Nonlinear Damage Research Articles

Nonlinear ultrasonic concrete crack identification with deep learning based on time-frequency image

ABSTRACT By combining time-frequency images and deep learning models, the nonlinear ultrasound signals can be classified, detected, and predicted, using the nonlinear coefficient as a fundamental label for training deep learning models. This integrated approach enables quantitative identification and real-time monitoring of concrete damage, promoting the widespread adoption of nonlinear ultrasonic techniques in engineering applications. As a basis, the relationship between damage variations and nonlinear coefficients is discussed by performing nonlinear ultrasonic damage testing on concrete specimens with different crack lengths and angles. The testing signals are converted into time-frequency images using the short-time Fourier transform and the continuous wavelet transform, and both types of images are combined for data augmentation and input into the deep learning model for training, with nonlinear coefficients serving as labels for the time-frequency images. The MobileNetV2, VGG16, and ResNet18 deep learning models are trained separately on time-frequency image datasets for the length specimens, the angle specimens, and the length-angle specimens, and the performance of the different models is evaluated and compared. The results show that all three models have accuracy rates above 94%, indicating good identification performance. Finally, with the example, the nonlinear coefficients of the testing signals are compared with the labels of the nonlinear coefficients in the time-frequency images identified by the deep learning model, which confirms the high accuracy of damage identification by the deep learning model.

A prince for the sleeping beauty - NFT for soliton signal processing

The soliton, the eigen-solution of nonlinear Schrodinger equation (NLSE), has been investigated in many branches of physics. The first prediction of a soliton in optical fiber could be dated back to 1973. Since then, numerous theoretical and experimental works on solitons have been carried out, including soliton communication and soliton generation in fiber lasers. However, due to the constraints of hardware and digital signal processing methods, research on solitons have been stalled for decades. Recently, the nonlinear Fourier transform (NFT) has attracted significant attention in the field of optical fiber communications and soliton-based signal processing, which provides a powerful mathematical framework for analyzing and understanding the behavior of solitons in optical fibers, enabling the development of novel signal processing techniques. The NFT technique has brought the soliton back to life. It has been widely recognized that in nonlinear frequency domain, the nonlinear crosstalk resulting from the Kerr effect is practically negligible, and fiber nonlinearity damage caused by the Kerr effect can be accounted for as a linear transform factor. Moreover, NFT has been demonstrated for the analysis of laser radiation, highlighting its potential in characterizing ultrafast pulses in the nonlinear frequency domain. In this submission, we review the advancements of NFT concerning both in soliton communication and characterization, focusing on practical implementation aspects. With many practical implementation aspects still being open, our mini review is aimed to assist researchers in evaluating the potential, identifying challenges, and envisioning future directions in NFT-based signal processing technologies. And wake up the sleeping beauty – the soliton!

Meso to macro connections to capture fatigue damage in cemented materials

Fatigue-induced damage is a common issue in cemented materials, involving the progressive formation and complicated propagation of fatigue cracks. These cracks typically localise on weak or fracture planes, leading to inhomogeneous deformation within the material. Thus, accurately predicting the fatigue phenomenon becomes challenging due to the material’s inhomogeneity and the complex evolution of cracks, from initiation to propagation and eventual failure. To address this challenge, this paper presents a constitutive model that accounts for strain discontinuity across fracture planes by employing kinematic enrichment. This enhancement facilitates interaction between the material responses of cracks and the outer bulk, thereby contributing to the overall macro behaviour of the materials. Moreover, the proposed model incorporates a new cohesive-frictional fatigue model that couples damage mechanics and bounding surface plasticity to describe the fatigue behaviour of fracture planes/cracks. Since the proposed model features a characteristic length scale, it exhibits size-dependent behaviour and helps overcome the issue of mesh dependence. The model's validity is demonstrated through its ability to capture nonlinear fatigue damage under constant/variable cyclic loading and to simulate the propagation of fatigue fracture process zones. Furthermore, the model effectively captures the significant influence of stress amplitudes on the fatigue lives of materials, making it an essential tool for predicting and mitigating fatigue-induced damage in cemented materials.

