Browsing by Author "Bisht, Neeraj"
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ThesisItem Open Access Analysis of unsymmetrical cracks emanating from a circular hole placed centrally in a thin plate using FEM(G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand), 2021-02) Nisha Rani; Bisht, NeerajAlmost all of the structural failures occur due to cracks propagation. Holes, cavities, inclusion are perfect site for crack nucleation and growth ultimately leading to fracture. However, holes are sometimes inevitable in structures to provide some functionality. In the present study an investigation has been made to ascertain the parameter that would play a role in failure of structures if cracks emanate from these holes. A plane stress condition is assumed. Finite element method is used. Different like and alike cracks emanating from a hole have been studied. The effect of various parameters like crack inclination angle, crack length ratio, hole diameter and biaxiality factor have been studied. The presence of a secondary crack has two type of effect viz. intensification and shielding. The increase in the crack inclination angle of secondary crack changed the mode of loading from mode I to mode II. The value of mode I SIF for crack tip A increases significantly as the hole diameter increases from 1 to 3mm. The decrease in mode II SIF is seen to be phenomenal as diameter (d) of hole increases to 2mm. After 2mm diameter, mode II SIF further increases significantly producing intensification effect. At d=3mm, mode I is 0.60 times mode II. The hole diameter has greater impact as both stress intensity factor continuously increases. It can be concluded that hole diameter is going to play a critical role in determining structural integrity. The value of mode I decreases significantly of crack tip A as the crack length ratio is increased from 0.5 to 1.5. Whereas mode II stress intensity factor decreases to a2/a1=1. When both the crack tips A and B are further apart from each other stress intensity factor decreases. The value of mode I and mode II stress intensity factor decreases significantly as the crack length ratio (a2/a1) is increased from 0.5 to 1.5. Since these kind of scenarios are almost certain to happen in structures, the findage may help in ascertaining the life before failure and the mechanism associated is to take the necessary steps before any unfortunate incident happen.ThesisItem Open Access Effects of crack branching on fracture parameters under biaxial static loading(G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand), 2019-09) Saxena, Harshit Kumar; Bisht, NeerajThesisItem Open Access Effects of randomly oriented secondary cracks on the fracture parameters in a rectangular plate under static loading(G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand), 2019-08) Ansari, Gulfam Akhtar; Bisht, NeerajIn the present work, a numerical study using finite element is performed to investigate the effects of randomly oriented secondary cracks on the fracture parameters in a rectangular plate under static loading. Crack is damage that often occurs in members of structures and may cause the sudden serious failure of the structures. The effects of the presence of crack on fracture parameters like stress intensity factor and T-stress of specimen has been the subject of various investigations. However, the parametric studies like the effect of crack offset distance, crack size, orientation and number of crack present on the fracture parameters of the specimen are scarce in the literature. The finite element software ANSYS is used to simulate the fracture parameters. Numbers of studies were conducted to study the accuracy of ANSYS and the meshing parameters on which the accuracy depends. Two types of crack geometries were considered viz. parallel cracks and inclined cracks with different crack ratios. Also, the effect of several secondary cracks was studied. The presence of secondary cracks induced a shielding effect on the primary crack. The presence of secondary crack results in the development of mode II SIF. The mode mixing, however, was minimal and the mode II SIF was insignificant compared to mode I SIF. It is observed that when the cracks are closer to each other the shielding effect is high and as the cracks move away the shielding effect decreases. With the increase in inclination angle intensification effect is decreases. The shielding was also higher for a greater number of neighbouring cracks. Higher length of secondary cracks also increased the shielding effect. A correlation between SIF and T stress was also developed and it was seen that they are highly correlated. T stress can also be an important alternative fracture parameter to study crack interaction problems. Statistical analysis was performed to study the impact of various parameters in comparison to each other for all the geometries it was seen that the crack offset distance has a major influence on SIF compared to the crack ratios. Also, inclined cracks were seen to have a profound impact on SIF compared to parallel cracks. Multi-site damage is a common occurrence in aircraft and nuclear industries and the results of the study can contribute to accessing the structural integrity of the structure and estimate the in-service life of the component.ThesisItem Open Access Experimental and numerical investigation into the effect of cracks offset distance and crack length ratios on the fatigue life of Aluminium alloy 7075(G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand), 2022-02) Rathi, Aditi; Bisht, NeerajAA7075 is a widely used material in various industries like automotive and aircraft. Failure of material in these applications can cause a great loss of life. It has