Degradation Rules Research Articles

Fatigue life prediction of CFRP laminates with stress concentration lamina level failure criteria

This paper presents a progressive fatigue damage model to predict the damage progress and the fatigue life of composite laminates under cyclic loading. First, the maximum stress criterion was applied in the fiber direction for fiber failure (FF), and Puck’s failure criteria were employed in the matrix direction in which the fracture plane is defined to determine the inter-fiber fracture (IFF). Next, material degradation rules consisting of strength and stiffness degradation were derived, and different degradation rules according to the presence of failure and failure mode were utilized for each material. The proposed model was implemented into the UMAT subroutine of ABAQUS for the finite element (FE) analysis with tension–tension cyclic loading. Finally, the progressive fatigue damage model was validated with flat-bar specimens with various lay-ups ([0]8, [90]8, [30]16, [02/902]s, [0/902]s, [0/904]s) and compared with the experimental data of static and fatigue tests. The fatigue life prediction was also conducted on the pin-loaded quasi-isotropic (QI) laminates. The simulation results showed a good agreement with the experimental data and the ability to capture the damage progress of composite laminates during their lifetime.

Degradation of contaminants of PPCPs by photocatalysis for water purification: Kinetics, mechanisms, and cytotoxicity analysis

Pharmaceuticals and personal care products (PPCPs) have drawn increasing regulatory attention and research interest in recent years. Since it does not require any additional dissolved oxidants, heterogeneous photocatalytic technology has attracted much interest in the efficient degradation of PPCPs in recent years. The present study examined the degradation kinetics of PPCPs using Fe-ZnS@TiO2/nickel foam photocatalytic system (ZTN PS) in Milli-Q water and a solid surface water background, including estrone, diclofenac, cyclophosphamide, triclosan, and sulfamethoxazole. To evaluate ZTN PS, MF-treated water samples from the Songhua River (SR) were obtained and used as reaction matrices with spiked additions of PPCPs. The influence of single ion addition on degradation kinetics was investigated to determine the degradation rule under various water parameter conditions. Using high-resolution mass spectrometry to identify transformation products (TPs), potential degradation pathways of a few PPCPs were hypothesised. During photocatalysis, the oxidation properties of different oxidants (photogenic holes, OH, O2−) on different structural sites of PPCPs were analysed. To examine possible environmental impacts of PPCP degradation by ZTN PS, cytotoxicity and estrogen (ER) receptor-binding activity were evaluated. It was found that ZTN PS substantially reduced cytotoxicity and estrogenic activity while degrading PPCPs in Milli-Q water. Also, the presence of complex substances in water did not significantly affect the toxicity of mixed PPCP degradation TPs. However, comparing natural water to Milli-Q water, the toxicity and ER-binding activity of TPs under natural water background increased marginally (9%–13％). Thus, this study aimed to understand the effects of post-ZTN PS PPCPs and TPs on human and environmental health at the cellular level.

Slip behavior of stud connectors of steel-concrete composite beams in the whole process of fatigue loading

The slip between steel-concrete composite beams will affect structural overall performance. It is necessary to master the slip degradation rule of stud connectors in their service life. Eleven push-out specimens of stud connectors were designed and fabricated to perform static, fatigue, and residual slip tests. The slip growth and distribution characteristics of stud connectors during the full process under fatigue and static load were analyzed. An improved stud load-slip model, considering ultimate slip, was established under monotonic loading, based on statistical data and the literature. Considering the cumulative increase in stud connector slip and degradation of bearing capacity due to fatigue damage, a load-slip calculation model for the full process of studs under any number of fatigue load cycles was established and verified by test values. Finally, the influence of key parameters in stud connector slip was discussed. Results showed that stud slip can be divided into cumulative slip during fatigue loading and residual slip after fatigue loading. During fatigue loading, stud cumulative slip increased in three stages of “fast-slow-rapid,” accounting for 10, 80, and 10% of fatigue life, respectively. After fatigue loading, residual and total stud slip decreased with increased fatigue cycles, which indicated that overall stud deformation performance gradually deteriorated due to increased fatigue damage. Calculated values from the proposed full-process load-slip model for studs were in good agreement with experimental results. Parameter analysis showed that total stud slip increased with increased upper limit of fatigue load and stud diameter.

