The modified mapping-collocation (MMC) method is applied to analyze a circumferential crack in an isotropic curved beam. Based on the method a MATLAB code was developed to obtain the stress field. Incorporating the stress correlation technique, the opening and sliding fracture mode stress intensity factors (SIF)s of the crack for the beam under pure bending moment load case are calculated. The MMC method aims to solve two-dimensional problems of linear elastic fracture mechanics (LEFM) by combining the power of analytic tools of complex analysis (Muskhelishvili formulation, conformal mapping, and extension arguments) with simplicity of applying the boundary collocation method as a numerical solution approach. Qualitatively, a good agreement between the computed stress contours and the fringe shapes obtained from the photoelastic experiment on a plexiglass specimen is observed. Quantitatively, the results are compared with that of ANSYS finite element analysis software. The effect of crack size, crack position and beam thickness variation on SIF values and mode mixity is investigated.

Le béton présente une rupture quasi-fragile du fait de la présence d’une zone d’élaboration de la rupture principalement microfissurée et de taille conséquence, se développant en avant du front de fissure. L’objectif de ces travaux consiste à mettre en évidence le processus d’évolution de la zone d’élaboration et l’étendue de cette dernière, et ce, sur la base d’une campagne d’essai Wedge Splitting suivie de simulations numériques aux éléments-finis utilisant le modèle d’endommagement isotrope de Fichant – La Borderie à l’échelle mésoscopique. Expérimentalement, les courbes de résistance obtenues dans le cadre de la Mécanique Linéaire Élastique de la Rupture équivalente attestent d’un phénomène de confinement précoce de la zone d’élaboration manifestement lié à la géométrie testée et aux propriétés du béton étudié.Les simulations numériques obtenues sur la base du modèle d’endommagement sont en accord avec les résultats expérimentaux et conduisent également à soupçonner ce phénomène de confinement. Par la suite, la simulation numérique est à nouveau utilisée sur cette même géométrie de spécimen mais en réduisant les propriétés de rupture de la matrice cimentaire afin de diminuer la taille de la zone d’élaboration. Les résultats de cette nouvelle simulation montrent un développement libre de la zone d’élaboration suivie d’une propagation auto-similaire de la fissure principale attestée par la présence d’un régime plateau de la courbe de résistance correspondante.Une analyse détaillée du champ d’endommagement puis du champ d’énergie restituée est réalisée et permet de mettre en évidence un critère de développement de la zone d’élaboration fondée sur une valeur maximale du taux local de restitution d’énergie d’endommagement. / Concrete exhibits a quasibrittle fracture due to the existence of a large fracture process zone (FPZ), mainly microcracked, which develops ahead of the crack front. The aim of the current work consists in highlighting the FPZ development and its extent. For that purpose,an experimental campaign using Wedge Splitting Test was carried out and followed by finite element simulation using Fichant – La Borderie isotropic damage model acting at the mesoscale of concrete. Experimental analysis exhibits that by the use from Resistance curves estimated in the framework of equivalent Linear Elastic Fracture Mechanics, the used geometry combined to the studied concrete properties are subjected to a confinement of FPZ. Numerical simulations achieved by the damage model are in agreement with experimental results and also seem to show FPZ confinement. There after, numerical simulations are used again on the same specimen geometry but by decreasing fracture properties of cementitious matrix, in order to minimize the FPZ size. Numerical results exhibit that the FPZ was now freely developed and followed by a self-similar propagation of the main crack as shown by the existence of a “plateau” value on the corresponding Resistance curve. A numerical analysis is performed and leads to the propositionof a FPZ development criteria based on a maximal value of the local damage energy release rate.

