Modeling of Short Fiber Reinforced Polymer Composites Subjected to Multi‐block Loading

Applied Composite Materials - Short Fiber Reinforced Composite (SFRC) structures exhibit multiple microstructures (due to material flow during the process). They are generally subjected to variable...     

Multirange Fractals in Materials: Applications to Fracture and Mechanical Alloying under Ball Milling

A new model of multirange fractals is proposed to explain the experimental results observed on the fractal dimensions of the fractured surfaces in materials. A new expIanation to the WilIiford's multifractal curve on the relationship of fractal dimension with fracture properties in materials has been given. It shows the importance of fractorizing out the effect of fractal structure from other physical causes and separating the appropriate range of scale from multirange fractals.Mechanical alloying process under ball milling as a non-equilibrium dynamical system has been also analyzed     

Absolute refractometry of dry gas to ±3 parts in 10⁹

We present a method of measuring the refractive index of dry gases absolutely at 632.8 nm wavelength using a Fabry-Perot cavity with an expanded uncertainty of <3×10?? (coverage factor k=2). The main contribution to this uncertainty is how well vacuum-to-atmosphere compression effects (physical length variation) in the cavities can be corrected. This paper describes the technique and reports reference values for the refractive indices of nitrogen and argon gases at 100 kPa and 20 °C with an expanded uncertainty of <9×10?? (coverage factor k=2), with the additional and larger part of this uncertainty coming from the pressure and temperature measurement.     

Characterization and Properties of Nanostructured Surface Layer in a Low Carbon Steel Subjected to Surface Mechnaical Attrition

A nanostructured surface layer was synthesized on a low carbon steel by using surface mechanical attrition (SMA) technique,The refined microstructure of the surface layer was characterized by means of different techniques, and the hardness variation along the depth was examined,Experimental results show that the microstructure is inhomogeneous along the depth ,In the region from top surface to about 40 μm depth,the grain size increases from about 100 nm to 1000 nm ,The grain refinement can be associated with the activity of dislocations After the SMA treatment, the hardness of the surface layer is enhanced significantly compared with that of the original sample ,which cam primarily be attributed to the grain refinement.     

Characterization and Properties of Nanostructured Surface Layer in a Low Carbon Steel Subjected to Surface Mechanical Attrition

A nanostructured surface layer was synthesized on a low carbon steel by using surface mechanical attrition (SMA)technique. The refined microstructure of the surface layer was characterized by means of different techniques,and the hardness variation along the depth was examined. Experimental results show that the microstructure is in homogeneous along the depth. In the region from top surface to about 40 /zm deep, the grain size increases fromabout 10 nm to 100 nm. In the adjacent region of about 40~80 /zm depth, the grain size increases from about 100nm to 1000 nm. The grain refinement can be associated with the activity of dislocations. After the SMA treatment,the hardness of the surface layer is enhanced significantly compared with that of the original sample, which canprimarily be attributed to the grain refinement.     

Analytic Hierarchy Process(AHP)to Optimize the Service in a Water Supply Network

Decision making in drinking water supply networks is increasingly complex due to the large number of variables involved.In order to make better decisions it is necessary to use adequate and robust methodologies.This paper presents the application of the Analytic Hierarchy Process(AHP)related to the operation of the drinking water supply network of the city of Chihuahua,Mexico,where two possible alternatives are delineated with the objective to optimize the service.The application of AHP was carried out in 24 sectors that have substantial differences in their efficiency but with instrumentation and measurement in all the variables contemplated by the operating agency,with a population of 221,722 inhabitants which represent a 30%of the total population of the city,the results indicate that the best alternative is the one with less criteria to be controlled and fewer repercussions on the cost of operation and investment in the rehabilitation and replacement of the network.     

