Prakash Chandra Gope

Silica—Styrene—Butadiene Rubber Filled Hybrid Composites: Experimental Characterization and Modeling

The mechanical behavior of epoxy matrix composites filled with nanosized silica particles and styrenebutadiene rubber is discussed. Scanning electron microscopy analysis and tensile test carried out at different crosshead speeds on the silicastyrenebutadiene rubber epoxy nanocomposites indicated the absence of particle aggregation and a reinforcing effect in terms of increased elastic modulus, yield, and ultimate strength. The results of wear test in pin-on-disc mode and hardness test on Rockwell R scale showed that the nanosized silica particles could improve the wear resistance of the epoxy matrix even though the content of the filler is at a relatively low level (1.02.0 wt%). This makes it possible to develop novel type of epoxy-based material with improved wear resistance for various applications. About 4070% increase in impact strength has been noticed due to addition of 0.51.5 wt% of styrenebutadiene rubber in 1.0 wt% silica-filled epoxy compos- ite. A good correlation between mechanical properties and weight contents of the filler materials, hardness and ultimate strength, and hardness and wear rate has been observed.The mechanical behavior of epoxy matrix composites filled with nanosized silica particles and styrene-butadiene rubber is discussed. Scanning electron microscopy analysis and tensile test carried out at different crosshead speeds on the silica-styrene-butadiene rubber epoxy nanocomposites indicated the absence of particle aggregation and a reinforcing effect in terms of increased elastic modulus, yield, and ultimate strength. The results of wear test in pin-on-disc mode and hardness test on Rockwell R scale showed that the nanosized silica particles could improve the wear resistance of the epoxy matrix even though the content of the filler is at a relatively low level (1.0-2.0 wt%). This makes it possible to develop novel type of epoxy-based material with improved wear resistance for various applications. About 40-70% increase in impact strength has been noticed due to addition of 0.5-1.5 wt% of styrene-butadiene rubber in 1.0 wt% silica-filled epoxy composite. A good correlation between mechanical properties and weight contents of the filler materials, hardness and ultimate strength, and hardness and wear rate has been observed.

Scatter Analysis of Fatigue Life and Prediction of S–N Curve

In this study, the effects of salt solution, the presence of notch on fatigue life scatter, and sample size selection for estimation of fatigue life under different probabilities and confidence levels have been investigated. Comparison has been made with smooth specimen tested in air medium. It is seen that notches have significantly higher effect than other factors (salt solutions, smooth geometry, etc.). The minimum number of specimens required for fatigue life estimation within tolerable error, Ro, at different fatigue testing conditions has also been presented both for log normal and Weibull distribution models. It has been found that estimation of fatigue life using Weibull model needs higher sample size than log normal model. Beyond a certain sample size, fatigue life estimation is independent of sample size. The article also presents a method for minimum sample size selection procedure to estimate fatigue life or to draw S–N curve.

Application of artificial neural network for predicting crack growth direction in multiple cracks geometry

Summary of predicted and experimental results. The crack growth under multiple cracks is highly influenced by neighbouring cracks.No mathematical relation is available to predict the crack initiation direction.ANN has been used to predict crack growth direction in multiple crack geometry.The effect of degree of input variables and hybrid combination of activation functions is studied.Nonlinear and linear activation functions are used through the one and two-hidden layer ANN.The experimental dataset as first or second degree were used.Higher order input variables are found to be more suitable. The objective of this study is to design an efficient artificial neural network (ANN) architecture in order to predict the crack growth direction in multiple crack geometry. Nonlinear logistic (sigmoid and tangent hyperbolic) and linear activation functions have been used through the one- and two-hidden layer ANN. 85 tests were conducted on aluminium alloys under different crack positions, defined by crack tip distance, crack offset distance, crack size, and crack inclination with loading axis. The experimental data set as first degree or second degree were used to train 22 proposed ANN models to predict the output for new data sets (not included in the training sets). The model results were then compared with the experimental data. It was observed that ANN model with combinations of activation functions and two hidden layers predict the crack initiation direction with good accuracy when higher order input variables are presented to the network.

Mode I fracture toughness of bio-fiber and bio-shell particle reinforced epoxy bio-composites

The effect of bio-fibres and bio-particles on the fracture toughness has been investigated. Epoxy resin is used as matrix material and different bio-fibers such as banana fiber, bagasse fiber, coconut fiber and particles such as silica and walnut shell particle with different wt% are added as reinforcing material. The mode I fracture toughness tests are conducted in a servo hydraulic universal testing machine. The results show that the fracture toughness of bio-composites reinforced with 20 wt% bagasse or 10 wt% coconut fiber are 1.108 MPa √m and 1.094 MPa √m, respectively which are about 8% and 7% higher than neat epoxy. Addition of 2 wt% of silica with 20 wt% of bagasse shows 60% increment of fracture toughness with respect to bagasse and 72% increment with respect to neat epoxy. Hybridisation of bagasse with banana fibers shows 54% decrease in fracture toughness as compared to bagasse and 13% increase as compared to banana. The overall fracture toughness of hybrid bio-composite of 10 wt% coconut fiber and 20 wt% of walnut shell particle is 1.367 MPa √m which is about 25% higher than coconut fiber reinforced bio-composite.

