Damage Mechanisms In Materials Research Articles

Machine learning based damage identification in SiC/SiC composites from acoustic emissions using autoencoders

Developing the ability to leverage machine learning (ML) to identify damage mechanisms in heterogeneous materials from their acoustic emissions (AE) has wide-reaching ramifications for multi-modal experimentation. It would allow researchers to augment damage triangulation, lifetime prediction, and high-resolution optical studies with complementary mechanism-informed data streams. However, developing this capability hinges on the collection of ground truth acoustic libraries from damage in realistic geometries. Due to time and monetary considerations, there is a dearth of ground truth libraries which can be used to robustly characterize ML mechanism identification frameworks. Addressing this gap, we present a multi-modal acoustic emission and x-ray computed tomography study where AE is gathered, and subsequently labeled, from SiC/SiC unidirectional composites under monotonic tension. This library is used to demonstrate that acoustic signals from early fiber breaks are obscured by matrix cracking. A first-order micromechanical model is used to explain the origin of this obscuring effect, and identify fundamental limitations of unsupervised frameworks. An autoencoder-based anomaly detector approach is used for the first time to overcome these limitations, additionally demonstrating that the frequency distribution of fiber break acoustic signals is narrow. Implications of these findings for enhanced multi-modal testing and online health monitoring are discussed, and strategies for implementation of supervised damage mechanism identification frameworks are proposed.

Advancing Hydrogen Gas Utilization in Industrial Boilers: Impacts on Critical Boiler Components, Mitigation Measures, and Future Perspectives

This review sets out to investigate the detrimental impacts of hydrogen gas (H2) on critical boiler components and provide appropriate state-of-the-art mitigation measures and future research directions to advance its use in industrial boiler operations. Specifically, the study focused on hydrogen embrittlement (HE) and high-temperature hydrogen attack (HTHA) and their effects on boiler components. The study provided a fundamental understanding of the evolution of these damage mechanisms in materials and their potential impact on critical boiler components in different operational contexts. Subsequently, the review highlighted general and specific mitigation measures, hydrogen-compatible materials (such as single-crystal PWA 1480E, Inconel 625, and Hastelloy X), and hydrogen barrier coatings (such as TiAlN) for mitigating potential hydrogen-induced damages in critical boiler components. This study also identified strategic material selection approaches and advanced approaches based on computational modeling (such as phase-field modeling) and data-driven machine learning models that could be leveraged to mitigate potential equipment failures due to HE and HTHA under elevated H2 conditions. Finally, future research directions were outlined to facilitate future implementation of mitigation measures, material selection studies, and advanced approaches to promote the extensive and sustainable use of H2 in industrial boiler operations.

Analytical simulation of the effects of local mechanisms and microstructure on the creep response of unidirectional ceramic matrix composites

A micromechanics-based method has been developed to analyze the creep response of uncoated ceramic matrix minicomposites. Although the global stress level at which the creep response is analyzed is lower than the composite proportional limit, local stresses are assumed to be high enough that localized damage is present in the composite in the form of matrix microcracks. To model the composite creep response including the effects of matrix cracking, a fiber shear lag-based methodology is employed. In this approach, stresses are assumed to vary in the fiber as a function of time and distance from the crack plane. The varying stresses are then used to compute the overall creep strain for the composite. Various assumptions regarding the level of matrix microcracking in the composite, and the level of creep in the fiber and matrix in various portions of the composite unit cell, are also examined. The creep response of the fiber is modeled using a linear Burgers model. The model is applied to a SiCf/SiC unidirectional minicomposite system. The computed creep results are compared to experimentally obtained values. The effects of the local fiber volume fraction on the overall creep response of the composite are also studied. This work will allow increased understanding of the key material damage mechanisms and load sharing that take place during creep conditions and can be expanded to provide improved analysis methods for full macrocomposites.

An experimental investigation on the failure behavior of sandstone with filled fissure under triaxial multilevel cyclic loading

AbstractRoadways are common in infrastructure of the underground engineering. The surrounding rocks of these roadways are often allowed to work with flaws and are subjected to cyclic loading with variable magnitude. However, the existing experimental data regarding their behavior are insufficient. This study investigated how confining pressure and the inclination of pre‐existing fissures affect the mechanical properties and failure mechanisms of sandstones from the Lu‐Xi coal roadway in Shandong Province. Utilizing triaxial cyclic experiments along with real‐time acoustic emission (AE) monitoring, the findings were presented with respect to the evolution of strength as well as deformation behaviors, failure modes, and AE event frequency. Finally, the impact of the above two factors on damage mechanisms of preflawed sandstone materials were detailed discussed in terms of the fracture mechanics. This study highlights the importance the buried depth and flaws for the rock engineering and the sensitivity of sandstone's mechanical responses in changes in the lateral restriction and fissure angle.

