Stationary Crack Research Articles

Investigation of Fatigue Performance for In-Service Asphalt Pavement Mixtures Using Push-Pull Fatigue Test

With the increasing service life of asphalt pavements, fatigue cracking has become a typical distress that significantly affects the structural lifespan of in-service asphalt pavements. To address the issues of high variability in laboratory fatigue tests and the poor correlation between test results and actual pavement cracking conditions, this study collected field core samples from in-service highways with varying degrees of cracking. The study employed push-pull fatigue tests on asphalt mixtures and linear amplitude sweep tests on extracted and recovered asphalt to evaluate fatigue performance. Quantitative relationships between transverse crack spacing and fatigue indices were established. With the inclusion of laboratory-compacted asphalt mixtures, the relationship between transverse crack spacing and the average pseudo-stiffness degradation rates was well described by a logarithmic function (R2 = 0.928), while the apparent damage capacity achieved a stronger correlation (R2 = 0.945). The findings demonstrate that the push-pull fatigue test, based on a viscoelastic continuum damage model, shows high stability and repeatability, with the coefficients of variation for the indices consistently below 11%. Compared to the average pseudo-stiffness degradation rates, the apparent damage capacity demonstrates better discriminative capability as an evaluation index for the intermediate-temperature fatigue performance of asphalt mixtures. The fatigue life from linear amplitude sweep tests on extracted and recovered asphalt from core samples shows a high degree of consistency with the patterns observed in various parameters of push-pull fatigue tests. The findings confirm the reliability of the push-pull fatigue test for evaluating intermediate-temperature fatigue performance of asphalt mixtures and provide the necessary theoretical support for establishing a fatigue performance evaluation system for in-service asphalt pavements.

A bond strength analysis of carboncor asphalt layer on road surfaces

Transport infrastructure is a critical component of socio-economic development, particularly in rapidly urbanizing Vietnam, where increasing traffic congestion poses significant challenges. Road surface quality and durability are essential factors in ensuring the efficiency and longevity of the transportation system. Carboncor Asphalt (CA) material, with its superior resistance to cracking, water damage, and harsh weather conditions, is a promising solution for road surface construction in Vietnam. However, there is a limitation of research on the mechanical behavior of carboncor asphalt in the specific climatic and environmental conditions of the country. To address this knowledge gap, this study investigates the shear behavior of a carboncor asphalt layer interfaced with both asphalt concrete and cement concrete surface layers. A comprehensive range of laboratory tests is conducted to assess the bond strength between the carboncor asphalt layer and the overlying road surfaces. Results indicate a negative correlation between temperature and bond strength for the overlay carboncor asphalt layer on both asphalt and cement concrete substrates. Notably, bond strength demonstrated a significant increase over time. The findings in this study are expected to have significant implications for road construction and maintenance using CA overlay in Vietnam. By providing a scientific foundation for material selection, design, and construction of road surfaces tailored to local conditions, this study aims to enhance investment efficiency and reduce maintenance costs

In-Plane Analysis of Micro-Cracks Using Modified Couple-Stress Elasticity

Based upon the modified couple stress theory, we devise a procedure to analyze multiple interacting micro-cracks subject to the mixed mode deformation in an isotropic elastic plane. First, we carry out the asymptotic analysis of the displacement field at the tip of a stationary crack. The dominant term of displacement field reveals that the symmetric part of the stress tensor, which is energy conjugate to the strain tensor, is not singular. In contrast, the couple stress tensor has square root singularity at a crack tip. Furthermore, we use the Fourier integral transform to obtain the solution to an edge dislocation in an isotropic plane. Asymptotic analysis of the obtained solutions shows Cauchy singularity in the location of the edge dislocation. The integral equations for several interacting parallel micro-cracks are constructed via the distributed dislocation technique. These equations are solved numerically for the density of dislocations on a micro-crack surface. The effects of intrinsic material length scale on the stress field of a crack and the interaction between two parallel micro-cracks are studied.