Concrete, which was hitherto considered as a brittle material, has shown much better softening behavior after the post peak load than anticipated. This behavior of concrete did put the researchers in a quandary, whether to categorize concrete under brittle materials or not. Consequently concrete has been called a quasi-brittle material. Fracture mechanics concepts like Linear elastic fracture mechanics (LEFM) and Plastic limit analysis applicable to both brittle and ductile materials have been applied to concrete to characterize the fracture behavior. Because of quasi-brittle nature of concrete, which lies between ductile and brittle response and due to the presence of process zone ahead of crack/notch tip instead of a plastic zone, it is found that non-linear fracture mechanics (NLFM) principles are more suitable than linear elastic fracture mechanics (LEFM) principles to characterize fracture behavior. Fracture energy, fracture process zone (FPZ) size and the behavior of concrete during fracture process are the fracture characteristics, which are at the forefront of research on concrete fracture. Another important output from the research on concrete fracture has been the size effect. Numerous investigations, through mathematical modeling and experiments, have been carried out and reported in literature on the effect of size on the strength of concrete and fracture energy. Identification of the sources of size effect is of prime importance to arrive at a clear analytical model, which gives a comprehensive insight into the size effect. With the support of an unambiguous theory, it is possible to incorporate the size effects into codes of practices of concrete design. However, the theories put forth to describe the size effect do not seem to follow acceptable regression. After introduction in Chapter-1 and literature survey in Chapter-2, Chapter-3 details the study on size effect through three point bend (TPB) tests on 3D geometrically similar specimens. Fracture behavior of beams with smaller process zone size in relation to ligament dimension approaches LEFM. The fracture energy obtained from such beams is said to be size independent. In the current work Size effect law (Bazant et al. 1987) is used on beams geometrically similar in three dimensions with the depth of the largest beam being equal to 750mm, and size independent fracture energy G Bf is obtained. In literature very few results are available on the results obtained from testing geometrically similar beams in three dimensions and with such large depth. In the current thesis the results from size effect tests yielded average fracture energy of 232 N/m. Generally the fracture energies obtained from 2D-geometrically similar specimens are in the range of 60-70 N/m as could be seen in literature. From 3D-geometrically similar specimens, the fracture energies are higher. The reason is increased peak load, could be due to increased width. The RILEM fracture energy Gf , determined from TPB tests, is said to be size dependent. The assumption made in the work of fracture is that the total strain energy is utilized for the fracture of the specimen. The fracture energy is proportional to the size of the FPZ, it also implies that FPZ size increases with increase in (W−a) of beam. This also means that FPZ is proportional to the depth W for a given notch to depth ratio, because for a given notch/depth, (W−a) which is also W(1 − a ) is proportional to W`because (1 − a ) is a constant. WWThis corroborates the fact that fracture energy increases with size. Interestingly, the same conclusion has been drawn by Abdalla & Karihaloo (2006). They have plotted a curve relating fracture process zone length and overall depth the beam. In the present study a new method namely Fracture energy release rate method is suggested. In the new method the plot of Gf / (W−a) versus (W−a) is obtained from a set of experimental results. The plot is found to follow power law and showed almost constant value of Gf / (W−a) at larger ligament lengths. This means that fracture energy reaches a constant value at large ligament lengths reaffirming that the fracture energy from very large specimen is size independent. The new method is verified for the data from literature and is found to give consistent results. In a quasi-brittle material such as concrete, a fracture process zone forms ahead of a pre-existing crack (notch) tip before the crack propagates from the tip. The process zone contains a scatter of micro-cracks, which coalesce into one or more macro-cracks, which eventually lead to fracture. These micro-cracks and macro-cracks release stresses in the form of acoustic waves having different amplitudes. Each micro or macro crack formation is called an acoustic emission (AE) event. Through AE technique it is possible to locate the positions of AE events. The zone containing these AE events is termed the fracture process zone (FPZ). In