Global Journal of Engineering Sciences (GJES)
Artificial
Smart Composites: Bionics Principles
Authored by Serge Shilko
Opinion
The search for effective ways
to achieve the synergy of the matrix and structurally active (reinforcing,
antifriction, etc.) dispersed and spatially oriented fibrous fillers is a
general trend in the development of composite materials science. Despite the significant
amount of experimental data available and the variety of matrix materials,
modifiers and technologies, it is relevant to develop new approaches to
creating structural and functional composites with rapid prototyping and
testing of products based on them.
Along with lately requisite
properties such as stability of physical and mechanical characteristics,
linearity of the equation of state and unambiguity of response to disturbance,
there arose a problem of a complex active response to varying outer conditions.
Other words, a tendency is observed of increasing number of material functions
acquiring the features of intellectual systems [1].
New opportunities are
associated with the development of an interdisciplinary concept that provides
for the joint use of the achievements of the physics and mechanics of solids,
multiscale modeling of structurally heterogeneous materials [2,3], as well as
bionics, nano-, additive and new information technologies (conception of
digital twins).
In particular, research in the
field of cybernetics [4], principles of self-organization [5] and bionics
developing ideas about the basic laws of life, contributes to innovation in all
technical fields, without exception, from prosthetics to global control and
production systems.
Living systems optimized
evolutionarily have been and remain a source of effective design, technological
and material science solutions. Biomaterials are characterized by appropriate
adaptive reactions to changes in external conditions, which contributes to the
achievement of extremely valuable stress-strain, tribological and other
indicators (equal strength, lack of gravity, self-healing, damping, ultra-low
friction, etc.).
So, obvious prototypes of
these materials turn to be biosystems, from the one hand, and computer
monitored technical systems able to reproduce intellectual behavior using
sensor, processor and executive functions (including effector function and
response action), from the other hand, plus feedforward and feedback. Although
means of these properties’ realization can’t be similar in artificial materials
and above-mentioned natural prototypes, generalizations obtained at the
junction of the materials science, bionics and cybernetics allow to formulate
the conceptual principles and to consider probable ways of the named
interdisciplinary problem solution.
Recent reviews and
terminological discussions in the field have confirmed actuality of the
structural and functional analyses of smart composites, including functional
nanomaterials. However, papers, devoted to such materials are commonly reduced
to creation of sensors and actuators. Less attention has received principles
and models of intellectual (processor) reactions in artificial materials. The
development of adaptive composites allows us to hamper the failure process and
promotes reliability and service life of products for different technical
applications.
It is fundamentally important
to describe the heterogeneity and mobility of the interphase boundary in
bionically adequate materials, take into account the feedback between the
diagnosed and output parameters, and analyze the processes of structure
self-organization in real time. To this end, micromechanical representations,
variational methods for solving problems on a moving boundary, regularization
methods for solving inverse problems, etc., as well as experimental methods for
studying the structure and local mechanical properties (atomic force
microscopy, tomography) are involved.
The proposed opinion in
structural design of bionically adequate composites under development includes:
• taxonomy [6] of materials
based on a multidimensional structural and functional analysis and the theory
of synergetic.
• development of
micromechanical models of materials (porous, granular, polymers, reinforced
composites, biological tissues) with the allocation of a representative volume
and structural units of the deformable medium.
• the formulation of the
physical mechanisms of functioning of smart materials, as thermodynamically
open systems with metastable phase composition and feedbacks, in which
automatic expedient restructuring of the structure is realized under extreme
external influence in accordance with a given criterion of optimality.
• mathematical justification
of the ability to control the deformation, friction, and fracture modes of
artificial composite materials to implement their smart (quasi-biological)
behavior, in particular, based on solutions to the problems of localizing the
moving interfaces, including determining the optimal gradient of the
interfacial layers.
Some words about
classification of materials with account of interrelations found between
structure and functions as well as analysis and modeling of a subclass of
intellectual systems, namely adaptive composite materials. These assumptions
are based on the theory of functional systems and synergism [5]. Three
generations of materials which can be discriminated in the proposed
classification.
The first generation
is traditional materials including monofunctional media whose properties are
determined by the nature and initial quality of a single component. The next
are traditional composites with a prominent structural hierarchy, being also
monofunctional. They are characterized by stability of inner and external
boundaries, i.e. fixed structure of components, intermediate layers and the
composite as a whole.
Adaptive materials
with coordinated functions and active behavior belong to the third advanced
generation of materials. These systems perceive outer effects at unchanged
function owing to, presumably, structural self-organization. In this
connection, the mobility of the component boundaries should be remembered as an
indispensable property of smart materials, which is not present in traditional
composites.
