Page 16 - Mechanics Analysis Composite Materials

Chapter 1

INTRODUCTION

1.1. Structural materials

Material is the basic element of all natural and man-made structures. Figuratively
speaking it materializes the structural conception. Technological progress is
associated with continuous improvement of existing material properties as well as
with expansion of structural material classes and types. Usually, new materials
emerge due to necessity to improve the structure efficiency and performance, but as
a rule, new materials themselves in turn provide new opportunities to develop
updated structures and technology, while the latter presents material science with
new problems and tasks. One of the best manifestations of this interrelated
process in development of materials, structures, and technology is associated with
composite materials to which this book is devoted.
Structural materials should possess a great number of physical, chemical and
other types of properties, but there exist at least two principal characteristics that
are of primary importance. These characteristics are stiffness and strength that
provide the structure with the ability to maintain its shape and dimensions under
loading or any other external action.
High stiffness means that material exhibits low deformation under loading.
However, saying that stiffness is an important property we do not mean that it
should be necessarily high. Ability of structure to have controlled deformation
(compliance) can be also important for some applications (e.g., springs; shock
absorbers; pressure, force, and displacement gauges).
Shortage of material strength results in uncontrolled compliance, i.e., in failure
after which a structure does not exist any more. Usually, we need to have as
high strength as possible, but there are some exceptions (e.g., controlled failure of
explosive bolts is used to separate rocket stages).
Thus, without controlled stiffness and strength the structure cannot exist.
Naturally, both properties depend greatly on the structure design but are
determined by stiffness and strength of the structural material because a good
design is only a proper utilization of material properties.
To evaluate material stiffness and strength, consider the simplest test - a bar with
cross-sectional area A loaded with tensile force F as shown in Fig. 1.1. Obviously,

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