INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN ENGINEERING AND TECHNOLOGY (IJARET)

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1 INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN ENGINEERING AND TECHNOLOGY (IJARET) International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 ISSN (Print) ISSN (Online) Volume 3, Issue 2, July-December (2012), pp IAEME: Journal Impact Factor (2012): (Calculated by GISI) IJARET I A E M E FAILURE ANALYSIS OF PIN LOADED GLASS EPOXY/POLYSTYRENE COMPOSITE PLATES D.Lingaraju 1, *, K.Srinivas 2, B.A.Ranganath 2 1. Aditya Institute of Technology and Management, India (*Corresponding Author) 2. Maharaj Vijayaram Gajapati Raj College of Engineering, India ABSTRACT Composites are becoming an essential part of today s materials because they offer advantages such as low weight, corrosion resistance, high fatigue strength, faster assembly etc. Composites are used as materials in making aircraft structures to golf clubs, electronic packaging to medical equipment and space vehicles due to their good mechanical properties. In the practical use of the composite materials in structures, some geometrical discontinuities like cut outs and holes are necessary for some functions such as riveted and bolted joints. Therefore it is necessary to study the failure behaviour at these joints. In this study, behaviour of pin loaded laminated composite plates with different dimensions are observed experimentally. The aim is to investigate the stress and failure load and failure mode in laminated glass epoxy/polystyrene composite plates with one circular hole. The hole of the plate is subjected to a traction force by rigid pin. The analysis is then extended to find the effect of varying K/D and W/D. It is observed that the strength of the specimen increases with the increase in K/D and W/D to an extent and then becomes constant. W/D has a greater effect on the mode of failure. Keywords: Pin Load, Failure analysis, FRP, Epoxy, Polystyrene. INTRODUCTION Composite civil and mechanical structures are appearing more frequently in load-bearing applications because of their low cost, lightweight and environmental resistance. Low cost glass-fiber/plastic composites are used in the process industry when the environment is highly hostile and metal corrosion is a serious problem. In the practical use of the composite materials in structures, some geometrical discontinuities like cut outs and holes are necessary for some functions such as riveted and bolted joints. Therefore it is necessary to study the failure behaviour at these joints. For this reason and because civil structures are designed for 137

2 longevity, it is becoming increasingly important that engineers have tools to design composite structures for both life and strength. Typical failure mechanisms for the pin loaded-joint configuration are shown in Figure-1. The joint fails in one of these three modes or a combination of these. The strength of the joint is the least of normal, shearing and bearing strengths. The mode of failure depends on the type of strength which is the least. In general, failure of a joint means either the failure of the plate or the failure of the pin / joint. The normal mode of failure occurs for plate while shearing and bearing modes of failure occur either for plate or pin depending on which is weaker. In the present work, the pin is considered to be rigid and therefore the failure is considered only in the plate. (a) (b) (c) Figure-1: Modes of failure (a) Normal (b) Shear (c) Bearing FU-KUO Chang et.al. [1] Studied the progressive damage model for notched laminated composites subjected to tensile loading. The model is capable of assessing damage in laminates with arbitrary ply-orientations and of predicting the ultimate tensile strength of the notched laminates. The failure strength and failure mode of bolted connections of glass woven fabric composites was investigated by H.J.LIN et.al. [2]. the failure criteria and the material degradation model were successfully used to model the behaviour of laminates subjected to in-plane loads. They considered five types of failures: matrix failure in tension, matrix failure in compression, fiber failure in tension, fiber failure in compression and fiber- matrix debonding failure. Experimental results showed that laminates with moulded-in holes are stronger when the edge distance is small. When the edge distance is large, specimens with moulded-in holes have about the same strength as those with drilled holes. Camanho et.al. [3] developed a three-dimensional finite element model to predict damage progression and strength of mechanically fastened joints in carbon fiber-reinforced plastics that fail in the bearing, tension and shear-out modes. Aktas et.al. [4] investigated failure strength and failure mode of a mechanically fastened carbon-epoxy composite plate of arbitrary orientation. Bearing strength and failure modes were taken as functions of three variables: orientation angle of fibers, E/ D, and W/ D. By changing the value of one of the variables while keeping the values of the others constant, experimental and numerical analyses were performed. Dano et.al. [5] carried out analysis on single mechanically fastened joint in fiberreinforced plastics. A finite-element model was developed to predict the response of pinloaded composite plates. The model takes into account contact at the pin-hole interface, progressive damage, large deformation theory, and a non-linear shear stress-strain relationship. 138