Thermal cracking of effective decontamination and recycling of lubricating oil: mechanisms, conditions, and performance enhancements

Abstract Thermal cracking of SAE 40 lube oil contamination is a critical process for maintaining the efficiency and longevity of industrial machinery and automotive engines. This study investigates the mechanisms and outcomes of thermal cracking as a method to decompose and remove contaminants from lube oil (SAE40) and investigates the possibility of the use of solid coke produced as residue after the cracking process. The research also examines the optimal conditions for thermal cracking, including temperature ranges, heating rates, and the influence of catalysts. Analytical techniques such as thermogravimetry (TGA), Fourier-transform infrared spectroscopy (FTIR), and thermograms (DSC) are employed to characterize the chemical composition of the solid produced after treatment. This result reveals that the produced coke after the treatment demonstrates the resin capability, and it can be used as a binder or additive in lower temperature applications. This study underscores the potential of thermal cracking as an effective method for recycling contaminated lube oil, thereby contributing to sustainability and cost-efficiency in industrial maintenance practices.

A novel disc bend test specimen for realistic measuring of tensile strength in pavements under transverse cracking condition

A novel disc bend test specimen for realistic measuring of tensile strength in pavements under transverse cracking condition

Automated high-resolution asphalt pavement crack segmentation using deep convolutional neural networks with repeated hierarchical feature fusion

ABSTRACT Automated collection and detection of asphalt pavement crack conditions are essential for evaluating road conditions and maintenance planning. However, determining crack conditions accurately and efficiently has been challenging due to their small object-to-background information ratio, poor contrast with defect-free regions, and vulnerability to noise, such as stains and shadows. We approach this challenge by developing a series of methods that generate high-resolution asphalt pavement crack segmentation, the HRCrack series, which attends to hairline cracks by repeatedly fusing hierarchical features learned using convolutional neural networks. We validated and compared the models with ten widely used models on six open crack datasets. The results demonstrated that our models outperformed the considered methods on the self-made and six open-source datasets. Our best-performing model, HRCrack48, achieved an optimal dataset scale (ODS) F1 score of 0.948 on the self-made dataset. Our smallest model, HRCrack18s, was the fastest (25 FPS) while still providing competitive performance.

Hydrogen-rich gas generation from enhanced catalytic cracking of biomass tar and related model compounds on Ni-Fe/ASA@HZSM-5 catalyst: Pathways and mechanisms

This study focused on the design of complex tar model compounds (CTMC) and synthesized a highly efficient aluminum dross (ASA) combined with HZSM-5 molecular sieve co-loaded bimetallic Ni-Fe catalyst (Ni-Fe/ASA@HZSM-5), comprehensively evaluated the catalytic cracking of real tar and its model compound by adjusting the injection amount and injection state of tar, and catalyst types to obtain hydrogen-rich gas with high H2 and low CO2 content. The results showed under the conditions of the injection amount of 0.6 mL/min, pyrolysis temperature of 600 °C, reforming temperature of 800 °C in the liquid phase, Ni-Fe/ASA@HZSM-5 displays excellent catalytic cracking performance with CTMC conversion efficiency of 87.80 % (79.46 % of gas yield and 34.20 vol% of H2 yield). The possible cracking paths between different components of CTMC in the Ni-Fe catalytic system were summarized by the experimental data and product distribution, the catalytic mechanism of Ni–Fe based catalysts can be attributed to the formation of a Ni-Fe alloy and the synergistic effect of ASA and HZSM-5 co-carrier. Further, the catalytic cracking pathway of CTMC was enhanced in the gas phase, the higher CTMC conversion efficiency of 93.68 %, gas yield (a mass fraction of 82.51 %) and H2 (a volume fraction of 33.59 %) were obtained from catalytic cracking of CTMC, the liquid yield decreased by 12.39 %, significantly improved the cracking degree and gas production capacity of CTMC. The real tar showed the same catalytic pyrolysis path and product distribution. Under the same cracking conditions, the yields of gas, liquid and char were 84.85 %, 12.00 % and 3.15 % respectively, and obtained the hydrogen yield of 55.29 mL/g. The CTMC simplifies the cracking process and reduces polymerization, provides insights into the cracking mechanisms of heavy components in biomass tar. Furthermore, the synergy of Ni and Fe contributed to greater activity for CTMC and real tar cracking, ASA combined with HZSM-5 molecular sieve co-loaded bimetallic Ni-Fe catalysts have a promising application potential as highly efficient catalysts for tar removal and reutilization.

