Cracking Behavior Research Articles

Bending performance of lightweight aggregate concrete beam subjected to reinforcement corrosion: Experimental and numerical study

The application of lightweight aggregate concrete (LWAC) benefits the structural behavior of long-span and high-rise buildings. However, the corrosion-related durability issue of bending elements made of LWAC has remained unresolved for decades, and the bending performance of corroded LWAC beam, including load-bearing capacity, stiffness, cracking, and etc., has not yet been clearly defined due to limited knowledge in the available literature. This study aims to investigate the bending performance of LWAC beams subjected to reinforcement corrosion, and the test results provide valuable data for addressing the research gap relevant to the topic and contribute fundamental knowledge to the promotion of structural LWAC elements. Seven reinforced LWAC beams were tested to examine the cracking behavior, characteristic loads and deflections, deformation ability, and distribution of cross section strain at various moments. The modelling method considering the effect of rebar corrosion for LWAC beam was proposed. It was concluded that the corrosion of longitudinal rebar led to decreased cracking, yielding, and ultimate moment of LWAC beam, while the corrosion of stirrups increased the cracking moment and had little effects on the yielding and ultimate moments. The ductility of the tested specimens initially decreased and then increased with the raising corrosion level of the longitudinal rebar, which was attributed to the variation in bond performance between the rebar and LWAC. All tested beams exhibited a yielding deflection smaller than 1/235 of the span length. The strain distribution of the mid-span cross-section exhibited a nonlinear feature with increasing mass loss of the corroded longitudinal steel rebar. The proposed modelling procedure considering the corrosion effect showed good agreement with the test results, and a preliminary analysis of the bending performance of LWAC beams with different steel reinforcement corrosion ratios was completed. Data Availability StatementAll data, models, or code that support the findings of this study are available from the corresponding author upon reasonable request.

Cracking and Precipitation Behavior of Refractory BCC–B2 Alloys Under Laser Melting Conditions

Cracking and Precipitation Behavior of Refractory BCC–B2 Alloys Under Laser Melting Conditions

A new intracellularly regulated release pattern controlled by coordinated carrier cracking and drug release

To further develop intracellular delivery systems of macromolecular drugs, understanding the cracking mechanisms and drug release behaviors of environment-responsive carriers, as well as their intrinsic linkages, is essential for achieving personalized or diversified delivery of macromolecular drugs. Herein, we designed a class of degradable dendritic mesoporous nanoparticles (DDMSNs), utilizing very large cavities and tetrasulfide bonds in the skeleton to achieve high drug loading and release within tumor cells. To comprehensively understand and develop intracellular drug delivery systems, this study delved deeper into the delivery of tetrasulfide-bonded DDMSNs, including chemical reactions, cracking kinetics, and release kinetics. First, the drug release of the DDMSNs within the cytoplasm was closely related to the chemical reaction of tetrasulfide bonds. Thus, based on experiments, the oxidation–reduction mechanism of tetrasulfide-bonded DDMSNs was explained, and the relationship was elaborated between cracking and drug release of the DDMSNs with different sulfur contents. To further explore this relationship, the cracking behavior, drug-loading capacity and release capacity of the DDMSNs was investigated with the different sulfur contents in different simulated environments, and in MDA-MB-231 cancer cells. Inspired by the reaction kinetic calculations, we analyzed the cracking and drug release behavior of the DDMSNs, and ultimately achieved dual cracking secondary drug release of the carriers by controlling the content of sulfur elements. Here, we report improved biomedical materials for advanced, customized, and intentional intracellular delivery of therapeutic macromolecules, in which theoretical calculations and experimental components were combined to study the mechanism of drug release influenced by carrier cracking, providing essential guidance for designing advanced drug delivery systems through a chemical engineering method.