3 Bulent Murat Icten et.al. [6] investigated the possibility of predicting the properties of the joint from the properties of the material measured with standard tests. A composite rectangular plate of length L+E and width W with a hole of diameter D, with a hole at a distance E, from the free edge of the plate was taken as the specimen. A rigid pin was located at the center of the hole and a uniform tensile load P was applied to the plate. A compression testing was applied to the specimen to fan-out failure in net tension, shear out mode, and bearing mode. A progressive damage model was applied which consisted of three: stress analysis, failure criteria, and property degradation rules. The two dimensional finite element method was used to determine the failure load and failure mode using Hoffman and Hashin criteria. The mechanical properties of the composite material were obtained from standard tests. Load displacement curves for various W/D, the effect of W/D ratio, and orientation on bearing strength were plotted and results were in close agreement with the experimental results. Okutan et.al. [7] performed an investigation to study the response of pin-loaded and laminated composites. Tensile tests were performed on E/glass epoxy composites for two different ply orientations such as [0/±45] s and [90/±45] s. For each ply orientation, 20 different geometries were chosen. The major focus of the study was to characterize the failure mechanisms and to evaluate the effect of geometric dimensions on the bearing, shear-out and net tension strengths of pinned joints. For this purpose, the specimens were tested to find first failure and final failure load. Tayfun Gulem et.al. [8] carried out a study to deal with the bearing strength, failure mode and failure load in a woven laminated glass vinyl ester composite plate with circular hole subjected to a traction force by a rigid pin. They investigated for two variables; the distance from the free edge of the plate to- the diameter of the hole (E/D) ratio and the width of rectangular plate-to-the diameter of the hole (W/D) ratio numerically and experimentally. The effects of preload moment, moisture and interference-fit on bearing strength and failure mode in pin-jointed and bolted carbon epoxy plates which were subjected to a traction force studied by Servet Kapti et al. Two different geometrical parameters, end distance to pin diameter ratio (E/D) and width to pin diameter ratio (W/D), were considered experimentally. E/D and W/D ratios were selected ranging from 1 to 4 and from 2 to 4, respectively. The test results showed that the ultimate failure loads were directly affected by the geometrical parameters, preload moments and interference-fit. Tsai-Wu criterion was used to determine bearing strength corresponding to first failure load [9]. Alaattin Aktas et al. [10] studied the Failure load and failure mode of glass-epoxy composite plates with single and double parallel pinned-joints have analysed experimentally and numerically. Two variables were investigated during analyses; the distance from the free edge of plate to the diameter of the first hole (E/D) ratio (2, 3, 4, 5), and the width of the specimen to the diameter of the holes (W/D) ratios (2, 3, 4, 5). The effect of the clearance and interference-fit on the failure mode, failure load and bearing strength of the pin-loaded joints subjected to traction forces are examined by Binnur et al. [11]. A failure investigation was performed to determine the failure mode and bearing strength of mechanically fastened bolted-joints in glass fiber reinforced epoxy laminated composite plates, experimentally. Two different geometrical parameters, the edge distanceto-hole diameter ratio (E/D) and plate width-to-hole diameter ratio (W/D) were considered. For this purpose, E/D ratio was selected from 1 to 5, whereas W/D ratio was chosen from 2 to 5. since an important target of this study was observed by Faruk Sen et al. [12] and reported the changing of failure mechanism under various preloads. 139

