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  • 1
    Electronic Resource
    Electronic Resource
    Creep in chipboard (1981)
    Springer
    Wood science and technology 15 (1981), S. 125-144 
    Details
    ISSN: 1432-5225
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary The effect of moisture and level of stressing on the rate of creep and time to failure is studied for UF and MUF bonded particleboard. Response curves were fitted to a 4-element rheological model with a high degree of accuracy for four levels of stressing and for three levels of relative humidity at 20°C. Values of relative creep increased with time and also with increased levels of stress and r.h. The ratio of stress to deflection — presented either as the creep modulus or as isochronous curves — decreased rapidly with time. Particleboard is demonstrated to exhibit non-linear viscoelastic properties, particularly at the higher levels of stress. Deflection was increased and time to failure decreased when r.h. was raised from 65 to 90 per cent, but no significant statistical change was noted between 30 and 65 per cent r.h. Increased levels of stress caused a decrease in both deflection and time to failure. Greater deflection at failure and longer time to failure were recorded for MUF board, but for the UF board the 90 per cent r.h. had a more pronounced effect in increasing deflection and decreasing the time to failure. Predictions are made on the long-term stress loadings for different humidity conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00367859
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  • 2
    Electronic Resource
    Electronic Resource
    Creep in chipboard (1984)
    Springer
    Wood science and technology 18 (1984), S. 205-224 
    Details
    ISSN: 1432-5225
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary Samples of five chipboards, one waferboard, one plywood, one fibre building board and Scots pine timber were loaded in four point bending at a stress equivalent to 60 per cent of the short term failing stress under five combinations of temperature and relative humidity for a period of six months, or until prior failure. Irrespective of whether creep behaviour was assessed in terms of total deflection, viscous component of deflection, relative creep, creep modulus, or deflection at, or time to failure, significant differences were obtained with variations both in temperature and relative humidity. The effect of temperature, at fixed humidity, was slightly greater between 20°C and 30°C than between 10°C and 20°C, while the effect of humidity was appreciably greater between 65% and 90% rh than between 30% and 65% rh. Fitting of hyperbolic curves to the data permitted the prediction of creep behaviour with a good degree of fit at any combination of temperature and humidity within the experimental range. Differences in response to environmental conditions existed among some of the boards. Thus the ranking order of the materials was slightly different under variable humidity than it was under variable temperature. It was possible to describe these differences in terms of the variation that occurred among the materials in the relative proportion of the elastic, viscoelastic and viscous components of deflection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00367534
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  • 3
    Electronic Resource
    Electronic Resource
    Creep in chipboard (1985)
    Springer
    Wood science and technology 19 (1985), S. 83-91 
    Details
    ISSN: 1432-5225
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary Although previous papers in this series have shown that a 4-element rheological model can provide a very good representation of the creep deflection of chipboard in bending, a new set of long-term data shows that it has certain limitations as a model for predicting deflection up to 31/2 years. It was deduced in a earlier paper (Pierce et al. 1979) that the linear viscous flow component was likely to predict higher than actual deflections over a long period. This paper shows that view to be correct, and puts forward a modified 4-element model in which the viscous component is non-linear with respect to time. The resulting 5-parameter model is shown to be superior to the 4-parameter model for long-term predictions of creep deflection particularly at the lower stress levels, although it appears that the viscoelastic and viscous components of deflection are not as realistic as in the 4-parameter representation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00354756
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  • 4
    Electronic Resource
    Electronic Resource
    Creep in chipboard (1990)
    Springer
    Wood science and technology 24 (1990), S. 181-189 
    Details
    ISSN: 1432-5225
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary 4- and 5-parameter rheological models were used to pedict deflections at from 7 to 10 years from 24 weeks data. Comparison with actual deflection confirmed the unsuitability of the 4-parameter model as a predictive tool, while the range in prediction errors over 20 specimens for the 5-parameter model was +23% to -26%. The standard error, though not the mean prediction error was reduced by approximately one half by extending the data accumulation period to 39 weeks. Thus the 95% confidence limits in predicting deflections at 2,555 days (7 years) from 39 weeks data was +13% to -20% for all data, and +6% to -19% for data at 20 °C, 65% r.h.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00229053
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  • 5
    Electronic Resource
    Electronic Resource
    Creep in chipboard (1992)
    Springer
    Wood science and technology 26 (1992), S. 429-448 
    Details
    ISSN: 1432-5225
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary Matched samples to those used in a previously reported investigation (under constant environments employing eight board materials and solid wood) were subjected to five different levels of stress under four different cyclic environments for periods of six months. Relative creep increased slightly and linearly with respect to stress within the range of stress levels adopted, as well as increasing with severity of the environment. All materials showed greater sensitivity to alternating humidity than to alternating temperature. The effects of the three prinicipal variables (stress level, environment, material), and the strong interactions among them, were quantified using analysis of variance and found to be similar to those under constant environments: the effect of environmental condition was found to be far greater on relative creep than that of either stress level or material. Averaging over all conditions and stress levels, relative creep increased progressively among timber, plywood, waferboard, chipboard and fibreboard, though this ranking order varied at different stress levels and environments due to the presence of strong interactions. At a stress level of 30% and a time of 43,200 minutes, the relative creep under alternating humidity of 30↔90% was on average fourteen times greater than that under a constant humidity of 65% (averaging across the nine materials); however, there was considerable divergence among the materials in this ratio. At the same level of stressing, the mean relative creep for all materials under an alternating temperature of 10↔30 °C was 1.6 times higher than at a constant temperature of 20°C. The ranking order of materials in their sensitivity to alternating temperature was different to that under alternating humidity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00229247
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  • 6
    Electronic Resource
    Electronic Resource