Phase-field modelings of fracture investigate the influence of interfacial effects on damage and optimal material distribution in brittle inclusion-matrix structures

This present work uses the phase-field modelings to investigate the influence of interfacial effects on damage and mechanical behavior, as well as the optimal distribution of the inclusion shape within brittle inclusion-matrix structures in various typical cases. These two constituent phases in the structures are assumed to be either isotropic or anisotropic. To achieve these goals, this work will: (i) use the phase-field modelings either considering or neglecting interfacial debonding, and the anisotropic phase-field modeling; (ii) determine and incorporate the strain tensor orthogonal decompositions into each specific phase-field modeling to enhance the accuracy and effectiveness of the simulation methods; (iii) combine the phase-field modelings with the BESO topology optimization algorithm to analyze the influence of interfacial effects on relationship curves and the optimal distribution of the inclusion shape. Through proposed numerical examples, it is demonstrated that the interfacial effects strongly influence crack paths, behavior curves, and optimal material distribution in structures. When considering interfacial effects, cracks are almost unable to penetrate into the inclusion phase. However, when neglecting interfacial effects, cracks propagate into the inclusion phase. This reason makes the structure more difficult to damage than when considering the interfacial effects, as evidenced by greater peak load values in behavior curves and greater total fracture resistance of the material. Especially in the example of inclusion phase optimization, the total fracture resistance value of the case neglecting interfacial effects is more than 107.9% greater than that considering interfacial effects.

Impact of Impurity Ions in Secondary Circuit Water on Cracking Behaviour of PWR Steam Generator 690TT Tube

Impact of Impurity Ions in Secondary Circuit Water on Cracking Behaviour of PWR Steam Generator 690TT Tube

Microstructural characterization of AISI 440C stainless tool steel fabricated by laser powder bed fusion

Abstract The microstructure of a stainless tool steel AISI 440C fabricated by laser powder bed fusion (L-PBF) without pre-heating of the build plate was characterized by multi-scale experimental methods. In combination with thermodynamic calculations, the solidification and cooling-down procedures were analyzed with the intention to understand the cracking behavior of high carbon tool steels processed by L-PBF. The results showed a fully austenitic structure in the as-built sample with sub-micro cellular structures and nano-sized carbides decorating the cell walls. Significant segregation exists merely at the intersection of cell walls while it is absent along high angle grain boundaries. Factors contributing to crack-free AISI 440C are discussed, providing guidelines for future L-PBF fabrication of high-carbon tool steels.

Rate dependent C* fracture parameter using the optimized wedge-split test geometry and vision-based automated crack tip detection

Typical monotonic load-line displacement (LLD) control and crack mouth opening displacement (CMOD) control cracking tests are limited to singular loading rates and testing temperatures. These experimental protocols are not designed to derive a fundamental fracture parameter capable of relating to the viscoelastic property and cracking behavior of asphalt concrete (AC). On the other hand, a multi-rate LLD-control monotonic fracture experiment is capable of capturing the viscoelastic cracking behavior of AC by providing the rate-dependent fundamental C* fracture parameter as an output. Crack length and crack speed parameters are combined with reaction loads to calculate the rate-dependent C* parameter. The current C* experiment protocol implements manual processing of video images and exhibits high variability. The study aims to optimize the wedge-split geometry and improve the C* fracture parameter calculation protocol by applying an automated vision-based crack detection system and recording the crack growth path, considering the horizontal and vertical movement of the crack tip with higher accuracy. The three notch lengths (5, 15, and 30 mm) were evaluated. Plant and laboratory-produced mixes with varying stiffness and fracture characteristics were included in the testing program. An optimized notch length for the test geometry was determined based on the on-specimen strain field observed using the digital image correlation (DIC) technique and crack path analysis. The optimum notch length was found to be 15 mm due to consistent strain localization at the crack tip and less crack deviation in the horizontal direction. The main contribution of this paper is the proposed vision-based crack path detection method, which enables measuring the crack path's true crack length and maximum horizontal deviation. The developed protocol and optimization of the testing geometry led to a significant improvement of the existing C* testing protocol, resulting in higher data quality and consistent results. The proposed protocol was validated using three comparable and distinctively different lab-produced mixtures. The results show that the C* experiment effectively differentiated between the mixes based on crack speed and the C* parameter.

