Strength Prediction of Basalt Filaments

Jiří Militký, Vladimír Kovačič

Textile Faculty, Technical University of Liberec 461 17 Liberec, Czech Republic

Outline

Basalt rocks

Fibers formation

Basic properties

Bundle strength prediction

Mechanism of fracture

Basaltic rocks

Basalt is generic name for solidified lava which poured out the volcanoes

Basaltic rocks are melted approximately in the range 1500 – 1700 C.

When this melt is quickly quenched, it solidificated to glass like nearly amorphous solid.

Slow cooling leads to more or less complete crystallization, to an assembly of minerals.

Augite Plagioclase

Olivine

Basalt composition

Chemical composition:

silicon oxide SiO2 (optimal range 43.3 – 47 %)

Al2 O3 (optimal range 11 – 13 %)

CaO (optimal range 10 – 12 %)

MgO (optimal range 8 – 11 %)

Other oxides are almost always below 5 % level

Essential minerals plagiocene and pyroxene (augite) make up perhaps 80% of basalts

Filaments formation

Classical procedure

Heat transfer from walls to center

High power (4 kWh/kg)

Long pre heating 8 hours

Spinneret materials (Platinum, rhodium)

Microwave heating

Heat transfer from center to walls

Low power (1 kWh/kg)

Short pre heating 3 hours

Spinneret materials (ceramics)

Melt after 5 min at 1300oC

Properties of Basalts

Basalts are more stable in strong alkalis that glasses.

Stability in strong acids is low

Basalt products can be used from very low temperatures (about –200 C) up to the comparative high temperatures 700 – 800 C.

At higher temperatures the

structural changes occur.

Model: Rz=a1+(100-a1)*exp(-a2*t)

y=(54,883416)+(100-(54,883416))*exp(-(0,0628529)*x)

t [hod]

Rz [

%]

C:1

C:2

C:3

C:4

C:5 C:6

60

65

70

75

80

85

90

95

100

105

0 5 10 15 20

Materials

Commercial basalt filament roving 320 tex from

company Kaneniy Vek (abbreviation KV) and basalt

filament roving 330 tex from company Basaltex

(abbreviation BAS) were used.

The diameters of individual fibers extracted from these

roving were measured from longitudinal views by using

of image analysis. From mean values the mean numbers

of fibers in roving were computed.

KV = 952 BAS = 975

Property Basalt

Density[kgm-3] 2733

Softening temp. [C] 960

Experiments

The strength of individual fibers and roving was measured on Instron TM4200 automatic testing device in standard conditions.

The fibers were mounted into paper frame before testing.

The 65 measurements of fiber breaking stress f [GPa] and corresponding fiber strain f [-] were realized.

The basalt roving strength was measured under the same conditions.

Fibrous Bundle Strength I

Assumptions:

The fiber strength obeys two parameter Weibull distribution.

Fibrous bundle is composed from parallel straight fibers clamped at both ends.

When a fiber breaks, the load is carryings by survived fibers (distributed equally among the rest of fibers).

The changes of bundle geometry and dimensions during extension are neglected.

Computation:

Estimation of fiber Weibull parameters from experimental mean strength and standard deviation.

Estimation of parallel fibrous bundle of fibers strength.

Fibrous Bundle Strength II

Let the fiber distribution is Weibull two-parameter type

The mean fiber strength and corresponding standard

deviation are

Γ(.) is gamma function. For known and computed from

experimental data is parameter C evaluated by iterative

solving of equation

1 exp C

f fF A

f

fs

1 1

1Cf A

C

1

2

2

21

11

1f f

Cs

C

f fs

1

2

2

21

1 01

1f f

Cs

C

1;9C

Fibrous Bundle Strength III

Fibrous bundles distribution - Daniel's result, that for large

bundles (number of fibers in cross section N is more that 100) is

bundle strength approaching to normal distribution

Mean strength of fibrous bundle is equal to

Standard deviation of fibrous bundle is

2

2

1exp

22 .

b b

b

bb

Hss

1 1

.exp 1Cf AC

C

2

11 1exp 1 expC

b fs AC NC C

Fiber utilization

factor

b

f

Approximation

For the case of Weibull distribution of fiber strength and

normal distribution of bundle strength the simple approximate

relation for utilization of fiber strength in bundle was derived

is variation coefficient of fiber strength.

Utilization of fiber strength in bundle

is function variation coefficient of fiber

strength only.

exp / 1 , 0,909vu

fu u u u

v f

In figure is solid line computed according to definition

and dashed line is computed by approximate relation. The

circle corresponds to 35% fiber strength variation

coefficient and 0,56 utilization of fiber strength in bundle

Results

Material KV BAS

Fiber diameter [m] 12.96 13.74

Fiber fineness [tex] 0.336 0.377

Mean fiber strength [GPa] 3.58 2.79

SD fiber strength [GPa] 1.06 0.45

CV fiber strength [%] 29.61 16.29

Mean bundle strength exp. [GPa] 1.35 0.92

SD bundle strength exp. [GPa] 0.13 0.06

Mean bundle strength pred. [GPa] 2.13 1.97

SD fiber strength pred. [GPa] 2.81 0.98

Fiber strength utilization factor 0.377 0.330

Mechanism of fracture

Surface of fibers is very smooth without flaws or crazes

Fracture occurs due to nonhomogenities in fiber volume (probably near the small crystallites of minerals)