Equivalent Void Research Articles

Effective Elastoplastic Damage Mechanics for Fiber-reinforced Composites with Evolutionary Complete Fiber Debonding

A micromechanical damage mechanics framework is proposed to predict the overall elastoplastic behavior and interfacial damage evolution of fiberreinforced ductile composites. Progressively debonded fibers are replaced by equivalent voids. The effective elastic moduli of three-phase composites, composed of a ductile matrix, randomly located yet unidirectionally aligned circular fibers, and voids, are derived by using a rigorous micromechanical formulation. In order to characterize the homogenized elastoplastic behavior, an effective yield criterion is derived based on the ensemble area averaging process and the first-order effects of eigenstrains. The resulting effective yield criterion, together with the overall associative plastic flow rule and the hardening law, constitutes the analytical framework for the estimation of effective elastoplastic damage responses of ductile composites containing both perfectly bonded and completely debonded fibers. An evolutionary interfacial fiber debonding process, governed by the internal stresses of fibers and interfacial strength, is incorporated into the proposed framework. The Weibull's function is employed to describe the varying probability of fiber debonding. Further, comparison between predictions and available experimental data are presented to illustrate the potential of the proposed methodology.

Evaluation of Superpave Mix Design for Low-Volume Roads in New Jersey

This research project explored the implementation of the Superpave® mixture design system for use on low-volume roads in New Jersey by comparing them with well-performing Marshall mixtures. The research used a reverse-engineering approach to examine mixture blend gradations, volumetric properties, performance, and durability of well-performing Marshall mixtures compared with Superpave mixtures for low-trafficlevel applications. In addition, the research evaluated the number of gyrations needed to produce equivalent air voids to the well-performing Marshall mixtures in the Superpave gyratory compactor. The gradations of the fine-graded Marshall mixtures from four suppliers were used to develop corresponding Superpave mixtures in the lab. The comparison of the Superpave and Marshall mixtures showed that they had similar volumetric, rutting, fatigue, permeability, and average asphalt binder thickness characteristics. The research also established relationships between Gsb or Gmm and the number of gyrations n...

Evaluation of Superpave Mix Design for Low-Volume Roads in New Jersey

This research project explored the implementation of the Superpave® mixture design system for use on low-volume roads in New Jersey by comparing them with well-performing Marshall mixtures. The research used a reverse-engineering approach to examine mixture blend gradations, volumetric properties, performance, and durability of well-performing Marshall mixtures compared with Superpave mixtures for low-traffic-level applications. In addition, the research evaluated the number of gyrations needed to produce equivalent air voids to the well-performing Marshall mixtures in the Superpave gyratory compactor. The gradations of the fine-graded Marshall mixtures from four suppliers were used to develop corresponding Superpave mixtures in the lab. The comparison of the Superpave and Marshall mixtures showed that they had similar volumetric, rutting, fatigue, permeability, and average asphalt binder thickness characteristics. The research also established relationships between Gsb or Gmm and the number of gyrations needed to reach air void levels similar to the Marshall mixtures.

Are isolated stable rigid clasts in shear zones equivalent to voids?

Particles in shear enclose important information about a rock's past and can potentially be used to decipher the kinematic history and mechanical behavior of a certain outcrop or region. Isolated rigid clasts in shear zones often exhibit systematic inclinations with respect to the shear-plane at small angles, tending towards the instantaneous stretching direction of the shear zone. This shape preferred orientation cannot be easily explained by any of the analytical theories used in geology. It was recently recognized that a weak mantle surrounding the clast or a slipping clast–matrix interface might be responsible for the development of the observed inclinations. Physical considerations lead us to conjecture that such mantled, rigid clasts can be effectively treated as voids that are not allowed to change their shape. The resulting equivalent void conjecture agrees well with numerical and field data and has the following important geological implications. (i) Clasts in shear zones can have stable positions in simple shear without the requirement of an additional pure shear component. (ii) The stable orientation can be approached either syn- or antithetically; hence, the clast can rotate against the applied shear sense. (iii) The strain needed to develop a strong shape preferred orientation is small ( γ≈1) and therefore evaluations based on other theories may overestimate strain by orders of magnitude. (iv) The reconstruction of far-field shear flow conditions and kinematic vorticity analysis must be modified to incorporate these new findings.

Lock-in Phenomenon of a Pitching Hydrofoil with Cavitation Breakdown (Unsteady Fluid Force Characteristics and Visualization of Flow Structure)

A cavitating hydrofoil falls into the self-induced oscillation under some oscillation frequencies and cavitation numbers. Especially, the violent cavitation breakdown occurs periodically while shedding the vortex cavitation when the sheet cavity lengthens near at the trailing edge. It causes the unsteady and nonlinear fluid forces acting on the hydrofoil. This nonlinear phenomenon has not been clarified as yet when the breakdown frequency shedding the vortex cavitation locks in the pitching frequency of the cavitating hydrofoil. The experiment was carried out for a pitching and cavitating NACA hydrofoil in the TMIT cavitation tunnel. The pitching lift coefficient was clarified by load cell measurement with the cavity length and the reduced frequency as parameters. Moreover, particle and bubble image processing technique for PIV is applied to this unsteady cavitation flow. Accordingly, the equivalent void fraction, the velocity vector and the vorticity map including the inner cavity are qualitatively and quantitatively visualized under the shedding vortex cavitation lock-in phase.