Damage mechanisms analyses in DP steels using SEM images, FEM, and nonlocal peridynamics methods

An investigation is performed to study the damage mechanisms of dual phase steels using experimental analysis, local finite element simulation, and nonlocal peridynamics (PDs) method. The uniaxial tensile tests and preparation of metallography and SEM images have been used to peruse the pattern of deformation and voids in different phases. Understanding of the relationship between real microstructure and damage mechanisms can often not be obtained from microstructural investigation using experiments only. Here, a novel numerical approach is presented to investigate damage mechanisms in multiphase materials at micro scale level using both local and nonlocal numerical analyses and microstructural images from a scanning electron microscope (SEM). The nonlocal PDs method is capable to overcome many challenges associated with convergence problems in other numerical methods and to detail-oriented study of damage initiation and propagation autonomously. In this study, images of real microstructure are used as RVEs and imported to the FEM software and PD-developed code. Moreover, the effects of different constitutive models for the interface of ferrite and martensite phases on the bond breakage and damage patterns have been also investigated.

Uniaxial deformation behaviors and mechanism of Ti–6Al–4V alloy with bi-oriented grains

It is of great importance to investigate the deformation and damage mechanisms of polycrystalline materials with soft crystal orientations, considering the soft grains are usually the fatigue crack initiation sites. In this study, a Ti–6Al–4V alloy fully consisted of <01 1‾ 0> and <1‾ 21‾ 0> α (soft) grains was prepared and its uniaxial deformation behavior was investigated. Interestingly, no significant asymmetry on the tension-compression yield strength was found in this alloy with bi-grain orientations, though mechanical asymmetry was generally found in the traditional Ti alloys with strong texture. After high temperature solution treatment, the preferred bi-orientations were retained and the asymmetry degree of yield strength did not change, showing an excellent stability in texture and mechanical performance. Deformation mechanisms during tension and compression were studied and discussed. This work provides a new understanding on the deformation and damage mechanisms in the grains with soft crystal orientations, and may guide the microstructural design of Ti alloy for pursuing high mechanical and fatigue performances in the future.

Multiscale simulation study on radiation aging of EPDM and preparation of radiation-resistant materials

With the wide application of ethylene propylene diene monomer (EPDM) in the field of nuclear engineering, exploring the radiation aging mechanism of EPDM is of great significance to improve the radiation resistance of EPDM composites. In this paper, the radiation aging mechanism of EPDM was investigated by a combination of experiments and multiscale simulations, and EPDM composites with excellent radiation resistance were prepared. The radiation aging mechanism of EPDM involves the crosslinking and degradation of molecular chains. The aging of EPDM starts from the breakage of α-H in the 5-ethylidene-2-norbornene monomer. In addition, the screening strategy of radiation-resistant additives was proposed. Antioxidants N, N′-diphenyl-p-phenylene-diamine (H), N, N′-ditolyl-p-phenylenediamine (DTPD), and N, N′-di-2-naphthyl-p-phenylenediamine (DNP) were taken as the main research objects, and quantitative analysis was carried out from the aspects of chemical protection and physical protection. The screening results showed that DNP has excellent radiation resistance and migration resistance. The prepared EPDM-DNP composites showed outstanding radiation resistance with 94% tensile strength retention after 300 kGy irradiation. This work contributes to understand the mechanisms of radiation-induced material damage and guides the design of radiation-resistant materials.

Effect of dislocation defects on the nano-scratching process of 4H–SiC

To investigate the influence of defects on the damage mechanism of 4H–SiC, this study primarily conducted molecular dynamics simulations of a single diamond abrasive indentation process and carried out subsequent nanoindentation experiments on 4H–SiC samples. The simulation and experimental results were compared, and the force–displacement curves showed consistent trends. On this basis, the scratching simulation of an ideal material and a single diamond abrasive particle containing 4H–SiC with dislocation defects was carried out to study the influence of internal dislocation (screw dislocation and edge dislocation) in 4H–SiC and its position on the material damage mechanism during scratching, and the development and evolution of internal dislocation were further analyzed. The results reveal that the presence of internal dislocations in the material is one of the causes of the formation of dislocation loops.