Chapter-4, a study on the evolution of fracture process zone is made using AE technique. In the AE study, the fracture process zone is seen as a region with a lot of acoustic emission event locations. Instead of the amplitudes of the events, the absolute AE energy is used to quantify the size of the process zone at various loading stages. It has been shown that the continuous activities during the evolution of fracture process zone correspond to the formation of FPZ, the size of which is quantified based on the density of AE events and AE energy. The total AE energy released in the zone is found to be about 78% of the total AE energy released and this is viewed as possible FPZ. The result reasonably supports the conclusion, from Otsuka and Date (2000) who tested compact tension specimens, that zone over which AE energy is released is about 95% can be regarded as the fracture process zone. As pointed out earlier, among the fracture characteristics, the determination of fracture energy, which is size independent, is the main concern of research fraternity. Kai Duan et al. (2003) have assumed a bi-linear variation of local fracture energy in the boundary effect model (BEM) to showcase the size effect due to proximity of FPZ to the specimen back boundary. In fact the local fracture energy is shown to be constant away from boundary and reducing while approaching the specimen back boundary. The constant local fracture energy is quantified as size independent fracture energy. A relationship between Gf , size independent fracture energy GF , un-cracked ligament length and transition ligament length was developed in the form of equations. In the proposed method the transition ligament length al is taken from the plot of histograms of energy of AE events plotted over the un-cracked ligament. The value of GF is calculated by solving these over-determined equations using the RILEM fracture energies obtained from TPB tests. In chapter-5 a new method involving BEM and AE techniques is presented. The histogram of energy of AE events along the un-cracked ligament, which incidentally matches in pattern with the local fracture energy distribution, assumed by Kai Duan et al. (2003), along the un-cracked ligament, is used to obtain the value of GF , of course using the same equations from BEM developed by Kai Duan et al. (2003). A critical observation of the histogram of energy of AE events, described in the previous chapter, showed a declining trend of AE event pattern towards the notch tip also in addition to the one towards the specimen back boundary. The pattern of AE energy distribution suggests a tri-linear rather than bi-linear local fracture energy distribution over un-cracked ligament as given in BEM. Accordingly in Chapter-6, GF is obtained from a tri-linear model, which is an improved bi-linear hybrid model, after developing expressions relating Gf , GF , (W−a) with two transition ligament lengths al and blon both sides. The values of Gf , and GF from both bi-linear hybrid method and tri-linear method are tabulated and compared. In addition to GF , the length of FPZ is estimated from the tri-linear model and compared with the values obtained from softening beam model (SBM) by Ananthan et al. (1990). There seems to be a good agreement between the results. A comparative study of size independent fracture energies obtained from the methods described in the previous chapters is made. The fracture process in concrete is another interesting topic for research. Due to heterogeneity, the fracture process is a blend of complex activities. AE technique serves as an effective tool to qualitatively describe the fracture process through a damage parameter called b-value. In the Gutenberg-Richter empirical relationship log 10N=a−bM, the constant ‘b’ is called the b-value and is the log linear slope of frequency-magnitude distribution. Fault rupture inside earth’s crust and failure process in concrete are analogous. The b-value, is calculated conventionally till now, based on amplitude of AE data from concrete specimens, and is used to describe the damage process. Further, sampling size of event group is found to influence the calculated b-value from the conventional method, as pointed out by Colombo et al. (2003). Hence standardization of event group size, used in the statistical analysis while calculating b-value, should be based on some logical assumption, to bring consistency into analytical study on b-value. In Chapter-7, a methodology has been suggested to determine the b-value from AE energy and its utilization to quantify fracture process zone length. The event group is chosen based on clusters of energy or quanta as named in the thesis. Quanta conform to the damage stages and justify well their use in the determination of the b-value, apparently a damage parameter and also FPZ length. The results obtained on the basis of quanta agree well with the earlier results.

