Residual Mechanical Performance Research Articles

Mineralogical, chemical and physico-mechanical properties of fired bricks for refractory industry applications

This study aims to characterize soils for their use in the refractory industry applications. Two types of hydromorphous soil were sampled in the locality of Minkoameyos in the neighbouring city of Yaoundé-Cameroon: multicolored soil clay (A001) and grey soil clay (A002). Mineralogical, chemical and physico-mechanical properties were investigated. Bricks made from these soils were heated at 900 °C, 1100 °C and 1200 °C temperatures. Physico-chemical properties showed that these soils are light (A002), silty (A001), inorganic and acidic, with pH values of 5.45 and 4.47 for A001 and A002, respectively. Chemical analysis revealed that these soils are essentially composed of silica (40 and 46%), alumina (35.9 and 32.5%) and coloring oxides (8.5 and 6.3%) for A001 and A002 samples, respectively. Mineralogical analyses of these soils revealed the presence of quartz, kaolinite, illite and muscovite. Bricks heated at 900 °C, 1100 °C and 1200 °C showed a variation in color from orange to reddish brown for A001 sample; from light orange yellow to dull orange for A002 sample and a sound ranging from dull to slightly metallic. Residual mechanical performance showed a slight drop in strength at the heating temperature of 900 °C (8.8 and 8.3 MPa for multicolored soil clay A001 and grey soil clay A002, respectively). This temperature seems sufficient for this type of floor. Above 900 °C, the impact of carbon is significant. These results showed that Minkoameyos hydromorphous soils clay have remarkable properties and can produce refractory materials.

Effects of ultrasonic vibration on residual stress distribution and local mechanical properties of AA6061/Ti6Al4V dissimilar joints by resistance spot welding

The joining of dissimilar titanium and aluminum alloys has potential applications in railway and aerospace industries, owing to substantial weight reduction and better economic viability. In this study, the residual stress distribution and local mechanical performance of ultrasonic-assisted resistance spot welding (UaRSW) welds were investigated. The welding current, welding time, and electrode force of the RSW process were set as 9.0 kA, 350 ms, and 1.0 kN respectively, and the frequency and power of ultrasonic vibration were 20 kHz and 800 W. The residual stress was evaluated by X-ray diffraction (XRD) method and numerical simulation, and these methods showed a reasonable match. There was tensile residual stress distributed on RSW welds and UaRSW welds, but the value of residual stress was reduced by about 30% at welding nugget and 20% at heat affected zone (HAZ) with the ultrasonic vibration, the reduction of residual stress in UaRSW welds was attributed to the more uniform temperature distribution and lower plastic deformation resistant of AA6061. The welding peak temperature was decreased from 1673.4 °C to 1584.2 °C with the ultrasonic vibration, resulted from the modified Al/Ti contact surface and reduced contact resistance. The miniature tensile test results showed the improvement of mechanical performance by ultrasonic vibration. The maximum load of welding nugget region increased from 19.6 N to 22.3 N, and the elongation obtained 10% increase. This hybrid welding technique shows a potential to improve the quality of welds with ensured efficiency, which is also simple to realize automation in the manufacturing industry.

Influence of synthetic fibers on the performance of ultra-high performance concrete (UHPC) at elevated temperatures

Adding synthetic fibers to ultra-high performance concrete (UHPC) is an effective method for improving its resistance to high temperatures. This study examined the impact of different synthetic fibers on high-temperature spalling and corresponding residual mechanical performance of UHPC, including compressive strength, elastic modulus, and flexural strength. This study conducted high-temperature tests on UHPC with different synthetic fibers (PET, PP, NY, PVA, PAN fibers) and analyzed their microscopic morphology after exposure to 200 °C using scanning electron microscopy (SEM). The findings revealed that conventional steel fiber UHPC (without synthetic fibers) experienced severe spalling only after 400 °C. To some degree, synthetic fibers enhanced the resistance of UHPC to high-temperature spalling, but significant differences were observed among the different fibers. PP fibers provided the most significant improvement in high-temperature resistance, followed by NY fibers, while other fibers were less effective. Although the contributions of different synthetic fibers to high-temperature resistance varied, the differences in compressive strength and elastic modulus of UHPC with different synthetic fibers after high-temperature exposure were not substantial. NY fibers, despite being slightly less effective than PP fibers, provided superior flexural performance at both room and high temperatures compared to PP fibers. Both PP fibers and NY fibers inhibited high-temperature spalling of UHPC and maintained its mechanical performance. Even at 1050 °C, UHPC that did not spall retained residual mechanical performance, with compressive strength, elastic modulus, and flexural strength after exposure to 1050 °C being 24.4 %, 29 %, and 26.8 % of their respective values at room temperature.

