R. Velmurugan

Experimental and analytical study of high velocity impact on Kevlar/Epoxy composite plates

In the present study, impact behavior of Kevlar/Epoxy composite plates has been carried out experimentally by considering different thicknesses and lay-up sequences and compared with analytical results. The effect of thickness, lay-up sequence on energy absorbing capacity has been studied for high velocity impact. Four lay-up sequences and four thickness values have been considered. Initial velocities and residual velocities are measured experimentally to calculate the energy absorbing capacity of laminates. Residual velocity of projectile and energy absorbed by laminates are calculated analytically. The results obtained from analytical study are found to be in good agreement with experimental results. It is observed from the study that 0/90 lay-up sequence is most effective for impact resistance. Delamination area is maximum on the back side of the plate for all thickness values and lay-up sequences. The delamination area on the back is maximum for 0/90/45/-45 laminates compared to other lay-up sequences.

Prediction of Properties of Coir Fiber Reinforced Composite by ANN

In the present study the mechanical properties of coir reinforced epoxy resin composite is predicted by using ANN approach. The experimental study by using short coconut coir fibers reinforced with Epoxy LY556 resin composite is reported in earlier studies. The coir fibers collected from Orissa, India, used in lengths of 5, 20 and 30 mm with 30 % fiber and 70 % matrix are used. Experiments conducted as per ASTM standards, and results of tensile, flexural, and impact strengths are reported. It is also reported that the fiber length is having significant effect on the properties of composites. The traditional experimental methods used in obtaining the properties of composites is expensive, require human resources, time consuming and human errors may occur. To reduce the above drawbacks, the present study is under taken to develop a weighted matrix between input (Fiber Length) and output (properties). ANN’s training and its testing are adopted to fix the appropriate weighted matrix which in turn prognosticates the appropriate mechanical properties of coir fiber reinforced epoxy resin composites. Similar trend in the variation of tensile strength, flexural strength and impact strength were obtained in the prediction using ANN and they compared well with the experimental results reported.

Prediction of Flexural Properties of Coir Polyester Composites by ANN

In the present study flexural strength of coir fiber reinforced polyester composite is predicted by using Artificial Neural Network. Randomly oriented coir fibers of length 10 mm were used to cast 3 mm, 5 mm and 6 mm thick specimens with fiber volume fraction of 10 %, 15 %, 20 % and 25 % respectively. The flexure tests were conducted as per ASTM D7264. From the experimental results it is observed that the flexural strength increased up to 20 % fiber volume fraction and then it decreased. Further flexural strength is found to increase with increase in the thickness of composite specimens also. Composite specimen of 5 mm thickness with 20 % fiber volume fraction recorded the highest flexural strength of 141.042 MPa. An Artificial Neural Network is adopted with supervised training approach to fix the optimum weighted matrix. Predicted results of flexural strength are also presented. Both the experimental and predicted results of flexural strength depict the similar trend. The error between predicted and experimental results is less than 5.00 %, hence Artificial Neural Network can be effectively adopted to prognosticate the flexural strength of coir fiber reinforced polyester matrix composites; which reduces the expensive manual involvement and its related errors during conduction of experimental programme. Artificial Neural Network results can be obtained quickly than the experimental results.

Effect of velocity and fibres on impact performance of composite laminates – Analytical and experimental approach

ABSTRACT In the present work, an analytical model is proposed to obtain the damage area of the composite laminates at below ballistic limit velocities. The model is based on the fact that total kinetic energy of the projectile is absorbed by different energy absorbing mechanisms taking place in laminates during impact. Depending upon the projectile velocity, some or all energy absorbing mechanisms observed are; fibre breakage, deformation of fibres, delamination, matrix cracking and cone formation on the back face of the laminates. The accuracy of the model is then assessed by comparing its predictions for damage area and specific energy absorption with the experimental values for two different types of fibres (glass and kevlar) as well as glass/kevlar hybrid combinations. Experimental results are also used to quantify and compare the specific energy absorption capacity of the glass/epoxy, kevlar/epoxy and glass/kevlar/epoxy laminates. It is observed that the glass/kevlar/epoxy laminates in which kevlar percentage is 27.5% w/w showed 20% improvement in specific energy absorption as compared to the glass/epoxy laminates.

Numerical and experimental study of multimode failure phenomena in GFRP laminates of different lay-ups

ABSTRACT Induced delamination due to low velocity impact results in degradation of load-carrying capacity of composite structures especially when loading is predominantly in compression. In this paper, size, shape and orientation of delamination that occur due to low velocity impact is obtained by numerical modelling and results are validated through experiments. Initially, numerical model is validated for single-mode fracture tests like double cantilever beam and end-notch flexure. Multimode failure phenomenon like low velocity impact was also simulated for different lay-ups such as cross-ply, angle-ply and quasi-isotropic and validated through experiments. Low velocity impact testing of laminates was done using drop weight impactor, and experimentally obtained force–time and energy–time history were compared with numerical results. Good match is obtained between simulations and experiments. Delamination size was also compared and it is found that numerical model correctly predicts the size, shape and orientation of delamination for all lay-ups.

