Evaluation of spring-back risk at cutting operations for wind-thrown trees

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  • 風倒木の切断処理における跳ね返り危険度の評価
  • フウトウボク ノ セツダン ショリ ニ オケル ハネカエリ キケンド ノ ヒョウカ

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Abstract

Spring-back risk at manual cutting operations was evaluated to discuss the differences among 6 wood species by using elastic strain energy as a predictor, which was obtained from bending rupture test of logs. Furthermore, decrease of the risk considering stress relaxation in wind-thrown tree stems was evaluated by bending-stress relaxation test. We also discussed the validity of evaluating the differences in spring-back risks among species by using small clear specimens. Considering characteristic value of MOR2/Eb for logs, the risks of mizunara (Quercus crispula), shirakamba (Betula platyphylla), sugi (Cryptomeria japonica) and karamatsu (Larix kaempferi) were significantly greater than those of akaezomatsu (Picea glehnii) and todomatsu (Abies sachalinensis). In the stress relaxation test for logs, the relaxation speed decreased within 2 days after the test started and kept it nearly constant after the seventh day. No effect of diameters and species on the stress relaxation curves was found for almost all the specimens. It was suggested that spring-back risks could be estimated using mechanical properties obtained by small clear specimen tests.

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