Annals of Warsaw University of Life Sciences - SGGW

Calculated stress concentration factors for all observed elliptical hole halfaxises ratios
and fiber orientations are given in Table 2.
Table 2. Stress concentration factors
Picea
Stress concentration factor
Excelsa a/b=5 a/b=2 a/b=1 a/b=1/2 a/b=1/5
� � 0�
1.85 3.13 5.26 9.53 20.61
� � 90�
1.13 1.33 3.13 4.37 6.26
- 3.79 - 3.79 -3.79 -3.79 -3.79
CONCLUSION
When fibers orientation is along the x� – axis, (i.e.: �= 0°), compression stress ��
around the elliptical hole is negligible. Locations with maximum values always occurs at
� � 90�
and 270°. Moreover, the maximum value of the stress concentration factor increases
when the hole axes ratio a b decreases.
In the case that wood fibers are perpendicular on loading stress direction, great
concentration of stresses is caused by compression stress � � in locations about � � 0�
and
180°. These SCF are negative numbers, and moreover for all halfaxises ratios these ones are
equal. Positive SCF increases when the hole axes ratio a b decreases but corresponding stress
concentration factors are smaller as in the cases when �= 0°. Locations of the positive stress
concentration factors change from angle � � 22�
up to 158° and from 202° up to 338°.
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