High-strength Metal Research Articles

Influence of alloying elements on the mechanical properties of high-strength weld metal

ABSTRACTHigh-strength lightweight constructions are a crucial part of transportation systems and steel constructions optimised for low energy consumption. In this investigation, the aim is to understand the influence of different alloying elements on the mechanical properties of all-weld metal samples of high-strength filler metals. Metal-cored wires with adjusted chemistry were produced and the measured yield strength is compared with calculated values which were obtained by thermodynamic and kinetic simulations. By increasing the content of the matrix alloying elements, no increase in strength could be achieved, but compared to that, higher strength was obtained by the addition of Ti, Nb and Al in combination. Furthermore, the influence of different Ti, Al and N contents is presented and discussed.

Bending Reinforcement of Full-Scale Timber Beams with Mechanically Attached GFRP Composite Plates

This paper presents the results of an experimental campaign aimed to evaluate the performance of timber beams strengthened in bending using GFRP (Glass Fiber Reinforced Polymer) plates mechanically attached with high-strength metal screws. Modest ratios of GFRP composite reinforcement can increase beam load-carrying capacity and manipulate failure mode from the brittle tensile in the unreinforced beams to a more extensible failure in the strengthened timber beams. Application of mechanical reinforcement presents a solution of reversibility, compatibility and durability for reinforced timber. The experimental campaign focused on load-deflection relationship and failure modes in order to increase the bending capacity and stiffness of the timber beam. Oak beams with dimensions 145 x 145 x 2450 mm were reinforced with un-bonded pultruded GFRP plates. Hexagon head coach screws 16 mm diameter, 130 mm length, grade 8.8, were used to mechanically attach the reinforcement along with 34 mm outer diameter fender washers, distributing the fastening load away from the screw’s position. All beams were tested until failure under the four-point bending configuration. Experimental results demonstrate the effectiveness of the reinforcement method and ability to reversibly repair the timber, representing a capability to be utilised in the new constructions or restoration of timber structures.

A REVIEW OF THEORECTICAL CONCEPTS OF HYDROGEN CRACKING IN METALS AND ALLOYS

Today the demand for high-strength metal materials to be used in critical structural elements and facilities that operate under variable temperature and stress conditions is steadily growing economic and engineering tendency. However increased strength features of a metal are opposed by its reduced plasticity so the metal often becomes unfit for large plastic straining. In this case solid body brittle failure starts and this process is quite often of random character, which may result in big financial loss and human injuries. Available literature contains little information on delayed failure issues in principle, however, many research findings demonstrate that the decisive role in this process belongs to hydrogen that interacts with different types of micro-defects in the matrice. In order to understand why a more easy propagation of dislocations from the crack tip down results in embrittlement it is necessary to study the crack growth pattern in inert media for plastic materials. Common features of different hydrogen embrittlement processes make it possible to conclude that a solid theory should be based on consolidated concepts of hydrogen-induced failures with taking into account the synergism of metal-hydrogen systems, i.e. the change in embrittlement mechanism in the process of the material structural self-organization at different structure-scale levels. Here a very important issue is to investigate the response of the material fine structure (structural relaxation) to the influence of a hydrogen medium under various straining temperature and speed conditions. Such investigation should be conducted with the help of electronic microscopes by applying acoustical emission and inner friction methods. Thanks to them it is possible to study the auto-wave nature of metal plastic deformation and to identify the most typical sustainable dissipative structures that emerge during the material self-organizing under combined impact of tensile stress and corrosive media.

Nanostructured high-strength alloys.

Metallurgy Low-density magnesium alloys are a promising type of material for making lighter vehicles and improving fuel efficiency. One challenge for lightweighting is developing high-strength magnesium alloys. Wu et al. created a dual-phase magnesium thin film with near-ideal strength. The alloy consists of small nanocrystalline cores surrounded by glass, combining the benefits of both phases to create the high-strength alloy. The strategy for creating this type of nanostructure should translate to other types of alloys, opening a different pathway to creating high-strength metals. Nature 10.1038/nature21691 (2017).