Parametric Influences of Geometric Dimensions on High Temperature Mechanical Behaviors and Damage Mechanisms of Ceramic Matrix Composite and Superalloy Double Bolted Joints

Given multiple material performance advantages, ceramic matrix composite (CMC) material has become one of the most promising hot structural materials used for thermal protection system in hypersonic vehicles. Under harsh thermal exposure of vehicles in flight, the design of connection structure would be a critical issue in improving load-carrying efficiency and ensuring service safety of aircraft structures in service environments. However, little attention was paid on mechanical behavior and its factors affecting the mechanical property of CMC joining at elevated temperature. To address this concern, a 3D finite element model coupled with progressive damage analysis is carried out to predict high temperature tensile properties and failure behavior of single-lap, double-bolt CMC/superalloy joints assembled by two serial protruding-head bolts. In the implementation of progressive damage analysis of 2D plain-woven C/SiC composites, a user-defined subroutine UMAT including a nonlinear constitutive model, 3D Alvaro failure criterion and Tan’s material degradation rule were embedded into the general package ABAQUS® through Fortran program interface. A parametric study considering geometries of joints was performed to evaluate their resultant influence on high temperature tensile behavior and the associated damage mechanisms for the CMC/superalloy double-bolt joint. New findings were provided for full exploitation of high performance through geometric design of ceramic matrix composite hot structure for hypersonic aircraft.

Study on hysteretic performance of welded T-joints circular tube on platform considering seawater corrosion

In this study, the macroscopic hysteretic mechanical behaviour of welded circular tube T-joints corroded by seawater was evaluated through hysteretic mechanical performance tests. Full immersion accelerated electrochemical corrosion tests with a proportioned seawater medium were conducted on steel specimens obtained from tube joints. The generalised degradation rule of the mechanical performance of the material with the development of corrosion was obtained via a monotonic tensile test of steel specimens. The hysteresis test of corroded joints revealed that corrosion and cyclic loading have degradation effects on joint strength, stiffness, bearing capacity, and energy dissipation. At a low number of cycles, the effect of corrosion is generally greater than that of cyclic loading. A hysteretic skeleton model that can determine the ultimate load of the corroded joint was established based on the load–displacement curve. Moreover, the hysteretic rules that describe the degradation characteristics of the loading and unloading stiffness were established. Finally, the hysteresis model of corrosion joints was proposed. The model was validated using experimental results, and we demonstrated that it can accurately reflect the effect of the degree of corrosion and loading process on the hysteretic characteristics of joints.

Remaining useful life prediction for rolling bearings based on similarity feature fusion and convolutional neural network

As a critical content of condition-based maintenance (CBM) for mechanical systems, remaining useful life (RUL) prediction of rolling bearing attracts extensive attention to this day. Through mining the bearing degradation rule from operating data, the deep learning method is often used to perform RUL prediction. However, due to the complexity of operating data, it is usually difficult to establish a satisfactory deep learning model for accurate RUL prediction. Thus, a novel convolutional neural network (CNN) prediction method based on similarity feature fusion is proposed. In this paper, the similarity features are extracted based on the correlation between statistical features and time series. After sensitive feature screening, eligible features are applied to develop a health indicator (HI), which can be used to define the bearing failure stages and reduces the complexity of the CNN model. Subsequently, a one-dimensional CNN is established to predict the RUL of bearing, and the HI is utilized to train the prediction model. The proposed approach is verified by FEMTO bearing datasets and IMS bearing datasets. And the experimental results reveal the superiority and effectiveness of the feature fusion-based CNN method in constructing HI and accurate RUL prediction.

