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Research And Application Of Fracture Mechanics Model Of Stope Roof Under The Coupling Of Direct Roof And Basic Roof, Li Jinhua, Zheng Chengxian, Gu Shuancheng, Wu Baolin, Wang Xiong, Song Yongjun

Coal Geology & Exploration

Periodic weighting is a typical characteristic of mine pressure. Accurate prediction of stope periodic weighting step is an important way to effectively reduce the occurrence of stope accidents. Aiming at the influence of the coupling between the basic roof defects and the direct roof on the periodic weighting step, the stope roof was regarded as a finite plate model with cracks. According to the coordinate deformation mechanism of the overburden rock, the fracture mechanics model of the stope roof was established based on the fracture mechanics theory. On this basis, the periodic weighting step function under the coupling between the …

Full-Life Fatigue Analysis Of Vertical Retort Based On Fracture Mechanics, Liu Jin-Peng, Zhang Li-Mei, Huang Zhi-Gang

Food and Machinery

Objective: The fatigue strength of a new type of vertical retort under the cyclic load of heat engine was studied, especially the residual fatigue life of the pot body after the crack appeared and the factors affecting the fatigue crack propagation of the germicidal pot. Methods: The mechanical characteristics of retort under sterilization and three kinds of cyclic loads were analyzed by Workbench, the design fatigue life of the retort under three alternating stresses was studied based on the S-N curve. The effect of the initial crack size, pressure and temperature on the stress strength factor and residual fatigue life …

Propagation Process Of Hydraulic Fracture Crossing An Orthogonal Discontinuity, Lei Chen, Guang-Qing Zhang, Min Zhang, Yu-Jie Cao, Li-Ji Shen

Rock and Soil Mechanics

Massive developed discontinuities are the salient geological features of unconventional oil and gas reservoirs, and the hydraulic fractures’ capabilities of crossing the discontinuities concern the stimulation effects of hydraulic fracturing. To study the development of the fracture process zone (FPZ) when the hydraulic fracture orthogonally propagates through a discontinuity, the self-designed visual fracturing equipment was adopted to carry out hydraulic fracturing tests on sandstone plates with a prefabricated unbounded friction interface. Based on the digital image correlation method, the displacement and strain characteristics during the hydraulic fracture propagation across the orthogonal interface were monitored in real time. The test results …

The Impact Of Contact Geometry On Sea Ice Stress And Fracture At The Scale Of Ice Floes, Michael J. May

Dartmouth College Master’s Theses

Observations of stress and strain at the scale of ice floes are necessary to fill a gap in our understanding of sea ice mechanical behavior. Current climate and ice dynamics models represent ice mechanical properties using stress-strain relationships largely determined at laboratory-scale (<1m) or from regional-scale (10+km) deformation observations. The former scale does not include all mechanisms of deformation operating in the ice pack; the latter aggregates multiple modes of deformation into non-physical fluid analogies. The Sea Ice Dynamics Experiment (SIDEx) was run in Feb-Mar 2021 to fill this gap, observing stress and strain at the scale of sea ice failure processes. Here we present stress sensor observations. Stress gages (N=31) were deployed over a 4.5km² area in the southern Beaufort Sea to observe in-situ stress. These data were analyzed in the context of deformation observations from satellite imagery and local laser and radar interferometers to explain the drivers of sea ice stress variations before and after fracture. Three case studies between 14 March and 24 March, during which fractures propagated through …

Stress Intensity Factor - Simple Solution For A Complex Problem, Hamid A. Ghassri, Alberto Mello

Beyond: Undergraduate Research Journal

This research explores the modeling of a cracked structure using a linear elastic finite element method (FEM) analysis with the objective of determining the stress intensity factor (SIF) for complex geometries. The analysis uses a mapping of the stress concentration area ahead of the crack tip to asymptotically determine the SIF. For model calibration, Irwin’s approximation method was used in two known crack case solutions subjected to a uniform tensile loading (Mode I – Opening) with fixed geometric dimensions. With focus on aircraft airworthiness application, two more complex geometries with irregular stress distributions were analyzed and the results were extracted …

Atomistic Simulation Of Hydrogen Embrittlement Of Grain Boundaries In Metals, Jiaqing Li

University of Wollongong Thesis Collection 2017+

It has been known for about a century that hydrogen contamination causes severe degradation in the mechanical properties of metals. This phenomenon is generally termed as ‘hydrogen embrittlement’ (HE). In this thesis, the underlying mechanisms behind HE phenomenon were elucidated on an atomic scale. The H segregation at various grain boundaries (GBs) and its influence on the structure, mechanical properties, deformation mechanisms and failure response of GBs were examined by atomistic simulations.

