Failure Mode Changes Research Articles

Fixation strength of conformal additively manufactured Ti6Al4V implants in large animal model

Additive manufacturing (AM) enables patient-specific lattice-based implants with porosity engineered to encourage bone ingrowth and to mimic bone’s mechanical stiffness. The strength of the bone-implant interface can be measured through a destructive ‘push-out’ testing. The aim of this study is to explore the effect of implant-bone stiffness ratio (γ) on the push-out force using numerical simulation and a small experimental study. Numerical simulations of an implant-bone interface during a push-out test showed a fundamental change of failure mode for γ ranging from 0.1 to 10. For the geometry considered, the largest push-out forces were predicted for γ ≈ 0.7, essentially doubling the push-out force compared to a solid titanium implant. The experimental and simulation results also demonstrated that using an intermediate stiffness metal implant lattice geometry, γ ≈ 1.35, does not significantly improve the peak force of the push-out test compared to the solid implant. For the experimental study, critical-sized defects were simulated via robotic bone resection in the right lateral distal femur of a group of ~ 2.5-year-old healthy sheep, and then solid or lattice-based Ti6Al4V implants inserted. The femurs were harvested 6 months after implantation. Nine of the implanted femurs (six solid and three lattice-based) were used for fixation testing. The experimental study showed no significant difference in push-out force between a solid and moderately stiff lattice metal implant as indicated by the numerical simulation.

Enhancing crashworthiness characteristics of modified hexagonal honeycomb structural panels through stretching and bending of ribs

The effects of stretching and bending of concave, convex, and horizontal ribs on the energy absorption characteristics of modified hexagonal honeycomb structural panels are investigated under in-plane quasi-static compression loading conditions. In this regard, five hierarchical modified structural panel configurations were fabricated using polylactic acid material (PLA) via a fused filament 3D printer, ensuring uniform wall thickness in the 1.5–2 mm range. The panels included the regular hexagonal panel (RHP), regular hexagonal panel with concave rib (RHCP), regular hexagonal panel with convex rib (RHXP), regular hexagonal panel with concave and horizontal ribs (RHCRP), and regular hexagonal panel with convex and horizontal ribs (RHXRP). In-plane quasi-static compressive loading tests were conducted to analyze crush resistance characteristics, and buckling modes of the modified honeycomb panels were examined through experimental and finite element analysis procedures. The result indicates that the specific energy absorption capacity (SEA) of RHXRP is increasing significantly compared to the SEA capacity of other categories of the structures. The changes in failure modes and increased crush energy absorption characteristics of modified RHP with the introduction of concave, convex, and horizontal ribs are elaborated.

Cryogenic Failure Behaviors of Al–Mg–Si Alloy Tubes in Bulging Process

Abstract Cryogenic medium pressure forming has been developed to form the complex-shaped tubular components, in which the needed shape and tube diameter directly determine the complex evolution of biaxial stress in bulging process. The superposition of biaxial stress and cryogenic temperature complicates the deformation behaviors, especially for the final fracture and bulging limit, which determine the forming quality of components. Therefore, the effects of tube geometry on failure orientation and fracture strain of Al–Mg–Si alloy tubes under cryogenic biaxial stress were elucidated, by utilizing cryogenic free bulging with different length–diameter ratios. The failure orientations and corresponding damage modes under different bulging geometric conditions were revealed. The influence mechanism of tube geometry and temperature on the failure mode was analyzed theoretically. A fracture model was established to predict the fracture strain in cryogenic bulging. The failure mode changes from circumferential cracking to axial cracking with the decreasing length–diameter ratio, owing to the stress sequence reversal induced by the significant nonlinearity of the stress path under a small length–diameter ratio. The failure mode can inverse under a larger length–diameter ratio of 1.0 at −196 °C because of the enhanced nonlinearity, which is promoted by the improved plasticity at cryogenic temperature. The established model based on the more accurate assessment of hardening ability during deformation can accurately predict the fracture strain with an average deviation of 10.6% at different temperatures. The study can guide deformation analysis and failure prediction in the cryogenic forming of aluminum alloy tubular parts.

