Initial Stage Of Damage Research Articles

Dynamic nonlinearities for identification of the breathing crack type damage in reinforced concrete bridges

Reinforced concrete structures experience nonlinear vibration response because of softening in concrete due to damage, which results in unstable vibration. Thus, considering the nonlinearity in vibration for assessment of damage is imperative to identify the actual damage scenario. Nonlinearity is predominant during the initial stage of damage when cracks start developing in the concrete exhibiting nonlinear breathing-crack mechanism. By suitably extracting nonlinear features from ambient/forced vibration, information on initial stage of damage (primarily breathing-crack) in large concrete structures can be obtained. In the present study, evaluation of nonlinear dynamic features from an experimental model of a reinforced concrete bridge girder-deck system is investigated. The damage scenarios in the bridge girder is experimentally simulated by monotonically applied static load at different levels. Vibration responses are acquired using the accelerometers positioned at regular intervals, so that the global system behaviour can be assessed. Damage features at various damage levels are evaluated based on the signal statistics, amplitude dependency, harmonics, phase-plane information and so on. The breathing-crack behaviour of the bridge girder during initial damage stages is investigated and the existence of sub- and super-harmonic components in the frequency spectra is distinctly evidenced and their amplitudes are quantified. The change of skewness pattern of the frequency spectra with increasing damage level is also evaluated. A distinct variation in phase space portrait is observed with increase in damage levels. It is found that, in spite of presence of inherent material nonlinearity, nonlinearity caused through system damage, even at initial stages of damage, is predominant and could be distinctly captured without any baseline information. The identified nonlinear vibration characteristics showed a remarkable relevance in detecting breathing-crack type damage in weakly nonlinear bridge. The investigated damage features from this study would pave the way for real-time baseline free assessment and identification of damage in concrete structures.

Fault-tolerant elastic-plastic lattice material.

The paper describes a fault-tolerant design of a special two-dimensional beam lattice. The morphology of such lattices was suggested in the theoretical papers (Cherkaev and Ryvkin 2019 Arch. Appl. Mech. 89, 485-501; Cherkaev and Ryvkin 2019 Arch. Appl. Mech. 89, 503-519), where its superior properties were found numerically. The proposed design consists of beam elements with two different thicknesses; the lattice is macro-isotropic and stretch dominated. Here, we experimentally verify the fault-tolerant properties of these lattices. The specimens were three-dimensional-printed from the VeroWhite elastoplastic material. The lattice is subjected to uniaxial tensile loading. Due to its morphology, the failed beams are evenly distributed in the lattice at the initial stage of damage; at this stage, the material remains intact, preserves its bearing ability, and supports relatively high strains before the final failure. At the initial phase of damage, the thinner beams buckle; then another group of separated thin beams plastically yield and rupture. The fatal macro-crack propagates after the distributed damage reaches a critical level. This initial distributed damage stage allows for a better energy absorption rate before the catastrophic failure of the structure. The experimental results are supported by simulations which confirm that the proposed fault-tolerant material possesses excellent energy absorption properties thanks to the distributed damage stage phenomenon. This article is part of the theme issue 'Modelling of dynamic phenomena and localization in structured media (part 2)'.

Experimental research on seismic damage of a full-web SRC frame structure

An experiment was conducted to investigate the seismic damage of a full-web steel-reinforced concrete (SRC) frame structure. A 1/3 scale, 2-bay, 3-story model of the full-web SRC frame was designed and constructed, and the load-displacement hysteretic curve, stiffness and strength degradation, displacement ductility, energy dissipation, crack propagation, failure mechanism, damage parameter, and evolution of seismic damage were investigated under low-reversed cyclic lateral loading. Based on an existing seismic damage model, the damage index was calculated and cumulative damage of the frame model was determined. The experimental results showed that the damage process of the full-web SRC frame structure consisted of four stages - namely, the undamaged stage, initial damage stage, stable development stage, the rapid development stage. Frame beams were damaged first, followed by damage to frame columns; Frame beams experienced the greatest damage. The damage value was largest for the first floor of the structure. Damage values calculated with the two methods were similar and accurately reflected the evolution of seismic damage. The research results can provide a theoretical basis for post-earthquake damage assessment of a full-web SRC frame structure.

