Crack Development Research Articles

Compressive Fracture Behavior and Acoustic Emission Characteristics of Sandstone under Constant Crack Water Pressure

Abstract Engineering rock containing flaws or defects under a large water source is frequently subject to the couple influence of constant crack water pressure and geostress. To investigate the fracture behavior of precracked rock under hydromechanical coupling with constant crack water pressure, compression tests were conducted on red sandstone specimens containing a single crack of different angles using a device to realize the constant crack water pressure during loading, and the failure process of rock specimens was monitored by acoustic emission (AE) technique. The results show that the presence of constant crack water pressure has a significant promotion effect on the development of shear wing cracks, and the promotion effect is influenced by the prefabricated crack angle and water pressure. As the constant crack water pressure increases, the failure mode of the 0° precrack specimen changes from “X”- shear failure to the single oblique shear failure along the shear wing crack direction, the main failure crack of the inclined precracked specimens (precrack angles of 15°, 45°, and 60°) changes from a small acute angle with the prefabricated crack to a direction along the shear wing crack, and irregular cracks occur at the chipped prefabricated crack in the 90° precracked specimen. With an increase in the constant crack water pressure, the average energy for a single hit, cumulative AE energy, and cumulative AE hits decrease, and the proportion of the tensile cracks increases and that of the shear cracks decreases.

DEVELOPMENT AND OPTIMIZATION OF PALM NUT CRACKING AND SEPARATING MACHINE

This study presents a locally manufactured palm kernel cracking and separating machine designed to address the challenges associated with traditional palm kernel cracking procedures, including discomfort, tension, labor intensity, time consumption, unnecessary costs, and complexity. The machine, equipped with a 3hp electric motor operating at a shaft speed of 1430rpm, demonstrated efficient performance by cracking 1kg of palm nuts in an average of 47.58 seconds. The palm nuts are divided into three categories: uncracked, partially cracked, and cracked, with average weights of 0.06kg, 0.08kg, and 0.85kg, respectively. Among the cracked palm nuts, unbroken kernels weighed 0.83kg, and broken kernels weighed 0.02kg. The machine attained a throughput capacity of 76kg/hr and a cracking efficiency of 85.32%. The utilization of MATLAB resulted in the creation of a predictive model for optimal cracking efficiency. This model revealed that 1kg of palm kernels fed into the machine yielded 0.88kg of broken palm nuts, 0.10kg of separated shells, 0.02kg of fibrous material, and an overall cracking efficiency of 88%. Compared to traditional manual cracking methods, this mechanized system provides a faster, less labor-intensive, and more productive method of palm kernel cracking.

Experimental and theoretical analysis of FRP-confined square lightweight aggregate concrete columns under axial compression

The structure of an FRP-confined square lightweight aggregate concrete (LWAC) column was investigated, and it was found to significantly decrease the self-weight while improving the deformation capacity and bearing capacity. Twelve FRP-confined LWAC columns and three unconfined LWAC columns underwent monotonic axial compression tests. The influences of the FRP thickness and type on the compressive performance, stressstrain relationship and strain cloud maps were investigated based on digital image correlation (DIC) technology. Both types of FRP materials demonstrated a noticeable enhancement in both the strength and deformation capacity of LWAC, with CFRP having the greatest effect on strength and BFRP having the greatest effect on ductility. Compared to LWAC columns without confinement, the compressive strength of LWAC confined by BFRP or CFRP increased by 9.4∼21.9% and 24.9∼53.3%, respectively, and the ultimate strain increased by 10.6–14.2 times and 8.0–10.9 times, respectively, with increasing the thickness of FRP. DIC technology was used to accurately measure changes in the strain and the crack development of the specimens, thereby obtaining an accurate rupture strain of the FRP material. The existing models were evaluated using test data, and new models were proposed for FRP-confined square LWAC.

