Acceptable Toughness Research Articles

Monitoring performance of a new smart geosynthetic under drawing test

Geosynthetics are widely used in civil engineering reinforcements owing to their high strength, acceptable toughness, and ease of transportation. However, traditional geosynthetics do not have the capability to monitor damage inside the soil. Therefore, in this paper, a new sensor-enabled piezoelectric geobelt (SPGB) is developed to measure the deformation of reinforced-soil structures. In-soil drawing tests are conducted to investigate the sensing performance of the SPGB. Variations in the voltage and impedance signals of the SPGB with the drawing displacement under different damage conditions are investigated. The results show that with the increase of drawing displacement, SPGB undergoes tensile deformation followed by pullout damage. In tensile deformation, the signal response of SPGB is related to strain. As the strain increases, the output voltage first increases and then decreases, and the impedance gradually decreases. In the pullout damage phase, the signal response of SPGB is related to the contact area between SPGB and soil. As the drawing displacement increases, the contact area between SPGB and soil gradually decreases, the output voltage gradually decreases, and the impedance gradually increases. Therefore, the SPGB, as a sensor-enabled geosynthetic, provides a reinforcing function to the soil body and simultaneously performs in-soil catastrophe identification.

Al(Si)/Al2O3 and NiAl(Si)/Al2O3 co-continuous composites obtained by low temperature Reactive Metal Penetration of dense silica preforms.

Interpenetrating network Al(Si)/Al2O3 composites, obtained by a reactive metal penetration process, where pure aluminum metal reacts with a dense amorphous silica preform, are an interesting class of metal/ceramic composites, with two continuous networks of metal (Al-Si alloy) and ceramic (Al2O3). These composites have high stiffness and hardness, while retaining acceptable toughness and good thermal and electrical conductivity, and can be used in wear or thermal management applications. A second infiltration step with nickel allows to substitute the Al(Si) alloy with an intermetallic, obtaining an interpenetrating network NiAl(Si)/Al2O3 composite, with very high hardness and melting point. While in the standard process the temperature for obtaining the Al(Si)/Al2O3 composites is in the 1100-1200 °C range, in this paper we studied instead the 700-1000 °C temperature range and its effect on the microstructure of the final NiAl(Si)/Al2O3 composite. After the first infiltration step, the microstructure of Al(Si)/Al2O3 composites depends on both temperature and time of the treatment. At 700-800 °C and for reaction time of 1-2 hours, the grain size is completely sub-micrometric. When temperature and time of reaction increase, islands with a coarser microstructure, of micrometric size, form, reaching a fully micrometric coarser microstructure at 1100-1200 °C. The islands formation is due to the transformation from transition aluminas, formed at low temperature and low reaction time, to α-alumina, while at high temperature α-alumina forms directly. In a second step, the Al(Si) metal network was replaced with an intermetallic one, by contacting the composite with liquid nickel, that reacted with the Al(Si) alloy forming an Al-Ni-Si intermetallic. The temperature and duration of the first infiltration step strongly influences not only the microstructure of the Al(Si)/Al2O3 composite but also of the final NiAl(Si)/Al2O3 one, that is finer when the first step (reaction of aluminum with silica) occurs at lower temperature.

Determination of the ductile-to-brittle transition temperature of NIOMOL 490 K steel welded joints

This paper is dedicated to the ductile–brittle transition behaviour of the microalloyed structural steel NIOMOL 490 K. This steel grade is used for welded pressure vessels subjected to dynamic loads and operating at sub-zero temperatures. Therefore, it must have an acceptable toughness. Due to its importance for the safety assessment of pressure vessels, a characterization of this steel was carried out using the Charpy V-notch impact test in the temperature range between −60 °C and + 60 °C. The notches were located in parent material, heat affected zone and weld metal. In this paper, the tensile strength properties at ambient temperature and the nil ductility temperature in the temperature range from −60 °C to + 60 °C are presented.

Silver nanoparticles-coated 2D glass-flakes reinforced polyurea composites with high thermal conductivity, acceptable toughness and thermal stability

Silver nanoparticles-coated 2D glass-flakes reinforced polyurea composites with high thermal conductivity, acceptable toughness and thermal stability

Structural and Mechanical Properties of Fluorine-Containing TaCxNy Thin Films Deposited by Reactive Magnetron Sputtering