Failure Rate Model of Materials under Uncertain Constant Amplitude Cyclic Load

Failure rate is an important reliability index of mechanical components. Failure rate is usually used to characterize the degradation rule of material performance under the cyclic load, which is critical to fatigue life prediction as well as reliability assessment of Ti–6Al–2Sn–4Zr–6Mo (Ti-6246) alloy. In order to reveal the probability characteristics of failure rate of Ti-6246 alloy under uncertain cyclic load, the equation of P-S-N curve is studied in this paper. Firstly. The probability density function for fatigue life under uncertain cyclic loading is derived from the probability density function for external stresses. A probabilistic model for the failure rate is then presented based on the basic assumptions. It is assumed that the failure rate and fatigue life of the material depend on the same damage state. Finally, the validity of the proposed model is verified by the Ti-6246 alloy fatigue test. The results show that the fatigue life of Ti-6246 alloy is more affected by material parameters (internal factors) than stress (external factors) under uncertain constant amplitude cyclic loading.

Quantitative structure-activity relationship (QSAR) guides the development of dye removal by coagulation

QSAR modeling could be a promising tool for guiding the development of novel and cost-effective environmental technologies. As an example, it could be widely used to analyze the degradation rules of organic pollutants in various decomposition methods. However, a lack of systematic research on a particular removal method is significant in revealing the decomposition rule of pollutants more accurately and guiding industrial applications. In this study, six coagulation systems (MnO2/Fe(OH)3/AlCl3/FeCl3/CaCl2/MgCl2) were used as examples to remove 38 dyes under three pH conditions, and the characteristics and differences of these systems were explored by QSAR modeling. The results showed that the removal effect by MnO2 under acidic and neutral conditions and Fe(OH)3 under acidic conditions were quantitatively described mainly by bond order (BO) and Fukui index (f (+) and f (0)), which reflected that oxidative degradation dominated. In contrast, most of the critical parameters of other systems were molecular descriptors represented by ∑q(O) (the total charge of all the oxygen atoms in the molecule) and SAA (surface area of a molecule), which reflected that electrostatic adsorption and hydrogen-bond adsorption processes dominated.

Effect of multi-walled carbon nanotube on reactive powder concrete (RPC) performance in sulfate dry-wet cycling environment

Sulfate erosion is one of the most harmful chemical corrosions, which can cause the durability problem of a cement-based material. Multi-walled Carbon nanotubes (MWCNTs) are nanomaterials that can be utilized as an additive for cement-based material. However, the research on the durability of MWCNTs modified cement-based material under sulfate dry-wet cycles is rare. The purpose of this research is to understand the effect of MWCNTs on the mechanical and microstructure properties of reactive powder concrete (RPC) during dry-wet cycles with a high concentration of sulfate. The sulfate accelerated erosion phenomenon of RPC with or without carbon nanotubes were discovered. In this research, the degradation rule of RPC subjected to sulfate erosion was investigated from several directions including compressive strength changes, mass loss, and variation of relative dynamic elastic modulus (RDEM). Moreover, the microstructure and phase composition of RPC were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. Inner pores and porosity were tested by X-ray computed tomography (CT) images. The results show that with the addition of MWCNTs, RPC showed better sulfate resistance and the type of sulfate is related to the property of corroded RPC. MWCNTs not only fill the pores and cracks within the samples, but also form bridges between cracks, which strengthens the resistance to sulfate attacks. In addition, the MgSO4 solution caused more expansion damage to RPC compared with the Na2SO4 solution in this research.