The p21 dependent G2 arrest of the cell cycle in epithelial tubular cells links to the early stage of renal fibrosis

Renal fibrosis is accompanied by the progression of chronic kidney disease. Despite a number of past and ongoing studies, our understanding of the underlying mechanisms remains elusive. Here we explored the progression of renal fibrosis using a mouse model of unilateral ureter obstruction. We found that in the initial stage of damage, where extracellular matrix was not yet deposited, proximal tubular cells arrested at G2 of the cell cycle. Further analyses indicated that the cyclin-dependent kinase inhibitor p21 is partially involved in the G2 arrest after the damage. A newly produced monoclonal antibody against p21 revealed that levels of p21 were sharply upregulated in response to the damage during the initial stage but dropped toward the later stage. To investigate the requirement of p21 for the progression of renal fibrosis, we constructed the novel p21 deficient mice by i-GONAD method. Compared with wild-type mice, p21 deficient mice showed exacerbation of the fibrosis. Thus we propose that during the initial stage of the renal damage, tubular cells arrest in G2 partially depending on p21, thereby safeguarding kidney functions.

The influence of longitudinal crack on mechanical behavior of shield tunnel lining in soft-hard composite strata

Concrete cracking is a common structural defect of segmentally lined tunnels. In this article, the tunnel between Shangteng station and Dadao station of Fuzhou metro line one, which mainly passes through the two-layered (sand and medium-weathered granite) composite strata, was taken as an example to study this issue. First, the cracking situation of segmental linings was investigated from on-site inspection and the cracking mechanism is revealed through numerical simulation. Then, similarity model tests were conducted to study the mechanical response of lining with a non-through longitudinal crack. Finally, a new numerical approach for cracked segment was put forward to analyze the mechanical behavior of lining with multi-cracks. The results show that: (1) Longitudinal cracks and corner cracks are the main cracking types of segment, and the difference in jacking thrusts determines the cracking patterns. (2) The influence of crack on inner force distribution along tunnel perimeter shows joint truncation effect and amplification effect of heterogeneous formation, and the influencing degree can be classified into three levels: serious effect, general effect and weak effect. (3) The failure process of lining has four distinct stages: elastic stage, initial damage stage, ultimate limit stage, and unstable stage. In addition, the pre-existing crack will develop along the longitudinal direction and be crushed under the action of external load in most cases. (4) The influence of multi-cracks on the inner forces of lining shows no coupling effect. In addition, the asymmetrically mechanical response of lining is affected by two factors: the difference in mechanical parameters of layered strata and the difference in stiffness of cracked and non-cracked sections. (5) The damage degree of crack, the depth of surcharged soil, and the proportion of soft soil in the tunnel section are the three main factors influencing the safety of lining.

Progressive failure process of secondary lining of a tunnel under creep effect of surrounding rock

During the operation of tunnels, a problem that is encountered often is the cracking of secondary lining caused by the time-dependent deformation of weak surrounding rocks. In this article, the Dujia mountain tunnel, which is situated in a weak and crushing phyllite stratum, was taken as an example to study this issue. First, we conducted a field investigation of the cracking situation of the secondary lining. Then, the similarity model test and particle-discrete-element numerical approach were used to study the failure process of the secondary lining. The results showed that the similarity model test and the results of numerical simulation were consistent with respect to the order in which cracks occurred and the final failure pattern. The progressive failure process can be divided into four stages, i.e., (1) the elastic stage, (2) the initial damage stage, (3) the ultimate limit stage, and (4) the instability stage. For a lateral pressure coefficient (λ) > 1, cracks initially appeared at the left haunch, the right haunch, and the spandrel due to bending damage caused by large-eccentricity compression. For λ = 1, cracks appeared first at the left arch springing because of the compressive and shear damage. For λ < 1, the bending damage first occurred at the spandrel. For the secondary lining with pre-existing cracks, micro-cracks were first generated where pre-existing cracks initially existed, and one or two hinges appeared at the location of the pre-existing cracks when the structure was in its ultimate limit stage. A void behind lining influenced the cracking pattern of the secondary lining in three different ways, i.e., (1) no effect; (2) the order in which cracks emerged was affected, but the final fracture pattern was not; and (3) the order in which cracks emerged and the final fracture pattern were affected.

