Research On Vibration-based Non-destructive Detection Methods Of The Elastic Modulus Of Glued Laminated Beams

Research on vibration-based detection of the elastic modulus is essential process in evaluating the performance of lumber and improving the utilization of our limited forest resources. In this research, a vibration-based measurement is developed for measuring the modulus of elasticity of glued laminated beams. The feasibility and validity of a simply-supported beam vibration theory were examined under various boundary conditions.A brief description of the main work in this thesis is presented here.1. A accurate, feasible test method for glued laminated beams is determinated by several types and modes of vibration and the signal and signal processing method of the vibration test.2.Under the condition of simply supported beams, the transverse vibration method determinate vibration frequency with different measuring point. Among them, when the point in the middle of the span, the vibration frequency is the most stable, the time domain and the frequency domain graph are the most clear and reliable.3.Compared with sawn timber and glued laminated beams with dynamic and static elastic modulus, the correlation between them is analysed and the equation of linear regression is calculated. It is observed that the correlation of the dynamic and static elastic modulus of glued laminated beams is better than that of sawn timber. In order to determine, under the conditions of simply supported beams, transverse vibration testing elastic modulus of glued laminated beams is feasible.4. Compared with the test value, the frequency of the sawn timber and glued laminated beams with different layers and different length is respectively calculated by using the Euler-Bernoulli formula, Timoshenko formula and finite element method. It is observed that the the more layers of glued laminated beams, the higher accuracy of the frequency calculated by the Euler-Bernoulli formula is. And it is in line with the theoratical derivatioin rule.5.According to the comparison of the data, the elastic modulus of glued laminated beams can be calculated by the Euler-Bernoulli formula when the ratio of span and depth is higher than 20. The elastic modulus of glued laminated beams can be calculated by the corrected Euler-Bernoulli formula when the ratio of span and depth is between 10 and 20. The elastic modulus of glued laminated beams can not be determinated by the transverse vibration method when the ratio of span and depth is lower than 10.