| Diffuse poprous wood birch(Betula platyphylla Suk.)and ring porous wood ash (Fraxinus mandshurica Rupr.) were chosen respectively as materials to study the effect of temperature ranging from 20℃to 180℃on bending mechanics, stress relaxation of bent wood and the fixation of bending set, which can not only enrich wood mechanics, but also can provide some valuable data and theory guide for wood bending technology in wood industry.Experiment was divided into two parts:①Effects of temperature on bending mechanics were studied by revelation of the relationship between temperature and mechanical indexes such as modulus of elasticity, proportional limit stress, failure stress, proportional limit strain, failure strain and tough factor. Temperature range was divided into two parts accoreing to the temperature controlling meadium, the first was the range from 20℃to 100℃of water saturated condition, the second range was from 80℃to 180℃for ethylene glycol saturated condition.②Effects of temperature on stress relaxation and its set of bent wood:Stress relaxation of bent wood at constant temperatures and during even temperature elevation process in two temperature ranges from 20℃to 80℃and from 80℃to 180℃were respectively studied by the revealation of the relationship between temperature and both residual stress and stress relaxation rate. After the stress relaxation, bent sets were measured at the room condition and the effects of stress relaxation on bent set were analysised.Base on the above studies, the following conclusions were achieved:1. Bending mechanics at 20℃: For both air dried birch and ash wood, coefficient of variation for each mechanical index deriving from tangential loading direction was bigger than that deriving from radial loading. When loading on the same direction, each specific mechanical index of air dried birch was bigger than that of ash wood. Modulus of elasticity, proportional limit stress and failure stress of water saturated wood were all less than those of air dried wood, but failure strain of water saturated wood was much bigger than that of air dried wood, while the difference of proportional limit strain between water saturated condition and air dried condition was little, which indicated that water could enlarge the plastic deformation of wood.2. Bending mechanics at constant temperatures:①At constant temperatures ranging from 20℃to 100℃of water saturated condition, the higher the constant temperatures, the less modulus of elasticity, proportional limit stress and failure stress of water saturated wood would all be, while proportional limit strain were almost equal at different constant temperatures, however, failure strain and tough factor increased as a result of temperature elevation, which indicated temperature can enlarge the plastic deformation.②At constant temperatures ranging from 80℃to 180℃of ethylene glycol saturated condition, the higher the temperature, the less proportional limit stress, failure stress, proportional limit strain, failure strain and modulus of elasticity would be. However, proportional limit stress, failure stress and modulus of elasticity of ethylene glycol saturated birch wood were bigger than that of ethylene glycol saturated ash wood, while proportional limit strain and failure strain of ethylene glycol saturated birch were less than that of ethylene glycol saturated ash. At constant temperatures ranging from 80℃to 180℃, though factor of ethylene glycol saturated birch decresase with the elevation of temperature while that of ethylene glycol saturated ash wood.3. Stress relaxation of bent wood:①At contant temperatures ranging from 20℃to 80℃, the effecst of strain level on stress relaxation of both water saturated birch and ash wood were more clear than that of temperature. Temperature elevation could clearly increase stress relaxation, the bigger temperature elevation, the less residual stress and the bigger relaxation rate would be.②At constant temperatures ranging from 80℃to 180℃, the higher temperature, the less residual stress. However, the effect of temperature on relaxation rate depended on the concrete temperatures,When stress relaxation was tested at constant temperatures ranging from 80℃to 120℃, relaxation rate changed little, but when the temperature ranged from 120℃to 180℃, the higher the temperature, the less relaxation rate would be.③For ethylene glycol saturated birch wood, the specimens failed during stress relaxation when temperature elevated from 80℃-120℃. For the ethylene glycol saturated ash wood, the specimens failed during stress relaxation when temperature elevated from 80℃-140℃. For the specimens used for stress relaxation during the whole temperature elevation, residual stress during each elevation relaxed to a tiny value and almost equal.4. Bent Set:①For water saturated specimens whose stress relaxation were tested at constant temperatures ranging from 20℃to 80℃, the set became almost constant 24 hours after the end of the stress relaxation. Meanwhile the higher constant temperature at which stress relaxation was tested, the bigger the set would be. Set of specimens experiencing stress relaxation during temperature elevation was bigger than those of specimens experiencing stress relaxation at the beginning constant temperature of elevation, also, the more the temperature elevation, the bigger the bent set.②For ethylene glycol saturated wood whose stress relaxation were tested at constant temperatures ranging from 80℃to 180℃, their set became almost constant 48 hours after the end of the stress relaxation. As for bent set, the effects of temperature ranging from 80℃to 120℃on it were not clear. But for these whose stress relaxation were tested at constant temperatures ranging from 130℃to 180℃, the higher the temperature, the bigger the bent set would be. For ethylene glycol saturated wood whose stress relaxation were conducted during temperature elevation from 80℃-170℃to 180℃, the sets were almost equal, which were bigger than those of specimens experiencing stress relaxation at the corresponding beginning constant temperatures of elevation.
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