Corrosion-induced deterioration and fracture mechanisms in ultra-high-performance fiber-reinforced concretet

Ultra-high-performance fiber-reinforced concrete (UHPFRC) is an excellent material for harsh environments, but corrosion will change its internal microstructure and complicate the fracture evolution, bringing great difficulties in evaluating the long-term service life. Limited attention has been paid to the fracture mechanism of the UHPFRC upon corrosion. In the present study, integrating acoustic emission (AE) and digital image correlation (DIC) techniques are used to assess the micro/macrocracking characteristics of the specimens upon various corrosion degrees. Results show that the 56-day corroded UHPFRC with 2 vol% presents a remarkable decrease rate of 32%, 29% and 30% in the flexural stiffness, flexural strength and compressive strength. During the loading process, compaction of the original defects induced by fiber corrosion is concentrated in the elastic stage, the newborn cracks triggered by loading mainly occur in the strain-hardening stage, and the expansion of cracks mainly lies in the strain-softening stage. Corroded UHPFRC specimens with higher corrosion damage have a greater maximum strain value at the crack. In addition, the failure mode changes from shear crack failure to a brittle failure of tensile crack as corrosion damage increases. The macroscopic destruction of the corroded UHPFRC is a manifestation of internal microdamage evolution in fiber corrosion and matrix deterioration.

Research on impact resistance of ZK61m magnesium alloy thin plate under different working conditions

To study different working conditions on the impact resistance of ZK61m magnesium alloy thin plate, includes radius of curvature of the projectile (Caliber-radius-head, CRH) and number of layers in the target plate. The impact resistance of magnesium alloy plate by the shape of the projectile head was analyzed through experiments and simulations, the ballistic limit (BLV) of the target plate and the failure mode of the target plate under different CRH projectile impacts were obtained. The experimental results show that the BLV of the target plate decreases with the increase of CRH value and the failure mode changes from shear punch plug failure to tensile cracking failure. The numerical simulation results show that the Lode parameter dependent MMC fracture criterion is closer to the experimental results; the MMC fracture criterion was selected to analyze the effects of CRH and the number of target plate layers on the impact resistance of magnesium alloy thin plates. It was found that the impact resistance of the target plate changes slowly and then increases rapidly with the increase of the CRH value; its impact resistance showed a linear decrease with the number of target plate layers increase.

A modeling strategy for the shear and flexural performance prediction of SFRC beams without stirrups accounting for the variability of properties

AbstractThe behavior of steel fiber reinforced concrete (SFRC) is highly dependent on mix design, where the properties of its components, such as cementitious matrix and fibers, impact the physical and mechanical properties of the composite. Incorporating steel fibers into concrete modifies its physical properties, potentially leading to fiber segregation and resulting in a nonuniform distribution of the fibers within the material. In experimental studies, an increase in fiber volume has been found to change the failure mode of SFRC beams from shear to flexure, and numerical investigations have shown that randomness in fiber distribution can significantly influence the behavior of the composite. Therefore, this study aims to develop a numerical model that considers variations in material properties to simulate the change in the failure mode of SFRC beams due to variations in fiber volume. The failure and yielding parameters were initially established and integrated into the concrete damaged plasticity (CDP). Subsequently, the response of both steel and concrete to tension or compression stresses was ascertained. Finally, the appropriate meshes and finite elements were chosen for the simulation. In the final approach, two methods were employed to introduce randomness into the beam. One divided the beam into different vertical segments: 30, 45, and 90, and the other combined vertical and horizontal segments: 30 vertical with 4 horizontal, 45 vertical with 5 horizontal, and 90 vertical with 10 horizontal. A script was developed in Python to automatically insert the properties. The numerical model successfully captured the change in failure mode from shear to flexure resulting from fiber volume increase. Vertical and horizontal segments increased toughness due to crack deviation, better predicting cracking pattern and loading capacity for the highest fiber contents.