Shear-enhanced compaction during non-linear viscous creep of porous calcite–quartz aggregates

In this paper, we extend the previous studies of semi-brittle flow of synthetic calcite–quartz aggregates to a range of temperatures and effective pressures where viscous creep occurs. Triaxial deformation experiments were performed on hot-pressed calcite–quartz aggregates containing 10, 20 and 30 wt% quartz at confining pressure of 300 MPa, pore pressures of 50–290 MPa, temperatures of 673–1073 K and strain rates of 3.0×10−5/s, 8.3×10−5/s and 3.0×10−4/s. Starting porosity varied from 5 to 9%. We made axial and volumetric strain measurements during the mechanical tests. Pore volume change was measured by monitoring the volume of pore fluid that flows out of or into the specimen at constant pore pressure. Yield stress increased with decreasing porosity and showed a dependence on effective pressure. Thus, the yield stress versus effective pressure can be described as a yield surface with negative slope that expands with decreasing porosity and increasing strain hardening, gradually approaching the envelope of strength at 10% strain, which has a positive slope. Creep of porous rock can be modeled to first order as an isolated equivalent void in an incompressible nonlinear viscous matrix. An incremental method is used to calculate the stress–strain curve of the porous material under a constant external strain rate. The numerical simulations reproduce general trends of the deformation behavior of the porous rock, such as the yield stress decreasing with increasing effective pressure and significant strain hardening at high effective pressure. The drop of yield stress with increasing porosity is modeled well, and so is the volumetric strain rate, which increases with increasing porosity.

Flow Visualization of Cavitation with Particle and Bubble Image Processing

The new PIV image processing method is proposed to apply to the cavitation flow field. Two CCD cameras take each image shots of good quality utilizing the difference of the scatter light intensity between the seeding particles and the bubbles. From the image of the seeding particles, the cavitation aspect information such as the equivalent void fraction and the cavity boundary is obtained by using the binary process of the light intensity. From both images of the seeding particles and the bubbles, two velocity informations are obtained individually inside or outside area of the cavity by using the cross correlation method and finally composed into one. For the evaluation of this PIV measurement and processing, the experiment was carried out about the wake vortex cavitation flow behind a wedge. And also, cavity boundary, equivalent void fraction, velocity vector and vorticity map were discussed in detail.

A study of the large voids in the spatial distribution of galaxy clusters in the Northern Galactic Hemisphere

We present a mapping of the large voids (D 50 h 1 Mpc) in the spatial distribution of clusters of galaxies in the Northern Galactic Hemisphere in a vol- ume dened by galactic latitude b +30 and redshift z 0.14. Rich clusters with spectroscopically measured or photometrically estimated redshifts are used as tracers of the large-scale structure of the Universe. An automated void-search and analysis procedure which identies a void as a system of intersecting empty spheres is applied, al- lowing for a description of the void dimensions, volumes and shapes more complete than in previous investigations. A number of void catalogues corresponding to dierent tracer types, dierent sources of redshift data, and dier- ent versions of the search method have been generated and analysed. Visualizations of the 2-D and 3-D distributions of voids are presented. The estimated mean dimensions of the voids of R 1a ndR 0 Abell/ACO clusters are De = 105.0 5.6h 1 Mpc and De = 87.2 4.1h 1 Mpc, respectively, whereDe is the equivalent void diameter. We have identied the poor clusters, groups, and galaxies pop- ulating the voids of rich clusters and constructed radial density proles of the voids, which show the presence of a void hierarchy. studies of their properties (geometrical parameters, con- tent, environment) are of great importance for testing ba- sic assumptions in the contemporary theoretical models and scenarios of the formation and evolution of the LSS. One major complication in void studies arises from the diculty to obtain spatial distributions of the tracers of the LSS with spectroscopically measured redshifts which are fairly complete in volumes both wide and deep. From this point of view the use of rich clusters of galaxies as

Theoretical investigation of the possibility of independent electromagnetic testing of two local inclusions in a conducting half space

We study the problem of finding the electromagnetic field of a plane wave scattered by two inclusions placed in an isotropic conducting nonmagnetic half space and develop a technique for numerical calculation of the equivalent dipole moments for both independent and interacting inclusions. The equivalent voids of dipole moments and their electromagnetic fields are analyzed numerically. The results of this investigation can be used in designing methods and equipment for independent electromagnetic nondestructive testing of several inclusions.

Probabilistic model of limit strains in sheet metal

A mathematical model is presented in which the mean value and standard deviation of limit strains are obtained for forming a sample of sheet metal parts in a repeatable stretch forming process. It is assumed that tearing originates in defects in the material which can be characterized by an equivalent population of voids which have an exponential size distribution. The model predicts that for a given material the mean limit strains in forming many pieces will increase with material thickness, severity of overall strain gradient and with decreasing volume fraction of equivalent voids. Numerical results indicate that the relationship between formability and volume fraction is approximately of an inverse logarithmic nature. The behaviour of the model using arbitrary values of parameters describing the equivalent void population is in good agreement with many phenomena observed in sheet metal forming.

Experimental evidence for the stochastic theory of particle flow under gravity

Experimental evidence is presented for a recent stochastic theory of flow which represents the convergent flow of cohesionless particles under gravity toward an open orifice as equivalent to a counterflow of voids from the orifice upward through the bed by biased random flight; the theory is summarized in a new phenomenological form. Data, taken from the literature, were obtained from cells initially loaded with alternate layers of differently colored granular material. The theory predicts that after a fixed flow, each layer develops a depression such that if z o is the original height of a given layer above the orifice and z m is the corresponding height of the depression minimum, then for three-dimensional flow a plot of z m 2 vs. z o 2 for different layers will yield a straight line of slope one; the intercept gives statistical information concerning the equivalent void jumps. For two-dimensional flow, the corresponding theoretical plot is z m 3 2 vs. z osu 3 2 Data plotted from several sources conform closely to the above predictions, provided z o is not too large for a given flow. The latter discrepancy is qualitatively explained by a transient effect requiring the density to fall to a certain level before steady-state flow can occur.