CIB-W18 Timber Structures – A review of meeting 1-43 2 MATERIAL ...

More documents

Recommendations

Info

2.4 FRACTURE MECHANICS 19-6-3 K Wright and M Fonselius Fracture toughness of wood - Mode I Abstract Mode I fracture toughness of wood can be detemined with CT-specimens, as proposed in the ASTM-standard. In the different orthotropic systems the value of fracture toughness KIC was 200 - 360 kNm -3/2 for pine and 200-340 kNm -3/2 for spruce. The coefficients of variation were about 10 %. The values fit well with those presented in the literature. Because of the great nonlinearity, for plywood), the K IC value is not a valid material parameter. For the comparison, K I -values were calculated of the maximum load to be 130 - 300 kNm -3/2 . The coefficient of variation was about 10 % for the TL-systems. Lathe checks weaken the TR and RT systems. If the fracture toughness is considered to be proportional to the density, the correlation for pine and spruce is R 2 = 0.6. The numerical value of fracture toughness in kNm -3/2 is roughly the same as the density in kg/m 3 . If fracture toughness is considered to be a linear combination of the square of density and other variables, somewhat better correlations are achieved: for pine and spruce R 2 = 0.8. Discussion The different emphasis in the Fonselius and Wrights works complicates the comparison of the values. However, because the density of spruce is lower than that of pine, the fracture toughness also is lower, as expected. Accordingly, the K-fracture toughness for plywood is about the same as for spruce, but the nonlinearity is larger: therefore plywood will show a larger J-value. The CT-specimen seems to give reliable fracture toughness values. The isotropic polynomial solution is near the values calculated by the means of compliance measured in the J-test. Compared with the results found in the literature (Wright and Leppavuori 1984), the following can be stated. – The relations between the orthotropic fracture systems are not species independent. For Douglas Fir, the TR and RT systems are much stronger than for our materials, but the TL-system is somewhat weaker than found for pine. A possible reason for this is the different amount of rays in these species. The size of the tree used to make specimens out of, also may influence. In our cases the annual rings had a visible curvature. Douglas Fir stems are usually larger, so the specimens have likely been more ideal. – Density is the most important parameter indicating the TL-RL fracture toughness, besides of the angle of the fracture plane. Roughly, the numerical value of-KIC fracture toughness in kNm-3/2 is the same as the density in kg/m3 – The effect of moisture is not satisfactory clarified. Our results point to an insensitivity to moisture, but sensitivity to moisture gradients. In the literature, no clear tendency is found. – The influences of size and loading rate are negligible when common short-term loading is used. – The PLV-results show clearly the difference between rotary-peeled and sawed plies; they give more uniform K Ic values for the different fracture systems. 19-6-4 K Wright Fracture toughness of pine - Mode II Abstract Mode II fracture toughness has been studied by means of beam specimens. The material used was of the same lot of Pinus Silvestris as in the previous mode I tests. In short term tests, the value of KIIC fracture toughness was found to be 1760 kNm -3/2 . Fracture toughness is best predicted by density and the quarter of density. Moisture content, annual ring angle or other variables had no effect. Correlations were mostly poor, which may depend on the relatively large fracture toughness of the wood from northern Finland compared to its density. In the long-term tests, the deflection growth was proportional to the bending stress and the 1/3th power of time. The 90 % stress level corresponded to a median life time of 5 h. Conclusions – The fracture toughness values calculated by different methods do not markedly deviate from each other. Stress intensity depends linearly on, the crack length. CIB-W18 Timber Structures – A review of meeting 1-43 2 MATERIAL PROPERTIES page 2.30