Tato závěrečná práce je shrnutím výzkumu smykově zatěžovaných trhlin, který proběhl v průběhu čtyř let doktorského studia jejich autora Ing. Stanislava Žáka (Středoevropský technologický institut, Vysoké učení technické v Brně). Předložená práce je zaměřena na prohloubení znalostí v oblasti pokročilé lomové mechaniky, konkrétně pro smykové zatěžování trhlin kombinované s případy geometrických odchylek trhlin od běžně používaných modelů. To mimo jiné znamená návrh nových přístupů a modelů a popis součinitelů intenzity napětí pro geometricky komplikované trhliny. První část práce je věnována shrnutí současných přístupů v lomové mechanice a dále i popisu numerických metod, použitých v dalších výpočtech. Kromě klasických přístupů se tato část textu zabývá i novějším výzkumem zaměřeným na smykové zatěžování trhlin, speciálně pro dva typy zkušebních těles – válcový vzorek s obvodovým vrubem a trhlinou zatížený prostým smykem nebo krutem a CTS těleso umožňující zatížení trhliny v módech I, II a také v jejich kombinaci I+II. Další část textu je zaměřena na konkrétní výpočty lomových parametrů při použití nových modelů s komplikovaným čelem trhliny. Teoretické řešení lomových parametrů pro oba výše zmíněné modely je porovnáno s experimentálními výsledky, získanými v navazujících projektech. U modelu válcového vzorku je popsána možnost zjednodušení budoucích modelů těles s podobným typem komplikované trhliny a současně je na něm popsán lokální vliv zubatosti čela trhliny na indukci lokálního zatížení v módu II při globálním zatížení v módu III. Tyto výsledky jsou přímo propojeny s experimentální kvantifikací únavového šíření lomu při zatížení v módu III. CTS těleso je použito k popisu vlivu drsnosti trhliny na součinitele intenzity napětí. Na tomto modelu je pozorován jak globální pokles hodnoty KII při zvyšující se drsnosti trhliny, tak i lokální změny v namáhání trhliny podél jednotlivých nerovností. Výsledky potvrzují, i pro dosud málo zkoumané smykové zatěžování, že mikrostruktura lomových ploch a čela trhliny má vliv na lomové parametry. Rozšiřují tak současné znalosti v oboru lomové mechaniky popisem geometrického stínění čela trhliny pro zátěžné módy II a III.

The lifetime of plastic pipes for water supply and other applications is demanded to exceed at least 50 years. Such a long lifetime is difficult to prove by standard testing methods like the hydrostatic pres-sure test. However, it is possible to calculate an estimation of the lifetime, as the most frequently oc-curring mechanism of failure of plastic pipes is the creep crack propagation and subsequent failure. The method is based on describing the crack propagation by parameters of the linear-elastic fracture mechanics. An important part of this method is a finite element simulation of crack propagation in a pipe loaded by various types of loads. Residual stress, a side product of solidification after extrusion, is one of these loads. This thesis begins with an introductory part and literature review of the relevant topics – most of all the typical material properties of the pipe materials, mechanisms of failure, methods of residual stress determination suitable for plastic pipes and their results, methods of testing the materials and calculating lifetime. After the introduction, the problems to be solved are defined. The description of the residual stress state in the wall of various plastic pipes is the main topic. Both tangential (hoop) and axial residual stress in pipes of different dimensions and materials are determined using a combination of experiments and numerical simulations. Also, a simplified method of tangential residual stress is designed that can provide a sufficiently precise description of the tangential resid-ual stress state and is not difficult to carry out. A method to include the residual stress in the lifetime calculations and its influence on the lifetime is also dealt with. Apart from residual stress, the influence of soil loads in case of a buried pipe is studied. The residual stress can also influence the experimental determination of crack growth rate. If the CRB (cracked round bar) test is used to measure the crack growth rate, the crack can propagate asymmetrically due to the presence of residual stress in the specimens, which affects the results. Based on a finite element simulation of crack propagation in a CRB specimen, the severity of the influence is assessed.

