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Grupo de intereses compartidos

Público·58 miembros
Cameron Esparza
Cameron Esparza

My.Sims-iTWINS Crack Free

Developing next-generation materials with controlled twinning behaviors offers promising opportunities for improved mechanical properties [1, 2] and performance in engineering applications (e.g., gas turbine engines [3] and lightweight automotive structures [4]). Among materials that exhibit twinning [5,6,7,8], magnesium [9,10,11,12] is an example of a light-weight metal where slip and twinning, as the two main crystallographic mechanisms, play a decisive role in its mechanical response; here, twinning is favorable on pyramidal 1012 \(\langle 1011\rangle \) systems at room temperature [13]. In magnesium, single twinning occurs through contraction [14] and extension strains [15] along the c-axis [16]. Recent twinning studies have focused on observations of asymmetric twin growth due to heterogeneous grain deformation in the vicinity of the twin [17, 18]. We understand that interaction of twin boundaries with other defects (i.e., voids and self-interstitials) increases the likelihood for void nucleation, cracking, and premature failure, leading to degradation of material performance and reduction of material lifetime [19, 20]. Recent efforts have also been made to model the twin local stress accurately by means of neighboring grains to accommodate the transformation [21]. In engineering applications, there is a broad interest in incorporating magnesium in high strain-rate applications (e.g., aerospace [22]), where twin growth and evolution limits the mechanical performance [23]. However, knowledge gaps in understanding twin growth [24], thickening [25], and interactions [26] need to be addressed before the adoption of magnesium-based alloys into these applications; these are studied herein for a single crystal Mg material system.

My.Sims-iTWINS Crack


Finally, simulations have been performed to study the effect of twin-twin and twin-defect interactions (Fig. 4). Understanding these interactions is an important step toward developing better predictive models for designing materials with tailored properties [101,102,103,104] and microstructures [105,106,107,108]. Damage in materials is studied by phase-field models [109,110,111,112,113], and we use phase-field approach herein for twin interactions. These interactions [114] may result in the formation of twin-twin junctions that may cause strain hardening [115] and crack initiation [116, 117], leading to a strong influence on the overall material performance. First, the change of area fraction of the middle twin as a function of time for a different number of embryos is illustrated in Fig. 4(a). Only the middle embryo is considered in the analysis in order to better isolate the interactions and reduce boundary effects. The location of the twins for the three embryo cases is illustrated in the inset. In Fig. 4(a), it is shown that increasing the number of twins leads to a decrease in the twin area fraction of the middle embryo as a result of its interaction with the other twins. The difference of the twin area fraction for multi-embryo cases becomes larger at later time instants. This finding is important as it highlights the effects of twin interactions on twin evolution, where experimental measurements are currently very limited [118]. Next, the spatial variation of the order parameter and the corresponding shear stress at \(t = 10 \) and \(t = 20 \text ps\) are depicted in Fig. 4(b). This result reveals insights into the expansion of the twin domain through the accumulation of large plastic shear strain at the nano-scale [119].

The homogeneous growth in the twin area is exemplified in the top left inset in Fig. 4(b), where the twins have not changed in shape until \(t = 10 \text ps\). The corresponding shear stress distribution at \(t = 10 \text ps\) is shown in the bottom left inset, where the shear stress inside the twins is negative while it is positive in the matrix. The heterogeneous stress distribution around the twins is due to a sudden change in the stresses within the twin interfaces, associated with the need to accommodate deformation in this region [40]. From the spatial shear stress distribution, it is observed that the local shear stress reaches a minimum in the center of each twin. Outside the twins, the shear stress is lower at the bottom left and top right twins because of the constraining effect of the adjacent twins to the middle one. In the right insets, the deviatoric deformation in twin morphology at \(t = 20 \text ps\) is identified due to the interaction of the twins with each other and the disturbing of the stress field by them. The stress distribution in the vicinity of the twin-matrix interfaces at \(t=20 \text ps\) is heterogeneous as a result of high stress concentrations in the matrix near the twin boundaries. It is also shown that the middle twin experiences a maximum shear stress resulting from the compressive forces generated by the other twins. The local stress concentration is one main interaction of crack and twins where some nucleation site appears in the interfaces inside and around the interface [120].