Distance self-attention network method for remaining useful life estimation of aeroengine with parallel computing

Remaining useful life (RUL) estimation of aeroengine is significant in the health monitoring, operation and maintenance of aircrafts. Traditional deep learning methods fail to consider the degradation rules of aeroengine and have low computational efficiency for RUL estimation. Therefore, a novel deep learning architecture called distance self-attention network (DSAN) is developed based on self-attention and parallel computing on time series. In the proposed DSAN method, a distance function is developed to improve the matching ability of self-attentions and optimize the feature extraction capability, and the fusion layer inspired by the computation of recurrent neural network (RNN) is developed to fuse historical information and real-time data. The effectiveness of the DSAN method for RUL estimation is validated by utilizing the Commercial Modular Aero Propulsion System Simulation (C-MAPSS) data provided by NASA. It is revealed that the DSAN method is superior to the typical methods such as convolutional neural network (CNN) and long-short term memory (LSTM), because the root mean square error (RMSE) decreased by 7.3%∼ 25.3%, and the Score reduced by 28% ∼51.8%. The efforts of this paper provide a promising method for aeroengine RUL estimation, which has the potential to support the health monitoring and predictive maintenance of multi-sensor systems.

Investigation on fatigue life prediction and reliability design of 304 stainless steel manufactured by laser metal deposition

Laser metal deposition (LMD) is an advanced technology to manufacture the specimen by layer-by-layer method. In this paper, the fatigue tests of 304 stainless steel (SS304) smooth specimens manufactured by LMD are conducted with the stress ratio of −1 and the frequency of 10 Hz. Considering that the fatigue crack is caused by the material defect on the subsurface, the fatigue life of smooth specimen under the different cyclic stress amplitudes are predicted based on the dislocation model, equivalent initial crack size and empirical formula. Lognormal, two-parameter Weibull and extreme maximum value distributions are applied to describe the fatigue life of the smooth specimens at the different cyclic stress amplitudes. The result shows that two-parameter Weibull distribution has the best ability to describe the fatigue life distribution. Based on two-parameter Weibull distribution, the probabilistic-stress-number ( P- S-N) curves at the four different reliability levels are plotted. Combined with the material strength degradation rule, the design checkpoint method is adopted to analyze the fatigue life reliability of smooth specimens under the different cyclic stress amplitudes. The reliability results are close to those of two-parameter Weibull distribution.

Modelling pre-fatigue, low-velocity impact and post-impact fatigue behaviours of composite helicopter tail structures under multipoint coordinated loading spectrum

This paper aims to numerically study progressive pre-fatigue, low-velocity impact (LVI) and post-impact fatigue (PIF) damage behaviours of a full-scale composite helicopter tail structure under multipoint coordinated loading spectrum. A mixed progressive damage algorithm incorporating residual strength and stiffness degradation rules and failure criteria is developed for progressive fatigue and LVI damage analysis of plain-weave (PW) and unidirectional (UD) composites. Novel global–local​ FE modelling technique is proposed for parallel computation and real-time data transferring of global–local FE models in progressive pre-fatigue, LVI and PIF damage modelling of helicopter composite tail structure. The numerical predictions from this work agree well with experimental data from previous literature, indicating that the mixed algorithm and global–local FE modelling technique can effectively analyse the impact damage tolerance of large full-scale composite aircraft structures.

Continuum damage dynamics of a large-scale flexible multibody system comprised of composite beams

Herein, a continuum damage dynamic model of a large-scale flexible multibody system comprising composite beams is proposed based on the framework of the absolute nodal coordinate formulation. To accurately model the continuum damage dynamics of a multibody system, the Hashin criterion is adopted to describe damage initiation during dynamics. A type of nonlinear evolution law is used to characterize the value of material damage. Furthermore, a material stiffness degradation rule is introduced to describe the process of structural damage. A formulation for the damage element elastic force and its Jacobian are derived based on the second Piola–Kirchhoff stress tensor. Two dynamic numerical examples, including a deployment dynamic analysis of the spatial beam structural unit, are conducted to verify the availability and applicability of the proposed model.

