Volume 15 (2015): Edizione 2 (June 2015)

A total hip replacement is a procedure that requires removal of the affected joint lesions and replacing it with artificial elements. Nevertheless, like any invasive surgery, it is associated with the risk of complications, including joint infection, fracture of the bone during and after surgery, scarring and limitation of motion of the hip, and loosening of the prosthesis. In this work we present and describe the results of its investigations. In order to determine the mechanism of failure, a broken stem components were analyzed by means of macroscopic and microscopic observations and hardness measurements. The hardness, microstructure and chemical composition of the broken part of the hip stem were analyzed. Microscopic examination revealed numerous defects in material. Among them are pores and emptiness, located on the outskirts of the tested samples and a plurality of micro-cracking, debonding and delamination of the material due to the overloading of a fatigue character. There were no changes caused by intergranular corrosion or pitting, which may indicate for an even distribution of the major alloying components such as chromium and nickel. Observations of the material by using scanning electron microscopy (SEM), clearly proved that the destruction was caused by material fatigue. The investigation showed that the crack had originated due to a high stress concentration on the lateral corner section of the stem. Large surface of the fatigue crack zone area indicated for small stresses and small crack propagation velocities. There was a clear correlation between the grain size of the steel hardness. The results of hardness test revealed a significant increase hardness of stem in relation to the normative values. In addition, the measured average grain size is less than the standard accepted. Using Solid Works simulation and FEM a model of the stem was created and analyzed in terms of strength and rated the distribution of the generated stress. The finite-element analysis confirmed that there is the highest stress concentration in the middle of the stem

The paper presents research results of isothermal oxidation of Ti-25Al-12.5Nb alloy. Oxidation was carried out in 9%O₂+0,2%HCl+0,08%SO₂+N₂ atmosphere at the temperature of 700 and 750 ºC.

The article provides basic information about the shrinkage of concrete and discusses the major impact on the size and course of the shrinkage. There are the guidelines to estimate the shrinkage strain of concrete bridge structures for the high tensile strength-SCI in accordance with PN-EN 1992-2. The article presents the results of experimental studies which aim was to analyze the course of shrinkage in two types of specimens made of different composition mixes. The studies have also made possible to verify the actual size of the shrinkage strain and designated ones on the basis of the PN-EN 1992-2.

Impact behaviour of glass fibre /epoxy composites with nano- SiO₂ modified resin was studied in terms of low velocity impact after water exposure. Nanocomposites with 1%, 2%, 3% 5% 7% nano-SiO₂ (Nanopox- Evonic) were investigated. Peak impact load and impact damage area as a function of nanoparticle contents were compared for dry specimens and for samples exposed to water (0.7 %wt. 1.7% water absorbed) at 1J, 2J 3J impact energies. For unmodified composite peak force was higher than for 3% modified specimens and higher for dry specimens than those exposed to water. Impact damage areas were plotted as a function of water contents for modified and unmodified samples. Failure modes were illustrated using SEM micrographs. Numeropus matrix cracks were the dominating failure mode in dry speciemens both unmodified and the modified. Fibre fracture was observed at 3J impact energy in all dry unmodified samples, however water exposure prevented early fibre fracture in nanocomposites. The proposed energy absorption mechanism is nanoparticles debonding.