been observed that multiple side damage is a common occurrence in these applications and it becomes important to study the interaction of these kinds of multiple cracks. In the present study, the fatigue life of AA7075 has been observed and its variation due to the crack-offset distance and crack length ratio was analyzed. Fatigue tests were conducted on specimens prepared according to the standard ASTM E647. FEM was used for the determination of stress intensity factor. SED criterion was used to evaluate the direction of the crack propagation. It was observed that specimen having multiple cracks have higher fatigue life than that of specimen with single crack. Specimen with lower crack-offset distance and similar crack length has the highest fatigue life because of the shielding effect present between the two parallel cracks. As the crack tips starts moving far from each other, interaction starts diminishing. Von-Mises distribution and plastic zone size were studied, based on which it was again observed that specimen having lower crack-offset distance and similar crack length have lower von-Mises distribution and larger plastic zone size. This again concludes that specimen with nearer cracks of similar length have highest fatigue life.ThesisItem Open Access Optimization of resistance spot welding process parameters for cold rolled mild steel lap joint based on tensile shear strength(G. B. Pant University of Agriculture and Technology, Pantnagar, 2022-10) Pankaj Kumar; Bisht, NeerajOwing to its numerous applications weld characteristics of cold rolled mild steel grade IS 513 CR 1 was investigated. Resistance spot welding, one of the most versatile welding technology was used for the purpose. The three most important parameters of the RSW namely welding current, welding time and electrode pressure were varied and the influence on the Tensile Shear Strength (TSS) was evaluated. The experiments were carried out according to Taguchi's L9 orthogonal array and Taguchi analysis was used in optimization. A lap joint of dimensions 120mm x 30 mm x 1.5mm was welded using a 100 kVA timer, current-controlled CSP-100PR Spot Welder, to create an overlap of 3 mm thickness. According to Taguchi’s L9 OA welding current cycles of 5, 10 and 15 were selected. During the welding process, the welding current was changed by adding 2 kA from 10 to 14 kA and the electrode pressure were taken to be 4, 5 and 6 bar. The Main effects plots revealed the optimal setting for the process parameters as welding current of 14 kA (Level 3), welding time of 15 cycles (Level 3), and electrode pressure of 4 bar (Level 1). The optimized process parameters showed the maximum TSS of the spot weld joint. ANOVA was carried out to identify the significant process parameters affecting the weld strength. Furthermore, the contribution of welding current was found to be 67.38% which had the maximum influence on the TSS of the welded joint. The contour plots showed that on increasing welding current and welding time with decreasing electrode pressure the Tensile Shear Strength of lap joint was increased by 55.78%, 26.27% and 33.65% respectivelyThesisItem Open Access Thermo-mechanical characterization of rice husk and rice husk ash reinforced epoxy bio-composite(G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand), 2015-06) Bisht, Neeraj; Gope, P.C.Use of natural fibre along with polymeric matrix has been vigorously pursued in the last decade because of their advantages of being environment friendly, biodegradable and economical. However the inherent hydrophilic nature of fibres and hydrophobic nature of polymers pose compounding difficulties leading to non-uniform dispersion of fibres in matrix consequently leading to decrease in efficiency of composites. However these compounding difficulties can be overcome by certain modifications which can make the fibre and the matrix more compatible. In the present work rice husk along with epoxy resin has been used to develop a composite material. To reduce the inherent conflicting nature of resin and rice husk, rice husk fibres are pre-treated with NaOH. Furthermore effect of addition of another reinforcement rice husk ash on the mechanical and physical characters of the composite has been studied. Addition of rice husk to the resin results in deterioration of various mechanical properties due to the natures of the two constituents discussed above. However the decrease in mechanical strength up to 20 wt% reinforcement is insignificant and statistical analysis shows that 10 wt% and 20 wt% reinforced composites have similar behaviour. Keeping in mind the economical and environmental advantages of replacing larger quantity of polymer RH reinforcement of 20% by weight has been taken as optimum filler loading. Further to make fibre and matrix compatible, rice husk particles are pre-treated with NaOH solution of different concentration. It is observed that NaOH treatment has profound impact on the mechanical properties. However excessive deterioration of fibres at higher levels of NaOH concentration (higher than 8%) results in decrease in mechanical strengths. Silica addition also improved the properties marginally when silica was added in smaller quantities of 0-1%. At higher filling levels there was reduction in mechanical strength. SEM tests were conducted to predict the mechanism behind the changes that occurred in properties at every stage of work. The present work can provide an insight into the application of rice husk and product of its thermal degradation for developing bio-composites which are more environment friendly and at the same time have superior properties than the polymeric materials which have unfortunately become an integral part of our day to day life.