Crack tip flipping under mode I tearing: Investigated by X-ray tomography

The fracture surface morphology that results from mode I tearing of ductile plate metals depends heavily on both the elastic-plastic material properties and the microstructure. Severe tunneling of the advancing crack tip (resulting in cup-cup, or bath-tub like fracture surfaces) can take place in a range of materials, often of low strength, while tearing of high strength metals typically progress by the shear band failure mechanism (slanting). In reality, however, most fracture surfaces display a mixture of morphologies. For example, slant crack propagation can be accompanied by large shear lips near the outer free plate surface or a complete shear band switch - seemingly distributed randomly on the fracture surface. The occasionally observed shear band switch of mode I slant cracks, related to ductile plate tearing, is far from random as the crack can flip systematically from one side to the other in roughly 45° shear bands. This "flipping" action of a slanted crack remains to be fully understood, and the present study serves to share details on the phenomenon by exploiting X-ray tomography scanning to access the plate interior and the very crack tip. Throughout, the focus is on a crack tip where the flip is underway. Extensive growth of single edge cracks under mode I loading is achieved in a purpose build test set-up. Here, considering a 4mm plate of normal strength / high strain hardening steel which has been found to display successive flipping of the slant crack face. While undergoing a shear band switch, such that the flipping mechanism is active, the plate tearing test is interrupted and the crack tip extracted for further investigation. The conducted X-ray tomography scans reveal the failure process ahead of the advancing crack tip to resemble the ductile slant crack growth governed by local thinning and moderate crack tip tunneling. However, small shear lips form at the outer free plate surface, well behind the 45° slant (tunneling) crack tip, as the flipping action engages. Upon further loading, the shear lips subsequently grow to form a set of secondary crack fronts at an angle to the primary tunneling slant crack. Eventually, these secondary crack fronts catch up on the primary slant crack front and overtake the growth to complete the shear band switch. Once the crack slants, an out-of-plane action occurs due to the loss of symmetry in the system. It is this out-of-plane action which is believed to set-off the flipping mechanism.

Adiabatic shear banding assisted dynamic failure: Some modeling issues

Adiabatic shear banding (ASB) is a precursor of failure of high strength metals and alloys when submitted to impact and other high strain rate loading. As a mechanism of plastic flow localization triggered by a thermo-mechanical instability in the context of dynamic plasticity, ASB causes a discontinuity of the strain/strain rate field. In the present paper, some models available in literature are assessed regarding their ability to reproduce ASB features and further consequences. Some tracks for further developments in the field are also given.

Технології зварювання для виготовлення і ремонту металевих конструкцій із високоміцних сталей

Технології зварювання для виготовлення і ремонту металевих конструкцій із високоміцних сталей

The fatigue failure analysis and fatigue life prediction model of FV520B-I as a function of surface roughness in HCF regime

Abstract

First-principles study on adsorption mechanism of hydrogen on tungsten trioxide surface

With the development of modern industrial technology, tungsten products prepared from normal tungsten powder cannot meet the demands of industry. The tungsten product produced from ultra-fine tungsten powder exhibits high strength, high toughness, and low metal plasticity-brittleness transition temperature, which greatly improves the performance of materials. Hence, it is necessary to carry out theoretical research on the micro adsorption dynamics during hydrogen reduction of tungsten trioxide to prepare ultra fine tungsten powder. In order to understand crystal characteristics of WO3 and WO3(001) surface characteristics, and to provide beneficial theoretical support for reaction law of hydrogen reduction on the WO3(001) surface, the mechanisms of H atom adsorption on cubic WO3 and WO3(001) surface are studied by the first-principles calculation based on the density functional theory (DFT) plane wave pseudo-potential method. The results show that theoretically calculated band gap of the cubic crystalline WO3 is 0.587 eV. There are two kinds of WO3(001) surfaces, WO-terminated (001) surface and O-terminated (001) surface. The W-O bond length and the bond angle of W-O-W structure change after the geometric optimization of the surface, and thus the surface relaxation is realized. The WO-terminated (001) surface shows n-type semiconductor characteristics while the O-terminated (001) surface shows p-type semiconductor characteristics. Four adsorption configurations of H atoms on the WO-terminated (001) surface and the O-terminated (001) surface, including H-O2c-H, H-O2 cH-O2c, H-O1c-H, and H-O1cH-O1c, are calculated. Among them, the adsorption energy of the H-O1c-H configuration is the smallest (-3.684 eV) with the shortest bond length of H-O bond (0.0968 nm), and hydrogen atoms lose the most of electrons (0.55e), which indicates that the H-O1c-H adsorption configuration is the most stable one. The band gap of the H-O1c-H configuration increases from 0.624 eV to 1.004 eV after adsorption, while the bandwidth of valence band is almost unchanged. The results about the density of states (DOS) reveal that 1s state of the H atom interacts with 2p and 2s states of the O atom. Strong isolated electron peaks are formed to be at about -8 and -20 eV. The outermost O1c atoms of O-terminated (001) surface contain an unsaturated bond, facilitating the bonding between two H atoms and one O1c atom. Thus, two H atoms and one O1c atom form chemical bonds respectively, and an H2O molecule is generated, leaving an oxygen vacancy on the surface after adsorption reaction. By combining experimental observations with simulation results, the mechanism of hydrogen reducing tungsten trioxide can be elaborated profoundly from a micro view.