First, H segregation at various GBs was studied in this thesis. The results indicated that H segregation properties were very sensitive to GB structures. The effects of H …

Investigation Of Mode I-Ii-Iii Fracture Of Brittle Spheres With A 60° Internal Crack Using 3d-Ilc, Hai-Jun Wang, Shu-Yang Yu, Zi-Xuan Tang, Lei Tang, Ran Ren, Jin Xu

Rock and Soil Mechanics

As one of the perfect geometries in nature, sphere is common in daily and industrial life. The mechanical properties of sphere are of great significance to engineering safety and numerical simulation. Internal cracks or defects are inherent properties of materials and have an important influence on the mechanical properties of materials. However, the internal crack of the sphere is not considered in the current research due to the limit of technology. Thus, understanding of the propagation of internal cracks of brittle spheres is limited. In our study, internal cracks were created in glass sphere samples by 3D-ILC (3D-internal laser-engraved crack). …

Effect Of Selfsame Microparticles On Epoxide Amine Network Formation And Matrix Mechanics, Travis Palmer

Dissertations

Epoxide amine matrices are widely utilized in aerospace carbon fiber reinforced polymer (CFRP) composites having engendered significant reductions in weight and fuel consumption. This dissertation focuses on the effect of constrained space during network formation on the matrix mechanics of these highly complex composite systems. Precipitation polymerization conditions are developed to prepare epoxide amine microparticles (EMs) based on tetraglycidyl-4,4’-methylenedianiline (TGDDM) and isophorone diamine (IPDA). Surface functionality of EMs is tuned via control of epoxide to reactive amine hydrogen ratio, where unreactive, amine- and epoxide-functional EMs are prepared. We demonstrate that EMs are polydisperse, but can be filtered, yielding low dispersity …

Understanding Large Strain Deformation Behavior Of Physically Assembled Triblock [Aba] Copolymer Gels In B-Selective Solvents, Satish Mishra

Theses and Dissertations

Physically assembled gels are widely applicable in the food industry, biomedical devices, drug delivery, and soft robotics due to their tunable mechanical properties and thermoreversibility. The mechanical responses of these gels originate from their microstructure. Therefore, factors affecting the gel microstructure like polymer molecular weight, solvent quality, and polymer concentration play a significant role in determining their mechanical behavior. Gel microstructure also changes during the deformations resulting in a deviation from the structure-property relationship established for the low deformations. During large deformations, other factors like stress relaxation, poroelasticity, and polymer chain entanglement contribute significantly to the gel response. This complexity …

Effects Of Steel Type And Sandblasting Pretreatment On The Solid-Liquid Compound Casting Characteristics Of Zinc-Coated Steel/Aluminum Bimetals, Jesik Shin, Taehyeong Kim, Kyoungmook Lim, Hoon Cho, Daeho Yang, Changyeol Jeong, Sung Yi

Mechanical and Materials Engineering Faculty Publications and Presentations

Effects of zinc-coated steel type and steel surface sandblasting pretreatment in the solid-liquid compound casting of layered type steel/aluminum bimetals were investigated. The Zn coating behavior and its effects on interfacial microstructure evolution and fracture mechanism were also discussed. The aluminum fluidity in thin plate type flow channels formed by the steel insert and the mold wall primarily depended on the insert surface roughness and secondarily on the wettability. As-galvanized (GI) steel/aluminum bimetal joints showed the bonding strength of 20 MPa and more, while galvannealed (GA) steels showed poor bonding. The interfacial bonding zone consisted of most Al13Fe4, Al8Fe2Si, Al4.5FeSi …

An Investigation Into A Proposed Size-Insensitive Fracture Toughness Parameter Obtained From Quasi-Static Fracture Toughness Tests, William G. Tilson

Theses

Material fracture properties are characterized by means of specimen level material tests, such as ASTM Standard E399 Standard Test Method for Linear-Elastic Plane-Strain Fracture Toughness KIc of Metallic Materials. Recent investigations into certain high-toughness alloys have demonstrated a specimen size effect on the results of E399 tests. This thesis describes an experimental investigation into a proposed alternative analysis method for E399 tests that produces a specimen size insensitive result, termed KIsi. The work demonstrates that the alternative approach reduced the specimen size effect, validates assumptions on crack extension, and evaluates proposed test validity requirements. Suggestions for improvements to the KIsi …

