Issue 54

B. Bartolucci et alii, Frattura ed Integrità Strutturale, 54 (2020) 249-274; DOI: 10.3221/IGF-ESIS.54.18

Figure 5: Box-plots of density. a) hardwood species; b) softwood species.

Fracture toughness (K IC ) The graphs regarding fracture toughness (Fig. 6) provide information about the influence of wood orthotropy directions. Specifically, for hardwoods the results were found in directions RL, TL, TR, and RT. Box plots reveal that K IC are variable values among the different species of hardwood and in the different directions (TL, RL, RT and TR): RL direction presents values under 1000 kPa·m ⁰⸱⁵ , except for ash with K IC = 1160 kPa·m ⁰⸱⁵ ; TL direction has the lowest values, and they are all comparable to each other. The main differences are found in the graphs giving information on RT and TR directions. In RT direction walnut (Wal) and cherry (Ch) have highest values (respectively 1453 kPa·m ⁰⸱⁵ and 1498 kPa·m ⁰⸱⁵ ) (ID5 [13]) while birch (Bir) has a range of values with larger dispersion. In TR direction it can be noticed a decreasing K IC trend for walnut, cherry, and birch, and in addition, while oak and beech (Bee) values remain comparable to each other, except for the data dispersion. Softwood data analysis presented in Fig. 7 relates to all the possible 6 directions (LR and LT in addition to the previous ones cited for hardwood). It can be noticed that these values are similar among the different species even in the different directionalities. In general, all the values are under 800 kPa·m ⁰⸱⁵ in RL, TL, TR, and RT directions. The exceptions are found for LT and LR directions that have higher and more dispersed values. For example, the fracture toughness for pine in LR

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