On the nominal transverse shear strai to characterize the severity of creasing, TAPPI JOURNAL April 2018
ABSTRACT: A transverse shear strain was utilized to characterize the severity of creasing for a wide range of tooling configurations. An analytic expression of transverse shear strain, which accounts for tooling geometry, cor-related well with relative crease strength and springback as determined from 90° fold tests. The experimental results show a minimum strain (elastic limit) that needs to be exceeded for the relative crease strength to be reduced. The theory predicts a maximum achievable transverse shear strain, which is further limited if the tooling clearance is negative. The elastic limit and maximum strain thus describe the range of interest for effective creasing. In this range, cross direction (CD)-creased samples were more sensitive to creasing than machine direction (MD)-creased samples, but the differences were reduced as the shear strain approached the maximum. The presented develoment provides the foundation for a quantitative engineering approach to creasing and folding operations.
Application: The provided equation characterizing the shear experienced by the paperboard increasing can be used to determine multiple crease tool configurations that yield the same effect on creasing (relative crease strength or springback). The range of interest in shear strain is identified for practical evaluation and further studies of creasing and folding. The differences between MD and CD creasing is further illuminated.
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