TaN thin-film coatings are well known for their good mechanical properties, acceptable toughness, as well as good biocompatibility. However, the friction coefficient of these films is sometimes too high, or the hemocompatibility is poor. The purpose of this study is to reduce the friction coefficient and increase the hydrophobicity of TaN coatings by introducing carbon and fluorine into the coatings. This study has never been conducted by other researchers. Fluorine-containing tantalum carbonitride (i.e., F–TaCxNy) top layers were deposited on TaN/Ta interlayers by reactive sputtering with fixed nitrogen and various hexafluoroethane (C2F6) mass flow rates. During the deposition process, C2F6 gas with various mass flow rates was added. After deposition, these F–TaCxNy multi-layered films were then characterized using XRD, XPS, FTIR, FESEM, WDS, a nano-indenter, a water contact-angle measurement system, and a tribometer. The tribological tests were carried out in the environment with and without humidity. The surface energies of the films were examined with water contact-angle variation. According to structural analysis, TaN phase would transform to TaCxNy with the increase in the C2F6 mass flow rate, which would result in a decrease in the friction coefficient and an increase in hydrophobicity. The films’ hardness (H, increased at most by 20%), elastic modulus (E), and H/E ratio first increased then decreased, most likely due to the increase in relatively soft C–F bonding. According to the results obtained from tribotesting, it was found that an increase in carbon and fluorine contents in the films reduces the friction by more than 30%, and wear rate by more than 50%. More importantly, the effects of moisture on the friction coefficient can be minimized to almost nothing. In a water contact-angle study, the contact angle increased from 60° to 85° with the increase in C2F6 mass flow rates. This evidence illustrated that hemocompatibility of the TaN thin film can be significantly enhanced through the formation of Ta–C and C–Fx bonding. The chemical composition and bonding status of these films, especially the existence of C–Fx bonds, were studied by FTIR and XPS. In sum, with the increased C2F6 mass flow rate, the carbon and fluorine contents in the films increased, while the nitrogen content decreased. The structure, bonding status, and compositions varied accordingly. The tribological behaviors were significantly improved. Furthermore, by carrying out tribotesting in humid air and a dry argon environment, it was confirmed that the greater the fluorine content, the less sensitive the films would be to environment change. This is attributable to the induced lower surface energy and reduced adsorption to water vapor due to the increase in C–Fx bonds. The successfully fabricated and studied F–TaCxNy films could be applied in many areas such as artificial blood vessels, or precision components in an atmospheric or vacuum environment.

Determination of ductile-to-brittle transition temperature of NIOMOL 490K steel welded joints

This paper is devoted to the ductile–brittle transition behavior of high strength low alloyed structural steel NIOMOL 490K. This steel grade is designed for welded pressure vessels exposed to dynamic loads, operating at temperatures below zero, and that is why it must have acceptable toughness. Due to its importance for the safety assessment of pressure vessels, a characterization of this steel with Charpy V-notch test in range of temperature between-60 ⁰C and +60 ⁰C was undertaken. Ductile-to-brittle transition temperature curves were generated in the present study by using instrumented Charpy pendulum impact test on V-notch specimens. Notches were located in the parent material, heat-affected zone and weld metal. The nil-ductility temperature and tensile properties in temperature range from -60 ⁰C to +60 ⁰C are presented in this paper. We used different test temperatures to better understand ductile-to brittle transition response than just use either Charpy energy or other related ductility criteria.

Robustly superhydrophobic polylactic acid nonwoven membranes for efficient oil/water separation

Oily wastewater is an urgent issue that threatens the ecosystem and human health. Superhydrophobic porous materials are widely concerned as promising candidates for effective oil/water separation and oil adsorption. However, superhydrophobic porous materials are still confronted with frustrations such as complex preparation processes and secondary pollution to the environment. Superhydrophobic porous materials with biodegradability and a relatively simple preparation process are more attractive to practical application and environmental protection. In this work, biodegradable and industrially applied polylactic acid (PLA) nonwoven materials were used as porous membranes, then PLA nanoparticles were loaded on the membrane surface to construct the hierarchical rough structure. The modified PLA nonwoven membrane (nano-PLA) shows superhydrophobicity and efficient oil/water separation performance. Moreover, strong mechanical strength and acceptable toughness are obtained. This work offers an easily controlled and industrially used pathway for the design of robust, highly selective, and biodegradable oil/water separation materials.

A steel-like unalloyed multiphase ductile iron

This work highlights a new process for direct manufacturing of ductile iron that is based on the innovative combined technology of quenching and partitioning, and low-temperature-transformation of nano bainite as used for high strength steels. In this process, a commercial unalloyed ductile iron is austenitized at 890 °C for 20 min, then rapidly quenched to 180 °C for 5 s, and finally partitioned at 220 °C for 240 min. A maximum tensile strength of more than 1600 MPa, a hardness of 55 HRC at an elongation in excess of 5%, and the number of repeat tensile fatigue failure of 2.5 × 104 cycles at a stress amplitude of 600 MPa, are achieved. This is comparable to those of a high strength carbon alloy steel. These properties are due to the synergistic strengthening and toughening effects of a multiphase structure comprising tempered martensite, bainitic ferrite and retained austenite in the matrix, and a spherical graphite morphology. This work provides a guidance on how to produce unique steel-like ductile iron with a high level of strength and acceptable toughness.

