High Strength Steel Research Articles

Tensile behaviour of a novel grouted sleeve splice for high-strength rebars

This study introduces a novel type of grouted sleeve fabricated from a standard low-alloy seamless steel pipe using cold-rolling techniques. The main goal is to achieve an effective connection between the high-strength steel (HSS) reinforcements in the joints of precast concrete structures. To investigate the structural performance of the developed splice under uniaxial tensile loading, 24 coupler specimens configured with 28 mm diameter HRB600 reinforcements were prepared. Two primary parameters, namely the embedded length of the spliced bar and number of inner concentric ribs rolled on the sleeve, were considered. By conducting direct pullout tests, the performance of the developed splices was thoroughly assessed based on the failure mode, bond stiffness, bond ductility, and strength. The test results demonstrated that increasing the bar embedded length and number of inner ribs enhances the initial bond stiffness and ductility of the splice. Increasing the quantity of inner ribs only in the inelastic region of the splice is effective for improving its tensile capacity. For grout splices with large-diameter HSS bars, an embedded length of 8db is recommended to guarantee bar fracture failure and satisfy the specification requirements. This length exceeds that of splices with normal-strength reinforcements. Finally, a formula was proposed to estimate the inelastic region length and tensile strength of the proposed splice.

Strain partitioning characterization of advanced high strength steels using in-situ tensile tests with Micro digital image correlation – Methodology and analysis

This research investigates experimental methods used to extract and quantify meso-scale strain partitioning of five different advanced high strength steels (AHSS), using in-situ uniaxial tensile testing within a SEM. A slightly notched uniaxial tensile specimen was developed to ensure that localisation (necking) occurred in the middle of the specimen where SEM images of the deformed microstructures were captured. Micro digital image correlation (μDIC) was conducted using the etched microstructure up to high nominal strain of ~0.5 within the neck. The effect of step size, subset size and SEM magnification were investigated to produce the highest resolution strain distribution contours. The strain distribution throughout the microstructure was extracted from 10,000× magnification micrographs and a method was developed to quantify the average strain partitioning for every level of nominal strain imposed during the tensile test. The high strength differential between ferrite and martensite grains within two dual-phase steels (DP800, DP980GI), resulted in a high level of average strain partitioning that increased linearly with respect to the applied nominal strain. The three-phase (martensite-bainite-ferrite) CP980 steel had a similar (to DP) level of strain partitioning at low nominal strains, but as deformation within the neck increased, the rate of strain partitioning decreased due to the presence of the moderate strength bainite grains. Single-phase MS1500 (martensite) and TWIP (retained austenite) exhibited low average strain partitioning levels due the single-phase and large grain size microstructures of these materials. The average strain partitioning ratio was shown to be ~1 for the dual-phase steels, and reduced to 0.45 for the highest ductility TWIP material.

Fatigue assessment for tower bolts of floating offshore wind turbine considering preload loss due to ambient temperature creep

A framework for fatigue assessment for tower bolts of floating offshore wind turbine (FOWT) taking into account the impact of preload loss due to ambient temperature creep and plastic deformation is proposed. The ambient temperature creep of high strength steel is modeled in terms of Norton’s theory. The residual preload of tower bolt is predicted by a detailed finite element (FE) model of the threaded bolt connection. Subsequently, the residual preload is applied to the FE model of the entire tower segment to achieve the stress range of the bolts. Fatigue life prediction is finally conducted using the Palmgren-Miner’s (PM) rule based on S-N curves, with corrections by effects of mean stress and bolt sizes. A fatigue assessment for tower bolts of a 5MW FOWT is then performed to demonstrate the capability of the proposed framework. Moreover, impact of initial preload, thread friction coefficients and flange gap on preload loss and fatigue life of tower bolts are discussed.

A study of hydrogen trapping behaviors in Nb and V carbides in α-Fe matrix by first-principles calculations

The introduction of nanosized carbides (NbC, TiC, VC, etc.) into a matrix is one of the most efficient approaches for improving the hydrogen embrittlement resistance of traditional high strength steels. In the present work, first-principles calculations were used to investigate the characteristics of hydrogen trapping at NbC/bcc-Fe and VC/bcc-Fe interfaces. Hydrogen atoms prefer to occupy the tri2-site in bulk NbC and VC lattices and perfect NbC and VC lattices cannot trap H atoms. H atoms can segregate at perfect NbC/Fe and VC/Fe interfaces, in which the solution energies of the H atoms at the NbC/Fe interfaces are lower. The carbon vacancies at the carbide/Fe interfaces can act as relatively deep hydrogen traps but are unfavorable for formation owing to their high formation energies. Other interstitial sites at interfaces containing carbon vacancies can trap H atoms more strongly than perfect interfaces. Compared with the NbC/Fe interface, it is more probable for H atoms to be trapped by high-density vacancies in the interior of VC carbides once H atoms obtain sufficient energy under certain conditions, eg. at high temperatures.