Effect of Interface Form on Creep Failure and Life of Dissimilar Metal Welds Involving Nickel-Based Weld Metal and Ferritic Base Metal

For dissimilar metal welds (DMWs) involving nickel-based weld metal (WM) and ferritic heat resistant steel base metal (BM) in power plants, there must be an interface between WM and BM, and this interface suffers mechanical and microstructure mismatches and is often the rupture location of premature failure. In this study, a new form of WM/BM interface form, namely double Y-type interface was designed for the DMWs. Creep behaviors and life of DMWs containing double Y-type interface and conventional I-type interface were compared by finite element analysis and creep tests, and creep failure mechanisms were investigated by stress-strain analysis and microstructure characterization. By applying double Y-type interface instead of conventional I-type interface, failure location of DMW could be shifted from the WM/ferritic heat-affected zone (HAZ) interface into the ferritic HAZ or even the ferritic BM, and the failure mode change improved the creep life of DMW. The interface premature failure of I-type interface DMW was related to the coupling effect of microstructure degradation, stress and strain concentrations, and oxide notch on the WM/HAZ interface. The creep failure of double Y-type interface DMW was the result of Type IV fracture due to the creep voids and micro-cracks on fine-grain boundaries in HAZ, which was a result of the matrix softening of HAZ and lack of precipitate pinning at fine-grain boundaries. The double Y-type interface form separated the stress and strain concentrations in DMW from the WM/HAZ interface, preventing the trigger effect of oxide notch on interface failure and inhibiting the interfacial microstructure cracking. It is a novel scheme to prolong creep life and enhance reliability of DMW, by means of optimizing the interface form, decoupling the damage factors from WM/HAZ interface, and then changing the failure mechanism and shifting the failure location.

Strengthening of Laminated Veneer Lumber Slabs with Fiber-Reinforced Polymer Sheets—Preliminary Study

Analyzing the feasibility of reinforcing new and existing wooden structures is a valid problem, being the subject of numerous scientific papers. The paper presents the preliminary results of a study on reinforcing Laminated Veneer Lumber (LVL) panels with composite materials bonded to exterior surfaces using epoxy resin. Glass-Fiber-Reinforced Polymer (GFRP) sheets, Carbon-Fiber-Reinforced Polymer (CFRP) sheets, and Ultra-High-Modulus (UHM) CFRP sheets were used as reinforcement. The variables in the analysis were the type of reinforcement and the number of reinforcement layers. The tests were carried out on small samples (45 × 45 × 900 mm) subjected to the so-called four-point bending test. Reinforcement positively affected the mechanical properties of composite section. The highest increases in load bearing were 37 and 48% for two layers of GFRP and CFRP, respectively. The bending stiffness increased up to 53 and 62% for two layers of CFRP and UHM CFRP, respectively. There was a change in failure mode from cracking in the tension zone for unreinforced beams to veneer shear in the support zone (for CFRP and GFRP sheets) and sheet rupture (UHM CFRP). Good agreement was obtained for estimating bending stiffness with the presented numerical and mathematical model; the relative error was up to 6% for CFRP and GFRP and up to 20% for UHM CFRP. This preliminary study proved the effectiveness of combining LVL with FRP sheets and indicated their weak spots, which should be further analyzed to improve their competitiveness against the traditional structures. The key limitation was the shear strength of LVL.

Micro-dissolution mechanism and macro-mechanical behavior of red-bed soft rock under dry-wet cycle

The microscopic pore characteristics of rocks have an important influence on their macroscopic mechanical behavior. The micro-pore dissolution mechanism of red-bed soft rock was revealed by the dry-wet cycle method, and its macroscopic mechanical behavior was studied by a series of uniaxial compression tests. The results show that with an increase in the number of dry-wet cycles, the micro-pore dissolution and micro-grain spalling of red-bed soft rock result in its porosity increasing nonlinearly. Under the action of the axial load, the number of micro-fractures increases and evolves from tensile fracture to shear fracture, and the macroscopic failure mode changes from brittle splitting failure to ductile conical failure.