The main goal of this work is the comparison of the size of the plastic zone at the crack tip for two analysis methods: an analytical linear method and an elastic-plastic analysis employing the Finite Element method (ANSYS software). All calculations were made for a crack loaded under pure shear modes. These types of loading are not sufficiently described in the literature. The first part of this work introduces the problem with the crack tip plastic zone using both linear and nonlinear fracture parameters. The second part is dedicated to the construction of the Finite Element model in the ANSYS software. The geometry of the samples and the loading levels were chosen to match an existing experimental test of the impact of shear modes on the crack behavior. In the third part of this thesis, the plastic zone radii for pure shear modes II and III are estimated using several methods and the results are compared. In the last part of this work, the same procedure as in the previous part is applied on a mixed-mode II+III loading. A result of this thesis is the assessment of the application limits of the linear analysis method used to estimate the size of the plastic zone at the crack tip for a specific geometry and material model.

This work is focused on the evaluation of the selected fracture parameters of quasi-brittle material, especially concrete, and an assessment of their dependence on the size and shape of the fracture process zone developing at the tip of the macroscopic crack during fracture. For this purpose, experimentally obtained loading diagrams published in the scientific literature have been utilized. These diagrams have been processed into a form enabling creation and calibration of numerical models of these tests in the ATENA FEM program. The results obtained from simulations of the three-point bending tests on beams of four sizes, with three notches lengths, using the created numerical models were used for determination of fracture parameters of concrete. Results of the work consist of the determined values of the specific energy dissipated for creation of new surfaces of the effective crack and an estimation of the specific energy dissipated in the volume of the fracture process zone, which exhibits specific parameters for each beam size and notch length.

The aim of this master thesis is to explore the influence of frictional forces to the stress and strain on the straight crack tip loaded in shear modes. The first section summarizes the most important things from the field of fracture mechanics. Especially theoretical knowledge about fracture parameters (stress intensity factor, J – integral) and their determination in computational environment ANSYS Workbench. The second part deals with computational modeling. At the beginning, is created the model of material, the model of geometry, the model of loads, etc. Then it is possible to solve the direct problem outlined in the introduction. A result of this thesis is the assessment of how the friction influences the fracture parameters in shear modes II and III.

[pt] A avaliação da propagação de trincas de fadiga inclui a identificação da direção da trinca, o conhecimento do Fator de Intensidade de Tensões (SIF) equivalente, a determinação de uma taxa de crescimento de comprimento de trinca por número de ciclos da/dN e o estabelecimento de uma regra de propagação de trinca conectando SIF e da/dN, como uma regra de tipo Paris. Quando ocorrem cargas mistas e não proporcionais, esses parâmetros ainda não são totalmente compreendidos. Esta tese trata de algumas das variáveis que influenciam a propagação de trincas sob carregamento no modo misto não proporcional. A técnica de Correlação de Imagens Digitais (DIC) foi utilizada para a aquisição de imagens de corpos de prova submetidos a carregamento proporcional e não proporcional cíclico. Dois tipos de corpos de prova foram utilizados. Primeiramente, dois corpos de prova planos foram testados; um disk compact tension (DCT, em inglês) e um compact tension modificado (C (T) em inglês). Eles foram submetidos a carregamento cíclico induzindo o modo I de abertura de trinca ou modos I e II de abertura de trinca proporcionais. Em segundo lugar, os dados DIC adquiridos anteriormente, e em outro lugar, para cinco tubos finos sujeitos a carregamento cíclico foram analisados. Os tubos finos tiveram entalhes usinados a partir dos quais as trincas por fadiga iniciaram e se propagaram. Esses cinco tubos finos foram submetidos a diferentes casos de carga proporcional e não proporcional. Um corpo de prova tipo tubo fino foi exposto a carga axial e apresentou modo de abertura de trinca tipo I. Os outros quatro foram submetidos a carregamento de torção ou carga axial-torcional mista e exibiram todos os três modos de abertura de trinca