Indian Institute of Technology Hyderabad (IITH) is a premier institute of science and technology established in 2008. IITH has been consistently ranked in the&nbsp;<a href="https://iith.ac.in/reports/" rel="noopener noreferrer">top 10 institutes</a>&nbsp;in India for Engineering&nbsp;<a href="https://www.nirfindia.org/2021/EngineeringRanking.html" rel="noopener noreferrer" target="_blank">according to NIRF</a>&nbsp;making it one of the most coveted schools for science and technology in the country.

IITH offers&nbsp;<a href="https://iith.ac.in/academics/under-graduate/">undergraduate programs</a>&nbsp;in all the classical engineering disciplines, applied sciences, design, as well as several modern interdisciplinary areas. Students are given a flexibility to explore a broad set of areas, and potentially pursue a minor or double major in a discipline that is not their own. Students who wish to seek a deeper understanding of their own discipline are strongly encouraged to get involved in cutting-edge research with the help of a faculty to mentor them, and earn an Honors in their own field.

The very foundation of IIT Hyderabad is based on&nbsp;<a href="https://iith.ac.in/research/">research and innovation</a>. The vibrant research culture is evident from the number of patents and publications that IITH produces consistently every year. IITH offers&nbsp;<a href="https://iith.ac.in/academics/programmes-offered/">graduate programs</a>&nbsp;at both a masters, and a doctoral level, in several diverse areas. There are separate programs for technology, design, science, and liberal arts. The&nbsp;<a href="https://iith.ac.in/academics/post-graduate/">MTech program</a>&nbsp;is offered in various modes and durations to cater to the ever-growing need of postgraduate level professionals in the country.

IITH encourages and supports&nbsp;<a href="https://iic-iith.netlify.app/index.html" rel="noopener noreferrer" target="_blank">innovation and entrepreneurship</a>&nbsp;at every stage. The minor program in entrepreneurship is open to all students of IITH, and many of the courses are offered by industrialists who are entrepreneurs themselves. There are various&nbsp;<a href="https://iith.ac.in/research/centres-incubators/">innovation centers and incubators</a>&nbsp;that promote entrepreneurship and help mentor young innovators. IITH has been very successful in building tie-ups with leading academic institutions around the globe.

IITH enjoys a very special relationship with Japanese universities and industries that goes beyond academic and research collaborations. In fact, some of the iconic buildings in IITH campus will carry the signature of Japanese architecture.

IITH creates a unique holistic ecosystem for education that offers interactive learning, a very flexible academic structure, cutting-edge research, strong industry collaboration, and entrepreneurship. This is an environment which enables students and faculty to translate their dreams into realities.

IIT Hyderabad

Repair of a cracked aircraft structure by an adhesively bonded composite patch has gained lot of importance in extending the fatigue life as well as improving the structural integrity of it. In the present work, an experimental study is carried out using digital image correlation (DIC) technique to analyze the behavior of single and double-sided adhesively bonded patch repair of an inclined center cracked aluminium panel subjected to uniaxial tensile loading. Further, the shear strain distribution in the adhesive layer is also estimated using the DIC technique. Shear strain concentration at the overlap edge in the adhesive layer is very high leading to patch debonding. Further, optimum patch dimension and patch thickness for the given cracked panel are arrived using a genetic algorithm-based optimization technique in conjunction with finite element analysis (FEA). With the optimum patch configuration, a 3-D FEA is further carried out and the obtained results are compared with the experimental prediction from DIC. The DIC prediction correlates with FEA contours on overall basis. © 2014 The Author(s).

World University root node

Department of Mechanical and Aerospace Engineering

Journal of Reinforced Plastics and Composites

Experimental investigation of adhesively bonded patch repair of an inclined center cracked panel using DIC

The problem of damage evolution in composite structures, the way it propagates, performance and behavior is of paramount importance in utilizing them for structural applications. In the present work, an experimental study is carried out using digital image correlation (DIC) technique to analyze the behavior of adhesively bonded patch repair of carbon/epoxy unidirectional composite laminates under tensile loading. The damaged panel is repaired with both double and single sided circular patch made of same parent material. Damage initiation and propagation in notched and repaired panel as well as patch debonding is studied using 3D-DIC. Also a 3-D finite element analysis is carried out and obtained strain values are compared with the experimental prediction. They are found to be in good agreement. © 2013 Elsevier Ltd. All rights reserved.

