Monday 6:00 PM

February 27, 2017

Room: Hall B1

Location: San Diego Convention Ctr

Characterizing materials observed with an imaging system such as micro-CT or FIBSEM is common. Grayscale image processing workflows typically involve noise reduction, segmentation, and volumetric or slice-by-slice analysis of structures of interest. These techniques introduce error that must be understood by the researcher. We present a workflow that reduces error when acquiring cross-sectional measurements of long, tortuous structures through grayscale images. A centerline is calculated through the structure after segmentation. Oblique slicing is performed with this centerline as an axis, where the normal of each slice face is tangential to the centerline. This is in contrast to another method of performing cross-sectional measurements in which slicing occurs strictly along an orthogonal direction to the voxel grid. The measurements obtained using centerline-driven slicing is compared to measurements from orthogonal slices for micro-CT datasets of a stented vessel and a tooth canal as examples.

Recent research in the educational aspects of compressible shock wave phenomena and gas dynamics has revealed a novel information theoretic approach to the teaching of the subject. furthermore the same proposed methodology can be used for increasing the fidelity of model development and created simulations of such phenomena. the need for such a paradigm shift is to establish necessary and sufficient conditions for model development, validation and verification. in particular what is proposed is in actuality a form of coding itself that minimizes confounding circumstances especially prevalent in complex geometries and evaluative conditions. the result is an improved understanding and decision making capability in practitioners of compressible gas dynamics.

Calcium ferrite is the main binding phase for high-basicity sinter. The production and structure of calcium ferrite have greatly influence on the quality of sinter. Ultrasonic vibration was introduced into calcium ferrite melt in order to develop a new sintering process. Based on the acoustic refraction and reflection principles, ultrasonic propagation between amplitude transformer and calcium ferrite melt has been analyzed and discussed. In addition, numerical simulation of ultrasonic propagation in calcium ferrite melt has also been carried out with integration method and finite element method, respectively. The distributions of characteristic quantities including acoustic pressure and sound intensity in calcium ferrite melt were obtained, and the effects of ultrasonic power and frequency on acoustic pressure distribution were also investigated. The results show that different ultrasonic frequency makes different acoustic pressure distribution in calcium ferrite melt, while ultrasonic power has little effect on it.

The size limitation of ab initio calculations impedes first principles simulations of crystal defects at nanometer sizes. We have developed an ab initio-accuracy model to predict formation energies of defect clusters with various geometries and sizes which combines the discrete nature of energetics of interstitial clusters and continuum elasticity. The present discrete-continuum model is then applied to interstitial dislocation loops with <100> and 1/2<111> Burgers vectors, and to C15 clusters in body-centered-cubic crystals Fe, W and V, to determine their relative stabilities as a function of size. Further, the formation energies predicted by the discrete-continuum model can be used in multi-scale techniques including kinetic Monte Carlo simulations and cluster dynamics or dislocation dynamics studies. Moreover, the present energetic model can be adapted in order to address the free energy landscape of defects in body-centered-cubic metals up to the melting temperature.

In this work, coupling between the polycrystal plasticity based on the elastic-plastic self-consistent (EPSC) theory and implicit continuum finite elements is extended to work with shell elements. The plane-stress state present in shell element is accommodated by the EPSC model operating at every FE integration point. The Jacobian matrix needed to facilitate efficient coupling is derived for the imposed state of stress. The developed model is used to simulate cup-drawing and continuous bending under tension processing of anisotropic AA6022-T4 sheets. To quantify the uncertainties involved in simulations involving shell element, the same simulations are performed using the continuum elements and the differences between the two formulations are highlighted. Finally, the simulation results of both approaches are compared with the experimental measurements and the predictive capabilities discussed.

Finite element modeling of high-strain-rate systems such as the cold spray process has become more common with the significant increase in high performance computing. Advances in high-strain-rate material models beyond the basic Johnson-Cook constitutive model have improved finite element predictions and the ability to model the physics of the bonding process. Finite element analysis has been helpful in understanding the particle impact event and has laid the foundation for the development of spray parameters for certain material systems. Historically, cold spray impact models were not advanced enough to investigate changes in microstructure and secondary phase content due to their complexity and a limit in computing resources. A finite element model has been developed using multiple software tools and advanced characterization methods to investigate the effect of secondary phases and grain sizes on a single cold spray particle impact. The effect of secondary phases are investigated and compared against experimental results.

Multi-scale computational model was used for the investigation of deformation and fracture of close packed hexagonal (HCP) alloys under stress pulse loadings. The model takes into consideration the distribution of grain sizes, average size and concentration of precipitates. Model describes the shear stress relaxation under tension and compression at the homologous temperature below 0.5. The numerical results on dynamic and quasi-static deformation of Zr−1 vol. % Nb alloy are good agreed with experimental data. Strain rate sensitivity of the yield stress of Zr-Nb alloys at fixed temperature depends on Nb concentration, and grain size distribution. It is shown that Zr-Nb alloys exhibit significant difference in the resistance to plastic deformation under compression and tension at high strain rates. It was predicted the spall strength of Zr−Nb alloys with precipitation strengthening is higher in comparison of Zr.