Estimation of Concrete's Porosity by Ultrasounds

AbstractDurability of concrete depends strongly on porosity; this conditions the intensity of the interactions of the concrete with the aggressive agents. The pores inside the concrete facilitate the process of damage, which is generally initiated on the surface. The most used measurement is undoubtedly the measurement of porosity accessible to water. The porosimetry by intrusion with mercury constitutes a tool for investigation of the mesoporosity. The relationship between concrete mixtures, porosity and ultrasonic velocity of concrete samples measured by ultrasonic NDT is investigated. This experimental study is interested in the relations between the ultrasonic velocity measured by transducers of 7.5mm and 49.5mm diameter and with 54kHz frequency. Concrete specimens (160mm diameter and 320mm height) are fabricated with concrete of seven different mixtures (various W/C and S/S+G ratios), which gave porosities varying between 7% and 16%. Ultrasonic velocities in concrete were measured in longitudinal direction. Finally the results showed the influence of ratio W/C, where the porosity of the concretes of a ratio W/C _0,5 have correctly estimated by ultrasonic velocity. The integration of the concretes of a lower ratio, in this relation, caused a great dispersion. Porosity estimation of concretes with a ratio W/C lower than 0,5 became specific to each ratio

Finite element analysis of the behaviour of a crack in the orthopedic cement

In this paper, the finite element method is used to analyse the crack behaviour in the orthopedic cement of the total hip replacement by computing the stress intensity factors (SIFs) arround the crack tip. In this work, three cases are studied: crack emanating from a cavity, interaction effect of the crack emanating from a cavity with another cavity and the interaction effect of two cracks emanatingfrom two cavities. The stress intensity factors under mixed mode problems at the crack tip are computed for three zones of prosthesis: proximal, median and distal. The obtained results show that the crack initiated from a micro-cavity in the distal zone of cement can be propagated at the same time by opening and shearing of its lips. It is contrary to that initiated in the proximal zone which cannot be propagated. The mechanical behaviour of cracks in the medial zone depends of the crack initiation position

Spin coated (M

(Mx, Zn 1-x O), M= Sn, Al nanofibers properties were investigated. Pure and M-doped zinc oxide films were fabricated onto a glass substrate by a facile and low cost spin coating route. X-rays analysis reveals that films crystallize with a wurtzite structure according to (002) orientation. The transmittance in the visible range was as high as 88 % at 550 nm. The doping increased slightly the transmittance, the as-grown films were high transparent in VIS and IR ranges. The optical band gap was a little bit changed by doping. AFM 3D-views revealed that grains were nanofibers with the size of 18.22, 18.23 and 44.27 nm respectively for pure, Al and Sn-doped ZnO films

3D FE analysis of the behavior of elliptical cracks on orthopedic cement of the total hip prosthesis

An explicit analysis conducted on the crack behavior in chirurgical cement (Polymethylmethacrylate – PMMA) used for Total Hip Prosthesis (THP) is of great importance in collecting information about the nature of the phenomenon of loosening of the cement application. The rupture of the orthopedic cement is practically the main cause of this loosening. Understanding different rupture mechanisms give a great value in advancing the durability of the cemented total prosthesis. The purpose of this study is to analyse cracks behavior, initiated in the cement that links the femoral-stem with the bone, using the Finite Element Analysis Method (FEM). The present study brings into focus the variation of the stress intensity factor in modes I, II and III. This rupture criterion is used according to the nature of crack, its orientation and its location in the orthopedic cement. At first, the level and distribution of the equivalent von Mises stress is analysed, which is induced in the medial, proximal and distal parts of the bone cement. Then, the behavior of different geometric forms of an elliptical crack is evaluated which are located and initiated within the body of these three parts