Nonlinear processes and laser damage induced by a temporally modulated nanosecond UV laser beam. Part I: stimulated Brillouin scattering

Phase modulation is currently applied on pump laser beams propagating in thick optical elements to avoid optical damage induced by Brillouin backscattering. The experimental measurements show that adding a 2 GHz amplitude modulation to such a phase-modulated laser beam can compromise this optical preservation by increasing the Brillouin backscattering signal. These results are confirmed and explained with a theoretical analysis, developed in the perturbative regime, and with the numerical results obtained by solving three-wave coupling equations. Particularly, we show that when the frequency of the amplitude modulation is a harmonic of the phase modulation frequency, the Brillouin gain value is increased and can exceed the one obtained without amplitude modulation.

Nonlinear processes and laser damage induced by a temporally modulated nanosecond UV laser beam. Part II: Kerr self-focusing

In this paper, we study the impact of Kerr self-focusing on laser-induced damage of fused silica with temporal modulation. In our experiments, temporal modulations are generated with high bandwidth amplitude modulators between 2 and 10 GHz. Measurement of the spatial profile after propagation is made possible due to a dedicated imaging setup. First results without temporal modulation experimentally and numerically show that the nonlinear gain increases exponentially with intensity. Complementary experiments with temporal modulation at different frequencies show an increase in the nonlinear gain. Eventually, we show that laser-induced damage is enhanced with amplitude modulation, with a dependence on the frequency of the amplitude modulation. Optimization of phase modulation allowed us to mitigate backwards stimulated Brillouin scattering and to focus on the sole impact of Kerr self-focusing on laser-induced damage.

Using a non-linear mixed model behavior of CZM to predict the damage in single lap bonded joint with Bi-composite graded materials

The present work is a numerical prediction based initially on a reliable model validated by experiments under the same conditions used as ours with new concepts in Bi-composite plates. A system formulation approach of the adhesive in ductile and nonlinear damage behavior is used in this analysis This ductility is developed by the CZM technique implemented using the MATLAB program in ABAQUS computer code. For a numerical prediction of the ductile behavior of the adhesive, the CZM model is an extension of the pure modes (I and II) previously characterized in block by tests. This extension is trapezoidal in increasing stresses of the adhesive in its behavior law. The single lap joint configuration allows us to stress the glue joint to mixed-mode loading. The resistance of the assembled structures remains conditioned by the behavior of the adhesive until it is damaged and the rigidity of the attached plates. Therefore, our objective in this work is to cause the plasticization damage of the adhesive at different responses and levels. For this, the bi-composite graduation in concept and in graduation index largely plays the role of evaluation parameters. In order to test the adequacy for a good resistance, three different concepts of graduation in Bi-composite were proposed such as: concept1-concept1, concept2-concept2, and simple concept-simple concept. By these two cases of assemblies, these concepts have the advantage of having different assembly possibilities, The proposed concepts of graduated bi-composite plates showed an overcapacity of resistance on the assembly. The latter becomes important in the adequacy of concept of these assembled plates. Similarly, the results show that different responses and levels cause the damage by effect of these concepts.

Study on Creep Characteristics and Nonlinear Fractional-Order Damage Constitutive Model of Weakly Cemented Soft Rock

Study on Creep Characteristics and Nonlinear Fractional-Order Damage Constitutive Model of Weakly Cemented Soft Rock

Analysis of Mechanical Properties and Failure Mechanism of Lightweight Aggregate Concrete Based on Meso Level.

The relationship between the macroscopic mechanical properties of lightweight aggregate concrete and its microstructure is a hot topic in the discipline of concrete materials. It is very meaningful to provide an efficient numerical analysis method to conduct a meso-level analysis. This study proposes an automatic dissection algorithm and adapts the calculation program of the base force element method to conduct a non-linear damage analysis. In the numerical simulation, three groups of 100 mm × 100 mm × 100 mm specimens were selected for the uniaxial compression experiment and uniaxial tensile experiment, respectively. The average tensile strength of the numerical simulation for the uniaxial compression test was 21.86 MPa. The stress-strain softening curve, stress contour plot, strain contour plot, and damage plot of the light aggregate concrete were also analyzed. These research results provide data for analyzing the failure mechanism of light aggregate concrete and reveal the failure mechanism of light aggregate concrete. At the same time, the reliability of the proposed algorithm is verified. Our aim is to provide a more efficient and accurate analysis of meso-damage in lightweight aggregate concrete, which benefits industries involved in production, construction, and structural engineering.

Three-dimensional nonlinear model of rock creep under freeze-thaw cycles.