Effects Of Alkali-Silica Reaction On The Fracture Behavior Of Concrete, Walker Daniel Trent

Masters Theses

With the majority of nuclear power plants in the United States approaching their operational life span, it has become important to reevaluate their durability. In partnership with other research institutions, Oak Ridge National Laboratory (ORNL) has allocated resources to identify mechanisms for degradation of structural components in these power plants. Among these degradation mechanisms, alkali-silica reaction has proven to be common. The University of Tennessee–Knoxville has partnered with the Fusion and Materials for Nuclear Systems Division of Oak Ridge National Laboratory to evaluate the effects of this reaction.Alkali-silica reaction in concrete structures has become a subject of interest in the …

Failure Mechanisms In Tribological Coatings And Energy Materials Subjected To Different Environments And Temperatures, Guanhong Sun

Electronic Theses and Dissertations

The objective of this research is to develop advanced material characterization and mechanical testing methods for C-, Mo- based and ferrous tribological coatings to be used in lightweight engines, and manufacturing of lightweight materials. These new characterization methods are also applied to the investigation of damage processes in energy materials, namely to investigate degradation in C- based electrodes used in Li-ion batteries. Evaluations of the damage mechanisms in these materials under static and sliding contact stress conditions, as well as under different environments and temperatures encountered under the actual service conditions create several challenges. Accordingly, an in-situ mechanical testing set-up …

The Influence Of Heating And Cooling Rates On Tbc Failure In High Heat Flux Tests, Philip Howell, Uwe Rettig, Thorsten Steinkopff, Ramesh Subramanian, Andreas Wolff, Stefan Lampenscherf

Thermal Barrier Coatings V

High heat flux testing is a commonly used procedure to investigate TBC failure modes. Samples of TBC on superalloy are thermally cycled, with the TBC being heated and the superalloy subjected to forced cooling in order to induce a temperature gradient. Typically conditions are deliberately chosen to be more aggressive than in the engine in order to induce TBC delamination or complete spallation within a few days. We have developed a test bench with a CO2 laser as the heat source which, unlike the more commonly used burner rigs, allows exquisite control of the heating and cooling rates. An optical …

Finite Element Analysis Of 3d Printed Aircraft Wing, Julian M. Rogers

University Honors Theses

3D printing has allowed complex designs to be produced which were impossible to create using conventional manufacturing processes. Aircraft wings are optimized as much as possible given manufacturability considerations, but more complex geometry could provide the same strength for less weight, increasing aircraft performance. Although carbon fiber composites are some of the best known materials for conventional optimized aircraft wings, current 3D printing technology cannot produce this material. Instead, it is currently limited to metals and polymers. To determine if the more complex geometry which can be produced by 3D printing can offset the material limitations, a carbon fiber composite …

Fracture Criterion For Surface Cracks In Plates Under Remote Tension Loading, Taoufik El Mountassir

Theses and Dissertations

Surface-crack configurations are among the most important crack problems in the aerospace industry. The residual strength of a surface-cracked component is complicated by three-dimensional variation of the stress-intensity factor around the crack front and plastic deformations, which vary from plane stress at the free boundary, to nearly plane-strain behavior in the interior. In 1973, a two-parameter fracture criterion (TPFC) was developed to analyze fracture behavior of surface-crack configurations. Estimates were made around the crack front for fracture initiation—the critical parametric angle. Recently, NASA developed the Tool for Analysis of Surface Cracks (TASC) software that predicts critical location. This thesis is …

Advanced Numerical Modelling Of Dynamic Fractures In Rock, Gaetano Venticinque

University of Wollongong Thesis Collection 2017+

The application of numerical analysis towards modelling real world problems requires fundamental understanding of the system behaviour as it occurs in nature. The choice of the numerical model schemes depends largely on the modelled problems that may be either: static equilibrium such as simulation of the stable mine excavation, continually yielding/caving strata such as goaf formation or dynamic events to simulate fast propagation of fractures in brittle rock or other dynamic behaviour. My original contribution to knowledge is the novel development of a simple explicit, dynamic numerical scheme for solving complex nonlinear dynamic fracture mechanisms in rock. This was delivered …