Study on Acoustic Emission Characteristics and Damage Evolution Law of Shale under Uniaxial Compression

Investigating the correlation between acoustic emission (AE) parameters and damage mechanisms in rock mechanics can help understand rock damage evolution under loading and provide a theoretical basis for engineering support and safety detection. Therefore, this paper presents experimental works on the correlation between AE and failure mechanisms of rock mass under uniaxial compression stress, with the aim of capturing the damage evolution leading to a new damage constitutive model. The experimental results indicate that the uniaxial compression process of shale can be divided into four stages according to AE characteristics. AE signals are minimal during the crack compaction and elastic stages. The crack initiation strength σci, which is approximately 55% of the uniaxial compressive strength, is identified when the cumulative AE counts and damage factor begin to increase slowly. When axial stress reaches the damage strength σcd, which is approximately 80% of the uniaxial compressive strength, a significant number of AE signals are generated. AE phenomena can be observed during the unstable crack development and post-crack stages. Considering the initial damage to the rock, the damage factor D initially decreases and then increases with increasing cumulative ring-down counts rather than exhibiting a monotonic increase. The damage factor D is proportional to the cumulative AE counts N in the stage before rock failure.

Effect of interface treatment on the flexural performance of existing RC bridge beams strengthened with UHPC

As one of the most innovative cement-based materials, ultra-high performance concrete (UHPC), with excellent durability and mechanical properties, has been widely used in strengthening existing bridges. In this study, in-situ four-point bending tests were carried out to investigate the flexural behavior of precast reinforced concrete (RC) hollow slab beams in service for 15 years strengthened with UHPC. Among them, three hollow slab beams were strengthened with UHPC, and the interface treatment was chiseling, planting rebars, and a combination of chiseling and planting rebars, respectively. The remaining one without any strengthening treatment was used as the control specimen. To evaluate the enhancement effect of different interface treatments on UHPC-strengthened beams, the cracking load, ultimate load, crack development and failure modes of UHPC-strengthened beams were analyzed. Results indicated that the stiffness, deflection capacity and flexural capacity of UHPC-strengthened beams was significantly improved. Meanwhile, the stiffness of UHPC-strengthened beams in the pre-damage stage was increased by 49%–94%, when compared with the unstrengthened beam. Correspondingly, the ultimate flexural capacity was increased by 29%–38%. The interface chiseling treatment was more favorable to enhance the deformation capacity of UHPC-strengthened beams. The interface planting rebar treatment was more favorable to enhancing the ductility of UHPC-strengthened beams. The crack development was effectively suppressed by the interface chiseling and planting rebars together. This contributes to a higher load capacity reserve for UHPC-strengthened beams. The bearing capacity under serviceability limit state of the UHPC-strengthened beams was increased by 1.25, 2, and 2.5 times through the interface treatments of chiseling, planting rebars, and a combination of both, respectively.

Recycled coarse aggregate from parent concrete with supplementary cementitious materials under freeze-thaw environment: Recyclability, environment and economic evaluation

In order to improve the utilization efficiency of waste concrete in cold regions, this paper studied the properties of parent concrete (PC) and its recycled coarse aggregate (RCA) based on ordinary Portland cement (OPC), fly ash (FA), silica fume (SF), and ground granulated blast-furnace slag (GGBS) combination optimization in freeze-thaw (F-T) environment. The influence of supplementary cementitious materials (SCMs) on the frost resistance of PC was analyzed by compressive strength and relative dynamic elastic modulus. The recyclability potential of RCA was evaluated by the apparent density, water absorption, crushing index and attached mortar content. In addition, the phase composition and microstructure of RCA were analyzed by XRD and SEM, respectively, and the degradation mechanism of PC during F-T process was analyzed. Finally, the environment and economic benefits from cradle to cradle is analyzed. The results showed that PC containing SCMs had good frost resistance. The PC with a binder system of 75 % OPC +15 % FA + 10 % SF had the smallest F-T damage at 0.068, and its RCA quality could be upgraded from Class III to II after mechanical grinding. This combination of cementitious materials reduced harmful pores in concrete and inhibits the development of cracks during F-T cycles. In addition, it had a carbon emission 18 % lower than that of traditional concrete, with cost-effectiveness of 1.054. This research can provide a low-carbon and economic strategy for the preparation and recycling of waste concrete in cold regions.

