High-strength structural steel and ultra-high-performance concrete (UHPC) are being researched in many countries to expand their potential for wider application in civil engineering. This study ...investigated the shear performance of stud connectors in high-strength steel (fy = 690 MPa)-UHPC composite beams. A total of 6 pushout specimens, classified into three groups, were tested under static load. The test parameters included the diameter (13 mm/19 mm) and layout of the studs (single-stud/grouped-stud). The grouped-stud specimens were studied for assembly construction in composite beams. Based on the experimental results, empirical formulae for the load–slip curve of single-stud and grouped-stud specimens were proposed. Experimental results indicated that the failure mode of all the high-strength steel-UHPC pushout specimens was stud shank failure. The diameter of the studs significantly affected their shear performance. The shear capacity and shear stiffness of studs with a 19 mm diameter were 82.4% and 46.0% greater than those of studs with a 13 mm diameter, respectively. The layout of the studs had little effect on their shear capacity, with a 2.7% difference in shear capacity between single-stud and grouped-stud specimens on average. However, the stud arrangement had a great effect on the shear stiffness per stud. When the studs were arranged in a group, the shear stiffness per stud was 19.6% lower than the single-stud specimen on average because of the group effect. Although the grouped-stud specimens take advantage of assembly construction, the shear stiffness per stud decreased in the grouped-stud specimens. It was found that high-strength steel has little effect on the shear performance of studs compared with normal steel in pushout specimens. However, UHPC significantly improves the shear capacity and shear stiffness compared with normal concrete, but the ductility become relatively poor because of the higher elastic modulus of UHPC. In this paper, a formula for calculating the shear stiffness of grouped-stud specimens is also proposed based on the energy equivalent model. The main reason for the group effect is thought to be the ineffectiveness of concrete between studs in shear resisting owing to the short distance of studs. Thus, the shear stiffness per stud decreased in the grouped-stud specimens.
•The hydrogen influence was studied by using the linearly increasing stress test.•The decrease in yield strength was attributed to solid solution softening by hydrogen.•Hydrogen assisted fracture ...occurred after the onset of necking and competed with ductile fracture.•There was no hydrogen assistant sub-critical crack growth at stresses below the ultimate tensile strength.
This paper studied the influence of hydrogen on some dual-phase (DP), quenching and partitioning (Q&P), and twinning-induced plasticity (TWIP) advanced high-strength steels (AHSS). All steels exhibited hydrogen sensitivity, manifested by (i) decreased yield strength (by a maximum of 13%) attributed to solid-solution softening by hydrogen, and (ii) reduced ductility (maximum decrease of reduction of area was from 65% to 9%), caused by hydrogen assisted fracture processes after the onset of necking. There was no sub-critical crack growth below the ultimate tensile strength. The hydrogen influence increased with increasing strength, more negative charging potential, and decreasing stress rate.
•The influence of hydrogen on MS1700 was investigated using the linearly increasing stress test (LIST).•MS1700 exhibited some hydrogen embrittlement (HE) at high hydrogen fugacities.•There was ...minimal hydrogen sensitivity in 3.5 wt% NaCl at the open circuit and zinc potentials.•The hydrogen influence was manifested in the reduction of ductility and the occurrence of shear fracture.•The thermal treatment associated with paint baking enhanced HE susceptibility.
The influence of hydrogen on a 1700 MPa martensitic advanced high-strength steel was investigated and compared with similar steels. MS1700 exhibited some hydrogen embrittlement for cathodic hydrogen charging in 0.1 M NaOH and 0.1 M HCl, but minimal hydrogen sensitivity for hydrogen charging in 3.5 wt% NaCl at the open circuit and zinc potentials. The hydrogen influence was manifested as a reduction of ductility and the occurrence of shear fracture. The heat treatment associated with paint baking increased the hydrogen embrittlement susceptibility. The higher hydrogen sensitivity of MS1700 was attributed to enhanced hydrogen trapping due to the higher carbon and martensite content.
