Effect of temperature on strain ratio at point A

S. Kalyanasundaram, S. DharMalingam, S. Venkatesan and A. Sexton. 8

3.2 Effect of forming parameters on strain ratio at point A

In considering temperature effects on strain ratios at point A, we can see from Figure 4 that the mean-strain ratio ranges from 0.82 to 0.95, which is well within the metal biaxial stretch region, 0 β 1.0, and balanced biaxial is given by a strain ratio of 1.0. As found in the major-strain analysis the strain ratio at point A also shows the same two temperature groups. Figure 4: Main-factor effects at point A for mean strain ratios at different depths

3.2.1 Effect of temperature on strain ratio at point A

Within the low temperature group, mean strain ratio ranges from 0.82 to 0.95 while in the high-temperature group it ranges from 0.83 to 0.88. Close to balance biaxial stretch could be reached only at room temperature 25°C at a depth of 10 mm. At 20mm and 30mm depth the average mean strain ratio is almost similar for both temperature groups. In the low- temperature group, the average mean strain ratio reduces as depth increases with the following rate, 6.1 from 10mm to 20mm and 2.7 from 20mm to 30mm. Reduction of the average mean-strain ratio indicates that the forming mode is converging away from balanced biaxial stretch as depth increases. It is also observed that for each depth only the mean-strain ratio at room-temperature is the highest, and as the sample is preheated, from a range of 60°C- 100°C, the mean-strain ratio reaches a plateau. Any preheat under the glue melt condition gives almost the same mean-strain ratios at their respective depths. For the high-temperature group, the mean-strain ratio remains constant at approximately 0.83 for forming temperature 130°C, while at 150°C it converges to 0.88. For the high-temperature group the average mean-strain ratio also reduces as depth increases. The decrease in average mean-strain ratio is as follows, 1.25 from 10mm to 20mm and 0.1 from 20mm to 30mm. This indicates that the average mean-strain ratio converges as depth increases as was found in the low- temperature group. The high-temperature group mean-strain ratio moves from 0.83 to 0.88, showing that the material system has a more balanced biaxial strain increment as the temperature increases. Comparing the strain-ratio window between the depths, the low- temperature group has a larger mean-strain ratio window, 0.82 to 0.95, from 10mm to 30mm 0.7 0.75 0.8 0.85 0.9 0.95 1 25 60 80 100 130 140 150 2 7 14 Temperature ⁰C Binder force kN M ea n S tr a in R a ti o 10 mm 20 mm 30 mm S. Kalyanasundaram, S. DharMalingam, S. Venkatesan and A. Sexton. 9 forming depth while the high temperature group has a small mean strain ratio window, 0.83 to 0.88, for the same depth, showing that there is no sudden change in the strain path. This observation supports our previous hypothesis that the softening of the composite layer, reduction in the stiffness at high temperature and the glue melt condition do affect the formability of this material system.

3.2.2 Effect of binder force on the strain ratio at point A