Synergistic effects of aggregate-void distribution on low-temperature fracture performance and crack propagation of asphalt concrete under mode I and mode II fracturing

Mesoscopic structures of asphalt concrete play an important role in low-temperature cracking behavior. Existing studies mainly focus on a single feature of the mesoscopic structure, neglecting the spatial distribution and synergistic effects of aggregates and voids, especially in Mode II fracturing. The results show that: in the case of −5 °C and Mode I fracturing, the fracture trend is less affected by the spatial distribution of mesoscopic structure, and tending to spread through aggregate and asphalt mastic along the shortest path. In the case of −5 °C and Mode II fracturing, the crack is easily affected by the distribution of large particle size aggregates in the initial zone, but not by the uneven distribution of voids. In the case of 10 °C and Mode I fracturing, the dominant large aggregate particle size influence on the path is weakened, and the effect of void distribution on the cracking path is perceptibly increased. In the case of 10 °C and Mode II fracturing, the location of large-particle aggregate determines the main streak of fractures, and the uneven distribution of void space determines the occurrence of fracture bending.

Finite element modeling of active cracking in actively reinforced concrete pavement slab exposed to fluctuating temperature

The continuously reinforced concrete pavement (CRCP) system grapples with challenges such as non-uniform transverse crack patterns and the need for substantial reinforcement. Field research on the Belgian CRCP sections along motorway E313 indicates that active cracking induced by partial surface saw-cuts consistently leads to transverse crack patterns. This study introduces an innovative modification to the CRCP: the actively reinforced concrete pavement design (ARCP). The ARCP leverages partial surface saw-cuts to reduce reinforcement needs by replacing continuous-length steel bars with partial-length counterparts. The main objective of the present study is to develop a 3D finite element (FE) model capturing the active cracking behavior of ARCP under realistic external temperature variations. Comparative analysis with CRCP considers early-age crack patterns, crack strain development, and the distribution of maximum steel stress for different steel ratios (0.67%, 0.75%, and 0.85%). FE simulation results align with field data, indicating that ARCP exhibits similar early-age cracking behavior to CRCP but with a significant 24 to 42% reduction in total reinforcement. This innovation presents a promising avenue for addressing CRCP challenges while optimizing material usage in pavement construction.

Impact of stained- and cemented-type sandstone natural fractures on stress-weathered cracking behavior

Impact of stained- and cemented-type sandstone natural fractures on stress-weathered cracking behavior

Circular Economy of Construction and Demolition Waste for Nanocomposite Cement: XRD, NMR, Vickers, Voltammetric and EIS Characterization.

In this paper, we present the structural, mechanical and electrical properties of composite cement materials that can be widely used as substituent for cement. We start with the characterization of a composite cement sample using an analysis of X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) spectra. The measurements of the Vickers hardness, cyclic and sweep linear voltammetry and electrochemical impedance spectroscopy (EIS) of composite cement materials were also recorded. This study compared the effect of the different nanocomposites added to cement on the mitigation of the alkali-silica reaction, which is responsible for the swelling, cracking and deleterious behavior of the material. The enhancement in Vickers hardness was more pronounced for composite cement materials. In contrast, the values of Vickers hardness decreased for the composite cement containing mortar and the control sample, suggesting that the long-term performance of cement was compromised. In order to obtain information about the bulk resistance of the composite cement material, electrochemical impedance spectroscopy (EIS) data were employed. The results suggest that for composite cement materials, there is an improvement in bulk electrical resistance, which can be attributed to the lower amounts of cracks and swelling due to lower expansion. In the control sample, a reduction in the bulk resistance suggests the formation of microcracks, which cause the aging and degradation of the material. The intersection of arcs in the EIS spectrum of the mixed composite cement sample gradually increased by an alkaline exposure of up to 21 days and finally shifted towards a low value of high frequency with an increase in alkaline exposure of up to 28 days.

