INVESTIGATION OF DAMAGE DETECTIONS ON GLASS/JUTE-EPOXY, GLASS- EPOXY AND JUTE-EPOXY COMPOSITE BEAMS

International Journal of Mechanical and Production Engineering Research and Development (IJMPERD) ISSN (P): 2249–6890; ISSN (E): 2249–8001 Vol. 10, Issue 3, Jun 2020, 401–408 © TJPRC Pvt. Ltd.

INVESTIGATION OF DAMAGE DETECTIONS ON GLASS/JUTE-EPOXY, GLASSEPOXY AND JUTE-EPOXY COMPOSITE BEAMS WITH AN EDGE CRACK USING MODAL ANALYSIS VENKATA SUSHMA CHINTA & P RADHAKRISHNA PRASAD Assistant Professor, Chaitanya Bharathi Institute of Technology(A), Hyderabad, India ABSTRACT Now a day, the use of composite structures is increased in many engineering fields, emphasis on detecting damages becomes crucial in recent times. Non-destructive methods gaining importance in this scenario, in which the damage in a structure is detected by the structure vibration characteristics. The property like stiffness of the laminate is dependent on modal parameters. So, any change in natural frequency of structure could be easily related to stiffness of structure by which the damage in the structure can be easily detected.

The present work is focused on damage detection method of cantilever beam with crack at edge, which has been studied using finite element method ANSYS. Three composite beams are taken for study. They are Glass-Epoxy beam,

analysis to distinguish between undamaged and damaged states. By varying crack depth at a location from fixed end and crack location from fixed end, the change in behavior of model like natural frequency is estimated using ANSYS. KEYWORDS: Glass-Epoxy Beam, Jute-Epoxy Beam, Glass/Jute-Epoxy Beam & ANSYS

Received: Mar 28, 2020; Accepted: Apr 18, 2020; Published: May 06, 2020; Paper Id.: IJMPERDJUN202037

Original Article

Jute-Epoxy beam, Glass/Jute-Epoxy Beam. The activity is then to observe the selected indicators derived from modal

1. INTRODUCTION Nayak [1] determined the natural frequencies of hybrid glass/carbon composite. By using fast Fourier analyzer, the experimental values are estimated which compared against ANSYS values. Douka [2] have used a method for finding the depth and location of crack in a beam having double crack and established that any variation on the size and location of the cracks effect a shift in the anti-resonance of the cracked beam. This method makes use of a Plexiglas to detect the location of crack and characteristic both analytically & experimentally. Crack can also be identified by using the variations in anti-resonance property and natural frequency. Cam [3] has investigated to anticipate the location of the crack and its depth in a cracked beam structure using impact echo method. The frequency signals obtained in crack free beam and cracked beam are studied & compared. Irshad [4] diagnosed cracked composite cantilever beam by measurement of vibration and for finding damage intensity and severity using Radial based function neural networks technique. Sanjay [5] studied frequency measurement for the diagnosis of damage in laminated composites. Abdeldjebar [6]did Vibration tests, which were useful to arrive the elasticity modulus in two directions. This technique is employed to materials of composite like glass / polyester.

Experimental results made on a specimen in free vibration showed the efficiency of this method. Obtained results were validated by a comparison to results stemming from static tests. Lee [7] has presented a paper based on nondestructive analysis to locate the crack. The lowest four frequencies of the crack structure are used by finite element method analysis. Then, Armors Rank ordering method is used considering the above four natural frequencies to obtain the approximate crack location. A FEM model have been developed applying the result of crack positioned www.tjprc.org

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range. This methodology adopted to determine the crack size. The actual crack locations are then determined by Gudrun son's equation using the determined crack size and aforementioned natural frequency. Liu[8] have applied a new technique called Gabor wavelet transform to the dispersive wave analysis for the detection of damage in a fibre embedded composite beam. The location of crack and depth of the crack are determined from the crack reflected wave. Heydari[9]carried out vibration analysis of a beam with an open edge crack using continuous model. Modified Galerkin projection method is used to solve the open edge crack. The obtained results were compared with FEA output. Soham[10]found defects in structure such as cracks, which could leads to severe damage of the structure with the time which necessitates identifying the crack extent of damage before failure without terminating the system.

