Crack Resistance Research Articles

Preferential fatigue cracking at basal twist grain boundary (BTGB) in bimodal Ti-5Al-4V alloy: Dislocation activities and crack initiation

In recent years, (0001) twist grain boundaries (BTGBs) located in primary α grain clusters were identified as fatigue crack nucleation sites in different Ti alloys. In the present study, crack initiation was investigated in a bimodal Ti-5Al-4V alloy subjected to low-cycle fatigue and dwell-fatigue loadings at room temperature. The low fraction of primary α grains was not associated with a lack of sensitivity to BTGB cracking. Transmission electron microscopy and electron back-scattered diffraction were used to characterize BTGBs in the initial microstructure. The fatigue mechanisms were then analyzed with a focus on dislocation activity. αp grains adjacent to cracked BTGBs contained a high dislocation density. It was primarily composed of planar slip bands of <a> dislocations. In addition, <c+a> dislocations were noticed in the vicinity of cracked BTGBs. They supposedly pertain to crack tip plasticity during growth, and no evidence of a role of an incoming slip event in crack nucleation was obtained. Also, basal slip bands extending across adjacent grains were found to emerge from BTGBs. This feature provides an easier path for crack extension when growth along the grain boundary becomes difficult owing to a deviation from the basal plane. Atom probe tomography analyses evidenced V and Fe segregation at a grain boundary with a significant deviation from the BTGB configuration. This suggests a possible contribution of local solute segregation to the high cracking resistance of general αp / αp grain boundaries. This work provides new insights into the mechanisms involved in cracking of BTGB in Ti alloys subjected to cyclic loadings.

Research on the influence of finish rolling technique parameters on H2S corrosion resistance behavior of pipeline steel in the thickness direction

Abstract Natural gas was an important energy for human society’s development, and there was still a great demand for this type of energy. It required pipeline steel for energy transport and had excellent hydrogen-induced cracking resistance. Thermomechanical controlled processing (TMCP) was a frequently used manufacturing method for pipeline steel. It was necessary to research the effect of finish rolling technique parameters on the H2S corrosion resistance behavior of pipeline steel in the thickness direction, especially concerning microstructure and hardness in the thickness direction. So, for the research, optical microscope (OM), hydrogen-induced cracking tests (HIC), and hardness tests were used to study the effect of finish rolling technique parameters on H2S corrosion resistance. As finish rolling deformation increases, deformation can effectively conduct from surface to center and reduce the average hardness gap between the surface and the center. It can also generate finer microstructure and smaller hardness differentials from the thickness direction. All these can enhance the hydrogen-induced cracking resistance.

Fiber Showdown: A Comparative Analysis of Glass vs. Polypropylene Fibers in Hot-Mix Asphalt Fracture Resistance

Cracks in asphalt mixtures compromise the structural integrity of roads, increase maintenance costs, and shorten pavement lifespan. These cracks allow for water infiltration, accelerating pavement deterioration and jeopardizing vehicle safety. This research aims to evaluate the impact of synthetic fibers, specifically glass fiber (GF) and polypropylene fiber (PPF), on the crack resistance of Hot-Mix Asphalt (HMA). An optimal asphalt binder content of 5% was used in all sample designs. Using the dry mixing technique, GFs and PPFs were incorporated into the HMA at dosages of 0.50%, 1.00%, and 1.50% by weight of the aggregate. The effects of these fibers on the mechanical fracture properties of the HMA were assessed using Semi-Circular Bending (SCB), Indirect Tensile Asphalt Cracking Tests (IDEAL-CTs), and Three-Point Bending (3-PB) tests. This study focused on fracture parameters such as fracture work, peak load, fracture energy, and crack indices, including the Flexibility Index (FI) and Crack Resistance Index (CRI). The results from the SCB and IDEAL-CT tests showed that increasing GF content from 0.5% to 1.5% significantly enhances the flexibility and crack resistance of HMA, with FI, CRI, and CT Index values increasing by 247.5%, 55%, and 101.35%, respectively. Conversely, increasing PPF content increases the mixture’s stiffness and reduces its crack resistance. The PP-1 mixture exhibited higher FI and CT Index values, with increases of 31.1% and 10%, respectively, compared to the PP-0.5 mixture, based on SCB and IDEAL-CT test results. The SCB, IDEAL-CT, and 3-PB test results concluded that fibers significantly influence the fracture properties of bituminous mixtures, with a 1% reinforcement dosage of both PPFs and GFs being optimal for enhancing performance across various applications.

