Impact Bending Fatigue of Wood
Keywords:
Impact bending, fatigue, defect size, Shorea negrosensis FoxwAbstract
Repeated impact tests were conducted using a four-point bending method on an impact machine of the dropping type to obtain fundamental information on the impact bending fatigue of a wood board with a circular hole at the center of its width. Test material used was Red Lauan (Shorea negrosensis Foxw.).
Strain distribution along the specimen length due to repeated impact blows is affected by the radius of the hole (r). In the case of the 15-mm-radius specimen, the strain distribution is opposite that of the control specimen (specimen without a hole). Fracture was classified into two types according to r. The relation between the impact fracture load (P1) and the number of impact blows to fracture (N) is expressed by P1 = a·N m (a, m: constant). Fatigue of the 5-, 10-, 15-mm-radius specimen is faster than that of the 2-mm-radius or control specimen. Among the former specimens, the fatigue becomes larger with decrease in r. The notch sensitivity is 0.12-0.32 in the case of the 5-, 10-, 15-mm-radius specimen and only 0.004 in the case of the 2-mm-radius one in the impact bending fatigue test. The ratio of the impact fracture load to that of the control specimen decreases with r and N except for the case of the 2-mm-radius specimen.
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