Experimental study on stiffness deterioration of cracked RC hollow-core slab beams

To accurately assess the performance degradation of RC hollow-slab beam after service, in-situ static load tests were carried out on a RC hollow-slab beam bridge with a span diameter of 11.25 m, which is part of the Chongqing–Chengdu Highway Viaduct. Indoor single-girder static load tests were also carried out to study the deflection concrete strain and reinforcement strain at key locations on the hollow-slab beam. Crack development was recorded to investigate the stiffness degradation law of hollow-core slabs. Inverse secant stiffness–residual deflection and inverse secant stiffness–maximum crack width relationship models were established. Results show that the calibration coefficients obtained in the in-situ static load tests were greater than one, indicating potential for stiffness deterioration and insufficient structural safety reserves during service. The initial crack width was increased and extended upwards before the test beam yielded, with many new vertical cracks in the pure bending zone which extended continuously. The slope of deflection curve was larger before yielding and smaller after yielding, the secant stiffness of RC hollow-slab beam was exponentially decreased with load before yielding and changed linearly with load after yielding. The inverse secant stiffness–residual deflection and inverse secant stiffness–maximum crack width curves of the test beam were approximately bilinear, with a larger slope at the beginning of the test and a smaller slope in the plastic phase.

Experimental study on failure mechanical properties and acoustic emission characteristics of soft rock–coal combination under dynamic disturbance

This study aims to investigate the failure mechanical properties of deep soft rock–coal combinations when subjected to dynamic disturbance. Hence, uniaxial compression and dynamic disturbance experiments were conducted on samples of muddy sandstone, coal, and soft rock–coal combinations using a creep disturbance dynamic impact loading experimental system. This study analyzed the damage properties of soft rock–coal combinations under dynamic disturbance by combining sample failure characteristics, energy evolution, and waveform signals of samples using the acoustic emission system. Results indicate that the peak strength and modulus of elasticity of the soft rock–coal combinations under uniaxial compression and dynamic disturbance are intermediate between those of coal and rock. The strength deterioration effect of the rock–coal combinations under dynamic disturbance is obvious, and the peak strength of the roof–coal and coal–floor combinations are reduced by 6.17% and 10.30%, respectively. Dynamic disturbances increase the degree of damage to the rock–coal combinations, which is accompanied by large amounts of coal fragments and large fragments of the rock–coal combinations. The failure to the sample is primarily caused by the extension of tensile damage, with the development of shear cracks playing a secondary role. The soft rock-coal combinations undergo small-scale damage at the initial disturbance (N1), with large main frequency eigenvalues. Large-scale damage occurs at the time of failure (N2), with smaller main frequency eigenvalues, sharp fluctuations in the acoustic emission signal, and peaks in the absolute AE energy and counts.

Effect of base material temper condition on precipitate evolution and mechanical properties of 2195 Al[sbnd]Li alloy friction stir welding joints

In this study, 2195 AlLi alloy plates with different temper conditions (O, T4 and T8) were subjected to friction stir welding (FSW). Precipitate evolution of the three FSW joints (2195-O/T4/T8 joint) was investigated by transmission electron microscopy (TEM). Mechanical properties of these joints were analyzed using micro-hardness and tensile test. Efforts were made to explore the correlation between precipitates, mechanical properties and fracture behavior of the joints. It can be found that the precipitates from the base material are unevenly dissolved in the nugget zone (NZ) of the 2195-O joint, while the original precipitates mostly disappear in NZ of the 2195-T8 joint, and change a little in the NZ of the 2195-T4 joint. In the thermal-mechanically affected zone (TMAZ) of the 2195-O and 2195-T4 joint, precipitates are almost unchanged, while in the TMAZ of the 2195-T8 joint, most of the precipitates are dissolved and the residual is significantly coarsened. Little change of precipitates occurs in the heat affected zone (HAZ) of the 2195-O joint. T1 newly forms in the HAZ of the 2195-T4 joint (T4-HAZ), while this precipitate is mainly dissolved and coarsened in the HAZ of the 2195-T8 joint (T8-HAZ). Moreover, both grain boundary phases (GBPs) and precipitate-free zone (PFZ) are generated in the T4-HAZ and T8-HAZ. Hardness profile is represented as a “n” shape in the 2195-O joint due to significant harden of the NZ, a “wave line” shape in the 2195-T4 joint attributed to the slight change of precipitation degree, and a “w” shape in the 2195-T8 joint mainly owing to the dissolution and coarsening of T1. The three joints are all broken in their weak regions during tensile test and have a similar fracture behavior, indicating that the crack initiation and development are related to the GBPs and PFZ.