Damage behavior of low velocity impact test on glass fiber reinforced poly (ethylene terephthalate) composites

In this study, to enhance the properties of recycled poly (ethylene terephthalate) (r-PET), the direct fiber feeding injection molding (DFFIM) process with un-modified and modified check ring designs were used to fabricate glass fiber reinforced recycled PET (GF/r-PET) composites. The new generated GF/r-PET composites were performed and compared with commercial GF/PET composites to extensive study on the impact properties. The results indicate that the distributional fiber length in the range of 0-800 μm of conventional injection molding process lead to the brittle fracture behavior and low absorbed energy. More existing fiber length in the range of 1000-3800 μm of DFFIM un-modified check ring develops the impact properties as more ductile behavior and energy absorption especially in the initial damage stage. Meanwhile, 3800-8000 μm remaining fiber length provided a small increase in the initial internal damage stage compared to those of 0-3800 μm but it efficiently improves the absorbed energy at the damage propagation energy stage.

Effects of Cyclic Loading on the Mechanical Properties of Mature Bedding Shale

We investigated the mechanical properties of mature bedding shale under cyclic loading conditions, with an application to the design of hydraulic fracturing in shale gas wells. Laboratory experiments were conducted on shale samples under two principal loading orientations. Testing results showed that accumulated fatigue damage occurs in a three‐stage process. Analysis of fatigue damage at different maximum stress levels shows that fatigue life increases as a power‐law function with maximum stress decreasing. And the maximum stress significantly affects the fatigue life. Further, the elastic part of shale rock deformation was recovered in the unloading process, whereas the irreversible deformation remained. The irreversible deformation, growth trend, and accumulation of the total fatigue were directly related to the fatigue damage. This process can be divided into 3 stages: an initial damage stage, a constant velocity damage stage, and an accelerated damage stage, which accounted for about one‐third of the fatigue damage. Shale rock is a nonhomogeneous material, and the bedding is well developed. Its fatigue life differs greatly in two principal loading orientations, even under the same loading conditions. All of these drawn conclusions are of great importance for design of hydraulic fracturing in shale gas wells.

Effect law of Damage Characteristics of Rock Similar Material with Pre-Existing Cracks

In order to further study the failure mechanism for rock similar materials, this study established the damage model based on accumulative AE events, investigated the damage characteristics for rock similar material samples with pre-existing cracks of varying width under uniaxial compression load. The equipment used in this study is the self-developed YYW-II strain controlled unconfined compression apparatus and the PCIE-8 acoustic emission (AE) monitoring system. The influences of the width of the pre-existing cracks to the damage characteristics of rock similar materials are analyzed. Results show that, (1) the damage model can better describe the damage characteristics of rock similar materials; (2) the tested samples have three stages during failure: initial damage stage, stable development of damage stage, and accelerated development of damage stage; (3) with the width of pre-existing cracks vary from 3mm to 5mm, the damage of rock similar materials increases gradually. The outcomes of this study provided additional values to the research of the failure mechanism for geotechnical similar material models.

