Biomedical Engineering Reference
In-Depth Information
obtain the tensile strength of concrete materials (ASTM, 1984). The diametrical compression
test also called the Brazilian disc test or the diametrical tensile test was considered a reliable
and accurate method to determine the strength of brittle and low strength material.
An interesting parameter is the tensile strength, σ
r
, which is the maximum nominal tensile
stress value of the material. What is defined here is the horizontal tensile stress at the
initiation of the large vertical crack at the centre of the disc. For the calculation of the tensile
stress in the middle of the disc, Eq. (2) was used, corresponding to a plane stress condition.
The usual way in evaluating the tensile strength from diametral compression test is by
substituting the maximum load value into Eq. (2).
P
2
P
(2)
r
S
Dt
where P is the maximum applied load, D diameter, t thickness of the disc and σ
r
the tensile
strength (or mechanical strength).
The essays were realized by means of a device by using “LLOYD EZ50” on cylindrical
samples of 6 mm approximately of thickness and 20 mm of diameter. At least six specimens
were tested for each test condition. An average of the values was then calculated. The results
dispersal is in the order of 15 %.
3. Results and discussion
3.1 Characterization of powder
Table 1 shows the SSA of β-TCP powder, Fap powder and different β-TCP - Fap composites,
the average grain size D
BET
(calculated by equation (1)) and the particle size distribution
data (measured by granulometric repartition). The difference between the value deducted
by SSA and by granulometric repartition was probably due to the presence of agglomerates
in the initial powder. The SSA of different β-TCP - Fap composites increases with the
percentages of Fap whereas the average grain size deceases (Table 1). This result shows the
effect of Fap additive in tricalcium phosphate matrix. Indeed, the grain of Fap has a dense
morphology by report β-TCP, which was responsible of the increasing of different
composites SSA.
Compound
SSA (m
2
/g)
1.00
D
BET
(µm)
0.20
D
50
(µm)
(a)
0.20
d
b
Fap
29.00
0.07
6
3.190
β-TCP
0.70
2.80
5
3.070 (β)
2.860 (α)
β-TCP - 13.26 wt% Fap composites
2.90
0.67
-
3.086
β-TCP - 19.90 wt% Fap composites
3.32
0.58
-
3.094
β-TCP - 26.52 wt% Fap composites
3.80
0.51
-
3.101
β-TCP - 33.16 wt% Fap composites
4.37
0.44
-
3.110
β-TCP - 40 wt% Fap composites
5.24
0.36
-
3.118
a
: Mean diameter,
b
: theoretical density.
Table 1. SSA and average grain size obtained by different analysis of various compounds.
Fig. 1 shows the dilatometric measurements of a different powder used in this study (β-TCP,
Fap and different β-TCP-Fap composites). The sintering temperatures began at about