Fracture Analysis In Biomimetic Bouligand Architectures, Nobphadon Suksanqpanya

Open Access Dissertations

The Bouligand structure, which is found in many biological materials, is a hierarchical architecture that features uniaxial fiber layers assembled periodically into a helicoidal pattern. Many studies have highlighted the high damage-resistant performance of Bouligand structures and its biomimetic materials. One of the outstanding species with the Bouligand structures is the smashing Mantis Shrimp, Odontodactylus Scyllarus, (or stomatopod) due to its capability of generating high speed, high acceleration blows using its raptorial appendage to defeat highly armored preys. The load-bearing part of this appendage, the dactyl club, contains an interior region, which is mainly characterized by the Bouligand structure. This …

Riemann-Hilbert Formalism In The Study Of Crack Propagation In Domains With A Boundary, Aleksandr Smirnov

LSU Doctoral Dissertations

The Wiener-Hopf technique is a powerful tool for constructing analytic solutions for a wide range of problems in physics and engineering. The key step in its application is solution of the Riemann-Hilbert problem, which consists of finding a piece-wise analytic (vector-) function in the complex plane for a specified behavior of its discontinuities. In this dissertation, the applied theory of vector Riemann-Hilbert problems is reviewed. The analytical solution representing the problem on a Riemann surface, and a numerical solution that reduces the problem to singular integral equations, are considered, as well as a combination of the numerical and analytical techniques …

Corrosion Fatigue Crack Growth Behavior At Notched Hole In 7075-T6 Under Biaxial And Uniaxial Fatigue With Different Phases, Ali Khawagi

Theses and Dissertations

This research investigates fatigue crack propagation behavior in both air and saltwater (3.5% NaCl) environments from pre-cracked notched circular hole in a 7075-T6 cruciform specimen. With stress ratio of 0.5, biaxility stress ratio of unity, and frequency of applied load of 10 Hz, the crack growth behavior was investigated under in-plane biaxial tension-tension fatigue with 45⁰, 90⁰ and 180⁰ phase difference conditions and then compared to previous fatigue tests with no phase difference to study the effect of changing the phase differences between the applied loads on the crack growth rate. Finite Element Analysis (FEA) was used to calculate cyclic …

Analysis Of Short Crack Growth In Particulate Composites, Ying Zhang, Tsuchin P. Chu, Ajay Mohan Mahajan, Chi Tsieh Liu

Dr. Ajay Mahajan

This paper presents the analysis of the short-crack propagation and growth in particulate composite materials by using the image correlation techniques and fracture mechanics theory. The fracture mechanics model for a long crack does not work very well with short-crack propagation when the initial crack length is less than 5.1 mm (0.2 inch). In order to investigate the short crack effect, a series of tests of particulate composite specimens with long and short cracks have been performed and the results were recorded on a video tape. These test data were analyzed to determine the strain fields near the crack tip, …

Criteria For Crack Deflection-Penetration In Ebc Coated Ceramics: A Parametric Study, Ali Abdul-Aziz, Ramakrishna T. Bhatt, Joseph E. Grady

United States National Aeronautics and Space Administration: Publications

This article discusses results obtained from a parametric study to analytically evaluate the impingement of a crack at the interface of an environmental barrier coating (EBC) and a monolithic Silicon nitride (Si₃N₄) layered ceramics substrate. The study establishes a correlation that leads to determine if the crack is arrested or advanced by either penetrating or deflecting along the EBC/substrate interface. A finite-element-based fracture mechanics methodology is utilized to perform these calculations. Critical parameters determining penetration-deflection conditions in relation to EBC’s physical characteristics, such as porosity level, voids, and mini cracks, are determined for a single layer …

Dynamic Calibration And Analysis Of Crack Tip Propagation In Energetic Materials Using Real-Time Radiography, Ali Butt

Theses

Crack propagation in a solid rocket motor environment is difficult to measure directly. This experimental and analytical study evaluated the viability of real-time radiography for detecting bore regression and propellant crack propagation speed. The scope included the quantitative interpretation of crack tip velocity from simulated radiographic images of a burning, center-perforated grain and actual real-time radiographs taken on a rapid-prototyped model that dynamically produced the surface movements modeled in the simulation. The simplified motor simulation portrayed a bore crack that propagated radially at a speed that was 10 times the burning rate of the bore. Comparing the experimental image interpretation …

