Application Of Strain Modal Analysis In Detection Of Mechanical Structural Damage

Structure in use, would be suffering the role of the normal working load and the effect of a variety of unexpected external factors. This will allow a partial structural damage. When the accumulation of local damage to a certain extent, the overall structure will lead to sudden failure. For important structures, the occurrence of damage and structural failure will cause a major safety accidents and economic losses. Therefore, to ensure the safety of mechanical structures and systems to work need regular or on-line damage detection of mechanical structures, finding the location and extent of injury as soon as possible.Then repair or improve the damage structural real-time to avoid catastrophic accidents.This paper, starting from the practical application of engineering, combined the method of strain modal analysis and the work modal theory applied to cantilever beam damage detection. Specific research process is as follows:1. By analyzing the structural damage identification method of the status and problems, made a detailed study on the strain modal analysis method with specific object of study.2.By numerical simulation of indirect damage detection, experimental study, obtained the general impact law of damage location and extent to the modal parameters (frequency, damping, mode shape).In this paper use the strain mode shapes and strain mode deviation as indicators of damage identification in beam damage recognition.Strain mode shapes is very sensitive of non-modal joint damage, especially for the injury occurs in the vicinity of the peak area of a certain order mode. Strain mode mutations in the vicinity of injury, and mutations amplify with the degree of the increase of the amount of damage.3.Calculate strain mode from the acceleration signal.According to longitudinal strain theory of the material mechanics, obtained the relationship between strain and displacement. Displacement signal can be obtained from acceleration by quadratic integral. Calculate strain mode from the acceleration signal, analysis of the feasibility of this approach from the point of error. The main error source of calculation is the phase error in the process of signal subtraction for the two measuring points. To reduce this phase error, proposed a minimum variance-based approach, and verified the feasibility of this method through experiments. This method can make the future testing and diagnosis more convenient and efficient.4. Make the strain mode and operating modal comprehensive applied to structural damage detection. This article combined strain mode with operating modal, described the basic principles of strain operating modal and parameter identification methods in frequency domain. For the combination of strain mode and operating modal proposed a new data processing and modal parameter identification methods. Validated the feasibility of this method by cantilever beam test.Overall, this article synthesized strain modal analysis method and the basic theory of operating modal applied to damage detection of cantilever beam. Derived by theoretical analysis and experimental validation, analyzed the feasibility and effectiveness of the proposed method.