Passivity breakdown and the pitting behavior of ultra-high strength 300 M and S280 steels, which are commonly employed for aircraft landing gear, in the presence of chloride has been explored and ...compared, and the data were interpreted using the point defect model (PDM). The breakdown behavior was studied using cyclic potentiodynamic polarization while SEM and digital confocal microscopy were employed to explore the micro morphology and depth distribution of pits. The cumulative distributions in the breakdown voltage are near-normal, which are consistent with the PDM, assuming the distributions of potential breakdown sites in terms of the cation vacancy diffusivity for different concentrations of chloride are normal. Compared to 300 M, S280 steel exhibits shallower pitting and is more resistant to breakdown. From the potential scan rate dependence of the breakdown potential, the critical areal cation vacancy concentration, ?, resulting in passivity breakdown, is 8.6 ... 10 13 No.cm -2 for 300 M and 2.4 ... 10 13 No.cm -2 for S280. These values are structurally in close agreement with the calculated results, considering the vacancy condensation is either on the cation sublattice of the barrier layer or on the steels lattice.
•Material responses and compression capacities of press-braked S690 angle and channel section stub columns were studied.•Thirty-six tensile flat and corner coupon tests on press-braked S690 angle and ...channel sections were conducted.•A total of twenty-four press-braked S690 angle and channel section stub columns were tested.•Numerical models were developed and validated against test results, and then used to perform parametric studies.•Current design codes and direct strength method were assessed against test and numerical results.
This paper reports an experimental and numerical investigation into the cross-section behaviour and compression resistances of press-braked S690 high strength steel angle and channel section stub columns. The experimental study was carried out on four equal-leg angle sections and eight plain channel sections with a range of cross-section sizes (covering both non-slender and slender sections), and included thirty-six material tensile flat and corner coupon tests, initial local geometric imperfection measurements and twenty-four concentrically loaded stub column tests. The experimental study was then supplemented by a numerical modelling programme, where numerical models were firstly developed to simulate the test structural responses and subsequently adopted to derive further numerical data. The experimentally and numerically derived results were utilised to assess the applicability of the Eurocode Class 3 slenderness limits for hot-rolled and welded sections to their cold-formed (press-braked) counterparts. The results of the assessment generally revealed that the Eurocode Class 3 slenderness limits for hot-rolled and welded sections can be safely adopted for the classification of press-braked (cold-formed) S690 high strength steel angle and channel sections subjected to compression. The accuracy of the codified design provisions established in Europe, North America and Australia/New Zealand as well as the direct strength method (DSM) to the design of press-braked S690 high strength steel angle and channel section stub columns was also assessed, based on the test data and numerical results. The North American, Australian and New Zealand standards were found to result in accurate and consistent compression capacity predictions for press-braked S690 high strength steel channel section and non-slender angle section stub columns, but greatly underestimate the compression capacities for those slender angle section stub columns, while the European code and DSM were shown to yield overall precise and consistent design compression capacities.
•Bond tests were conducted between high/ultra-high strength steel and ultra-high modulus CFRP laminates.•Both single-sided and double-sided schemes were adopted.•Numerical simulation was performed on ...bond behaviour.•A theoretical bond model was developed to estimate the bond strength.
With the increasing applications of high and ultra-high strength steel (HSS/UHSS) in engineering structures, there is a need to address rehabilitation and strengthening of such steel grades using carbon fibre reinforced polymer (CFRP). The bond between HSS/UHSS and CFRP is vital to ensure the efficiency of the strengthening. The existing bond study was focused on mild steel as substrate, with very limited work on HSS up to the grade of S690. Since HSS/UHSSs are designed to undergo much higher loading in service, much higher shear stress is expected in the adhesive layer, leading to a higher chance of premature debonding. In this paper, the bond between HSS/UHSS plates and ultra-high modulus (UHM) CFRP laminates under static tensile loading is studied experimentally, numerically and theoretically. Both single-sided and double-sided schemes were adopted. The numerical simulation using LS-DYNA software package was implemented and a reasonable agreement with the experimental results is found. A theoretical bond model was developed to relate the bond strength to the imposed strain in the steel member outside the bonded region.
