Pressurized Interfacial Failure of Soft Adhesives

Interfacial separation of soft, often viscoelastic, materials typically cause the onset of instabilities, such as cavitation and fingering. These instabilities complicate the pathways for interfacial separation, and hence hinder the...

Study of structure formation in aluminum filled polytetrafluoroethylene after explosive compression

The features of the structure formation in polytetrafluoroethylene filled with 10 and 30% (vol.) aluminum after static and explosive pressing have been studied. It was revealed that after static pressing during sintering, interphase separation occured, which is confirmed by the formation of structures of the «closed buds» type. After explosive pressing with sintering, fibrils between polytetrafluoroethylene and aluminum and a polymer layer covering metal particles were found, and there was no interfacial separation that indicates the formation of a strong adhesive bond and is confirmed by the formation of aluminum fluoride.

Non-dimensional thermoelastic model of a compound annular cylinder in a stress-free state with internal heat generation

A non-dimensional, axisymmetric, thermal-stress model for a three-layer cylinder with internal heating has been developed. Such a geometry is encountered in an annular target for isotope production. The middle cylinder is the heat generating source with an assumed thermal expansion coefficient that is smaller than that of the other two cylinders enclosing it. Hence, the development of the solution is based on the assumption that interfacial separation occurs at the interface of the middle cylinder and the outer cylinder, while contact is reinforced between the middle cylinder and the inner cylinder. The commercial finite element code Abaqus FEA is used to obtain a numerical model which is validated using the developed analytical solution. The non-dimensional analytical solution has been presented in a simplified, generalized form, and can be applied to either of the cylinders by adjusting a few parameters. The non-dimensional variable groupings allow physical insight into how the stresses and temperature distributions evolve. A detailed solution procedure along with a discussion of the results has been provided.

Well-Adhered Copper Nanocubes on Electrospun Polymeric Fibers

Electrospun polymer fibers can be used as templates for the stabilization of metallic nanostructures, but metallic species and polymer macromolecules generally exhibit weak interfacial adhesion. We have investigated the adhesion of model copper nanocubes on chemically treated aligned electrospun polyacrylonitrile (PAN) fibers based on the introduction of interfacial shear strains through mechanical deformation. The composite structures were subjected to distinct macroscopic tensile strain levels of 7%, 11%, and 14%. The fibers exhibited peculiar deformation behaviors that underscored their disparate strain transfer mechanisms depending on fiber size; nanofibers exhibited multiple necking phenomena, while microfiber deformation proceeded through localized dilatation that resulted in craze (and microcrack) formation. The copper nanocubes exhibited strong adhesion on both fibrous structures at all strain levels tested. Raman spectroscopy suggests chemisorption as the main adhesion mechanism. The interfacial adhesion energy of Cu on these treated PAN nanofibers was estimated using the Gibbs–Wulff–Kaischew shape theory giving a first order approximation of about 1 J/m2. A lower bound for the system’s adhesion strength, based on limited measurements of interfacial separation between PAN and Cu using mechanically applied strain, is 0.48 J/m2.

Prediction of the normal contact stiffness between elastic rough surfaces in lubricated contact via an equivalent thin layer

In this work, the normal contact stiffness of lubricated rough interface is evaluated theoretically by describing the lubricated rough interface as an equivalent thin layer. Layer parameters, including equivalent thickness and effective Young’s modulus, are used to characterize the normal contact stiffness by incorporating the contributions of asperity contact and lubricant contact simultaneously. On the basis of layer parameters, the normal contact stiffness of lubricated rough interface is obtained as a function of interfacial separation, surface topography, and properties of contacting solids and lubricants. Effects of surface topographies and lubricant types on the normal contact stiffness are investigated at varying interfacial separations and contact area fractions. The proportion of solid stiffness and lubricant stiffness from the total normal stiffness is also discussed. Numerical solutions reveal that the normal contact stiffness depends sensitively on the lubricant property at initial contact, whereas the influences of surface topographies become obvious with the decrement of interfacial separation or increment of contact area fraction. Comparisons between the predicted values of normal contact stiffness and experimental data for both dry interface and lubricated interface are presented to validate the rationality of the developed model.

RESEARCH OF FEATURE OF STRUCTURE FORMATION IN PTFE-ALUMINUM COMPOSITE MATERIALS DURING SINTERING

The structure formation in fluoroplastic-aluminum composite materials during sintering after static pressing was studied. The concentration of dispersed aluminum was 30% vol.. After sintering, interfacial separation was observed in the fluoroplastic-aluminum composite materials, which is formed during crystallization due to shrinkage, which indicates a low adhesion of the filler to the polymer. Sintering of composite materials in a closed volume leads to the formation of a material with a lower porosity than when sintering in a free volume.