Influence of Ti element on the microstructure and crack of modulated WC-strengthened Ni-based alloy coatings by laser cladding

For laser cladding of WC reinforced Ni50A Ni-based alloy coatings can cause cracks and porosity. Cracks and pores will restrict the application and performance of the coating. In order to improve the crack condition of the coating, the influence of alloying element Ti on the crack was investigated by introducing it. Cracks in the coatings were eliminated. When the addition amount of Ti is 3wt%, the morphology and properties of the coating are the best. The phase composition, microstructure, elemental distribution and grain orientation of the coatings were characterised using X-ray Diffractometry (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Spectrometer (EDS), Electron Backscatter Diffraction (EBSD) and Transmission Electron Microscopy (TEM). The hardness and abrasion resistance of the coatings were tested using microhardness tester and friction tester. The results show that a large number of second phases are present in the coating when Ti particles are not added. The introduction of Ti element disperses the localised stresses in the Ni50A-WC coating. The macroscopic morphology of Ni50A-WC coating was improved. The introduction of Ti reduced the area of the second phase within the coating. The introduction of Ti generated TiC/TiWC2 in situ. However, the introduction of Ti increased the dilution rate and decreased the strength of the coating. Therefore, the microstructure of the coating can be controlled and the macroscopic defects of the coating can be improved by adjusting the addition ratio of Ti elements.

GDTE-based crack diagnosis for planetary gear: Mechanism, validation, and advantages compared to vibration-based technology

Effective health monitoring and fault diagnosis technologies are crucial to timely grasping the operation status of the planetary gear train (PGT). In this study, the mechanism for global dynamic transmission error (GDTE)-based crack diagnosis of PGT is revealed from dynamic responses and validated through experiments, and the advantages of this new technique are compared with the commonly used vibration-based technology. Initially, a dynamic model of the PGT considering various crack degrees and transfer path effects is established, and the effectiveness of the model response is verified through experiment. Subsequently, GDTE and vibration signals under different crack conditions are statistically analyzed in time domain and frequency domain to evaluate the differences in the ability to reveal gear failure information. Ultimately, the reasons for the different distribution of fault characterization information in the two signals are explained from a dynamic perspective. The results show that GDTE-based fault diagnosis exhibits greater sensitivity to gear crack degree compared to vibration-based monitoring technology, with both time and frequency domain responses containing richer fault characteristic information, particularly in low-frequency regions. The fault characteristics concentrated in higher-frequency regions in the vibration signal are mainly caused by the modulation between gear crack shock and the gear single and double tooth alternating meshing shock. Conversely, fault frequencies in GDTE signals are mainly found in low-frequency regions, as fault shocks in GDTE signals directly correlate with the rotational frequency of the cracked gear. Modulation effects and attenuation on the transfer path are identified as the main reasons for the weaker representation of gear fault information in vibration signals compared to GDTE signals.

Evaluation for anti-cracking performance of polyurethane grout based on overlay test

Polyurethane grouting has garnered increasing attention in road maintenance, owing to its exceptional interfacial adhesion, mechanical robustness, and chemical resilience. In comparison to conventional SBS-modified asphalt, polyurethane grout offers superior durability and demonstrates an enhanced capacity to inhibit crack propagation within asphalt mixtures. This study investigates the anti-cracking performance of polyurethane grout in comparison to traditional SBS-modified asphalt, utilizing the Overlay Test (OT) to simulate real-world conditions of reflective cracking in asphalt pavements. Results demonstrate that polyurethane grout significantly enhances the crack resistance of asphalt mixtures, manifesting superior durability and resistance to crack propagation at a controlled temperature of 25°C, with a marked increase in the number of loading cycles relative to the control. However, the performance of polyurethane grout is notably diminished under adverse conditions of low temperatures and water immersion. The investigation employs a multi-index evaluation, with gray correlation analysis delineating the efficacy of various indices in appraising crack resistance. Recommending the use of loading cycles, allowable failure times, and cumulative fracture energy as key metrics.