Deterioration of mechanical properties and damage mechanism of flue gas desulfurization gypsum backfill under long-term erosion of chloride salt solution

Flue gas desulfurization gypsum (FGDG), a solid waste material generated by power plants, offers a cost-effective solution for preparing backfill materials. Concurrently, given that most backfill materials are exposed to mine water erosion, an investigation into the mechanical performance degradation and damage mechanisms of FGDG backfill materials subjected to prolonged chloride salt erosion is crucial for ensuring the stability of goaf backfills (by goaf, we mean the area or space that remains underground after the extraction of valuable minerals). This study explores the mechanical properties and damage mechanisms of backfill samples treated with varying concentrations of chloride. The findings indicate that over time, the mass of the sample initially decreases, experiences a slight increase, and then gradually declines. Simultaneously, the strength and structure of the sample deteriorate rapidly, followed by a partial recovery. The rebound in sample mass is attributed to an incomplete hydration reaction that continuously transforms free water into bound water. Microstructure analysis techniques, such as X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM), reveals that the degradation in mechanical strength and structure is a consequence of chloride salt erosion. Subsequent reuse is facilitated by the formation of Friedel's salt resulting from the reaction between hydration products and chloride ions, filling voids in the sample and impeding further chloride ion erosion into the deeper regions. Notably, FGDG exhibits outstanding reuse performance in prolonged and high-concentration chloride ion environments. This study serves as a reference for understanding the deterioration mechanism and practical application of backfills in chloride-rich environments.

ASSESSMENT OF INHIBITORS' PERFORMANCE ON CORROSION DEGRADATION OF CARBON STEEL IN FLOW ENVIRONMENTS USING ROTATING CYLINDER ELECTRODE (RCE)

This study investigates sweet corrosion mitigation methods focusing on the efficacy of inhibitors. Specifically, it examines the performance of two types of inhibitors: water-soluble and oil-soluble. Utilising a Rotating Cylinder Electrode (RCE) setup, turbulence is induced in saline solutions to assess the impact of inhibitors on the corrosion of carbon steel. Scanning Electron Microscopy (SEM) is employed to analyse corrosion degradation patterns and material damage mechanisms. Given the prevalent use of inhibitor injection in the oil sector, it is crucial to evaluate and compare the effectiveness of various inhibitors to recommend optimal options and further studies. The findings contribute to advancing corrosion mitigation strategies, providing insights into the performance of inhibitors in flow environments and aiding in the development of more effective corrosion control measures for carbon steel structures. The inhibitors under study are sourced from local oil company vendors. With a projected duration of six months and a total budget of KD 9850, this investigation aims to provide valuable insights into corrosion mitigation strategies

Effect of fretting wear on TC4 alloy prepared by laser shock peening at high temperature

The fretting wear properties of a nanocrystalline layer with laser shock peening (LSP) on the surface of Ti–6Al–4V (TC4) alloy were investigated to improve the fretting friction performance at 25 °C and 500 °C. The fretting operation characteristics and material damage mechanism of the LSP–TC4 alloy were investigated through a friction dissipation model and two kinds of operation fretting models. The contact morphology and three-body behaviour on the surface were also revealed. The wear resistance performances of the strengthened surfaces exceeded those of unreinforced surfaces at 25 °C and 500 °C but the LSP-treated alloy was more stable at 25 °C. As revealed in the operation fretting models, the fretting running region of the LSP layer consisted of a mixed slip regime and gross slip regime. The material response area was composed of slight and abrasive wear areas at 500 °C. The improved fretting fatigue resistance of TC4 alloy was attributed to the refined internal organisation and high-density dislocation organisation of LSP, which inhibits the initiation and propagation of fatigue cracks.

Quantification of micro-damage evolution process in ceramics through extensive analysis of multi-source heterogeneous data

Due to the randomness of hard and brittle material damage evolution, assessing damage and interpreting mechanisms is challenging. This study focuses on analyzing material damage mechanisms by employing extensive multi-source heterogeneous data to extract quantitative information. A machine vision-based method for detecting and assessing defects in ceramics was proposed, achieving 98 % accuracy. Leveraging this method in scratching experiments, the progression of damage and micro-failure mechanisms in Si3N4 was investigated through the analysis of defect area distribution, force and acoustical signals. Results revealed that the distribution of defect areas conforms to a three-parameter Weibull distribution. At scratch depths of 0.01, 0.02 mm, approximately 90 % of damage accumulated within 1e2–1e4 μm2; conversely, 0.03–0.06 mm led to a decrease to 30 – 40 %. Extensive crack propagation occurs within 0.02–0.03 mm, resulting in the intersecting formation of spalling blocks. Damage evolution occurs in three stages: shallow and small cracks with scattered spalling blocks in the first stage, deep and long cracks with continuous and irregularly shaped spalling blocks in the second stage, and nearly no cracks with continuous and regularly shaped blocks in the third stage. This study not only proposes an efficient method to detect and evaluate ceramic defects, but also deeply understands the evolution process of material damage mechanism. Considering defect distribution and statistical trends, this research not only provide guidance for the optimization of machining parameters, especially in the scene of specific precision and high removal rate. At the same time, the damage evolution and failure mechanism of Si3N4 provide useful experimental basis and data support for deepening the understanding of material behavior during ultra-precision grinding.