Fiber Synergy of Polyvinyl Alcohol and Steel Fibers on the Bond Behavior of a Hybrid Fiber-Reinforced Cementitious Composite.

Based on multi-scale characteristics inherent in the cracking process of cementitious composites, fibers with different geometric dimensions are simultaneously used to restrain the formation and development of cracks at different scales. Accordingly, hybrid fiber-reinforced cementitious composites (HyFRCCs) exhibit excellent bond behavior and deformation capacity in terms of tension and compression, accompanied by higher damage tolerance. Using these benefits of the mechanical properties of HyFRCCs, the structural performance of HyFRCC structures under complex loading conditions can be improved. To objectively evaluate the contributions of all fibers to the mechanical properties of HyFRCCs, steel macro-fibers, and polyvinyl alcohol (PVA) micro-fibers were used to design several reinforced cementitious composites. Four of the specimens were mono-fibrous cementitious composites, three specimens were cementitious composites reinforced with hybrid fibers, and one was a non-fibrous cementitious composite. The synergy effect of the steel and PVA fibers was analyzed using various fiber combinations. The results indicated a significant enhancement of the bonding properties of HyFRCCs through the incorporation of PVA and steel fibers. Specifically, the peak bond strength, peak slip displacement, and residual bond strength exhibited increments ranging from 31.0% to 41.7%, 60.6% to 118.4%, and 34.6% to 391.3%, respectively, in comparison to the reference test block. Notably, the combined presence of the PVA and steel fibers consistently demonstrated a positive confounding effect on the residual bond strength. However, negative confounding effects were observed in terms of the peak bond strength and peak slip displacement, particularly with 1.0% steel fiber content and 0.5% PVA fiber content.

Effect of Freeze-Thaw Cycle and Moisture Content on Compressive and Energy Properties of Alkali Slag Ceramsite Concrete

Freeze-thaw cycle and moisture content are important factors for structural strength degradation in cold areas. Using coal gangue and slag to prepare alkali slag ceramsite concrete (ASCC) can implement the reuse of solid waste of coal gangue and slag. To study the influence of ceramsite content and moisture content on compressive strength and energy characteristics under freeze-thaw cycles (FTCs), uniaxial compression tests were conducted for ASCC with different moisture contents (dry, 4%, 5%, and 6%) and ceramsite contents (0%, 25%, 50%, 75%, and 100%) after 20 FTCs. The results show that the stress-strain curves of ASCC with different moisture contents and ceramsite contents all undergo four stages under FTCs, namely initial compaction, elastic deformation, crack development, and post-peak failure. The addition of coal gangue ceramsite makes concrete failure show certain ductility characteristics. Both compressive strength and ultrasonic pulse velocity decrease with the moisture content, and elastic energy utilization rate of wet ASCC is better than that of dry ASCC. The compressive strength, ultrasonic pulse velocity, and energy characteristics all decrease with the increase of ceramsite content.

Acoustic emission characteristic of sandstone and sandstone like material under multi-path loading.

