Biomedical Engineering Reference
In-Depth Information
8
7
6
Quasi-static
5
4
3
Impact
2
1
0
0 0 0 0 0 0 0
Crystallinity (%)
Fig. 2. Dependence of crystallinity on the critical energy release rate under a quasi-static and
an impact loading conditions.
(a) X c =2.7%, static
(b) X c =2.7%, impact
(c) X c =55.8%, static (d) X c =55.8%, impact
Fig. 3. Polarized micrographs of crack growth behavior.
Fig.4 shows FE-SEM micrographs of the fracture surfaces of the PLA samples. For the
amorphous sample tested at the static rate, the fracture surface exhibits deep concavities and
hackles due to multiple craze formation (Fig.4(a)). The fracture surfaces of the crystallized
samples (Fig.4(c)) appears to be smoother than the amorphous one, corresponding to the
decrease of the toughness values. The impact fracture surface of the amorphous sample
(Fig.4(b)) is obviously smoother than the static one, corresponding to the decrease of G IC . It
is noted that drawing fibrils are also observed on the impact fracture surface, suggesting
that effect of high strain-rate exists. Roughness of the impact fracture surface appears to
increase with increase of crystallinity comparing the surfaces shown in Figs.4(b) and (d). For
the impact surface of the highly crystallized sample (Fig.4(d)), relatively fine roughness
exists suggesting the increase of G IC as crystallinity increases.
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