Hydrogen charging can relax compressive residual stresses caused by shot peening

Surface engineering to generate compressive stresses via processes such as shot peening is commonly employed to mitigate fracture or fatigue failures in metallic systems. Localized plastic deformation is used to generate the generally biaxial compressive elastic stresses. This study examined the residual stress conditions and local mechanical performance of medium carbon steel in a quenched and tempered state. Electrolytic hydrogen charging of peened samples led to a permanent reduction in the compressive surface stress while concurrently hardening the surface. Slight changes in elastic modulus when solute hydrogen was present could not explain the resulting change in the measured residual stress; a reduction in X-ray peak breadth suggests that the combined effects of elastic stresses and solute hydrogen caused local dislocation annihilation and re-organization of the dislocation structure in the severe plastically deformed layer, leading to a lower magnitude and shallower depth of compressive residual stress on the peened surface after hydrogen charging.

Recycling glass fiber-reinforced plastic in asphalt concrete production

<abstract> <p>Glass fiber-reinforced plastics (GFRP) have been produced in large quantities for over half a century and nowadays their waste has become a problem worldwide. Their recycling is difficult because they are predominantly manufactured from thermosetting matrices that are not suitable for secondary processing. Only few technologies are able to target full-scale utilization of residual mechanical performance at recycling, with the replacement of gravel in asphalt concrete being one of them. The possibility of introducing crushed GFRP (GFRP crumb) into asphalt concrete and its impact on mechanical characteristics have been investigated in our study. As the source of GFRP, road noise-protection fence was chosen due to large quantities of its waste accumulated in urban economy. Several approaches to produce crumbs were attempted with only shredding being successful. The GFRP crumb has provided excellent mechanical performance of asphalt concrete fabricated by standard routine. In particular, the improvement in compressive modulus was 40%, even under conditions of elevated asphalt concrete temperature at 50 ℃. Besides, introduction of GFRP crumb reduced the overall weight of asphalt concrete mixture, providing further reduction of a carbon footprint. The results obtained indicated that recycling of GFRP waste as replacement of gravel in asphalt concrete provides an economically and environmentally safe solution.</p> </abstract>

Post-fire behavior of square hollow section column connections using thread-anchored blind bolts

The Thread-anchored Blind Bolt (TBB) is anchored using a special bolt hole with threads on the component to be connected. TBB is ideal for closed-section component connections as it can be installed from one side. Post-fire performance of TBB bolted Square Hollow Section Column Connections (SHSCC) was studied through tests. The full-process method was adopted to simulate the entire fire progression from start to finish. The analysis focused on the effect of temperature and load on the residual mechanical performance of TBB bolted SHSCC under post-fire conditions. Four different failure modes of TBB bolted SHSCC were identified. The failure mode of TBB bolted SHSCC depended on the configuration of the connection, including the thickness of the column and end-plate, as well as the TBB diameter. The threaded hole provided reliable anchorage to TBB before the SHSCC yielded, demonstrating the excellent applicability of TBB, even with thin column walls. The load ratio and temperature showed little influence on the SHSCC failure mode. TBB bolted SHSCC could recover most of its resistance after cooling from fire, indicating good post-fire performance. Comparative tests between TBB and Standard Bolt (SB) connected SHSCC were also conducted. SHSCC with the same configuration, but bolted by different bolts, exhibited the same failure mode. Moreover, TBB bolted SHSCC with a sufficiently thick wall could replace SB bolted SHSCC.

