A Variable-Impulse Hammer Impact Test (VIHIT) Method for Improved Mode Shape Identification

Area of Science:

• Mechanical Engineering
• Civil Engineering
• Vibration Analysis

Background:

• Impact hammer testing is crucial for structural health monitoring (SHM).
• Traditional methods face limitations due to uncontrolled factors like swing power and operator consistency, especially in nonlinear structures.
• Existing research often avoids hammer testing, opting for drop mass systems or operational modal analysis (OMA).

Purpose of the Study:

• To develop a more accurate experimental modal analysis (EMA) approach for impact hammer testing.
• To address the reliability issues of conventional impact hammer testing in structural dynamics.
• To characterize nonlinear dynamic behavior and improve mode shape extraction.

Main Methods:

• Introduced Variable Impulse Hammer Impact Testing (VIHIT) using a single-input single-output (SISO) roving hammer and fixed accelerometer.
• Evaluated the imaginary component of the frequency response function (FRF) at various test locations using multiple impulses of varying magnitude.
• Utilized inverse FRF analysis to extract nonlinear damping ratios and establish reproducible trends across different impulse levels.

Main Results:

• Demonstrated reduced mode shape variability compared to conventional averaging techniques.
• Successfully characterized impulse-dependent damping ratios in degraded timber beams, ranging from 0.02 to 0.04.
• Showcased the method's ability to accurately extract modal properties, mode shapes, and nonlinear dynamic behavior.

Conclusions:

• VIHIT offers a more accurate and reliable approach to impact hammer testing for SHM.
• The method effectively addresses variability in testing by establishing reproducible trends.
• This technique provides enhanced characterization of nonlinear dynamic behavior in structures.