International Journal Metallurgical & Materials Science and Engineering (IJMMSE) ISSN 2278-2516 Vol. 3, Issue 3, Aug 2013, 15-22 ©TJPRC Pvt. Ltd.
STRESS ANALYSIS IN COTTON POLYESTER COMPOSITE MATERIAL
VIJAYKUMAR CHAUDHARY & PIYUSH P GOHIL Department of Mechanical Engineering, Chandubhai S Patel Institute of Techology, Charotar University of Science and Technology, Changa, Gujarat, India
ABSTRACT
Composites are one of the most advanced and adaptable engineering materials. This paper presents results from experimental work on Cotton Polyester Composite (CPC) made from polyester resin reinforced with cotton fibers. The results from this study revealed that the structural performance of cotton fiber composites is satisfactory and may be used for structural application. ANSYS software packages, based on the Finite Element Analysis (FEA) is used to predict stress distribution.
KEYWORDS: Cotton Polyester Composite (CPC), Finite Element Analysis (FEA), Tensile Testing
INTRODUCTION
Fiber-reinforced polymer composites have played a dominant role for a long time in a variety of applications for their high specific strength and modulus. The interest and development of composites making use of natural fibers, aimed for structural applications, is growing from a long-term sustainable perspective. A prime reason for selecting natural fibers for new products is that the net contribution to the greenhouse effect is minimal [1]. Natural fibers are classified into three categories. These are plant fibers, animal fibers and mineral fibers. Plant fibers are important types of natural fibers and these are generally comprised mainly of cellulose, hemi-cellulose, lignin, pectin. Prominent natural fibers are cotton, jute, flax, ramie, sisal and hemp. Cellulose fibers are mainly used in manufacturing of paper and cloth. This fiber is categorized into seed fibers, leaf fibers, bast fiber/ stem fiber, fruit fiber, stalk fiber [2]. From an environmental perspective, natural fibers are biodegradable and are carbon positive since they absorb more carbon dioxide than they produce [3]. It is producible with low investment at low cost, which makes the material an interesting product for low-wage countries [4]. So, the use of natural fiber composites starts gaining popularity in engineering applications [5]. This is due to the fact that this material possesses characteristics that are comparable to conventional materials. The possibilities of utilizing natural fibers are being realized and as a result there are numerous examples where natural materials have found application in a number of diverse sectors from automotive and construction industries, to leisure based products [6]. Among all natural fibers, cotton is well known for its excellent absorbency, comfort properties, and natural feel [7]. Cotton fibers are the most important natural vegetable textile fibers used in spinning to produce apparel, home furnishings and industrial products [8]. Reclaimed cotton is mainly used as a low cost fiber to “fill” composites used as interior parts in the automotive industry [9]. According to Karus et al. [10] in 2003 approximately 45,000 t of reclaimed cotton fibers were used in the German automotive industry for interior applications. Cotton fiber is a lightweight, eco-friendly, and bio-degradability material. Although strength properties are somewhat lower than carbon fiber and it is less stiff but it is typically far less brittle and the raw materials is much less expensive. Looking to the inadequate data availability for cotton fiber composites the area need to be focused with in depth study [11]. Therefore, it is decided to procure cotton fiber from local market to carry out experimentation.
Tensile Tests are performed for several reasons. The results of tensile tests are used in selecting materials for engineering applications. Tensile properties frequently are included in material specifications to ensure quality. These 16 Vijaykumar Chaudhary & Piyush P Gohil properties often are measured during development of new materials and processes, so that different materials and processes can be compared [12]. The characteristic obtained from tensile tests are used both for material characterization and for estimations of load-carrying capacity [9].
Stress analysis is a complicated and repeated routine work. Even an experienced engineer cannot avoid taking much time in routine calculating [13].With the advancement of computers, finite element analysis has become one of the most important tools available to an engineer for design analysis. The finite element analysis is one of the most general procedures for solving complex analysis problems [14].
The aim of the present study is to examine the basic mechanical properties through experimental testing and FEA simulation. Useful results are gathered for composites with cotton fiber tested in tension.
COMPOSITE PREPARATION
The composite material used in this research was prepared using cotton fiber woven mats of 0.5 mm thickness as reinforcement. The matrix material was polyester resin. Looking to the relative advantages and qualities of polyester resin [15] and ease of availability in nearby market vicinity polyester have been selected. The plate specimens were fabricated using the hand lay-up process. In order to accelerate the curing process the accelerator (Cobalt) and Methyl Ethyl Ketone Peroxide (MEKP) as binder were added in a proportion of 1% on volume base. The curing for composite specimen plate was carried out at room temperature and was allowed to cure for 24 hours. Figure 1 shows the prepared composite plate. The nominal value 11.91% of fiber weight fraction was achieved for the prepared CPC.