Experimental Characterization Of Cu Free-Air Ball And Simulations Of Dielectric Fracture During Wire Bonding, Sai Sudharsanan Paranjothy

Open Access Theses

Wire bonding is the process of forming electrical connection between the integrated circuit (IC) and its structural package. ICs made of material with low dielectric constant (low-k) and ultra low-k are porous in nature, and are prone to fracture induced failure during packaging process. In recent years, there is increasing interest in copper wire bond technology as an alternative to gold wire bond in microelectronic devices due to its superior electrical performance and low cost. Copper wires are also approximately 25% more conductive than Au wires aiding in better heat dissipation. At present, validated constitutive models for the strain rate …

An Inverse Pod-Rbf Network Approach To Parameter Estimation In Mechanics, Craig A. Rogers, Alain Kassab, Eduardo Divo, Ziemowit Ostrowski, Ryszard Bialecki

Eduardo Divo

An inverse approach is formulated using proper orthogonal decomposition (POD) integrated with a trained radial basis function (RBF) network to estimate various physical parameters of a specimen with little prior knowledge of the system. To generate the truncated POD-RBF network utilized in the inverse problem, a series of direct solutions based on FEM, BEM or exact analytical solutions are used to generate a data set of temperatures or deformations within the system or body, each produced for a unique set of physical parameters. The data set is then transformed via POD to generate an orthonormal basis to accurately solve for …

A Variational Model For Fracture And Debonding Of Thin Films Under In-Plane Loadings, A. A. León Baldelli, J. F. Babadjian, B. Bourdin, D. Henao, C. Maurini

Faculty Publications

We study fracture and debonding of a thin stiff film bonded to a rigid substrate through a thin compliant layer, introducing a two-dimensional variational fracture model in brittle elasticity. Fractures are naturally distinguished between transverse cracks in the film (curves in 2D) and debonded surfaces (2D planar regions). In order to study the mechanical response of such systems under increasing loads, we formulate a dimension-reduced, rate-independent, irreversible evolution law accounting for both transverse fracture and debonding. We propose a numerical implementation based on a regularized formulation of the fracture problem via a gradient damage functional, and provide an illustration of …

Design Guidelines To Frp Strengthened Reinforced Concrete Structures : An Emphasis On Developing Plate-End Debonding Failure Criterion, Rajesh Babu Vuddandam

Dissertations

As an alternative to the overwhelming costs of rebuilding structures, rehabilitation of existing structures has become the focus of many researchers in the past few decades. To strengthen a reinforced concrete beam for flexure, fiber reinforced polymer (FRP) composites are usually bonded externally to the tension side of the structural element. Although, the usage of FRP has progressed and has been implemented in a number of projects worldwide, the behavior of FRP rehabilitated structures has yet to be appropriately considered for design purposes. For design, current design guidelines address conventional failure modes like concrete crushing, steel yielding and FRP rupture. …

Early Prediction Of Fracture In Bodies Bounded By Random Rough Surfaces, Hector Medina

Theses and Dissertations

Under certain loading conditions, surfaces topography coupled with materials degree of brittleness can significantly compromise the mechanical performance of structures. The foregoing remains valid even if roughness is intentionally introduced for engineering reasons. In either case, stress can concentrate. The case of the stress concentration in surfaces having randomly distributed pits is a problem that, although being very practical, yet it remains unsolved. The complexity of a random configuration renders difficult the problem of analytically finding relationships between surface parameters and markers indicative of mechanical failure. Another difficulty is the reproducibility of replicates of specimens possessing random rough surfaces, for …

Applications Of The Variational Approach To Fracture Mechanics, Ataollah Mesgarnejad

LSU Doctoral Dissertations

In this study we present the variational approach to fracture mechanics as a versatile tool for the modeling of the fracture phenomenon in solids. Variational fracture mechanics restates the problem of initiation and propagation of cracks in solids as an energy minimization problem. The edifice of this energy minimization problem is such that unlike other methods (e.g. extended finite element method XFEM, cohesive-zone methods) the variational approach to fracture mechanics, diminishes the need for an a priori knowledge of the crack path or ad hoc assumptions in the form of path selection laws. We will show applications of the variational …

Material Specific Load Combination Factors For Option 2 Fad Curves, Matt Saxon Schaser

ETD Archive

No abstract provided.