A rate–dependent cyclic cohesive zone model incorporating material viscoelasticity and fatigue damage accumulation effects

Numerical simulation and analysis of high–frequency fatigue crack growth rates (FCGRs) have long been a challenging task in vibration fatigue assessment. The frequency effect on FCGRs can be effectively modeled through strain rate hardening. Additionally, the cyclic cohesive zone model (CCZM) has demonstrated good accuracy in simulating quasi–static fatigue crack growth (FCG). In this study, a rate–dependent cyclic cohesive zone model (RCCZM) is proposed by integrating the strain rate hardening term from the Johnson–Cook (J–C) model and the dynamic fracture toughness model with the CCZM. A linear scaling method is employed to improve both the speed and accuracy of FCGR predictions. The model is validated by comparing the theoretical range of FCGRs for aluminum alloys, based on dislocation dynamics theory, with experimental data for titanium alloys, and the extent of influence of the strain rate correction parameter is thoroughly analyzed. The RCCZM model demonstrates high reliability and accuracy, confirming that the frequency effect on metal FCGRs is primarily due to the strain rate’s impact on strength, with minimal effect from fracture toughness.

Biologically inspired adaptive crack network reconstruction based on slime mould algorithm.

The dynamic crack propagation trajectories play a crucial role in enhancing our understanding of spatial mechanisms involved in crack expansion. However, visualization of internal cracks under complex crack conditions has always been a challenge. Biological networks have been honed by many cycles of evolutionary selection pressure and are likely to yield reasonable solutions to such combinatorial optimization problems. This study applied the slime mould algorithm to improve the accuracy of internal crack localization in rocks and employed Minimum spanning tree and Gaussian mixture model to construct the crack propagation trajectories. By introducing the concept of bond length, the evolution characteristics of crack levels were effectively characterized. Research results showed that this approach effectively preserves essential crack localization information while mitigating the influence of interfering parameters, providing crack characterization results that exhibit high consistency with actual fracture patterns. The curves of cumulative bond length and relative bond length over time conform to the trend of a Growth/Sigmoidal curve. The strength of the bond was correlated with the temporal process of crack propagation. This result could be helpful for analyzing crack trajectories and predicting rock stability.

25 years field test history and fatigue damage analysis for a scrapped ladle crane

Fatigue performances of ladle cranes will gradually decrease with the increase of service years. The service history and the fatigue damage of a scrapped ladle crane were investigated and analyzed in this paper. The test history of the ladle crane was collected and concluded, and the statistical parameters of lifting capacity and the crack condition during service were determined. The last comprehensive field test before scrapping the ladle crane was introduced in detail and the damage evolution was analyzed. The geometry measurement showed that the main girders’ stiffness had changed obviously. The stress test of the crack-prone positions of the metal structure revealed their remaining bearing capacity and the damage evolution characteristics. Further analysis proved that the static stiffness of the main girder has a closer relationship with damage deterioration. Some material property inspections were carried out for samples cut from the scrapped crane’s main girder, which were of the load-carrying part and the non-load-carrying part respectively. Results showed that the elastic modulus and hardness of the materials decreased evidently after service, while other mechanical properties did not change significantly. This study will provide useful references for further understanding of the fatigue characteristics and evolution behaviors of ladle cranes.

