scholarly journals Evaluation of Damage Process of a Coating by Using Nonlinear Ultrasonic Method

Coatings ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 440
Author(s):  
Chunguang Xu ◽  
Lei He ◽  
Shiyuan Zhou ◽  
Dingguo Xiao ◽  
Pengzhi Ma
Keyword(s):  
Tensile Stress ◽  
Order Parameter ◽  
Evaluation Method ◽  
Early Stage ◽  
Ultrasonic Method ◽  
Nonlinear Coefficient ◽  
Damage Index ◽  
Second Order ◽  
External Loading ◽  
Nonlinear Ultrasonic

During the service or external loading of the surface coating, the damage accumulation may develop in the coating or at the interface between the substrate and the coating, but it is difficult to measure directly in the early stage, so the acoustic nonlinear parameters are used as the early damage index of the coating. In this paper, the nonlinear wave motion equation is solved by the perturbation method and the new relationship between the relative ratio of second-order parameter and third-order parameter was derived. The nonlinear ultrasonic testing system is used to detect received signals during tensile testing of for the specimen with Al2O3 coatings. It is found that when the stress is less than 260 MPa, the appearance of the coating has no obvious change, but the nonlinear coefficients measured by the experiment increase with the increase of the tensile stress. By comparing the curves of nonlinear coefficients and stress respectively, the fluctuation of curves the second-order nonlinear coefficient A2 and the relative nonlinear coefficient β′ to stress is relatively small, and close to the linear relationship with the tensile stress, which indicates that the two parameters of the specimen with Al2O3 coatings are more sensitive to the bonding conditions, and can be used as an evaluation method to track the coating damage.

scholarly journals Fatigue Damage Evaluation of Compressor Blade Based on Nonlinear Ultrasonic Nondestructive Testing

2021 ◽  
Vol 9 (12) ◽  
pp. 1358
Author(s):  
Pengfei Wang ◽  
Weiqiang Wang ◽  
Sanlong Zheng ◽  
Bingbing Chen ◽  
Zengliang Gao
Keyword(s):  
Fatigue Damage ◽  
Ultrasonic Testing ◽  
Evaluation Method ◽  
Early Stage ◽  
Nonlinear Coefficient ◽  
Crack Size ◽  
Compressor Blade ◽  
Three Dimensional Model ◽  
Micro Cracks ◽  
Nonlinear Ultrasonic

Nonlinear ultrasonic testing is highly sensitive to micro-defects and can be used to detect hidden damage and defects inside materials. At present, most tests are carried out on specimens, and there are few nonlinear ultrasonic tests for fatigue damage of compressor blades. A vibration fatigue test was carried out on compressor blade steel KMN, and blade specimens with different damage degrees were obtained. Then, the nonlinear coefficients of blade specimens were obtained by nonlinear ultrasonic testing. The results showed that the nonlinear coefficient increased with the increase in the number of fatigue cycles in the early stage of fatigue, and then the nonlinear coefficient decreased. The microstructures were observed by scanning electron microscopy (SEM). It was proven that the nonlinear ultrasonic testing can be used for the detection of micro-cracks in the early stage of fatigue. Through the statistical analysis of the size of the micro-cracks inside the material, the empirical formula of the nonlinear coefficient β and the equivalent crack size were obtained. Combined with the β–S–N three-dimensional model, an evaluation method based on the nonlinear ultrasonic testing for the early fatigue damage of the blade was proposed.

scholarly journals Properties of GH4169 Superalloy Characterized by Nonlinear Ultrasonic Waves

2015 ◽  
Vol 2015 ◽  
pp. 1-8
Author(s):  
Hongjuan Yan ◽  
Chunguang Xu ◽  
Dingguo Xiao ◽  
Haichao Cai
Keyword(s):  
Fatigue Life ◽  
Yield Strength ◽  
Tensile Stress ◽  
Fatigue Testing ◽  
Extreme Values ◽  
Nonlinear Coefficient ◽  
Ultrasonic Waves ◽  
Nonlinear Ultrasonic ◽  
Nonlinear Wave Motion ◽  
Gh4169 Superalloy

