The Degeneration On Mechanical Properties Of Aged Wood And Corresponding Damage Constitutive Model

Timber structure is the outstanding representative of the ancient architecture in China, which carries the traditional culture, scientific value of China. But due to its long history, wood have been subjected to ultraviolet radiationt, decayed by fungus, the change of weather and moisture for a long time, which lead to their change of appearance and degeneration of mechanics performance. Due to that, in this paper, these three damage factors of wood has been studied, which can provide the reference to further study of the protection of ancient timber structure.Chinese Fir, which is the most widely used in the ancient timber structure of Yangzhou area, was used as specimen material in this study. The changes happened in this specimen during the experiment were be observed and recorded, so as to prove the degenerated constitutive model of damaged wood.(1) The artificial environment was designed to model three environment. The specimen were subjected to the UV radiation, decayed by fungus, and the alternating moisture and temperature recyle, which can lead to varying damaged degrees of wood.(2) The specimen damaged by different environment were tested, and the physical, mechanics index, such as density, friction coefficient, compression strength parallel to grain, compression strength perpendicular to grain, tensile strength parallel to grain, shear strength parallel to grain and so on were obtained. Thus, the relationship of the varying degrees of wood damage and mechanical properties were discovered.(3) Some modern testing techniques such as SEM, XRD, FTIR were used to analyze the damaged mechanism of wood, which was used to observe change of the supermicro structure, the relative crystallinity and the chemical component. Thus, the reason of the change of mechanical property can be found.(4) The model of damage-stress-strain can be built after the experiment. So the rule of decay of mechanical performance can be proved, and the corresponding material property model and failure criterion were proposed.In this paper, some beneficial exploration has been done in terms of the model of the environment, the measurement and the assessment of damage model. However, due to the limitations of the experimental period, the long-term damaged characteristic of specimen can be further studied.