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This paper presents a study on non-destructive crack detection and localization by nonlinear laser ultrasonic and state-space-based method, without using any reference data from the undamaged structure. After irradiated by laser pulse, ultrasonic waves will be generated and propagate in a structure. The corresponding waves are recorded by a transducer placed at a fixed point on the structure. State space based attractors are reconstructed based on the recorded data, and a nonlinear crack-sensitive metric called average local attractor variance ratio (ALAVR) is extracted to detect the differences between adj acent attractors, hence the crack. Furthermore, laser scanning technique is proposed to locate the crack on the structure. The proposed technique has been successfully used for detecting and locating artificial crack in an aluminum plate and an actual sand inclusion crack in a compressor body.

Laser ultrasonic has been widely investigated for its high spatial resolution, non-contact generation and distant testing. In this study, the laser induced waves on a cylinder is simulated based on an explicit finite element model, and the location of the surface-breaking crack is determined using signal enhancement of surface waves on the cylinder. A feature is extracted based on wavelet packet transform and singularity value decomposition (WPT-SVD) to gauge the depth of surface-breaking crack. The simulation results show that the feature is sensitive to the surface-breaking crack, with an accurate location determined by an enhancement of surface waves when the crack is close to the laser source. This study provides a potential application for testing surface-breaking cracks on the rotating cylindrical component.

The appearance of damage on metallic structures is inevitable due to complex working environments. Non-destructive testing (NDT) of these structures is critical to the safe operation of the equipment. This paper presents a non-destructive damage detection, visualization, and quantification technique based on laser-generated ultrasonics. The undamaged and damaged metallic structures are irradiated with laser pulses to produce broadband input ultrasonic waves. Damage to the structures plays the role of a nonlinear radiation source of new frequencies. Usually these new frequencies are too weak to be detected directly. Here, the state space predictive model is proposed to address the problem. Based on the recorded responses in the time domain, the state space attractors are reconstructed. Damage to the structures is shown to change the properties of the attractors. A nonlinear damage detection feature called normalized nonlinear prediction error (NNPE) is extracted from the state space to identify the changes in the attractors—and hence the damage. Furthermore, the damage is visualized and quantified using the NNPE values extracted from the entire area by using a laser scanning technique. Experimental results validate that the proposed technique is capable of detecting, visualizing and quantifying artificial damage to aluminum alloy plates and actual fatigue cracks to a twin-screw compressor body.

C23H21NO6, triclinic, P1̄ (no. 2), a = 7.624(4) Å, b = 9.197(5) Å, c = 15.058(5) Å, α = 94.13(3)°, β = 102.27(3)°, γ = 106.72(3)°, V = 977.9(8) Å3, Z = 2, R gt(F) = 0.0662, wR ref(F 2) = 0.1733, T = 296(2) K.

As the optical penetration depth and thermal diffusion effect are small, shear waves and longitudinal waves generated by a laser pulse in thermoelastic regime are generally weak in metallic materials. The method of laser ultrasonic is rarely applied to inspect the inner cracks. In this paper, phased array laser ultrasonic is developed to focus and steer shear waves and longitudinal waves, and obtain inner crack characteristics. Firstly, a two-dimensional laser phased array finite element model is established. Secondly, based on this model, a study on numerical simulation of interaction between shear waves and cracks is conducted by adjusting time delay of laser phased array. It is found by analysis that the position of cracks can be determined by monitoring changes of polarity of shear-tip-shear (STS) diffraction received on the surface of metallic materials and the depth of cracks can be determined by the time of flight of STS diffraction and shear-tip-longitudinal (STL) diffraction. Last of all, a study on numerical simulation of interaction between longitudinal waves and cracks is also conducted. This study provides a possible method for the detection of inner cracks in metallic materials.

Cylindrical structures play an important role in industrial fields. The surface crack is a typical defect in the cylindrical structures. Non-destructive surface crack detection of these structures is critical to the safe operation of the equipment. In this study, the signal enhancement of the scanning laser line source (SLLS) method is investigated by a numerical simulation method to identify the location and depth of the surface crack in the aluminum cylinder. A fully coupled explicit finite element model is established to study the signal enhancement of cylindrical surface waves on the aluminum cylinder. The simulation results indicate that the signal enhancement of the SLLS is more sensitive to the surface crack of a cylinder than that of the scanning laser detection (SLD) because of the wider span and higher peak. Due to the phase shift characteristics of surface waves on the cylinder, the maximum peak-to-peak amplitude of signal enhancement in the SLLS method (the SLLS peak) is affected by the detection position and diameter of the cylinder. Therefore, an optimization approach for detection position in SLLS is proposed for the location of surface crack on the cylinder. The locations of the surface crack on the solid cylinders with different diameters are investigated using simulated laser ultrasonic field data. Moreover, we find that the SLLS peak for signal enhancement can effectively respond to the crack depth within a limited scope which is dependent on the directivity pattern of the longitudinal waves.