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Published: 8 June 2024

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1

KALEEL, IBRAHIM. "Computationally-efficient multiscale models for progressive failure and damage analysis of composites." Doctoral thesis, Politecnico di Torino, 2019. http://hdl.handle.net/11583/2729362.

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2

GARCIA, DE MIGUEL ALBERTO. "Hierarchical component-wise models for enhanced stress analysis and health monitoring of composites structures." Doctoral thesis, Politecnico di Torino, 2019. http://hdl.handle.net/11583/2729658.

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3

Webber, Kyle Grant. "Effect of Domain Wall Motion and Phase Transformations on Nonlinear Hysteretic Constitutive Behavior in Ferroelectric Materials." Diss., Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/22695.

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The primary focus of this research is to investigate the non-linear behavior of single crystal and polycrystalline relaxor ferroelectric PMN-xPT and PZN-xPT through experimentation and modeling. Characterization of single crystal and polycrystalline specimens with similar compositions was performed. These data give experimental insight into the differences that may arise in a polycrystal due to local interaction with inhomogeneities. Single crystal specimens were characterized with a novel experimental technique that reduced clamping effects at the boundary and gave repeatable results. The measured experimental data was used in conjunction with electromechanical characterizations of other compositions of single crystal specimens with the same crystallographic orientation to study the compositional effects on material properties and phase transition behavior. Experimental characterization provided the basis for the development of a model of the continuous phase transformation behavior seen in PMN-xPT single crystals. In the modeling it is assumed that a spatial chemical and structural heterogeneity is primarily responsible for the gradual phase transformation behavior observed in relaxor ferroelectric materials. The results are used to simulate the effects of combined electrical and mechanical loading. An improved rate-independent micromechanical constitutive model based on the experimental observations of single crystal and polycrystalline specimens under large field loading is also presented. This model accounts for the non-linear evolution of variant volume fractions. The micromechanical model was calibrated using single crystal data. Simulations of the electromechanical behavior of polycrystalline ferroelectric materials are presented. These results illustrate the effects of non-linear single crystal behavior on the macroscopic constitutive behavior of polycrystals.
4

Gu, Xiaohong. "Micromechanics of model carbon-fibre/epoxy-resin composites." Thesis, University of Manchester, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.488261.

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5

McClain, Michael Patrick. "A micromechanical model for predicting tensile strength." Thesis, This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-10052007-143117/.

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6

Keralavarma, Shyam Mohan. "A micromechanics based ductile damage model for anisotropic titanium alloys." [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-2620.

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7

Mihai, Iulia. "Micromechanical constitutive models for cementitious composite materials." Thesis, Cardiff University, 2012. http://orca.cf.ac.uk/24624/.

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A micromechanical constitutive model for concrete is proposed in which microcrack initiation, in the interfacial transition zone between aggregate particles and cement matrix, is governed by an exterior-point Eshelby solution. The model assumes a two-phase elastic composite, derived from an Eshelby solution and the Mori-Tanaka homogenization method, to which circular microcracks are added. A multi-component rough crack contact model is employed to simulate normal and shear behaviour of rough microcrack surfaces. It is shown, based on numerical predictions of uniaxial, biaxial and triaxial behaviour that the model captures key characteristics of concrete behaviour. An important aspect of the approach taken in this work is the adherence to a mechanistic modelling philosophy. In this regard the model is distinctly more rigorously mechanistic than its more phenomenological predecessors. Following this philosophy, a new more comprehensive crack-plane model is described which could be applied to crack-planes in the above model. In this model the crack surface is idealised as a series of conical teeth and corresponding recesses of variable height and slope. Based on this geometrical characterization, an effective contact function is derived to relate the contact stresses on the sides of the teeth to the net crack-plane stresses. Plastic embedment and frictional sliding are simulated using a local plasticity model in which the plastic surfaces are expressed in terms of the contact surface function. Numerical simulations of several direct shear tests indicate a good performance of the model. The incorporation of this crack-plane model in the overall constitutive model is the next step in the development of the latter. Computational aspects such as contact related numerical instability and accuracy of spherical integration rules employed in the constitutive model are also discussed. A smoothed contact state function is proposed to remove spurious contact chatter behaviour at a constitutive level. Finally, an initial assessment of the performance of the micromechanical model when implemented in a finite element program is presented. This evaluation clearly demonstrates the capability of the proposed model to simulate the behaviour of plain and reinforced concrete structural elements as well as demonstrating the potential of the micromechanical approach to achieve a robust and comprehensive model for concrete.
8

Bandorawalla, Tozer Jamshed. "Micromechanics-Based Strength and Lifetime Prediction of Polymer Composites." Diss., Virginia Tech, 2002. http://hdl.handle.net/10919/26445.

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With the increasing use of composite materials for diverse applications ranging from civil infrastructure to offshore oil exploration, the durability of these materials is an important issue. Practical and accurate models for lifetime will enable engineers to push the boundaries of design and make the most efficient use of composite materials, while at the same time maintaining the utmost standards of safety. The work described in this dissertation is an effort to predict the strength and rupture lifetime of a unidirectional carbon fiber/polymer matrix composite using micromechanical techniques. Sources of material variability are incorporated into these models to predict probabilistic distributions for strength and lifetime. This approach is best suited to calculate material reliability for a desired lifetime under a given set of external conditions. A systematic procedure, with experimental verification at each important step, is followed to develop the predictive models in this dissertation. The work begins with an experimental and theoretical understanding of micromechanical stress redistribution due to fiber fractures in unidirectional composite materials. In-situ measurements of fiber stress redistribution are made in macromodel composites where the fibers are large enough that strain gages can be mounted directly onto the fibers. The measurements are used to justify and develop a new form of load sharing where the load of the broken fiber is redistributed only onto the nearest adjacent neighbors. The experimentally verified quasi-static load sharing is incorporated into a Monte Carlo simulation for tensile strength modeling. Very good agreement is shown between the predicted and experimental strength distribution of a unidirectional composite. For the stress-rupture models a time and temperature dependent load-sharing analysis is developed to compute stresses due an arbitrary sequence of fiber fractures. The load sharing is incorporated into a simulation for stress rupture lifetime. The model can be used to help understand and predict the role of temperature in accelerated measurement of stress-rupture lifetimes. It is suggested that damage in the gripped section of purely unidirectional specimens often leads to inaccurate measurements of rupture lifetime. Hence, rupture lifetimes are measured for [90/0_3]_s carbon fiber/polymer matrix specimens where surface 90 deg plies protect the 0 deg plies from damage. Encouraging comparisons are made between the experimental and predicted lifetimes of the [90/0_3]_s laminate. Finally, it is shown that the strength-life equal rank assumption is erroneous because of fundamental differences between quasi-static and stress-rupture failure behaviors in unidirectional polymer composites.
Ph. D.
9

Hu, Lianxin. "Micromechanics of granular materials : Modeling anisotropy by a hyperelastic-plastic model." Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI133.

