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PURPOSE:This study aimed to identify differences in ankle laxity in chronic ankle instability (CAI), coper, and control groups, and a correlation between ankle laxity, self-reported function, and perceived instability.METHODS: Sixty-six participants (22 CAI patients, 22 copers, and 22 controls) selected by recommendations of the International Ankle Consortium volunteered for this study. Foot and Ankle Ability Measure Activities of Daily Living (FAAM-ADL), FAAM-Sports, and Ankle Instability Instrument (AII) were used to assess participants’ self-reported function and perceived instability. The FAAMADL and FAAM-Sports are reported as a percentage. Higher scores indicate better function. The AII is reported as “yes” responses while more “yes” responses indicate higher instability. Three trials of anterior/posterior (A/P) displacement and inversion/eversion (I/E) displacement were assessed by an instrumented ankle arthrometer. Greater displacement indicates higher laxity. The ankle positioned in sagittal- and frontal-plane neutral while A/P and I/E displacement were assessed with 125 N and 4 N-m, respectively. The means of three trials were used for data analysis. One-way ANOVA and Tukey post-hoc comparisons (α=0.05) were performed to identify differences in ankle laxity between groups. Pearson correlation analysis was performed to identify a relationship between ankle laxity, self-reported function, and perceived instability.RESULTS: CAI patients show greater A/P displacement compared to control group (p

This work examines the influence of changes in grain boundary (GB) strength on microstructure dependent crack propagation in polycrystalline tungsten (W). The property of focus is brittleness index (BI) originally introduced by Evans and Marshall in 1976 and 1979, respectively, used in order to quantify the extent of brittleness of a material. In an earlier work, GBs of Ni-doped polycrystalline W have been characterized for embrittlement using ab-initio quantum mechanical simulations as a function of Ni atomic volume fraction and GB thickness. This work focuses on quantifying the influence of GB strength on microstructure dependent crack propagation. Continuum mechanical GB strength properties and effective W grain properties are derived from ab-initio simulation based stress–strain curves. The crack propagation simulations when GBs are considered of finite width are based on an extended finite element (XFEM) framework. Simulations that consider GBs of infinitesimal width due to mesh resolution issues are based on a combined XFEM-cohesive finite element model that employs cohesive elements at GBs. Analyses of crack propagation through finite width GBs focus on understanding the role of square root of length scale dimension in the original BI formulation. Based on analyses of crack propagation through finite width GBs oriented at angles varying from $$0^{\circ }\,\hbox {to}\,90^{\circ }$$ with respect to advancing crack, a quantitative criterion based on a failure index which predicts crack propagation path in polycrystalline W is proposed and examined.

Grain boundaries (GBs) in nickel (Ni)-doped tungsten (W) are found to have thickness as a function of the level of saturation of W atoms with respect to Ni atoms in the GBs. While the unsaturated Ni-doped W GBs have average thickness of approximately 0.3 nm, the saturated Ni-doped W GBs have twice the average thickness (∼0.6 nm). The present work examines (1 1 0)–(2 1 0) W GB mechanical strength as a function of thickness using an ab initio calculation framework based on Car–Parrinello molecular dynamics (CPMD) simulations. The atomic fraction of Ni atoms is varied to understand the influence of Ni addition and its correlation with thickness variation on the GB mechanical strength. In the case of GBs with 0.3 nm thickness, the variation of peak tensile strength as a function of Ni atomic fraction variation from 5% to 50% is negligible. However, in the case of 0.6 nm GB, the changes in the peak tensile strength are significant with the maximum peak tensile strength observed in the case of 58% Ni atomic fraction. Analyses examine electron density of states and phonon dispersion relations to delineate the role of atomic level bond strength in thickness dependent GB mechanical strength. The thickness dependent GB strength variation is found to be strongly correlated to the thickness dependent change in lower acoustic mode phonon frequencies. At the same time Ni atomic fraction dependent change in GB strength is found to be strongly correlated to the corresponding changes in electron density of states. Based on the analyses performed, an analytical relation to predict GB peak tensile strength as a function of atomic cohesive energy, GB thickness (level of saturation), and the Ni atomic fraction is proposed.

