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Strain hardening cementitious composites (SHCCs) are a type of cementitious material reinforced with randomly distributed short fibers that exhibit tensile strain hardening behavior and prominent crack resistance. The tensile behavior of SHCCs could be significantly affected by the distribution of the fiber orientation. In large-scale specimens, the distribution of the fiber orientation is close to ideal three-dimensional uniform random distribution. However, fiber orientation distributions in laboratory SHCC specimens are influenced by the specimen dimensions (width and thickness) and casting process, resulting in neither ideal two-dimensional nor three-dimensional uniform random distribution. Therefore, the performance of large-scale SHCC specimens may be overestimated in analysis when directly using the tensile properties of SHCCs obtained from uniaxial tensile tests of small specimens. Since the uniaxial tensile tests of large-scale SHCC specimens are difficult to be conducted, theoretical evaluation of the tensile properties of mass SHCCs in large-scale specimens were conducted by modifying the uniaxial tensile test results of small specimens. In this paper, closed-form probability distribution models for fiber orientations that consider the influence of the specimen width and thickness were theoretically derived. The effects of the specimen width and thickness on the tensile properties of SHCCs were studied by applying the proposed method to the uniaxial tensile numerical model of SHCCs, while uniaxial tensile specimens with two different geometries and dimensions were tested for verification. Both the analytical and experimental results showed that, within a certain range, the width and thickness of the specimens significantly influenced their ultimate tensile strength and ultimate tensile strain. To relate the uniaxial tensile test results of laboratory-sized specimens to that of mass SHCC in large scale specimens, reduction factors for the stress–strain rel

A microstructural model is presented to assess pit-to-crack transition and corrosion fatigue strength in pitted components in different environments. The model is first validated using available experimental data in the literature for pitting corrosion fatigue strength and S-N curves for both carbon and stainless steels. The value of the method proposed and its applicability is then shown by the development of fatigue knock down factor maps to the in-air S-N curve. Finally, the influence of pit local topology on pit-to-crack transition damage tolerance and the links to the NDE methods quantitative resolution necessary to account for defect shape or acuity in structural integrity assessments are discussed

To meet the demand for low-cost, lightweight, portable and building-integrated solar cells, developing flexible and cost-efficient photo-active hybrid films is of significant interest. In this work, we investigate the mechanical properties of hybrid layers consisting of mesoporous TiO 2 filled with poly(3-hexylthiophene-2,5-diyl) (P3HT) as a function of the number of bending cycles. The TiO 2 /P3HT layers are deposited on flexible PET substrates at low temperatures (≤140 °C), which is beneficial for reducing the processing energy input and in turn lowering the production costs. Non-filled and partially filled mesoporous titania films are studied for comparison. The surface morphology is examined with scanning electron microscopy (SEM) before and after the bending tests. The inner film morphology is characterized with grazing incidence small-angle X-ray scattering (GISAXS). Based on the observed morphology, micromechanical models are used to analyze the mechanical properties of the investigated films. The results show that the TiO 2 /P3HT layers have a low elastic modulus and P3HT helps to stabilize the titania nanostructures against fracture. The SEM observations are well explained with the established models in a quantitative way., QC 20190614