The effect of TiO 2 as a pigment in a polyurethane/polysiloxane hybrid coating/aluminum interface based on damage evolution

Abstract The effect of titanium oxide as an additive on the performance of a polyurethane/polysiloxane hybrid coating was characterized by an electrochemical approach. The performance evolution was quantified by exposing the hybrid coating on an aluminum substrate to NaCl solution at pH 5 over time. Real-time measurements were performed to quantify and correlate the mechanisms that occur at the coating/substrate interface. Electrochemical impedance spectroscopy (EIS) quantified the hybrid coating/substrate interface performance over the course of the 263 days of exposure, and electrically passive elements described and characterized the degradation/performance stages upon exposure to the acidic NaCl solution. The addition of TiO2 produced hydrophobicity functionality, and TiO2 acted as a physical barrier layer that influenced the initial damage stage. Different exposure times were associated the different stages of damage evolution for the hybrid coating and coating/substrate interfaces. Electrochemical testing with high-resolution techniques such as AFM (atomic force microscope) and IFM (infinite focus microscope) characterized the coating surface and the interface performance and resolved the surface and defect formation observed with different levels of TiO2 content. Of the systems tested, the system with 10 wt% TiO2 provided the best corrosion inhibition.

Numerical study of dynamic response and failure analysis of spherical storage tanks under external blast loading

The performance of energy infrastructures under extreme loading conditions, especially for blast and impact conditions, is of great importance despite the low probability for such events to occur. Due to catastrophic consequences of structural failure, it is crucial to improve the resistance of energy infrastructures against the impact of blasts. A TNT equivalent method is used to simulate a petroleum gas vapor cloud explosion when analyzing the dynamic responses of a spherical tank under external blast loads. The pressure distribution on the surface of a 1000m3 spherical storage tank is investigated. The dynamic responses of the tank, such as the distribution of effective stress, structural displacement, failure mode and energy distribution under the blast loads are studied and the simulation results reveal that the reflected pressure on the spherical tank decreases gradually from the equator to the poles of the sphere. However, the effects of the shock wave reflection are not so evident on the pillars. The structural damage of the tank subjected to blast loads included partial pillar failure from bending deformation and significant stress concentration, which can be observed in the joint between the pillar and the bottom of the spherical shell. The main reason for the remarkable deformation and structural damage is because of the initial internal energy that the tank obtained from the blast shock wave. The liquid in the tank absorbs the energy of impact loads and reduces the response at the initial stage of damage after the impact of the blast.

Earthquake Damage Monitoring for Underground Structures Based Damage Detection Techniques

Urban railway systems are located under populated areas and are mostly constructed for underground structures which demand high standards of structural safety. However, the damage progression of underground structures is hard to evaluate and damaged underground structures may not effectively stand against successive earthquakes. This study attempts to examine initial damage-stage and to access structural damage condition of the ground structures using Earthquake Damage Monitoring (EDM) system. For actual underground structure, vulnerable damaged member of Ulchiro-3ga station is chosen by finite element analysis using applied artificial earthquake load, and then damage pattern and history of damaged members is obtained from measured acceleration data introduced unsupervised learning recognition. The result showed damage index obtained by damage scenario establishment using acceleration response of selected vulnerable members is useful. Initial damage state is detected for selected vulnerable member according to established damage scenario. Stiffness degrading ratio is increasing whereas the value of reliability interval is decreasing.

Method of estimation of residual operation life of materials under long-term statistic loading

In the modern machine building production with high level of competitiveness, the great importance plays the performance and reliability of parts and components of various machine building structures, which often operate under a power impact of various factors. In this regard, there is a need to improve the methods of diagnostics of the condition of the material for fabrication of these constructions. The study determined the current value of the accumulated damage of the material, which was performed using the proposed experiment-calculated method of estimation of the residual operation life of the material under the long-term statistic loading, and which was based on the experimental determination of three values of the accumulated damage at the initial stage of damage. The authors proposed to use the value of specific work of deformation as a criterion of damage, which allowed the identification of damage parameter as the ratio of the current and total values of the specific work of deformation. The developed method of kinetic diagrams of damage allows the reliable estimation of the exhausted and residual operation life of the material. Thus, the results of the research are of scientific and practical interest. The authors showed the possibility of constructing a method of rapid diagnostics estimation of damage of the material in relation to the operating structures

