International Journal of Scientific Engineering and Science Volume 7, Issue 11, pp. 25-28, 2023. ISSN (Online): 2456-7361 25 http://ijses.com/ All rights reserved Effect of Polyester Resin Fraction and Sisal Fiber on Composite Tensile Strength Badaruddin Anwar 1 , Djuanda 2 , Muhammad Ansyarullah 3 1,2,3 Department Mechanical Engineering Vocation, Makassar State University, Makassar, South Sulawesi, Indonesia E-mail: badaruddin.anwar@unm.ac.id Abstract— Sisal fiber is a hard fiber produced from the extraction process of the leaves of the sisal plant. In this study, sisal fiber was used as a composite reinforcing material. This research aims to determine the effect of the composition of polyester resin and sisal fiber on tensile strength. This type of research is experimental research carried out by mixing polyester resin and sisal fiber. The dimensions of the tensile test specimens were made according to the tensile testing standard ASTM D 638 with three types of volume variations for polyester resin and sisal fiber, namely 90%: 10% for three specimens, 85%: 15% for three specimens, and 80%: 20% for three specimens. The number of specimens in this study was 9 specimens. The tensile testing equipment used is a Universal Testing Machine with type RF-2425. The tensile test results for a composition of 90% polyester resin and 10% sisal fiber showed a maximum stress of 22.993 N/mm2 and a strain of 2.245%. In a comparison of 85% polyester resin and 15% sisal fiber, a maximum stress of 37.931 N/mm2 and a strain of 2.342% were obtained. And in a comparison of 80% polyester resin and 20% sisal fiber, a maximum stress of 39.317 N/mm2 and a strain of 2.692% were obtained. So it can be concluded that the more the mixture of sisal fibers in the composite, the higher the tensile strength value of the composite. Keywords— Composite, Polyester Resin, Sisal Fiber, Tensile Strength. I. INTRODUCTION The use of materials applied as components in a structure is based on a high increase in mechanical properties. Engineers always carry out various research studies to engineer new materials that have better mechanical properties, such as new composite materials. Fiber-reinforced composites are the most widely developed type of composite. (Fahmi, et al, 2014). The Sisal plant (A. Sisalana L) is a plant whose stems and leaves are fused, has strong fibers, can live on thinly cultivated land (lots of surface stones) or is classified as critical land. The strength of sisal fiber is stronger than other fibers, and is resistant to high salt levels. Sisal plants mostly grow on chalky hillsides and dry climates. This plant is produced by Brazil as the largest producer of sisal in the world, China, Kenya, Tanzania, Managaskar, Indonesia and Thailand. Sisal plants in Indonesia are developed in Bali, Madura Island, South Malang, and in Sumbawa Regency. Farmers plant sisal plants on the sidelines with secondary crops such as corn, peanuts or soybeans. (Basuki, T. et al., 2017). A composite is an engineered material consisting of two or more materials where the properties of each material are different from each other, both chemical and physical properties and remain separate in the final result of the material. Composite materials have many advantages, including low specific gravity, higher strength, corrosion resistance and cheaper assembly costs. (Yunus et al. 2020). According to (Widodo et al. 2022) Composites are materials produced from mixtures made of two or more materials that combine different chemical and physical properties to produce new materials with different properties. The properties of composite materials are a combination of the properties of its constituents, namely matrix and fiber (reinforcement). These two properties have different functional roles, the fiber functions as a material reinforcement, and is called reinforcement, while the matrix functions as an adhesive for the fibers and assembles them into a solid material unit, because the fibers are bonded to each other. The mixture of the two produces a material that is hard, strong and light. Fiber has the property that it can be easily changed in shape by cutting or molding according to needs. The matrix material is generally resin, which binds the fiber material and forms a strong material. The main point of making composite materials is to improve the properties, especially the mechanical properties of the matrix. In making composites, fiber and matrix are needed. Fiber functions as a reinforcing element that determines the mechanical properties of the composite because it transmits the load transmitted by the matrix. Along with the increasingly rapid development of technology, it has encouraged the discovery of several alternative technologies as a way to meet society's needs, especially in materials, the materials needed are high quality materials and have high mechanical properties. Therefore, composite materials are being reintroduced using synthetic fibers combined with polymer materials as a matrix, the aim of which is to obtain high strength and stiffness. Based on the background of the problem, the researchers conducted research on the effect of the composition of polyester resin fractions and sisal fibers on the tensile strength of composites. II. RESEARCH METHOD The material used in the composite manufacturing process is a mixture of polyester resin and fiber. 1) Sisal fiber 2) Polymer fluid 3) Catalyst Determining variations in test specimens. Specimen variations used in this research, namely 1) 90% polyester resin : 10% sisal fiber