First-principles study of absorption mechanism of hydrogen on W20O58 (010) surface

With the development of modern industrial technology, tungsten products prepared from traditional tungsten powder cannot meet the demands of industry. However, the properties of tungsten products produced from ultra-fine tungsten powder have been greatly improved:they have high strength, high toughness, and low metal plasticity-brittle transition temperature. Hence, it is necessary to carry out theoretical research of the micro-adsorption dynamics during hydrogen reduction of W20O58, which is beneficial to synthetizing ultra-fine tungsten powder. In this article, to comprehend the crystal characteristics of W20O58 (010) surface and provide the theoretical reaction law for hydrogen reduction on W20O58 (010) surface, the absorption mechanism of H2 molecule on W20O58 (010) surface is studied by the first-principles calculation based on density functional theory in a plane wave pseudo-potential framework. The results show that the indirect band gap of W20O58 is 0.8 eV, indicating that it has metallic characteristic. The W20O58 (010) surface has different terminations, i.e., WO-terminated (010) surface and O-terminated (010) surface. After the geometrical optimization of the two surfaces, the W–O bond length and bond angle of W–O–W are both changed. In addition, six absorption configurations of H2 on W20O58 (010) surface, including WO-L-O1c, WO-V-O1c, WO-L-O2c, WO-V-O2c, O-L-O1c and O-V-O1c, are chosen to be investigated. The calculation results show that the WO-L-O1c, WO-V-O1c and WO-L-O2c absorption system are unstable, while the WO-V-O2c, O-L-O1c and O-V-O1c absorption configuration are stable. When H2 molecule is dissociated into two H atoms, the absorption energies of the three stable configurations are-1.164 eV,-1.021 eV and-3.11 eV, respectively. It is obvious that the O-V-O1c absorption configuration is the most stable one. The analysis of density of states reveals that the 1s state of H atom interacts with the 2p and 2s states of O atom. The outermost O1c atom of O-terminated (010) surface contains an unsaturated bond, which results in the formation of bonding between two H atoms and O1c atom. As a result, an H2O molecule is formed and an oxygen vacancy on the surface is generated after absorption reaction. By combining experimental observations with simulation calculations, the mechanism of hydrogen reduction of W20O58 can be revealed from a microscopic view.

Direct Metal to Metal Imprinting for developing 1-step Manufacturing Process of Patterned Metal Surface

Metallic surface with nano structured patterns, namely metal nano engineered surface (M-NES) has been attracting more and more attention due to its remarkable characteristics such as structural color based on photonic crystal, hologram, super-hydrophobicity, interspecific bonding with enlarged surface area, and so on. In the present study, direct metal to metal nano-imprinting was developed to achieve 1-step manufacturing process of metal nano-engineered surface. Using a high-strength metal stamp, nano structures were directly transcribed to a ductile metal film or curved/3D surfaces. Metal stamp was made by nickel electroforming on a master template fabricated by photo-lithography, nano-second laser machining, or anodic aluminum oxide. We used pure Al (99.999%) as substrates of the metal nano-imprinting. The metal nano-imprinting was carried out based on the conventional imprinting method by regulating pressure. The nano-imprinted metal NESs were examined by examined by microscopy.