Grain boundary (GB) embrittlement in nanostructured metals intended for high temperature applications is considered an important detriment. In the present work, embrittlement in a nickel (Ni)-doped tungsten (W) 〈1 0 0〉–〈2 1 0〉 GB is examined using ab initio simulations based on Car Parrinello molecular dynamics (CPMDs) framework. The atomic fraction of substituted Ni atoms in the examined W GB and simulation temperature are varied in order to understand the strength of the W GB as a function of temperature. An increase in the Ni atomic fraction in the W GB from 12.5% to above 25% value leads to a peak in yield strength and reduction in the strain corresponding to the ultimate tensile strength which can be characterized as embrittlement. While the elastic modulus does not show a dependence on Ni atomic fraction variation and temperature, the yield strength, the ultimate tensile strength, and the fracture strength show an appreciable dependence. Addition of Ni atoms adds localized peaks in f -orbital electron density of states which is found to contribute to increase in the bond strength with increase in Ni atomic fraction. Based on analyses performed, a relation expressing tensile strength of the examined W GB as a function of W surface energy, Ni atomic fraction, and simulation temperature is derived. The relation is shown to predict temperature dependent strength of examined Ni-doped W GB that fits the simulation data.

ContextA methodology is needed to model software specification with both timing diagram and Simulink/Stateflow (SL/SF) and to convert timing diagram model into SL/SF model. ObjectivesThis paper aims to propose a timing diagram drawing method and the algorithm to convert a timing diagram model into the equivalently behaving SL/SF model. MethodWe add a few extra features to those of the typical timing diagrams. The extra features were chosen by the field engineers' requests and the survey of many different commercial models. This paper proposes the formal method to describe the timing diagram. Based on the formal description, the converting algorithm translates a timing diagram into the SL/SF model. ResultsBy providing a path from timing diagram to SL/SF, system specifications can be described with both SL/SF and timing diagram. This paper addresses the details of outcomes that the proposed method was successfully applied to modeling "Theft watch system" and "Automotive power window controller. The proposed method has been successfully applied to other commercial systems, and to the models provided by Mathworks. ConclusionThis paper proposed a methodology to describe system specification with both timing diagram and SL/SF. The strategy might help designers more efficiently describe specifications. In addition, the mixed specification can be simulated in SL/SF, and the specification can utilize other third party SL/SF tools such as test case generation or model check utilities.

Based on a recent discovery of premelting-like grain boundary segregation in refractory metals occurring at high temperatures and/or high alloying levels, this project investigated grain boundary segregation and embrittlement in tungsten (W) based alloys. Specifically, new interfacial thermodynamic models have been developed and quantified to predict high-temperature grain boundary segregation in the W-Ni binary alloy and W-Ni-Fe, W-Ni-Ti, W-Ni-Co, W-Ni-Cr, W-Ni-Zr and W-Ni-Nb ternary alloys. The thermodynamic modeling results have been experimentally validated for selected systems. Furthermore, multiscale modeling has been conducted at continuum, atomistic and quantum-mechanical levels to link grain boundary segregation with embrittlement. In summary, this 3-year project has successfully developed a theoretical framework in combination with a multiscale modeling strategy for predicting grain boundary segregation and embrittlement in W based alloys.

