1 Introduction
2 Materials and methods
2.1 Wood specimens and thermo-hydro-mechanical (THM) treatment
Sample | Conditions | ||
---|---|---|---|
C: no heat, no pressure | B1: 2.0 mm initial | B2: 1.6 mm initial | |
Testing RH | 30% RH | 50% RH | 65% RH |
Tests | MOR | Creep at 20% of MOR | Creep at 30% of MOR |
2.2 Determination of modulus of rupture
2.3 Dynamic mechanical analysis
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Creep strain—deformation occurring after the target stress is reached until unloading.
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Instantaneous strain—deformation occurring from initial loading until the target stress is achieved.
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Creep compliance—strain variation under a constant, target stress.
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Recovery compliance—strain variation when releasing a constant, target stress to zero load.
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Relaxation recovery—amount of deformation recovered after the load is released at a given time.
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Dynamic mechanical analysis variables—storage modulus (E′), loss modulus (E′′), and the ratio between the two (tanδ).
3 Results and discussion
3.1 THM treatment
Specimen group | Initial OD density [ρ1] [g/m3] | Post density [ρ2] [g/cm3] | Density ratio (ρ2/ρ1) | Initial thickness (T1) [mm] | Densified thickness (T2) [mm] | Thickness ratio (T1−T2)/T1 |
---|---|---|---|---|---|---|
B1 | 0.66 (± 0.01) | 1.24 (± 0.08) | 1.87 (± 0.10) | 2.03 (± 0.04) | 1.12 (± 0.07) | 0.45 |
B2 | 0.66 (± 0.04) | 1.15 (± 0.09) | 1.75 (± 0.13) | 1.57 (± 0.04) | 0.93 (± 0.07) | 0.41 |
Control (C) | 0.69 (± 0.01) | – | – | 1.02 (± 0.07) | – | – |
3.2 MOR determination and effect of conditioning
Specimen group | RH [%] | EMC [%] | Set-Recovery [%] | MOR [MPa] |
---|---|---|---|---|
B1 | 30 | 4.4 (± 0.26) | 13 (± 15) | 203 (± 5.80) |
50 | 6.2 (± 0.14) | 22 (± 13) | 191 (± 27.0) | |
65 | 7.1 (± 0.38) | 20 (± 10) | 181 (± 12.3) | |
B2 | 30 | 4.3 (± 0.26) | 18 (± 21) | 183 (± 46.7) |
50 | 6.3 (± 0.34) | 16 (± 18) | 194 (± 52.5) | |
65 | 7.1 (± 0.24) | 21 (± 19) | 190 (± 47.4) | |
C | 30 | 6.3 (± 0.18) | – | 148 (± 5.00) |
50 | 9.0 (± 0.31) | – | 138 (± 16.2) | |
65 | 9.5 (± 0.20) | – | 124 (± 14.6) |
3.3 Creep behaviour at different loads and relative humidity environment
Specimen group | RH [%] | 20% Loading | 30% Loading | ||
---|---|---|---|---|---|
Instantaneous strain [%] | Creep strain [%] | Instantaneous strain [%] | Creep strain [%] | ||
B1 | 30 | 0.180 (± 0.017) | 0.015 (± 0.002) | 0.275 (± 0.027) | 0.025 (± 0.003) |
50 | 0.180 (± 0.023) | 0.016 (± 0.002) | 0.237 (± 0.016) | 0.024 (± 0.004) | |
65 | 0.172 (± 0.021) | 0.017 (± 0.003) | 0.267 (± 0.044) | 0.028 (± 0.008) | |
B2 | 30 | 0.176 (± 0.025) | 0.014 (± 0.002) | 0.241 (± 0.054) | 0.022 (± 0.007) |
50 | 0.183 (± 0.030) | 0.016 (± 0.002) | 0.233 (± 0.031) | 0.022 (± 0.004) | |
65 | 0.181 (± 0.059) | 0.018 (± 0.006) | 0.317 (± 0.044) | 0.035 (± 0.009) | |
C | 30 | 0.177 (± 0.014) | 0.018 (± 0.002) | 0.274 (± 0.018) | 0.036 (± 0.003) |
50 | 0.182 (± 0.013) | 0.020 (± 0.002) | 0.237 (± 0.043) | 0.029 (± 0.007) | |
65 | 0.176 (± 0.012) | 0.020 (± 0.003) | 0.266 (± 0.015) | 0.039 (± 0.008) |
Comparison | Estimate [µm2/N] | 95% CI [µm2/N] | p-value |
---|---|---|---|
MOR 20%–MOR 30% | 0.75 | − 2.69 to 4.19 | 0.6663 |
B1–B2 | − 1.49 | − 6.54 to 3.56 | 0.7623 |
B1–C | − 22.32 | − 27.38 to − 17.27 | < 0.0001 |
B2–C | − 20.84 | − 25.89 to − 15.78 | < 0.0001 |
30% RH–50% RH | 0.53 | − 4.53 to 5.58 | 0.9663 |
30% RH–60% RH | − 7.95 | − 13.0 to − 2.90 | 0.0009 |
50% RH–65% RH | − 8.48 | − 13.5 to − 3.43 | 0.0004 |
Comparison | Estimate [µm2/N] | 95% CI [µm2/N] | p-value |
---|---|---|---|
MOR 20%–MOR 30% | 0.11 | − 3.56 to 3.77 | 0.9542 |
B1–B2 | − 2.84 | − 8.22 to 2.54 | 0.4225 |
B1–C | − 21.98 | − 27.36 to − 16.59 | < 0.0001 |
B2–C | − 19.14 | − 24.52 to − 13.75 | < 0.0001 |
30% RH–50% RH | 2.50 | − 2.89 to 7.88 | 0.5131 |
30% RH–60% RH | − 6.70 | − 12.1 to − 1.32 | 0.0107 |
50% RH–65% RH | − 9.20 | − 14.6 to − 3.81 | 0.0003 |
Specimen group | RH [%] | 20% Loading | 30% Loading |
---|---|---|---|
Relaxation recovery [%] | Relaxation recovery [%] | ||
B1 | 30 | 98.7 (± 0.52) | 98.9 (± 0.90) |
50 | 98.5 (± 1.03) | 98.9 (± 0.82) | |
65 | 98.7 (± 1.09) | 98.2 (± 0.65) | |
B2 | 30 | 99.8 (± 0.63) | 99.3 (± 0.43) |
50 | 98.7 (± 0.58) | 98.7 (± 0.51) | |
65 | 99.0 (± 0.15) | 97.8 (± 0.59) | |
C | 30 | 97.7 (± 1.03) | 97.5 (± 0.29) |
50 | 97.9 (± 1.02) | 97.0 (± 0.78) | |
65 | 97.3 (± 0.69) | 96.2 (± 1.16) |