How does the heterogeneous interface influence hydraulic fracturing?

Under the influence of the nonlinear fluid-solid coupling, hydraulic fracture exhibits various propagation modes (such as toughness- or viscosity-dominated), which stem from the competition between the solid deformation and fluid flow. Based on the homogeneous assumption, the basic theoretical analysis has divided toughness and viscosity scales in the tip region. However, regarding more realistic and complex geological conditions, like layered heterogeneity, knowledge of fluid-driven fracture propagation is still unclear. This work establishes a theoretical model and solving approach to reveal the multiscale asymptotic behavior during hydraulic fracture passing through the heterogeneous interface (i.e., discontinuous elastic properties). The influence of material discontinuity, regarded as the remote force, in the near-tip, intermediate, and far-field scales is analyzed by the asymptotic analysis and validated by the numerical solutions. Notably, solutions at the intermediate scale manifest as individual feature owing to the heterogeneity: as the crack in front of the interface, just a specific transition solution governed by the property and position of the interface appears; once the crack tip passes the interface, the interface-governed transition solution and interface solution occur simultaneously and interact as the crack tip moves away from the interface. Such multiscale property results in the interface-governed fluid-solid interaction in the tip region, and finally leads to changes in interface failure and propagation mode. On the one hand, the criterion for interface failure should be modified by simultaneously incorporating the heterogeneity of solid domain and multiscale nature of tip solution, especially for viscosity- or interface-dominated propagation regimes. On the other hand, the propagation mode in a heterogeneous domain is controlled by two characteristics: traditional l/lmk for toughness-viscosity competition associated with c/Lμ for material discontinuity effect proposed in the present work. These insights provide the theoretical foundation for modeling hydraulic fracture propagation in layered heterogeneous domains.

Effect of geopolymer concrete cover on improving tensile and transverse shear behaviors of BFRP bars after exposure to high temperature

The integration of high-temperature resistant geopolymer concrete, reinforced with basalt fiber reinforced polymer (BFRP), addresses several challenges encountered by conventional reinforced concrete structures, such as elevated energy consumption, substantial carbon emissions, and susceptibility to steel corrosion. To investigate the impact of geopolymer concrete cover on the mechanical performance of BFRP bars after high temperature treatment, this study conducted mechanical tests on a total 406 tensile specimens and 406 transverse shear specimens, spanning a temperature range from ambient temperature to 700 °C. The BFRP bars with diameters of 6 mm, 12 mm, and 16 mm underwent heat treatment durations of 0 h, 1 h, 2 h, and 3 h. Subsequently, they were examined for mass loss rat, residual tensile properties, and residual shear strength following natural cooling. Notably, this study also compared the impact of different geopolymer concrete cover thickness (30 mm, 40 mm, and 50 mm) on these performance parameters. The test results revealed that with an increase in heating temperature, the resin of BFRP experienced decomposition, leading to alterations in surface morphology, as well as changes in tensile and shear failure modes. In the temperature range of 400 °C to 700 °C, bare BFRP bars exhibited a significant decrease in both tensile and transverse shear strengths, with strength loss rates ranging from 50% to 90%. Moreover, the degradation in shear strength was comparatively slower than that in tensile strength. The presence of geopolymer concrete cover effectively mitigated the strength degradation of BFRP bars following high temperature treatment, and this protective effect improved with an increase in the concrete cover thickness. Additionally, scanning electron microscope (SEM) analysis was employed to elucidate the damage mechanisms for both bare and geopolymer concrete-covered BFRP bars. SEM results indicated that the deterioration induced by high temperature treatment gradually propagated radially from the edge to the core area of the bar. Finally, a simplified calculation model was adopted to evaluate the residual tensile strengths of BFRP bars wrapped in geopolymer concrete after high temperature treatment.