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Afin de modéliser le comportement des géométariaux sous des charges complexes, plusieurs études et travaux expérimentaux ont été réalisées afin d’établir des modèles constitutifs relatifs. Une caractéristique importante des matériaux granulaires est que la relation entre la contrainte et la déformation et ce même dans le domaine élastique n’est pas linéaire, contrairement aux réponses du métal. Il a également été constaté que la réponse contrainte-déformation des matériaux granulaires montre les caractéristiques de l’anisotropie induite, ainsi que les non-linéarités. En outre, l’anisotropie induite par la contrainte se produit pendant le processus de chargement sur les sols, par exemple, les charges ou les déplacements. Dans ce travail, un nouveau modèle qui est une combinaison de modèle hyperélastique Houlsby et modèle élastoplastique Plasol a été proposé. Ce nouveau modèle a pris en compte la réponse non linéaire de la contrainte dans le domaine élastique et plastique, et l’élasticité anisotrope a également été bien considérée. En outre, les problèmes de l’écoulement de la déformation plastique a été calibré par un algorithme d’intégration approprié. Plus tard, le nouveau modèle a été vérifié en utilisant la méthode numérique et comparé aux expériences de laboratoire dans des conditions triaxiales axisymmétriques. Les résultats de comparaison ont montré un bon effet de simulation du nouveau modèle qui a juste utilisé un seul ensemble de paramètres pour un sol spécifique dans différentes situations de contraintes. Ensuite, l’analyse de la nouvelle variable interne du modèle, c’est-à-dire l’exposant de pression, a montré que la valeur de l’exposant de pression qui correspond au degré d’anisotropie a eu un effet évident sur la réponse contrainte-déformation. De plus, ce type d’effet est également affecté par la densité et l’état de drainage des échantillons. En s’appuyant sur un nouveau modèle, un facteur de sécurité qui fait référence au critère de travail de deuxième ordre a été adopté et testé dans un modèle axisymétrique et un modèle de pente réel. Il a montré que la valeur négative ou la diminution spectaculaire du travail global normalisé de second ordre se produit lors d’une défaillance locale ou globale avec apparition d’énergie cinétique. Cette caractéristique du travail du second ordre peut également être affectée par l’exposant à pression variable. Enfin, un nouveau modèle a également été comparé à un modèle élastoplastique qui considère à la fois l’anisotropie élastique et la dilatation anisotrope, c’est-à-dire le modèle SANISAND modifié. Les avantages et les inconvénients ont été illustrés dans les résultats de comparaison
In order to model the behavior of geometarials under complex loadings, several researches have done numerous experimental works and established relative constitutive models for decades. An important feature of granular materials is that the relationship between stress and strain especially in elastic domain is not linear, unlike the responses of typical metal or rubber. It has been also found that the stress-strain response of granular materials shows the characteristics of cross-anisotropy, as well as the non-linearities. Besides, the stress-induced anisotropy occurs expectedly during the process of disturbance on soils, for example, the loads or displacements. In this work, a new model which is a combination of Houlsby hyperelastic model and elastoplastic Plasol model was proposed. This new model took into account the non-linear response of stress and strain in both elastic and plastic domain, and the anisotropic elasticity was also well considered. Moreover, the overflow problem of plastic strain in plastic part was calibrated by a proper integration algorithm. Later, new model was verified by using numerical method and compared with laboratory experiments in axisymmetric triaxial conditions. The comparison results showed a good simulation effect of new model which just used one single set of parameters for a specific soil in different confining pressure situations. Then the analysis of new model internal variable, i.e., pressure exponent, illustrated that the value of pressure exponent which corresponds to the degree of anisotropy had an obvious effect on the stress-strain response. Moreover, this kind of effect is also affected by the density and drainage condition of samples. Basing on new model, a safety factor which refers to the second-order work criterion was adopted and tested in axisymmetric model and actual slope model. It showed that the negative value or dramatic decreasing of global normalized second-order work occurs accompanying with a local or global failure with a burst of kinetic energy. This feature of second-order work can also be affected by the variable pressure exponent. At last, new model was also compared with an elastoplastic model which considers both anisotropic elastic and anisotropic dilatancy, i.e., modified SANISAND model. Both advantages and disadvantages were illustrated in the comparison results
10

Abdelal, Gasser F. "A three-phase constitutive model for macrobrittle fatigue damage of composites." Morgantown, W. Va. : [West Virginia University Libraries], 2000. http://etd.wvu.edu/templates/showETD.cfm?recnum=1485.

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Thesis (Ph. D.)--West Virginia University, 2000.
Title from document title page. Document formatted into pages; contains xiii, 183 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 180-183).
11

Hammad, Bashar Khalil. "Modeling, Simulation, and Analysis of Micromechanical Filters Coupled with Capacitive Transducers." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/27744.