Composites Part B: Engineering

Whole-field strain analysis and damage assessment of adhesively bonded patch repair of CFRP laminates using 3D-DIC and FEA

Composite repair is gaining importance for extending the service life of aging aircrafts. There are many parameters like patch thickness, patch layup configuration and patch shape influencing the performance of composite repair. Therefore a need exists to prioritize them. In this work a 3-D finite element analysis has been conducted to get an optimum composite patch shape applied on an inclined center cracked panel, repaired by symmetrical patch. The patch shapes considered are circle, rectangle, square, ellipse and octagon. Also SIF reduction is compared for the same volume of patch. It is observed that extended octagonal patch shape performs better in case of SIF reduction. © 2012 Elsevier Ltd. All rights reserved.

Towards optimization of patch shape on the performance of bonded composite repair using FEM

In the present work, an experimental and numerical study is carried out to analyze the behaviour of adhesively bonded joints in symmetrical patch repaired CFRP laminate under tensile load. In first part of the experimental study, digital image correlation (DIC) technique is employed for material characterization of adhesive and composite as per ASTM standard and they are used in numerical simulation. In second part, same technique is used to analyze the strain field distribution developed in existing adhesive layer between composite panel and patch. High peel and shear strain develops near the overlap end which eventually lead to debonding of patch are analyzed using 2D DIC. Two different kind of adhesive materials are considered in this study. The effect of nature of adhesive and patch edge tapering on strain distribution in the adhesive layer is also closely examined. The failure mechanism is also studied. Finally, the experimental results are compared with the numerical predictions and they compare good. © QinetiQ Ltd 2013.

ICCM International Conferences on Composite Materials

Adhesive strain measurement in patch repaired CFRP laminate using 2D DIC

Aircraft repair is gaining importance for extending the fatigue life of aging aircrafts and also for improving its structural integrity. Among various repair techniques, bonded composite repair is mostly preferred. In this paper, a three-dimensional finite element analysis is carried out to study and compare the performance of single- and double-sided patch on center-cracked aluminum panel. The effects of different parameters such as patch layup, patch thickness and patch material on the stress intensity factor is highlighted. It is shown that the mechanics of double-sided repair is completely different from the single-sided repair. Also, it is found that double-sided repair is more efficient than single-sided repair. In case of single-sided repair, alternative patch material like unbalanced lamina or transversely graded material is proposed. It is observed that there is significant reduction of stress intensity factor with transversely graded patch in case of single-sided repair. © The Author(s) 2012 Reprints and permissions: sagepub.co.uk/journalsPermissions. nav.

Design of composite patch reinforcement applied to mixed-mode cracked panel using finite element analysis

Photoelasticity is a whole field experimental technique to obtain stress fields in both 2-D and 3-D elasticity problems. The accuracy of parameter evaluation by digital photoelastic techniques depends on the choice of the optical arrangements for parameter estimation, the inherent error in optical elements and any misalignments introduced during experimentation. A generic approach to simulation of error in digital photoelasticity by Jones calculus is presented in this paper. Of late it has been shown that the quarter-wave plate mismatch error is varying and is not a constant value. The present simulation accounts for inherent variable error in quarter-wave plates and also accommodates the error arising due to the optical misalignment of the various optical elements. The applicability of the new methodology is shown for different phase shifting techniques. A comparative study among various techniques is done regarding sensitivity to general error sources and it is found that the ten-step method is the least sensitive among them all. Therefore usage of the ten-step method is thus recommended while using manual polariscope for digital photoelastic applications. © 2011 Elsevier Ltd. All rights reserved.