Achieving excellent properties of resistance spot welded 2GPa-grade press hardened steel and galvanized DP980 steel via double-pulse

Obtaining the excellent resistance spot welding (RSW) properties of press hardened steel is a challenge due to the high strength with 2GPa-grade. In this study, the microstructure, mechanical properties of the RSW weld in 2GPa-grade PHS and galvanized DP980 steel were investigated. During the single pulse welding, the coarse columnar martensite is generated in the fusion zone (FZ). The low peak load is 13.2 kN for tensile-shear (TS) loading and 3.4 kN for cross-tension (CT) loading and the corresponding failure energy is 6.5 J and 16.7 J, respectively. The fracture mode under two loading conditions is partial thickness-partial pullout (PT-PP) mode. To enhance mechanical properties, the suitable double pulse welding was applied. Compared with that of the single pulse weld, double pulse weld has three special zones in FZ: the Re-melted FZ with columnar martensite, the recrystallization zone (RX-zone) with equiaxed martensite and the tempering zone (T-zone) with tempered columnar martensite. The peak load under the TS and CT loading is significantly improved by 39 pct and 44 pct and the failure energy for TS loading is enhanced by 38 pct and 186 pct for CT loading, respectively. The failure mode changes from the PT-PP mode to the pullout failure (PF) mode for CT loading in double pulse welds.

Research on Meso‐Damage Experiment and Simulation in the Anchorage Bonding Interface Between Rock Bolt and Rock Mass

Anchorage failure occurs mostly at the anchorage interface, and the mechanical mechanism of the anchorage interface is the key point and difficulty in the analysis and research of anchorage. In order to study the mechanics and failure mechanism of the anchorage interface, the shear failure characteristics of the anchorage interface and the deformation rule of the anchored rock under different rib spacings were analyzed through the indoor plane anchorage pull‐out test. Reasonable rib spacing can significantly improve the shear strength of the anchored solid. Finite element software ABAQUS was used to create an axisymmetric plane model of rock bolt pull‐out under different rib conditions to simulate the whole process of rock bolt pull‐out and anchorage interface failure. The results show that during the pull‐out process of anchorage rock mass, stress concentration zones occur at rib corners, and peak shear stress moves to the depths of the anchorage section. As the load increases, cracks emerge from the top of the rib and the edge of the rib angle of the rock bolt and propagate to the deep anchorage along the edge of the costal angle, resulting in damage at the rock mass interface. Load–displacement curves of different transverse rib shapes, heights, widths, and spacings indicate that rib changes affect the anchor‐bearing limit. The anchoring failure mode changes from rib wear and spreading slip, rib shear convex body propagation to interfacial crack propagation, and rib causes varying degrees of damage to the surrounding rock mass. Therefore, reasonable rib parameter improvements can enhance anchoring force performance.

Improvement of Composite Beam with Web Opening Using Posttensioning Tendons under Static and Cyclic Loadings

In practice, the passage of service utilities through web opening causes a significant load‐carrying capacity loss and introduces a change of failure mode of the composite beam. This study aims to improve the load‐carrying capacity and stiffness of open‐web composite beams subjected to static and cyclic loading using posttensioning tendons. To achieve the desired objective, 18 mechanical models have been developed using ABAQUS by considering the shape and location of the web opening, span/depth ratio, and degree of connection as study parameters. The finite element analysis result was validated with experimental results from relevant literature. Results indicate that the external posttensioning tendons increase load‐carrying capacity to 25.05% for rectangular and 20.61% for circular web opening under static loadings. Under cyclic loading, the improvement is 9.24% for rectangular while 2.50% reduction in deflection has been observed for circular web opening. As a span‐to‐depth ratio increased as 11.54, 15.38, and 23.08, the load‐carrying capacity improved by 26.35%, 20.67%, and 8.65%, respectively, for static loadings. Likewise, 2.03%, 1.24%, and 4.95% improvement were observed under cyclic loadings, respectively. Furthermore, compared to one row of 16 mm shear stud provision, the load‐carrying capacity increased by 30.67% for connection in two rows under cyclic loading.