Formulation Design and Optimization of High-Performance Concrete for Enhanced Properties

High-performance concrete, as a crucial construction material, finds extensive applications in critical engineering projects. This paper focuses on the formulation design and optimization of high-performance concrete. By analyzing the impact of different admixtures, additives, and mix proportions on concrete properties, the methods for enhancing concrete strength, durability, and crack resistance are explored. The study integrates experimental and simulation approaches to provide theoretical and practical support for the reliable application of high-performance concrete.

Effect of High Temperature on Micro-Structure and Mechanical Properties of Fiber-Reinforced Cement-Based Composites

Synthetic fibers can effectively inhibit the formation and propagation of micro-cracks in concrete, significantly reducing the number and scale of cracks within the concrete matrix, thereby enhancing the concrete’s crack resistance and seepage prevention capabilities. In this study, two types of synthetic fibers, polyvinyl alcohol (PVA) and polypropylene (PP), were incorporated into cement mortar to investigate their microstructural evolution at elevated temperatures and their influence on the mechanical properties of the mortar. Both fibers were added at a volume content of 0.5%. The mortar samples were subjected to the following temperature conditions: 20 °C (ambient), 200 °C, 400 °C, and 500 °C. The results indicate that the synthetic fibers employed in this study improved the tensile properties of the mortar at room temperature (20 °C). This enhancement persisted up to 400 °C, beyond which, at 500 °C, the mechanical properties of the fiber-reinforced mortar deteriorated significantly. At 400 °C, the tensile strength of the PVA group increased by approximately 16% compared to the unblended fiber group (JZ) and by about 45% compared to the PP group. After treatment at 500 °C, the tensile strength of mortar specimens in the PVA group and the PP group decreased by 36.47% and 24.14%, respectively, compared with that at 20 °C. The porous structure formed due to the high-temperature ablation of the synthetic fibers contributed to relieving the internal pressure within the mortar.

Mechanochemical Upcycling of Waste Polypropylene into Warm-Mix Modifier for Asphalt Pavement Incorporating Recycled Concrete Aggregates.

To solve the problems on resource utilization and environmental pollution of waste concrete and waste polypropylene (PP) plastics, the recycling of them into asphalt pavement is a feasible approach. Considering the high melting temperature of waste PP, this study adopted a thermal-and-mechanochemical method to convert waste PP into high-performance warm-mix asphalt modifiers (PPMs) through the hybrid use of dicumyl peroxide (DCP), maleic anhydride (MAH), and epoxidized soybean oil (ESO) for preparing an asphalt mixture (RCAAM) containing recycled concrete aggregate (RCA). For the prepared RCAAM containing PPMs, the mixing temperature was about 30 °C lower than that of the hot-mix RCAAM containing untreated PP. Further, the high-temperature property, low-temperature crack resistance, moisture-induced damage resistance, and fatigue resistance of the RCAAM were characterized. The results indicated that the maximum flexural strain of the RCAAM increased by 7.8~21.4% after using PPMs, while the sectional fractures of the asphalt binder were reduced after damaging at low temperature. The use of ESO in PPMs can promote the cohesion enhancement of the asphalt binder and also improve the high-temperature deformation resistance and fatigue performance of the RCAAM. Notably, the warm-mix epoxidized PPMA mixture worked better close to the hot-mix untreated PPMA mixture, even after the mixing temperature was reduced by 30 °C.

Fracture evolution characteristics of asphalt concrete using digital image correlation and acoustic emission techniques

