Conclusions and Future Activities

The comparative evaluation of outdoor and accelerated weathering with newly developed flexible joint test specimen has started. After 12 months of natural weathering and 3500 h of accelerated weathering in xenon and carbon-arc weathering device, the following conclusions, as summarized below, can be drawn.

• Influences by chemical type of sealant: Although there are differences in the extent of damages, some degradation was observed in all chemical types of sealants except silicone.

• Influences of expansion/compression amplitude: A strong acceleration of degradation induced by the mechanical cycling was observed. However, the expansion/compression amplitude (±15 % versus ±30 %) showed only very little influence.

• Influence of light source in accelerated weathering: Although stronger surface degradation was observed in the open-flame carbon-arc weathering device than in the xenon-arc lamp weathering device until 2000 h of irradiation, a similar level of degradation was observed in both weathering devices after 3000 h of irradiation.

• Correlation between outdoor and accelerated exposures: Similar degradation features were ob­served in outdoor and accelerated weathering, however the natural weathering period (12 months) is too short to discuss a correlation between natural and accelerated weathering at present.

The efficiency of the new test method for weatherability of sealant simulating the in-service condition of seal joints by using a newly developed flex-joint test specimen has been confirmed. This new test

specimen is not expensive and allows a reduction in the total number of specimens employed by exposing the sealants simultaneously in a single specimen to compression and extension movements up to ±30 % of the joint width. The data obtained with this flex-joint test specimen will be used to design sealed joints in the future.

While the degradation of sealants has been evaluated by the quantification of surface crazing in this report, a more complete quantification of degradation is being planned for the future, including the evaluation of the depth of cracks.

www. astm. org

Hiroyuki Miyauchi[48] [49] and Kyoji Tanaka1