Experimental Modal Analysis (EMA) is the field of measuring and analyzing dynamic response of a structure when it was excited. EMA is the useful procedure in dynamic verifying Finite Element Analysis (FEA) results, using modal analysis to determine modal parameters (natural frequency, damping ratio, mode shapes) of the structure. The simple method for obtaining modal parameters is using roving impact test to identify natural frequencies, damping ratios, and mode shapes of the structure. Thus, the modal testing machine is used for accurate impact test. The machine will guide a modal hammer to hit onto a grid mark of the specimen and prevent the hammer from bouncing and hit at the same position twice. Otherwise, the double hitting will resulted in error of data recording. Other than that, the specimens have to be clamped firmly to avoid from noises during the test.
This paper using modal analysis method to investigate dynamic response of specimens to simulate aircraft structural behaviors by varying rivet pitches and specimen holes which conforms to AC 43.13-1B of the FAA. In experiment, modal hammer and accelerometer are used to measure hitting force and specimen accelearation respecticvely. After that, the force and the acceleration signals will be transformed into speed and displacement data as the function of time and frequency. In computation, finite element analysis method (FEA) is used alongside with modal analysis, in order to generate specimen properties emulating the actual dynamic responses obtained from the experiment. In short, natural frequencies achieved from the experiment, and mode shapes obtained from the FEA being used to compare the frequency trends. Meanwhile, mode shape of a plain specimen and riveted specimen are used to compare the vibration trend. They have similar pattern which indicated it has correct machine set up and experiment result. Which mean these data from preliminary study is valid to be used for further study.
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การทดลองและวิเคราะห์การสั่นสะเทือนของจุดยึดบนโครงสร้าง อากาศยานที่ยึดด้วยรีเวท MS20426AD ด้วยวิธีโมดัลอนาไลซิส : EXPERIMENTAL MODAL ANALYSIS OF AIRCRAFT STRUCTURAL JOINTS VIBRATION USING MS20426AD RIVET