The qualitative
transition of materials from the passive to active functioning is shown in
Table 2. Naturally, prerequisites of such a transition are formed at the levels
of two preceding generations. Thus, transformation of one physical field into
another (e.g., piezo- or photo effects) is probable at the stage of
monofunctional material. The creation of qualitatively new (emerged), including
forecast properties, is a logical continuation of the additive and synergetic
principles of composite production. This precedes the development of adaptive
composites, being a subclass of smart systems with the dominating adaptive
strategy.
The suggested
classification makes it possible to forecast other unknown materials of the
intellectual type, for example, capable of self-destruction “kamikaze”, those
ensuring partial or full restoration “regenerators” and materials offering
programmed control of the environment (“cyber”) and implicit (“incognito”)
ones. These subclasses constitute a new type of “ecophilous” materials which
behavior supports homeostasis of the environment.
Relative simplicity of
adaptive composite materials is due to their orientation aimed to fulfill only
the adaptive function of the part or a system in contrast to a higher status of
the materialmedium subclass (Table 2). However the adaptive composite is formed
rather in time than by a mechanical mixing of structural components, and
revolutionizes as a specific unit by coordinating interrelated physical
processes based on an imparted optimum criterion. In this case, the emergence
of macrostructure is specified by origination of collective modes under the
action of fluctuations, there competing and, finally, by selection of the most
accommodated mode or their combination. The structures themselves could be
described in physical terms as types of adaptation to outer conditions.
Reaction of a material
due to mutual coordination of structural and functional parameters of
microsystems characterizes it as an open self-regulating system. Selection of
the mode of behavior in response to outer effect does not arise from the
principle of the least action, neither from the principle of compulsion (Gauss
principle) nor from that of the utmost probability. Active response systems
eliminate (or subordinate) contingency. This makes grounds to speak about a
programmed behavior of the system, i.e. the decision is made according to the
inner criteria determined by the structure itself and system parameters, which
substantiates the necessity of direct and reverse connection channels.
It follows from the
above said that to form a more complex processor function of smart materials it
is possible to use the universe phenomenon of self-organization, which is not
limited to only systems of higher organization and functional complexity and
isn’t a monopoly of bio- or social systems. A self-organizing system is
understood as a system capable of stabilizing parameters under varying outer
conditions through directed ordering of its structural and functional relations
aimed at withstanding entropic factors of the environment, which helps to
preserve its characteristics as an integral formation [5].
The material formed by
combining its components acquires the characteristics of a composite structure,
which is a notion nonequivalent to the structure of its constituents. This fact
raises composite materials to a higher structural level and admits the
probability of per layer differentiation of the functions in order to reach the
integral control system. In our view, to realize adaptation mechanism to outer
conditions in composite materials, it’s worthwhile considering the combination
of different scale physical processes, where we single out at least 4
structural levels: molecular, mesoscopic, macroscopic and polycomponental.
The molecular level is
the basic one at programming material behavior. This is because its scale in
polymer composites corresponds to cooperative effects of segmental mobility and
conformal rebuilding that provide conditions for self-organization in
high-molecular bodies. Just here the processor function is realized as a
capacity for estimating variations due to outer effects and as a tool
formulating the character and force of response based on stationary
characteristics of the microsystem. Also, the effector function is fulfilled
here for exciting reverse reactions by varying characteristics of the
microsystem on a self-organization base.
The mesoscopic level performs
the sensor function as an ability to perceive outer effects. Non-equilibrium
processes are initiated at this level changing molecular structure and
supporting the interaction of direct and reverse channels between the levels.
The macroscopic level makes
provision for the mobile function as a reorganization of the initial subsystems
(components) aimed at preserving the behavior model.
The mobile function is also
realized at the polycomponental level, though intention in this case to provide
the system (material = article) functioning as a whole.
To organize control, the
processes relating to the mention levels should be coordinated using functional
links between them.
It is to be remembered that
polymer composites are potential carriers of intellectual properties. Namely,
they are sensitive to physical fields, i.e. show a sensor function; make it
possible to carry out the actuator function (shape memory of thermosetting
resins, etc) and, finally, among all other artificial material media they most
closely approach the living nature (bio tissues are usually built of
high-molecular compounds).
The study of synergetic
phenomena in nonliving nature as a linking element between analogous processes
in original objects will, in our opinion, provide a possibility to find
structural-andfunctional bio prototypes of smart composites.
Conclusion
• The systematic analysis of
the problem of developing bionically adequate smart composites has enabled us
to trace evolution of structural organization of artificial materials, to
clarify the mechanisms of adaptation to the external action, and to disclose,
to a certain degree, the effect of structure on formation of the optimum back
reaction.
• It seemed that mathematical
description of smart composite structures is formulated as a problem on
localizing moving interfaces. The study of synergetic phenomena in the
nonliving nature and analogous processes in biological objects will, in our
opinion, provide a possibility to find structural-andfunctional prototypes of
adaptive composites.
• Time will tell, to what
extent the proposed approaches may prove to be fruitful and useful for the
materials science and the material production as a whole.
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