In areas with large differences between day and night temperature, the freeze-thaw cycle and frost heaving force in rock mass generate cracks within the rock, which seriously threatens the stability and safety of geotechnical engineering structures and surrounding buildings. This problem can be solved by developing a reasonable model that accurately represents the rock creep behavior. In this study, we developed a nonlinear viscoelastic-plastic creep damage model by introducing material parameters and a damage factor while connecting an elastomer, a viscosity elastomer, a Kelvin element, and a viscoelastic-plastic element in series. One- and three-dimensional creep equations were derived, and triaxial creep data were used to determine the model parameters and to validate the model. The results showed that the nonlinear viscoelastic-plastic creep damage model can accurately describe rock deformation in three creep stages under freeze-thaw cycles. In addition, the model can describe the time-dependent strain in the third stage. Parameters G1, G2, and η20' decrease exponentially with the increase in the number of freeze-thaw cycles while parameter λ increases exponentially. These results provide a theoretical basis for studying the deformation behavior and long-term stability of geotechnical engineering structures in areas with large diurnal temperature differences.

Demonstration high-order QAM transmission based on one-bit delta-sigma modulation in radio-over-fiber system

In the letter, we propose to use delta-sigma modulator (DSM) technology to transmit OFDM high-order QAM signals in a single-carrier radio-over-fiber (RoF) system, and conduct experimental verification. The experiment demonstrates the transmission of OFDM-256/1024/4096 QAM signals using one-bit DSM in the W band in a 20 km SSMF and 1 m wireless RoF system, and successfully realized that the BER of OFDM-256 and 1024 QAM after system transmission is lower than the hard decision forward error correction (HD-FEC) threshold of 3.8 × 10−3, and the BER after 4096 QAM transmission is lower than the soft decision forward error correction (SD-FEC) threshold of 4.0 × 10−2. The combination of DSM and the photonics-aided RoF solution can effectively solve the problem that the nonlinear damage caused by the bottleneck of the optoelectronic device in the RoF system limits the transmission of high-order QAM signals, and it is expected to be applied in the future 6G optical wireless network.

A versatile and highly efficient algorithm to generate representative microstructures for heterogeneous materials

In this study, a novel approach based on the maximum penetration-biased (MPB) algorithm is proposed to rapidly generate representative volume elements (RVEs) for advanced composites. This method is capable of handling various microstructural features such as nonuniform distribution of high-volume fractions, concave or convex inclusions and the control of inter-inclusion distances. Statistical functions from short-range to long-range demonstrate that the resulting microstructures are complete spatial random, and the microstructures observed in realistic composites can be reproduced by the proposed algorithm. Accurate prediction for the elastic properties and transverse isotropy of the generated microstructures with varying inclusion shapes using homogenization method further verify the validity of the developed method. A nonlinear damage study compared to the circular inclusion reveals that the capsule shape leads to a reduction of strength of unidirectional fiber reinforced composites under transverse tension or compression while the lobular inclusion presents a deterioration of strength under tension but an enhancement of strength in compression. The MPB algorithm provides an effective tool for micromechanical assessment, quantitative research and data-driven studies such as machine learning of composites.

Casting and spinning aluminum alloy wheel fatigue properties and life prediction study

AbstractTo accurately predict the fatigue life of cast aluminum alloy wheels, based on the results of finite element calculation and simulation, this work selected the rim area, inner flange and spoke areas to conduct systematic tensile and high‐cycle fatigue tests. The results show that the tensile properties of A356‐T6 cast aluminum alloy wheels are similar in various areas, but the fatigue properties are significantly different. Plastic deformation can improve the fatigue strength of the aluminum alloy, but the fatigue properties are also affected by deformation uniformity and other factors. Based on the difference of mechanical properties in different areas, this study also selected the characteristic loading spectrum to predict the fatigue life of wheels. A linear and a nonlinear damage accumulation were employed. The above methods are not only applicable to the wheel, but also provides a new idea for the life prediction of key parts in the engineering field.

Structural nonlinear damage identification based on the information distance of GNPAX/GARCH model and its experimental study

In the structural health monitoring (SHM) of civil engineering, most of the structural damage is nonlinear damage, such as breathing cracks and bolt looseness. Under the excitation of external loads, the time-domain response data of the structure produced by these nonlinear damages have nonlinear features. In order to solve the time-domain nonlinear damage identification problem of complex structures, this paper proposes a nonlinear damage identification method based on the information distance of GNPAX/GARCH (general expression of system identification for linear and nonlinear with polynomial approximation and exogenous inputs/generalized autoregressive conditional heteroskedasticity) model. First, an order determination method based on Bayesian optimization to select the order of the GNPAX/GARCH model was proposed, and the GNPAX/GARCH model was established for damage identification. Then, the redundant structural items of GNPAX/GARCH model were removed by the model optimization method based on the structural pruning algorithm. Finally, the information distance of the GNPAX/GARCH model conditional heteroscedasticity series between the baseline state and test state was derived, and the structural damage source locations were determined according to the information distance. A three-story frame structure experiment and a stand structure experiment were used to verify the effectiveness of the proposed method. The results show that the proposed method can effectively identify the nonlinear damages caused by the component breathing crack and joint bolt looseness, verifying its robustness to the nonlinear damage identification of the multi-story and multi-span complex structures.

