Development of a Closed-Loop High-Cycle Resonant Fatigue Testing System

• Published in: Experimental mechanics Vol. 52; no. 3; pp. 275 - 288
• Main Authors: Yun, G. J., Abdullah, A. B. M., Binienda, W.
• Format: Journal Article
• Language: English
• Published: Boston Springer US 01.03.2012; Springer
• Subjects: Biomedical Engineering and Bioengineering; Characterization and Evaluation of Materials; Control; Dynamical Systems; Engineering; Exact sciences and technology; Fracture mechanics (crack, fatigue, damage...); Fundamental areas of phenomenology (including applications); Lasers; Measurement and testing methods; Optical Devices; Optics; Photonics; Physics; Solid Mechanics; Structural and continuum mechanics; Vibration; Scanning laser vibrometer; Bending fatigue; Experimental fatigue testing; Closed-loop testing; Vibration-based testing; Resonant fatigue; High-cycle fatigue; Shaker controller; Metallic structure; Optical interferometry; Structure integrity; Feedback regulation; Vibration test; Test bar; Vibrometer; Crack propagation; Fatigue test; Resonance frequency; Vibration source; Actuator; Dynamic response; Closed loop; Vibration; Fatigue; Laser interferometer; Optical measurement; Control loop; High frequency
• ISSN: 0014-4851; 1741-2765
• DOI: 10.1007/s11340-011-9486-z

In this paper, a vibration-based testing methodology to assess fatigue behavior of a metallic structure is presented. To minimize the testing duration, the test setup is designed for a base-excited multiple-specimen arrangement driven in a high-frequency resonant mode, which allows completion of fatigue testing in an accelerated period. The shaker operates in closed-loop control with dynamic specimen response feedback provided by a scanning laser vibrometer. A test coordinator function is developed to synchronize the shaker controller and the laser vibrometer and complete the closed-loop scheme: the test coordinator monitors structural health of the test specimens throughout the test period, recognizes change in specimen dynamic behavior due to fatigue crack initiation, terminates test progression, and acquires test data in an orderly manner. The test methodology is demonstrated with cantilever specimens that are clasped on the shaker armature with specially-designed clamp fixtures. Experimental stress evaluation is carried out to verify the specimen stress predictions. A successful application of the experimental methodology is demonstrated by validation tests with Al 6061-T6 aluminum specimens subjected to fully-reversed bending stress.