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found for structural components. In practice this is not sufficient for reliable service of

structures and energy parameters should be used in addition, such as toughness.

Figure 15: a. Monolayer of carbon atoms. b. Single-walled nanotube (SWNT). c. Covalent bond

between basal carbon atoms and bond between basal planes. d. diameters of carbon materials

Table 2: Modulus of elasticity, fracture stress and strain for structural materials (based on /1/)

Material

Modulus of elasticity, TPa Fracture stress, GPa

Fracture strain, %

Steel 4340

0.207

1.6 ÷ 1.7

Tungsten

0.4

0.76

3.5

Zirkonia (ZrO

)

0.2

0.8 ÷ 1.5

Kevlar fibres

0.06 ÷ 0.15

3.6 ÷ 4.1

2.5 ÷ 1

Epoxy

0.0035

0.005

Diamond

0.7 ÷ 1.2

1.05

Carbon fibres

0.20 ÷ 0.75

4.0 ÷ 7.0

0.5 ÷ 1.8

Carbon nano tube

1 (0.50 ÷ 5.50)

15 ÷ 63

5 ÷ 15

Carbon multiwall

nano tube

0.1 ÷ 1.2 (tension)

1.7 ÷ 2.4 (compression)

1.28 ± 0.59 (bending)

10 ÷ 66

100 ÷ 150

14.2 ± 0.8

Many assumptions and simplifications are induced for macro structures in order to

achieve uniform interpretation of parameter values. Following facts should be respected:

Stress is defined as the relation between of applied load and cross section properties

of component or specimen, neglecting the microstructure of material.

Stress and strain tensors, applied in mathematical structural analysis, are defined for a

homogeneous continuum, and applied for inhomogeneous structure.

Yield strength of material, determined by standardized testing method, again with

corresponding limitations, is generally accepted strength parameter in design.

Considering the dimension and composition of nano material it can be clear why the

strength parameters data of nano materials are not yet completely available, especially

those for CNT materials. In this case strength is also presented by the load in a moment