Negative Kaons in Dense Baryonic Matter

Kaon polarization operator in dense baryonic matter of arbitrary isotopic composition is calculated including s- and p-wave kaon-baryon interactions. The regular part of the polarization operator is extracted from the realistic kaon-nucleon interaction based on the chiral and 1/N_c expansion. Contributions of the Lambda(1116), Sigma(1195), Sigma*(1385) resonances are taken explicitly into account in the pole and regular terms with inclusion of mean-field potentials. The baryon-baryon correlations are incorporated and fluctuation contributions are estimated. Results are applied for K- in neutron star matter. Within our model a second-order phase transition to the s-wave K- condensate state occurs at rho_c \gsim 4 \rho_0 once the baryon-baryon correlations are included. We show that the second-order phase transition to the p-wave $K^-$ condensate state may occur at densities $\rho_c \sim 3\div 5 \rho_0$ in dependence on the parameter choice. We demonstrate that a first-order phase transition to a proton-enriched (approximately isospin-symmetric) nucleon matter with a p-wave K- condensate can occur at smaller densities, \rho\lsim 2 \rho_0. The transition is accompanied by the suppression of hyperon concentrations.Comment: 41 pages, 24 figures, revtex4 styl

Computational Implementation of a Thermodynamically Based Work Potential Model For Progressive Microdamage and Transverse Cracking in Fiber-Reinforced Laminates

A continuum-level, dual internal state variable, thermodynamically based, work potential model, Schapery Theory, is used capture the effects of two matrix damage mechanisms in a fiber-reinforced laminated composite: microdamage and transverse cracking. Matrix microdamage accrues primarily in the form of shear microcracks between the fibers of the composite. Whereas, larger transverse matrix cracks typically span the thickness of a lamina and run parallel to the fibers. Schapery Theory uses the energy potential required to advance structural changes, associated with the damage mechanisms, to govern damage growth through a set of internal state variables. These state variables are used to quantify the stiffness degradation resulting from damage growth. The transverse and shear stiffness of the lamina are related to the internal state variables through a set of measurable damage functions. Additionally, the damage variables for a given strain state can be calculated from a set of evolution equations. These evolution equations and damage functions are implemented into the finite element method and used to govern the constitutive response of the material points in the model. Additionally, an axial failure criterion is included in the model. The response of a center-notched, buffer strip-stiffened panel subjected to uniaxial tension is investigated and results are compared to experiment

Impact compressive failure of GFRP unidirectional composites

Science and Engineering of Composite Materials911-

Efficient High-Fidelity Two-Scale Computational Model for Progressive Failure Analysis of Fiber Reinforced Composites via Refined Beam Models

An efficient high-fidelity two-scale computational model for progressive failure analysis of fiber reinforced composite is presented. The computational model is based on a class of refined beam finite elements called Carrera Unified Formulation (CUF), a generalized hierarchical formulations which yields refined structural theory via variable kinematic description. The two-scale framework consists of a macro-scale model to describe the structural level components (e.g: open-hole specimens, coupons) and a sub-scale micro-structural model encompassed with a representative volume element (RVE). The RVE is modeled with real composite constitutents, e.g., fiber and matrix with details about packing and heterogeneity. Various classes of RVE architecture is taken into account by randomly embedding multiple fibers in the constituent matrix. Component-Wise approach (CW), an extension of CUF beam model based on Lagrange-type polynomials, is used to model the constituents in the RVE. CW model enables one to use a detailed physical desciption of RVE by placing the problem unknowns on it’s physical surface. The two scales are interfaced through the exchange of strain, stress and stiffness tensors at every integration point in the macro-scale model. The energy based crack band theory (CBT) is implemented within the sub-scale model to predict the progressive damage growth in the individual constituents. Mesh objective results are obtained by scaling the post-peak softening slope of stress-strain constitutive relationship. The ability of CUF beam models to obtain accurate 3D-like stress fields at a reduced computational cost(approximately one order of magnitude of degrees of freedom less as compared to standard 3D brick elements) leads to a computationally efficient framework. Numerical predictions includes failure parameters such as stress-strain response,damage contours and ultimate strength and are validated against experimental results

Experimental study on dynamic compressive failure of unidirectional CFRP composites

Materials Science Research International53202-205MSRI

Ductile–brittle transitions in the fracture of plastically-deforming, adhesively-bonded structures. Part I: Experimental studies

AbstractRate effects for adhesively-bonded joints in steel sheets failing by mode-I fracture and plastic deformation were examined. Three types of test geometries were used to provide a range of crack velocities between 0.1 and 5000mm/s: a DCB geometry under displacement control, a wedge geometry under displacement control, and a wedge geometry loaded under impact conditions. Two fracture modes were observed: quasi-static crack growth and dynamic crack growth. The quasi-static crack growth was associated with a toughened mode of failure; the dynamic crack growth was associated with a more brittle mode of failure. The experiments indicated that the fracture parameters for the quasi-static crack growth were rate independent, and that quasi-static crack growth could occur even at the highest crack velocities. Effects of rate appeared to be limited to the ease with which a transition to dynamic fracture could be triggered. This transition appeared to be stochastic in nature, it did not appear to be associated with the attainment of any critical value for crack velocity or loading rate. While the mode-I quasi-static fracture behavior appeared to be rate independent, an increase in the tendency for dynamic fracture to be triggered as the crack velocity increased did have the effect of decreasing the average energy dissipated during fracture at higher loading rates

Digital videographic measurement of tooth display and lip position in smiling and speech: reliability and clinical application.

INTRODUCTION: Tooth display and lip position in smiling and speech are important esthetic aspects in orthodontics and dentofacial surgery. The spontaneous smile and speech are considered valuable diagnostic criteria in addition to the posed social smile. A method was developed to measure tooth display in both smile types and speech. METHODS: The faces of 20 subjects were individually filmed. Spontaneous smiles were elicited by a comical movie. The dynamics of the spontaneous smile were captured twice with a digital video camera, transferred to a computer, and analyzed on videoframe level. Two raters were involved. Posed social smiles and speech records were also included. Reliability was established by means of the generalizability theory. It incorporated rater, replication, and selection facets. RESULTS: Generalizability coefficients ranged from .99 for anterior teeth to .80 for posterior teeth. The main sources of error were associated with rater and selection facets. The replication facet was a minor source of error. CONCLUSIONS: This videographic method is reliable for measurement of tooth display and lip position in spontaneous and posed smiling and speaking. Application of the method is warranted especially when obtaining an emotional smile is difficult, such as cleft lip and palate or disfigured patients