Weak Interface Research Articles

Enhance the tribological performance of soft AISI 1045 steel through a CrN/W-DLC/DLC multilayer coating

Special equipment vehicles typically operate in complex environments, leading to wear and failure of the chassis's rotary seal shaft predominantly made of soft AISI 1045 steel. An effective approach to prolong the service life is to apply a hard coating on the working surface. Previous research have primarily concentrated on the coating for hard high-speed steel. However, the significant disparity in physical characteristics between soft AISI 1045 steel and the hard coating results in a weak interface adhesion. This study produces a CrN/W-DLC/DLC multilayer coating on the soft AISI 1045 steel with strong interfacial adhesion and superior friction and wear property through modulation of the CrN transition layer thickness. The multilayer coating consists of five layers, a CrN transition layer, a Cr layer, a Cr/WC alternating layer, a W-DLC/DLC alternating layer, and the topmost DLC layer. The thickest CrN interlayer coating achieves the Lc2 and Lc3 value of 13.9 ± 0.2 N and 20.4 ± 0.9 N. The optimized CrN/W-DLC/DLC coating reduces the internal stress of the DLC coating and enhances its adhesion. Importantly, the average friction coefficient and wear cross-sectional area of the CrN/W-DLC/DLC multilayer coatings decrease accordingly. The thickest CrN interlayer coating exhibits superior outstanding wear resistance evidenced by an average friction coefficient of 0.119, a steady-state friction coefficient of 0.097 and a wear volume of 1.508 × 106 μm3. The presence of a high proportion of sp2 bonds in the thickest CrN interlayer coating, which are susceptible to graphitization, along with a thicker transition layer that enhances the coating's support, leads to narrower wear traces. The primary wear mechanisms observed in the friction and wear test of CrN/W-DLC/DLC coatings are oxidative wear and tribo-abrasive wear. The work provides a significant promise for application in vehicle rotary seal components and a theoretical reference for enhancing the wear resistance of the seal surface.

Efficient and Highly Stable Lateral Perovskite Single‐Crystal Solar Cells through Crystal Engineering and Weak Ion Migration

AbstractThe lateral device structure for perovskite solar cells (PSCs) has garnered significant attention, primarily due to its elimination of the need for expensive transparent electrodes. However, the performance of lateral devices, which are more sensitive to crystal quality and charge carrier transport bottlenecks, has lagged far behind the predominant vertical PSCs. Herein, by modulating the crystal nucleation and growth processes of thin FA0.75MA0.25PbI3 (FA = formamidinium; and MA = methylammonium) single crystals, crystal quality and carrier transport are improved, resulting in a power conversion efficiency (PCE) of 12.64%, a record for lateral PSCs. Investigation of the device's stability reveals that iodide ion migration is suppressed due to a reduction in the iodide vacancy concentration combined with weak interface iodide ion migration. It is shown that the latter effect is a result of the perpendicular direction of the ion migration and the electric field in the lateral PSCs. Consequently, these lateral single‐crystal PSCs display remarkable operational stability, retaining 100% of their initial PCE after 1200 h of steady‐state output at the maximum power point voltage (Vmpp) under 1 sun illumination. This work highlights the advantages of lateral single‐crystal devices and their potential to address key ion migration issues of PSCs.

Fabrication of bamboo-inspired continuous carbon fiber-reinforced SiC composites via dual-material thermally assisted extrusion-based 3D printing

Ceramic matrix composites (CMCs) structural components encounter the dual challenges of severe mechanical conditions and complex electromagnetic environments due to the increasing demand for stealth technology in aerospace field. To address various functional requirements, this study integrates a biomimetic strategy inspired by gradient bamboo vascular bundles with a novel dual-material 3D printing approach. Three distinct bamboo-inspired structural configurations Cf/SiC composites are designed and manufactured, and the effects of these different structural configurations on the CVI process are analyzed. Nanoindentation method is utilized to characterize the relationship between interface bonding strength and mechanical properties. The results reveal that the maximum flexural strength and fracture toughness reach 108.6 ± 5.2 MPa and 16.45±1.52 MPa m1/2, respectively, attributed to the enhanced crack propagation resistance and path caused by the weak fiber-matrix interface. Furthermore, the bio-inspired configuration enhances the dielectric loss and conductivity loss, exhibiting a minimum reflection loss of −24.3 dB with the effective absorption band of 3.89 GHz. This work introduces an innovative biomimetic strategy and 3D printing method for continuous fiber-reinforced ceramic composites, expanding the application of 3D printing technology in the field of CMCs.