There were numerous studies concerned with damage identification through the analysis of commonly measured modal parameters, particularly the mode shapes and frequencies, but not many of them deal with hybrid natural fibre reinforced composites.

2. PROBLEM FORMULATION Three composite beams are taken for analysis. They are Glass-Epoxy beam, Jute-Epoxy beam, Glass/Jute-Epoxy Beam. The dimensions of the cantilever beam taken for analysis are length 200mm, width 10mm and depth 20 mm is as shown in figure 1.

Figure 1: Cantilever Beam.

The variation of parameters like depth, location of crack had significant effect on the natural frequency of these composites. To find natural frequency, for each beam by varying the position of the crack from fixed end and by varying the depth of crack at each position the natural frequencies are found. Five positions of crack from fixed end are taken for analysis. They are 40 mm, 80 mm, 100 mm, 120 mm, 140 mm. The depth of crack at each location taken as 2 mm, 4 mm, 6 mm, 8 mm and 10mm.

Different cases of crack location and depth considered for each plate. So, for each plate total 26 cases are considered. For three plates together, 78 cases solved in ANSYS. A Cantilever beam area of required dimension is created in ANSYS. Element SHELL 181 is selected for analysis. Then, in shell lay-up number of layers is selected. The material properties for Glass-Epoxy and Jute-epoxy lamina are taken from [11], [12].For Glass-Epoxy beam 30 layers selected to make a thickness of 10 mm and each layer thickness is selected as 0.33 mm. Density of lamina is given as 1943 Kg/m3.

Then meshing is done. Modal analysis is done after giving boundary conditions. First 5 mode shapes and corresponding frequencies are noted.

For Jute-Epoxy beam 9 layers selected to make a thickness of 10 mm and each layer thickness is selected as 1.11 mm. Density of lamina is given as 1310 Kg/m3. Then, meshing is done. Modal analysis is done after giving boundary conditions. First 5 mode shapes and corresponding frequencies are noted.

Impact Factor (JCC): 8.8746

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Investigation of Damage Detections on Glass/Jute-Epoxy, Glass-Epoxy and Jute-Epoxy Composite Beams with an Edge Crack using Modal Analysis

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For Glass/Jute-Epoxy beam 15 alternate layers of Glass, Jute selected to make a thickness of 10 mm. Then meshing is done. Modal analysis is done after giving boundary conditions. First 5 mode shapes and corresponding frequencies are noted. For Cracked models stress concentration is defined at the crack tip using KSCON command as shown in figure 2, and it is found that total 16,488 elements are created. In ANSYS, the stress concentration at key point is given as follows:

Figure 2: Strees Concentration Defined at Crack Tip for Glass-Epoxy (Location 40mm Depth 10 mm).

3. RESULTS AND DISCUSSIONS The figure 3 to figure 7 shows mode shapes of Glass/Jute-Epoxy Un cracked beam. The first natural frequency is found from ANSYS as 143.57 HZ, Second natural frequency is found as 272.15HZ, third natural frequency is found as 880.39HZ.Fourth natural frequency is found as 1440.4HZ and fifth natural frequency is found as 1586.7HZ.

Figure 3: First Mode Shape of Uncracked Glass/Jute-Epoxy Beam whose Natural Frequency is 143.57 HZ.

Figure 4: Second Mode Shape of Uncracked Glass/Jute-Epoxy Beam whose Natural Frequency is 272.15HZ.

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Figure 5: Third Mode Shape of Uncracked Glass/Jute-Epoxy Beam whose Natural Frequency is 880.39HZ.

Figure 6: Fourth Mode Shape of Uncracked Glass/Jute-Epoxy Beam whose Natural Frequency is 1440.4HZ.