DEVELOPMENT OF A MICROGEAR ENDURANCE TEST SYSTEM AND A BASIC STUDY OF LUBRICATING CONDITIONS FOR MICRO SPUR GEAR

It has become possible to manufacture highly precise, high-strength metal microgears in recent years. On the other hand, a systematic evaluation of the load-carrying characteristics of microgears is not reported. Therefore, we developed an endurance test system for the microgear. Further, we considered the lubricating conditions for the microgear. We obtained the following results: (1) Even if the operating time is very short under very low operating conditions, it is confirmed that the damage to of meshing teeth will progress rapidly. (2) Depending on the operating conditions, it is expected that maintain sufficient lubrication condition which dropped a slight amount of the lubricating oil. (3) At a rotational speed that scattered the lubricating oil, it was observed the clumps by melt in tooth tip. (4) It is possible that the endurance test system that we developed can achieve appropriate meshing because a certain wear was observed over the tooth face width.

Comparative analysis of the processing accuracy of high strength metal sheets by AWJ, laser and plasma

Experimental tests were carried out on two high-strength steel materials (Ramor 400 and Ramor 550). Quantification of the dimensional accuracy was achieved by measuring the deviations from some geometric parameters of part (two lengths and two radii). It was found that in case of Ramor 400 steel, at the jet inlet, the deviations from the part radii are quite small for all the three analysed processes. Instead for the linear dimensions, the deviations are small only in case of laser cutting. At the jet outlet, the deviations raised in small amount compared to those obtained at the jet inlet for both materials as well as for all the three processes. Related to Ramor 550 steel, at the jet inlet the deviations from the part radii are very small in case of AWJ and laser cutting but larger in case of plasma cutting. At the jet outlet, the deviations from the part radii are very small for all processes; in case of linear dimensions, there was obtained very small deviations only in the case of laser processing, the other two processes leading to very large deviations.

Tailored heat treated accumulative roll bonded aluminum blanks: failure under bending stresses

Ultrafine-grained accumulative roll bonded (ARB) sheet metals of aluminum alloys have a high potential for lightweight construction. The mechanical properties can be enhanced regarding strength and ductility by the combination of ARB and a local heat treatment according to the Tailor Heat Treated Blanks technology. The present investigation focuses on the failure behavior of ultrafine-grained ARB blanks. Due to the low formability of these high-strength ARB metals, a detailed understanding of the failure mechanisms is essential. For this purpose, an established approach to determine the different stages of damage of the material for conventional materials is now applied to multilayered aluminum in the as-received and heat-treated condition. In this context, air bending tests are used to qualify and quantify the bending and forming behavior of ARB sheets of AA1050A and AA6016 aluminum alloys.

Fundamental Study for Development of an Anti-Icing Pavement System Using Carbon-Fiber Sheet

PURPOSES : This paper aims to develop a road pavement de-icing system using carbon sheet to replace the older snow de-icing method. Carbon sheet is a light and high-strength metal. Hence, various bodies of research for its applications in many industries have progressed. METHODS : The experiment was conducted in a laboratory. The carbon sheet supplied voltage through a power supply system, and produced heat transfers to the concrete surface. Various factors, such as pavement material, carbon sheet width, penetration depth, and freezing-thawing resistance, were considered in the conducted experiments to confirm the heating transfer efficiency of the carbon sheet. RESULTS : The carbon sheet used was a conductor. Therefore, it produced heat if voltage was supplied. The exposed carbon sheet on the atmosphere did not affect the carbon sheet width when it provided constant voltage. However, the sheet showed different heating behaviors by width change when the carbon sheet penetrated into the concrete. Moreover, the freezing-thawing resistance was decreased by the carbon sheet with increasing width. CONCLUSIONS : The experiments confirmed the possibility of developing a road snow melting system using a carbon sheet. The antiicing system using the carbon sheet to replace the traditional anti-icing system has disadvantages of environmental pollution risk and electric leakage. The pavement also improved its toughness resistance. The utilization value will be very high in the future if carbon sheet heat loss can be minimized and durability is improved.