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The first objective of this Dissertation is to present a methodology to calculate analytically the mode shapes and corresponding natural frequencies and determine critical buckling loads of mechanically coupled microbeam resonators with a focus on micromechanical filters. The second objective is to adopt a nonlinear approach to build a reduced-order model and obtain closed-form expressions for the response of the filter to a primary resonance. The third objective is to investigate the feasibility of employing subharmonic excitation to build bandpass filters consisting of either two sets of two beams coupled mechanically or two sets of clamped-clamped beams. Throughout this Dissertation, we treat filters as distributed-parameter systems. In the first part of the Dissertation, we demonstrate the methodology by considering a mechanical filter composed of two beams coupled by a weak beam. We solve a boundary-value problem (BVP) composed of five equations and twenty boundary conditions for the natural frequencies and mode shapes. We reduce the problem to a set of three linear homogeneous algebraic equations for three constants and the frequencies in order to obtain a deeper insight into the relation between the design parameters and the performance metrics. In an approach similar to the vibration problem, we solve the buckling problem to study the effect of the residual stress on the static stability of the structure. To achieve the second objective, we develop a reduced-order model for the filter by writing the Lagrangian and applying the Galerkin procedure using its analytically calculated linear global mode shapes as basis functions. The resulting model accounts for the geometric and electric nonlinearities and the coupling between them. Using the method of multiple scales, we obtain closed-form expressions for the deflection and the electric current in the case of one-to-one internal and primary resonances. The closed-form solution shows that there are three possible operating ranges, depending on the DC voltage. For low DC voltages, the effective nonlinearity is positive and the filter behavior is hardening, whereas for large DC voltages, the effective nonlinearity is negative and the filter behavior is softening. We found that, when mismatched DC voltages are applied to the primary resonators, the first mode is localized in the softer resonator and the second mode is localized in the stiffer resonator. We note that the excitation amplitude can be increased without worrying about the appearance of multivaluedness when operating the filter in the near-linear range. The upper bound in this case is the occurrence of the dynamic pull-in instability. In the softening and hardening operating ranges, the adverse effects of the multi-valued response, such as hysteresis and jumps, limit the range of the input signal. To achieve the third objective, we propose a filtration technique based on subharmonic resonance excitation to attain bandpass filters with ideal stopband rejection and sharp rolloff. The filtration mechanism depends on tuning two oscillators such that one operates in the softening range and the other operates in the hardening range. Hardware and logic schemes are necessary to realize the proposed filter. We derive a reduced-order model using a methodology similar to that used in the primary excitation case, but with all necessary changes to account for the subharmonic resonance of order one-half. We observe that some manipulations are essential for a structure of two beams coupled by a weak spring to be suitable for filtration. To avoid these complications, we use a pair of single clamped-clamped beams to achieve our goal. Using a model derived by attacking directly the distributed-parameters problem, we suggest design guidelines to select beams that are potential candidates for building a bandpass filter. We demonstrate the proposed mechanism using an example.
Ph. D.
12

AZİZOĞLU, YAĞIZ. "Micromechanical Numeric Investigation of Fiber Bonds in 3D Network Structures." Thesis, KTH, Hållfasthetslära (Avd.), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-144036.

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In manufacturing of paper and paperboard, optimized fiber usage has crucial importance for process efficiency and profitability. Dry strength of paper is one of the important quality criteria, which can be improved by adding dry strength additive that affect fiber to fiber bonding. This study is using the micromechanical simulations which assist interpretation of the experimental results concerning the effect of strength additives. A finite element model for 3D dry fiber network was constructed to study the effect of bond strength, bond area and the number of bonds numerically on the strength of paper products. In the network, fibers’ geometrical properties such as wall thickness, diameter, length and curl were assigned according to fiber characterization of the pulp and SEM analyses of dry paper cross-section. The numerical network was created by depositing the fibers onto a flat surface which should mimic the handsheet-making procedure. In the FE model, each fiber was represented with a number of quadratic Timoshenko beam elements where fiber to fiber bonds were modelled by beam-to-beam contact. The contact model is represented by cohesive zone model, which needs bond strength and bond stiffness in normal and shear directions. To get a reasonable estimate of the bond stiffness, a detailed finite element model of a fiber bond was used. Additionally, the effect of different fiber and bond geometries on bond stiffness were examined by this model since the previous work [13] indicated that the bond stiffness can have a considerable effect on dry strength of paper. The network simulation results show that the effect of the strength additive comes through improving the bond strength primarily. Furthermore, with the considered sheet structure, both the fiber bond compliance and the number of bonds affect the stiffness of paper. Finally, the results of the analyses indicated that the AFM measurements of the fiber adhesion could not be used directly to relate the corresponding changes in the bond strength. The fiber bond simulation concluded that fiber wall thickness has the most significant effect on the fiber bond compliance. It was also affected by micro-fibril orientation angle, bond orientation and the degree of pressing.
13

Marklund, Erik. "Micromechanism based material models for natural fiber composites /." Luleå : Luleå University of Technology, 2005. http://epubl.luth.se/1402-1757/2005/84.

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14

Haberman, Michael Richard. "Frequency dependent micromechanical model of viscoelastic materials with coated inclusions." Thesis, Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/16835.

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15

YI, WEITAO. "MICROMECHANICS BASED COMPOSITE MATERIAL MODELS FOR CRASHWORTHINESS FINITE ELEMENT SIUMLATION." University of Cincinnati / OhioLINK, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=ucin990541929.

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16

Masters, Nathan D. "A Self-Retracting Fully-Compliant Bistable Micromechanism." BYU ScholarsArchive, 2003. https://scholarsarchive.byu.edu/etd/86.

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The purpose of this research is to present a class of Self-Retracting Fully-compliant Bistable Micromechanisms (SRFBM). Fully-compliant mechanisms are needed to overcome the inherent limitations of microfabricated pin joints, especially in bistable mechanisms. The elimination of the clearances associated with pin joints will allow more efficient bistable mechanisms with smaller travel. Small travel, in a linear path facilitates integration with efficient on-chip actuators. Tensural pivots are developed and used to deal with the compressive loading to which the mechanism is subject. SRFBM are modeled using the Pseudo-Rigid-Body Model and finite element analysis. Suitable configurations of the SRFBM concept have been identified and fabricated using the MUMPs process. Complete systems, including external actuators and electrical contacts are 1140 μm by 625 μm (individual SRFBM are less than 300 μm by 300 μm). These systems have been tested, demonstrating on-chip actuation of bistable mechanisms. Power requirements for these systems are approximately 150 mW. Testing with manual force testers has also been completed and correlates well with finite element modeling. Actuation force is approximately 500 μN for forward actuation. Return actuation can be achieved either by external actuators or by thermal self-retraction of the mechanism. Thermal self-retraction is more efficient, but can result in damage to the mechanism. Fatigue testing has been completed on a single device, subjecting it to approximately 2 million duty cycles without failure. Based on the SRFBM concept a number of improvements and adaptations are presented, including systems with further power and displacement reductions and a G-switch for LIGA fabrication.
17

Hsu, Su-Yuen. "Finite element micromechanics modeling of inelastic deformation of unidirectionally fiber-reinforced composites." Diss., Virginia Tech, 1992. http://hdl.handle.net/10919/39842.