– The short-term tests had a mean moisture content of 14 % and density of 420 kg/m3. Fracture toughness was 1760 kNm-3/2. This is 5.4 times mode I TL fracture toughness, which fits well the literature study. – In regression analysis, significant variables were density ρ and ρ2, but the correlation was low, R = 0.54. – The long-term tests gave fracture only by 90 % stress level; median life-time was 5 h. The stress level 45 % proved to be too low. – Deflection increase rate was for the thin specimens twice that for thick specimens. The deflection increase rate was proportional to t1/3 – Crack growth could not be studied due to the rapid fracture process. CIB-W18 Timber Structures – A review of meeting 1-43 2 MATERIAL PROPERTIES page 2.31
Page 1 and 2: CONTENT 2.1 COMPRESSION PERPENDICUL
Page 3 and 4: 23-12-4 H Riberholt, J Ehlbeck, A F
Page 5 and 6: 30-17-1 F Rouger A new statistical
Page 7 and 8: CIB-W18 Timber Structures - A revie
Page 9 and 10: 2.1 COMPRESSION PERPENDICULAR TO GR
Page 11 and 12: for solid sawn lumber and glulam ha
Page 13 and 14: The discussion is supplemented by t
Page 15 and 16: Figure 3. Load-deformation curves f
Page 17 and 18: The results indicate a clear affini
Page 19 and 20: which has been already mentioned ab
Page 21 and 22: served when testing whole CLT panel
Page 23 and 24: 2) The mechano-sorptive effects in
Page 25 and 26: and codified; optimised strategies
Page 27 and 28: 36-11-1 R H Leicester, C H Wang, M
Page 29: For handling of moisture effects in
Page 33 and 34: criteria, they may offer decisively
Page 35 and 36: Conclusion The relation between the
Page 37 and 38: the laminations were determined and
Page 39 and 40: 27-12-3 E Serrano, H J Larsen Influ
Page 41 and 42: shear stress offered by competing s
Page 43 and 44: e alarmed when a significant check
Page 45 and 46: Measurement of shear deflections du
Page 47 and 48: 41-12-2 M Frese, H J Blass Bending
Page 49 and 50: tures". The Centre Technique du Boi
Page 51 and 52: By setting γG = γQ1 = γQ2 = …
Page 53 and 54: ment. For instance, extreme distrib
Page 55 and 56: method which was commonly used in c
Page 57 and 58: 2.7 LOAD DURATION 6-9-3 T Feldborg,
Page 59 and 60: son curve", derived from small clea
Page 61 and 62: 19-9-4 U Korin Non-linear creep sup
Page 63 and 64: 24-9-1 T Toratti Long term bending
Page 65 and 66: Summary Based on the analysis of th
Page 67 and 68: when a dry period is followed by a
Page 69 and 70: - Jansson and Leijten both demonstr
Page 71 and 72: - The used methods and technologies
Page 73 and 74: ISO, generally through the technica
Page 75 and 76: ed. The significance of the choice
Page 77 and 78: However, there is another equally i
Page 79 and 80: 25-17-3 D W Green, J W Evans Moistu
Page 81 and 82:
tion of settings. Since this proced
Page 83 and 84:
posed approach is that the reliabil
Page 85 and 86:
Conclusion It was concluded that th
Page 87 and 88:
- The difference between E in edge
Page 89 and 90:
On the basis of long-term experienc
Page 91 and 92:
Conclusions The possibilities of vi
Page 93 and 94:
Finland and Norway). Consequences w
Page 95 and 96:
Fig. 1. A wind-induced compression
Page 97 and 98:
emphasis on the modelling of the ef
Page 99 and 100:
some trends are apparent. Based on
Page 101 and 102:
- A higher COV of the raw material
Page 103 and 104:
Visual grading of wood into strengt
Page 105 and 106:
4 X(1 � X) Y �1� X � 3s�1
Page 107 and 108:
F112 and F122. It is however shown
Page 109 and 110:
strength tends to increase with ris
Page 111 and 112:
y assuming a normal distribution. E
Page 113 and 114:
19-12-3 F Colling Influence of volu
Page 115 and 116:
- WF/Ww: 2:1 The single span three
Page 117 and 118:
40-6-2 M Poussa, P Tukiainen, A Ran
Page 119 and 120:
2.12 SIZE AND CONFIGURATION FACTORS
Page 121 and 122:
While the estimates of the size eff
Page 123 and 124:
ters for all grades and species. Si
Page 125 and 126:
Modelling of length-wise distributi
Page 127 and 128:
different things that affect the si
Page 129 and 130:
sponds to the statistical approach
Page 131 and 132:
fects. As a summary we may, for the
Page 133:
More important than the volume effe
show all

CIB-W18 Timber Structures – A review of meeting 1-43 2 MATERIAL ...

Create successful ePaper yourself

Delete template?

Save as template?