Study on Failure Energy per Unit Area of Concrete Specimens Based on Minimum Energy Dissipation Theory.

In order to study the strength change of concrete specimens under different loading conditions, based on the principle of minimum energy dissipation, the damage energy per unit area of concrete was studied. By using finite element numerical simulation software for concrete specimens with different failure modes of tension, pressure, bending and torsion, a double-broken line damage constitutive model is adopted. The failure forms of concrete specimens under different loading conditions, as well as the failure area and failure energy of each specimen during loading, are simulated and analyzed. The failure energy per unit area under different failure modes was quantitively calculated, the relationship between the failure area and failure energy consumption under different failure modes was analyzed. The results show that, under different failure modes, the failure area of concrete specimens is different, the energy consumed during failure is different, and the strength is different. However, no matter how the failure mode changes during the failure process, the failure energy W per unit area remains constant and fluctuates in the range of 2.0~6.0 mJ/cm2, which is related to the physical properties of concrete itself.

Analysis of wind time-varying performance of reinforced concrete electric pole under Marine atmospheric environment

Bearing capacity calculation model of concrete electric pole considering concrete long-term performance degradation and steel corrosion is established. The horizontal bearing capacity and wind resistance of typical concrete electric pole under Marine atmospheric environment are analyzed with service time. The effects of concrete protective layer thickness, stirrup diameter and strength coefficient on the long-term wind resistance of electric pole are discussed. It is found that with the increase of service time, the shear strength of the concrete pole deteriorates faster than that of the flexural strength, and the failure mode changes from bending failure to shear failure. The wind resistance of the pole after long service can be improved by increasing the thickness of the protective layer, adopting larger diameter stirrup and higher strength coefficient. The bearing capacity calculation model of concrete electric pole considering concrete long-term performance degradation and steel corrosion is established. The horizontal bearing capacity and wind resistance of typical concrete electric pole under Marine atmospheric environment are analyzed with service time. The effects of concrete protective layer thickness, stirrup diameter and strength coefficient on the long-term wind resistance of electric pole are discussed. It is found that with the increase of service time, the shear strength of the concrete pole deteriorates faster than that of the flexural strength, and the failure mode changes from bending failure to shear failure. The wind resistance of the pole after long service can be improved by increasing the thickness of the protective layer, adopting larger diameter stirrup and higher strength coefficient.

Microstructure characteristics and mechanical performances of the dissimilar welded joint of Q&P980 and Q&P1180 steels subjected to the paint-baking heat treatment

The dissimilar welded joints of Q&P980 and Q&P1180 steels with and without paint-baking heat treatment were investigated and their microstructures were characterized using confocal laser scanning microscope (CLSM), electron backscatter diffraction (EBSD), scanning electron microscope (SEM) and transmission electron microscope (TEM) in order to understand the change of mechanical performances of the welded joints. The two Q&P steels have slight differences in compositions, but the obviously varying fraction of tempered martensite and thus the difference in the tensile strength. Prior to paint-baking heat treatment, the dissimilar welds exhibit a lower martensite fraction of the intercritical heat-affected zone (ICHAZ) in the Q&P980 side compared to the Q&P1180 side, and it is not affected by the paint-baking treatment. After the treatment, the occurrence of carbides and the coarsening of martensite in the whole welded joint, as well as the decomposition of retained austenite in the ICHAZ, are observed. The paint-baking treatment also causes the decreasing microhardness values of all regions. Especially, the significantly decreasing microhardness in the fusion zone compared to other heat-affected zones results in a partial pull-out failure mode compared to a full pull-out failure mode without paint-baking treatment. The change in failure mode and the softening of the martensitic matrix are found to be responsible for the increase in the peak load and the energy absorption of the dissimilar welded joint of Q&P980 and Q&P1180 steels.