The nonlinear wave motion equation is solved by the perturbation method. The nonlinear ultrasonic coefficientsβandδare related to the fundamental and harmonic amplitudes. The nonlinear ultrasonic testing system is used to detect received signals during tensile testing and bending fatigue testing of GH4169 superalloy. The results show that the curves of nonlinear ultrasonic parameters as a function of tensile stress or fatigue life are approximately saddle. There are two stages in relationship curves of relative nonlinear coefficientsβ′ andδ′ versus stress and fatigue life. The relative nonlinear coefficientsβ′ andδ′ increase with tensile stress when tensile stress is lower than 65.8% of the yield strength, and they decrease with tensile stress when tensile stress is higher than 65.8% of the yield strength. The nonlinear coefficients have the extreme values at 53.3% of fatigue life. For the second order relative nonlinear coefficientβ′, there is good agreement between the experimental data and the comprehensive model. For the third order relative nonlinear coefficientδ′, however, the experiment data does not accord with the theoretical model.

scholarly journals Assessment of sensitization in AISI 304 stainless steel by nonlinear ultrasonic method

2013 ◽  
Vol 26 (5) ◽  
pp. 545-552 ◽  
Author(s):  
Saju T. Abraham ◽  
S. K. Albert ◽  
C. R. Das ◽  
N. Parvathavarthini ◽  
B. Venkatraman ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Ultrasonic Method ◽  
304 Stainless Steel ◽  
Aisi 304 Stainless Steel ◽  
Aisi 304 ◽  
Nonlinear Ultrasonic ◽  
Nonlinear Ultrasonic Method

An Analysis of the Robust Convergent Method for a Singularly Perturbed Linear System of Reaction–Diffusion Type Having Nonsmooth Data

2021 ◽  
pp. 2150056
Author(s):  
Sheetal Chawla ◽  
Jagbir Singh ◽  
Urmil
Keyword(s):  
Uniform Convergence ◽  
Order Parameter ◽  
Source Term ◽  
Reaction Diffusion ◽  
Shishkin Mesh ◽  
Second Order ◽  
Singularly Perturbed ◽  
Diffusion Type ◽  
Bakhvalov Mesh ◽  
Second Order Parameter

In this paper, a coupled system of [Formula: see text] second-order singularly perturbed differential equations of reaction–diffusion type with discontinuous source term subject to Dirichlet boundary conditions is studied, where the diffusive term of each equation is being multiplied by the small perturbation parameters having different magnitudes and coupled through their reactive term. A discontinuity in the source term causes the appearance of interior layers on either side of the point of discontinuity in the continuous solution in addition to the boundary layer at the end points of the domain. Unlike the case of a single equation, the considered system does not obey the maximum principle. To construct a numerical method, a classical finite difference scheme is defined in conjunction with a piecewise-uniform Shishkin mesh and a graded Bakhvalov mesh. Based on Green’s function theory, it has been proved that the proposed numerical scheme leads to an almost second-order parameter-uniform convergence for the Shishkin mesh and second-order parameter-uniform convergence for the Bakhvalov mesh. Numerical experiments are presented to illustrate the theoretical findings.

Photocross-Linked Second Order Nonlinear Optical Polymers

1990 ◽  
Vol 214 ◽  
Author(s):  
Y. M. Chen ◽  
B. K. Mandal ◽  
J. Y. Lee ◽  
P. Miller ◽  
J. Kumar ◽  
...  
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Nonlinear Optical ◽  
Nonlinear Coefficient ◽  
Second Order ◽  
Optical Polymers ◽  
Nlo Properties ◽  
Polymeric Thin Films ◽  
Nonlinear Optical Polymers ◽  
Novel Method

ABSTRACTWe report a novel method to obtain stable second order nonlinear optical (NLO) properties in polymeric thin films. Photocross-linking between the NLO active molecules and a photoreactive polymer is achieved by UV irradiation subsequent to poling. The thin film exhibits a nonlinear coefficient d33of 16.5 pm/V at a doping level of 20% by weight of NLO active molecules and possesses quite stable second order nonlinear optical properties

scholarly journals Nondestructive Evaluation of Thermal Barrier Coatings Interface Delamination Using Terahertz Technique Combined with SWT-PCA-GA-BP Algorithm