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Part I (Efficient Endochronic Finite Element Analysis: an Example of a Cyclically Loaded Boron/Aluminum Composite): A convenient and efficient algorithmic tangent matrix approach has been developed for 3-D finite element (FE) analysis using the endochronic theory without a yield surface. The underlying algorithm for integrating the endochronic constitutive equation was derived by piecewise linearization of the plastic strain path. The approach was employed to solve a micromechanics boundary value problem of a cyclically loaded unidirectional boron/6061 aluminum composite. All the FE results consistently demonstrate superior numerical stability and efficiency of the proposed method. Extensions of the method to endochronic plasticity with a yield surface and to the plane stress case are also presented. Part II (Simple and Unified Finite Element Formulation for Doubly Periodic Models: Applications to Boron/Aluminum Composites): A simple and unified weak formulation and its convenient FE implementation have been proposed. The weak formulation is valid for any doubly periodic model under uniform 3-D macro-stress, and serves as a common rational foundation of different FE approaches. The algorithmic tangent matrix approach for the endochronic theory has been incorporated into the FE formulation to model isothermal, rate-independent plastic macro-deformation of unidirectional fibrous composites with idealized two-phase micro-structure and backed-out inelastic matrix properties. Methods for determining inelastic material parameters of the matrix have been established. Numerical results for a B/6061 AI composite subjected to on-axis and off-axis monotonic tensile loadings are in good agreement with experimental data. The micromechanics model also shows the potential for quantitative characterization of complicated cyclic behavior. Finally, some effects of model geometry on overall plastic response of the B/6061 AI composite are discussed from the viewpoint of theoretical-experimental correlation.
Ph. D.
18

Norouzi, Siavash. "A Micromechanical Model for Numerical Study of Rock Dilation and Ductility." Thesis, New Mexico Institute of Mining and Technology, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10688951.

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The newly implemented micromechanical model in the CA2 computer program was studied in this work. The purpose was to address some of the issues in the numerical studies involving the Bonded Particle Model (BPM) including unrealistically low qu/σ t ratios, overall dilation behavior, and the post-failure response of rocks. The plasticity model allows both tensile and shear softening of the filling material at the contact points of the particles. It is shown that for a more ductile material, there is less scatter of micro-cracking at the peak load. Furthermore, the ductility parameter appears to be a good tool in controlling the ratio of compressive to uniaxial tensile strength of rock. While the ductility of the filling at the contact points of the particles has a drastic effect on the macroscopic post-peak rock behavior in the direct tensile testing, its role in dictating the post-peak rock behavior in compression is negligible and needs further study. The combined effect of ductility and initial micro-cracking on rock strength characteristics was studied as well. The numerical results suggest that the ratio of Brazilian to direct tensile strength of the simulated material is affected by the initial micro-crack intensity; this ratio is around 1 for a material with no initial micro-cracks but it gradually increases as the initial micro-crack intensity is increased. In terms of the overall dilation behavior, it is shown that the macro-dilation angle can be controlled by means of the micro-dilation angle in a positive correlation provided that the average grain size is sufficiently small or when a joint is involved. As the grain size increases, the resulted macro-asperities suppress the functionality of the micro-dilation angle and consequently, the macro-dilation angle cannot be controlled. Further, it is shown that the genesis pressure can help to govern the overall dilation behavior. This parameter is also able to control the post-peak behavior of a bonded particle system. It is shown that high values of the genesis pressure yield to more brittle BPM system with greater dilation angles and steeper post-peak curves.

19

Lee, Seon-Jae. "Micromechanical model for predicting the fracture toughess of functionally graded foams." [Gainesville, Fla.] : University of Florida, 2006. http://purl.fcla.edu/fcla/etd/UFE0013705.

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20

Pilla, Srikanth. "Integration of Micromechanical and Probabilistic Analysis Models of Nanocomposites." University of Toledo / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1134422032.

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21

Bai, Jie. "A homogenization based continuum plasticity-damage model for ductile fracture of materials containing heterogeneities." Columbus, Ohio : Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1211910660.

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22

Averill, Ronald C. "Nonlinear analysis of laminated composite shells using a micromechanics-based progressive damage model." Diss., This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-07282008-134259/.

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23

Sreeranganathan, Arun. "Realistic micromechanical modeling and simulation of two-phase heterogeneous materials." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/24607.

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Thesis (Ph.D.)--Materials Science and Engineering, Georgia Institute of Technology, 2008.
Committee Chair: Gokhale, Arun; Committee Member: Gall, Kenneth; Committee Member: Garmestani, Hamid; Committee Member: Kurtis, Kimberly; Committee Member: Thadhani, Naresh
24

Berner, Joseph Michael. "Finite element analysis of damage in fibrous composites using a micromechanical model." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1993. http://handle.dtic.mil/100.2/ADA277226.

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Thesis (M.S. in Mechanical Engineering and Mechanical Engineer) Naval Postgraduate School, December 1993.
Thesis advisor(s): Young W. Kwon. "December 1993." Includes bibliographical references. Also available online.
25

Xiao, Long. "A structural micromechanical model of large deformation behavior of red blood cells." Connect to online resource, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1458440.

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26

Åström, Jan. "Micromechanical models of the elasticity and fracture of fibre networks /." Åbo : Åbo akademi, 1996. http://catalogue.bnf.fr/ark:/12148/cb41444383f.