Figure 7: Fifth Mode Shape of uncracked Glass/Jute-Epoxy Beam whose Natural Frequency is 1586.7HZ. The Table.1 shows first 5 natural frequencies of uncracked Glass-Epoxy, Jute-Epoxy and Glass/Jute- Epoxy. It is observed from the table that the natural frequencies of Glass-Epoxy are more compared to Glass-Jute Epoxy and JuteEpoxy beams. Jute-Epoxy has lowest natural frequencies among the three. The Mode5 natural frequency of Glass-Epoxy beam is 1671.5Hz.The Mode5 natural frequency of Glass/Jute- Epoxy is 5% lower than that of Glass-Epoxy, whereas JuteEpoxy beam has 8% lower than Glass-Epoxy.

Table 1: Natural Frequencies of Uncracked Beams Glass/JuteGlass-Epoxy Jute-Epoxy Epoxy Mode1 147.15 131 143.57 Mode2 292.04 260 272.15 Mode3 899.24 811 880.39 Mode4 1464 1325.1 1440.4 Mode5 1671.5 1529 1586.7 3.1 Natural Frequency by Varying the Length and Depth is Constant The figure 8 shows variation of Mode1 natural frequency of the beams by keeping depth of the crack constant as 2mm and varying the position of the crack from fixed end. When compared to the un cracked Glass-Epoxy beam, the cracked GlassEpoxy beam at location 40 mm from fixed end having crack depth of 2mm loses its natural frequency by 10%, whereas GlassEpoxy beam with crack location at 160mm having depth of crack 2mm loses its natural frequency by 2% only. Similarly, the Impact Factor (JCC): 8.8746

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Investigation of Damage Detections on Glass/Jute-Epoxy, Glass-Epoxy and Jute-Epoxy Composite Beams with an Edge Crack using Modal Analysis

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cracked Glass/Jute-Epoxy beam at location 40 mm from fixed end having crack depth of 2mm loses its natural frequency by 10%, whereas beam with crack location at 160mm having depth of crack 2mm loses its natural frequency by 2% only compared to un cracked Glass/Jute-Epoxy beam. So, it is understood that the beam with crack near to free end is stiffer than the beam with crack near to fixed end. It is also found that among all the beams, Glass-Epoxy beam has highest natural frequency at all the locations of crack. Glass/Jute-Epoxy has natural frequency more than the Jute-Epoxy beam and less than the Glass-Epoxy beam. Jute-Epoxy beam has lowest natural frequency at all locations of crack.

Figure 8: Mode1 Natural Frequency vs. Location of the Crack from Fixed End. 3.2 Natural frequency by varying the depth and location of crack is constant: The figure 9 shows variation of Mode2 natural frequency of the beams by keeping location of the crack from fixed end constant as 40 mm and varying the depth of the crack from 2mm to 10 mm. It is observed from the graph that as the depth of the crack increases the natural frequency decreases. Among all, the beams Glass-Epoxy beam has highest natural frequency at all the depths of crack and Glass/Jute-Epoxy has natural frequency less than Glass-Epoxy beam. Jute-Epoxy beam has lowest natural frequency at all depths of crack.

Figure 9: Mode2 Natural Frequency vs. Depth of the Crack.

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4. CONCLUSIONS From the results, it is evident that when crack initiated in the beam its natural frequency decreases i.e., the stiffness of the beam decreases. In this paper finding of natural frequencies of cracked and un cracked Glass-Epoxy beam, Glass/JuteEpoxy hybrid composite beam, Jute-Epoxy beam is done successfully using ANSYS. With increase in depth of crack at any location from fixed end, the natural frequency decreases. If the location of crack is far away from the fixed end, then the natural frequency is more than as that of crack nearer to fixed end. Glass-Epoxy beam has more natural frequency at all crack positions and depths. Glass/Jute-Epoxy composite have natural frequency less than Glass-Epoxy beam and more than Jute-Epoxy beam. So, we can use glass fibre as partial reinforcement in place Jute fibre to increase the natural frequency of a structure.

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