Konstantinos N. Athanassiadis
Alexander Technological and Educational Institute of Thessaloniki Department of Automation, Laboratory of Metrology
Composite materials (CM), often shortened to composites, are engineered materials made from two or more constituent materials functioning as matrix and reinforcement (Hull and Clyne 1996; Milton 2001; Strong 2007; Chung 2010). A composite material is characterized by a complex structure. Composite Materials are successfully used in various sectors of science (naval, aerospace, automotive industry and technology), replacing traditional materials such as timbers, metals and ceramic (Carlsson, Donald F. Adams et al. 2002; Strong 2007; Chung 2010). This is due to their unique attributes, such as non-existence of erosion, rust and also the fact that they demonstrate great resistibility in high temperatures. All the advantages mentioned before have made CM popular in industrial applications.
The continuously wider use of Composite Materials (CM) in various sectors of human activities imposes the growth of new methods and the construction of new appliances in order to study their physical and chemical attributes, such as density and effective atomic number, in high temperatures. The effective atomic number Zf and the density p are among the parameters which characterize the technological, and exploitation attributes of materials and their derivatives (Plotnikov and Pschenicniji 1973; Chudakov and Anshakov 1982; Celi 1992; Athanassiadis 1994).
Existing instruments for measuring and control of the physical and chemical properties of CM, the parameters of the technological processes don’t satisfy fully the needs of research institutions and industrial enterprises. In many industrial enterprises definition of density of various materials during production is inherently confusing. The problem is particularly pronounced in developing and manufacturing of composite materials for which the density is one of the most important characteristics, directly or indirectly defines the quality composites and products from them.
The effective atomic number Zeff and density p, parameters that play fundamental role in the behavior of materials under high temperatures are determined with the State-of-the-art techniques. These techniques determine these quantities by the average value in the total volume of the measured sample and in particular, statically after the effect of high temperature (Chudakov and Anshakov 1982).
Thus, it is expected that the creation of methods for no-contact, non-destructive control of Zeff and density p of local parts of the material samples will allow the clarification of the
physical and mathematical models of degradation of the composite materials under conditions of high temperatures. In addition, it will assist in the improvement of the technical characteristics of parts and elements of CM, due to utilization under conditions of high temperature (up to 3000 K), and make the better possible selection of the material based on its thermal and physical properties, at the stage of product creation (Celi 1992; Athanassiadis 1994).
Radioisotope methods and appliances constitute effective means of non-destructive testing – NDT of many CM attributes. Particular characteristics, like the no-contact measurements, the high productivity, the conformity, and the relatively simple instrumentation needed, have extended the use of methods based on photon radiation transmission to the radioactive control of materials (Athanassiadis 1994). Use of low-energy sources of ionizing radiation (with an energy Ey < 100 keV) is appropriate to improve the measurement sensitivity in controlling light environments with low thickness sensed layer (Chudakov and Anshakov 1982). Although in this case we need to take into account variations of element composition of samples.
Radiation у-methods have comparative simplicity of implementation while providing satisfactory direction of monochromatic radiant flux. Selecting composition and energy radiation can ensure the prevalence of that kind of interaction, which contributes to maximizing information about controlled sample (Athanassiadis 1994). Depending on the effects of interaction of y-quant with matter and scattering geometry there are resonance and non-resonance absorption methods of scattered radiation, as well as combined methods of у-control (multi-beam methods) (Athanassiadis, Anshakov et al. 1993; Athanassiadis 2007; Athanassiadis, Chudakov et al. 2008).