The cracking damage of asphalt concrete significantly affects the service life of pavement. The objective of this research is to investigate fracture mechanisms of asphalt concrete by employing a synergistic approach combining digital image correlation (DIC) and acoustic emission (AE) techniques under three-point bending tests. Firstly, the crack tip opening displacement (CTOD) and the fracture process zone (FPZ) derived from DIC were utilized to classify fracture stages and describe the entire crack propagation process. Meanwhile, AE-related parameters were applied to detect the internal damage and fracture characteristics. Subsequently, the results from DIC and AE were utilized for comparative analysis to evaluate the cracking resistance of different materials. Finally, the fractal dimension and AE b-value were used to distinguish the characteristics of the critical damage conditions. The results indicated that both techniques are effective in classifying the fracture stage of asphalt concrete. DIC can visualize and analyze crack propagation processes and paths on concrete surfaces, especially at the stage of macrocrack initiation and propagation. AE allows for continuous monitoring and highly sensitive detection of early-stage damage inside concrete. The distinct advantages of DIC and AE result in different fracture stage identification results at the early stage, but consistent after the appearance of macrocracks. Based on the relationship between CTOD and AE cumulative count, a simple approach is proposed to directly evaluate the cracking resistance of different asphalt concretes. The formation of macrocracks in asphalt concrete can be reflected by a shift where the correlation dimension drops steeply to the minimum value, and a minimum inflection point in the AE b-value curve acts as a precursor of complete fracture. The research offers an in-depth insight of both surface deformation and internal damage, thus enhancing the understanding of crack growth behavior and fracture process in asphalt concrete.

The Influence and Mechanism of Curing Methods and Curing Age on the Mechanical Properties of Yellow River Sand Engineered Cementitious Composites.

This study investigates the potential use of Yellow River sand (YRS) sourced from the lower reaches of the Yellow River in China as a sustainable and cost-effective substitute for quartz sand in Engineered Cementitious Composites (ECC). With an annual accumulation of approximately 400 million tons in this region, YRS presents a substantial resource. ECC specimens with 100% YRS replacement with quartz sand were subjected to various curing methods: natural, steam, standard, and sprinkler. Extensive mechanical testing including flexural, compressive, uniaxial tensile, and four-point flexural tests was conducted. Additionally, Scanning Electron Microscope (SEM) and Mercury Intrusion Porosimetry (MIP) analyses investigated microscopic mechanisms influencing macroscopic mechanical properties. Finally, the mechanical properties of the YRS-ECC test block after 14 days of standard curing and the traditional sand ECC test block were compared and analyzed. The results indicate that ECC specimens with 100% YRS substitution under natural curing show an optimal ultimate tensile strain of more than 4%, providing the best resistance to the reduction in ultimate flexural load and deflection due to aging. Steam curing enhances flexural and compressive strength, achieving an ultimate flexural load of 5 kN and a maximum deflection of 4.42 mm at 90 days. SEM analysis revealed lower C-S-H gel density under natural curing and higher under steam curing, enhancing fiber pull-out in steam-cured specimens. The MIP tests demonstrated that natural curing had the highest porosity (32.86%) and average pore size (51.69 nm), whereas steam curing resulted in the smallest average pore size, with 44% of pores under 50 nm. Compared with traditional sand, it is found that the ultimate bending load and deflection of YRS-ECC are 5.7% and 9.4% higher than those of traditional sand ECC, respectively, and its ultimate tensile strength and strain are also improved. These findings highlight YRS as a sustainable alternative to natural sand in ECC, with natural curing proving the most effective for superior mechanical performance, including tensile strain, crack resistance, and durability.

Creep fatigue interaction at high temperature in C630R ferritic/martensitic heat-resistant steel

The study investigated the creep-fatigue interaction behavior, fracture mechanism, and microstructure evolution of C630R ferritic/martensitic heat-resistant steel at 630 °C and 1% strain amplitude. The results indicate that C630R ferritic/martensitic heat-resistant steel exhibits noticeable cyclic softening behavior, with a decrease in the softening ratio from 0.46 to 0.40 as loading time increases. Microstructure evolution was examined using optical and scanning electron microscopes, revealing the appearance of secondary cracks on the longitudinal section of the sample. These cracks exhibited a curved expansion trend with multiple deformations and highly bifurcated micro-cracks at a low loading time of 30s. However, when the load holding time was increased to 300s, the fatigue cracks tended to expand in a straight line with fewer branches. Furthermore, the observed crack growth path under different loading times showed enrichment in Fe and Cr, with the crack tip containing Cr oxide, which helped prevent fatigue crack propagation. As the loading time increases, the rise in crack closure resulting from oxidation leads to a decrease in crack propagation. Electron backscatter diffraction observation revealed the formation of numerous substructures and recrystallized grains after varying holding times, enhancing the material's resistance to crack propagation. Moreover, the study found that with increasing load dwell time, the deformed grains decreased, and substructural grains became dominant (57.68% and 62.77% under 30s and 300s, respectively). This increased crack resistance resulted in shorter secondary cracks under prolonged load retention, with the secondary crack length decreasing from 146.36 μm at 30s loading time to 109.09 μm at 300s loading time. Additionally, the kernel misorientation angle value decreased significantly after different loading times, leading to a higher likelihood of cracks or holes forming in regions with high KAM values, where low-angle grain boundaries were formed.