Numerical simulation of molten pool flow behavior in ultrasonic vibration-assisted gas tungsten arc welding of low-alloy high-strength steel

The beneficial effects of ultrasonic vibration-assisted arc welding on the performance of welded joints have been experimentally confirmed. However, the mechanism of the influence of ultrasonic vibration on the temperature and flow fields of the welding pool is still not clear, which also limits further application prospects of this technology. The present study established a three-dimensional molten pool model for ultrasonic vibration-assisted gas tungsten arc (UV-GTA) welding of low-alloy high-strength steel, considering free deformation of the molten pool surface and different ultrasonic vibration amplitudes. The temperature field evolution and the molten pool flow behavior under various ultrasonic vibration amplitudes were systematically analyzed. Compared with GTA welding, the ultrasonic vibration in UV-GTA welding enhanced uniformity of the temperature distribution in molten pool. Moreover, the larger the ultrasonic amplitude in UV-GTA welding, the smaller the depth of the molten pool and the time required for the molten pool to reach a quasi-steady state, but the larger the maximum flow rate at the surface as well as at the center of the molten pool. At an ultrasonic vibration amplitude of 40 μm, the molten pool depth in UV-GTA welding decreased by 34.8% compared with GTA molten pool depth. The time for this UV-GTA molten pool to reach a quasi-steady state was just 0.57s, and the maximum velocity at its center increased by 88.1% over that of the GTA molten pool. Comparative analysis of the UV-GTA molten pool and the GTA molten pool revealed a shorter circulating flow field on the upper surface and periodic variations in the internal flow field motion. The simulation outcomes closely align with the experimental findings, confirming both the validity of the model and the accuracy of the pertinent conclusions. This research may lay a solid theoretical foundation for further systematic exploration of the wider application prospects of ultrasonic vibration-assisted arc welding.

Fracture behavior of corroded high-strength steel butt weld joints based on a modified ductile-to-brittle transition CAFE model

Fracture behavior of corroded high-strength steel butt weld joints based on a modified ductile-to-brittle transition CAFE model

Carbon fiber reinforced polymer (CFRP) laminates: flexural strengthening method for prestressed concrete beams with anchorage loss

Abstract Post-tensioning (PT), a method of pre-stressing, involves the use of high-strength steel strands/ tendons to reinforce concrete or other materials. On the contrary, Carbon Fiber-Reinforced Polymers (CFRP) are lightweight, high-strength materials with used to strengthen concrete structures by adhering the polymer to the concrete element. Challenges with post-tensioned elements include reverse curvature of the post-tensioning strands, tendon misplacement, and frequent damage in the anchorage and dead-end zones. These difficulties frequently cause bulging of the surrounding concrete, even at lower stress levels, and can lead to concrete bursting when tension exceeds certain threshold. This study investigates into the potential of CFRP strengthening technique to improve the flexural capacity of post-tensioned concrete beams with anchorage loss. Through an experimental program, the study compares the performance of control beams to those reinforced with different layers of CFRP. The results of this study demonstrated that there was a significant increase in flexural capacity, ranging from 45.31% to 78.62% for single layers and 87.17% to 153% for double layers of CFRP sheet. Additionally, the research examines how different levels of prestressing and CFRP wraps influence crack formation and delamination patterns of carbon fiber, with promising results. It was also noted that optimal usage of CFRP fibers and tendons is found to be critical. The study suggests exploring alternative fiber types and orientations for future study.

Numerical Simulation of Fatigue Crack Growth and Fracture in Welded Joints Using XFEM—A Review of Case Studies

