Rheological Behavior of Douglas-Fir Perpendicular to The Grain at Elevated Temperatures
Keywords:Creep, drying, Douglas-fir, mechano-sorptive effect, shrinkage, tension, compression
The rheological properties of Douglas-fir lumber under tangential tension and compression were investigated with a small testing machine in a pressure vessel. The strain fields for matched test samples were monitored remotely with a high-resolution video camera. The required steady- and unsteady-state equilibrium moisture contents (EMCs) were achieved by controlling the total pressure in the absence of air. The moisture content (MC) was monitored with a quartz spring sorption balance. Creep at a constant MC of 10% and mechano-sorptive (MS) effect during drying were measured for temperatures up to 82 C.
The results indicated that the MS strain is the dominant component of the stress-induced strain in drying of small wood samples under load. At 65.6 C, the MS strain in compression along the tangential direction was about three times larger than that in tension under the same stress level and MC change. An increase in temperature from 32.2 C to 82 C led to an increase in MS strain under compression. Constitutive equations quantifying the combined effect of mechanical loading and moisture change were developed and fit to experimental data, and material parameters for various strain components were evaluated.
Armstrong, L. D. 1972. Deformation of wood in compression during moisture movement. Wood Sci. 5:81-86.nArmstrong, L. D., and R. S. T. Kingston. 1962. The effect of moisture content changes on the deformation of wood under stress. Aust. J. Appl. Sci. 13:257-276.nChristensen, G. N. 1962. The use of small specimens for studying the effect of moisture content changes on the deformation of wood under load. Aust. J. Appl. Sci. 13:242-256.nControl EG. 1989. Measurement and control software, user's manual. Quinn-Curtis, Newton, MA. 136 pp.nErickson, R. W. 1989. Mcchano-sorptive phenomena in drying red oak. Pages 79-91 in Proceedings, IUFRO International Conference on Wood Drying, Seattle, WA.nEspenas, L. D. 1952. Minutes of annual meeting of western dry kiln clubs. Redding, CA. May.nGrossman, P. U. A. 1976. Requirements for a model that exhibits mechano-sorptive behaviour. Wood Sci. Technol. 10:163-168.nGrossman, P. U. A., L. D. Armstrong, and R. S. T. Kingston. 1969. An assessment of research in wood rheology. Wood Sci. Technol. 3:324-328.nHearmon, R. F. S., and J. M. Paton. 1964. Moisture content change and creep of wood. Forest Prod. J. 14(8): 357-359.nHisada, T. 1979. Creep and set of wood relating to kiln drying, II. Effect of stress level on tensile creep of wood during drying. Mokuzai Gakkaishi 25:697-706.nHisada, T. 1980. Creep and set of wood relating to kiln drying. IV. Effect of stress level on compressive creep and set of wood during drying. Mokuzai Gakkaishi 26: 519-526.nHisada, T. 1981. Creep and set of wood relating to kiln drying. V. Effect of temperature on creep of wood during drying. Mokuzai Gakkaishi 27:381-389.nIrving, D. C. 1989. A study of load-induced microde-formation within wood-based structural members using optical scanning techniques, M.S. thesis, Oregon State University, Corvallis, OR. 106 pp.nKelly, S. S., T. G. Rials, and W. G. Glasser. 1987. Relaxation behaviour of amorphous components of wood. J. Mater. Sci. 22:617-624.nLeicester, R. H. 1971. A rheological model for mechano-sorptive creep of beams. Wood Sci. Technol. 5:211-220.nMårtensson, A., and S. Thelandersson. 1990. Effect of moisture and mechanical loading on wooden materials. Wood Sci. Technol. 24:247-261.nMcMillen, J. 1955. Drying stresses in red oak: Effect of temperature. Forest Prod. J. 5(4):230-241.nMcMillen, J. 1968. Transverse strains during drying of 2-in. ponderosa pine. USDA Forest Serv. Res. Pap. FPL 83. Forest Prod. Lab., Madison, WI. 26 pp.nPalka, L. C. 1973. Predicting of specific gravity, moisture content, temperature, and strain rate on the clastic properties of softwoods. Wood Sci. Technol. 7:127-141.nRanta-Maunus, A. 1975. The viscoelasticity of wood at varying moisture content. Wood Sci. Technol. 9:189-205.nRice, R. W., and R. L. Youngs. 1990. The mechanism and development of creep during drying of red oak. Holz. Roh- Werkst. 48:73-79.nSalin, J. G. 1992. Numerical prediction of checking during timber drying and a new mechano-sorptive creep model. Holz Roh- Werkst. 50:195-200.nSalmén, N. L. 1975. Viscoclastic properties of in situ lignin under water-saturated conditions. J. Mater. Sci. 10:3090-3096.nSchniewind, A. P. 1966. On the influence of moisture content changes on the creep of beech wood perpendicular to the grain including the effects of temperature and temperature change. Holz. Roh- Werkst. 24:87-98.nSchniewind, A. P. 1968. Recent progress in the study of rheology of wood. Wood Sci. Technol. 2:188-206.nSchniewind, A. P., and J. D. Barrett. 1972. Wood as a linear orthotropic viscoelastic material. Wood Sci. Technol. 6:43-57.nTakahashi, A., and T. Yamada. 1966. Studies on the drying set of wood. I. Tensile creep in relation to the non-equilibrium state in the wood-water system, especially the dependence on load. Mokuzai Gakkaishi 12:6-10.nUSDA Forest Service. 1987. Wood handbook: Wood as an engineering material. Agric. Handb. 72. Forest Prod. Lab., Washington DC. 466 pp.nWu, Q. 1993. Rheological behavior of Douglas-fir as related to the process of drying. Ph.D. dissertation, Oregon State University, Corvallis, OR. 228 pp.nWu, Q., and M. R. Milota. 1994. Effect of creep and mechano-sorptive effect on stress development during drying. Drying Technol. 12(8):2057-2085.nYoungs, R. L. 1957. The perpendicular to grain mechanical properties of red oak as related to temperature, moisture content, and time. USDA Forest Serv. Rep. FPL-2079. Forest Prod. Lab., Madison, WI.n
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