Quasi-static tensile failure mechanism analysis of CFRP/Al countersunk electromagnetic riveted joints with different rivet-hole clearances

CFRP/Al countersunk riveting can meet the requirements of aircraft aerodynamic shape and lightweight joining. This paper reports an experimental study on the forming mechanism and quasi-static tensile failure of single-lap electromagnetic riveted joints with varying rivet-hole clearances. The aim is to quantitatively evaluate their deformation characteristics and mechanical properties. The failure process and fracture mechanism are revealed through the use of digital image correlation (DIC) and scanning electron microscope (SEM). The results demonstrate that the rivet-hole clearance has a significant impact on the initial damage and mechanical properties of riveted joints. The interference is not uniformly distributed in the Al sheet and the CFRP sheet. Increasing the clearance can delay the occurrence of damage of the laminate under external load. As the clearance increases, the riveted joint failure mode changes from rivet sheared off to manufactured head fracture and rivet pull-off, and the rivet fracture shows a brittle- ductile mixed fracture mode. Additionally, the initial riveting damage of the joint does not determine the final extent of damage to the laminate after failure, and the bearing damage of CFRP laminates increases with the increase in the load-carrying capacity of the joint.

High-temperature mechanical properties and failure modes of UHSS wire for cable-supported bridge

The frequency of fire accidents in cable-supported bridges is increasing, but the ultra-high strength steel (UHSS) wire for cable-supported bridges lacks a unified expression of the degradation law of its high-temperature mechanical properties. Therefore, for the emerging 1960 and 2060 MPa UHSS wires, a series of steady-state tests are carried out in this study. The stress-strain response, elastic modulus, yield strength, ultimate strength, ultimate strain, and failure strain of the UHSS wires in the temperature range of 20–900 °C are obtained, as well as the failure parameters such as elongation and shrinkage after rupture. Based on the test data, a calculation model suitable for the prediction of the degradation law of high-temperature mechanical indicators of 1670‐–2060 MPa UHSS wire is established. Experimental investigations show that the stress-strain development process of UHSS wire at elevated temperature can be described by a three-stage model. Due to differences in chemical composition and manufacturing process, there are significant differences in the degradation patterns of mechanical indicators of different steel materials at elevated temperatures. The failure mode of the steel wire is brittle failure when the temperature does not exceed 200 °C, but the failure mode changes from brittle failure to plastic failure when the temperature exceeds 200 °C. Compared with the existing experimental results, it is obvious that the high-temperature mechanical indicator degradation model of high-strength steel wires proposed in this study can be used as input data for computer models to evaluate the fire resistance of cable members of cable-supported bridges.

Potential change of failure modes and time-dependent behavior of RC beams under a marine atmospheric environment

Stirrups always corrode earlier than the longitudinal steel bars in RC beams, and the corrosion degree is higher. Stirrups will lose their bearing capacity due to corrosion, leading to a decrease in shear strength. Thus, the failure mode may change from bending to shear failure. Previous studies have proposed models to predict corroded RC beams' flexural and shear behavior, respectively. The missing link in these models was the absence of the change of failure modes on the structural behavior. This paper covers the authors' study of corroded RC beams, investigating the effects of reinforcement corrosion on the transformation of failure modes. A numerical simulation was performed to analyze RC beams' time-dependent behavior and failure modes. The effects of the concrete cover thickness, the corrosion initiation time, the concrete strength, and the reinforcement configuration were also investigated. The analysis showed that the stirrups corroded earlier than longitudinal steel bars, leading to potential shear failure rather than bending failure. The larger diameter of stirrups could be adopted in the design to delay the deterioration of structural behavior and the transformation of failure mode. Prolonging the corrosion initiation time using thicker concrete cover thickness and higher strength of concrete is also effective.