Analysis on Factors Affecting the Self-Repair Capability of SMA Wire Concrete Beam

Crack expansion of concrete is the initial damage stage of structures, which may cause greater damage to structures subject to long-term loads or under extreme conditions. In recent years, the application of intelligent materials to crack self-repair has become a hotspot among researchers. In order to study the influence of factors on the self-repair capability of shape memory alloy (SMA) wire concrete beam, both theoretical and experimental methods were employed for analysis. For the convenience of experiment, composite materials (epoxy cement mortar and silicone polymer clay) instead of concrete were used. The SMA wires were externally installed on and internally embedded in epoxy resin cement mortar beams and silicone polymer clay beams. Comparison of crack repair situation between two installation methods turns out that both methods possess their own advantages and disadvantages and should be employed according to the actual situation. The influence of unbonded length on the self-repair capability of embedded type SMA wire beams and the necessary minimum unbonded length to achieve self-repair function were studied. The results state clearly that the longer the unbonded length is, the better the crack repair situation is.

Mechanisms of damage initiation in a titanium alloy subjected to water droplet impact during ultra-high pressure plain waterjet erosion

Impingement of ultra-high pressure plain waterjets (PWJ) has been considered as a promising surface treatment technology (e.g. peening, milling, cleaning) for some difficult-to-machine engineering materials (such as titanium alloys). However, a comprehensive understanding of the mechanisms of damage initiation on such materials under PWJ impingement has not been established. This paper presents an in-depth investigation into the initial material damage mechanisms which are observed during impingement of a PWJ onto polished samples of an α−β titanium alloy—Ti–6Al–4V, and the influence of the microstructure of the alloy on the initial damage modes. A series of single-track erosion trials were carried out and scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to examine the resulting damage. It was found that the microstructural features of Ti–6Al–4V influence the development of damage, with grain boundaries exhibiting lower resistance to damage than grains themselves. Under waterjet impingement, the initial stage of damage is associated with deformation resulting in grain tilting; a combination of impact damage and lateral outflow jetting then results in preferential damage to the grain boundary regions. Hydraulic penetration into the damaged grain boundaries results in the formation and expansion of microvoids and pits, firstly along the grain boundaries and then across the grains. The subsequent damage is linked with the effects of both hydraulic penetration and lateral outflow jetting on the increasingly roughened surface.

Cavity Growth Simulation in 2.25Cr–1Mo Steel Under Creep-Fatigue Loading

High temperature components in thermal power plants are subjected to creep-fatigue loading where creep cavities initiate and grow on grain boundaries. Development of a quantitative evaluation method of cavity growth is important for reliable maintenance of these components. In this study, a creep-fatigue test was carried out at 600°C on 2.25Cr–1Mo steel in a scanning electron microscope, and continuous observation of cavity growth behavior during the test was made. Based on the cavity growth observation, existing cavity growth models were modified and the simulated results using the modified model were compared to the observed cavity growth behavior. From the observation, spherical shape cavities initiate and grow up to their length of 2μm on the grain boundaries at the initial stage of damage, and then these cavities change their shape to cracklike and grow until their length reaches around 10μm. Finally, cracklike cavities coalesce with each other to form one microcrack along a grain boundary. It can be concluded that cavity growth rates are controlled by diffusion and power law creep under constrained conditions, based on the theoretical consideration of cavity growth mechanism. Through these discussions, a new cavity growth model was proposed by modifying conventional models. Both spherical and cracklike cavity growth rate equations were derived from the modified cavity growth model. It was indicated that the measured cavity growth rate was well predicted by the growth rate equations, derived from the modified model, and a cavity growth simulation result corresponds to the change in the maximum cavity size with number of cycles under the creep-fatigue loading.