Numerical simulation of fatigue crack growth in welded joints is not well represented in the literature, especially from the point of view of material heterogeneity in a welded joint. Thus, several case studies are presented here, including some focusing on fracture, presented by two case studies of mismatched high-strength low-alloyed (HSLA) steel welded joints, with cracks in the heat affected zone (HAZ) or in weld metal (WM). For fatigue crack growth, the extended finite element method FEM (XFEM) was used, built in ABAQUS and ANSYS R19.2, as presented by four case studies, two of them without modelling different properties of the welded joint (WJ). In the first one, fatigue crack growth (FCG) in integral (welded) wing spar was simulated by XFEM to show that its path is partly along welded joints and provides a significantly longer fatigue life than riveted spars of the same geometry. In the second one, an integral skin-stringer panel, produced by means of laser beam welding (LBW), was analysed by XFEM in its usual form with stringers and additional welded clips. It was shown that the effect of the welded joint is not significant. In the remaining two papers, different zones in welded joints (base metal—BM, WM, and HAZ) were represented by different coefficients of the Paris law to simulate different resistances to FCG in the two cases; one welded joint was made of high-strength low-alloyed steel (P460NL1) and the other one of armour steel (Protac 500). Since neither ABAQUS nor ANSYS provide an option for defining different fatigue properties in different zones of the WJ, an innovative procedure was introduced and applied to simulate fatigue crack growth through different zones of the WJ and evaluate fatigue life more precisely than if the WJ is treated as a homogeneous material.

Experimental Investigation on Bending Properties of DP780 Dual-Phase Steel Strengthened by Hybrid Polymer Composite with Aramid and Carbon Fibers

Lowering passenger vehicle weight is a major contributor to improving fuel consumption and reducing greenhouse gas emissions. One fundamental method to achieving lighter cars is to replace heavy materials with lighter ones while still ensuring the required strength, durability, and ride comfort. Currently, there is increasing interest in hybrid structures obtained through adhesive bonding of high-performance fiber-reinforced polymers (FRPs) to high-strength steel sheets. The high weight reduction potential of steel/FRP hybrid structures is obtained by the thickness reduction of the steel sheet with the use of a lightweight FRP. The result is a lighter structure, but it is challenging to retain the stiffness and load-carrying capacity of an unreduced-thickness steel sheet. This work investigates the bending properties of a non-reinforced DP780 steel sheet that has a thickness of 1.45 mm (S1.45) and a hybrid structure (S1.15/ACFRP), and its mechanical properties are examined. The proposed hybrid structure is composed of a DP780 steel sheet with a thickness of 1.15 mm (S1.15) and a hybrid composite (ACFRP) made from two plies of woven hybrid fabric of aramid and carbon fibers and an epoxy resin matrix. The hybridization effect of S1.15 with ACFRP is investigated, and the results are compared with those available in the literature. S1.15/ACFRP is only 5.71% heavier than S1.15, but its bending properties, including bending stiffness, maximum bending load capacity, and absorbed energy, are higher by 29.7, 49.8, and 41.2%, respectively. The results show that debonding at the interface between S1.15 and ACFRP is the primary mode of fracture in S1.15/ACFRP. Importantly, S1.15 is permanently deformed because it reaches its peak plastic strain. It is found that the reinforcement layers of ACFRP remain undamaged during the entire loading process. In the case of S1.45, typical ductile behavior and a two-stage bending response are observed. S1.15/ACFRP and S1.45 are also compared in terms of their weight and bending properties. It is observed that S1.15/ACFRP is 16.47% lighter than S1.45. However, the bending stiffness, maximum bending load capacity, and absorbed energy of S1.15/ACFRP remain 34.4, 11.5, and 21.1% lower compared to S1.45, respectively. Therefore, several modifications to the hybrid structure are suggested to improve its mechanical properties. The results of this study provide valuable conclusions and useful data to continue further research on the application of S1.15/ACFRP in the design of lightweight and durable thin-walled structures.

Hydrogen Embrittlement of Galvanized Press-Hardened Steels: A Review

Press-hardened steels (PHS), as an alternative to traditional steels and aluminum alloys, combine great mechanical performance with low manufacturing costs. PHS are martensitic steels with ultimate tensile strength (UTS) up to 2000 MPa. These steels are commonly coated with zinc-based coatings (PHS GI) consisting of multiple Zn–Fe phases to enhance corrosion resistance. However, similar to all high-strength steels, PHS are known for their elevated susceptibility to hydrogen embrittlement (HE). Absorption of atomic hydrogen into the steel lattice can lead to a transition from a ductile to a brittle fracture mechanism and decrease the stress necessary for fracture initiation. This review examines the microstructure of PHS GI with a focus on how the manufacturing process influences key parameters of the coating. The material’s susceptibility to HE is discussed in the following sections, along with the potential for hydrogen introduction through corrosion in atmospheric environments. The relationship between the content of hydrogen and its effects on fracture behavior is discussed, along with the corrosion behavior of PHS GI. The potential areas for future research and development of PHS GI with increased HE resistance are proposed.

