3.1 | FRACTURE TOUGHNESS UNDER QUASI-STATIC CONDITION
Quasi-static fracture tests were performed in accordance with GB/T
21143-200718. Three-point bending specimens were
adopted, and the thickness (\(B\)), width (\(W\)), length (\(L\)), span
(\(S\)), and initial crack length (\(a_{0}\)) are 10 mm, 20 mm, 100 mm,
80 mm and 12 mm, respectively. The tests were performed with the
electro-hydraulic servo fatigue testing machine. Three repetitive test
results of the load-deflection curves are presented in Figure 4.
The quasi-static fracture toughness (\(K_{\text{IC}}\)) is determined by
\(K_{\text{IC}}=\left[\left(\frac{S}{W}\right)\frac{F_{Q}}{\left(B^{2}W\right)^{0.5}}\right]g_{1}\left(\frac{a_{0}}{W}\right)\)(3)
\(g_{1}\left(\frac{a_{0}}{W}\right)=\frac{3\left(\frac{a_{0}}{W}\right)^{0.5}\left[1.99-\left(\frac{a_{0}}{W}\right)\left(1-\frac{a_{0}}{W}\right)\left(2.15-\frac{{3.93a}_{0}}{W}+\frac{2.7a_{0}^{2}}{W^{2}}\right)\right]}{2\left(1+\frac{2a_{0}}{W}\right)\left(1-\frac{a_{0}}{W}\right)^{1.5}}\)(4)
where \(F_{Q}\) is the value of the load at the intersection point of
the load-deflection curve and the line (OFd ). The
slope of OFd is 0.96 times of that of the initial
linear part of the load-deflection curve18.
Substituting the \(F_{Q}\) values 5421 N, 5598 N and 5493 N into
Equation (3), the fracture toughnesses (\(K_{\text{IC}}\)) of 63.4
MPa.m0.5, 64.8 MPa.m0.5, and 62.1
MPa.m0.5 are obtained for the three tests,
respectively. The average fracture toughness is 63.4
MPa.m0.5.