Mechanistic Pavement Modeling of Typical Brazilian Pavements: Cohesive Zone Fracture Modeling and Continuum Damage Modeling

Pavement performance evaluation with respect to fatigue cracking has seen a major shift toward more rigorous mechanistic models that can capture the complex damage response of the mixtures more accurately. This study utilized two mechanistic methods (cohesive zone [CZ]-based fracture modeling and continuum damage [CD] modeling) to study the cracking behavior of asphalt mixtures and subsequently predict the damage-associated performance of pavements. A Superpave mixture designed for Brazilian highway conditions was selected to evaluate the two modeling approaches for the performance of the mixture when utilized as a surface course within typical Brazilian highway pavements. The mixture was first evaluated for its linear viscoelastic properties, and then the damage characteristics of the mixture were obtained through two different experiments: the semi-circular bending (SCB) beam test and the cyclic fatigue (CF) test. The SCB tests performed at different loading rates were used to obtain the model parameters of the nonlinear viscoelastic CZ model with a Gaussian damage evolution criterion, while the CF tests were performed at different strain amplitudes, and the mixture-specific damage characteristic curve and the fatigue failure criterion were obtained using the simplified-viscoelastic continuum damage model. From a design perspective, three pavement structures that varied in geometry (pavement layer thickness) and underlying layer properties were selected while retaining the same asphalt mixture. The three pavement scenarios were evaluated for the fatigue cracking performance from each of the mechanistic modeling methods. The results indicate that both methods rank the performance of the pavement structures in a similar manner, while the damage initiation and progression were seen to be different because of the different mechanics in modeling cracks.

Experimental investigation on solidification cracking & intergranular corrosion of AISI 321 & AISI 316 L dissimilar weld on pulsed current gas tungsten arc welding (PCGTAW)

Dissimilar metal combinations are frequently employed in the power generation and nuclear industries. Where stainless steel piping systems are connected to pressure vessels made of low-alloy steel, the subsystems of liquid rocket engines also have different, dissimilar material combinations. Dissimilar welding plays a vital role in ensuring the integrity, performance, and reliability of components and structures operating in cryogenic environments, in this study, plates of AISI 316L and AISI 321, each 5 mm thick, were successfully joined using the pulsed current gas tungsten arc welding (PCGTAW) technique with optimized process parameters. These weld joints are mostly present in rocket engines subjected to a cryogenic environment. Due to the low temperature environment, the metallurgical properties of these joints change, which affects their mechanical properties. As it is a structural part, PCGTAW welding is most common method for joining this kind of material.In this work, Microstructural analysis of the weldment revealed a combination of vermicular, lacy, and acicular ferrite morphologies in the fusion zone at the root, mid, and crown locations.Furthermore, no solidification cracking was detected in the weldments based on the optical micrograph and SEM results. Intergranular corrosion (IGC) testing indicated the absence of a ditch structure, suggesting that the heat-affected zone (HAZ) on both sides of the weld joint was not being susceptible to sensitization. However, the HAZ of the AISI 316L side exhibited coarser grains compared to AISI 321. Analysis of tensile properties revealed a significant influence of the testing environment on the tensile strength of the dissimilar welded joints. At room temperature, the average ultimate tensile strength (UTS) was measured as 621 MPa. Remarkably, at cryogenic conditions, the average tensile properties significantly increased to 1319 MPa.Microhardness analysis showed the highest hardness associated with the AISI 321 side. The fusion zone exhibited a large deviation in the hardness profile (205 ± 10 HV), with the highest average hardness observed in the middle part of the weld. However, the hot cracking behavior of the weld was investigated by using a suutula diagram at various locations of the weld. The investigation revealed that the Creq/Nieq ratio exceeded the critical threshold value, effectively diminishing the propensity for hot cracking in the fusion zone. Overall, these findings underscore the effectiveness of the PCGTAW technique in joining dissimilar materials, as well as the importance of microstructural and mechanical property evaluations, especially under extreme operating conditions such as cryogenic temperatures.Paraphrase.