Effect of Cerium Content on Non–Metallic Inclusions and Solidification Microstructure in 55SiCr Spring Steel

The effect of cerium content (0, 0.011, 0.017, 0.075 wt%) on non-metallic inclusions and solidification microstructures of 55SiCr high-strength spring steel was experimentally studied, along with thermodynamic calculations. The results show that Ce addition changes the type and size of inclusions in this steel and influences the characteristics of the solidification microstructure. In the sample without Ce addition, the main inclusions are MnS, SiO2, SiO2–MnS, and CaO–SiO2–MgO, and the equiaxed ratio in the solidification structure is 44.63%. However, when Ce content increases to 0.011 wt%, the inclusions in the steel become mainly Ce–S, Ce–O–S, and a small amount of MnS, and the equiaxed ratio increases to 50.42%. As the Ce content increases to 0.017 wt%, the inclusions are predominantly Ce–S, Ce–O–S, and Ce–O–S–Ca, while some Ce–P and Ce–O–P–C inclusions are also observed. The equiaxed ratio increases to 67.63%, showing the best effect on heterogeneous nucleation during solidification. When Ce content in the steel reaches 0.075 wt%, the Ce-containing inclusions are Ce–S, Ce–O, Ce–P, Ce–P–O, and Ce–O–S–As, and the size becomes larger. The formation mechanism of inclusions is explained by Gibbs free energy calculations and thermodynamic diagrams.

Optimisation of Flexible Forming Processes Using Multilayer Perceptron Artificial Neural Networks and Genetic Algorithms: A Generalised Approach for Advanced High-Strength Steels

Flexibility is crucial in forming processes as it allows the production of different product shapes without changing equipment or tooling. Single-point incremental forming (SPIF) provides this flexibility, but often results in excessive sheet metal thinning. To solve this problem, a pre-forming phase can be introduced to ensure a more uniform thickness distribution. This study represents advances in this field by developing a generalised approach that uses a multilayer perceptron artificial neural network (MLP ANN) to predict thinning results from the input parameters and employs a genetic algorithm (GA) to optimise these parameters. This study specifically addresses advanced high-strength steels (AHSSs) and provides insights into their formability and the optimisation of the forming process. The results demonstrate the effectiveness of the proposed method in minimising sheet metal thinning and represent a significant advance in flexible forming technologies applicable to a wide range of materials and industrial applications.

Estimation of the axial capacity of high-strength concrete-filled steel tube columns using artificial neural network, random forest, and extreme gradient boosting approaches

Estimation of the axial capacity of high-strength concrete-filled steel tube columns using artificial neural network, random forest, and extreme gradient boosting approaches

An accelerated corrosion-fatigue testing method for marine high-strength steel based on equivalence principle of fatigue crack growth

The corrosion-fatigue test is widely used to assess marine equipment. However, due to the low-frequency and high-cycle loading of marine equipment in service, conventional test methods require long cycle times and high costs. This makes it challenging to meet the rapid evaluation demands associated with equipment development effectively. In this study, an accelerated corrosion test method was proposed for steel by adjusting the composition, temperature, pH and H2O2 concentration of environment. Fatigue crack growth tests were conducted under various corrosion environments and load frequencies. The matching relationships between corrosion fatigue acceleration multiplier, corrosion environment parameters and load parameters were established. Additionally, a corrosion fatigue acceleration test method was proposed based on the equivalent principle of fatigue crack growth. The results show that effective coupling between corrosion and fatigue can be achieved by gradually reducing the load frequency as the stress intensity factor amplitude increases throughout the crack growth process. It is consistent with the trend of fatigue crack growth rate in the seawater environment. The 4.85% fatigue life deviation and the 15.68 times corrosion fatigue acceleration can be achieved by our method. This work improves the accuracy and reliability of fatigue performance evaluation for offshore equipment.

Computer simulation of the truck cabin tests to find ways to meet the requirements of the UNECE Regulation 29