Solidification cracking susceptibility of alloy 718 during additive manufacturing and evaluating method

Although hot cracks frequently occur during metal additive manufacturing (AM), there are very few fundamental studies on the cracking behaviour and susceptibility. In this study, a horizontal tensile-type hot cracking test was investigated for evaluating the solidification cracking susceptibility of alloy 718 quantitatively during AM, particularly in laser powder bed fusion. The factors influencing the cracking susceptibility were also examined. The solidification cracking was reproduced by the melting of the AMed specimen with a tensile load under conditions of heat source simulating the AM process. The critical initial tensile stress for solidification crack initiation could apply as an evaluation index for cracking susceptibility. The critical initial stress decreased with increasing the laser power. A similar tendency was observed during the melting of the powders set on tiny groove for simulating AM process. The critical strain rate for solidification cracking (CST) was derived by a thermal elastic–plastic analysis using the critical initial stress measured experimentally. The CST at the laser power of 1125 W was higher than that of 1000 W for no crack condition. Therefore, high CST corresponding to penetration shape with high laser power induce to deteriorate the solidification cracking susceptibility.

A novel approach to enhance the structural integrity of a bottom-edge cracked I-beam with piezoelectric actuators

Structural health monitoring and repair have become increasingly crucial in confirming the safety and longevity of damaged structures. This study presents a novel approach to enhancing the structural integrity and extending the fatigue life of a bottom-edge cracked I-beam by applying piezoelectric actuators strategically placed along the crack location by actively suppressing crack propagation. An innovative actuation system induces controlled deformations in the I-beam, effectively reducing the Stress Intensity Factor (SIF) and preventing crack propagation. The efficacy of the proposed approach is validated through a series of numerical results on the ABAQUS platform, including static loading, fatigue loading, and crack growth monitoring. Various parameters, like maximum loading capacity under static loading, interpretation of crack growth rate, and service life, are monitored and analyzed throughout the cyclic loading process. The results demonstrate that the application of 500 V to the piezoelectric actuators significantly reduces the SIF by 16.62% under a 2 kN total load, a 2.86% enhanced maximum load-carrying capacity is obtained, delayed crack propagation is found after repair, and a 72.67% extended service life is achieved under a load range of 0.2 kN to 2 kN. Overall, the outcomes of this research lead to the development of innovative and efficient techniques for delaying the propagation of cracks, thereby preventing the premature onset of catastrophic failure of cracked I-beams.

Research on the dynamics and mechanism of thermal cracking of coal-based endothermic hydrocarbon fuels

Thermal cracking of endothermic hydrocarbon fuels (EHF) plays an important role in the endothermic process when the fuel temperature exceeds the supercritical temperature. To gain a deeper understanding of the thermal cracking behavior of EHF, this work discusses the thermal cracking law and reaction mechanism of coal-based EHF at different temperatures through static thermal cracking experiments, and establishes a total molecular reaction dynamics model containing 34 species and 24-step reactions based on product distribution. The results show that in the temperature range of 450℃ to 500℃, the gas phase yield of the fuel increases linearly from 8 % to 56 %, and the conversion rate reaches up to 96.1 %. The kinetic reaction of thermal cracking conforms to the primary kinetic equation, the cracking rate constant k is between 1.08×10−4∼7.92×10−4 s−1, the activation energy Ea=184.47±11.5 kJ∙mol−1, and the precursor factor lnA=21.61±3.0. Gas phase products include hydrogen, methane, ethane, ethylene, propane and butane. Liquid phase products include paraffins, alkyldecahydronaphthalenes and aromatic hydrocarbons. As the cracking depth increases, the degree of fuel branching first increases and then decreases, up to 0.33. Paraffins and alkyldecahydronaphthalenes are gradually converted into olefins, cyclic olefins, benzene, naphthalene, indene, fluorene and pyrene and other compounds. Based on the product distribution, the reaction mechanism of thermal cracking of coal-based EHF is speculated to include single-molecule β-cracking, bimolecular F-S-S, intramolecular H-transfer, cyclization and isomerization mechanisms.

