Model for damage evolution through dynamic stiffness degradation in three wood species subjected to very high cycle fatigue
摘要
The main objective of this research project is to characterize the evolution of fatigue damage produced by a flexural excitation device in three types of wooden beams of different species, namely Pinus pseudostrobus, Quercus scytophylla, and Cedrela odorata. A stiffness degradation model is proposed that considers an acceleration of damage as it increases. The methodology used for this purpose is based on laboratory measurement of the first natural frequency of the wooden beams using the impact and sensing technique and vibration detection using an accelerometer for subsequent computer data processing. The first natural frequency is measured before fatigue testing begins. The theory of fatigue degradation dictates that a material loses stiffness over the course of working cycles. Measurements of the first natural frequency of the wooden beams are taken after more than 19 million cycles, verifying this behavior in the laboratory. The results obtained show a decrease in natural frequency, which translates into a loss of stiffness. The order of 107 cycles was reached for all beams, and a reduction of 19.06% in the stiffness of Cedrela odorata, 16.83% for Pinus pseudostrobus and 11.20% for Quercus scytophylla was observed. Based on the experimental data and using a simple exponential degradation model as a basis, a new model for damage evolution is proposed that considers degradation accelerating as damage increases and approaches failure. The experimental data are compared with the data obtained using the proposed model, obtaining a correlation coefficient (R2) of 0.998 for Pinus pseudostrobus, 0.950 for Quercus scytophylla, and 0.835 for Cedrela odorata. The model fits the experimental data very well for Pinus pseudostrobus and Quercus scytophylla but not as well for Cedrela odorata.