BACKGROUND: Ensuring the required level of passive safety of trucks is a relevant task. To solve this problem, it is necessary to use computer simulation methods. AIM: Search for the ways to ensure the passive safety of trucks by choosing the appropriate cabin design. MATERIALS AND METHODS: During the study, the method of virtual simulation of the truck cabin tests was used in accordance with the requirements of the UNECE Regulation 29. RESULTS: A simulation model of a truck cabin has been developed, which makes it possible to conduct the computer simulation of the tests according to the UNECE Regulation 29. The main requirement of the UNECE Regulation 29 is retaining sufficient space in the cabin to accommodate the driver’s dummy inside it after its testing. As a part of the study, the properties of the material (steel) used for manufacturing of prototype cabins of the truck under development were determined, and the tested specimens were obtained by dissecting the prototype of the cabin, so the obtained results take into account the technological history of the material. The obtained data on the properties of the materials were used in the development of the simulation model of the cabin. The developed and used simulation model takes into account all the design features of the cabin under study, including the location and properties of welding points. Various options of cabin design changes and their impact on the ability to meet the requirements of the UNECE Regulations 29 are investigated. It has been found that it is not possible to fully comply with the requirements of the UNECE Regulation 29 only by increasing (within reasonable limits) the thickness of individual elements of the cabin frame and/or using high-strength steel for their manufacturing. Based on the analysis of the deformation of the prototype cabin frame during the Test C according to the UNECE Regulation 29 Revision 2, proposals for changes to the cabin design to meet the requirement of the UNECE Regulation 29 are formulated. CONCLUSION: The results of the study indicate the prospects of the proposed changes to the cabin design.

Exploring Through-Thickness Residual Stress Distribution in Double V-Groove Multipass Welds of High-Strength Low-Alloy Steel and the Impact of Mechanical Restraints

Exploring Through-Thickness Residual Stress Distribution in Double V-Groove Multipass Welds of High-Strength Low-Alloy Steel and the Impact of Mechanical Restraints

Dynamic Deep Learning to Predict Mechanical Properties of High-Strength Low-Alloy Steels

Dynamic Deep Learning to Predict Mechanical Properties of High-Strength Low-Alloy Steels

Effect of Interlayer Temperature on Microstructure and Properties of High-Strength Low-Alloy Steel Manufactured Using Submerged-Arc Additive Manufacturing (SAAM).

Controlled interlayer temperature has a profound impact on both the microstructure and mechanical properties of the deposited components. In this study, thin-walled structures made of high-strength low-alloy steel were fabricated using the submerged-arc additive manufacturing process. The effects of varying temperature on the microstructure and mechanical properties of the components were studied. The results showed that the cooling rate within T8/5 decreased as the interlayer temperature increased, which caused the microstructure to transition from a fine-grained structure dominated by bainitic ferrite and granular bainite to a coarse-grained structure dominated by polygonal ferrite. The measurement of mechanical properties showed that due to the influence of the fine-grained structure, the components with low interlayer temperatures exhibit excellent hardness, high strength, and outstanding ductility and toughness. Furthermore, a faster cooling rate disrupts the stability of carbon diffusion, resulting in the development of increased quantities of residual austenitic films within the components with controlled low interlayer temperatures. This augmentation in residual austenite films strengthens the components' ductility and toughness, enabling the deposited components to exhibit exceptional impact toughness in low-temperature environments.

Modeling and analysis of creep at elevated temperature analysis on thin-walled profile structures

Abstract High-strength steel plays a crucial role in aerospace because of its excellent performance. The high temperatures experienced during a spacecraft’s re-entry to Earth may result in creep in the steel, potentially leading to structural failure, so the finite element software is utilized in this paper to establish a calculation model and analyze the impact of temperature and fire duration on the creep strain of high-strength I-section steel beams under elevated temperatures. Among them, the high-temperature parameter significantly affects the creep strain variation of the mid-span element of the high-strength I-section steel beam. When the temperature parameter is increased by 100%, the maximum creep strain variation of the mid-span component of the beam will increase by about 24%. Under the exact increase, the maximum creep strain variation of the high-temperature duration parameter will only increase by about 3.78%; thus, when conducting a high-strength steel structure, fire resistance analysis should mainly consider the influence of temperature on its creep at elevated temperature strain.

Stub column behaviour of high strength steel square hollow sections with semi-circular stiffeners

This paper proposes a novel high strength steel square hollow section with semi-circular stiffeners, aiming to delay or eliminate premature local buckling failure of the steel tube and lead to improved compressive performance. A total of 9 stiffened and unstiffened stub columns were tested to investigate the failure modes and compressive responses. The test results showed that the stiffened sections achieved significantly higher compressive strength with delayed local buckling failure compared to the unstiffened counterparts. Tensile coupons were extracted from flat, corner and curve portions of the steel tubes in order to determine the corresponding material properties. Finite element (FE) models were established to numerically simulate the tested stub columns, in which both failure modes and load-end shortening curves could well replicate the test results. Parametric studies were then implemented using the validated FE model to extend the dataset. The obtained test and numerical results were used to assess the applicability of existing design standards and methods. It was found that EC3, ANSI/AISC 360-22, AS 4100 and Direct Strength Method (DSM) could be safely adopted in cross-section classifications and cross-section capacity predictions.