1 experimental and numerical evaluation of residual mechanical performance of carbon/epoxy laminated coupons after integration of solid battery cells for aeronautical applications

The present study deals with a numerical and experimental evaluation of the residual mechanical performance of a quasi-isotropic carbon/epoxy laminated composite plate in which solid battery cells have been integrated. Firstly, the mechanical properties of the multifunctional Reinforced Multilayer Stack (RMS) battery cells have been determined thanks to dedicated multi-instrumented tests, while those of the AS4/8552 composite material have been extracted from the literature and validated by comparisons with tensile tests on plates without battery, considered as a reference case. Then, on the basis of the recommendations obtained from a virtual test campaign using FE simulations, a 16-ply laminated composite plate containing 6 solid battery cells was manufactured with a modified curing cycle that preserves the electrical properties of the batteries while ensuring the mechanical properties of the composite material. Various control methods, such as CT-scan and optical analysis, were used to demonstrate the promising quality of the manufactured composite coupon with embedded cells. Finally, a mechanical tensile test was carried out to experimentally determine the reduction in mechanical properties. The analysis of such a test with non-linear FE simulation has allowed a better understanding of the damage and failure process when solid battery cells are integrated into high performance laminated composite structures designed for the aeronautical industry.

Effective Platform Heating for Laser Powder Bed Fusion of an Al-Mn-Sc-Based Alloy.

Platform heating is one of the effective strategies used in laser powder bed fusion (LPBF) to avoid cracking during manufacturing, especially when building relatively large-size components, as it removes significant process-induced residual strains. In this work, we propose a novel and simple method to spare the elaborate post-processing heat treatment typically needed for LPBF Al-Sc alloys without compromising the mechanical properties. We systematically investigated the effects of LPBF platform heating at 200 °C on the residual stress relief, microstructure, and mechanical performance of a high-strength Al-Mn-Sc alloy. The results reveal that LPBF platform heating at 200 °C is sufficient to largely relieve the process-induced residual stresses compared to parts built on an unheated 35 °C platform. Meanwhile, the platform heating triggered the dynamic precipitation of uniformly dispersed (1.5-2 nm) Sc-rich nano-clusters. Their formation in a high number density (1.75 × 1024 m-3) resulted in a ~20% improvement in tensile yield strength (522 MPa) compared to the build on the unheated platform, without sacrificing the ductility (up to 18%). The improved mechanical properties imply that platform heating at 200 °C can strengthen the LPBF-synthesised Sc-containing Al alloys via in situ aging, which is further justified by an in situ measurement study revealing that the developing temperatures in the LPBF part are within the aging temperature range of Al-Sc alloys. Without any post-LPBF treatments, these mechanical properties have proven better than those of most Al-Sc alloys through long-time post-LPBF heat treatment.

Behaviour of T-shaped stiffened concrete-filled steel tubular stub columns after uniform and non-uniform fire exposure

The post-fire behaviour of T-shaped stiffened concrete-filled steel tubular stub columns was investigated by the heating and residual mechanical performance tests. Key parameters, such as heating duration, number of surfaces exposed to fire and the influence of the stiffening steel bars, were studied. Temperature distribution, failure modes, mid-height strain curves, and load-displacement curves were obtained and discussed. The study reveals that the number of fire-exposure surfaces significantly affects the temperature distribution of the specimen section. Both the bearing capacity and compressive stiffness decrease with the increase of fire exposure surfaces and heating time, whereas the ductility follows an inverse pattern. The transverse stiffeners can enhance the mechanical performance of these stub columns, especially for ductility.

Low-Speed Impact and Residual Mechanical Performance of the BR1200HS/AA6082 Self-Piercing Riveted Joints

To investigate the low-speed impact response of the BR1200HS steel and AA6082 aluminum alloy self-piercing riveted (SPR) joint, low-speed impact tests with impact energies of 2.5 J, 5.0 J, 7.5 J, 10.0 J, 12.5 J, 15.0 J, 20.0 J, and 30.0 J were conducted utilizing a drop hammer impact tester. The results show that with the increased impact energy, the visual breakages of the SPR joints become more severe. The maximum impact energy the joints can sustain ranges from 10.0 J to 12.5 J. When the impact energy is less than 12.5 J, the contact force/energy–time curves show similar variations. Moreover, as the impact energy increases, total uptake energy value (Et), maximum uptake energy value (Ef), and maximum contact force (Fm) of the joints increase gradually. The low-speed impact energy has little effect on the maximum static tensile force of the impacted joints. However, the residual energy values decrease with the increase in impact energy. The tensile failure form of the joints is the pulling out of the rivets from the lower plates, and the low-speed impacts have no significant effect on the tensile failure form of the joints.

