Shape Of Microvoids Research Articles

A review on theory and application of plastic meso-damage mechanics

Meso-damage mechanics differs from continuous damage mechanics, which pays more attention to the evolution of meso-structure in materials. It combines physical and mechanical processes to link meso-structure evolution of materials to their macro-mechanical behavior through some average method. The development of meso-damage mechanics provides an alternative method for describing the damage behavior of materials and a new research topic in plastic damage mechanics. Therefore, this paper reviews the development of plastic meso-damage mechanics and illustrates the development of meso-damage mechanics with the most representative and application prospect Gurson-Tvergaard-Needleman (GTN) model as an example. The development of GTN meso-damage mechanics model has undergone developing from the initial meso-voids volume evolution equation to the establishment of the meso-damage constitutive equation and the vigorous development of various improved GTN damage models. The improvement and optimization of GTN meso-damage model in the shape of micro-voids and shear correction, and its important position and application status in meso-damage mechanics are emphatically discussed in this paper. The purpose of this review is aimed at providing an insight into the advantages of meso-damage mechanics model and some problems in the existing research background of its application, and to present the future development prospects, which provides great potential for further research and innovation of plastic meso-damage mechanics of materials.

A micromechanical study of porous composites under longitudinal shear and transverse normal loading

The mechanical response of porous unidirectional composites under transverse normal and longitudinal shear loading is studied using the finite element analysis. The 3D model includes discrete and random distribution of fibers and voids. The micromechanical failure mechanisms are taken into account by considering the mixed-mode interfacial debonding and pressure-dependent yielding of the matrix using the modified Drucker–Prager plasticity model. The effect of the micromechanical features on the overall response of composite is discussed with a focus on the effect of microvoids and interfacial toughness. Finally, the computational prediction of the porous composite in the transverse normal-longitudinal shear stress space is obtained and compared with Puck’s model. The results show that both interfaces with low fracture toughness and microvoids with even small void volume fraction can significantly reduce the macroscopic strength of composite. The size and shape of microvoids can also microscopically lead to different crack paths.

Mechanism for spherical dome and microvoid formation in polycarbonate using nanojoule femtosecond laser pulses

Spherical domes are created on the surface of polycarbonate samples, and microvoids are formed within the bulk using only a femtosecond oscillator with pulse energy of just 0.47 nJ. Size of spherical domes and shape of microvoids are controlled by changing the laser focus inside the material. Their formation is explained by a combination of heat accumulation and dome formation dynamics, where the dome acts as a microlens shifting the laser focus within the sample. The technique described here provides a simple avenue for fabricating smooth microlens arrays of various sizes and opens the possibility for direct fabrication of complex three-dimensional microfluidic channels in transparent materials.

Electrokinetic properties of surface modified PETP fibres

The microporous structure of unmodified poly (ethylene terephthalate) PETP fibres was investigated by small-angle X-ray measurements in order to determine the content, size and shape of micro-voids in the fibres. Because of the compact and highly crystalline morphology of the chemically weakly reactive PETP fibres, the rate of diffusion within the fibres or adsorption on the surface is very low. Therefore a technique for modifying polyester fibre surface to change the dyeability, water sorption properties and electrokinetic characteristics have been suggested and used. It includes the adsorption of some electrolytes on the fibre surface. In order to study the obtained fibre surface changes the zeta-potential ζ was determined by streaming potential measurements as a function of pH. PETP fibres exhibit high negative ζ plateau value, due to their strong hydrophobicity and non-ionic character. The application of the surfactant changes the electrokinetic properties with respect to the adsorption process conditions.

Highly faceted growth shape of microvoids in icosahedral Al-Mn-Pd

Faceted microholes in icosahedral Al-Mn-Pd quasicrystals form by condensation of thermal vacancies, typically during annealing in the temperature range above approximately 700oC. Prolonged annealing at temperatures between 750 and 830oC leads to the growth of large and highly faceted microholes through a classical Ostwald ripening process. The indexing of all facets of such a microhole is presented. The idealized morphology is found to correspond to an icosahedral polyhedron with 302 facets.

Tridirectional X-Ray Patterns of Oriented Film at Wide and Small Angles

Drawn, oriented film of polyethylene terephthalate was studied by means of an x-ray diffraction technique in which the x-ray beam was directed in three mutually perpendicular directions: (1) through the film, (2) and (3) in the plane of the film, parallel and normal to the direction of draw. Patterns were obtained in each of these directions for the diffractions occurring at both small and large angles. This combination of patterns provides a picture of the film's polymer texture with these parameters: size, orientation, and arrangement of crystallites; extent of amorphous material; shape of microvoids. In this film the crystallites have planar orientation and are 45 A wide in the plane. A long period of 125 A exists in the direction of draw and is comprised of 75-A crystallite length and 50-A amorphous material. There is evidence that the film is composed of lamellae about 60 A thick; these lamellae are stacked in a staggered arrangement such that the crystallites in one lamella are adjacent to the amorphous regions in the lamella below. The small angle diffraction evidence cannot be reconciled with the ``coiled ribbon'' arrangement recently proposed in the literature to explain off-meridional diffraction spots.