VARTM) process allows a greater degree of automa- tion than does hand lay-up, provides an improved work environment (fewer volatile emissions), im- proves product quality, and is more cost-effective. The VARTM or the patented SCRIMP (Seemann com- posite resin infusion molding process) 2,3 processes have been developed as alternative low cost methods for the manufacture of composite structures. The resin infusion processes lend themselves to the use of near net shape textile preforms manufactured through a variety of automated textile processes such as knitting and braiding. 4 The challenge facing the resin infusion techniques is to design a robust process that will con- sistently ensure complete infiltration and cure of a geometrically complex shape preform with the high fiber volume fraction needed for structural applica- tions. One major disadvantage of the resin infusion processes is that they require long duration and high temperature cure cycles to cure the resin-saturated performs fully. Relatively little research has been reported on the mechanical performance of carbon fiber/unsaturated polyester composites despite its importance in many dynamically loaded structures. 5,6 Although the num- ber of combinations of carbon fabrics and unsatu- rated polyester resin are popular among designers, relatively small amount of data is available. Correspondence to: M. Sarikanat (mehmet.sarikanat@ege. edu.tr). Journal of Applied Polymer Science, Vol. 102, 4554–4564 (2006) V V C 2006 Wiley Periodicals, Inc.