An intelligent colony optimization imaging method for composites health monitoring using ultrasonic guided wave

Depth profiling of residual stress distribution in surface treated metallic structures using nonlinear ultrasonics

Robotic hammer peening (RHP) is a cold-working technique to improve the fatigue life of metallic structures by inducing compressive residual stress in the near-surface region. Measuring the depth profiling of residual stress distribution plays an important role in process design towards the advanced manufacturing of metallic structures. This study investigates the use of the nonlinear ultrasonic method to measure the residual stress profiles through the frequency-dependent penetration depth approach. Stainless steel specimens were treated with varying RHP intensities, and their morphological evolutions were characterized with a step-profilometer. The amplitudes of the second and third harmonic components of the longitudinal critically refracted (LCR) and Rayleigh waves were measured and analyzed. The effect of the surface roughness on the acoustic nonlinearity parameters before and after polishing at various peening intensities was briefly discussed. The results show a large variation in the acoustic nonlinearity parameter at the surface layer, indicating the potential of the proposed nonlinear ultrasonics for the measurement of depth profiling of residual stress.

Ultrasonic imaging of delamination in thick CFRP laminates using an energy-compensation reverse time migration method

In ultrasonic reflection method, the precision of defect detection in thick carbon fiber reinforced plastics (CFRP) is compromised by acoustic energy attenuation. An energy-compensation reverse time migration (ECRTM) method is proposed to identify multiple defects accurately. Forward and backward wavefields are formed using the finite element method within an anisotropic acoustic model based on the Christoffel equation and Bond transformation. To enhance the imaging quality of CFRP laminates, a novel cross-correlation imaging condition is introduced to compensate for energy dissipation caused by geometric diffusion and variations of the far-field radiation intensity at the emitter with the propagation direction. Employing ultrasonic detection technology with a multi-element array, numerical and experimental research on defect imaging was conducted, considering delamination with various sizes and positions in a multidirectional CFRP laminate. In comparison to other ultrasonic imaging methods, the near-surface artifacts in RTM images are mitigated by the far-field radiation directivity factor, while the deep information is enhanced by the geometric diffusion compensation factor in the ECRTM images. As a result, the precise position of delamination in CFRP laminates is achievable, demonstrating superior imaging capabilities, especially for deep delamination.