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27

AMINJIKARAI, SRINIVASA BABU. "A STRAIN RATE DEPENDENT 3D MICROMECHANICAL MODEL FOR FINITE ELEMENT SIMULATIONS OF PLAIN WEAVE COMPOSITE STRUCTURES." University of Cincinnati / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1070549522.

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28

Jiang, Tianci. "Impact & penetration studies simplified models and and materials design from AB initio methods /." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10443.

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In recent impact and penetration mechanical tests, steel projectiles (AISI4340) were impacted into targets like concrete with striking velocities (1200 m/s to 1500 m/s). Results indicated a material removal from the nose of the projectile, phase changes of the projectile materials, a reduction in the length of the projectile, and a blunting of the nose shape. These observations cannot be explained by current theories and numerical integration code that are used to study impact and penetration mechanics. Thus, the objectives of the thesis research are to (a) formulate and characterize the mechanisms responsible for the material erosion of the impacting projectile and the mass loss from the nose region; and (b) to determine the physical properties of alloy steels that are important to penetration mechanics from ab initio methods. The results can be used to design new projectile materials that can provide the desired penetration characteristics. These objectives are accomplished by investigating two related problems. The first problem is to formulate simplified models that can explain the penetration mechanics. The new models include the varying cross-section nose, changes of yield stress behind the shock wave and high strain rate phase transitions. Nose erosion effects, and time-dependent penetration path can be determined by integrating ODEs. A cavity expansion theory model is used to obtain the target resistance that is responsible slowing and deforming the penetrating projectile. The second problem concerns the determination of the constitutive relations from ab initio methods. The equation of state (EOS) and magnetic moments for alloy steels are investigated by using a special quasirandom structure technique and ab initio methods. Specifically, EOS for an interstitial disordered alloy Fe1-x-yNixCy is developed. First, the EOS of iron and phase transition of iron are studied and validated. Second, Nickel is considered to investigate the substitutional disordered alloy Fe1-x-yNixCy. Third, Carbon is placed at an interstitial position in the substitutional disordered alloy. These investigations will form foundation for future work involving new projectile with steel nose and shank made of multifunctional structural energetic materials.
29

Kilic, Mustafa Hakan. "Three-dimensional micromechanical models for the nonlinear analysis of pultruded composite structures." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/20735.

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30

Parietti, Lucie. "Micromechanical finite element model for constitutive elastoplastic analysis of unidirectional fiber-reinforced composites." Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-06232009-063447/.

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31

Macchi, Juan Agustin. "Phase transformations, microstructure heterogeneities and resulting mechanical properties in as-quenched and tempered martensitic steels." Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0248.

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Les aciers martensitiques sont connus et utilisés depuis des millénaires, mais l'origine de leur résistance et de leur écrouissage est restée une source de controverse. Depuis quelques années, la compréhension de leur comportement mécanique est en train de changer de paradigme. De nombreux chercheurs ont mis en évidence l'intérêt de ne pas décrire la martensite en lattes comme une microstructure homogène mais plutôt comme un agrégat multi phasé, un composite, résultant de la nature séquentielle de la transformation de phase à basse température. Selon ces nouveaux schémas, le comportement de la martensite est contrôlé par les hétérogénéités microstructurales, c'est-à-dire la distribution spatiale des tailles des lattes, des dislocations, des ségrégations de carbone et des carbures, et pas seulement par leurs valeurs moyennes. A ces éléments microstructuraux observables s'ajoutent de grandes distributions de contraintes internes hydrostatiques et déviatoriques résultant du processus de transformation de phase displacive. Ce travail contribue à ce nouveau mouvement en fournissant une description quantitative de ces distributions dans les aciers martensitiques trempés et revenus et leur impact sur leurs comportements mécaniques grâce à une approche micromécanique complète. Nous avons d'abord développé une méthodologie pour déterminer les densités de dislocation dans la martensite et dans l'austénite le long de la transformation par des expériences in situ de DRXHE. Sur la base d'un raisonnement métallurgique, la distribution spatiale de la densité de dislocation ainsi que le durcissement associé ont été estimés pour la première fois. Des expériences de revenu en DRXHE in situ ont également été réalisées pour caractériser la restauration de l'état trempé. Une approche originale de modélisation tenant compte de la distribution spatiale des dislocations a été mise en place pour prédire la diminution de leur densité lors d'un traitement thermique. De même, les microtextures des microstructures étudiées ont été étudiées par MEB-EBSD afin d'évaluer la distribution en taille des différentes caractéristiques de la martensite, comme les lattes, les blocs, les paquets et les grains d'austénite antérieurs. Une approche statistique combinant cette dernière contribution au durcissement avec celle associée aux dislocations explique avec succès la distribution observée de la limite d'élasticité locale dans les microstructures telles que trempées.Des expériences de revenu DRXHE in situ et des observations complémentaires APT et MET ont été utilisées pour caractériser également l'état de précipitation respectif des carbures de transition et de la cémentite ainsi que les ségrégations de carbone au cours des traitements thermiques. Tout ce travail expérimental a servi à développer et calibrer un modèle de transformation de phase pour calculer la ségrégation du carbone sur les dislocations, les carbures de transition et les états de précipitation de la cémentite. Ce modèle a par exemple permis de prédire la suppression de la précipitation des carbures de transition dans les aciers à très faible teneur en carbone. L'étude du revenu est nécessaire pour comprendre le renforcement dû au seul carbone dans la martensite.Enfin, notre modèle micromécanique original décrivant le comportement de la martensite comme une transition élastique/plastique étendue tient compte du durcissement combiné précédent dû aux effets de taille et aux dislocations, de la distribution des contraintes internes dues à la transformation et de l'état de revenu (relaxation, restauration, ségrégation et état de précipitation). Le modèle explique avec succès la résistance et l'écrouissage des aciers étudiés (trempés et revenus)
Martensitic steels have been known and used for millennia now, but the origins of their strength and work hardening have remained a source of controversy. Since few years, the understanding of their mechanical behavior is changing paradigm. Many researchers have put into evidence the interest not to describe lath martensite as an homogeneous microstructure but more as a multiphase aggregate, a composite, resulting from the sequential nature of the phase transformation at low temperature. According to such new schemes, the martensite behavior is controlled by the microstructural heterogeneities, ie. the spatial distribution of lath sizes, of dislocations, of carbon segregations and of carbides and not only by their mean values. To these observable microstructural elements are added large distributions of hydrostatic and deviatoric internal stresses resulting from the displacive phase transformation process. This work contributes to this new movement by providing a quantitative description of these distributions in as-quenched and further tempered martensitic steels and their impact on their mechanical behaviors thanks to a complete micromechanical approach.We have first developed a methodology to determine the dislocation densities in martensite and in austenite along the transformation by in situ HEXRD experiments. Based on a metallurgical reasoning, the spatial dislocation density distribution as well as its associated hardening were estimated for the first time. In situ HEXRD tempering experiments were also performed to characterize the recovery from the as-quenched state. An original modeling approach accounting for the spatial distribution of dislocations was set up to predict their density decrease during a heat treatment.In the same way, the microtextures of the studied microstructures were investigated by SEM-EBSD in order to assess the size distribution of the different features of martensite, as laths, blocks, packets and prior austenite grains. A statistical approach combining this latter contribution to the hardening with the one associated with dislocations explains successfully the observed distribution of the local yield strength in the as-quenched microstructures.In situ HEXRD tempering experiments and additional APT and TEM observations were used to characterize also the respective precipitation state of transition carbides and cementite as well as the carbon segregations along heat treatments. All this experimental work has served to develop and calibrate a phase transformation model to calculate carbon segregation on dislocations, transition carbides and cementite precipitation states. Such model was for instance able to predict the suppression of transition carbide precipitation in very low carbon steels. The investigation of tempering is necessary to understand the strengthening due the sole carbon in martensite.Finally, our original micromechanical model describing the martensite behavior as an extended elastic/plastic transition accounts for the previous combined hardening due to size effects and dislocations, the distribution of internal stresses due to the transformation and the tempering state (relaxation, recovery, segregation and precipitation state). The model successfully explains the strength and work-hardening of the studied steels (as quenched and tempered)
32