Sparry calcite fracture fills and concretion body cements in concretions from the Flodigarry Shale Member of the Staffin Shale Formation, Isle of Skye, Scotland, entrap and preserve mineral and organic materials of sedimentary and diagenetic origin. Fatty acids are a major component of the lipids recovered by decarbonation and comprise mainly n-alkanoic and α-ω dicarboxylic acids. Two generations of fracture-fill calcite (early brown and later yellow) and the concretion body microspar yield significantly different fatty acid profiles. Early brown calcites yield mainly medium-chain n-alkanoic acids with strong even predominance; later yellow calcites are dominated by α-ω dicarboxylic acids with no even predominance. Both fracture fills lack the long-chain n-alkanoic and α-ω dicarboxylic acids additionally recovered from the concretion bodies. The absence of longer chain acids in the calcite spar fracture fills is inferred to result from the transport of fatty acids by septarian mineralising fluids whereby low-aqueous solubility of longer chain acids or their salts accounts for their relative immobility. Comparative experiments have been carried out using conventional solvent extraction on the concretion body and associated shales, both decarbonated and untreated. Extracted lipid yields are higher, but the fatty acids probably derive from mixed locations in the rock including both kerogen- and carbonate-associated lipid pools. Only experiments involving decarbonation yielded α-ω dicarboxylic acids in molecular distributions probably controlled mainly by fluid transport. Alkane biomarker ratios indicate very low thermal maturity has been experienced by the concretions and their host sediments. Septarian cracks lined by brown calcite formed during early burial. Microbial CO 2 from sulphate-reducing bacteria was probably the main source of mineralising carbonate. Emplacement of the later septarian fills probably involved at least one episode of fluid invasion.

Sulfate-filled fractures in fine-grained sediments on Mars are interpreted to be the result of fluid movement during deep burial. Fractures in the Dewey Lake (aka Quartermaster) Formation of southeastern New Mexico and west Texas are filled with gypsum that is at least partially synsedimentary. Sulfate in the Dewey Lake takes two principal forms: gypsum cement and gypsum (mainly fibrous) that fills fractures ranging from horizontal to vertical. Apertures are mainly mm-scale, though some are > 1 cm. The gypsum is antitaxial, fibrous, commonly approximately perpendicular to the wall rock, and displays suture lines and relics of the wall rock. Direct evidence of synsedimentary, near-surface origin includes gypsum intraclasts, intraclasts that include smaller intraclasts that contain gypsum clasts, intraclasts of gypsum with suture lines, gypsum concentrated in small desiccation cracks, and intraclasts that include fibrous gypsum-filled fractures that terminate at the eroded clast boundary. Dewey Lake fracture fillings suggest that their Martian analogs may also have originated in the shallow subsurface, shortly following the deposition of Martian sediments, in the presence of shallow aquifers.

The KTB pilot borehole in northeast Bavaria, Germany, penetrates 4000 m of gneiss, amphibolite, and subordinate calc-silicate, lamprophyre and metagabbro. There are three types of calcite in the drilled section: 1) metamorphic calcite in calc-silicate and marble; 2) crack-filling calcite in all lithologies; and 3) replacement calcite in altered minerals. Crack-filling and replacement calcite postdate metamorphic calcite. Multiple calcite generations in individual cracks suggest that different generations of water repeatedly flowed through the same cracks. Crack-filling mineral assemblages that include calcite originally formed at temperatures of 150-350??C. Presently, crack-filling calcite is in chemical and isotopic equilibrium with saline to brackish water in the borehole at temperatures of ???120??C. The saline to brackish water contains a significant proportion of meteoric water. Re-equilibration of crack-filling calcite to lower temperatures means that calcite chemistry tells us little about water-rock interactions in the crystal section of temperatures higher than 120??C. -from Author

The plane strain fracture toughness (K1c) at 23 degrees C and the fractography of zinc phosphate and zinc polycarboxylate cements, buffered glass ionomer liner, amalgam alloy admixed glass ionomer build-up material, and glass ionomer, microfilled and conventionally filled bis-GMA resin composite filling materials were analyzed by elastic-plastic short-rod and scanning electron microscopy methodologies. Results indicated that significant differences occurred in their K1c's from the lowest to the highest in the following groups of materials, (i) buffered glass ionomer, (ii) zinc phosphate, glass ionomer, zinc polycarboxylate, and alloy mixed glass ionomer, (iii) microfilled resin, and (iv) conventionally filled resin. All materials except the microfilled resin, which fractured via crack jumping, fractured via smooth crack advance. Filler debonding without any crack inhibiting process was related to materials with low K1c values. The incorporation of either buffering compounds or alloy particles into glass ionomer had no beneficial effect upon fracture toughness. This was in contrast to microfilled and conventionally filled resins where either crack blunting or crack pinning processes, respectively, were likely involved with their increased K1c's. For microfilled resin, distinct radial zones positioned around the chevron apex and characterized by plastically deformed deposited material were related to distinct crack jumps that occurred in the load versus displacement behavior. Finally, for the two remaining materials of zinc phosphate and polycarboxylate, particle cleavage and matrix debonding for the former and shear yielding for the latter occurred. 350c69d7ab

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