Using spline interpolation to select proportions of similar materials, a comparative analysis of the fracturing behavior of sandstone specimens and similar material specimens was conducted through Brazilian splitting tests under multi-path loading. The study revealed that during stepwise loading, both sandstone and similar materials exhibited memory effects and plastic deformation. However, under constant velocity loading, the relationship between force and displacement in sandstone showed linearity after compaction. Employing MATLAB optimization algorithms for the inversion of acoustic emission event information, the distribution of fracture points, and the evolution of cracks were analyzed. The findings indicated that under stepwise loading, both sandstone and similar materials exhibited banded distribution of peak frequencies, with sandstone concentrated in the mid-low-frequency range and similar materials leaning towards the low-frequency range. The amplitude-frequency characteristics of acoustic emission signals suggested that initially, sandstone produced low-frequency, low-amplitude signals. As cracks developed, these signals gradually transformed into high-frequency, high-amplitude signals, ultimately leading to macroscopic failure. The ringing counts and b-values of sandstone displayed an approximate "W" shape distribution, with a subsequent decrease in b-values during final failure. In contrast, the acoustic emission counts were inversely related to b-values. Similar materials exhibited slightly more acoustic emission counts than sandstone, with relatively lower b-values. The crack development process of both sandstone and similar materials was confirmed through these observations. From the perspective of section initiation and local damage, sandstone and similar materials exhibited similar failure characteristics. The proportions of quartz sand: cement: water = 9:1:0.9 in similar materials demonstrated the most similar characteristics to sandstone in terms of mechanical loading, acoustic emission features, and failure morphology. This suggests that these similar materials can be used as substitutes for sandstone in analogous simulation experiments. The study provides theoretical support for understanding rock fracture mechanisms, offers guidance for the selection and proportioning of similar materials, and holds significance for predicting and controlling rock fracture behavior in engineering applications.

Assessment of the possibility of quantitative identification of the Mannesmann effect using ductile fracture criteria

AbstractThis article presents a study to estimate the possibility of determining the shape and size of a Mannesmann effect crack using the finite element method. Experimental tests were carried out to obtain reference specimens with a crack. A rotational compression test of cylindrical specimens in a channel was used for the experimental studies. Finite element tests were carried out using nine ductile fracture criteria. In the first stage of the study, using the rotational compression test and the finite element method, the limit values of the fracture criteria were determined. In the second stage, the development of a Mannesmann effect crack was simulated using the limit values of the fracture criteria using the finite element method. Based on the analysis, it was found that the greatest agreement in terms of void shape and size obtained in finite element method and experiment was obtained for the Ayada criterion. Analysis of the progression of the shape of the void formed using the Ayada criterion showed that crack initiation occurs as a result of maximum principal stress. The development of the resulting void is the result of the action of the maximum shear stress as well as the maximum principal stress.

Investigating non-uniform corrosion induced concrete cover cracking with a fracture-contact coupled computational method

Corrosion of steel rebar causes cracks in concrete, significantly impacting the durability of reinforced buildings. While various computational methods aim to simulate this process, only a few successfully handle both internal corrosion pressure and surface crack width evolution. To address this limitation, the study introduces an innovative mesoscale fracture-contact coupled computational method that seamlessly integrates with ABAQUS. Unlike current methods, it creatively utilizes interface elements to model stress transfer and crack propagation under tension in concrete. Additionally, it includes an additional contact model to represent the material's response to compression and shear forces. These innovations allow for accurate simulation of plain concrete mechanical properties under both tension and compression, effectively illustrating the development and failure patterns of cracks in the reinforced concrete cover. After calibrating and validating the method, the study thoroughly analyzed the process of concrete cover cracking, considering factors such as water to cement ratio, spatial location, geometry and size of coarse aggregate, rebar diameter and cover thickness. The modeling results reveal the following findings: (i) Changes in the shape and size of coarse aggregates have minimal effects on internal pressure and crack width. (ii) Higher concrete strength correlates with increased pressure on the outer surface of the rebar in an almost linear fashion, but it has little impact on surface crack width. (iii) Increasing the bar diameter decreases rust pressure but results in more cracks and wider surface cracks. (iv) Augmenting the cover thickness intensifies rust-induced pressure while simultaneously widening surface cracks.