Feasibility and environmental assessment of introducing waste polyurethane from wind turbine blades as a modifier for asphalt

Recycled glass fibers from wind turbine blades have significant potential for enhancing the performance of asphalt mixtures. However, the impact of residual polyurethane (PU) components on asphalt performance remains uncertain, presenting a challenge to the high-value utilization of wind turbine blades in pavement engineering. This study investigates the effects of waste polyurethane (WPU) on the rheological properties and compatibility of SBS modified asphalt, widely used in pavement engineering under various temperature conditions. Molecular dynamics (MD) simulations were employed to analyze the underlying mechanisms. The results reveal that incorporating WPU improves the rutting factor and creep recovery rate of SBS modified asphalt, demonstrating superior high-temperature performance compared to SBS modified asphalt alone. The synergistic effect of WPU and SBS significantly enhances low-temperature crack resistance and overall asphalt compatibility. Additionally, the interaction between SBS and the four components of asphalt is strengthened, and diffusion mobility is reduced due to WPU incorporation. This indicates that WPU promotes a more compact structure and a higher relative concentration of SBS and the four components within the spatial system, thereby enhancing the stability of the WPU/SBS modified asphalt system. Furthermore, using WPU in asphalt mixtures not only avoids environmental pollution compared to traditional disposal methods but also offers considerable long-term economic benefits. Overall, WPU positively impacts the rheological properties and compatibility of SBS-modified asphalt, suggesting that processed wind turbine blades can be a viable solution for enhancing asphalt mixture performance.

Effect and mechanism of phase change lightweight aggregate on temperature control and crack resistance in high-strength mass concrete

Under temperature stress, high-strength mass concrete is brittle due to its high total heat of hydration. In this study, a control mixture of C55 high-strength mass concrete meeting the performance requirements was prepared. The effects of different functional aggregates on the thermal properties, such as setting and hardening rate, peak temperature, and temperature rise and fall rate in the early stage of cement hydration, as well as the effects of functional lightweight aggregates on the workability, mechanical properties, and deformation properties of concrete, were investigated in this paper using two types of aggregates with thermal insulation and phase change energy storage functions. The study shows that, in addition to having some early strength impacts and temperature management capabilities, thermal storage coarse lightweight aggregate (PCCLA) and thermal insulation fine lightweight aggregate (TIFLA) can both increase the workability and crack resistance of concrete. When it comes to temperature regulation, thermal storage coarse aggregate outperforms thermal insulation functional aggregate significantly. Thermal insulation fine aggregate can improve the rate of setting and hardening, while coarse thermal storage aggregate may work as in-situ self-heating curing in the early stages due to its phase change energy storage. This quickens the rate of setting and hardening and increases the resistivity of the set period, which in turn increases the rate of drying shrinkage.

Effects of vetiver root on cracking of expansive soils and its mechanistic analysis

The study investigated the reinforcing effect of vetiver root on soil by conducting outdoor planting tests and indoor root tests. The cracking indexes of soil specimens with varying root contents were analyzed, and a statistical model was established to determine the relationship between the cracking indexes, the number of dry and wet cycles, and the root content. The study revealed the crack evolution law of vetiver-reinforced expansive soil. The study explored the mechanism of the vegetation root in inhibiting the cracking of expansive soil and determined the optimal planting density of vetiver grass through outdoor planting tests. The results indicate that: The surface crack rate (CR), total crack length (CL), and crack number (CN) in the root-soil specimen exhibited exponential growth with an increase in the number of wet and dry cycles. This growth was more pronounced during the first and second cycles. The vetiver root could effectively reduce soil crack formation, and the specimen's cracking resistance is positively correlated with the root content. With the root content increased, the CR, CN, and CL decreased. The logistic model is suited to the CL of added root soil. The logistic model is more suitable for the growth model of the CR of the expansive soil with low root content, while the Boltzmann model is more suitable for the growth model of the CR of the expansive soil with high root content. Width of crack (CW) is better suited to the DoseResp growth model. The Boltzmann model is more applicable to the CN in expansive soils with low reinforcement, while the logistic growth model is more suitable for the development of CN above 0.21% root content. The development of the crack network was influenced by two key factors: the root content and the number of wet and dry cycles. Under the condition of planting roots, the development of crack networks in expansive soil differs from that of expansive soil with added roots, and there is no clear pattern to follow. The inhibitory effect of the vetiver root on cracking of expansive soil is related to the planting density of vetiver.