Modified Gutenberg–Richter Coefficient for Damage Evaluation in Reinforced Concrete Structures Subjected to Seismic Simulations on a Shaking Table

This paper presents analysis and discussion of the \(b\) - and ib-values calculated from the acoustic emission (AE) signals recorded during dynamic shake-table tests conducted on a reinforced concrete (RC) frame subjected to several uniaxial seismic simulations of increasing intensity until collapse. The intensity of shaking was controlled by the peak acceleration applied to the shake-table in each seismic simulation, and it ranged from 0.08 to 0.47 times the acceleration of gravity. The numerous spurious signals not related to concrete damage that inevitably contaminate AE measurements obtained from complex dynamic shake-table tests were properly filtered with an RMS filter and the use of guard sensors. Comparing the \(b\) - and ib-values calculated through the tests with the actual level of macro-cracking and damage observed during testing, it was concluded that the limit value of 0.05 proposed in previous research to determine the onset of macro-cracks should be revised in the case of earthquake-type dynamic loading. Finally, the \(b\) - and ib-values were compared with the damage endured by the RC frame evaluated both visually and quantitatively in terms of the inter-story drift index.     

Poly（Vinyl Chloride） Nanocomposites Prepared in the Suspension Polymerization Process,Part II,PVC Filled with Silica Nanofiller

Silica/PVC nanocomposites were prepared by VCM suspension polymerization in the presence of nanosilica （0.2-2.0 wt.% /VCM）. Unmodified nanosilica prepared by sol-gel method was used. The process of VCM polymerization in the nanofiller presence was carried out without disturbances. SEM and TEM analyses confirmed the presence of nanofiller both on the surface and in cross-sections of PVC grains. The filler distribution in polymer grains was uniform. TEM observations showed that nanosilica content in amount 〈_ 2.0% led to formation of crystalline phase. The base properties of PVC nanocomposites differed from neat PVC. An improvement in mechanical properties of PVC/nanosilica composites in comparison with commercial PVC has been found. The use of the nanofiller in an amount equal to 1.0 wt.%/VCM resulted in the largest increase in tensile strength with simultaneous highest elongation at break. An addition of 0.5 wt.% ofnanosilica improved impact strength of polymer nearly 40% in comparison with neat PVC.     

Fracture surface evolution and apparent delamination toughness in split composite beam specimens subjected to mixed mode I–III loading

The influence of specimen twisting during global anti-plane shear loading in composite split beam specimens is studied. Tests were conducted on specimens with different thicknesses and delamination lengths to produce different amounts of specimen twisting prior to fracture. It is shown that specimen twisting causes mode I stresses to develop, thereby producing mixed mode I–III conditions along the delamination front. This causes near-tip transverse cracks to initiate, prior to delamination advance, at an orientation related to the mode mix. Unlike in homogeneous materials, transverse crack extension is accompanied by planar delamination advance, and transverse crack rotation during extension is restricted by the laminate’s fibers. The overall fracture surface evolution is therefore strongly controlled by specimen geometry. The influence of these findings on the apparent delamination toughness as obtained from composite split beam and other types of mode III tests is discussed.     

Review Progress in Ostwald ripening theories and their applications to the γ′-precipitates in nickel-base superalloys Part II Nickel-base superalloys

The Lifshitz-Slyozof-Wagner (LSW) theory, which corresponds to a zero volume fraction approximation, was developed to model kinetics of precipitate growth from supersaturated solid solutions. The subsequent modifications of the LSW theory for the incorporations of various factors including volume fractions of precipitates to fit the experimental data from the coarsening precipitates were made by various workers during last twenty five years. The LSW theory and its modifications have been applied on the diffusion-controlled Ostwald ripening of the precipitate particles [Ni₃(Al,Ti)] in nickel-based superalloys. The important Ostwald ripening theories were reviewed in the part I of this paper, and the coarsening characteristics of the -precipitates in Ni-base high temperature superalloys are presented in detail in relation to these theories in the present part. A model developed by D. McLean can be used to predict the particle growth over service lifetimes in the case of relatively Al-rich nickel-base superalloys. Additional fundamental data (such as the precipitate-matrix interfacial energy, diffusivity of the component species of the particle, and the equilibrium solubility with a particle in nickel-based superalloys) can be obtained from experimental results for coarsening, if the concentration changes during coarsening can be measured precisely, using the methods developed by A. J. Ardell. Furthermore, the factors affecting the shape changes and splitting of the precipitate particles during the coarsening were also considered seperately since the classical Ostwald ripening theories can not explain the morphological changes.     

