Classification-of-materials

Amar Telidji Laghouat University
Ministry of Higher Education and Scientific Research
Mechanical department
Specialty: Industrial maintenance
1st Master
Module: introduction to materials
-Last name and first name :
 Lakhdari mohammed zakaria
 Djekidel zohir abdelnour
2020/2021
non-metallic materials

 Introduction:
In the case of materials subjected to mechanical loads, the use of
composite materials has allowed the optimization of the properties by the
use of substances which a priori, in a conventional material, would not be
present at the same time or at least not under the desired shape and this,
under conventional conditions of implementation by the laws of
equilibrium and chemical kinetics.
This increase in the number of degrees of freedom for the material implies
new possibilities (eganisotropy, material gradient, etc.) but also new
challenges such as questions related to the compatibility and stability of
materials. These issues can lead to new ones limitations of the possible
choices but this barrier is not immutable over time in view of the
development of new means of implementation (additive techniques,
friction -‐ mixing, etc.).
In principle, the field of application of composite materials is not
necessarily limited to aeronautics or transport for which maximizing the
stiffness / specific weight ratio is fundamental. However, the high cost of
these materials reduces their use for applications where the cost of
materials and implementation are critical, such as in the case of civil
engineering and to a lesser extent, for mechanical engineering.
In the composites sector, a notable development is in place, if the 1950s to
1980s focused on the development and use of polymer-based matrices
reinforced with glass, carbon or aramid fibers, alternatives are
developing more and more. These concern the choice of materials and
their implementation process, closely linked to the theoretical properties
actually obtained and their dispersion.

 Classification of materials :
Like many other things, materials are classified in groups, so that our
brain can handle the complexity. One can classify them based on many
criteria, for example crystal structure (arrangement of atoms and bonds
between them), or properties, or use. Metals, Ceramics, Polymers,
Composites, Semiconductors, and Biomaterials constitute the main
classes of present engineering materials. Metals: These materials are
characterized by high thermal and electrical conductivity; strong yet
deformable under applied mechanical loads; opaque to light (shiny if
polished). These characteristics are due to valence electrons that are
detached from atoms, and spread in an electron sea that glues the ions
together, i.e. atoms are bound together by metallic bonds and weaker van
der Waalls forces. Pure metals are not good enough for many applications,
especially structural applications. Thus metals are used in alloy form i.e. a
metal mixed with another metal to improve the desired qualities. E.g.:
aluminum, steel, brass, gold. Ceramics: These are inorganic compounds,
and usually made either of oxides, carbides, nitrides, or silicates of
metals. Ceramics are typically partly crystalline and partly amorphous.
Atoms (ions often) in ceramic materials behave mostly like either positive
or negative ions, and are bound by very strong Coulomb forces between
them. These materials are characterized by very high strength under
compression, low ductility; usually insulators to heat and electricity.
Examples: glass, porcelain, many minerals.

Metals :
These materials are characterized by high thermal and electrical
conductivity; strong yet deformable under applied mechanical loads;
opaque to light (shiny if polished). These characteristics are due to
valence electrons that are detached from atoms, and spread in an
electron sea that glues the ions together, i.e. atoms are bound together
by metallic bonds and weaker van der Waalls forces. Pure metals are not
good enough for many applications, especially structural applications.
Thus metals are used in alloy form i.e. a metal mixed with another metal
to improve the desired qualities. E.g.: aluminum, steel, brass, gold.
 Polymers :