Repair of a cracked steel member using CFRP strip

本计画系将碳纤维强化聚合物条（以下简称CFRP条）应用于疲劳裂缝修补之实验研究。2002年对裂纹试件进行了疲劳试验，在裂纹尖端钻止裂孔后，用CFRP条修补裂纹。从试验结果可知，修复后试件的疲劳极限随着CFRP带宽度的增加而增加。即使CFRP带的宽度小于裂纹长度，疲劳寿命也在低应力区迅速增加。2003年，对仅用CFRP条修补的裂纹试件进行了疲劳试验。在这种情况下，所有类型的样本均未显示疲劳极限。但是，在提高疲劳寿命方面有足够的效果。并且，宽CFRP条的修复效果优于窄CFRP条。此外，即使当CFRP条的宽度小于裂纹长度时，也可以判断该方法作为紧急修复是足够实用的。从上述研究可以看出，无论有无止动孔，CFRP带都适用于疲劳裂纹的修复。可以说，CFRP带的实际应用的可能性很高。

This project is an experimental study on an application of Carbon Fiber Reinforced Polymer strip, hereinafter called CFRP strip, to repair of a fatigue crack. The study was done for two years in 2002 to 2003.In 2002, fatigue tests were performed using a specimen with the crack which was repaired by patching the CFRP strip after drilling stop holes at the crack tips. It was known from the results of the tests that an endurance limit of the repaired specimen was increased according to increase of width of the CFRP strip. Even if width of the CFRP strip was shorter than the crack length, fatigue life was increased rapidly in the region of the low stress range. Therefore, it was able to be said that the repair effect had shown up notably.In 2003, fatigue tests were performed using a specimen with the crack which was repaired by only patching the CFRP strip. In this case, an endurance limit was not shown in all types of specimen. However, therewassufficient effect in an improvement of fatigue life. And, the wide CFRP strip showed higher repair effect than narrow CFRP strip. In addition, even when width of the CFRP strip was shorter than the crack length, it was judged that this method was enough practically as a first-aid repair. Moreover, the higher repair effect was shown in the region of the high stress range.From the above-mentioned studies, it was clear that the CFRP strip was applicable to repair of a fatigue crack with or without a stop hole. Possibility of practical use of the CFRP strip can be said to be high.