Comprehensive Understanding of TGO Morphology Effect on the Thermal Barrier Coatings Failure Under Free Edges

Abstract The growth stresses induced by the thermally grown oxide (TGO) will be amplified at the free-edge site, making the free-edge site a weak part of the thermal barrier coatings (TBCs). In this study, the TBCs failure behavior is investigated based on different TGO morphologies under free edges. The thermomechanical model is established by creating straight lines and simplified sinusoidal curves, respectively. Dynamic TGO growth is realized by the secondary development of the subroutine. The cohesive element is inserted at the TC/TGO interface to simulate the delamination. The stress evolution near different TGO morphologies under the influence of the free edge are examined. In addition, the interfacial cracking behavior near the free edge is also explored. The results show that the appearance of the free edge will deteriorate the stress condition in the nearby area, change the preferred cracking area, and induce the earlier failure behavior. The straight line morphology has the most “friendly” stress distribution. The sinusoidal curves have peaks and valleys, and different areas of the TGO shape are different under the influence of the free edge, but all of them have the effect of stress “convergence”. These results can provide significant guidance to develop the next-generation advanced TBCs.

Influence of discrete laser surface melting on hot cracking behavior and mechanical properties of Q235 steel

Modern industries demand higher mechanical properties from components. Traditional heat treatment methods often suffer from drawbacks such as high production costs, time-intensive processes, and labor-intensive procedures. The integration of bionic engineering with laser surface melting has given rise to Discrete Laser Surface Melting (DLSM) technology, effectively mitigating these shortcomings. Previous research has substantiated the capability of this technology to significantly enhance various metal properties. This study employed an Nd:YAG pulsed laser for the DLSM treatment of Q235 steel. The discrete laser surface melted (DLSMed) units were prepared on Q235 steel samples. Subsequent analysis utilized scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive spectroscopy (EDS) to examine the microstructure and chemical composition of the DLSMed samples. Surface profilometry, hardness testing, and X-ray stress testing were conducted to measure surface roughness, microhardness, and residual stress, respectively. Mechanical properties were evaluated using tensile and impact testing machines. Experimental findings revealed that the DLSMed sample's surface could be divided into three regions: the melting zone, the heat-affected zone (HAZ), and the substrate. The microstructure of the melting zone consisted of refined martensite. The depth and width of the DLSMed units exhibited a certain regularity with variations in the defocus distance. Increasing the defocus distance positively impacted grain refinement and hardness but also led to an increase in surface roughness. Residual stress increased within a specific defocusing range, but beyond this range, its variation lost regularity. Hot cracking behavior within the DLSMed unit encompassed four stages: crack nucleation, propagation, healing, and decomposition. Different defocusing distances and the distribution of DLSMed units significantly affected the tensile strength and impact toughness of the samples. As the defocusing distance increased, the tensile and yield strength of DLSMed samples with transverse units gradually decreased. In contrast, samples with longitudinal units showed a trend of first decreasing and then increasing in tensile and yield strength. The distribution of DLSMed units played a significant role in improving the tensile properties of Q235 steel. The contribution of three factors to the impact performance of DLSMed samples was ranked from high to low as hardness, grain size, and yield strength ratio. The soft phase (substrate) could absorb impact energy and convert it into strain energy stored in the DLSMed sample. Only when the distribution of DLSMed units (hard phases) aligned with the tensile direction could they effectively limit the plastic deformation and enhance the mechanical properties of Q235 steel. However, an increase in defocusing distance led to increased brittleness, deteriorating the mechanical properties of the DLSMed samples. Finally, this study unveiled the strengthening mechanisms of DLSMed samples, providing valuable insights for future applications in enhancing the mechanical properties of metals.