Vibration-assisted material damage mechanism: From indentation cracks to scratch cracks

Vibration-assisted grinding is one of the most promising technologies for manufacturing optical components due to its efficiency and quality advantages. However, the damage and crack propagation mechanisms of materials in vibration-assisted grinding are not well understood. In order to elucidate the mechanism of abrasive scratching during vibration-assisted grinding, a kinematic model of vibration scratching was developed. The influence of process parameters on the evolution of vibration scratches to indentation or straight scratches is revealed by displacement metrics and velocity metrics. Indentation, scratch and vibration scratch experiments were performed on quartz glass, and the results showed that the vibration scratch cracks are a combination of indentation cracks and scratch cracks. Vibration scratch cracks change from indentation cracks to scratch cracks as the indenter moves from the entrance to the exit of the workpiece or as the vibration frequency changes from high to low. A vertical vibration scratch stress field model is established for the first time, which reveals that the maximum principal stress and tensile stress distribution is the fundamental cause for inducing the transformation of the vibration scratch cracking system. This model provides a theoretical basis for understanding of the mechanism of material damage and crack propagation during vibration-assisted grinding.

3D strain pattern in additively manufactured AlSi10Mg from digital volume correlation

Although much research has focused on AlSi10Mg processed via laser-based powder bed fusion, the material deformation mechanisms at the microscale are still unclear. To improve the current understanding, 3D measurements of the strain field at the microstructural scale are needed to complement surface-based SEM observations. This work demonstrates that X-ray tomography combined with digital volume correlation can be used to measure the strain in the bulk of AlSi10Mg using the Si-rich particles contained in the heat-treated microstructure as markers. The method allows for measuring strains larger than 0.5 % with a spatial resolution of 35 μm and it can thus be used to study the impact of factors like porosity distribution or crystallographic texture on the material deformation and damage mechanisms.

A dimensional analysis based multi-scale thermal damage framework of brittle materials at elevated temperatures

Research on macro-scale damage prediction and micro-scale damage mechanisms of brittle materials at elevated temperatures is extremelyimportantto the design and application of practical engineering structures. In this study, a multi-scale thermal damage framework is proposed for both describing macro-scale damage evolution and collective micro-scale cracks behavior of brittle materials atelevatedtemperatures. In the framework, the evolution equation of ideal micro-crack system is deduced to establish the relationship between the macro-scale damage and the micro-scale crack nucleation and growth based on dimensional analysis method. To support the multi-scale thermal damage framework, the multi-scale damage of the benchmark fracture test of the Brazilian disk at elevated temperatures is predicted and compared with the experimental results. The results support the effectiveness and ability of the multi-scale thermal damage framework, which can achieve thermal damage prediction of brittle materials in macro-scale as well as physical mechanisms description in micro-scale.

Study on the influence mechanism of material damage on the cavitation erosion properties of hydraulic concrete

Flood releasing safety is one of the three major safety problems of high dams due to the high-water head and large discharge, and the safety problems caused by cavitation erosion are increasingly prominent, which has become one of the challenging problems for the safety of high dam flood discharge. Particularly, flood discharge and energy dissipation structures are susceptible to varying degrees of damage under external loading and material performance degradation. However, the action mechanism of damage-cavitation erosion for concrete remains unknown and unclear. In this paper, the cavitation erosion properties of concrete with different damage variables and the influence mechanism of damage-cavitation erosion are systematically studied. Based on the ultrasonic cavitation erosion tests of undamaged and damaged concrete, it is found that the mass loss, harshness, volume of pits, and depth of damaged concrete increased rapidly at first and then slowly, the maximum loss rate is almost dependent on the degree of damage, and its relationship with the damage degree can be described by a piecewise linear function. More importantly, a damage variable threshold for the step surge of concrete cavitation erosion is suggested. The cementitious material in damaged concrete is more prone to cavitation erosion due to the potential microcracks caused by the damage. Compared with the results of tests and simulations, the incentive mechanism of the surge of concrete cavitation erosion due to the concrete damage - microcrack initiation - strength and fatigue life reduction - microjet impact - water wedge excitation in cracks - development, expansion, and penetration of erosion pits is revealed. The influence mechanism revelation of damage-cavitation erosion for concrete will enrich the theory and technology of cavitation erosion risk assessment for hydraulic concrete structures.