Laboratory assessment of the impact of modified asphalt binder on mechanical properties of grouted macadam mixtures under various performance conditions

ABSTRACT Grouted Macadam (GM) mixtures are used for pavement coatings due to their strong load-bearing capacity and rutting resistance. However, weak asphalt-cement interface bonding reduces crack resistance performance of these mixtures. This study aimed to enhance this adhesion through implementing TEGO Addibit L300 additive at concentrations of 0.2, 0.3, and 0.4% by weight of asphalt binder. Various tests assessed additive’s impact on asphalt binder properties, including penetration, softening point, and kinematic viscosity. Adhesion properties were evaluated through sessile drop and semi-circular bending bonding strength tests. Additionally, GM mixture performance was assessed with mechanical tests such as 3-point bending strength, indirect tensile strength, and Marshall stability, considering two conditions: samples tested immediately after a 28-day curing period (non pre-conditioned samples), and samples tested after the same period followed by exposure to 60 ℃ for 16 h (pre-conditioned samples). Results revealed that the adhesion capacity of the asphalt binder significantly affected GM mixture performance in both conditions. Addition of TEGO Addibit L300 enhanced ductility and fracture energy by 53.9% and 45.2%, respectively, in non pre-conditioned samples. In pre-conditioned samples, the additive increased indirect tensile strength by up to 12.1%. The optimal dosage for improving GM materials performance was determined to be 0.3%.

Macroscopic properties and microscopic characterisation of an optimally designed anti-cracking stone base course filled with cement stabilised macadam

Stone base course filled with cement stabilised macadam (SFC) is a promising solution for addressing reflection cracks in semi-rigid base asphalt pavement due to its satisfactory crack resistance. However, its limited strength and construction challenges have impeded its widespread application. To overcome these challenges, an optimised mix proportion design method of SFC was proposed. Natural crushed limestones with specific particle sizes were selected to serve as skeletal coarse aggregates; fine aggregates and their proportions were step-by-step determined using aggregate and unconfined compressive strength tests. The multi-scale analysis integrating the performance tests and the microscopic detections was performed to evaluate the effectiveness of the proposed SFC, and compared with common cement stabilised macadam (CSM). The results indicate that the material exhibits satisfactory mechanical strength through a tightly interlocked skeleton structure and excellent crack resistance by dissipating strain energy and retarding cracking of SFC through the weak interface transition zone (ITZ).

Weak bond evaluation of lap bonding structures by SH guided waves using EMATs

ABSTRACT In this research, simulations and experiments were conducted for the bonding quality evaluation of an aluminum bonding structure, based on the SH guided wave analysis. In order to simulate the propagation of SH waves in the bonded structure, a 3D finite element model was established based on interfacial spring stiffness modeling. The frequency-wavenumber diagram was obtained by doing Fourier transform along the spatial axis in the time frequency domain simulation results. At the same time, the influence of the bonding interface weakening on the propagation characteristics of the guided wave was analyzed. The simulated dispersion curves of SH-guided waves in different bonding states were in good agreement with the theoretically results. In addition, a periodic permanent magnet electromagnetic acoustic transducer (PPM-EMAT) 3D finite element model was established. An optimized transducer was fabricated to excite pure SH0 mode. Then, a series of aluminum lap bonding structures with different bonding states were prepared. The effect of bonding interfaces on the propagation characteristics of SH waves was investigated. The interfacial spring stiffness can be determined when the STFT of the SH waves matches the theoretical dispersion curves. Thus, this method demonstrated an ultrasonic way to distinguish the weakening of the bonding structures.