A Study on Mechanical Properties of Raw Sisal Polyester Composites

Natural fibers are available in nature as byproducts of agricultural products of various countries around the world. It is observed that coir fibers is product obtained from coconut but jute and sisal fibers are obtained from plants grown in nature. These fibers are very abundantly available in nature can be used for structural construction practices. This increases the economic value of these fibers. In the present study an effort is made to study the mechanical properties of sisal fiber reinforced composite materials. In the present study, randomly oriented sisal fiber reinforced polyester matrix composite specimens of thicknesses 2 mm, 3 mm, 4 mm, 5 mm and 6 mm were fabricated by using hot compression moulding technique. Untreated sisal fibers of length 10 mm is used as reinforcement for casting the composite specimens. A mixture of polyester resin, methyl ethyl ketone peroxide and cobalt naphthenate of ratio 50:1:1 is used as matrix for the fabrication. Each composite panels of fiber volume fraction 10 %, 15 %, 20 %, 25 % and 30 % were tested for its tensile strength and flexural strength as per ASTM D-3039 and ASTM D-7264 respectively. From the experimental results it is observed that tensile strength and flexural strength were increasing up to 20 % fiber volume fraction and further found to be decreasing for fiber volume fractions of 25 % and 30 %. But in case of specimens of 6 mm thickness a small change in the trend of results is observed. The increase in tensile strength is found to be continuous up to 30 % of fiber volume fraction with a tensile strength of 22.938 MPa at 30 % fiber volume fraction.

Prediction of Properties of CRPCSC Particulate Composite by ANN

Determining the properties of Crushed Rock Powder, Cement, Sand and Coarse Aggregate (CRPCSC) particulate composite in a conventional way by conducting the experiments is time consuming and requires men and material. In the present study an effort is made to predict the spilt tensile strength and slump values of M20 and M35 grade CRPCSC particulate composite using artificial neural network (ANN). ANN is a computational model that is inspired by structure and functional aspects of biological neural network. ANN is used in many areas of research and development. In this study experimental results reported by earlier researchers are used. In the present study the spilt tensile strength and slump values of M20 and M35 grade CRPCSC particulate composite with different percentages of crushed rock powder replacement for sand is predicted. The results are also compared with conventional particulate composite (CSC) to find the optimum percentage of CRP replacement to sand. In the analysis, mix design proportion of CRPCSC particulate composite is used as input data to obtain the predicted values of split tensile strength and slump as output from ANN. Analysis of input and output data, network training, network testing and their validation is conducted and the results obtained from ANN analysis were comparable with the experimental results of CRPCSC report.

A Study on Mechanical Properties of Treated Sisal Polyester Composites

In the present study an attempt is made to determine the mechanical properties of sisal fiber reinforced polyester composites. Sisal fibers are the natural fibers obtained by processing the leaves of the sisal plants grown in nature. Sisal plant offers hard and strong strands of sisal fibers. The soft tissue of the sisal leaves is removed either physically or by using equipments. The fibers obtained are dried and brushed to remove the dirt left over to get the sisal fibers. In the present study, randomly oriented sisal fiber reinforced polyester matrix composite specimens of thicknesses 2 mm, 3 mm, 4 mm, 5 mm and 6 mm were fabricated by using hot compression moulding technique. 5% NaOH treated sisal fibers of length 10 mm is used as reinforcement for casting the composite specimens. A mixture of polyester resin, methyl ethyl ketone peroxide and cobalt naphthenate of ratio 50:1:1 is used as matrix for the fabrication of composite panels. Composite panels of fiber volume fraction 10%, 15%, 20%, 25% and 30% were casted and the test specimens were cut from the panels and tested for its tensile strength and flexural strength as per ASTM D-3039 and ASTM D-7264 respectively. From the experimental results it is observed that strength of tested specimens was found to show peak values at a fiber volume fraction of 20–25%.

Studies on shape memory alloy-embedded GFRP composites for improved post-impact damage strength

ABSTRACT Embedding shape memory alloys (SMAs) in composites is a promising method resistance against impact loading.In the present paper, an attempt is made to quantify the improvement in damage mitigation properties of FRP (fibre reinforced plastic)composites by embedding SMA.Numerical modelling of low velocity impact was carried out topredict the delamination in composites and composites embedded with SMA and steel wires. Through modelling, effect of location and quantity of SMA material in decreasing the impact induced delamination size was also studied.Compression after impact (CAI) tests were carried out on pristine and SMA hybrid composite (SMAHC)specimens to quantify the change in damage resistance. Experimental results show an improvement in compressive load-carrying capacity after impact in SMAHC as compared to pristine composites.Experimental results match well with numerical findings in terms of; location of placement of SMA wire and optimum quantity of SMA wires.

Buckling of thin walled composite cylindrical shell filled with solid propellant

This paper investigates the buckling of thin walled composite cylindrical tubes that are partially filled with solid propellant equivalent elastic filler. Experimental investigation is conducted on thin composite tubes made out of S2-glass epoxy, which is made by using filament winding technique. The composite tubes are filled with elastic filler having similar mechanical properties as that of a typical solid propellant used in rocket motors. The tubes are tested for their buckling strength against the external pressure in the presence of the filler. Experimental data confirms the enhancement of external pressure carrying capacity of the composite tubes by up to three times as that of empty tubes for a volumetric loading fraction (VLF) of 0.9. Furthermore, the finite element based geometric nonlinearity analysis predicts the buckling behaviour of the partially filled composite tubes close to the experimental results.