Optics and Lasers in Engineering

Sensitivity of isoclinic data using various phase shifting techniques in digital photoelasticity towards generalized error sources

With advancements in digital image processing and data acquisition, a separate branch of photoelasticity namely digital photoelasticity came into existence. Here, intensity information of the acquired image is used for the evaluation of whole-field photoelastic parameters. Digital photoelasticity provides only wrapped phasemaps of isoclinics and isochromatics and they have to be unwrapped in different ways for getting the continuous-phase values. In the case of the isochromatic phasemap, ambiguity removal prior to unwrapping is essential. In this paper, a 10-step phase-shifting methodology is proposed and a new strategy for obtaining the isochromatic phasemap free of ambiguity is demonstrated. Isoclinic unwrapping is performed by a new adaptive quality guided algorithm. Adaptive in the sense that isoclinic phase unwrapping is done autonomously even in the presence of isotropic points/π jumps occurring in the isoclinic phasemap. The isochromatic phasemap is also unwrapped using the quality guided path follower. The methodology is validated for the problem of a ring under diametral compression and later shown for three other models which have complex stress fields. Wherever possible, the parameters obtained by the new methodology are compared with analytical or numerical methods and the comparison is quite good. © 2008 Blackwell Publishing Ltd.

Strain

Adaptive quality guided phase unwrapping algorithm for whole-field digital photoelastic parameter estimation of complex models

In photoelasticity, the method of obtaining the individual values of principal stresses/normal stresses separately is referred to as stress separation. Shear difference is one of the widely used techniques for stress separation in photoelasticity and one needs the value of fringe order and the isoclinic angle free of noise at every pixel over the domain. For accurate parameter determination, a ten-step phase shifting approach which uses a plane polariscope for isoclinic determination and a circular polariscope for isochromatic determination is proposed. A new quality guided approach for isoclinic unwrapping is developed. Isochromatic phasemap free of ambiguous zones is obtained by a new methodology and is unwrapped by a quality-guided approach. Whole field evaluation of stress components and its representation is then presented. The models used in this study are intentionally subjected to moderate loads showing a high level of isochromatic-isoclinic interaction. In view of this, the isoclinic data has several kinks which is found to cause streak formation in the whole field representation of separated stress components. An outlier smoothing algorithm is proposed for getting a smooth variation of the digital photoelastic parameters over the domain. Use of such smoothed data for stress separation has removed the streaks and has also greatly improved the accuracy of the separated stress components. © 2007 Elsevier Ltd. All rights reserved.

Whole field evaluation of stress components in digital photoelasticity-Issues, implementation and application

Photoelasticity is the only whole-field experimental technique which can analyse both 2-D and 3-D elasticity problems. In digital photoelasticity one gets two phase maps, one corresponding to principal stress direction (isoclinic) and the other corresponding to principal stress difference (isochromatic). The phase maps for both isoclinics and isochromatics are to be unwrapped differently for obtaining continuous phase values. Autonomous phase unwrapping is one of die challenging issues and this paper focuses on recent advances on isochromatic phase map unwrapping. A comparative study of different autonomous phase unwrapping algorithm is done by solving a bench mark problem and a stress frozen slice with cut-outs. The need for domain delimiting in addition to domain masking is brought out while using autonomous phase unwrapping algorithms.

Fulltext

Sadhana - Academy Proceedings in Engineering Sciences

Assessment of autonomous phase unwrapping of isochromatic phase maps in digital photoelasticity

With the advent of PC-based digital image processing systems, automation of parameter estimation based on intensity processing from the entire field has now become simpler. Various methods for obtaining the isoclinic parameter using plane, circular, and mixed polariscopes have been reported in the literature. A comparative study has been conducted on the performance of these methods both qualitatively and quantitatively. The focus of the study is on how these algorithms provide the basic isoclinic data. To illustrate the performance, theoretically simulated and experimentally recorded images for a ring under diametral compression is used. The role of background light intensity and quarter-wave plate mismatch on the experimental evaluation of isoclinic data is brought out. © IMechE 2006.

Journal of Strain Analysis for Engineering Design

Comparative study of evaluation of primary isoclinic data by various spatial domain methods in digital photoelasticity

Photoelasticity is one of the most widely used techniques for experimental stress and strain analysis. With the availability of low cost digital image processing systems, a separate branch of photoelasticity known as digital photoelasticity came into existence providing whole-field values of the isoclinics (θ) and isochromatics (N) in a true sense. Among the several methods available for data acquisition, phase shifting / polarization stepping techniques are most widely used for their simplicity and accuracy. In this paper a new digital photoelastic method based on phase shifting using monochromatic light source is presented. It provides full field values of θ and N. The arrangement is carefully chosen with the intention of reducing the influence of quarter wave mismatch error in the evaluation of θ and N. The methodology is validated for the benchmark problem of a disk under diametral compression.