I, II e III. Os campos de deslocamento adquiridos experimentalmente com a técnica DIC foram processados para calcular independentemente o SIF para cada modo de abertura existente usando formulações de mecânica de fratura elástica linear (MFLE). Uma formulação delas utilizou dados de deslocamento de campo completos adquiridos em pequenas áreas que circundavam a ponta da trinca. Outra formulação usou dados adquiridos de um par de pontos localizados ao longo dos flancos opostos das faces da trinca. Os SIFs determinados foram usados para encontrar os SIFs equivalentes e faixas de SIF equivalentes usando o critério da tensão máxima de tração (para ambas as versões 2D e 3D de combinações dos modos I-II e modos I-II-III respectivamente) que implicitamente incluíram o ângulo de propagação de trinca. Verificou-se que a inclusão do SIF no modo III experimentalmente determinado efetivamente faz diferença nas faixas do SIF e dos SIF equivalentes estimados. A curva da/dN versus faixa do SIF equivalente foi elaborado com as taxas de crescimento de trinca medidas experimentalmente e as faixas de SIF que foram encontradas usando a suposição amplamente aceita de que as trincas cresceram na direção que maximiza a tensão de tração. Para isso, extensões do modelo de Schollmann et. al. e bem como o modelo de Erdogan-Sih, que são geralmente aplicados ao carregamento proporcional, foram usados para determinar os SIFs equivalentes e faixas de SIF equivalentes para os casos de carregamento proporcional e não proporcional. Finalmente, a segunda zona da regra de Paris (da/dN versus faixa do SIF equivalente) foi plotada para os cinco casos de carregamento nos tubos finos mostrando que eles caíram dentro de uma faixa razoavelmente fina e dispersa. / [en] Fatigue crack propagation assessment includes identifying the crack direction, knowing the equivalent Stress Intensity Factor (SIF) range, determining a crack length growth rate per number of cycles (da/dN), and establishing a crack propagation rule connecting the equivalent SIF and da/dN rate, such as a Paris type of rule. When mixed and non-proportional loading occur, those parameters are not fully understood yet. This thesis deals with some of the variables that influence crack propagation under non-proportional mixed mode loading. The Digital Image Correlation (DIC) technique was used to acquire images of test specimens subjected to cyclic proportional and non-proportional loading. Two types of specimen samples were used. Firstly, two different plate test specimens were tested; a disk compact tension (DCT), and a modified compact tension, C(T). They were subjected cyclic loading inducing crack opening mode I or proportional crack opening modes I and II. Secondly, the previously and elsewhere acquired DIC data for five thin tubes subject to cyclic loading were analyzed. The thin tubes had pre-fabricated slit-notches from which fatigue cracks initiated and propagated. Those five thin tubes were subjected to different cases of proportional and non- proportional loading. One tube specimen was exposed to axial loading and presented mode I crack opening. The other four were subjected to torsion loading or mixed axial-torsional loading and exhibited all three I, II and III crack-opening modes. The experimentally acquired DIC displacement fields were processed to independently calculate SIF for each existing opening mode using linear elastic fracture mechanics (LEFM) formulations. One formulation used full field displacement data acquired in small areas that surrounded the crack tip. Another formulation used data acquired from a pair of points located along the opposite crack flanks. The determined SIFs were used to find equivalent SIFs and equivalent SIF ranges using the maximum tensile stress criterion (for both 2D and 3D versions of combinations of modes I-II and modes I-II-III respectively) which implicitly included the crack propagation angle. It was found that the inclusion of the experimentally determined mode III SIF indeed makes a difference in the determined equivalent SIF and equivalent SIF ranges. A da/dN versus equivalent SIF ranges plot was drafted with the experimentally measured crack growth rates and the SIF ranges that were found by using the widely accepted assumption that the cracks grew in the direction that maximizes the tensile stress. For this, extensions of the Schollmann et. al. model as well as of the Erdogan-Sih model, which are generally applied to proportional loading, were used to determine equivalent SIFs and equivalent SIF ranges for the cases of proportional and non-proportional loading. Finally, the second stage of the Paris rule (da/dN versus SIF range) was plotted for the five thin tubes loading cases showing that they fell inside a reasonably thin scattered band.

