PSI - Issue 16

Róbert Beleznai et al. / Procedia Structural Integrity 16 (2019) 59–66 Róbert Beleznai et al. / Structural Integrity Procedia 00 (2019) 000 – 000

65

7

The obtained average heat flux is 138.36 W/m 2 . The thermal conductivity of the composite can be calculated as the following:

  q s T

138.36 0.015625 

W

(5)

λ

0.036

 



60

mK

Using the results of the comparison of the thermal conductivity of the composite material with the value of the larch (λ larch =0.0662 W/mK given by Pásztory et al. (2013)), it can be observed that the composite bridging element with 28.57 per cent of the cane fibres has almost twice better thermal insulation capability than the pure wooden beam.

4. Discussion

An increase of the volume ratio of the cane results in the lower stress level, therefore, the strength of the bridging element can be higher. In case of the pure wooden bridging element the load bearing surface is 125 × 900 = 112.500 mm 2 , while this value is strongly dependent on the fibre content in case of the composite element. The load bearing surface is 5.356 mm 2 for the volume ratio of 4.76, 21.426 mm 2 for the cane content of 19.05 and 32.139 mm 2 for the highest (28.57) volume ratio. It means that the load bearing capacity is proportional to the volume ratio of the composite material. Comparing the Young moduli of the cane and larch one can recognize that the cane has higher Young’s modulus, thus, smaller load bearing surface is enough to withstand the same load as for larch. The composite bridging element with 4.76 per cent of the cane already fulfil the requirements in terms of strength, while with the increased level of the volume ratio the strength value can be equal or exceed the load bearing capacity of the wooden bridging element. Plotting the stress and maximum value of deflection in the function of the volume ratio allows one to obtain the trends shown in Fig. 7. While the changes in the deflection are insignificant with variation in the volume ratio, much larger effect is observed in case of the stress level. With an increase in the volume ratio from 4.76 to 28.57 per cent, the stress level is decreased by 60 per cent. The higher volume ratio can be achieved only if the cane fibres will contact each other (no foam between fibres). It can be concluded that the composite bridging element with all the analysed volume ratios fulfil the strength requirements, even the highest level of cane content can provide higher strength than the pure wooden beam.

Volume ratio effect on the stress level.

Volume ratio effect on the maximum deflection.

Fig. 7. Influence of the volume ratio of the cane.