Effects of infiltration pressure on mechanical properties of Al–12Si/graphite composites for piston engines

In this work results for the flexural strength and the thermal properties of interpenetrated graphite preforms infiltrated with Al-12wt%Si are discussed and compared to those for packed graphite particles. To make this comparison relevant, graphite particles of four sizes in the range 15–124 μm, were obtained by grinding the graphite preform. Effects of the pressure applied to infiltrate the liquid alloy on composite properties were investigated. In spite of the largely different reinforcement volume fractions (90% in volume in the preform and around 50% in particle compacts) most properties are similar. Only the Coefficient of Thermal Expansion is 50% smaller in the preform composites. Thermal conductivity of the preform composites (slightly below 100 W/m K), may be increased by reducing the graphite content, alloying, or increasing the infiltration pressure. The strength of particle composites follows Griffith criterion if the defect size is identified with the particle diameter. On the other hand, the composites strength remains increasing up to unusually high values of the infiltration pressure. This is consistent with the drainage curves measured in this work. Mg and Ti additions are those that produce the most significant improvements in performance. Although extensive development work remains to be done, it may be concluded that both mechanical and thermal properties make these materials suitable for the fabrication of piston engines.

Ventilated Stone Veneer: Mechanical Behaviour, Calculation Methodologies, Major Pathologies and Existing Tests

The increase of building pathologies related to the use of stone materials and the use of ventilated stone veneers, requires the reformulation of design concepts in building façades and also the reformulation of the architectural project. The aim of this paper is to identify, analyze and evaluate synthetically building pathologies in stone ventilated façades in order to obtain the main technical conditions to be considered in the architectural design, by interpreting its mechanical behavior and capabilities to prevent such pathologies and to ensure the proper features during the building lifetime. The methodology is based on both laboratory stone tests and in situ tests about construction systems, by analyzing physical and mechanical behavior of the outer layer in relation to other building requirements. The results imply the need of proper sizing, specific quality control and practical application of calculation methods, to control high concentration pressures in ventilated façades by reaching appropriate project solutions. In conclusion, the research about different pathologies of stone ventilated façades, the study of their mechanical behavior, their anchorage and their connection with their constructive aspects, will help to improve the construction quality of the stone ventilated façade in buildings and to enhance the use of natural stone in modern architecture.