Self-Encapsulation of High-Entropy Alloy Nanoparticles inside Carbonized Wood for Highly Durable Electrocatalysis.

High-entropy alloy nanoparticles (HEAs) show great potential in emerging electrocatalysis due to their combination and optimization of multiple elements. However, synthesized HEAs often exhibit a weak interface with the conductive substrate, hindering their applications in long-term catalysis and energy conversion. Herein, a highly active and durable electrocatalyst composed of quinary HEAs (PtNiCoFeCu) encapsulated inside the activated carbonized wood (ACW) is reported. The self-encapsulation of HEAs is achieved during Joule heating synthesis (2060 K, 2 s) where HEAs naturally nucleate at the defect sites. In the meantime, HEAs catalyze the deposition of mobile carbon atoms to form a protective few-layer carbon shell during the rapid quenching process, thus remarkably strengthening the interface stability between HEAs and ACW. As a result, the HEAs@ACW shows not only favorable activity with an overpotential of 7mV at 10mA cm-2 for hydrogen evolution but also negligible attenuation during a 500 h stability test, which is superior to most reported electrocatalysts. The design of self-encapsulated HEAs inside ACW provides a critical strategy to enhance both activity and stability, which is also applicable to many other energy conversion technologies.

Carbon nanotube-induced localized laser heating toward simultaneously enhanced laydown efficiency and fracture toughness of in-situ consolidated glass fiber thermoplastic composites

Thermoplastic composites suffer from weak inter-tape bonding during high-rate laser-assisted automated fiber placement (L-AFP). Here, we propose a strategy to simultaneously enhance the laser heating efficiency and fracture toughness of glass fiber-reinforced polypropylene prepreg tape for L-AFP process by depositing carbon nanotubes (CNTs) on the tape surface by a low-cost bath coating process. CNTs function as efficient light absorbing and photothermal coating to promote molecular inter-diffusion and interfacial healing between successive tapes, as well as toughen the weak interface by CNT pull-out and rupture. A 56 % increase in the near-infrared laser absorption of tapes results in a 946 % improvement in the laydown rate. CNTs also remarkably improve transverse temperature uniformity. Furthermore, double cantilever beam and pants tearing tests show that 0.5 wt% CNTs improve the mode I interlaminar fracture toughness and mode III fracture strength by 17 % and 52 %, respectively, attributed to the enhanced molecular inter-diffusion and CNT bridging effect.

Enhancing strength-ductility properties of immiscible W–Cu composite by creating low-energy phase interfaces

The immiscible bimetallic composites play an important role in civilian industries and aerospace fields owing to their integrated mechanical and physical properties. However, metallic composites of immiscible constituents suffer from one critical drawback of weak interface bonding, which makes the composites particularly vulnerable at elevated service temperatures. Here we proposed a novel strategy to resolve the challenge by creating low-energy phase interfaces in a typical immiscible bimetallic W–Cu composite. This was achieved by in-situ reactions of WO3 and CuO with WC, which acts in a dual function as the reducing agent for the reactions and an interface forming agent. The sintered W-WC-Cu composite possessed a significant number of low-energy WC/W and WC/Cu interfaces and exhibited a compressive strength of 609 MPa and a compressive ductility of 22.6 % at 600 °C, which ranks among the highest in similar composites. The characteristics of WC/W and WC/Cu interfaces and their effects on the mechanical behavior of the composite were demonstrated by the timely and atomic-resolved high-temperature mechanical investigations. The introduced stable interfaces were also found to induce [1‾ 11]BCC→ [011]FCC phase transformation of W as another mechanism of plastic deformation in addition to dislocation activities in W and Cu. This study provides a new approach to greatly enhance the mechanical properties of the immiscible metallic composites.

