Speaker
Description
In the necking propagation of polypropylene (PP), deformation progresses unevenly within the test specimen; therefore, it is important to distinguish and characterize the mechanical responses of the necking-propagated and non-propagated regions. In this study, we investigated the effect of the loading condition on the relationship between necking propagation and local Vickers hardness.
Using a compact tensile testing apparatus compatible with a micro-Vickers hardness tester, we measured the hardness distributions in the necking-propagated and non-necking regions of PP specimens while maintaining a tensile load. We compared the obtained hardness distributions with those measured after unloading to examine the changes in hardness in both regions.
Under load-holding conditions, the hardness of the indentation propagation region was higher than that of the non-propagation region. On the other hand, after unloading, the hardness of the propagation region decreased compared to the load-holding state, while the hardness of the non-propagation region increased. As a result, the relative hardness of the two regions reversed, and the hardness of the propagation region became lower than that of the non-propagation region.
These results indicate that the spatial distribution of hardness differs depending on whether a tensile load is maintained during indentation. Therefore, caution is required when directly interpreting the hardness measured after unloading as the local deformation resistance during indentation propagation. When evaluating the mechanical behavior of polypropylene based on hardness, it is necessary to consider the load condition at the time of measurement and the deformation history up to that point.
| Conference Topics | Advanced Characterization Methods |
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