Peak shear stress reduction

The data were collected by Brookfield EZ-Yield software as shown in Figs. 8 and 9. The test parameters were as follows Spindle - 72, Immersion - Secondary, Zero Speed - 0.1 rpm. Wait Time - 30 s. Run Speeds - 0.05/0.5 rpm. The tests were carried out to either 105 % or 100 % torque reduction. Those tests carried out to 105 % torque reduction were trimmed down to include only those data points leading to and including the peak value of measured shear stress. The test data were exported as a Microsoft Excel spreadsheet. The data from the spreadsheet were then copied into a template developed by David Moonay to calculate the viscoelastic properties of the material. 

The elastic nature of fiber and shear stress concentration at the fiber ends affected the tan 6 value when incorporated in a composite material, which is related to the additional viscoelastic energy dissipation in the matrix material [15], Figure 13.8 shows a selection of tan 6 curves in which it can be seen that the tan 6 peak shifted to the higher temperatures, broadened, and decreased as the kenaf whiskers content increased. The decrease of tan 6 value indicated the reduction of macromolecular mobility of the fiber surface environment, whereas better interaction between kenaf whiskers and matrix can be concluded [16]. 

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