Song, Injun. "Damage analysis in asphalt concrete mixtures based on parameter relationships." Texas A&M University, 2004. http://hdl.handle.net/1969.1/1300.

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Asphalt pavements experience damage due to traffic loading under various environmental conditions. Damage can be caused by viscopl microcracks, fracture due to fatigue cracking, or fracture due to thermal cracking. Asphalt pavements have the capability to remedi s damage depending on binder surface and rheological properties, filler surface properties, and length of rest periods. Asphalt mastic (asphalt and fine aggregates) properties play an important role in controlling damage and healing. This dissertation development of a comprehensive methodology to characterize damage and healing in asphalt mastics and mixtures. The methodology reli ctive imaging techniques (X-ray CT), principles of continuum damage mechanics, and principles of micromechanics. The X-ray CT yield meter that quantifies the percentage of cracks and air voids in a specimen. The continuum damage model parameters are derived from p between applied stress and pseudo strain. The micromechanics model relates the damaged mastic modulus to a reference undamaged mo ationship is a function of internal structure properties (void size, film thickness, and percentage of voids), binder modulus, aggr and bond energy between binder and aggregates. The internal structure parameters are all obtained using X-ray CT and correlated. The developed methodology was used to characterize damage in asphalt mastic and mixture specimens tested using the Dynamic Mechanic A) and dynamic creep test. The damage parameter measured using X-ray CT correlated very well with the predictions of the continuum ics models. All damage parameters were able to reflect the accumulation of damage under cyclic loading and were also able to captur of moisture conditioning on damage. Although this dissertation focused on fatigue cracking at room temperatures, the methodology d used to assess damage due to different mechanisms such as permanent deformation and low temperature cracking.
33

Estrada, Jonathan Bartholomew. "Scaling the rock : a micromechanical model for the elastic properties of hydrated cement pastes." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/101860.

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Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 61-62).
Cement is the most widely produced material worldwide. However, the understanding on how its nanoscale composition affect its microscale mechanical properties is limited. In this thesis, a micromechanical model for the purpose of cement hydration simulation was developed and tested using HYMOSTRUC3D hydration software and a micromechanical particle with interphase model developed by Deng and Van Vliet. It was then tested against empirical micro- and nanoindentation tests done on samples synthesized, cured, and prepared in situ. Preliminary mechanical calculations coupled with the hydration software show good agreement with experimental data. Additionally, predicted ranges of effective particle moduli values were found in nanoindentation testing. These observations support the validity of treating high density C-S-H as an interphase between low density C-S-H and clinker particles.
by Jonathan Bartholomew Estrada.
S.B.
34

Varadarajan, Bhadri Narayanan. "MICROMECHANICS OF DEBOND GROWTH AND INTERFACIAL WEAR UNDER FATIGUE LOADING IN A TRANSPARENT CERAMIC COMPOSITE." University of Cincinnati / OhioLINK, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=ucin975352464.

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35

Guo, Jia-Yuarn. "Simplified micromechanical models for analysis of interface debonding in a fibrous composite." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1995. http://handle.dtic.mil/100.2/ADA306624.

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36

Dharmasena, Sajith Mevan. "A Multi-Channel Micromechanical Cantilever for Advanced Multi-Modal Atomic Force Microscopy." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1565883484835926.

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37

Zhang, Ningning. "A micromechanical study of the Standard Penetration Test." Doctoral thesis, Universitat Politècnica de Catalunya, 2020. http://hdl.handle.net/10803/668841.