Creep Void Growth Simulation of Local Area in a Steam Turbine Rotor

In order to reduce maintenance cost of high temperature components in aged thermal power plants, it is necessary to improve accuracy of remaining life assessment methods. High temperature components such as steam turbine rotors are operated under creep loading condition where creep voids initiate and grow on grain boundaries. Development of a void growth prediction method is important for reliable maintenance of these components. Purposes of this study are to clarify void growth behavior of a turbine rotor material under creep loading condition, and to develop void growth simulation program that can predict damage extension process in the components under actual operating condition quantitatively. Creep tests have been conducted on a 1Cr-Mo-V forging material and creep damaged specimens were produced by interrupting the tests. From observation of the creep damaged specimen, spherical shape voids initiate and grow up to their length of 2μm on the grain boundary at initial stage of damage, and then these voids change their shape to crack-like to grow until their length reaches around 10μm. Finally, crack-like voids coalesce each other to form one micro crack along grain boundary. It can be concluded that void growth rate is controlled by diffusion and power law creep under constrained condition based on theoretical consideration of void growth mechanism. Through these discussions, a new void growth model was proposed by modifying conventional models. A void growth simulation program was developed by incorporating the void growth model into a personal computer. It was confirmed that void growth process under the creep condition in the experiment was well predicted by the simulation program. The simulation program was also applied to predict creep void growth behavior in an actual steam turbine rotor during operation.

Coupling effects of heterogeneity and stress fluctuation on rupture

The coupling of mesoscopic strength distribution and stress fluctuation on damage evolution and rupture are examined. The numerical simulations show that there is only weak stress fluctuation at the initial damage stage when the mean field approximation is in effect. As the damage fraction becomes larger than the threshold value, the fluctuation is amplified significantly, and damage localization appears. The coupling between stress fluctuation, disordered heterogeneity and the damage localization may play an essential role in catastrophic rupture.

Damage processes and substrate surface design for CVD diamond films

Experimental results on the development of damage processes for CVD diamond (hereafter referred to as CVDD) films and substrate surface design are presented with the purpose of application to cutting tools. The initial stage of damage was investigated with a mechanically scanned acoustic microscope. It is shown that the damage is formed by development of cracks, which extends to the top surface. Delaminations around the cracks finally result in peeling off from the substrate. These facts suggest that interface structures inhibiting the extension of cracks and delamination around the cracks are advantageous for adhesion enhancement of CVDD films. Accordingly, the phase transformation of cemented carbide was investigated. As a result, it is demonstrated that by a specific surface treatment under H 2 plasma atmosphere, a surface structure, which is best suitable for the synthesis of CVDD films, can be obtained.

Damage Mechanism of Hybrid Composites with Nonwoven Carbon Tissue Subjected to Quasi-static Indentation Loads

Damage mechanisms of hybrid composites with nonwoven carbon tissue (NWCT) are investigated under a quasi-static indentation loading condition with a steel ball as an indentor. The damage level corresponds to an initial stage of damage due to an indentation loading, which leads to a strength degradation of the composite. The hybrid composites consist of the CFRP prepreg and the NWCT prepreg, which are made byinterleaving the NWCT prepreg into the CFRP layer interfaces. Four kinds of cross-plylaminates are studied; i.e., CFRP laminates ([05/905/05] and [03/903/03/903/03]) and hybrid laminates ([05//905//05] and [03//903//03//903//03]). Here, the symbol “//” means that the NWCT prepreg is located at an interface between CFRP layers. The hybrid effect is examined by investigating the delamination area and the absorption energyof two cross-plylaminates. As it has been recognized that the quasi-static indentation damage agrees well with the low velocity impact test results, the present static test results can then be used to understand the damage mechanism of low-energyimpact. The damaged parts of the specimens were observed bythe deplytechnique and the cut method which used a microscope. The NWCT interleaving’s effect was clarified based on the observation of the damage for the hybrid specimen’s cross-sections after indentation testing. The delamination area of the hybrid composites was reduced to about a half of the CFRP’s byindentation loading. It was clarified that the Mode II interlaminar fracture is predominant in the delamination bythe impact.