Vela Murali

Mechanism of Weld Formation during Friction Stir Welding of Aluminum Alloy

The present work aims at identification of process parameters for sound weld and to understand the mechanism of material matrix movement and weld formation in friction stir welding (FSW) of aluminum alloy. FSW experiments were conducted on 6 mm thick AA6061-T6 plates using various rotational and welding speeds. The welded plates were cut along the transverse direction to examine the macro defects. The defect size as a function of welding and rotational speed has been studied, and three parameter zones were identified. They are insufficient material flow zone, defects free zone, and excessive material flow zone. The sound zone is identified in the moderate rotational speed range for each welding velocity that occurs between the insufficient and excessive material flow zone. In the insufficient material flow zone, the defect size is found to be inversely proportional to rotational speed, whereas in the case of excessive material flow zone the defect size is directly proportional to rotational speed. As welding velocity increases, rotational speed is to be increased proportionally to form a sound weld. The relation between weld parameters, temperature, matrix movement, and weld formation has been established.

Tension and Compression Strength Evaluation of Composite Plates with Circular Holes

Modifications were made in the well-known inherent flaw model as well as in the stress fracture models namely, point stress criterion and average stress criterion for accurate prediction of notched tensile and compressive strength of composite laminates containing holes. The adequacy of these modified fracture models were examined by considering the fracture data of center-hole specimens made of carbon/epoxy composites, weft-knitted glass fiber composites, and pultruded composites. Any one of these three fracture models can be utilized to predict the notched strength.

Thermal model for friction stir welding of mild steel

Purpose – The purpose of this paper is to propose a three‐dimensional thermal model for friction stir welding of AISI 1018 mild steel to predict the thermal cycle, temperature distribution, the effect of welding parameters on power required, heat generation and peak temperature during the friction stir welding process.Design/methodology/approach – The mathematical expressions for heat generation during the friction stir welding process were derived. The simulations for various welding and rotational speeds were carried out on ANSYS software employing temperature and radius dependent moving heat source and applying the boundary conditions.Findings – The predicted thermal cycle, torque required and temperatures were found to be in good agreement with the experimental results. The heat generation and peak temperatures were found to be directly proportional to rotational speed and inversely proportional to welding speed. The rate of increase in heat generation and peak temperature were found to be higher at l...

Finite Element Analysis and Notched Tensile Strength Evaluation of Center-Hole 2D Carbon/Carbon Laminates

Finite element analysis (FEA) has been carried out on 2D carbon/carbon (C/C) laminates containing a central circular hole utilizing the ANSYS software package. The stress concentration factor obtained from the existing empirical relation is comparable with the FEA result. Utilizing the stress concentration factor and the un-notched tensile strength of the 2D carbon/carbon laminates, the notched tensile strength estimates are found to be highly conservative. Modifications are made in one of the stress fracture criteria of Whitney and Nuismer known as the point stress criterion to estimate the notched strength close to the test results.

Modified Average Stress Criterion to Predict the Fracture Strength of Various Lay-Ups of Carbon/Epoxy Laminates

The prediction of the fracture strength of carbon/epoxy laminates containing sharp notches through the damage model depends on the un-notched strength and the critical length of the damage zone ahead of the notch. In general, the critical length of the damage zone depends on the material, specimen, and size of the sharp notch. Modifications are made in one of the stress fracture criteria known as the average stress criterion for accurate prediction of notched tensile strength of composite laminates containing sharp notches. To examine the adequacy of these modifications, fracture data of center-cracked carbon/epoxy composite laminates with various lay-ups are considered. The notched strength estimates are found to be close to the test results. The modified average stress criterion is very simple to predict the notched tensile strength.

Interlaminar Fracture Behaviour of Hybrid Laminates Stacked with Carbon/Kevlar Fibre as Outer Layers and Glass Fibre as Core

The mode I interlaminar fracture toughness of hybrid laminate was investigated by conducting double cantilever beam test as per ASTM D5528. Unidirectional carbon or kevlar fibre was stacked as outer layers and glass fibre layers in quasi isotropic orientation was used as core. Layer configuration of the 12 ply symmetric laminate was taken as [H/H/G0/G135/G90/G45]s. H/H was varied as G0/G0, C0/G0, C0/C0, K0/G0 and K0/K0. These hybrid laminates were prepared by hand lay-up technique and post cured by compression at high temperature and pressure. The strain energy release rate (GIC) calculated using modified beam theory method was found to be better for the glass/carbon-epoxy hybrid laminates under mode I loading. Fractographic analysis of the delaminated surfaces shows fibre imprints and hackles. In glass/kevlar-epoxy hybrid laminate cusp was observed that could be formed due to shear loads acting on that laminate.

Experimental impact study on unidirectional glass-carbon hybrid composite laminates

Abstract In this experimental study, the impact response of unidirectional hybrid composite laminate was investigated. Hybrid laminates with different stacking sequences were fabricated, using unidirectional glass and carbon fiber as reinforcement and epoxy resin as matrix. ASTM standard D5628 was followed to conduct the experiment using the instrumented drop weight impact test apparatus. All the square specimens were tested at an impact velocity of 3.43 m/s and the time histories of force and energy absorbed were recorded. The impacted specimens and their X-ray images were visually inspected to understand the failure pattern. The experimental results showed that the addition of carbon fiber increases the impact strength by absorbing more force and energy. Furthermore, the laminate can be stiffened with the carbon fiber layers by interfacing glass fiber layers on either side.