Rapid Speed Loading Test
The rapid speed loading test was executed by using the rapid loading machine as shown in Figure 5. The aim of this dynamic test is to examine the rate-effect of LFRR and the loading speed was set at 0.01 m/sec, 0.1 m/sec and 1.0 m/sec. The load was measured by the 1,000 kN load cell and the displacement was measured by the laser type displacement sensor.
Figure 6 shows the dynamic load-displacement relations including static compression test results. It is found that the loading speed has remarkable effect on the load-displacement relation in case of
Fig. 7. Absorbed energy ~ loading speed relations.
Fig. 8. Weight dropping machine.
usual rubber when the displacement exceeds 10 mm. For example, the dynamic load is about 2.5 times larger than the static load at the displacement of 25 mm.
It is also noticed that from Figures 6c-6f that the initial yield load increases about 20%, but in plastic region after initial yield load, the dynamic load increases about 30-50% larger than the static one in case of LFRR. This may be caused that fiber breaks gradually and the LFRR becomes like the usual rubber. These facts mean that the usual rubber tends to be more sensitive in rate effect than LFRR.
Figure 7 represents the absorbed energy of LFRR and it is obvious that the absorbed energy of LMF25 in case of rapid speed loading (1.0 m/sec) becomes larger than those of R65, LMF5. It is also noticed that the absorbed energy increases as the fiber ply and fiber tensile strength increase.