Spatial separation of photocarriers and selective adsorption on flower-like core-shell heterojunction of Cr(VI) imprinted polymer@BiOI for boosted photocatalytic Cr(VI) reduction

BackgroundConstructing heterojunction photocatalyst is a well-established strategy for enhancing photocatalytic Cr(VI) reduction due to the heightened separation and transfer of photocarriers. Whereas, aimless and random transfer of photocarriers and low photocarrier utilization rate deriving from the weak interface interaction between heterojunction and Cr(VI) are still limited the photocatalytic reduction performance of Cr(VI). MethodsHerein, a flower-like core-shell heterojunction photocatalyst was designed by wrapping a pyridine-based Cr(VI) imprinted polymer (PCIP) onto flower-like BiOI to achieve spatial separation of photocarriers and selective adsorption of Cr(VI), resulting in an outstanding photocatalytic reduction performance of Cr(VI). Significant findingsIn the core-shell heterojunction, photocarriers could be spatially separated, and then brought about high-efficient photocatalytic Cr(VI) reduction close to the selective adsorption sites of Cr(VI). After measurement, the optimal PCIP@BiOI core-shell heterojunction, polymerized for ≈30 min, exhibited a robust photocatalytic reduction performance of Cr(VI), without adding any free radical sacrifice agents. Within 1 h, the aqueous solution containing 100 mg/L of Cr(VI) could be completely removed, and the photocatalytic reduction rate constant of Cr(VI) was ≈20 times superior to BiOI. This study presents a methodology for designing core-shell heterojunction photocatalysts on the basis of inorganic/organic conjunction for environmental remediation of high concentrations of Cr(VI).

Hydraulic fracturing in layered heterogeneous shale: The interaction between adjacent weak interfaces

Shale is known as the typical layered heterogeneous rock with multiple weak interfaces between different layers, and how to depict the propagation characteristic of fluid-driven fracture in such complex geological structures is critical for hydraulic fracturing engineering. Traditional investigations only focus on the intersecting behaviors of hydraulic fracture (HF) at a single weak interface. Herein, we reveal the propagation of HF in shale formation based on the extended finite element method (XFEM), where multiple weak interfaces and different rock properties are carefully considered in the sandwiched layered structure (SLS). The crack tip singularities at the weak interfaces due to the material discrepancy are characterized by the eigen-function expansion, and the unified enrichment function is constructed to evaluate the stress intensity factors (SIFs) directly without extra computations. The corresponding energy release rate (ERR) criteria are employed to determine the HF propagation direction. By the comprehensive analysis with various dip angles and material/structural properties, the propagation of HF moving across the layered heterogeneous shale is regarded as the interaction between adjacent weak interfaces. For the front weak interface, the inhibition effect could be seen in the fracture penetrating capacity by the rear interface, which reflects contrasting trends due to large material discrepancies of various weak interfaces. The propagation behavior at the rear weak interface is affected by the facilitation effect from the front interface, and the HF pre-offset at the front interface greatly enhances the facilitation effect on fracture penetrating through shale formations.

Reinforcements/matrix micro-interface evolution and properties of in-situ Ni60A/WC coatings prepared by laser cladding

Ni60A/WC in-situ reinforced composite coatings are prepared on Inconel 718 alloy by laser cladding. The reinforcements/matrix micro-interface evolution, microhardness, and corrosion resistance are investigated. The phases in the coatings are mainly composed of γ-Ni, M23C6, M7C3 and NbC. The reinforcements/matrix micro-interfaces concerned in the coatings mainly include WC/matrix micro-interface and M23C6/matrix micro-interface. The WC/matrix micro-interface evolution is divided into five stages, namely, WC enters the molten pool, the micro-interface begins to grow, the reinforcements enriched at the tip, the reinforcements fall off and the formation of the stable micro-interface. The microhardness of the coatings increases with increasing WC content. On one hand, the increase in WC content promotes the generation of in-situ reinforcements, and the large lattice mismatch between dispersed reinforcement particles and matrix hinders dislocation motion. On the other hand, the two-dimensional mismatch degree of WC and γ-matrix calculated by Bramfitt's two-dimensional mismatch degree formula is 9.77 %, indicating that WC particles can serve as particles for γ heterogeneous nucleation. The increase of WC particles plays the role of fine grain strengthening, so the microhardness of the coating increases. The effect of WC on the corrosion resistance is also analyzed. The reinforcements are mainly distributed in the grain boundaries, and the HRTEM results indicate that a large degree of lattice mismatch exists in the micro-interface of reinforcements and γ-matrix. The large degree of mismatch shows that the interface between the two phases is relatively weak, and the weak interface is easy to become the channel for corrosive ion (Cl−) diffusion.

