Many studies have presented stress-strain relationship of human hair, but most of them have been based on an engineering stress-strain curve, which is not a true representation of stress-strain behaviour. In this study, a more accurate 'true' stress-strain curve of human hair was determined by applying optical techniques to the images of the hair deformed under tension. This was achieved by applying digital image cross-correlation (DIC) to 10× magnified images of hair fibres taken under increasing tension to estimate the strain increments. True strain was calculated by summation of the strain increments according to the theoretical definition of 'true' strain. The variation in diameter with the increase in longitudinal elongation was also measured from the 40× magnified images to estimate the Poisson's ratio and true stress. By combining the true strain and the true stress, a true stress-strain curve could be determined, which demonstrated much higher stress values than the conventional engineering stress-strain curve at the same degree of deformation. Four regions were identified in the true stress-strain relationship and empirical constitutive equations were proposed for each region. Theoretical analysis on the necking condition using the constitutive equations provided the insight into the failure mechanism of human hair. This analysis indicated that local thinning caused by necking does not occur in the hair fibres, but, rather, relatively uniform deformation takes place until final failure (fracture) eventually occurs.
Tail breaking forces (TBFs) are measured for various process conditions to understand
phenomena such as short tail formation. TBFs obtained with several Cu wires are compared to find
the most suitable Cu wire type that improves consistent tail formation. In situ online TBF
measurement method is developed. The highest TBF obtained is 61.59 + 9.10mN. The highest Cpk
value obtained is 2.97 + 0.33 when lower specification limit of 10 mN is assumed.
In order to eliminate the chip cratering for copper wire applications in IC packaging, it is worthwhile to develop new Cu wire chemistries to obtain a soft copper wire with a soft free-air ball (FAB). The conventional hardness characterization of a new bonding wire is a labour intensive, time-consuming work. Therefore an on-line hardness characterization method is presented that enables the hardness comparison of a larger number of different wires within a shorter time. The influences of capillary change, bonding substrate metallization and temperature on this method is quantified. It is found these influences need to be held constant during a hardness comparison study. With this method, the wire and FAB hardness comparison of nine novel 2-mil copper bonding wires, Cu 1 to Cu 9, and one 2-mil Au wire are performed. The wire hardness (wireside) and FAB hardness are characterized. It is found that the Cu 4 and Cu 5 have the softest wireside hardness and FAB hardness.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.