A Study on the Material Removal Characteristics and Damage Mechanism of Lapping for Pressureless Sintered Silicon Carbide (SSiC) Microlens Cavity.

Microlens arrays have been widely employed to control the reflection, refraction, and diffraction characteristics of light due to its distinctive surface properties. Precision glass molding (PGM) is the primary method for the mass production of microlens arrays, of which pressureless sintered silicon carbide (SSiC) is a typical mold material due to its excellent wear resistance, high thermal conductivity, high-temperature resistance, and low thermal expansion. However, the high hardness of SSiC makes it hard to be machined, especially for optical mold material that requires good surface quality. The lapping efficiency of SSiC molds is quite low. and the underlying mechanism remains insufficiently explored. In this study, an experimental study has been performed on SSiC. A spherical lapping tool and diamond abrasive slurry have been utilized and various parameters have been carried out to achieve fast material removal. The material removal characteristics and damage mechanism have been illustrated in detail. The findings reveal that the material removal mechanism involves a combination of ploughing, shearing, micro-cutting, and micro-fracturing, which aligns well with the results obtained from finite element method (FEM) simulations. This study serves as preliminary reference for the optimization of the precision machining of SSiC PGM molds with high efficiency and good surface quality.

Special Issue Focus: Selected Papers from the 6th Symposium on Damage Mechanism in Materials and Structures

Special Issue Focus: Selected Papers from the 6th Symposium on Damage Mechanism in Materials and Structures

Study on the aging of three typical rubber materials under high- and low-temperature cyclic environment

Abstract As the key components of sealing applications, rubber seals are subject to complicated environmental conditions during the service lifetime. In this study, the aging of three typical rubber materials, ethylene–propylene–diene monomer rubber, liquid silicone rubber, and fluorine rubber, was tested under different high- and low-temperature cycle aging environments. The experimental results confirm that the reciprocating temperature cycle causes a type of fatigue failure, which could result in an increase in the rubber compression set. In addition, a novel accelerated aging test method was proposed based on the dominant damage mechanism of rubber material caused by the temperature cycle treatments. Based on this method, the long-term aging test results of rubber samples under high- and low-temperature cycle conditions can be predicted. This method could significantly shorten the aging test time and reduce the test cost.

Coupled microplane and micromechanics model for describing the damage and plasticity evolution of quasi-brittle material

Quasi-brittle materials exhibit significant heterogeneity due to their complex mesoscopic components and microdefects, and their macroscopic mechanical behavior depends strongly on crack initiation, propagation and friction-slip. In this study, by coupling microplane and micromechanics, a new constitutive model that can consider the mesoscopic damage and plasticity mechanisms of quasi-brittle materials is proposed. The microplane is used throughout the whole construction process for the model: first, a representative volume element (RVE) is established to characterize the mesoscopic structure of quasi-brittle materials, and the advantages of microplanes are fully exploited to characterize the equivalent cracks‒matrix system. Then, the relationship between macroscopic and microplane strains (stresses) is elucidated. Second, considering the unilateral effect for cracks, the expressions for the free energy potential functions for a microplane and for the RVE are established. Third, for each microplane, the damage criterion characterized by the damage driving force is constructed for the open and closed cracks, and in particular, a new plasticity criterion characterizing the static friction property coupled damage and dilatancy behavior during strain softening deformation is constructed. By considering the characteristics of the microplane to relate macroscopic and mesoscopic stress and strain, an efficient return mapping algorithm based on the Newton‒Raphson method is derived. Finally, the stress‒strain curves and the evolution of damage and plasticity are simulated under conventional triaxial compression, uniaxial tensile, direct shear and true triaxial compression stress paths, and the effectiveness of the model is verified by comparison to the experimental data. To better reflect the inherent correlation between mesoscopic damage and macroscopic mechanical behavior, a microplane configuration that can visually characterize the mesoscopic evolution characteristics of damage is established, and it is shown that the simulated results correspond well to the macroscopic deformation and failure pattern of granite samples under different loading paths.