Study On Bending Creep Performance And Time-temperature Superposition Principle Of White Oak Wood Pretreated By Steam

Static viscoelasticity is one of the critical mechanical performance parameters for the evaluation of long-term service lifetime and comprehensive performance of wood.Kelvin model,Burger model and Five-parameter model has been widely used to predict the short-term viscoelastic behavior of wood.Additionally,time-temperature equivalence theory was applied to simulate the long-term viscoelastic mechanical behavior of wood.However,little efforts have been found to investigate the effect of earlywood vessel belt on bending creep behavior of wood and predict the viscoelastic behavior of wood by six-parameter model.Therefore,the earlywood of white oak wood(Quercus alba L.)was selected as raw materials in this study.The effect of steam pretreatment and earlywood vessel belt on creep behavior or wood were investigated based on the numerical characterization of distribution characteristics of earlywood vessel on the cross section of specimens using software(MATLAB 2019 a).Besides,bending creep behavior of specimens was simulated by Six-parameter model and time-temperature equivalent theory.Scientific research is systematically carried out to reveal the relationship among microstructure,short-and long-term creep behavior of white oak wood,providing important theoretical basis and technical support.It also provides scientific significance for the improvement of precise wood processing and effective utilization of limited wood resources.The corresponding experimental results and conclusions are as follows:(1)The number and distribution state of vessels in specimens were consistent,providing basis for the investigation of creep behavior of white oak.However,there was no basically no earlywood vessel in the control group.The earlywood vessel belt,steam pretreatment temperature and test temperature had significant effects on bending creep performance of white oak wood.Strain of specimen was increased with the increasing test temperature under the same steam pretreatment condition.The corresponding rise ratio was also increased with the increase of test temperature.An obvious creep phenomenon was observed to specimen with increase of test temperature to 80°C.An obvious decrement in instantaneous strain and 45 min strain of specimen after steam pretreatment was generated in comparison with the untreated specimens.And the creep strain of specimen after steam pretreatment was lower than the control.Furthermore,the effect of earlywood vessel belt on creep behavior of specimens was obviously at the same steam pretreatment and test temperature.(2)Creep curves of specimens was simulated by Burger model,Five-parameter model and Six-parameter model in this study.The results revealed that the determination coefficient(R~2:0.99918～0.99998)obtained by Six-parameter model was greater than that obtained by Burger model and Five-parameter model under the same conditions.The actual creep process of wood can be well simulated by Six-parameter model with the excellent imitative effect.(3)A long-term curve of creep behavior of white oak wood on the base temperature of 20°C was obtained by translating the 45 min sort-term creep curves in accordance with time temperature superposition principle(TTSP)in this study.The time-temperature equivalent characteristics of bending creep of white oak wood were explored based on the synergistic effect of horizontal movement factor(a _T)and vertical movement factor(b _T).The simulate result revealed that relationship between horizontal movement factor(a _T)and test temperature of white oak wood met the requirement of WLF equation with the corresponding value of R~2greater than 0.93.It was concluded that the WLF equation can effectively describe the relationship of creep characteristics of wood between test time and temperature.