Roads are subjected to mechanical loads from the traffic as well as deteriorating mechanisms originating from the surrounding environment and climate. The damage arising is particularly severe during the winter season, when for example raveling, pot holes and cracks can emerge on the surfaces of asphaltic roads. These winter related damages are difficult to characterize and predict, partly due to the complexity of the asphalt material and partly since they cannot be linked to one single phenomenon but several, such as the (long term) existence of moisture, frost damage and frost heave, low temperature cracking and the embrittlement of the mastic at low temperatures. Further adding to the complexity is the combination of these phenomena which may accelerate the emergence and evolution of the damage mechanisms. This licentiate research project is mainly focusing on the emergence and development of frost damage in the asphalt layer but will include the effect of other damage mechanisms in its continuation. The goal of the project is to develop a multiscale model able to predict the damage development in an asphalt pavement during a desired period of time, to enhance maintenance predictions as well as pavement design choices. This licentiate thesis is the first part of this project and aims to lay the foundation of the multiscale model. To achieve this, a micromechanical model of frost damage in asphalt mixtures has been developed. This model couples the moisture and mechanical damage happening on the short and long term, caused by the infiltration of moisture and the expansion of water turning into ice during temperature drops. Both possible adhesive damage in the mastic-aggregate interface and cohesive damage in the mastic is included. In addition to the developed micromechanical model, this thesis presents the overall concept for the formulation of the multiscale model as well as discusses about its motivations and advantages., Vägar utsätts både för mekaniska laster från trafiken som kör på vägen samt för nedbrytande mekanismer härstammande från den omgivande miljön och klimatet. Skadorna som uppstår är särskilt stora under vintern, då till exempel stensläpp, potthål och sprickor kan uppstå på ytan av asfalterade vägar. Dessa vinterrelaterade skador är svåra att karakterisera och förutsäga, delvis på grund av det komplexa beteendet hos asfalt och delvis eftersom de inte härstammar från enbart ett fenomen utan flera, såsom existensen av fukt i asfalten (på lång sikt), frostskador, tjällyft, sprickbildning på grund av låg temperatur samt försprödningen av asfalt som sker vid låga temperaturer. Vidare påverkar dessa skademekanismer varandra vilket kan accelerera skadebildningen och utvecklingen, vilket ytterligare ökar komplexiteten. Detta licentiatforskningsprojekt fokuserar till största delen på uppkomsten och utvecklingen av frostskador men kommer även inkludera effekten av andra skademekanismer i dess fortsättning. Målet med detta forskningsprojekt är att utveckla en multiskalemodell som kan förutspå skadeutvecklingen i en asfaltsväg under en önskad tidsperiod, för att förbättra både underhållsprognoser samt designval. Denna licentiatuppsats är den första delen i detta projekt och syftar till att lägga grunden till multiskalemodellen. För att uppnå detta har en mikromekanisk modell av frostskador i asfalt utvecklats. Denna modell kopplar ihop fuktskadan och den mekaniska skadan som sker både på kort och lång sikt, orsakad av infiltrationen av fukt och expansionen av vatten som omvandlas till is vid sjunkande temperatur. Modellen inkluderar de möjliga skadorna som uppstår i både mastics och gränsskiktet mellan mastics och stenmaterialet. Utöver den utvecklade mikromekaniska modellen presenterar denna uppsats det övergripande konceptet för formuleringen av multiskalemodellen samt diskuterar dess motivering och fördelar., QC20190515

Some manufacturing processes of polymeric materials, such as injection molding or film blowing, cause the final product to be highly anisotropic. In this study, the mechanical behavior of drawn polyethylene (PE) tapes is investigated via micromechanical modeling. An elasto-viscoplastic micromechanical model, developed within the framework of the so-called composite inclusion model, is presented to capture the anisotropic behavior of oriented semicrystalline PE. Two different phases, namely amorphous and crystalline (both described by elasto-viscoplastic constitutive models), are considered at the microstructural level. The initial oriented crystallographic structure of the drawn tapes is taken into account. It was previously shown by Sedighiamiri et al. (Comp. Mater. Sci. 2014, 82, 415) that by only considering the oriented crystallographic structure, it is not possible to capture the macroscopic anisotropic behavior of drawn tapes. The main contribution of this study is the development of an anisotropic model for the amorphous phase within the micromechanical framework. An Eindhoven glassy polymer (EGP)-based model including different sources of anisotropy, namely anisotropic elasticity, internal stress in the elastic network and anisotropic viscoplasticity, is developed for the amorphous phase and incorporated into the micromechanical model. Comparisons against experimental results reveal remarkable improvements of the model predictions (compared to micromechanical model predictions including isotropic amorphous domains) and thus the significance of the amorphous phase anisotropy on the overall behavior of drawn PE tapes.

The topic of this work is assessment of ductile fracture initiation and development in different zones of welded joint of a high strength low alloyed (HSLA) steel. A combined experimental-numerical procedure is applied for determination of properties of the weld metal and the heat affected zone - HAZ. One tensile specimen with rectangular cross-section is tested, and the surface strains are determined using stereometric 3D measurement (measurement system Gom Aramis with two cameras and software solution). This methodology enabled formation of the stress-strain curves for micromechanical analysis of fracture of specimens with initial fatigue pre-cracks. Two different geometries are considered: standard single-edge notched bend (SENB) specimens and surface-cracked tensile specimens. The cracks were positioned either in weld metal or in HAZ - within the fine-grained part. Micromechanical model (complete Gurson model, by Z.L. Zhang) is applied for assessment of crack growth onset and stable growth. Higher resistance to ductile fracture initiation and crack growth in HAZ is successfully predicted, as well as constraint effect caused by different crack shapes.