Unveiling the composite rejuvenator efficacy on performance improvement of asphalt binder including high RAP contents

Since the incompatibility between crumb rubber (CR) and reclaimed asphalt binder (RAB) can cause sedimentation and limit its application, this study employed waste cooking oil (WCO) to pre-treat CR particles at different CR/WCO ratios, and assessed its impact on performance of asphalt binders including 30 % and 50 % RABs. Anti-aging and rejuvenation potentials of corresponding composite rejuvenators in binder blends were explored by Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC) tests, while the performance of corresponding binder blends was evaluated by bending beam rheometer (BBR), linear amplitude sweep (LAS), and multiple stress creep recovery (MSCR) tests. Furthermore, correlation analyses were performed to explore the relationships between the chemical and rheological parameters with a significance level below 0.05. The results confirmed the rejuvenation efficacy of composite rejuvenators in high RAB, and improvement in the critical low temperature of binder blends to a higher performance grade (PG) level compared to the non-treated CR modified binder. In addition, the fatigue cracking resistance was improved at the strain levels higher than 4 % in LAS test. However, the pre-swelled CR fairly compromised the rutting performance of binder blends compared to non-treated CR, its performance was still better than virgin binder. The correlation analysis suggested that it is possible to use chemical parameters as indicators for evaluating certain rheological properties.

Experimental investigations on the flexural behavior of UHPC wet joints for UHPC light-weight rigid frame arch bridges

Wet joints are critical parts of prefabricated ultra-high-performance concrete (UHPC) light-weight rigid frame arch bridges (LWRFAGs), so their mechanical behavior is important to the structural design and applications of these arch bridges. To explore suitable joint configurations and reinforcement arrangements for connecting UHPC components or arch ribs of a practical UHPC LWRFAG, this paper experimentally investigated flexural behavior of several prefabricated UHPC joint beams with various kinds of wet joints through four-point bending tests. Firstly, four different UHPC joint beams with different joint configurations were designed, including (i) vertical joint; (ii) rhombus joint; (iii) vertical joint with top and bottom strips; and (iv) rhombus joint with top and bottom strips, and their flexural performance were compared with a complete UHPC beam. The experimental results revealed that UHPC joint beam employing the rhombus joint with top and bottom strips exhibited superior flexural behavior and cracking resistance among four UHPC joint beams. Subsequently, to achieve optimal and robust joint configurations, bending performance of one complete UHPC beam and three large-scale UHPC joint beams with rhombus joints but different reinforcement arrangements were experimentally studied. It is observed that the beam with the welded twist reinforcements (specimen V-4) shown optimal flexural performance and cracking resistance. Finally, to explore the load transfer mechanism and effects of reinforcement parameters on flexural behavior of specimen V-4, the parametric studies were comprehensively performed using finite element analyses (FEA). This study could serve as both the experimental and theoretical reference for flexural design of UHPC beams with the rhombus wet joints.