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This thesis explores the potential of models based on the discrete element method (DEM) to study dynamic probing of granular materials, considering realistic particle-scale properties. The virtual calibration chamber technique, based on the discrete element method, is applied to study the standard penetration test (SPT). A macro-element approach is used to represent a rod driven with an impact like those applied to perform SPT. The rod is driven into a chamber filled with a scaled discrete analogue of a quartz sand. The contact properties of the discrete analogue are calibrated simulating two low-pressure triaxial tests. The rod is driven changing input energy and controlling initial density and confinement stress. Energy-based blowcount normalization is shown to be effective. Results obtained are in good quantitative agreement with well-accepted experimentally-based relations between blowcount, density and overburden. A comprehensive energetic balance of the virtual calibration chamber is conducted. Energy balance is applied separately to the driven rod and the chamber system, giving a detailed account of all the different energy terms. The characterization of the evolution and distribution of each energy component is investigated. It appears that the SPT test input energy is mainly dissipated in friction. The energy-based interpretation of SPT dynamic response proposed by Schnaid et al. (2017) is then validated in comparisons between static and dynamic penetration results. Moreover, microscale investigation provides important information on energy dissipation mechanisms. A well-established DEM crushing contact model and a rough Hertzian contact model are combined to incorporate both effects in a single contact model. The efficient user defined contact model (UDCM) technique is used for the contact model implementation. Parametric studies explore the effect of particle roughness on single particle crushing event. The model is then used to recalibrate the contact properties of the quartz sand, being able to use realistic contact properties and then correctly capture both load-unload behaviour and particle size distribution evolution. The calibration chamber results are exploited to investigate the relation between static and dynamic penetration test. This is done first for unbreakable materials and later for crushable and rough-crushable ones. It is shown that the tip resistance measured under impact dynamic penetration conditions is very close to that under constant velocity conditions, hence supporting recent proposals to relate CPT and SPT results. It is also shown that penetration resistance reduces if particles are allowed to break, particularly when roughness is also considered.
Esta tesis explora el potencial de los modelos basados en el método de elementos discretos (DEM) para estudiar el sondeo dinámico de materiales granulares, considerando propiedades realistas a escala de partículas. La técnica de cámara de calibración virtual, basada en el método de elemento discreto, se aplica para estudiar la prueba de penetración estándar (SPT). Se utiliza un enfoque de macroelemento para representar una barra impulsada con un impacto como los aplicados para realizar SPT. La varilla se introduce en una cámara llena de un análogo discreto escalado de arena de cuarzo. Las propiedades de contacto del análogo discreto se calibran simulando dos pruebas triaxiales de baja presión. La varilla se acciona cambiando la energía de entrada y controlando la densidad inicial y el estrés de confinamiento. La normalización del recuento de golpes basado en energía se muestra efectiva. Los resultados obtenidos están en buen acuerdo cuantitativo con relaciones basadas en experimentos bien aceptadas entre recuento de golpes, densidad y sobrecarga. Se realiza un balance energético integral de la cámara de calibración virtual. El balance de energía se aplica por separado a la varilla impulsada y al sistema de cámara, dando una descripción detallada de todos los diferentes términos de energía. Se investiga la caracterización de la evolución y distribución de cada componente energético. Parece que la energía de entrada de prueba SPT se disipa principalmente en fricción. La interpretación basada en la energía de la respuesta dinámica SPT propuesta por Schnaid et al. (2017) luego se valida en comparaciones entre los resultados de penetración estática y dinámica. Además, la investigación en microescala proporciona información importante sobre los mecanismos de disipación de energía. Un modelo de contacto de trituración DEM bien establecido y un modelo de contacto hertziano aproximado se combinan para incorporar ambos efectos en un modelo de contacto único. La técnica eficiente de modelo de contacto definido por el usuario (UDCM) se utiliza para la implementación del modelo de contacto. Los estudios paramétricos exploran el efecto de la rugosidad de las partículas en el evento de trituración de partículas individuales. El modelo se usa para recalibrar las propiedades de contacto de la arena de cuarzo, pudiendo usar propiedades de contacto realistas y luego capturar correctamente el comportamiento de carga y descarga y la evolución de la distribución del tamaño de partícula. Los resultados de la cámara de calibración se explotan para investigar la relación entre la prueba de penetración estática y dinámica. Esto se hace primero para materiales irrompibles y luego para materiales triturables y desmenuzables. Se muestra que la resistencia de la punta medida en condiciones de penetración dinámica de impacto es muy cercana a la de condiciones de velocidad constante, por lo tanto, respalda propuestas recientes para relacionar los resultados de CPT y SPT. También se muestra que la resistencia a la penetración se reduce si se permite que las partículas se rompan, particularmente cuando también se considera la aspereza.
38

Lukhi, Mehul. "Micromechanical Simulation of Fatigue in Nodular Cast Iron." Technische Universität Bergakademie Freiberg, 2020. https://tubaf.qucosa.de/id/qucosa%3A72791.

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In the present thesis, fatigue behavior of nodular cast iron (NCI) is investigated using micromechanical simulations. An elastic-plastic porous material experiences an increase in a void volume fraction with each cycle of loading. This is called void ratchetting. The hypothesis of this thesis is to explain the fatigue failure of NCI using void ratchetting mechanism. The strain-life, stress-life, notch support effect, and fatigue crack growth are studied using the micromechanical simulations. In all these studies, matrix material is defined as an elastic-plastic with isotropic/kinematic hardening. No damage law is used to define material degradation. The axisymmetric cell model is developed to study strain-life and stress-life approaches for fatigue. The cell model is subjected to cyclic loading and cycle by cycle simulations are carried out until failure. The failure of the cell model is defined based on the drop in the macroscopic response of the cell model. The notch support effect is investigated using a 2D plane strain model within stress-life concept. From the simulation results, strain-life and stress-life curves are extracted, and they are in qualitative and quantitative agreement with experimental data collected from literature. The fatigue crack growth is studied using a micromechanical cell model under small scale yielding conditions. The graphite particles are considered as voids, and they are resolved discretely in fracture process zone. The region outside of the fracture process zone is considered as a homogenized medium. When positive alternating loads are applied, ligaments in the fracture process zone show ratchetting behavior, which is responsible for an effective fatigue crack growth. This mechanism is relevant for the fatigue crack growth in NCI. The 2D plane strain boundary layer model is able to predict the effect of load ratio on threshold for the fatigue crack growth and the fatigue crack growth rate. The fatigue crack growth rate curves obtained from the simulations are compared with experimental data. It is essential to note that the void ratchetting (plastic collapse of the intervoid ligaments) is a crucial mechanism in NCI and more focus should be given to this mechanism as it is simple to implement and gives satisfying simulation results.
39

Kim, Jinkoo. "Micromechanical model for damage and failure of brittle materials : application to polycrystalline ice and concrete." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/11389.

