1. introduction
The main object of this study is the scale effect with the destruction of the wood. In the steel, Ji value is a material characteristic value so it does not depend on size. The more the size of specimen is large, the more the stress at Ji is small. So it is easy to make the dangerous judgment of destruction. This property can be found in the wood, we make the JIC test with Japanese larch.
2. Experimental Method
We made experiments is referred to in The Japan Society of Mechanical Engineers. The ratio of specimen's width, height and span is a one-two- eight ratio(Fig. 1). Their notches are height of half and added 1mm wide notch at first and infinitesimal wide notch at last 1mm. (Fig. 2) If the crack initiation is observed frequently three times within each 2seconds intervals, we defined the third sound as initial point of frequent sound. (Fig. 3) We stopped loading and colored the crack of specimens when we heard the sound of crack initiation. Also we stopped loading and colored it before or after the sound on each specimens. (Fig. 4) We aimed at the load to be static and monotonic loading at a speed of 0.5mm/min. We measured load, COD (Crack Opening Displacement), displacement of force and length of crack colored. And also we observed the sound of crack initiation.
3. Experimental Results
We measured the growth of internal crack by coloring. (Photo. 3) There are two types of the crack growth as wavelike or parabolic in any dimension. We show the results in Table. 2. We calculated the J integral value from the relation of load and displacement by the simple equation4).
4. Ji value worked out by coloring
We plotted the relationship between the J integral value and the average of the internal crack length (Δaave) on each series. (Fig. 8) We defined the J integral value at the y-intercept as Ji. We compared with Ji to the J integral value at the first sound, and we considered that it is useful to determine the fracture toughness value simply. (Fig. 12)
5. Scale effect in the fracture mechanics
It was observed generally good response that comparing the experimental value and the theoretical formula in applied the fracture mechanics. The scale effect was confirmed not just with the steel but also with the wood. So it can be said that the application of fracture mechanics to the destruction of wood is useful for crack propagation status confirmation.
6. Conclusion
1) It was observed generally good response that comparing the experimental value and the theoretical formula in applied the fracture mechanics. The scale effect was visible not just with the steel but also with the wood. So it can be said that the application of fracture mechanics to the destruction of wood is useful for crack propagation status confirmation.
2) We worked out Ji value with the average value of crack growth measured by coloring. We draw an approximate straight line by the least squares method with the plot of J-Δaave relationships, We established the J integral value of the y-intercept as Ji value.
3) We paid attention the J integral value at the first sound with the sound of the crack initiation. The average value of them was 69.0N/m. And the difference between the average value of each size and the average value of all was within 1%. It is useful for estimating Ji from this value.
