Experimental Investigations on the Relation of the Lubricant’s Flash Point and Quality of the Piston Made from Aluminium Alloy for its Application in Internal Combustion Engines

In the current paper there was made an attempt to develop an experimental method of physical (lubricant’s flash point Tfp) and subjective (forgings’ quality) parameters coupling for hot isothermal-like forging operation. The quality forgings could be manufactured both by high and low lubricant’s flash point. The increase of Tfp value in exothermal reaction follows to the increase of the released heat amount by the lubricant, because it needs more initial activation energy transmitted from the external source to initialize transformation of the material from one aggregate state into another (from liquid or solid into gaseous or sol-like). This can prevent the temperature decrease on the punch due to strong convective heat transfer with the environment through the building of the isolation temperature shield on the punch contact surface at the beginning of the punch stroke. On the other hand it can cause the defect building on the forgings like penetrations, which could not be eliminated during cleaning operation before mechanical treatment due to chemical interactions of the dissolved active agents, or unfilled sections.

A Theoretical Model to Fracture in Cell Membrane

A new stress function modelling the fails in biological tissue is here proposed. Under the assumption that the cell membrane may be modelled as neo-Hookean materials, we develop the problem in the framework of non-linear elasticity. We attempt to model the ice nucleation phenomenon when freezing and thawing occurs in cellular cryo-preservation. The ice seed generated surface can be either soft or wrinkled and, when the latter emerges a punch contact against the cell membrane takes place. Restricting our attention on opportune mono-dimensional sub-set, we extend the multiple critical points theorem at our model. We find a particular solution in agreement to the classical fracture models besides a response function in accordance to the stress and strain field distribution in biological materials.

AN APPROXIMATE FORMULATION OF THE EFFECTIVE INDENTATION MODULUS OF ELASTICALLY ANISOTROPIC FILM-ON-SUBSTRATE SYSTEMS

Frictionless contact between an arbitrarily-shaped rigid indenter and an elastically anisotropic film-on-substrate system can be regarded as being superposed incrementally by a flat-ended punch contact, the shape and size of which are determined by the indenter shape, indentation depth (or applied load) and elastic properties of film and substrate. For typical nanoindentation applications, the indentation modulus can thus be approximated from the response of a circular contact with pressure of the form of [1 - (r/a)2]-1/2, where r is the radial coordinate and a is the contact radius. The surface-displacement Green's function for elastically anisotropic film-on-substrate system is derived in closed-form by using the Stroh formalism and the two-dimensional Fourier transform. The predicted dependence of the effective modulus on the ratio of film thickness to contact radius agrees well with detailed finite element simulations. Implications in evaluating film modulus by nanoindentation technique are also discussed.