Experimental Evaluation of Mixed Mode Stress Intensity Factor for Prediction of Crack Growth by Phoelastic Method

Determination of stress intensity factors KI, KII, and constant stress term, σox is investigated. A theory of determining the stress intensity factors using photo-elastic method is formulated taking three stress terms. Three-parameter method of fracture analysis for determining the mixed mode stress intensity factors under biaxial loading conditions from photo-elastic isochromatic fringe data is used. A special biaxial test rig is designed and fabricated for loading the specimen biaxially. A simplified and accurate method is proposed to collect the data from isochromatic fringes. Taking specimen geometry and boundary conditions into account, regression models are developed for estimation of fracture parameters.

Influence of crack tip and crack offset distance on crack interaction and growth direction in multiple cracks

Purpose – This paper aims to deal with the study of interaction between multiple cracks in an aluminum alloy under static loading. Self-similar as well as non-self-similar crack growth has been observed which depends on the relative crack positions defined by crack offset distance and crack tip distance. On the basis of experimental observations, the conditions for crack coalescence, crack shielding, crack interaction, crack initiation, etc. are discussed with respect to crack position parameters. Considering crack tip distance, crack offset distance, crack size and crack inclination with loading axis as input parameter and crack initiation direction as output parameter, an artificial neural network (ANN) model is developed. The model results were then compared with the experimental results. It was observed that the model predicts the crack initiation direction under monotonic loading within a scatter band of ±0.5°. Design/methodology/approach – The study is based on the experimental observations. Growth ...

Evaluation of stress intensity factor of multiple inclined cracks under biaxial loading

A finite rectangular plate of unit thickness with two inclined cracks (parallel and non parallel) under biaxial mixed mode condition are modelled using finite element method. The finite element method is used for determination of stress intensity factors by ANYSIS software. Effects of crack inclination angle on stress intensity factors for two parallel and non parallel cracks are investigated. The significant effects of different crack inclination parameters on stress intensity factors are seen for lower and upper crack in two inclined crack. The present method is validated by comparing the results from available experimental data obtained by photo elastic method in same condition.

Fracture behaviour of epoxy biocomposite reinforced with short coconut fibres (Cocos nucifera) and walnut particles (Juglans regia L.)

Mixed-mode fracture characteristics of epoxy-based biocomposite reinforced with 20 wt% walnut shell particle and 10 wt% coconut fibres are investigated. The biocomposite is fabricated using the squeeze casting method. The positive aspect of hybrid combination of fibre and particle reinforcement is advocated by comparing mode I, mode II and mixed-mode I/II fracture surfaces under a scanning electron microscope. An edge-cracked semicircular arc specimen subjected to symmetric three-point bend (TPB) loading is suggested for fracture toughness testing of biocomposite material. A series of fracture tests are conducted on hybrid biocomposite using the proposed semicircular bend (SCAB) specimen geometry, TPB and four-point bend (FPB) specimens. The average mode I and II fracture toughness obtained from semicircular arc bend (SCAB) specimen are 1.319 MPa and 1.219 MPa m , respectively. The average values of modes I and II toughness obtained from TPB and FPB specimens are 1.267 and 0.754 MPa m . The overall ratio of mode I and mode II fracture toughness is found to be 0.762, which is very close to the predicted value of 0.87 by maximum tangential stress criterion. The results obtained from new SCAB geometry are validated with the results obtained from TPB and FPB specimen geometries by statistical significance test. Very good agreement is found between the experimental results obtained from TPB, FPB and the proposed SCAB specimens.

Water absorption and thickness swelling behavior of almond (Prunus amygdalus L.) shell particles and coconut (Cocos nucifera) fiber hybrid epoxy-based biocomposite

Abstract In this research, the suitability of almond shell and coconut fiber as a renewable agricultural residue for the manufacturing of biocomposite to be used as a replacement of wood was investigated. The use of agriculture waste as a reinforcement in composite may result in several environmental and socioeconomic benefits. A biocomposite containing different weight percentages of almond shell particle (10, 20, 30, 40, and 50 wt%) and coconut fiber (2, 4, and 6 wt%) mixed with 20 wt% almond shell particles was made using epoxy resin and 0.5 wt% tricresyl phosphate. The water absorption (WA), thickness swelling (TS), and morphology [scanning electron microscopy (SEM)] test of the biocomposite were determined. The rate of WA is less in saline water (SW) compared to rainwater (RW). The influence of the addition of coconut fiber is more compared with the almond shell particles for both the WA and TS.

Influence of crack offset distance on the interaction of multiple cracks on the same side in a rectangular plate

In the present work finite element method has been employed to study the interaction of multiple cracks in a finite rectangular plate of unit thickness with cracks on the same side under uniaxial loading conditions. The variation of the stress intensity factor and stress distribution around the crack tip with crack offset distance has been studied. Due to the presence of a neighbouring crack, two types of interactions viz. intensification and shielding effect have been observed. The interaction between the cracks is seen to be dependent on the crack offset distance. It is seen that the presence of a neighbouring crack results in the appearance of mode II stress intensity factor which was otherwise absent for a single edge crack. It can be said that the proximity of cracks is non-desirable for structural integrity. The von-Mises stress for different crack orientations has been computed. Linear elastic analysis of state of stress around the crack tip has also been done.