Multi-scale analysis and structural application of the synergistic enhancement effect of silane coupling agent on the interface between PVA/rubber and cement

This study employs polyvinyl alcohol (PVA) fibers and silane coupling agent (SCA) to augment rubberized concrete mechanical prowess. A multiscale investigation delves into the synergistic enhancement mechanism of SCA on the interfaces of PVA/cement and rubber/cement, considering macroscopic mechanical properties, microscopic structural characteristics, and nanoscale interface interactions. Initially, fundamental mechanical performance tests reveal a notable enhancement in compressive and flexural strength with the inclusion of SCA and PVA fibers in rubberized concrete. Subsequently, observations of corresponding composite concrete slices are conducted using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FT-IR). The results manifest gel and polymer filling interface gaps, with SCA fostering a tighter amalgamation of the two interfaces, effectively rectifying interface defects and elucidating its bonding effects at the microscopic interface. Molecular dynamics (MD) modeling and simulation analyses of PVA/C-S-H and rubber/C-S-H, pre- and post-SCA modification, demonstrate that SCA mitigates interface effects, reinforcing hydrogen bonding, van der Waals interactions, Ca-H coordination bonds, and stability. This augmentation enhances interface adhesion energy, fortifying the weak interface bonding between PVA fibers, rubber, and inorganic silicate (C-S-H). Ultimately, portal frame experiments substantiate that incorporating fiber rubberized concrete into structures not only fails to diminish but marginally enhances the load-bearing capacity of the framework. This research furnishes concrete and innovative solutions for sustainable development while providing a valuable reference for the future application of PVA fiber rubberized concrete materials in practical engineering endeavors.

Interlaminar Shear Strength Change and Storage Life Prediction of Carbon Fiber/Epoxy Composites with Hygrothermal Accelerated Aging.

In order to investigate the durability of fiber-reinforced polymer composites in hygrothermal environments, hygrothermal accelerate aging tests, for 360 days at 70 °C, RH70%; 70 °C, RH85%; 85 °C, RH70%; and 85 °C, RH85% and natural storage for 2 years in Guangzhou, China, were carried out for composite laminates. Then, the moisture absorption and interlaminar shear strength were measured. The hygrothermal damage mechanism of the composite was studied by Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and field emission scanning electron microscopy (FSEM). A dual stress storage life prediction model and the equivalent relationship between natural storage and hygrothermal acceleration were established. The results show that the order of moisture absorption rates, moisture absorption contents, and the severity effect order on the interlaminar shear strength is RH85%; 85 °C > 70 °C; RH85% > 85 °C; RH70% > 70 °C; and RH70%. The time to achieve an effective moisture absorption balance is opposite to this. The moisture absorption rate meets Fick's law before the effective moisture absorption balance, and then shows a linear trend. The interlayer shear strength still decreases exponentially with aging, which is mainly caused by the resin plasticization and interface weakening. Hygrothermal accelerated aging for 13.4831 days at 85 °C; RH85% is equivalent to that for one-year actual storage in Guangzhou. According to the failure criterion of shear strength decreasing to 77%, the storage life of T700/epoxy in Guangzhou is 14.4661 years.