Coatings ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 859
Author(s):  
Dongdong Ye ◽  
Weize Wang ◽  
Changdong Yin ◽  
Zhou Xu ◽  
Huanjie Fang ◽  
...  
Keyword(s):  
Neural Network ◽  
Thermal Barrier Coatings ◽  
Time Domain ◽  
Evaluation Method ◽  
Structural Integrity ◽  
Early Stage ◽  
Percentage Error ◽  
Thermal Barrier ◽  
Barrier Coatings ◽  
Interface Delamination

Thermal barrier coatings (TBCs) are usually subjected to the combined action of compressive stress, tensile stress, and bending shear stress, resulting in the interfacial delamination of TBCs, and finally causing the ceramic top coat to peel off. Hence, it is vital to detect the early-stage subcritical delamination cracks. In this study, a novel hybrid artificial neural network combined with the terahertz nondestructive technology was presented to predict the thickness of interface delamination in the early stage. The finite difference time domain (FDTD) algorithm was used to obtain the raw terahertz time-domain signals of 32 TBCs samples with various thicknesses of interface delamination, not only that, the influence of roughness and the thickness of the ceramic top layer were considered comprehensively when modeling. The stationary wavelet transform (SWT) and principal component analysis (PCA) methods were employed to extract the signal features and reduce the data dimensions before modeling, to make the cumulative contribution rate reach 100%, the first 31 components of the SWT detail data was used as the input data during modeling. Finally, a back propagation (BP) neural network method optimized by the genetic algorithm (GA-BP) was proposed to set up the interface delamination thickness prediction model. As a result, the root correlation coefficient R2 reached over 0.95, the various errors—including the mean square error, mean squared percentage error, and mean absolute percentage error—were less than or equal to 0.53. All these indicators proved that the trained hybrid SWT-PCA-GA-BP model had excellent prediction performance and high accuracy. Finally, this work proposed a novel and convenient interface delamination evaluation method that could also be potentially utilized to evaluate the structural integrity of TBCs.

scholarly journals Can we determine what controls the spatio-temporal distribution of d-excess and <sup>17</sup>O-excess in precipitation using the LMDZ general circulation model?

2013 ◽  
Vol 9 (5) ◽  
pp. 2173-2193 ◽  
Author(s):  
C. Risi ◽  
A. Landais ◽  
R. Winkler ◽  
F. Vimeux
Keyword(s):  
General Circulation Model ◽  
Order Parameter ◽  
General Circulation ◽  
Temporal Distribution ◽  
Circulation Model ◽  
Second Order ◽  
Polar Ice ◽  
Spatio Temporal ◽  
Different Origins ◽  
Second Order Parameter

Abstract. Combined measurements of the H218O and HDO isotopic ratios in precipitation, leading to second-order parameter D-excess, have provided additional constraints on past climates compared to the H218O isotopic ratio alone. More recently, measurements of H217O have led to another second-order parameter: 17O-excess. Recent studies suggest that 17O-excess in polar ice may provide information on evaporative conditions at the moisture source. However, the processes controlling the spatio-temporal distribution of 17O-excess are still far from being fully understood. We use the isotopic general circulation model (GCM) LMDZ to better understand what controls d-excess and 17O-excess in precipitation at present-day (PD) and during the last glacial maximum (LGM). The simulation of D-excess and 17O-excess is evaluated against measurements in meteoric water, water vapor and polar ice cores. A set of sensitivity tests and diagnostics are used to quantify the relative effects of evaporative conditions (sea surface temperature and relative humidity), Rayleigh distillation, mixing between vapors from different origins, precipitation re-evaporation and supersaturation during condensation at low temperature. In LMDZ, simulations suggest that in the tropics convective processes and rain re-evaporation are important controls on precipitation D-excess and 17O-excess. In higher latitudes, the effect of distillation, mixing between vapors from different origins and supersaturation are the most important controls. For example, the lower d-excess and 17O-excess at LGM simulated at LGM are mainly due to the supersaturation effect. The effect of supersaturation is however very sensitive to a parameter whose tuning would require more measurements and laboratory experiments. Evaporative conditions had previously been suggested to be key controlling factors of d-excess and 17O-excess, but LMDZ underestimates their role. More generally, some shortcomings in the simulation of 17O-excess by LMDZ suggest that general circulation models are not yet the perfect tool to quantify with confidence all processes controlling 17O-excess.

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