This study deals with the numerical prediction of ductile fracture initiation and development in welded joints of a high strength low alloyed steel. Having in mind the material heterogeneity in the joint zone, a combined experimental-numerical procedure is applied for determination of properties of the weld metal and heat affected zone - HAZ (both coarse-grained and fine-grained portion). Single smooth tensile specimen is tested, and the surface strains are determined during this test using stereometric measurement. Combined with numerical analysis, this enabled determination of stress-strain curves, which are subsequently used in numerical analysis of fracture of pre-cracked specimens. Two different geometries are considered: standard single-edge notched bend (SENB) specimens and surface-cracked tensile specimens. In each of them, the crack is positioned either in weld metal or between the coarse-grained and fine-grained HAZ. Micromechanical model (complete Gurson model, by Z.L. Zhang) is applied in numerical analysis. Higher resistance to ductile fracture initiation and crack growth in HAZ is successfully predicted, as well as constraint effect caused by different crack shapes.

Microstructure-elasticity relations for bone tissue engineering scaffolds are key to rational biomaterial design. As a contribution thereto, we here report comprehensive length measuring, weighing, and ultrasonic tests at 0.1 MHz frequency, on porous baghdadite (Ca3ZrSi2O9) scaffolds. The resulting porosity-stiffness relations further confirm a formerly detected, micromechanically explained, general relationship for a great variety of different polycrystals, which also allows for estimating the zero-porosity case, i.e. Young modulus and Poisson ratio of pure (dense) baghdadite. These estimates were impressively confirmed by a physically and statistically independent nanoindentation campaign. comprising some 1750 indents. Consequently, we can present a remarkably complete picture of porous baghdadite elasticity across a wide range of porosities, and, thanks to the micromechanical understanding, reaching out beyond classical elasticity, towards poroelastic properties, quantifying the effect of pore pressure on the material system behavior. (C) 2014 The Authors. Published by Elsevier B.V.

A model for the analysis of masonry periodic unit cells based on detailed micro-modeling principles is presented: an analytical model capable of calculating the orthotropic elastic properties of masonry composites. Several masonry typologies are investigated in the present paper, some of which have received very limited attention, such as Flemish bond walls.; The purpose of the model is to achieve the level of detail made possible by the use of detailed micro-modeling techniques while keeping computational costs at a minimum in order to be used as a basis for two-scale modeling of masonry.; The results obtained from the described model are compared with experimental data from the existing relevant literature as well as with numerical results obtained from the finite element analysis of masonry periodic unit cells. A parametric investigation is also performed, in which the accuracy of the model is compared against a FE benchmark., Peer Reviewed, Postprint (author’s final draft)

Bone remodeling is a process involving removal of mature bone tissue and subsequent formation of new bone tissue. This process is driven by complex actions of biological cells and biochemical factors, and it is sensitive to the loads applied onto the skeleton. Herein, we develop a mathematical framework describing this process at the (macroscopic) level of cortical bone, by combining, for the first time, bone cell population kinetics with multiscale bone mechanics. Key variables are concentrations of biological cells (osteoclasts, osteoblasts and their progenitors) and biochemical factors (RANK, RANKL, OPG, PTH, and TGF-beta), as well as mechanical strains, both at the ("macroscopic") level of cortical bone and at the ("microscopic") level of the extravascular bone matrix. Multiscale bone mechanics delivers, as a function of the vascular porosity, the relation between the macroscopic strains resulting from the loads, and the microscopic strains, which are known to modulate, either directly, or via poromechanical couplings such as hydrostatic pressure or fluid flow, the expression or proliferation behavior of the biological cells residing in, or attached to the extravascular bone matrix. Hence, these microscopic strains enter the biochemical kinetics laws governing cell expression, proliferation, differentiation, and apoptosis. Without any additional phenomenologically motivated paradigm, this novel approach is able to explain the experimentally observed evolutions of bone mass in postmenopausal osteoporosis and under microgravity conditions: namely, a decrease of bone loss over time.