Geometry dependent ductile to brittle transition of 10CrMoNbV ferritic–martensitic steel Manet II in terms of critical crack sizes

Abstract

The 10CrMoNbV Manet II cast has been selected as the reference ferritic–martensitic steel in the framework of the European Fusion Technology Programme. Charpy impact tests have been carried out in the ductile to brittle transition temperature range of this steel, such that a dynamic quasi-equilibrium has been achieved in the process zones of investigated specimens before brittle failure. This type of testing enables the evaluation of dynamic Weibull moduli and, consequently, dynamic Weibull master curves. Thus, Weibull parameters have been calculated for normal size and subsize Charpy impact specimens. The evaluated, geometry dependent dynamic Weibull master curves facilitate computation of the failure probability densities of the investigated steels as functions of scaled critical crack sizes or scaled initial defect sizes.     

Crack development in concrete structures due to imposed strains—Part II: Parametric study of a wall fully restrained at the base

Crack development due to imposed strains in concrete walls fully restrained at the base is studied in order to improve control of cracking. In this second paper the influence of reinforcement and concrete properties as well as geometry on crack width and crack spacing is studied. In a first paper a two-dimensional FE-method is described, with closing forces in cracks concentrated to spring elements. Temperatures changes are used as load and the calculations are performed stepwise with opening of nodes and implementation of spring elements. It is shown that the two-dimensional behaviour of the wall only gives about half the crack widths compared to a one-dimensional bar with the same percentage of reinforcement. The reason is that the restraint along the base will effectively facilitate distribution of cracking along the wall. The two-dimensional analysis shows that the crack widths are limited also by low reinforcement ratios. For the same reinforcement ratio the crack width will increase with tensile strength of the concrete. The geometry of the wall has very little influence on the cracking behaviour unless the wall is very short. Bond stiffness and bar diameter have a limited effect on the crack width in the wall.     

Magnetic field dependence of zero-sound attenuation close to the pair-breaking edge in3He-B due toJ=1−,J z =±1 collective modes

Our previous theory yielded for the Zeeman splitting of the imaginaryJ=1 collective mode in³He-B the result =2+0.25J _z ( is the effective Larmor frequency). In this paper we take into account the downward shift of the pair-breaking edge from 2 to 2₂– (₂ and ₁ are the longitudinal and transverse gap parameters). This leads to a complex Landé factor: the frequencies of theJ _z =±1 components become =2+0.39J _z , and the linewidths of these resonances become finite: =0.18. The coupling amplitudes of theJ _z =±1 components to density are found to be proportional to gap distortion, (₁–₂/(/)². Our results for the ultrasonic attenuation due to theJ _z =±1,J=1 modes are capable of explaining the field dependence of the attenuation close to the pair-breaking edge as observed by Dobbs, Saunders, et al. The observed peak is caused by theJ _z =–1 component: its height increases due to gap distortion as the field is increased, and the peak shifts downward in temperature and its width increases with the field due to the complex Landé factor. TheJ _z =+1 component gives rise to a corresponding dip relative to the continuum attenuation.     

Answer to comment on ‘Noiseless amplification in cavity-based optical systems with an internal two-photon process. II. Self-frequency-doubling laser and second-harmonic generation,self-down-converting laser’

Abstract

A simple method to achieve space-variant pattern recognition is proposed with a typical VanderLugt arrangement, in which the input pattern is modulated by a random binary phase function. The output correlation location can be programmed into the filter function. With the introduction of random binary phase modulation, the impulse response of either phase-only or binary phase-only filter function is not edge enhanced, resulting in higher Horner efficiency. Computer simulations are conducted to verify the proposed method.