Fatigue crack extension mechanism and mode-type analyses of martensitic steels for proposing fatigue strength evaluation method: Example of 18% Ni BCC martensitic steel

The fatigue properties of martensitic steels tend to differ significantly from those of low- and medium-strength steels. Even if the hardness is the same, the fatigue strength varies substantially depending on the microstructure. Thus, for using martensitic steel rationally and developing materials with high fatigue strength, it is desirable to establish a fatigue strength evaluation method that can consider the microstructural effects on fatigue properties. For this purpose, 18% Ni bcc martensitic steel was used as a model metal to conduct rotating-bending fatigue tests in this study. The fatigue crack behavior on the smooth specimen surface was examined, and the fracture surface morphology on both sides of the broken specimen and the microplastic strain distribution near the fatigue crack tip were analyzed. The results clarified the mechanism underlying fatigue crack extension (FCE). The analytical results revealed three types of FCE mechanisms dependent on the stress amplitude, stress state (i.e., plane stress or plane strain), and martensitic microstructure. Considering these mechanisms, a unique stress–life curve was predicted, and a particular fatigue crack shape and fractography were confirmed. The material indices were speculated to be the representative properties of martensitic steels.

The impact of loading rate on chloride induced stress corrosion cracking of 304L stainless steel

Abstract The influence of applied loading rate (dK/dt) on stress corrosion cracking (SCC) behavior in annealed 304L stainless steel immersed in 4.7 M MgCl2 solution was assessed at varying temperatures from 23 °C to 70 °C. Measured crack growth rates obtained under rising K loading (dK/dt > 0) are compared to those obtained during static K testing. A rising K-based loading protocol was found to yield more conservative crack growth rates across all temperatures, with the variation in crack growth rates (and therefore the dependence in loading rate) decreasing with increasing environmental severity.

Transient behavior of oxide fuels with controlled microstructure and Cr2O3 additive

Microstructure and Cr2O3 doping profoundly impact the thermal-mechanical properties and fracture of oxides fuels. It is a challenge to study the transient behavior of nuclear fuels under loss-of-coolant-event (LOCA). In this study, the crack behavior of UO2 pellets with controlled grain structure and Cr2O3 doping was tested with rapid power ramping (300−900 °C per min) mimicking a prototypical LOCA heating profile. Dense micron-sized UO2 pellets display well-maintained integrity without cracking with the ramping up to 1500 °C at a heating rate of 8 °C per second. Fracture occurs in both pure and Cr2O3-doped dense nano-sized UO2 pellets. The Cr2O3 doped oxide fuel pellet with a larger grain size (~ 22.2 μm) displays the best performance under LOCA testing due to its highest thermal conductivity under high temperature. FEA calculations suggest a temperature gradient across the fuel pellet during transient testing, resulting in residual stress and cracking, which can be correlated with their thermal-mechanical properties.

Investigating Size Effects on Gradient-Related Crack Behavior in Frozen Sand Samples: A Simplified Approach and Application

Investigating Size Effects on Gradient-Related Crack Behavior in Frozen Sand Samples: A Simplified Approach and Application

Fracture analysis of spatially graded piezoelectric-flexoelectric materials using XIGA

Dielectric Functionally Graded Materials (FGMs) exhibit superior flexoelectric properties. Gradual changes in material properties lead to large strain gradients and excellent flexoelectric responses. Cracks behave in a complex manner inside piezoelectric-flexoelectric FGMs subjected to electromechanical loading. An extended isogeometric analysis (XIGA)-based formulation is developed for flexoelectric FGMs with crack discontinuities. Ceramic-polymer FGMs of barium titanate (BTO) and polyvinylidene fluoride (PVDF) are selected for analysis since this material combination has shown better flexoelectric response solely due to gradation. A higher-order electromechanical J-integral is used to study the behavior of cracks. The fracture behavior of different crack geometries at various grading indices and levels of flexoelectricity is investigated. A crack interaction study is conducted with varying crack parameters. The length-scale effect on the energy release rate is also shown. A significant reduction in the energy release rate is observed in FGMs due to the flexoelectric effect.