Long-term experiments with end-cracked wooden beams |
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Authors: | Mikael Fonselius |
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Institution: | (1) Technical Research Centre of Finland Forest Products Laboratory, Box 207, SF-02151 Espoo, Finland |
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Abstract: | Summary The duration of load effect for the fracture thoughness in mode II loading (forward shearing mode) has experimentally been determined for wood. The end-cracked beam specimens used were exposed to a constant load which corresponds to a nominal load level between 60 and 85% of the short-term capacity. The relative humidity was kept constant at 65% for two experimental series and changed cyclically between 40 and 90% for six experimental series. The length of a whole cycle was two weeks. In contrast to constant humidity conditions the time to failure was drastically reduced. For an end-cracked spruce beam loaded to 75% of its short-term capacity the lifetime was reduced from 2.5 months to 4 days. |
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