Issue 46

G. B. Manjunatha et alii, Frattura ed Integrità Strutturale, 46 (2018) 14-24; DOI: 10.3221/IGF-ESIS.46.02 15 I NTRODUCTION merging environmental awareness and social concern, the unmanageable consumption of petroleum, and new system demands for eco- friendly materials with economic. Fiber-reinforced composite materials have some advantages such as high stiffness, relatively good resistance to environmental actions, recyclable, fatigue and failure resistance, etc. [1]. The natural fibers are a large amount of moisture absorbed. The absorption of water in a polymeric matrix is a volumetric diffusion process which follows the Fick’s law [2]. It’s an important issue nature life when composite materials are subjected to both mechanical loadings and exposed to severe environmental conditions [3]. In recent developments, the laminated polymer matrix composite materials are being extensively used in extreme environments. Correspondingly needs to be characterizing the fracture toughness over environmental conditions. This behaviour has been interrelated to the effect of moisture on matrix ductility, an amount of matrix deformation and the size of the plastic zone around the crack tip that occurs during fracture [4]. For fiber-reinforced composite materials, the interlaminar and/or intralaminar interface will have a great effect on their fracture mechanisms. The interface is probably the weakest part of a fracture process. Hence, the enhancement of interface behaviour is even more important [5]. The advance of fracture mechanics tests methods for the determination of delamination resistance or fracture toughness of fiber-reinforced polymer matrix composites is an active area of research [6]. Many machine elements have failed in the form of holes, notches, or cracks that are very significant factors influencing stress distributions in the structures. In such cases, stress cannot be defined as a strength parameter. Mechanical systems are designed by using the fracture mechanics' parameter as fracture toughness and can be used during the determination of the material strength against crack growth under external loads [7]. The increased use of polymer composites also requires the understanding of the fracture behaviour. Evaluation of damage and prediction of residual strength and fracture toughness is critical because the deboned can grow in an unstable manner and finally leads to catastrophic failure [8]. Fiber-reinforced composites used structural materials. Since these structures are to be used under some environmental conditions. It’s necessary for understanding the environmental effects on the fracture toughness and deformation behaviour to prevent damage to the structure. Among the many different kinds of environmental effect, the hydrothermal effect is one of the most important issues for polymeric composites [9]. Taguchi methods are statistical methods developed by Grenichi Taguchi to improve high-quality products at a low-cost [10]. By using the Taguchi techniques, industries are able to greatly reduce cycle time for both design and production. The objective of this technique is to optimize the settings of the process parameter values for improving performance characteristics. The design of parameters is the key step in the Taguchi method [11]. Design of Experiment (DOE) is one of the extensively used methods for experimental study. DOE is a statistical approach in which a mathematical model is established through experimental results. The trial data were developed in a pattern of L9 Orthogonal Array (OA) So possible output can be predicted based on the input parameters of the experimentation. Results can be analysed by using analysis techniques such as ANOVA and linear regression [12]. Experimental results are shown by plotting response surface methodology (RSM) graph. M ATERIALS AND EXPERIMENTAL METHODS Specimen Preparation he specimens used in the present study were fabricated using a hand lay-up technique. Main materials are jute fiber and epoxy polymer. The 40% of volume fraction as matrix material used is a medium viscosity epoxy resin (LAPOX L-12) and a room temperature curing hardener (K-6). It provides excellent resistance to alkalis and good adhesive properties [13]. Jute fiber of 60% used as reinforcement by volume fraction in this composite material. The specimens were dipped in seawater about 7, 14, 21 days. Fracture Testing The experiment was conducted on a computerized universal testing machine (UTM). For ENT, loading fixtures are used on the specimen to maintain a tensile load on the crack tip is uniaxial. The load was applied eccentrically to the specimen. Hence the fixture freely allows the material to rotate interns reduces the torsion effect. The crack will propagate across the laminate. For SENB, Specimen was placed in between the two jaws of the testing machine the dial gauge of extensometer and vernier scale which as placed on the vertical column of the machine must be set to zero. The Precracked specimen was loaded at the center of the specimen with suitable loading device. There are five trails were conducted for each condition of the specimen. E T