The development of new heterogeneous metallic materials with high resistance, such as multiphase steels, a/b Ti-alloys, or Al-alloys involving precipitate free zones, is often impeded by the lack of understanding and control of the damage and fracture mechanisms. The objective of the thesis has been to develop a multiscale modelling strategy in order to unravel the relationships between the micromechanisms of ductile fracture and the microstructure of heterogeneous alloys. The present work also contributes to enhancing the predictive capabilities of ductile fracture models regarding structural integrity assessment. More precisely, we have developed new extensions of a Gurson-type constitutive model describing the growth and coalescence of spheroidal voids, possibly not oriented parallel to the main loading direction. These extensions are essentially (i) a description of the void rotation and deformation under shear, (ii) a generalization of the Thomason criterion for the onset of coalescence accounting for the localization plane orientation, (iii) a new geometrical model for the internal necking process. The full model has been implemented in a home-made finite element code and validated towards finite element unit-cell calculations. Based on this model, we have investigated the influence of the microstructural features of homogeneous metallic materials on the different fracture mechanics parameters characterizing the fracture resistance such as JIc, CTOD, CTOA, plastic zone size, and JR. The multiscale modelling tool developed has been also applied to heterogeneous alloys with a specific focus on 7xxx aluminium alloys involving precipitate free zones along the grain boundaries and displaying a competition between transgranular and intergranular fracture modes. The study has contributed to a better understanding of the effect of the microstructural features, flow properties of the grain, and loading conditions on the preferential fracture mode, fracture strain teari, (FSA 3) -- UCL, 2009

Ductile fracture process includes three stages: void nucleation, their growth and coalescence. The voids nucleate due to the fracture or separation of non-metallic inclusions and secondary-phase particles from the material matrix. Micromechanical models based on the Gurson plastic flow criterion are often used for analysis of ductile fracture. They consider the material as a porous medium in which the effect of voids on the stress-strain state and plastic flow cannot be neglected. Another important property of the Gurson criterion is that the hydrostatic stress component influences the plastic flow of the material.

An attempt has been made to model the plane-strain fracture toughness, KIc, in Al-Zn-Mg-Cu alloy forgings subjected to overageing. The proposed model, based on the multiple micromechanisms, reveals the quantitative relations between fracture toughness, fraction of all fracture modes and microstructural parameters associated with multiscale-sized second-phase particles and precipitate-free zones. The new model is validated by the present quantitative data of microstructural and fractographic analysis performed along with mechanical tests on hot-forged plates in T73 condition. The relevant parameters changed by the compositional variations were determined in two orientations. It was found that the predicted KIc values represent the tendency of fracture toughness change well. The new model provides better agreement for the case of dominant transgranular fracture mode.

An attempt has been made to model the plane-strain fracture toughness, KIc, in Al-Zn-Mg-Cu alloy forgings subjected to overageing. The proposed model, based on the multiple micromechanisms, reveals the quantitative relations between fracture toughness, fraction of all fracture modes and microstructural parameters associated with multiscale-sized second-phase particles and precipitate-free zones. The new model is validated by the present quantitative data of microstructural and fractographic analysis performed along with mechanical tests on hot-forged plates in T73 condition. The relevant parameters changed by the compositional variations were determined in two orientations. It was found that the predicted KIc values represent the tendency of fracture toughness change well. The new model provides better agreement for the case of dominant transgranular fracture mode.

An attempt to develop a multiple micromechanism-based model for predicting plane-strain fracture toughness, KIc, of overaged 7000 alloy forgings has been made. The proposed model reveals the quantitative relations between the fracture toughness, fraction of the main fracture modes and parameters such as volume fraction, size and density of differently sized second-phase particles and precipitate-free zones. The new model is validated by the present quantitative data of microstructural and fractographic analysis performed along with mechanical tests on hot-forged plates subjected to the T73 temper. The relative parameters changed by the compositional variations were determined in the R-L and L-R orientations. It was found that the predicted KIc values well represent the tendency of fracture toughness change. The new model provides better agreement for the case of dominant transgranular fracture mode represented in the R-L orientation. .