ntergranular glassy films (IGFs) have been known to affect high temperature creep and fracture behavior of nanostructured ceramics significantly. Similar to IGFs in nanostructured ceramics, grain boundary (GB) embrittlement in nanostructured metals intended for high temperature applications is considered an important determinant of mechanical strength. GB embrittlement occurs through diffusion of a small atomic fraction of liquid metals such as nickel (Ni) in GBs of intrinsically ductile materials such as tungsten (W) during sintering or during high temperature operation. The problem of W GB embrittlement is not new. Toth and Lockington examined W GBs and found that Ni phase present at the surface of W powder before activated sintering had segregated along the W GBs afterwards. This was referred to as GB segregation, a fundamental contributor to GB embrittlement. Nieh presented an evidence of GB segregation of Ni in W using auger electron spectroscopy (AES). Gupta et al. used high resolution transmission electron microscopy (HRTEM) and AES to reveal the presence of nanometer-thick, Nienriched, disordered films at W GBs for the first time. While it is certain that Ni segregation in W GBs leads to embrittlement as well as material strength degradation, the effect of change in Ni atomic fraction in W GBs and the influence of such variation as a function of operation temperature on GB strength has not been characterized. Primary hindrances are the time scale limitations of molecular simulation methods to predict an equilibrium GB structure as a function of operating temperature in the presence of impurities and limitations of spectroscopy as well as microscopy based approaches in predicting atomic composition of nanometer sized GBs as a function of change in temperature. Another issue is the inability to predict GB mobility using molecular simulations while taking into account precise chemical composition due to molecular simulation time scale limitations. In this work, such limitations are circumvented by analyzing an experimentally observed - GB analyzed in the work of Gupta et al. The focus of the present work is on analyzing the influence of Ni doping in the examined W GB on its mechanical strength as a function of temperature while accounting for the effect of atomic level bond strength and lattice dynamics. W and W alloys have earlier been analyzed for their tensile strength and fracture strength. It has been shown that both temperature and Ni atomic fraction affects mechanical strength of nanostructured W. However, a relationship describing such has not been established. The GB structure experimentally observed by Gupta et al. is

Polycrystalline tungsten is considered as an important material in aerospace, automobile, and energy industries due to its excellent thermal and mechanical properties. While grain boundaries (GBs) are perceived to play a major role in polycrystalline tungsten failure resistance, experimental data are scarce on explicit contribution of GBs to tungsten failure resistance. The present work focuses on understanding the effect of GB property variation on fracture resistance of polycrystalline tungsten. The cohesive finite element method is used for the simulation of crack propagation in polycrystalline tungsten microstructures. The results show a significant effect of GB property variation on change of crack propagation patterns during tungsten fracture. A variation of 10% in GB fracture energy resulted in distinctly different crack patterns with different primary crack propagation direction and the microcrack density. Based on the observed microstructural fracture attributes, a relation between cohesive energy dissipation and microcrack density in polycrystalline tungsten microstructures is proposed.

Silicon carbide (SiC) is an important ceramic material usually found in polycrystalline form with grain boundary thickness ranging from a few nanometers to a few hundred nanometers and grains with multiple orientations with sizes of the order of few micrometers. The present work focuses on analyzing how the interplay between different orientations of SiC grains and different grain boundary thicknesses can be exploited for targeted improvement in the fracture resistance properties of SiC. Crack propagation simulations using the cohesive finite element method (CFEM) are performed on the finite element meshes developed on experimentally processed SiC morphologies. Analyses were performed at two different length scales: 300 μm × 60 μm (scale-1:Microscale) and 75 μm × 15 μm (scale-2:Mesoscale). Lower resolution microstructure at scale-1 does not explicitly consider the presence of grain boundaries (GBs). Higher resolution microstructure at scale-2 explicitly models GBs. Results indicate that the effect of change in grain orientation is on crack path only. The fracture resistance is not significantly affected. The presence of GBs may directly aid in strengthening a microstructure’s fracture resistance. However, indirectly it may weaken a microstructure by favoring the formation of microcracks. Significantly higher crack formation in grain interior while lower interfacial energy dissipation in comparison to interfaces indicates overall lower fracture strength of grain interiors in comparison to interfaces. If GBs are not accounted for, the second most influencing factor affecting fracture strength is the average grains size. Overall, it is mainly the GBs not the grain orientation distribution and grain size that significantly affects fracture strength.