Effect of nano-metakaolin on the early-age fracture properties of cement mortar

In this paper, the fracture performance of nano-metakaolin (NMK) cement mortar during early hydration period was investigated. Different NMK contents (0 %, 3 %, 5 %, 7 %) were considered, and three-point bending tests were conducted. The digital image correlation technology and acoustic emission technology were utilized to analyze P-CMOD curves, initial fracture toughness, unstable fracture toughness, fracture energy, cumulative AE hits, and cumulative AE energy, AE source locations of cement mortar at early hydration stages. Furthermore, SEM experiments were utilized to analyze the mechanism by which NMK affects fracture performance of cement mortar. The results indicate that the incorporation of NMK enhances the fracture properties of cement mortar, with the most suitable NMK content being 5 %. The addition of NMK increases the cracking load, peak load, and the CMOD at the peak load of the cement mortar at 3 d, 7 d, and 14 d. The cracking load and fracture energy of the cement mortar with 5 % NMK increase by 22.5 % and 35.7 % respectively, compared to ordinary cement mortar at 14 d. NMK enhances the initial fracture toughness and unstable fracture toughness of the cement mortar, improving its crack propagation resistance. The unstable fracture toughness of the cement mortar is the largest when the NMK content is 5 % at 14 d, which is 31.6 % higher than that of ordinary cement mortar. Furthermore, NMK increases the cumulative AE energy and fracture energy of the cement mortar, increasing the cumulative ring counts and cumulative AE hits, causing the crack propagation path to deviate and resulting in improved crack resistance. The cumulative ring counts and AE hits for the cement mortar with 5 % NMK are 42.9 % and 66.2 % higher, respectively, than those for ordinary cement mortar at 14 d. NMK significantly modifies the cement matrix, thereby enhancing the fracture resistance of cement mortar.

Experimental and Numerical Analysis of Flexural Properties and Mesoscopic Failure Mechanism of Single-Shell Lining Concrete

Despite ongoing research efforts aimed at understanding the structural response of steel fiber reinforced concrete (SFRC), there is very limited research on the failure characteristics and mesoscopic damage mechanism of SFRC, specifically when under flexure. In this study, a four-point bending test of plain concrete (PC) and SFRC with different fiber contents is carried out to investigate the flexural performance of SFRC. The crack propagation process, cracking load, ultimate load, and load-deflection curves of PC and SFRC beams are obtained. Additionally, the discrete element method (DEM), using PFC2D 6.0 software, is adopted to explore the mesoscopic properties of PC and SFRC. The test and simulation results of PC and SFRC beams are compared and analyzed, and some conclusions are drawn. The results show that steel fiber can efficiently improve the compressive strength of concrete when the fiber content is 30 kg/m3, and significantly improve the deformation resistance, crack resistance, and flexural capacity of concrete. The refined numerical models of PC and SFRC beams are established based on compressive strength and aggregate screening results. Through the numerical four-point bending test, the mesoscopic mechanical behaviors of models reveal the damage mechanism of SFRC. The horizontally distributed steel fibers bridge both sides of the cracks to resist crack development, and the vertically distributed steel fibers guide the cracks to the place with strong contact, thus resisting crack height development. The test results show that, for flexural properties, the optimal steel fiber content of SFRC is 31 kg/m3.

An Assessment of the Impact of Locally Recycled Cementitious Replacement Materials on the Strength of the Ultra-High-Performance Concrete

Withstanding extreme events is increasingly a significant challenge for the construction industry. Where civil infrastructures remain using traditional concrete, which has low tensile strength, poor durability, and weak crack resistance, in this regard, ultra-high-performance concrete (UHPC), with its outstanding mechanical properties and high strength, offers the prospect of wide application. This advanced technology allows for the fabrication of thin and light-dimensional structures to accelerate construction while increasing corrosion resistance to minimize maintenance intervention and extend the service life of the infrastructures. Despite this, UHPC is less eco-friendly due to consuming more cement than the usual material, which requires replacement materials, such as silica fume (SF) and rice husk ash (RHA), which are readily available from other local material production. This study proposes an experimental approach to assess the influence of SF and RHA content on the properties of UHPC. Different SF and RHA compositions will be adjusted to analyze their effects on slump flow, compressive strength, flexural strength, tensile strength, and the stress–strain relationship in UHPC tension testing. Based on the results, the most effective ratio is RHA replacing 50% of the SF in the UHPC mixture. Specialized tensile experiments reveal enhanced tensile strength with judicious RHA incorporation at 5-day and 28-day stages, particularly in initial crack and damage conditions. Stress–strain curves for 5% to 15% RHA samples show increased ductility, indicating that optimal RHA-SF ratios enhance UHPC cracking characteristics. Based on the results, a discussion on the appropriate proportions for utilizing most local materials will be derived, especially for regions of Vietnam. It is evaluated as a feasible and promising solution to reduce greenhouse gas emissions threatening global climate change.