Long-term stress relaxation behaviors and mechanisms of 2219 Al–Cu alloy under various temperatures and initial stresses

Large 2219 Al–Cu alloy aerospace integral components suffer from long-term stress relaxation aging (SRA) due to complex temperature and stress loads during aging treatment/forming and service process, which makes it difficult to ensure their appropriate residual stress and excellent mechanical and service properties. However, the research is limited to a thorough understanding of macroscopic and microscopic features and underlying mechanisms of the long-term SRA under multivariable aging conditions. Therefore, this study investigated macroscopic and microscopic features of long-term SRA under different temperatures (120 °C to 190 °C), initial stress levels (100 MPa to 250 MPa) and durations (0 h to 50 h) through stress relaxation curves, metallographic traits, Vickers hardness, tensile performance, dislocations and phases of precipitation. On the basis of experimental outcomes, the comprehensive mechanisms beneath SRA were unraveled through dislocation theory, multiphase strengthening mechanisms and thermodynamics, where the interplays of stress relaxation behavior with age-hardening response were taken into consideration. The results showed elevations in the rate of stress reduction as the temperature and initial stress rose. At an initial stress greater than the yield stress of alloy, a marked increase in stress relaxation was found, and the mechanisms transform from the intragranular motion of dislocations and diffusion of grain boundaries to the intragranular and intergranular motion of dislocations and migration of grain boundaries. The stress reduction rate rose sharply when the temperature exceeded 175 °C, and the dislocation movement mechanisms transform from gliding to climbing of dislocations. Stress relaxation is in nature progressive transformation of strain from elastic into a permanently inelastic state via the motion of dislocations, leading to the decrease of movable dislocations and the increase of immovable dislocations with more stable configurations. The age hardening is mainly determined by precipitation strengthening, supplementarily by dislocation strengthening, and obvious stress orientation effect (SOE) of G.P. zones and θ" phases degenerates strengthening effect. The interplay between stress relaxation behavior and age-hardening response influences the thermal–mechanical coupling SRA of 2219 Al–Cu alloy, which depends fundamentally on the motion of dislocations and their interplay with precipitated phases. This is a thermal activation process concerning the interplay between internal (age-hardening resistance) stress and external (initial) stress. The initial energy of elastic strain offers Gibbs free energy as the SRA driver, and a steady state of stress relaxation is attained with the lowest energy of elastic strain. These findings provide valuable insights into exploring innovative aging treatment/forming for optimizing residual stress, mechanical performance and service property in a synergistic manner.

Residual mechanical performance and rust characterization of self-prestressing UHPM subjected to chloride-induced corrosion

Chloride-induced corrosion poses extreme vulnerabilities to the strength degradation and delamination of reinforced concrete structures in the oceanic environment. For this reason, the self-prestressing effect produced from the synergy of the combined addition of expansive agent (EA) and steel fibre (SF) into the concrete is suggested to enhance the corrosion performance (cracking and degradation) of concrete-steel tubular columns (CSTCs). Four mortar mixtures were prepared with the no EA and SF, individual use of EA or SF and combined use. The corrosion rate was measured by the linear polarization resistance (LPR) method, while crack-width and pit-depth were measured with scanning electron microscopy (SEM). Test results revealed that the self-prestressing ultra-high-performance mortar (UHPM) prepared by the combined use of EA and SF reduced the corrosion rate, pit depth, and crack width up to 87.3%, 55.8%, and 68.3%, respectively. Furthermore, it also results in the highest residual compressive strength. The corrosion products characterized by using an energy-dispersive x-ray detector (EDX) and x-ray diffractometry (XRD) for self-prestressing UHPM were oxides with a volume ratio to parent iron of approximately 2, which is the lowest amongst all and justifies its superior performance.

