Search Results (10)

The risk of explosive spalling in high-strength cement-based materials during fire exposure poses a significant threat to structural integrity. To help mitigate this issue, this study explores the use of expanded polystyrene (EPS) beads as both a lightweight filler and a potential spalling-reduction agent in lightweight geopolymer and conventional cementitious mortars. Two EPS-containing mortars were developed: a lightweight alkali-activated slag (LWAS) mortar and a conventional lightweight Portland cement (LWPC) mortar, both incorporating EPS beads as a 50% volumetric replacement for sand. Specimens from both mortars were subjected to elevated temperatures of 200 °C, 400 °C, and 600 °C at a heating rate of 10 °C/min to simulate a rapid-fire scenario. Following thermal exposure, two cooling regimes were employed: gradual cooling within the furnace and rapid cooling by water immersion. Mechanical performance was evaluated through compressive, splitting tensile, and impact tests at room and elevated temperatures. Microstructural analysis was also conducted to examine internal changes and heat-induced damage. The results indicated that LWAS showed remarkable resistance to spalling, remaining intact up to 600 °C due to its nanoporous geopolymer structure, which allowed controlled steam release, while LWPC failed explosively at 550 °C despite EPS pores. At 400 °C, EPS beads enhanced thermal insulation in LWAS, lowering internal temperature by over 100 °C, but increased porosity led to faster strength loss. Both mortars gained strength at 200 °C from continued curing, yet LWAS retained strength better at high temperatures than LWPC. Microscopy revealed that EPS created beneficial fine cracks in the slag matrix but harmful voids in cement. Overall, LWAS composites offer excellent spalling resistance for fire-prone environments, though reinforcement is recommended to mitigate strength loss. Full article

Cracks in laser-cladded coatings represent a critical challenge that severely limits their industrial deployment. In this study, high-frequency pulsed direct current-assisted electrically assisted heat treatment (EAHT) was applied to repair cracks in laser-cladded Ni60/WC coatings deposited on 45# medium carbon steel. The influence of current density and treatment duration on crack arrest and healing behavior was systematically investigated. Dye penetrant testing and scanning electron microscopy (SEM) were employed to characterize the morphology and evolution of cracks before and after EAHT, while hardness, fracture toughness, and wear resistance tests were conducted to evaluate the mechanical properties. The results revealed that the crack repair process proceeds through three distinct stages: internal filling, nucleation and growth of healing points, and complete crack closure. The combined effects of Joule heating and current crowding induced by EAHT significantly facilitated progressive crack healing from the bottom upward. Optimal crack arrest and healing were achieved at a current density of 6.25 A/mm², resulting in a maximum fracture toughness of 10.74 MPa·m^1/2 and a transition of the wear mechanism from spalling to abrasive wear. This study demonstrates that EAHT promotes selective crack-tip heating and microstructural regulation through thermo-electro-mechanical coupling, thereby markedly enhancing the comprehensive performance of Ni-based WC coatings. Full article

The gear transmission system is a safety-critical component in rail transit, typically designed for a service life exceeding 20 years. Failure analysis of such systems remains a key focus for railway engineers. This study systematically investigates four representative cases of premature gear failure in high-speed trains using a standardized analytical procedure that includes visual inspection, chemical analysis, metallographic examination, scanning electron microscopy, and hardness testing. The results identify four primary root causes: subsurface slag inclusions in raw materials, inadequate heat treatment leading to a non-martensitic layer (∼60 μm) at the tooth root, grinding-induced temper burns (crescent-shaped "black spots") accompanied by a hardness drop of ∼100–150 HV, and insufficient lubrication. The interdependencies between these factors and failure mechanisms, e.g., fatigue cracking, spalling, and thermal scuffing, are analyzed. This work provides an evidence-based framework for improving gear reliability and proposes targeted countermeasures, such as ultrasonic inclusion screening and real-time grinding temperature control, to extend operational lifespans. Full article

Enhancing damage tolerance and wear resistance in Al–Si-based alloys under thermomechanical stress remains a key challenge in lightweight structural applications. This study investigates the microstructural and tribomechanical behavior of hypoeutectic Al–Si–(Cu)–Mg alloys with varying Cu:Mg ratios (3:1 vs. 1:3) under a T6 heat treatment. Alloys A and B, with identical Si contents but differing Cu and Mg levels, were subjected to multiscale microstructural characterization and mechanical and wear testing at 25 °C, 150 °C, and 250 °C. Alloy A (Cu-rich) exhibited refined α-Al(FeMn)Si phases and homogeneously dissolved Cu in the Al matrix, promoting lattice contraction and dislocation pinning. In contrast, Alloy B (Mg-rich) retained coarse Mg₂Si and residual β-AlFeSi phases, which induced local stress concentrations and thermal instability. Under tribological testing, Alloy A showed slightly higher friction coefficients (0.38–0.43) but up to 26.4% lower wear rates across all temperatures. At 250 °C, Alloy B exhibited a 25.2% increase in the wear rate, accompanied by surface degradation such as delamination and spalling due to β-AlFeSi fragmentation and matrix softening. These results confirm that the Cu:Mg ratio critically influences the dominant hardening mechanism—the solid solution vs. precipitation—and determines the high-temperature performance. Alloy A maintained up to 14.1% higher tensile strength and 22.3% higher hardness, exhibiting greater shear resistance and interfacial stability. This work provides a compositionally guided framework for designing thermally durable Al–Si-based alloys with improved wear resistance under elevated temperature conditions. Full article