Compression fracture specimens are ideally suited for miniaturization down to tens of microns. Fracture testing of thermal barrier coatings, ceramics and glasses are also best accomplished under compression or indentation. Compression fracture specimen of finite size with constant form factor was not available in the literature. The finite-sized specimen of edge cracked semicircular disk (ECSD) is designed which has the property of constant form factor. The novel ECSD specimen is explored further using weight function concept. This thesis, therefore, is mainly concerned with the design, development and geometric optimization of compression fracture specimen vis a vis their characterization of form factors, weight functions and isotropic points in the uncracked geometry. Inspired by the Brazilian disk geometry, a novel compression fracture specimen is designed in the form of a semicircular disk with an edge crack which opens up due to the bending moment caused by the compressive load applied along its straight edge. This new design evolved from a set of photoelastic experiments conducted on the Brazilian disk and its two extreme cases. Surprisingly, normalized mode-I stress intensity factor of the semicircular specimen loaded under a particular Hertzian way, is found constant for a wide range of relative crack lengths. This property of constant form factor leads to the development of weight function for ECSD for deeper analysis of the specimen. The weight function of a cracked geometry does not depend on loading configuration and it relates stress intensity factor to the stress distribution in the corresponding uncracked geometry through a weighted integral. The weight function for the disk specimen is synthesized in two different ways: using the conventional approach which requires crack opening displacement and the dual form factor method which is newly developed. Since stress distribution in the uncracked specimen is required in order to use weight function concept, analytical solution is attempted using linear elasticity theory. Since closed form solution for stresses in the uncracked semicircular disk is seldom possible with the available techniques, a new semi-analytical method called partial boundary collocation (PBC), is developed which may be used for solving any 2-D elasticity problem involving a semi-geometry. In the new method, part of the boundary conditions are identically satisfied and remaining conditions are satisfied at discrete boundary points. The classical stress concentration factor for a semi-in finite plate with a semicircular edge notch re-derived using PBC is found to be accurate to the eighth decimal. To enhance the form factor in order to test high-toughness materials, edge cracked semicircular ring (ECSR) specimen is designed in which bending moment at the crack-tip is increased significantly due to the ring geometry. ECSR is analyzed using nite element method and the corresponding uncracked problem is analyzed by PBC. Constant form factor is found possible for the ring specimen with tiny notch. In order to avoid varying semi-Hertzian angle during practice and thereby ensure consistent loading conditions, the designs are further modified by chopping at the loading zones and analyzed. Photoelastic isotropic points (IPs) which are a special case of zeroth order fringe (ZOF) are often found in uncracked and cracked specimens. An analytical technique based on Flamant solution is developed for solving any problem involving circular domain loaded at its boundary. Formation of IPs in a circular disk is studied. The coefficients of static friction between the surfaces of disk and loading fixtures, in photoelastic experiments of three-point and four-point loadings, are explored analytically to confirm with experimental results. The disk under multiple radial loads uniformly spaced on its periphery is found to give rise to one isolated IP at the center. Splitting of this IP into a number of IPs can be observed when the symmetry of normal loading is perturbed. Tangential loading is introduced along with normal loading to capture the effect of the composition on formation of IPs. Bernoulli's lemniscate is found to fit fringe order topology local to multiple IPs. Isotropic points along with other low fringe order zones including ZOF are ideal locations for material removal for weight reduction. Making a small hole in the prospective crack path at the IP location in the uncracked geometry might provide dual benefits: 1. Form factor enhancement; 2. Crack arrestor. Thus, this thesis describes experimental, theoretical and computational investigations for the design, development and calibration of novel compact compression fracture specimens.