Life performance of 40-year-old RC beams with different concrete covers and bar diameters in natural corrosion environments

This study entailed an experimental evaluation of the life performance of 40-year-old reinforced concrete (RC) beams with different concrete cover depths and tensile bar diameters. Beams that were naturally corroded in a marine environment were used in this study, and no artificial process was employed to accelerate the corrosion. Most existing evaluations of beams employ electrical acceleration, admixture, or exposure to designed chloride environments to aid corrosion. Given the paucity of studies on naturally corroded beams, this study is of significance regarding the design, service, and life assessment of RC structures. Two-point load bending test was employed to examine the residual mechanical performance. The corroded bars were extracted to assess the corrosion properties, while the mechanical properties were evaluated via a tensile test. The focus of this study was on evaluating the progress of deterioration and capacity loss in naturally aged beams. The results indicated that a concrete cover of 50 mm satisfies the requirements of a design service life of 50 years. Furthermore, the cross-sectional loss–ultimate capacity loss relationship is consistently linear for the RC beams. Thus, the estimation of ultimate capacity loss based on cross-sectional loss is acceptable in case of natural corrosion of the RC beams. Hence, the findings can contribute to the prediction of the life performance and maintenance of existing structures as well as to designing new structures.

An Experimental Investigation on Assessment of Residual Mechanical Performance of Basalt Fiber Reinforced High Strength Concrete at Elevated Temperature

An Experimental Investigation on Assessment of Residual Mechanical Performance of Basalt Fiber Reinforced High Strength Concrete at Elevated Temperature

Joining SiO2 based ceramics: recent progress and perspectives

Nowadays, SiO2 based material is one of the widest used materials in optical, microelectromechanical system, aerospace and some other industries. In practical application, SiO2 based materials are required to be joined with themselves or other heterogeneous materials to assemble products with various functions. And the joining quality directly affects the mechanical performances and functional properties of assembled products. Though many researchers studied different joining technologies, explored the microstructure of joining interface and tested after-joining properties, a review that summarizes the recent cutting-edge researches and development tendency of joining technologies for SiO2 based ceramics is still absent. Therefore, according to different applications and requirements, this review summarizes the widely used joining technologies and discusses corresponding joining mechanisms, current research progress and suitable applications. Due to the wide applications in specific industry, laser welding, anodic bonding and wafer bonding are discussed in detail. Further, brazing, the widest used method in SiO2 joining, has been elaborated deeply in its wetting mechanism, residual stress control, interfacial microstructure and mechanical performance aspects. In the end, this review proposed the future development trends of SiO2 ceramics joining, aiming at offering a full-view of potential improvements in SiO2 ceramic joining technologies.

Study of impact damage on composite laminates induced by strip impactor using DIC and infrared thermography

This paper studies the impact damage induced by strip impactors and residual mechanical performance of composite laminates using DIC and infrared thermography. A continuum damage model and a cohesive model were adopted to simulate the intralaminar and interlaminar behaviors, respectively. The results reveal that the delamination area and residual load capacity decrease as impact angle increases. During compression after impact (CAI) process, the strain concentration in damage area causes local buckling. After that the delamination and matrix damage initiate, followed by fiber damage. The whole laminates collapse when the fiber damage area covers the whole width of the damage area.

Influence of Elevated Temperatures on the Mechanical Performance of Sustainable-Fiber-Reinforced Recycled Aggregate Concrete: A Review

In recent times, the applications of fiber-reinforced recycled aggregate concrete (FRAC) in practical engineering have gained greater popularity due to its superior mechanical strength and fracture properties. To apply FRAC in buildings and other infrastructures, a thorough understanding of its residual mechanical properties and durability after exposure to fire is highly important. According to the established research, the properties and volume fractions of reinforcing fiber materials, replacement levels of recycled concrete aggregate (RCA), and heating condition would affect the thermal–mechanical properties of FRAC. This review paper aims to present a thorough and updated review of the mechanical performance at an elevated temperature and post-fire durability of FRAC reinforced with various types of fiber material, specifically steel fiber (SF), polypropylene (PP) fiber, and basalt fiber (BF). More explicitly, in this review article the residual mechanical properties of FRAC, such as compressive strength, splitting tensile capacity, modulus of elasticity, mass loss, spalling, and durability after exposure to elevated temperatures, are discussed. Furthermore, this study also encompasses the relationship among the dosages of fibers, replacement levels of recycled aggregate, and the relative residual mechanical properties of FRAC that would help in the optimum selection of the fiber content. Conclusively, this study elaborately reviews and summarizes the relevant and recent literature on recycled aggregate concrete containing SF, PP fiber, and BF. The study further provides a realistic comparison of these fibers in terms of the residual mechanical performance and durability of FRAC that would help in their future enhancements and applications in practical engineering.