Weak interface-induced repeated kinking of a central crack in a brittle multilayered plate under remote shear loading

Understanding the repeated kinking pattern of cracks is essential for controlling the complex fracture trajectories in multilayered composites. While previous studies have explored many aspects of fractures in layered materials, the conditions governing the repeated kinking behavior under basic loading modes remain largely unrevealed. This research elucidates the continual kinking condition for a central crack in a brittle, multilayered plate with closely-parallel weak interfaces under remote shear stresses. Using the strain energy release rate (SERR) ratio criterion, we analytically derived a closed-form solution to the condition through the equivalent crack concept. The solution specifies a value domain for the intersection angle and fracture toughness ratio of weak interfaces, where the load-guided direction competes closely with the weak interface-guided direction to shape the crack trajectory into a repeated kinking pattern. Our theoretical results, validated by a series of finite element (FE) simulations, clarify how closely-parallel weak interfaces induce repeated crack kinking in multilayered materials under remote shear loading. This research paves the way for the deeper understanding of intricate crack trajectories under mixed loads in various practical applications.

Effective cracking of heavy crude oil by using shock-induced nanobubble collapse: A molecular dynamics study

We investigate molecular mechanisms of hydrocarbon cracking in heavy crude oil promoted by nanobubble collapse due to ultrasound-originated shock wave. Our millions-atom molecular dynamics simulations reveal rapid flow of molecules, causing nanobubble collapse and formation of energetic nanojet with a mushroom-like shape. The nanojet apex exhibits extremely high temperature before and just after the bubble collapse, which makes a favorable condition for effective cracking of paraffin molecules. The cracking rate and portion of nanobubble-containing systems are larger than those of perfect system before the bubble collapse, and larger size of nanobubble is preferable for the cracking. The cracking efficiency is improved for the paraffin molecules with longer carbon chain.

Integrated FEM-Multibody Co-Simulation of Additively Manufactured Hip Prosthesis containing cracks.

The increase in life expectancy and attention to the quality of life of elderly people spurred the need, in the last decades, to increase the capabilities of medical and surgical techniques. Among these, the development of prosthetic implants has been a staple of biomedical engineering research since the 70’s. In order to satisfy the challenging demands, the latest novelties in industrial engineering are being tested in their applicability to subjects. The 3D printing of metal alloys can produce a highly customizable product, which, after the proper heat treatments, can possess adequate mechanical properties to ensure a satisfactory component life. Defective products are often the results of wrong or absent post-processing treatments which may cause an uncontrolled crack propagation and a premature total failure of the implant. The behavior of such a product, with various critical crack conditions, was investigated by an integrated MBD-FEM co-simulation environment, focused on a femur subjected to total hip replacement. It was concluded that the Stress Intensity Factor (SIF) computed by the model is compatible with the premature failures experienced by patients, and as such, this model opens the possibility for further analyses aimed at understanding the role of defects on the durability of prothesis

Assessment of the Crack Level in Silo Foundations Due to Settlement

A silo is a structure used to store bulk materials (bulk materials). Silos are generally used in agriculture as storage for grains and animal feed. The foundation silo must be designed to withstand the forces generated and accommodate the movements transmitted to the structure and foundation by the seismic ground motion design. The dynamic properties of the soil, the anticipated ground motion, the design basis for the strength and energy dissipation capacity of the structure, and the dynamic characteristics of the soil should be included in determining the foundation design criteria. In PT X, SILO structure serves as a place for livestock feed production, with the hope that it can last for a relatively long time. The condition of the existing SILO structure is currently some cracks in several parts of the piles and the bottom slab. The results of the visual inspection in the field regarding the condition and level of cracking in the silo foundation were compiled into a matrix inspection table using four categories: category 1 indicates no repairs needed, category 2 marked in green, represents an acceptable cracking condition with minor repairs, category 3 marked in yellow indicates moderate cracking that requires attention, and category 4 marked in red signifies major cracking or unacceptable conditions that require structural repairs. The results of the field inspection indicate that approximately 57% of the concrete slab foundation of the silo requires needs attention or repair. The condition of the plate/slab structure has some cracks measuring 0.3mm - 0.5mm, but injection and patching have been carried out. As for the condition of the silo foundation, about 30% requires needs attention and repair as well.