Concrete has good fire resistance. However, once exposed to rapidly increasing temperatures, concrete may suffer from thermal stress-induced spalling or pore pressure-induced spalling. Compared with normal-weight concrete (NWC), lightweight aggregate concrete (LWAC) has a low thermal conductivity and is more prone to cause a higher temperature gradient under the action of high temperatures. This poses a hidden concern to the fire safety of general LWAC structures. Therefore, this study aimed to investigate the temperature and the pore pressure distribution of LWAC slabs under one-dimensional heating tests and to compare them with NWC slabs. The test variables were the moisture content of the specimen (oven-dried and air-dried), target temperature (600 and 800 °C), and heating rate (5 and 10 °C/min). The temperature and the pore pressure distributions were measured separately by thermocouples and pressure gauges embedded in different positions of the specimen. The test results show that the maximum pore pressure (P_max) of the LWAC slabs was generally higher than that of the NWC slab at a distance of 10 mm from the heated surface when the specimen was in an oven-dried state. However, at 30 and 50 mm from the heated surface, the P_max of the NWC slab tended to be higher. This shows that the P_max distribution of the LWAC slab was closer to the heated surface when the specimen was in an oven-dried state, while the P_max of the NWC slab occurred further from the heated surface. Further, as the heating rate increased, a higher pore pressure was generated inside the specimen and the pressure rose more rapidly. In particular, at a target temperature of 800 °C and a heating rate of 10 °C/min, the corner spalling phenomenon appeared on the air-dried LWAC slab. Full article

Concrete is a heterogeneous material that consists of cement, aggregates, and water as basic constituents. Several cementitious materials and additives are added with different volumetric ratios to improve the strength and durability requirements of concrete. Consequently, performance of concrete when exposed to elevated temperature is greatly affected by the concrete type. Moreover, post-fire properties of concrete are influenced by the constituents of each concrete type. Heating rate, days of curing, type of curing, cooling method, and constituents of the mix are some of the factors that impact the post-fire behavior of concrete structures. In this paper, an extensive review was conducted and focused on the effect of concrete constituents on the overall behavior of concrete when exposed to elevated temperature. It was evident that utilizing fibers can improve the tensile capacity of concrete after exposure to higher temperatures. However, there is an increased risk of spalling due to the induced internal stresses. In addition, supplementary cementitious materials such as metakaolin and silica fume enhanced concrete strength, the latter proving to be the most effective. In terms of the heating process, it was clear that several constituents, such as silica fume or fly ash, that decrease absorption affect overall workability, increase the compressive strength of concrete, and can yield an increase in the strength of concrete at 200 °C. Most of the concrete types show a moderate and steady decrease in the strength up until 400 °C. However, the decrease is more rapid until the concrete reaches 800 °C or 1000 °C at which it spalls or cannot take any applied load. This review highlighted the need for more research and codes’ provisions to account for different types of concrete constituents and advanced construction materials technology. Full article

The oxidation behavior of body-centered cubic (bcc) structure Cr₂₀Mn₁₇Fe₁₈Ta₂₃W₂₂ refractory high-entropy alloy (RHEA) and the microdefects induced by hydrogen ions before and after oxidation were investigated. The results revealed that compared with oxidizing Cr₂₀Mn₁₇Fe₁₈Ta₂₃W₂₂ at 800 °C (6.7 °C/min) for 4 h (ST3, Ar:O₂ = 3:1), the heating procedure of oxidizing Cr₂₀Mn₁₇Fe₁₈Ta₂₃W₂₂ at 300 °C (6 °C/min) for 2 h and then increased to 800 °C (5 °C/min) for 4 h is more conducive to the production of oxides without spalling on the surface, i.e., HT1 (Ar:O₂ = 1:1), HT2 (Ar:O₂ = 2:1) and HT3 (Ar:O₂ = 3:1) samples. The oxidation of Cr₂₀Mn₁₇Fe₁₈Ta₂₃W₂₂ RHEA is mainly controlled by the diffusion of cations instead of affinities with O. Additionally, HT1 and HT3 samples irradiated with a fluence of 3.9 × 10²² cm⁻² hydrogen ions (60 eV) were found to have a better hydrogen irradiation resistance than Cr₂₀Mn₁₇Fe₁₈Ta₂₃W₂₂ RHEA. The microdefects in irradiated Cr₂₀Mn₁₇Fe₁₈Ta₂₃W₂₂ mainly existed as hydrogen bubbles, hydrogen-vacancy (H-V) complexes and vacancy/vacancy clusters. The microdefects in irradiated HT3 were mainly vacancies and H-V complexes, while the microdefects in irradiated HT1 mainly existed as vacancies and vacancy clusters, as large amounts of hydrogen were consumed to react with oxides on the HT1 surface. The oxides on the surface of the HT3 sample were more stable than those on HT1 under hydrogen irradiation. Full article