Effect of carbonation curing on the mechanical properties of belite-rich cement mortar exposed to elevated temperatures

The present study aims to investigate the residual properties of carbonation-cured belite-rich cement mortar exposed to a high temperature. The mortar was carbonation-cured with a 10% CO2 concentration for 28 days and was then exposed to elevated temperatures of 300 °C, 600 °C, 900 °C and 1200 °C. The findings revealed that the heat resistance of a cement mortar relative to that of standard water-cured sample was enhanced by carbonation curing. Moreover, it was noted that in comparison to Portland cement mortar, the residual mechanical performance was improved for the carbonation-cured belite-rich cement mortar sample. A physicochemical analysis revealed that the formation of thermally stable calcium carbonate due to carbonation curing was the primary cause of the enhanced residual properties. Furthermore, for samples exposed to 1200 °C, it was observed that the carbonation reaction products became thermally stable alite and belite phases.

Residual mechanical performance of lightweight fiber-reinforced geopolymer mortar composites incorporating expanded clay after elevated temperatures

This research provides an experimental investigation on the properties of fiber reinforced composite materials consisting of lightweight expanded clay aggregates (LECA) and polyvinyl alcohol (PVA) fibers. The influence of temperature (room temperature, 250°C, and 500°C) on the lightweight geopolymer mortar (LWGM) composite materials is also explored. LECA is used as a partial replacement to river sand with 60% and 80%. The base material utilized for LWGM is slag activated by a mixture of sodium silicate and sodium hydroxide solutions. The fresh properties in terms of workability and density were performed. A series of experiments, such as compression, flexural and uniaxial tensile strength tests, were executed to assess the mechanical properties of LWGM composite materials. In addition, the microscopic variations due to the elevated temperature were also evaluated by scanning electron microscopy (SEM) to understand the macro-scale behavior of the samples. The results indicated that increasing the level of LECA replacement caused a reduction in the density and compressive strength of the LWGM. Also, incorporating a 1% PVA fiber volume fraction significantly enhanced the flexural and uniaxial tensile behavior of LWGM composite materials. The compressive strength enhancements were observed at 250°C due to further geopolymerization, while compressive strength reductions were obtained at 500°C due to the vapor impact and difference in thermal expansion. In addition, the load-carrying capacity of all samples increased, and displacement capacity decreased under flexural tests at 250°C. However, the ductile behavior of the PVA incorporating specimens changed to brittle due to the melting of PVA fibers.

Residual mechanical properties and numerical analysis of recycled pebble aggregate concrete after high temperature exposure and cooled by fire hydrant

In urban fire, the structure will not only be subjected to high temperature, but also cooled by fire hydrant. This paper presents the experimental results of the residual mechanical performance and the complete compressive stress–strain relationship of recycled pebble aggregate concrete (RAC) after exposure to high temperature of 20 to 600 ℃ and cooled by fire hydrant. In the experiments, five different concrete compositions were designed by substituting natural coarse aggregates with recycled coarse aggregates at the replacement ratios of 0%, 30%, 50%, 70% and 100%. Results exhibit that with the increase of exposure temperature, the surface color of the specimens changes from light to dark, the mass of RAC first increases and then decreases, and the residual mass of RAC at 200 ℃ is higher than that at room temperature. The compressive strength and the strain at the peak point decrease rapidly with the increase of temperature. The compressive strength and the strain at the peak point fluctuate with the increase of aggregate replacement percentage, and the temperature and aggregate replacement percentage have little effect on the ductility of RAC. The residual bearing capacity calculation method and constitutive equation of RAC after high temperature exposure and cooled by fire hydrant are proposed and verified. The accuracy of the constitutive equation is verified by ABAQUS finite element analysis software.