Study on ultrasonic / hydraulic cavitation field for enhanced degradation of ceflor masonry in water

Based on ultrasonic cavitation, with low concentration of levofloxacin hydrochloride solution and cavitation product analysis, the degradation rules of levofloxacin hydrochloride were studied by ultrasonic, zero valent iron and zero valence iron (US / Fe0). The results showed that zero-valent iron promotes the degradation of levofloxacin hydrochloride solution by ultrasonic cavitation, and the degradation reaction fits the first-order reaction kinetic model, with a degradation rate constant of 6.3710-3min-1. Under the reaction conditions, the biodegradability of levofloxacin hydrochloride solution was significantly improved, and after 270min minutes of the reaction, the solution BOD5 / CODcr was increased from 0 to 0.421.

Carbohydrate degradation contributes to the main bioheat generation during kitchen waste biodrying process: A pilot study.

Biodrying is a promising method for processing kitchen waste (KW) with high moisture content into reusable solid recovered fuels (SRFs). During biodrying, a large amount of bioheat generated from biodegradation of biochemical components results in KW dehydration. However, the degradation rules of these components and their contribution to the bioheat in KW biodrying have not been systematically clarified. Here, a pilot experiment was performed to investigate the variations in biochemical components, hydrolase activities, and bioheat generation during three successive cycles of biodrying processes. Results showed that KW could be rapidly converted into SRFs with low calorific values of 6705-7062kJ/kg and moisture content of 31.26%-35.21%. Analyses of hydrolase activities and mean fluorescence intensity suggested that the biodrying process pioneered the degradation of lipids and proteins in the warming stages, while carbohydrates (i.e. amylum, celluloses, etc.) underwent rapid decomposition in a large extent in the high-temperature and cooling stages. Carbohydrates with minimal difficulty in degradation, contributed 73.37%-89.92% to the total degradation mass and 59.23%-60.80% to the bioheat source during the three-cycle biodrying process. The generated bioheat was 4.32-4.56 times the amount of the theoretical heat used for water removal, indicating that internal bioheat could significantly enhance water evaporation and was sufficient for the expected water removal mass. Therefore, the evaluation of the main components to bioheat generation and its utilization efficiency makes a prominent contribution that can greatly clarify the conversion of KW biodrying into SRFs in order to efficiently promote renewable bioenergy and support the bioeconomy.

Experimental study on the cyclic bond behavior of corroded rebar based on modified beam test

The corrosion of rebar results in the degradation of bond between rebar and concrete, thus is unfavorable to the safety of reinforced concrete structures. So far, many studies were undertaken to investigate the bond behavior of corroded rebars under monotonic loading, however, only a few considered the effect of cyclic loading. Moreover, in these researches, the bond behavior of corroded rebars under cyclic loading were generally studied with pull-out specimens, which cannot ensure an actual stress state of the rebar and concrete during loading. Therefore, in this paper, an experimental study is made to further investigate the cyclic bond behavior of corroded rebars based on a modified beam test, in which the stress state of the rebar and concrete is consistent with reality. Based on the test results, the effects of corrosion level and loading history on the bond stress at a given slip are evaluated. A cyclic bond-slip model is proposed, in which the degradation rule of bond stiffness is calibrated by the test results. The model is implemented in a user-defined bond element and validated with the test results. The predictions of the model show great agreement with the test results, meaning that the proposed model is feasible to simulate the bond stress-slip relationship of corroded rebars under cyclic loading.

Influence of Failure Criteria and Intralaminar Damage Progression Numerical Models on the Prediction of the Mechanical Behavior of Composite Laminates

This work evaluates the effectiveness of commonly adopted local damage evolution methods and failure criteria in finite element analysis for the simulation of intralaminar damage propagation in composites under static loading conditions. The proposed numerical model is based on a User Defined Material subroutine (USERMAT) implemented in Ansys. This model is used to predict the evolution of damage within each specific lamina of a composite laminate by introducing both sudden and gradual degradation rules. The main purpose of the simulations is to quantitatively assess the influence of the adopted failure criteria in conjunction with degradation laws on the accuracy of the numerical predictions in terms of damage evolution and failure load. The mechanical behavior of an open hole tension specimen and of a notched stiffened composite panel under shear loading conditions have been numerically simulated by Progressive Damage Models (PDM). Different failure criteria have been implemented in the developed Ansys USERMAT, together with sudden and gradual degradation rules based on the Continuum Damage Mechanics (CDM) approach. Numerical results have been validated against experimental data to assess the effects of the different failure criteria and damage evolution law on the global mechanical response and local damage predictions in composite laminates.