    Creep in chipboard (1979)
    Springer
    Wood science and technology 13 (1979), S. 265-282 
    Details
    ISSN: 1432-5225
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary Previous linear and curvilinear regression models for predicting the creep deflection of timber and timber products have failed to provide an adequately good fit. However, this paper shows that the 4-element (and to a lesser degree the 3-element) rheological model provides an extremely good fit to chipboard creep data. A set of experiments has been carried out on the creep behaviour of five commercially-available types of chipboard under 3-point sustained loading at constant temperature and humidity. This range of board types encompassed three types of glue — UF, MF/UF and Pf- and was loaded at two stress levels-30% and 60% of the short term ultimate stress. The lifetime of these specimens ranged from 25 days to over 31/2 years until either failure occurred or the load was removed. Creep curves based on 3- and 4-element rheological models have been fitted to the data from each specimen using an iterative least squares computer program which we developed. The validity of the two models is discussed, together with studies on the comparative behaviour of different board types and the use of the models as predictive tools.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00356969
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  • 7
    Electronic Resource
    Electronic Resource
    Modelling the creep behaviour of chipboard: The rheological approach (1998)
    Springer
    Wood science and technology 32 (1998), S. 261-272 
    Details
    ISSN: 1432-5225
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary The process of applying the rheological approach to describe creep deformation has been investigated using the 5-parameter model developed by Pierce and Dinwoodie (1977). A method utilising exponential curve fitting techniques was examined by attempting to produce fits to the first 6 months' data from long-term experiments (12 years). The procedure included a means of assessing the variability occurring in the derived model parameters which showed that acceptable fits were obtainable for only 3 out of the 20 data sets available. Further analysis of one of these data sets (that for cement-bonded particleboard, subjected to a stress level of 30% of the short-term ultimate in an environment of 25 °C and 90% relative humidity) revealed that the model attributed most of the creep deformation to the viscous component; resulting in an over-estimate of the deformation at 12 years when the 6-month fit was projected. An alternative approach to deriving the value of the model parameters is proposed, based on the theory underlying the model. The applicability of this approach was investigated using the above mentioned data set. It was found that the model can be constrained to give a more realistic ratio between the time-dependent components of deformation (ie. viscoelastic and viscous creep) for the material considered, thereby improving the accuracy of the projected creep deformation over the 12-year period.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00702894
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  • 8
    Electronic Resource
    Electronic Resource
    Creep in chipboard (1986)
    Springer
    Wood science and technology 20 (1986), S. 281-292 
    Details
    ISSN: 1432-5225
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary A considerable amount of data has been collected over the past few years on the rupture life of particleboard. This information is particularly valuable at the present time because there is increasing interest in the use of particleboard as a structural material. This paper presents a conventional analysis of the time to failure of three commercially available brands of particleboard at 20°C and at three fixed levels of relative humidity. A linear relationship is assumed between the logarithm of time to failure and stress level, and an improvement is made in the usual method of analysis by including censored specimens. The regression lines are projected forward to give estimates of the stress levels that can be sustained for a particular design life. It is found that the regression lines for 30 per cent and 65 per cent rh may be combined, but the specimens at 90 per cent rh are significantly lower in strength at any given time. One of the MUF bonded boards performs significantly better than a second MUF board over the long term, and this gives added weight to the view that there are other factors in the make-up and production of the board that are at least as important as the resin type itself.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00350986
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  • 9
    Electronic Resource
    Electronic Resource
    Creep in chipboard (1991)
    Springer
    Wood science and technology 26 (1991), S. 39-51 
    Details
    ISSN: 1432-5225
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary Ten samples from each of ten brands of commercial chipboard, covering a range of UF, MUF and PF resins, were stressed over a 5-year period at 30% of their short term ultimate bending strength, under protected external conditions. No relationship could be established for the term of the experiment between fluctuations in creep deflection and changes in environmental conditions. Exceptionally, for two short periods of time, relationships were established and these were in line with current views on mechano-sorptive behaviour. Differences in relative creep between the ten brands were significantly greater than those occurring between samples of any one brand. Although there were significant differences in relative creep among the six brands of MUF bonded boards, the relative creep of all these boards was significantly lower than those brands made with UF and high-alkaline cured PF resins. While most of the MUF bonded samples survived the duration of the experiment, all UF and PF samples failed before the end of the 5-year period. For the first 6 months of the experiment, the mean relative creep under protected external conditions was equal to, or slightly less than, that obtained in matched samples tested under a constant environment of 20°C 90% rh.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00225690
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  • 10
    Electronic Resource
    Electronic Resource
    Creep in chipboard (1991)
    Springer
    Wood science and technology 25 (1991), S. 225-238 
    Details
    ISSN: 1432-5225
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary Deflection under 4-point bending of a range of board types was measured for up to six months. Results were obtained under steady-state conditions of stress level (30%, 45%, 60%, 67.5% and 75% of the short term breaking stress), relative humidity (30%, 65% and 90% rh) and temperature (10°C, 20°C and 30°C). These results are presented in terms of relative creep and creep modulus. The relative creep for all board types increased with increasing stress level, increasing relative humidity and increasing temperature. An analysis of variance investigating variations between materials showed significant differences in relative creep. When the relative creep of all materials was compared over all conditions and all stress levels, plywood and waferboard had consistently low relative creep values. High alkaline cured PF chipboard and non-British Standard UF chipboard had consistently high relative creep values. The creep modulus of MUF bonded chipboard decreased with increasing log10 (time) under all conditions. Creep modulus also decreased with increasing stress level.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00223473
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