Figure 1: Prepared CPC Plate TEST SPECIMENS
The dimensional detail of prepared test specimen is given in Figure 2. The CPC specimens were produced as per ASTM standards ASTM D638-90 (165mm x 19mm x 2.6 mm) for tensile tests as shown in Figure 3 [16].
Figure 2: Dimensional Detail of Prepared Specimen as Per ASTM 638-90 Stress Analysis in Cotton Polyester Composite Material 17
Figure 3: Developed CPC Specimen TEST METHOD
The tensile tests were conducted on Instron 3382 Machine. These tests were carried out on specimens (165mm x 19mm x 2.6 mm) at room temperature. Specimens were placed in the grips and were and pulled until failure. The test speed was 5mm/min as per ASTM standards ASTM D638-90 [16] and laser extensometer was used to determine the elongation and tensile modulus. Each specimen was clamped in grips and loaded by uni axial tension.
Deformation in the middle part of the specimen was recorded by laser extensometer. Figure 4 shows the tensile testing apparatus for the various composites. During this process the mechanical properties, such as tensile strength, elongation and modulus of elasticity were determined.
Figure 4: Experimental Setup for Tensile Testing EXPERIMENTATION
To determine the required mechanical properties of CPC material, the tensile tests were performed. Table 1 shows result obtained from tensile testing of five CPC specimens. From the experimental result, Maximum tensile strength of CPC is 42.10 MPa and tensile modulus is 4.22 GPa. Load–Extension curves were recorded during the tests. Figure 5 shows tensile failure of five CPC specimens. Maximum Breaking load values obtained for five CPC specimens are presented in Figure 6. It shows that Specimens breaks at 141.95 kgf (mean value). To calculate the Maximum tensile strength following equation was used [17]. 18 Vijaykumar Chaudhary & Piyush P Gohil
σmax = Pmax/A
where:
σmax = maximum tensile strength, MPa
Pmax = maximum load prior to failure, N
A = average cross-sectional area, m2
Figure 5: Tensile Failure of CPC Specimens
Figure 6: Load - Extension Graph for Tensile Test Table 1: Result from Experiment of Tensile Testing for Five CPC Specimens
Max. Tensile Max. Tensile Specimen Strength Breaking Modulus No. (MPa) Load (N) (GPa) 1 39.58 1303.69 6.13 2 42.27 1326.54 1.78 3 39.09 1303.99 2.70 4 42.88 1440.30 5.01 5 46.66 1585.44 5.49 Mean 42.10 1392.05 4.22 Stress Analysis in Cotton Polyester Composite Material 19
FINITE ELEMENT ANALYSIS
Finite Element Analysis is a mathematical representation of a physical system comprising a part/assembly (model), material properties, and applicable boundary conditions (collectively referred to as pre-processing), the solution of that mathematical representation (solving), and the study of results of that solution (post-processing). It is one of the most general procedures for solving complex analysis problems.
The stress analysis in the field of structural mechanics is invariable complex and for many of the engineering problems; it is extremely difficult and tedious to obtain analytical solutions. In this situation, most of the practical problems are solved by numerical analysis, which provide approximate but acceptable solutions [18].
In this paper, for the linear static stress analysis, software package ANSYS was used. For performing finite element analysis the material was considered to be isotropic in nature and the boundary condition and load conditions applied as shown in Figure 7. The element type used for analysis work was shell 181-node 4 and the values of young modulus and poisson ratio were taken from Table 2 for material modeling. The nodal solution of tensile test by using ANSYS is shown in Figure 8.
Table 2: Mechanical Property of CPC Composite Materials [19, 20]
Mechanical Young Modulus Poisson Properties (GPa) Ratio Value 5.46 0.35
Figure 7: Boundary Condition Applied to the Model
Figure 8: Stress Distribution in the Model RESULTS AND DISCUSSIONS
Comparing experimental and FEA results, it is found that 7.39% percentage error exists. Results revealed that tensile results for numerical analysis are slightly differ from experimental results as shown in Table 3. This deviation of results occurred may be due to assumptions of material modeled as an isotropic, meshing limitation and manufacturing defects of composites like blow holes, porosity etc.
Table 3: Maximum Stress Values Max. Stress Parameters (MPa) FEA Value 45.46 Experimental Value 42.10 20 Vijaykumar Chaudhary & Piyush P Gohil
CONCLUSIONS
A Finite element analysis was carried out to determine tensile strength of CPC. With 7.39% deviation from experimental value, it is satisfied methodology of FEA for stress analysis for CPC. Due to good tensile strength of CPC, it may be employed to structural applications and also applicable for acoustic panels as use of cotton fibers in CPC.
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