Heat-induced spalling in concrete is a problem that has been the subject of intense debate. The research community has, despite all the effort invested in this problem, few certain and definitive answers regarding the causes of and the way in which spalling happens. A major reason for this difficulty is the lack of a unified method for testing, which makes comparing data from various studies against each other a difficult task. Many studies have been performed that show the positive effects of using synthetic micro-fibres, such as polypropylene (PP). The mechanism with which PP fibres improve heat-induced spalling resistance in concrete, however, remains a subject of debate. This paper, therefore, looks at the work that has been performed in the field of spalling (particularly spalling of self-compacting concrete (SCC)). Influencing factors are identified and their links to each other (as reported) are discussed. A particular emphasis is put on discussing the role of PP fibres and how they improve the behaviour of high-performance concrete (HPC) at elevated temperatures. A brief summary of the reviewed papers are provided for each of the influencing factors to help the reader navigate with ease through the references. An introduction to heat-induced spalling and the common causes (as reported in the literature) is also included to highlight the wide range of theories trying to explain the spalling phenomenon. Full article

This article presents a comprehensive thermomechanical analysis and failure assessment in the drilling of glass fiber-reinforced polymer (GFRP) composites with different thicknesses using a CNC machine and cemented carbide drill with a diameter of 6 mm and point angles of ϕ = 118°. The temperature distribution through drilling was measured using two techniques. The first technique was based on contactless measurements using an IR Fluke camera. The second was based on contact measurements using two thermocouples inserted inside the drill bit. A Kistler dynamometer was used to measure the cutting forces. The delamination factors at the hole exit and hole entry were quantified by using the image processing technique. Multi-variable regression analysis and surface plots were performed to illustrate the significant coefficients and contribution of the machining variables (i.e., feed, speed, and laminate thickness) on machinability parameters (i.e., the thrust force, torque, temperatures, and delamination). It is concluded that the cutting time, as a function of machining variables, has significant control over the induced temperature and, thus, the force, torque, and delamination factor in drilling GFRP composites. The maximum temperature recorded by the IR camera is lower than that of the instrumented drill because the IR camera cannot directly measure the tool–work interaction zone during the drilling process. At the same cutting condition, it is observed that by increasing the thickness of the specimen, the temperature increased. Increasing the thickness from 2.6 to 7.7 had a significant effect on the heat distribution of the HAZ. At a smaller thickness, increasing the cutting speed from 400 to 1600 rpm decreased the maximum thrust force by 15%. The push-out delaminations of the GFRP laminate were accompanied by edge chipping, spalling, and uncut fibers, which were higher than those of the peel-up delaminations. Full article

This paper investigates a potential application of hard-to-recycle plastic waste as polymeric addition in high strength concrete, with a focus on the potential to mitigate heat-induced concrete spalling and the consequent effects on the mechanical properties. The waste corresponds to soft and hard plastic, including household polymers vastly disposed of in landfills, although technically recyclable. Mechanical and physical properties, cracking, mass loss, and the occurrence of spalling were assessed in high strength concrete samples produced with either plastic waste or polypropylene fibers after 2-h exposure to 600 °C. The analysis was supported by Scanning Electron Microscopy and X-Ray Computed Tomography images. The plastic waste is composed of different polymers with a thermal degradation between 250 to 500 °C. Polypropylene (PP) fibers and plastic waste dispersed in concrete have proved to play an essential role in mitigating heat-induced concrete spalling, contributing to the release of internal pressure after the polymer melting. The different morphology of plastic waste and polypropylene fibers leads to distinct mechanisms of action. While the vapor pressure dissipation network originated by polypropylene fibers is related to the formation of continuous channels, the plastic waste seems to cause discontinuous reservoirs and fewer damages into the concrete matrix. The incorporation of plastic waste improved heat-induced concrete spalling performance. While 6 kg/m³ of plastic increased the mechanical performance after exposure to high temperature, the incorporation of 3 kg/m³ resulted in mechanical properties comparable to the reference concrete. Full article