Research on the multi-shear spring model for circular-section steel piers

The main damage caused by earthquakes to single-column circular-section steel piers is the bulged deformation at the bottom, generated by local instability. The refined shell-based finite element (FE) model can accurately simulate the deformational behavior, but it is still cumbersome and time-consuming to apply to the engineering design currently. Further, the existing simplified methods cannot be used in seismic response analyses under horizontal bidirectional earthquakes. Therefore, this paper uses the multi-shear spring (MSS) mechanical model as the basic model and proposes an MSS calculation model for circular-section steel piers. This model is applicable for horizontal bidirectional seismic response analysis and considers the local instability effect of steel plates. In this study, the load–deformation relationship of the modified Menegotto-Pinto model is employed in all directions as the hysteresis curve equation of the springs. The basic parameters of the corresponding models for different structures are determined according to the calculation results of the refined-shell models. In addition, the Ibarra-Krawinkler degradation rule is employed to simulate the degradation process of structural bearing capacity and stiffness, and the degradation parameters are identified. The pseudostatic and seismic time-history response analyses of steel piers with different width-to-thickness ratios verify that the proposed model has reliable calculation accuracy and greatly improved efficiency. The research in this paper provides a practical calculation method for the seismic response analysis of steel bridge piers.

Cyclic behavior of semi-rigid precast concrete beam-to-column subassemblages with rapid assembly connections

In this paper, the semi-rigid precast beam-to-column joint subassemblages based on corbel-shoe connection system with rapid assembly characteristics were proposed and experimentally investigated. Four full-scaled interior and exterior beam-to-column joints were prepared and tested under cyclic loading keeping a fixed axial compression ratio at 0.5. It was demonstrated that the tested beam-to-column specimens failed characterized by flexural failure of beam end instead of the column or joint core. The arch-like load-displacement curves and stable hysteretic behavior were captured. The proposed precast beam-to-column subassemblages could not only provide ease of construction process but perform well under simulated earthquake action. The similar bearing capacity, stiffness degradation rule and energy dissipation capacity between precast and monolithic joints provided evidence in support of this. Also, the ductility of precast interior and exterior subassemblies (3.8 and 3.3) was 15.2% and 23.1% higher than that of the monolithic counterparts (3.2 and 2.6). The degenerated four-linear restoring force model was proposed and verified. Moreover, the structural performance evaluation and semi-rigid characteristics of tested specimens were discussed.

Experimental study on seismic behavior of precast concrete beam-column joints using UHPC-based connections

Ultra-high performance concrete (UHPC) with high bond characteristics with reinforcing bars could significantly shorten the lap splice length of rebars. UHPC-based rebar lap splice connections offer larger tolerance and simpler operation than traditional rebar connection approaches, which could ease and accelerate the on-site construction process of precast concrete structures. This paper characterizes the seismic behavior of precast beam-column joints where the longitudinal rebars of columns are connected using UHPC with a lap length of 15 times rebar diameter (15db). Full-scaled cyclic tests on two precast joints and two corresponding monolithic joints to compare were carried out keeping a high axial compression ratio (n) at 0.5. It was demonstrated that the beam-column subassemblies failed characterized by flexural failure of beam end instead of the column or joint core. The arch-like load–displacement curves and stable hysteretic behavior were still captured considering the p-delta effect. The proposed precast beam-column joints with UHPC-based connections could achieve similar bearing capacity, ductility and stiffness degradation rule to the monolithic counterparts. The degenerated four-linear restoring force model was presented and verified. Moreover, the numerical simulation was also performed, and the predicted structural behavior was in agreement with the experimental results.