Comprehensive progressive damage analyses of mixed‐mode repaired panels: How composite patch sizes and layups affects restarting fatigue crack growth

AbstractIn this paper, comprehensive progressive damage analyses are performed to evaluate the effects of patch sizes and layups on restarting crack growth of single‐side repaired aluminum panels with central inclined cracks under high cycle fatigue loading. Complicated nonlinear damage behavior of adhesive bonding, composite patch, mixed‐mode cracks, and fatigue loadings require precise numerical tools to consider and analyze the coupling effects of various damages on fatigue life of such complex component. In progressive damage analysis, high cycle fatigue cohesive zone modeling is used for debonding of patch, and high cycle fatigue continuum damage model used for composite patches. Practical composite patch layups and sizes are selected in huge number of models, and the restarting crack growth life is predicted. The obtained results show the possibility of increasing the restarting crack growth life using an appropriate composite patch layup and geometry dimensions.

The Parametric High-Fidelity-Generalized-Method-of-Cells with phase-field damage micromechanical model for heterogeneous composites

A new coupled micromechanical-damage formulation is presented by directly integrating the phase-field (PF) modeling approach for fracture and damage with the Parametric High-Fidelity-Generalized-Method-of-Cells (PHFGMC) micromechanical model. The combined PHFGMC-PF approach is proposed for progressive damage analysis of multi-phase heterogeneous composites with evolving microstructure subject to general multi-axial remote loading. New variational equations are introduced to couple the macro/micro deformation and PF variables of the discrete finite volumes (subcells). An iterative computational formulation is also presented for the numerical solution of the overall nonlinear equations. The proposed approach can accommodate various phase-field damage models and fracture energy approximations. Two PF damage laws, available in the literature, are implemented. The proposed PHFGMC-PF model verification is first accomplished by solving the single-edge crack problem under tension and shear and comparing the results to a finite element PF (FE-PF) analysis. Results of the presented case studies demonstrate a comparable ability of the PHFGMC-PF to solve similar FE-PF non-periodic problems. Applications are presented for progressive damage of carbon-fiber-reinforced (CRP) composites. The PHFGMC-PF in-situ elastic and fracture properties are calibrated for the carbon-reinforced polymer IM7/977-3 composite material system at the fiber–interface–matrix constituents. The micromechanics-PF model can capture the composite overall nonlinear mechanical and damage responses compared to experimental data.

Refined simulation method and failure study of BGA package structure based on image drive

The packaging structure, internal defects, and external loads have a significant impact on the reliability and ultimate failure of chip performance. Therefore, establishing a refined model that considers multiple factors is of great significance for improving the reliability and optimizing design of packaging structures. For this purpose, this study firstly adopts CT scanning technology to reconstruct the ball grid array (BGA) package structure in three dimensions, optimize the finite element meshing, and analyze the drop behavior by using the finite element method based on nonlinear damage instantiation. In addition, to further investigate the effect of fine defects on the failure of the package structure, a simulation of the damage evolution behavior of a real defective solder ball structure under impact loading is implemented with the help of submodeling techniques. The research results provide a technical reference for the reliability analysis and multi-occasion structure design of aerospace BGA package structures.

Nonlinear progressive damage model for woven patch-repaired laminate composites

Laminated fiber-reinforced composite materials are vulnerable to damages arising due to impact events like accidental tool drops, bird strikes, etc., which significantly reduce the structural integrity of these materials. Therefore, one of the popular adhesively bonded repair techniques, i.e. patch repair is employed in this work. The present work focuses on developing a three-dimensional energy-based gradual degradation model for patch-repaired laminates, including the effects of shear non-linearity under tensile load. The model utilizes modified Hashin failure criteria for plain woven laminate and maximum shear stress criteria for the adhesive. Using the nonlinear model, the failure strengths for different pristine, drilled and repaired specimens with double-sided patches of [0]2 and [45]2 are studied. Tensile experiments in accordance with ASTM-D3039/D3039M are performed using Digital Image Correlation (DIC) and Acoustic Emission (AE) to validate numerical results. The simulated results based on the proposed model and experimental observations are used to compare the damage mechanisms of pristine, drilled, and patch-repaired laminates. It is observed that matrix cracking is majorly responsible for damage initiation. Subsequently, fiber–matrix debonding and fiber breakage account for the ultimate failure of pristine, drilled and repaired specimens. The developed model is used for studying the effect of different patch sizes of repaired specimens under tensile load.