Bioinspired 3D printed elastomer-hydrogel hybrid with robust interfacial bonding for flexible ionotronics

Hydrogels are widely used in flexible ionotronics due to their continuous conductive phase and good biocompatibility. However, their poor mechanical properties affect their stability and lifespan. It is a significant challenge to prepare hydrogels with both high conductivity and mechanical strength, as improving the mechanical properties often results in a tighter network, which reduces electrical conductivity. Human skin is composed of a stiff collagen fibril scaffold for resisting external damage, and a soft matrix that detect various stimuli through ion transport. Herein, inspired by the structure of human skin, a hydrogel composite with remarkable mechanical properties, high ionic conductivity, and self-healing property is prepared. The composite structure with 3D printed elastomeric skeleton and hydrogel matrix, addresses both the contradiction between the ionic conductivity and mechanical properties of hydrogels, as well as the difficulty of realizing complex macrostructures of the skeleton. The issue of weak interface in composites is resolved by creating interfacial covalent bonds. The composite’s self-healing property, combined with a robust interface, ensure the stability and longevity of the composite when used as flexible sensors. This novel approach of creating robust interface is also employed in the encapsulation of hydrogels and the fabrication of flexible microcircuits.

Nanoscale hydrate adhesion on organic surfaces

The future of addressing persistent gas hydrate blockages in oil and gas pipelines lies in the realm of surface material design, aimed at reducing environmental harm and energy inefficiencies associated with traditional chemical additives or heat-based approaches. A comprehensive understanding of hydrate-surface interactions is crucial for effective material-based solutions. Our study examined gas hydrate adhesion on diverse organic monolayer surfaces, utilizing Molecular Dynamics (MD) simulations to explore the impact of surface flexibility, gas concentration, and crack locations on hydrate adhesion strength. Results highlight the dependence of adhesion strength on surface functional groups. Hydrophobic interfaces are susceptible to weakening through a “gas coating”, while hydrophilic groups, like hydroxyl, strengthen adhesion through hydrogen bonding, altering the fracture behavior from adhesive failure to cohesive failure. Unexpectedly, the flexibility of monolayers has minimal influence, especially on hydrophobic surfaces. Tensile testing identified six distinct fracture interfaces, with the ice-hydrate interface displaying the highest adhesion strength, highlighting the detrimental impact of hydrogen bonding on interface weakening. These findings significantly deepen the understanding of soft surface properties influencing gas hydrate adhesion, offering a valuable guide for designing and fabricating highly efficient flexible anti-hydrate surfaces.

Interlayer stress transfer improvement in bi-layer graphene oxide /calcium silicate hydrate via CNTs

Previous studies have shown that the experimental values of mechanical properties of graphene oxide/calcium silicate hydrate (GO/CSH) are lower than theoretical values. The strengthening degree of graphene oxide (GO) on mechanical properties of calcium silicate hydrate (CSH) is quite different. This is mainly due to the weak interface between GO layer and CSH matrix. In order to further enhance the interlayer stress transfer and interfacial interaction between GO and CSH nanostructures, a series of CNTs are created in double GO layers to form a new double GO/CSH with different number of CNTs configuration (D-GO-CNTs/CSH nanostructures). The results show that the normalized pull-out energies and normalized shear stress values of double GO/CSH with hydroxyl groups (D-GO-OH/CSH) composites are enhanced by 26.58% and 33.33%, while the normalized pull-out energies and normalized shear stress values of double GO/CSH with epoxy groups (D-GO-Oo/CSH) are only enhanced by 14.29% and 15.38%. In addition, the CNTs leads to a greatly enhancement (about 2–3 times) in normalized interlayer stress transfer of D-GO/CSH nanostructures, while exerts a little adverse effect (about 10%) on the failure strain of D-GO/CSH nanostructures. According strain energy ratio and molecular dynamics analysis, the enhancement effects of interlayer stress transfer in D-GO/CSH model are the best when the number of CNTs is 3. It provides a new approach for actively enhancing the interlayer stress transfer and interfacial interaction of D-GO/CSH nanostructures.