4 International Journal of Advancedd Research in Engineering and Technology (IJARET), ISSN 0976 With the above study it has observed that a progressive damage analysis consists of three important steps: stress analysis, application of failure criteria and degradation of material properties according to failure mode. EXPERIMENTAL STUDY In this study, composite materials rectangular plates (length L, Width W, Thickness t) made on fiber-reinforced woven rove mat with a circular hole filled with rigid pin is used. The diameter (D) of the hole is fixed at a constant value of 5mm. The hole is located along the central line of the plate at a distance K from end of the plate. A uniform tensile load P is applied to the plate. Load is parallel to the plate and is symmetric with respect to the central line. Thus, the load cannot create bending moments about X, Y, Z axis. The set up is shown in figure-2. Figure-2: Geometry of a laminated composite plate with circular hole Geometry parameters: specimen width (W) or ratio of width to hole diameter (W/D), edge distance(k)or ratio of the edge distance to hole diameter(k/d), Specimen thickness (t),hole ratio(d)and pitch for multiple joints and the Length of the plate is L. TESTING PROCEDURE To find the failure load and the failure mode, a series of experiments were performed. The specimens were trimmed as depicted in figure-3. The effects of the pin location were studied by varying the width to diameter (W/D) ratio from 3 to 5, edge distance to diameter (K/D) ratio from 1, 2 and between two holes distance to diameter (K/D) ratio from 1 and 2. The experiments were carried out in tension mode on the Universal Testing Machine. The lower edge of the specimen clamped and loaded from the steel pin by stretching the specimens at a ratio 0.5 mm/min is shown in Figure-3. The load pin displacement diagrams for all composite configurations were plotted. Figure-3: Experimental setup for pin joint testing and test specimens (epoxy/ polystyrene) 140

5 TESTING Take the specimen holder and place the specimen in the holder using the pins and place that one in the UTM machine to get the shear and tension properties of that specimen and the load that withstand the plate and the deflection are as tabulated. The specimens with varying K/D and W/D the specimen failure, the load at which it can withstand is observed and the graphs and the results are discussed. In the analyses the diameter of the hole and the thickness of the plate were taken as constant. To understand the failure behavior of specimens with K/D and W/D, a parametric study was done and presented in this Paper. Effect of variation in K/D The diameter of the pinhole is kept constant and the W/D, K/D are varied to find the failure load. The effect of W/D, K/D are studied by taking the diameter of hole as D = 5 mm and for each value of this diameter K/D is varied as 1 2, 3 whereas W/D is varied as 3, 4, 5. Here W/D is varied when K/D=2. This brings up 9 different specimen models obtained from combinations of W/D and K/D. Load is applied on each specimen model till failure takes place. The failure load and failure mode are noted. BEARING STRENGTH W/D =3 K/D epoxy Figure-4: Bearing strength Vs K/D at W/D=3 for epoxy and polystyrene Fig-4 to 6 shows the graphs plotted between the Bearing strength and K/D. The observations from this graph are as follows: Bearing strength of different specimens with same W/D, K/D is found to increase with increasing W/D. This is because of the change in the width of the specimen. As W/D increases, the failure mode will be normal and shear. Firstly, it will be normal and by increasing the W/D value, the normal becomes shear. The bearing strength will slightly increase and become constant. Bearing strength for a specific diameter value initially increases as K/D increases, and then almost becomes constant with further increase in K/D. keeping D as constant, when K/D increases, the distance of the hole from one edge of the plate increases i.e. the hole simply shifts its position away from the edge of the plate towards the centre of the plate. This increases the shear strength of the specimen. 141

6 BEARING STRENGTH W/D =4 K/D EPOXY Figure-5: Bearing strength Vs K/D at W/D=4 for epoxy and polystyrene. BEARING STRENGTH W/D=5 epoxy K/D Figure-6: Bearing strength Vs K/D at W/D=5 for epoxy and polystyrene Effect of variation in W/D The effect of W/D is studied keeping the diameter of hole as D = 5mm and for each value of this diameter W/D is varied as 3, 4 and 5. Initially K/D is kept constant at 1and W/D at 3. This brings up 9 different specimen models obtained from combinations W/D ratio. Load is applied on each specimen model till failure takes place. Bearing strength and failure modes are noted. Graphs are plotted between the failure load and W/D for different values of K/D. From these figures the following observations are made while in case of epoxy as the material of the plate the following conditions are observed As K/D=1 is kept constant and then increasing W/D value results in increasing of Bearing strength, as that increases slightly and then kept constant this will because that the varying in width of the specimen and D as constant. the failure mode of the specimen are normal and shear takes place As K/D=2 is kept constant and varying the distance between hole and edge then increasing W/D value, then Bearing strength will increase as that increases and becomes decrease slightly and then it fails. This is because of the varying in width of the specimen and the distance between edge and hole and D as constant. Bearing is the failure type of mode. 142