High-strength copper-based alloy with excellent resistance to hydrogen embrittlement

High-pressure components are generally designed with safety factors based on the tensile strength (TS) of the material; accordingly, materials with higher TS permit designed components with thinner walls, which reduce the weight and cost of the parts. However, many high-strength metals are severely degraded by hydrogen. To this point, efforts to develop a high-strength metal with a TS far beyond 1000 MPa and excellent resistance to hydrogen embrittlement (HE) have failed. This study introduces a high-strength metal with an excellent HE resistance, composed of a precipitation-hardened copper-beryllium alloy with the TS of 1400 MPa. Slow strain rate tensile (SSRT) tests of both smooth and notched specimens were performed in 115-MPa hydrogen gas at room temperature (RT). The alloy had a relative reduction in area RRA ≈ 1 and a relative notch tensile strength RNTS ≈ 1, without degradation in either characteristic.

Producing High‐Strength Metals by I‐ECAP

Producing High‐Strength Metals by I‐ECAP

Dissimilar welded joints operating in sub-zero temperature environment

The vast expanses of the Arctic have for some decades been the subject of considerable scientific interest as regards potential industrial exploitation. However, the cold climatic conditions of the area pose major challenges, particularly with respect to the metals used, infrastructure design, and manufacturing techniques required for cold-resistant structures. Dissimilar welding of metals can supply added value (lightness, thermal difference) in the construction of Arctic structures, but the behavior of dissimilar high-strength metal welds in very cold environments remains under-investigated and improved understanding is required before such metals can be adopted for Arctic applications. The objective of this research is to identify possible difficulties arising from the use of dissimilar metal welds in Arctic structures, in particular the causes of potential defects and failures, and to propose means to remedy or prevent such failures through the adoption of suitable procedures and the choice of suitable metals. This study covers steels used for structural design of work in cold environments such as low-carbon content steels with tensile strength from 379 to above 586 MPa along with alloyed steels containing nickel (Ni) up to 4.5 % or chrome (Cr) and molybdenum (Mo) and stainless steels like austenitic stainless steels which keep their ductile properties even in sub-zero temperature. These steels are known for their better weldability and toughness. The methodology consists of a review of scientific articles and research experiments on the microstructures and physical and mechanical properties of dissimilar welded structures for low-temperature environments. In-service behavior is analyzed on the basis of literature data and the relationship between the types of structure failures and weld defects investigated. Finally, appropriate joints and applicable methods are proposed. The analysis shows that a microstructure with very large grains and a large HAZ are features that increase the size and prevalence of cracks. An acicular ferrite microstructure is required in the weld metal. Migration of carbon is a further aggravating factor for cracking. With nonferrous metals, the risk of undesired intermetallic compound hardness and brittleness increases, and processes that minimize the temperature of the HAZ are recommended. Heat treatment is recommended to refine the grains. The major implication of the work is that significant care is required in the selection of the base metal, electrodes and welding parameters, and appropriate heat treatments. Effective control of such factors can lead to improvement in the quality, reliability, and service life of Arctic welded structures.

Development of a Precipitation-Strengthened Matrix for Non-quenchable Aluminum Metal Matrix Composites

Recent developments in metal matrix composite-encapsulated ceramic armor show promise in lightweight armor technology. The system contains ceramic tiles, such as alumina, sandwiched between unreinforced aluminum or aluminum metal matrix composite (Al-MMC), which has a better toughness compared to the ceramic tiles. The sandwich structures should not be quenched during the fabrication, as the large mismatch in the coefficients of thermal expansion between the ceramic tiles and the unreinforced aluminum or Al-MMC creates internal stresses high enough to fracture the ceramic tiles. However, slow cooling of most commercial alloys creates large precipitates making solute unavailable for the formation of fine precipitates during aging. Here, we develop a non-quenched, high-strength metal matrix utilizing dilute Al-Sc-Zr alloys. We demonstrate that the dilute Al-0.09 Sc-0.045 Zr at.% alloy and the same alloy containing 0–4 vol.% alumina short fibers do not result in precipitation upon slow cooling from a high temperature, and can thereafter be aged to increase their strength. They exhibit a moderate strength, but improved ductility and toughness as compared to common armor aluminum alloys, such as AA5083-H131, making them attractive as armor materials and hybrid armor systems.

応力分布および拡散性水素濃度分布を考慮した局所限界条件に基づく高強度鋼溶接金属の低温割れ発生特性に関する検討

応力分布および拡散性水素濃度分布を考慮した局所限界条件に基づく高強度鋼溶接金属の低温割れ発生特性に関する検討