Table 3 A summary of the recommended practical considerations for mitigating the effect of stress concentration on the contact area, specimen diameter, and thickness, aggregates size, and load velocity on the Brazilian Test results.
Recommendation | Commentary | ||
|---|---|---|---|
Cushion (c)
| Length (thickness) (t c ) | \( t_{c} \ge t \) | \( {\text{Ideal contact}} \to \nu_{c} E_{s} = \nu_{s} E_{c} \) v s and E s represent the Poisson ratio and Young’s modulus of the sample, respectively v c and E c represent the Poisson ratio and Young’s modulus of the cushion material, respectively Andreev (1991), ISRM (2007), ASTM (2008), Mellor and Hawkes (1971), Wong and Jong (2013), and Hawkes and Mellor (1970) \( E_{\text{YOUNG}} = 10{\text{ GPa;}}\nu = 0.3 \) |
Thickness (g c ) | \( g_{c} \approx 0.01 \times D \) \( g_{\hbox{min} } = 0.254{\text{ mm}} \) | ||
Width (w c ) | \( w_{c} \ge w \), length of contact arc, defined by \( 2\alpha \) and by the loading set up | ||
Materials | Cardboard Plywood Chipboard | ||
Diameter (D) | D = 100 mm; D = 150 mm | ASTM (2003) | |
D min = 3×as max | Japanese Industrial Standards (1951) | ||
Maximum aggregates size (as) | \( as \le \frac{1}{3}D \) | A size that does not interfere with the thickness dimension of the disk | |
Japanese Industrial Standards (1951) | |||
Thickness (t ) | \( 0.2D \le t \le 0.7D \) | ASTM (2008) | |
\( t \le 0.2D \to {\text{plane stress}} \) \( t \ge 0.5D \to {\text{plane strain}} \) | Aliha (2013) and Yu et al. (2006) Load concentrated in two antipodal points | ||
\( \begin{aligned} t = 0.5D \to & {\text{the volume under stress is similar to the volume}} \\ \, & {\text{under a typical uniaxial tensile test}} \\ \end{aligned} \) \( t_{\hbox{min} } > 10{\text{ mm}} \) | Mellor and Hawkes (1971) | ||
Speed of displacement | \( 0.2\;{\text{inch/min}} \to \le 84.7\;\upmu {\text{m}}/{\text{s}} \) \( 0.7\;{\text{inch/min}} \to \ge 169\;\upmu {\text{m}}/{\text{s}}\;\left( {\text{viscoelastic samples}} \right) \) | ||
The rate of loading is adjusted such that the duration of each test is between 2 and 3 min | Carmona (2009) | ||