7 While in case of polystyrene as the material of the plate, the following conditions are observed As K/D=1 is kept constant, then increasing W/D value, then Bearing strength will increase as that increases slightly and then kept constant. This is because of the varying in width of the specimen and D as constant. The failure mode of the specimen are normal and shear takes place As K/D=2 is kept constant, then increasing W/D value, the Bearing strength will increase as that increases and becomes decrease slightly and kept constant This is because of the varying in width of the specimen and D as constant. The failure mode of the specimen is bearing. Table-1: W/D along bearing strength and failure mode Epoxy Bearing Strength Failure Mode Polystyrene Bearing Strength Failure Mode K= S W/D=3 K= S W/D=3 K= S K= B K= B K= B W/D=4 K= B W/D=4 K= B K= B K= B K= B K= B W/D=5 K= B W/D=5 K= B K= B K= B K= B+S K= B+S As compared to both the materials the strength is more to epoxy material and it can with stand high Bearing strength as compared to the polystyrene material composite plate CONCLUSIONS In the present work failure analysis on double pin loaded glass epoxy/polystyrene composite plates is performed for different values of E/D, K/D, and W/D. The following conclusions are drawn from this analysis. The analysis to find the effect of varying K/D and W/D. It is observed that the strength of the specimen increases with increase in K/D and W/D to an extent and then becomes constant. W/D has a greater effect on the mode of failure. The failure load of the specimen increases with increase in K/D as a result of increase in edge distance of the specimen and becomes constant for higher values. The failure load of the specimen increases with increase in K/D as a result of increase in edge distance of the specimen and becomes constant for higher values. As W/D increases the failure load initially increases then decreases or becomes constant as a result of increasing stress concentration factor. As the thickness of the specimen increases the failure load increases as a result of increase in cross sectional area of the specimen. 143

8 REFERENCE 1. Fu-Kuo Chang, Kuo-Yen Chang, (1987) A Progressive Damage Model for Laminated Composite Containing Stress Concentrations. Journal of Composite Materials, 21, H. J. Lin & C. C. Tsai, (1995) Failure Analysis of Bolted Connections of Composites with Drilled And Moulded-In Hole, Composite Structures, 30, P.P. Camanho and F.L. Matthews, (1999) A Progressive Damage Model for Mechanically Fastened Joints in Composite Laminates, Journal of Composite Materials, 33(24) AlaattIcn Aktas, Ramazan Karakuzu, (1999) Failure Analysis of Two- Dimensional Carbon-Epoxy Composite Plate Pinned Joint, Mechanics of Composite Materials and Structures, 6, Marie-Laure Dano, Guy Gendron and Andre Picard, (2000) Stress and Failure Analysis Of Mechanically Fastened Joints In Composite Laminates, Composite Structures, 50, Bulent Murat Icten and Ramazan Karakuzu, (2002) Progressive Failure Analysis of Pin- Loaded Carbon Epoxy Woven Composite Plates, Composites Science and Technology, 62, Buket Okutan and Ramazan Karakuzu, (2003) The Strength of Pinned Joints in Laminated Composites, Composites Science and Technology, 63, Ramazan Karakuzu, Tayfun Gulem, Bulent Murat Icten, (2006) Failure Analysis of Woven Laminated Glass Vinylester Composites with Pin-Loaded Hole, Composites Science and Technology, 72, Servet Kapti, Onur Sayman, Mustafa Ozen, Semih Benli, (2010) Experimental and numerical failure analysis of carbon/epoxy laminated composite joints under different conditions, Materials and Design 31, Alaattin Aktas, Huseyin Imrek, Yusuf Cunediog lu, (2009) Experimental and numerical failure analysis of pinned-joints in composite materials, Composite Structures 89, Binnur Gören Kiral, (2010) Effect of the clearance and interference-fit on failure of the pin-loaded composites, Materials and Design 31, Faruk Sen, Murat Pakdil, Onur Sayman, Semih Benli, (2008) Experimental failure analysis of mechanically fastened joints with clearance in composite laminates under preload, Materials and Design 29,

Three Dimensional Finite Element Analysis of Layered Composite Plate with Elastic Pin under External Uniaxial Loading

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