The role of microstructure was studied for dual-phase (DP), quenched and partitioned (Q&P), and twinning induced plasticity (TWIP) steels. The hydrogen influence changed the fracture mode at the ...ultimate tensile strength, there being no subcritical crack growth at a lower stress. The fractures initiated (i) in the hard martensite and/or at the interfaces of ferrite and martensite for DP steels, (ii) in the martensite and/or at the interfaces of retained austenite and martensite for Q&P steels, and (iii) at mechanical twins for TWIP steels. Tempering may improve the resistance to hydrogen of DP and Q&P steels.
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•The state-of-art of lightweight materials for automobiles is reviewed.•Representative materials are introduced with potential automotive applications, particularly on electric ...vehicles.•Given the recent advances in manufacturing, modeling, and characterization, both pros and cons of materials are summarized.•Solutions for future challenges are highlighted by developing advanced materials and/or improving the manufacturing.
The growing challenges on fuel economy improvement and greenhouse gas emission control have become the driving force for automakers to produce lightweight automobiles. Also, the weight reduction may contribute to superior recyclability and/or vehicle performance (e.g., improved driving economy, braking behaviors, and crashworthiness). One effective strategy is to develop and implement lightweight yet high-performance materials as alternative solutions for conventional automotive materials such as cast iron and steel. Herein, a systematic review of available lightweight materials to produce next-generation automobiles is provided, including light alloys, high-strength steels, composites, and advanced materials in the ongoing research. By investigating the entire life cycle of automotive materials, physical/mechanical properties, characterization, manufacturing techniques, and potential applications of specific lightweight materials are discussed. Both the advantages and drawbacks of the reviewed materials are summarized, yielding the appropriate application scenarios for different lightweight materials. Given the future challenges, on expectations, the development of versatile advanced materials or improvement of the manufacturing/treatment techniques can be rather promising to resolve the possible bottlenecks and, in turn, enables more capable, safer, durable, and environmental-friendly vehicles.
In this work, the hydrogen permeation behavior and sulfide corrosion cracking susceptibility of ultrafine grain high strength steel were studied under different concentrations of H2S and pH. The ...critical sulfide stress cracking factor (KISSC) displays an exponential decrease with trapped hydrogen concentration in the steel. High content of retained austenite and dislocations contribute to high trap density of atomic hydrogen within the ultrafine grain high strength steel. Austenite absorbed more hydrogen as potential cracking sites while bainite with large grain size helps to maintain sulfide corrosion cracking resistance.
•Hydrogen permeation current increases with increasing H2S concentration and decreasing pH.•High fraction of austenite makes nanostructured steel absorb more hydrogen.•An exponential relationship between KISSC and C0 was obtained.•The higher the absorbed hydrogen concentration, the lower KISSC.
A review on hot stamping Karbasian, H.; Tekkaya, A.E.
Journal of materials processing technology,
11/2010, Letnik:
210, Številka:
15
Journal Article
Recenzirano
The production of high strength steel components with desired properties by hot stamping (also called press hardening) requires a profound knowledge and control of the forming procedures. In this ...way, the final part properties become predictable and adjustable on the basis of the different process parameters and their interaction. In addition to parameters of conventional cold forming, thermal and microstructural parameters complicate the description of mechanical phenomena during hot stamping, which are essential for the explanation of all physical phenomena of this forming method.
In this article, the state of the art in the thermal, mechanical, microstructural, and technological fields of hot stamping are reviewed. The investigations of all process sequences, from heating of the blank to hot stamping and subsequent further processes, are described. The survey of existing works has revealed several gaps in the fields of forming-dependent phase transformation, continuous flow behavior during the whole process, correlation between mechanical and geometrical part properties, and industrial application of some advanced processes. The review aims at providing an insight into the forming procedure backgrounds and shows the great potential for further investigations and innovation in the field of hot sheet metal forming.
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