Enhanced mechanical and tribological properties of 3D printed short carbon fiber reinforced polyether ether ketone composites

AbstractMaterial extrusion additive manufacturing provides an effective solution for fabrication of highly customized polyether ether ketone (PEEK) composite parts with any complex shape. Nevertheless, compared with conventional methods, the mechanical strength of 3D printed carbon fiber reinforced PEEK (CF/PEEK) composites is unsatisfactory due to the weak interface bonding strength and high voids content induced by the temperature difference. To overcome this challenge, a temperature‐control 3D printer was used to investigate the effects of ambient temperature and annealing temperature on the microstructure, crystallization behavior and mechanical properties of 3D printed parts. Moreover, the tribological properties of parts printed at different ambient temperature were also studied under various contact pressure. Experimental results showed that the ambient temperature and annealing treatment directly affected the interfacial bonding (fiber/matrix, filament/filament, layer/layer), crystallinity of printed samples, thus affecting their mechanical and tribological properties. The CF/PEEK parts printed at high ambient temperature of 200°C exhibited outstanding mechanical and tribological properties. This study has positive significance for promoting the application of 3D printed PEEK composites in the field of structural load‐bearing and friction materials.Highlights Structure–property relationships for 3D printed CF/PEEK composites. The ambient temperature strongly affects the thermal and microstructural properties Interaction between crystallization and molecular interface diffusion. Interfacial bonding and crystallinity determine the mechanical properties. Tribological properties are highly dependent on applied pressures.

Mechanical properties and discrete element simulation of KH-560 modified polystyrene concrete

Polystyrene foam (EPS) concrete is a composite concrete material commonly used in construction, which has excellent thermal insulation and thermal insulation properties, but also has defects of weak bonding interface.KH-560 can significantly improve the characteristics of EPS particles and concrete matrix, which have different physical and chemical properties and are difficult to combine. In this study, the effects of different levels of KH-560 on the enhanced mechanical properties of EPS concrete were studied from the aspects of macroscopic mechanical properties, microstructure characteristics, chemical composition and discrete element simulation, and the mechanism of action was discussed. The results of mechanical experiments show that the compressive strength and flexural strength of EPS concrete mixed with KH-560 are higher than those of ordinary EPS concrete, and its mechanical properties gradually increase with the increase of KH-560 content. XRD, FT-IR and SEM observations showed that more C-S-H gels would be produced under the action of KH-560, which made the structure of the weak interface transition zone of EPS concrete more compact. The results of discrete element simulation show that the peak strength of EPS concrete increases with the increase of friction coefficient, but has little effect on its elastic modulus.

Insights into microstructure evolution and fracture mechanisms of welded joints of high strength steel patchwork components

The hot roll bending patchwork components of B1500HS uncoated ultra-high strength steel processed at industrial scale were welded with filler wire. The microstructure, grain orientation, mechanical properties and fracture behavior of the joint were investigated. The results showed that the weld metal (WM) was mainly composed of lath martensite and lower bainite (LB). Various microstructure appeared in different positions of the HAZ, among which martensite-austenite (M-A) constituents in the incompletely quenched zone and tempered martensite (TM) in the tempered zone were the key factors determining the performance of the joint. The welded joint exhibited complex structure and anisotropic mechanical response due to the decarburization and rolling texture of the original base material (BM). In the tempered zone, lath merge and boundaries disappear lead to the annihilation of dislocations, carbide precipitation leads to reduction of mobile dislocations, and recrystallization and recovery eliminate work hardening. The reduction of the effect of dislocation strengthening results in the formation of a softening belt at 6 mm from the center of the weld, with a minimum hardness of 266 HV. The tensile strength of the joint in the rolling direction (RD) was 983 MPa, and the fracture occurred in the softening belt. Both brittle and ductile fracture features were observed. The reason why the fracture occurs in the high temperature tempered zone instead of the incompletely quenched zone was the difference in the effect of “constraint strengthening”. Fracture occurred through delamination cracking along the “weak interface” owing to precipitated high-hardness cementite particles and the unfavorably oriented ferrite cleavage planes.