A study of fine-scale low-temperature cracking in geopolymer grouted porous asphalt mixtures based on real aggregate profile modeling

At a micro-scale level, grouted porous asphalt mixtures are multiphase composites consisting of aggregates, asphalt mortar, filler, asphalt mortar-aggregate interfacial transition zone, and asphalt mortar-filler interfacial transition zone. It exhibits different mechanical behavior under different temperatures and loading conditions. Compared with aggregate, asphalt mortar, and filler, the interfacial transition zone (ITZ) is more prone to damage at low temperatures, with both the fine structure and the nature of the contact interface having a significant effect on the overall strength and crack resistance of the material. To evaluate the influence of ITZ and filler material properties on the cracking resistance of the material, a grouted porous asphalt mixture model based on the real aggregate shape was established using finite element modeling. A cohesive zone model (CZM) was employed to characterize the internal mechanical behavior of the material, and a mesoscale damage simulation was performed for the grouted asphalt mixture. The study revealed the influence of different interfacial and filler material properties on the low temperature cracking resistance and proposed a design approach for anti-cracking grouted asphalt mixtures. The findings indicated that interfacial transition zone (ITZ) and filler properties play a crucial role on determining the damage characteristics. Increasing the ITZ and filler properties significantly enhanced the low temperature crack resistance of the grouted asphalt mixture.

On mechanical and tribological behaviour of microwave sintered TiN – 5 wt% Al2O3–5 wt% Y2O3 nanocomposite

Titanium nitride has potential applications in wide range of mechanical parts, cutting tools etc., primarily due to its high wear resistance. In the present study, a novel TiN-based nanocomposite was developed with nano additives alumina (Al2O3) and (Y2O3), 5 wt% each; using microwave irradiation at 900 W in ambient atmosphere. In-situ microwave sintering was carried out at a temperature of 1500 °C and 5 min holding time. The sintered nanocomposites achieved a relative density of ∼93%. XRD analyses showed that the major TiN phase was retained without any significant change in its peak positions after sintering. Minor phases of Y2Ti2O7 and Y3Al5O12 were formed during sintering due to chemical realignment of the constituent phases, were detected which acted as crack inhibitors. Microstructural studies indicated homogeneous distribution of the additives throughout the TiN matrix. The average Vickers microhardness of the TiN nanocomposites was ∼14 GPa, while indentation crack resistance was estimated within 3.9–4.0 MPa·m1/2. Wear and friction studies (ball-on-disc) of the microwave sintered TiN nanocomposite carried out with bearing steel ball under dry (unlubricated) and under deionised water (lubricated) sliding exhibited promising tribological behaviour. The friction coefficient (COF) between the contact pair was monitored within 0.5–0.6 after 45 min of dry sliding. Wear volume of the nanocomposite was obtained between 0.013 and 0.058 mm3 after 45 min of sliding (dry). Presence of iron oxides on worn surfaces confirmed mass transfer from the steel counterbody to the nanocomposite surface. Analyses of the worn surfaces showed that the wear mechanisms were predominantly abrasive and adhesive.

New strategy to simultaneously improve strength-toughness balance for low-carbon ultrastrong steel by multi-step heat treatment process

The quenching-partitioning-tempering (QPT) multi-step heat treatment process was employed to enhance the strength-toughness balance of low-carbon ultrastrong steel based on the controllable transformation-induced plasticity (TRIP) effect and co-precipitation strengthening. The aging embrittlement of ultrastrong steel, with an impact toughness of only 5.8 J at peak strength, has been effectively addressed through the QPT process. The sufficient reversed austenite (RA) can be obtained by controlling the partition temperature to 650 °C, followed by aging at 550 °C to fully re-precipitate nanoparticles. The volume fraction of RA in QPT650 steel reached 16.4 %, and the number density of nanoparticles increased dramatically, resulting in a high yield strength of 1233 MPa and excellent impact toughness of 60.4 J. The coarsening and re-precipitation of nanoparticles were clarified, and the strengthening increments of QPT650 steel reaches 584.6 MPa, and the substantial enhancement of Orowan strengthening is responsible for the high yield strength. The excellent impact toughness of QPT650 steel is attributed to the obvious TRIP effect of RA that consumes a large amount of crack propagation energy, and a small number of sheared nanoparticles provide limited micro-cracks, resulting in a strong crack resistance.