No abstract

The behavior of discrete or continuum structures under impact forces makes their risk and damage mechanisms more and more complex and may causes crack propagations between their different elements or plies even at low impact velocities. In this context, the internal structural failure and crack propagation analysis of composite materials under the effect of external solicitations has been studied. As a result, several microscopic and macroscopic defects may appear within the composite structure that may produce their destruction or the disaster of the hall material. To prevent this phenomenon, adaptable or "smart" materials are incorporated between the fibers of the material in order to control their health state and to determine the weakness of their structure or the beginning of their failure. Consequently they will adapt adequate answers by announcing specific modification or by causing specific actions of correction which will appear in the environment and will protect the material or the structure from the hall disaster. The application fields of these types of smart and adaptable materials are of a great importance in the areas of new technologies such as in tall buildings and bridges to prevent their disaster from the earthquakes and external excitations. They are also operationally used in space structures, in aeronautic constructions and in biomechanics or medical professions to control their behavior and to allow them to get to their initial positions after large deformations or high internal stresses before their total destruction. These materials or structures are made of new materials and/or systems which allow them to fell and control their own characteristics and their own state to attain a higher level of operational performance than those of conventional materials or structures.In our work, smart materials with shape memory alloy and piezoelectric materials, their definitions, their principle works and their super thermo elasticity phenomenon will be considered. The crack propagation analysis of a laminate composite material of carbon/epoxy types under the effect of the external forces was studied. It was found that during the appearance of cracking in the matrix, a discontinuity of the curve stress/strain is observed. It was also noted that the appearance of the cracks increases in a more particular way when the loads are applied perpendicularly to fibers. The control of this crack propagation was reached using adaptable sensors of PZT types and the finite element models to get the displacement at every nodal point. It was noted that the presence of delamination fibers is observed when the PZT static capacity induces a brutal increase in electrical tension which explain the apparition of the crack propagation. Keyword-Laminated Composites, smart materials, external solicitations, crack propagation, disaster protections and finite elements.I.

This study concerns a new ecological material, bio-sourced and with reduced environmental impact. The material in question is a composite made from date palm fibers and lime. For the development of this material, we were inspired by the techniques used for the manufacture of hemp concrete. The latter is widely used especially in France for the thermal insulation of buildings. The idea is to design an insulation material from the natural resources of the southern Algerian region. The material made is a lightweight concrete that could provide both thermal and acoustic insulation. By its porous morphology, it also has the ability to absorb water vapor when it is in an environment with high relative humidity and to release the vapor if the environment is dry. It could therefore play the role of a water regulator. Experimental investigations revealed interesting mechanical and hydrous properties. Measurements of the moisture buffer value (MBV) reveal that according to the current standard, the material is classified between good and excellent. As regards the mechanical strength, the material produced has an acceptable compressive strength.

Thin films of cobalt oxide (Co3O4) were prepared on glass substrates by the spray pyrolysis method using a solar concentrator (oven) manufactured in our laboratory. We used different processing temperatures (300° C, 350° C and 400° C). The structural, optical and electrical properties of the different samples were analyzed by X-ray diffraction (XRD), UV-Visible spectroscopy and the Hall effect measurement system. X-ray diffraction observations revealed that cubic crystals are created in all films produced, and the film structure is that of a single phase created with preferential orientation along the (311) axis in films at low temperatures, and the axis (111) for high temperatures. The grain sizes of our products vary between (22.62nm and 66.19nm), depending on the processing temperature. The optical band gap of the crystals obtained was measured. The results of the optical forbidden bands of the crystals obtained, indicated two bands of the values for each element (Eg1 and Eg2). We observed that the values of the effective optical forbidden bands increase by 2.547eV and 3.0731eV with the increase in the production temperature., In addition the film produced experiences a decrease in the Urbach parameters which vary between 162.20meV and 360.81meV depending on the increase in production temperatures. Finally, the films produced have electrical conductivity values of (1.090 [(Ω.cm)−1] to 1.853 [(Ω.cm)−1] and electrical resistivity values of 1.431 (Ω.cm) at 1.853 (Ω.cm), depending on the variation in the production temperature.