Two-dimensional material integrated micro-nano fiber, the new opportunity in all-optical signal processing

Abstract With the development of all-optical networks, all-optical devices have become a research hotspot in recent years. Two-dimensional materials, represented by graphene and black phosphorus, have attracted great interest in the scientific community due to their excellent optical, electrical, magnetic, and mechanical properties. Bridging the gap between fiber optics and nanotechnology, microfibers can interact with light and matter at the micro or even nanoscale. By combining two-dimensional materials with microfibers, composite waveguides can be formed. They have the advantages of high nonlinear effect, all-fiber structure, and high damage threshold, etc. The composite waveguide can be directly applied to optical fiber communication systems, and plays an important role in the field of all-optical signal processing with a huge application prospect. In this review, the properties of typical 2D materials are first introduced. Next, the preparation methods of the relevant equipments are introduced and compared. Then, the all-optical signal processing technology based on 2D material-integrated microfiber composite waveguide is reviewed. The latest developments of all-optical modulators, all-optical wavelength converters, all-optical logic gates and all-optical thresholding devices are presented. Finally, the challenges and opportunities for the future development of 2D materials-integrated microfiber optoelectronic devices are summarized.

Three-Dimensional Numerical Simulation for Lateral Distortional Buckling Behaviour of Steel-Concrete Composite Beams

Lateral Distortional Buckling (LDB) is a mode of instability in Steel-Concrete Composite (SCC) beams that is yet to be fully understood by the structural engineering research and design community. This work investigated numerical methods to understand the LDB behavior of SCC beams under negative moments that exhibit nonlinear behavior. Focus of the study was to develop and validate 3-Dimensional finite element (FE) models which capture the LDB behavior of SCC beams precisely. Detailed 3-Dimensional FE models of the SCC beams were developed using ABAQUS. For modeling concrete, a nonlinear damage plasticity model was considered. A quad-linear curve was used to describe the stress-stain relationship for the steel beam. The stress-stain relationship for the rebar was described using a bi-linear curve while an elastic perfectly plastic model was assigned to the headed stud shear connectors. Steel hardening behavior was simulated using an isotropic hardening model. The interaction between the concrete slab, steel beam, and studs was described using appropriate interface elements combined under suitable constraints. The FE model’s accuracy was validated by results obtained from previous experiments found in literature together with a brief description of the experiments done by previous researchers to ensure completeness. Validation of the model was done by comparing Moment-Rotation curves obtained from the experimental tests, lateral displacements of the bottom flange along the axial direction and comparison of the failure modes between the numerical model and experimental test specimens. It was observed that the maximum relative error for the ultimate moment capacity of the composite beams from FE analysis and the experimental tests was less than 2% which shows that the FE model was in strong agreement with the experimental results. Accordingly, the numerical model developed herein proves to be capable of accurately representing the LDB phenomenon.

Tosylate family crystals for optoelectronic applications

Since the discovery of lasers, high-quality nonlinear optical (NLO) single crystals have served as the foundation for the creation of novel, cutting-edge devices that meet societal demands. Modern optoelectronic applications such as telecommunication lasers, optical fibers, photodiodes, solar cells, etc. favor high-performance nonlinear optical single crystals with improved optical nonlinearity. Organic crystals are extensively explored for these applications because of their high NLO coefficient. This paper deals with the problems and advancements of organic nonlinear optical single crystals. Here, we review the growth and characterizations of various tosylate family crystals from the vast realm of organic single crystals and their potential applications in the field of optoelectronic devices. Various properties like linear and nonlinear optical, thermal, mechanical, and laser damage threshold values for these samples have been summarized. The attempts are made for highlighting how these tosylate (p-Toluenesulfonic acid based) family crystals can be realized into efficient optoelectronic devices by summarizing variously reported cut-off wavelengths and their wide transmission ranges.