In this paper the micromechanical approach to ductile fracture was applied in a study of constraint effect on crack growth initiation in mismatched welded joints. The single-edged notched bend specimens (precrack length a(0)/W=0.32) were experimentally and numerically analyzed. The coupled micromechanical model proposed by Gurson, Tvergaard and Needleman was used. Constraint effect was tested by varying widths of the welded joints (6, 12 and 18mm). High-strength low-alloyed (HSLA) steel was used as the base metal in a quenched and tempered condition. The flux-cored are-welding process in shielding gas was used. Two different fillers were selected to obtain over- and undermatched weld metal. The micromechanical parameters used in prediction of the crack growth initiation on precracked specimen were calibrated on a round smooth specimen. The difference in fracture behavior between over- and undermatched welded joints obtained in experimental results was followed by numerical computations of void volume fraction in front of the crack tip.

In this paper the micromechanical approach to ductile fracture was applied in a study of constraint effect on crack growth initiation in mismatched welded joints. The single-edged notched bend specimens (precrack length a 0/W=0.32) were experimentally and numerically analyzed. The coupled micromechanical model proposed by Gurson, Tvergaard and Needleman was used. Constraint effect was tested by varying widths of the welded joints (6, 12 and 18mm). High-strength low-alloyed (HSLA) steel was used as the base metal in a quenched and tempered condition. The flux-cored arc-welding process in shielding gas was used. Two different fillers were selected to obtain over- and undermatched weld metal. The micromechanical parameters used in prediction of the crack growth initiation on precracked specimen were calibrated on a round smooth specimen. The difference in fracture behavior between over- and undermatched welded joints obtained in experimental results was followed by numerical computations of void volume fraction in front of the crack tip.

A micromechanical model has been developed in order to capture the influence of a second population of voids on the coalescence of large primary voids. FE unit cell simulations have been performed by introducing the primary voids explicitly in a finite element mesh and by using a Gurson type model for the surrounding matrix in order to reproduce the influence of the second population. These simulations have guided the development of a closed-form void coalescence model. The new coalescence condition accounts for the softening introduced by the second population by integrating the Gurson model based on an approximate solution for the stress and strain field near the surface of the primary voids. The evolution of the primary voids is modelled using an advanced Gurson model involving an evolution law for the void shape. The model is applied to the prediction of the fracture strain of 6xxx aluminium alloys measured on smooth and notched round bars. The model successfully captures, without any parameter adjustment, the variation of the ductility as a function of the stress triaxiality for various shapes of the primary particles and various volume fraction of second population.

The aim of this work is to investigate and present a theoretical method to describe the anisotropic material properties of short glass fibre reinforced thermoplastics. In this work, the injection moulding process simulation in SIGMASOFT is combined with ABAQUS by a JAVA interface suggested, aiding a micromechanical model, in order to simulate a steady state response of short glass fibre reinforced thermoplastics under the application of a harmonic force., Minervavägen 22A, 37141 Karlskrona, Sweden. Phone: +46 (0) 736 123 110. Email: hamidgs@gmail.com, hagh04@student.bth.se

In the presented paper a micromechanical model based on a particular flow criterion of a porous solid has been applied. In this study crack initiation in the smooth specimen made of steel 22 NiMoCr 3 7 has been analyzed; the micromechanical model was incorporated into the finite element (FE) program. Initial data related to non-metallic inclusions were determined by the quantitative optical microscopy. The study was performed within the scope of ESIS TC8 Numerical Round Robin on Micromechanical Models, Phase II, Task A.... ., U radu je primenjen mikromehanički model zasnovan na posebnom kriterijumu plastičnog tečenja materijala. Nastanak prsline izazvan pojavom, rastom i spajanjem šupljina, analiziran je na osnovu ponašanja pri zatezanju glatke cilindrične epruvete izrađene od čelika 22 NiMoCr 3 7. Ulazni podaci za proračun koji se odnose na zastupljenost i veličinu nemetalnih uključaka su određeni optičkom mikroskopijom. Dobijeni rezultati ukazuju da primenjeni mikromehanički model može da se koristi za karakterizaciju materijala i analizu pojave prsline u standardnoj epruveti izrađenoj od konstrukcionog čelika, a da je kvantitativna metalurška analiza neophodna za opis prve faze žilavog loma - nastanak šupljina. .