Ultrasonic Linear and Nonlinear Behavior of Fatigued Ti–6Al–4V

Abstract

The change in ultrasonic nonlinear property of a titanium alloy subjected to cyclic loading has been studied, with an objective to develop a new characterization methodology for quantifying the level of damage in the material undergoing fatigue. In order to determine the degree of nonlinearity, the ultrasonic second harmonic generation technique has been used. The second harmonic signal was monitored during the fatigue process, and a substantial increase in the second harmonic amplitude (180% increase in nonlinear factor) was observed. This indicates that the second harmonic signal is very sensitive to the microstructural changes in the material caused by fatigue.

Quantitative assessment of fatigue damage accumulation in wavy slip metals from acoustic harmonic generation

“…Theoretical β versus percent total fatigue life curves for polycrystalline nickel and AA2024-T4 calculated from the model are given in Section 5. The results for AA2024-T4 are compared to the experimental measurements (Cantrell and Yost 4 1994, Na et al 1996, Nazarov and Sutin 1997, and Frouin et al 1999 indicate that each stage of the fatigue process may be characterized by a unique nonlinear relationship between an impressed stress perturbation (e.g., a sound wave) and a microelastic-plastic straining of the material. The straining is quantified by an experimentally determined nonlinearity parameter β that increases monotonically by several hundred percent over the fatigue life.…”

Dependence of microelastic-plastic nonlinearity of martensitic stainless steel on fatigue damage accumulation

“…Nonlinear acoustical experiments [7][8][9][10] indicate that metal fatigue may be characterized by a unique nonlinear relationship between an impressed stress perturbation (e.g., a sound wave) and a microelastic-plastic straining of the material at each stage of the fatigue process from the virgin to fracture. The straining is quantified by an experimentally determined material (acoustic) nonlinearity parameter β that increases monotonically by several hundred percent over the fatigue life.…”

“…(8)- (10). For 410Cb stainless steel we assume 26 n ≈ 3.0, B = 1.13 (penny-shaped cracks), and K 1c ≈ 60…”

New Trends in Materials Nondestructive Characterization Using Surface Acoustic Wave Methodologies

“…Ultrasonic microscopy utilizes high focused ultrasonic transducers to induce surface acoustic waves in the material which can be successfully used for local elastic property measurement, crack-size determination, as well as for interfacial damage evaluation in high temperature materials, such as metal matrix composites [38]. Nonlinear acoustics enables real-time monitoring of material degradation in aerospace structures [39].…”