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40

Haberman, Keith Rosakis Ares J. Rosakis Ares J. "A micromechanical constitutive model for the dynamic response of brittle materials "Dynamic response of marble" /." Diss., Pasadena, Calif. : California Institute of Technology, 2000. http://resolver.caltech.edu/CaltechETD:etd-12182007-113248.

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41

Morrissey, Ryan J. "Strain accumulation and shakedown in fatigue of Ti-6A1-4V by Ryan J Morrissey." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/17144.

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42

Suwatnodom, Prechaporn. "3-D micromechanical damage models, fiber pullout models and fracture toughness of discontinuous steel fiber reinforced cementitious composites." Diss., Restricted to subscribing institutions, 2008. http://proquest.umi.com/pqdweb?did=1562125051&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.

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43

Rome, Jacob I. "Experimental characterization and micromechanical modeling of the dynamic response and failure modes of concrete /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2002. http://wwwlib.umi.com/cr/ucsd/fullcit?p3061638.

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44

Khan, Kamran-Ahmed. "A time integration scheme for stress - temperature dependent viscoelastic behaviors of isotropic materials." [College Station, Tex. : Texas A&M University, 2006. http://hdl.handle.net/1969.1/ETD-TAMU-1146.

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45

Gydemo, Jessica. "Simulation of injection molded fiber reinforced polymers." Thesis, Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-62758.

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46

Gili, Ripoll José Antonio. "Modelo microestructural para medios granulares no saturados." Doctoral thesis, Universitat Politècnica de Catalunya, 1988. http://hdl.handle.net/10803/5916.

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Se ha llevado a cabo:

A) Un estudio de las propiedades básicas del suelo no saturado (tipo limo) a escala microestructural, incluyendo esqueleto sólido, fase liquida y fase gaseosa.

B) Elaboración de un modelo conceptual discontinuo de comportamiento. La geometría interna esta construida por partículas, agua retenida en forma de meniscos alrededor de los contactos y aire ocupando los restantes poros. La interfase liquido gas esta gobernada por la succión y la tensión superficial. Los meniscos tienen un efecto rigidizador del esqueleto.
Se observa la posible redistribución de la humedad y del aire, quedando acoplados en definitiva los aspectos mecánicos y de flujo.

C) En base a lo anterior, implementación de un modelo numérico discontinuo de ensayo de comportamiento basado en ordenador. Se ha adaptado y modificado el D.E.M. de P.A. Cundall (diferencias finitas explicitas en el tiempo), indicado en el caso que se trata, con no-linealidades geométricas. Se han desarrollado importantes algoritmos de control geométrico.

D) Verificación parcial del modelo y aplicación a casos típicos en suelo no saturado, especialmente el colapso.

En conjunto es una herramienta útil para su estudio y permite apreciar algunos interesantes mecanismos de actuación de la succión a escala microscópica.
47

Gili, Ripoll Josep Antoni. "Modelo microestructural para medios granulares no saturados." Doctoral thesis, Universitat Politècnica de Catalunya, 1988. http://hdl.handle.net/10803/5916.

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Se ha llevado a cabo:A) Un estudio de las propiedades básicas del suelo no saturado (tipo limo) a escala microestructural, incluyendo esqueleto sólido, fase liquida y fase gaseosa. B) Elaboración de un modelo conceptual discontinuo de comportamiento. La geometría interna esta construida por partículas, agua retenida en forma de meniscos alrededor de los contactos y aire ocupando los restantes poros. La interfase liquido gas esta gobernada por la succión y la tensión superficial. Los meniscos tienen un efecto rigidizador del esqueleto.Se observa la posible redistribución de la humedad y del aire, quedando acoplados en definitiva los aspectos mecánicos y de flujo.C) En base a lo anterior, implementación de un modelo numérico discontinuo de ensayo de comportamiento basado en ordenador. Se ha adaptado y modificado el D.E.M. de P.A. Cundall (diferencias finitas explicitas en el tiempo), indicado en el caso que se trata, con no-linealidades geométricas. Se han desarrollado importantes algoritmos de control geométrico. D) Verificación parcial del modelo y aplicación a casos típicos en suelo no saturado, especialmente el colapso.En conjunto es una herramienta útil para su estudio y permite apreciar algunos interesantes mecanismos de actuación de la succión a escala microscópica.
48

Thomas, Michael Andrew. "Framework for Cohesive Zone Model Based Multiscale Damage Evolution in a Fatigue Environment." Wright State University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=wright1308257790.

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49

Oikonomidis, Fokon Th. "Prediction of crack propagation in natural gas transmission pipelines by means of micromechanics and strain rate dependent models." Thesis, University of Bristol, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.541649.

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50

Oberhardt, Tobias. "A micromechanical model for the nonlinearity of microcracks in random distributions and their effect on higher harmonic Rayleigh wave generation." Thesis, Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54365.

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This research investigates the modeling of randomly distributed surface-breaking microcracks and their effects on higher harmonic generation in Rayleigh surface waves. The modeling is based on micromechanical considerations of rough surface contact. The nonlinear behavior of a single microcrack is described by a hyperelastic effective stress-strain relationship. Finite element simulations of nonlinear wave propagation in a solid with distributed microcracks are performed. The evolution of fundamental and second harmonic amplitudes along the propagation distance is studied and the acoustic nonlinearity parameter is calculated. The results show that the nonlinearity parameter increases with crack density and root mean square roughness of the crack faces. While, for a dilute concentration of microcracks, the increase in acoustic nonlinearity is proportional to the crack density, this is not valid for higher crack densities, as the microcracks start to interact. Finally, it is shown that odd higher harmonic generation in Rayleigh surface waves due to sliding crack faces introduces a friction nonlinearity.
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