Experimental Study on the Evolution Law of the Mechanical and Pore Characteristic Parameters of Set Cement under High- and Ultra-High-Temperature Treatments

Cement has been widely used as a structural material in many underground projects, and these projects often face high- or ultra-high-temperature environments, leading to the deterioration of the mechanical, porosity, and permeability properties of set cement, thereby increasing the risk of instability of underground structures. In response to this, two new temperature-resistant cement slurry systems were designed. Experiments were conducted on the changes in porosity and permeability of set cement after thermal treatment using low-field nuclear magnetic resonance technology (NMR), visual studies of pore and crack development were carried out using the argon-ion polishing field emission scanning electron microscopy (FE-SEM) and computed tomography (CT) methods. The research results show that as the thermal treatment temperature continued to rise, the compressive strength first increased (25 °C–200 °C) and then decreased (200 °C–600 °C). The porosity of the set cement first decreased (25 °C–115 °C) and then increased (115 °C–600 °C), and the penetration first slowly increased (25 °C–400 °C) and then rapidly increased (400 °C–600 °C). Visualization experiments were conducted on micro-cracks and the pore distribution of the set cement under high- and ultra-high-temperatures, which proved the evolution law of these characteristic parameters. The research results have vital reference significance for the protection of the structural stability of cement components when encountering high-temperature environments.

Effects of length-to-diameter ratio and strain rate on strain energy accumulation and dissipation in sandstone

To investigate the influence of the length-to-diameter (L/D) ratio and strain rate on the evolution of strain energy of sandstone under uniaxial compression, experimental tests were conducted using the RMT-150B rock mechanics test system. Specifically, uniaxial compression experiments (UCE), uniaxial loading-unloading experiment(ULUE) and uniaxial cyclic loading-unloading experiments (UCLUE) were performed. The results show that: 1) Based on an investigation of the Kaiser effect in UCLUE, it is postulated that a small degree of loading-unloading has negligible impact on the storage of strain energy in rock masses. The hypothesis regarding the limited influence of loading-unloading on the elastic strain energy storage of rocks is confirmed through a comparative analysis between the elastic strain energy storage in UCLUE and ULUE. 2) By analyzing the ESED and ISED of sandstone under different L/D ratios and strain rates, it is found that it follows the linear energy storage law. The evolution of elastic strain energy is not affected by strain rate. Therefore, the UCLUE at any strain rate can analyze the elastic strain energy of uniaxial compression experiment with the same size at any strain rate, and provide a new method for strain energy analysis at different length-diameter ratios and strain rates. 3) When the stress of sandstone samples of equal size is equal, the smaller the strain rate, the longer the loading experiment of sandstone, the more time the friction development and interconnection of cracks in sandstone are, and the more dissipated strain energy and input strain energy are generated. 4) Smaller L/D ratios are associated with larger ESED and DSED values in sandstone. As the stress intensifies, the ESED and DSED of certain sandstones with larger L/D ratios experience a sharp increase when approaching the failure stress. Under equal stress levels, it is possible for sandstones with larger L/D ratios to exhibit higher ESED and DSED values compared to those with smaller L/D ratios.

Cohesive element-based chemo-thermo-mechanical multi-field coupled cracking simulation of early-age concrete

Due to the intense exothermic hydration process, early-age concrete undergoes restrained shrinkage deformation, which can easily lead to cracks in concrete structures during construction. In order to accurately predict the adverse effects of early-age concrete cracking behavior, a cohesive element-based chemo-thermo-mechanical multi-field coupled cracking model of early-age concrete is proposed in this study. Parametric analysis shows that by selecting appropriate gap conductance, constitutive thickness, mesh size, and viscosity coefficient for the cohesive elements, the multi-field coupled cracking model can successfully simulate the entire cracking process of early-age concrete, and it has the ability to obtain crack development behavior based on the real displacement field jumps, coordinates, and damage of cohesive elements. The validation of the numerical examples reveals the competing mechanisms between thermal expansion and autogenous shrinkage in early-age concrete and accurately predicts the cracking strain, region, time, and width (within an order of magnitude) as reported in the literature.

Analysis of crack evolution of expansive soil embankment under extreme arid climate

With the increasing impact of global climate change, the frequency of extreme arid climates worldwide is rising. These extreme arid conditions can have adverse effects on expansive soil embankments. In this study, the digital image technology is used to study the crack development characteristics of expansive soil embankments. The findings indicate that the crack development process in expansive soil can be divided into three stages: slow development, rapid development, and stable development. During the drying process, cracks develop differently on the waterward side, the top of the embankment, and the backwater side of the embankment. Initially, cracks appear on the top of the embankment, and their degree of development is the highest in this area. The crack degree on the top of the embankment is approximately 2 to 3 times greater than that on the waterward and backwater sides. Furthermore, longitudinal cracks on the top of the embankment have been analyzed from both macro and micro perspectives. This study is expected to help analyze the underlying formation mechanisms of desiccation cracking-inducing geohazards and access the long-term performance of expansive soil embankments in arid climates.

SEM-Guided Finite Element Simulation of Thermal Stresses in Multilayered Suspension Plasma-Sprayed TBCs

This study presents novel insights into thermal stress development and crack propagation mechanisms in single- and multilayered suspension plasma-sprayed (SPS) coatings of gadolinium zirconate (GZ) and yttria-stabilized zirconia (YSZ), thermally treated at 1150 °C. By combining image processing with finite element simulation, we pinpointed sites of high-stress concentration in the coatings, leading to specific cracking patterns. Our findings reveal a dynamic shift in the location of stress concentration from intercolumnar gaps to pores near the top coat/thermally grown oxide (TGO) interface with TGO thickening at elevated temperatures, promoting horizontal crack development across the ceramic layers. Significantly, the interface between the ceramic layer and TGO was found to be a critical area, experiencing the highest levels of both normal and shear stresses. These stresses influence failure modes: in double-layer SPS structures, relatively higher shear stresses can result in mode II failure, while in single-layer systems, the predominant normal stresses tend to cause mode I failure. Understanding stress behavior and failure mechanisms is essential for enhancing the durability of thermal barrier coatings (TBCs) in high-temperature applications. Therefore, by controlling the interfaces’ roughness along with improving interfacial toughness, the initiation and propagation of cracks can be delayed along these interfaces. Moreover, efforts to optimize the level of microstructural discontinuities, such as intercolumnar gaps and pores, within the creaming layer and close to the TGO interface should be undertaken to reduce crack formation in the TBC system.

Development of Magnesium Aluminate (MgAl2O4) Nanoparticles for refractory crucible application.

Ceramics are the oxides of metals and nonmetals with excellent compressive strength. Ceramics usually exhibit inert behavior at high temperatures. Magnesium aluminate (MgAl2O4), a member of the ceramic family, possesses a high working temperature up to 2000°C, low thermal conductivity, high strength even at elevated temperatures, and good corrosion resistance. Moreover, Magnesium Aluminate Nanoparticles (MANPs) can be used in the making of refractory crucible applications. This study focuses on the thermal behavior of Magnesium Aluminate Nanoparticles (MANPs) and their application in the making of refractory crucibles. The molten salt method is used to obtain MANPs. The presence of MANPs is seen by XRD peaks ranging from 66° to 67°. The determination of the smallest crystallite size of the sample is achieved by utilizing the Scherrer formula and is found to be 15.3 nm. The SEM micrographs provided further information, indicating an average particle size of 91.2 nm. At 600°C, DSC curves show that only 0.05 W/g heat flows into the material, and the TGA curve shows only 3% weight loss, which is prominent for thermal insulation applications. To investigate the thermal properties, crucibles of pure MANPs and the different compositions of MANPs and pure alumina are prepared. During the sintering, cracks appear on the crucible of pure magnesium aluminate. To explore the reason for crack development, tablets of MgAl2O4 are made and sintered at 1150°C. Ceramography shows the crack-free surfaces of all the tablets. Results confirm the thermal stability of MANPs at high temperatures and their suitability for melting crucible applications.