Evaluation of Hardness, Sliding Wear and Strength of a Hypoeutectic White Iron with 25%Cr after Heat Treatments

Hypoeutectic white cast irons with a high chrome content are commonly used in the industrial mining sector where there is a demand for both high resistance to adhesive wear and an acceptable toughness for the absorption of impacts and falls of diverse materials. Through the application of a design of experiment (DoE) technique, factors related to thermal treatment are analyzed with respect to resistance to sliding wear, maximum rupture stress and toughness. The results show that, in order to increase resistance to adhesive wear, it is convenient to use destabilization temperatures of 1050 °C and tempering of two hours at 400 °C. This foments a very hard martensite and a high proportion of highly alloyed retained austenite, which, with low tempering, achieves a precipitation of carbides from this austenite with hardly any loss of hardness of the martensite. In order to increase the energy which this material is capable of absorbing until breakage, furnace cooling set at 150 °C followed by tempering at 550 °C would be favorable. Slower cooling implies a greater quantity of conditioned retained austenite, so that, following this, it may be transformed into lower bainite with a high density of finely dispersed precipitated carbides. Furthermore, this tempering also allows the transformation of martensite into ferrite with finely dispersed carbides.

Highly curable self-healing vitrimer-like cellulose-modified halloysite nanotube/epoxy nanocomposite coatings

Self-healing and self-repairing coatings are stimuli-responsive materials, which are of crucial importance in developing advanced smart systems. However, a few has been attempted to unveil the association between the microstructure and properties of self-healing organic coatings. Herein, silane coupled cellulose-functionalized halloysite nanotubes (HNT-C)/epoxy nanocomposite coatings showing vitrimer-like behavior were developed and their crosslinking, thermal, mechanical, and self-healing behaviors were discussed. Nanocomposites with variable pristine HNT and HNT-C contents (0.1, 0.3, and 0.5 wt%) were prepared, where epoxy/HNT-C (0.3 wt%) took Good cure label in terms of Cure Index, surprisingly with a cure enthalpy three times higher than that of blank epoxy. Moreover, the tensile strength and elongation at break of the assigned nanocomposite coating were enhanced by 16% and 56%, respectively. Evidence of cellulose functionalization was in SEM image provided from the fracture surface suggesting smooth breakup mechanism for epoxy and epoxy/HNT, in contrast to a roughly-broken fracture behavior for epoxy/HNT-C. Surface functionalization of nanotubes with cellulose decreased the relaxation time by five times in some cases, which was ascribed to the esterification reaction in the system. The self-healing behavior of the coatings through transesterification of β-hydroxyl ester at higher temperature was theoretically interpreted in terms of relaxation time of the epoxy chains. The vitrimers rapidly responded to the intra/inter molecular forces because of the transesterification reaction so that the ester groups were exchanged with hydroxyl groups that assisted autocatalytic reactions. The epoxy/HNT-C nanocomposites developed in this work are fast cure coatings with acceptable toughness and self-healing behavior.

Biocompatibility, osseointegration, antibacterial and mechanical properties of nanocrystalline Ti-Cu alloy as a new orthopedic material

The demands for high-performance biomaterials are driving the development of new metallic alloys with improved mechanical and biological responses. In this study, a nanocrystalline Ti-Cu intermetallic alloy was prepared by a powder metallurgy route, and its application as an orthopedic material was evaluated by the microstructural, mechanical, corrosion, antibacterial, cytotoxicity and osseointegration examinations. Microstructural characterization revealed the formation of TiCu and Ti2Cu3 as major phases with 23 nm grain size in the structure of the alloy. The synthesized alloy exhibited ultra-high hardness of 10 GPa, acceptable toughness of 8.14 MPam1/2, a ∼98 % anti-bacterial rate against S. aureus and E. coli, excellent cell viability to MG-63 osteosarcoma cells, and high osteoblast formation rate, which indicate a great potential of this alloy for biomedical application.

Influence of carbon content on microstructure and mechanical properties of 1000 MPa deposited metal by gas metal arc welding

The effects of carbon content (0.078–0.100 wt.%) on the microstructure and properties of 1000 MPa grade deposited metal produced by gas metal arc welding have been investigated. Experimental results show that the microstructure of the deposited metal was mainly composed of martensite, bainite and retained austenite. With increasing carbon content, the proportion of martensite increased, and the amount of bainite was reduced. High carbon content is beneficial to strength, but harmful to impact toughness, and thus, carbon reductions lead to the increase in impact toughness. When the carbon content was 0.100 wt.%, the lowest Charpy absorbed energy of 47 J at − 40 °C for the deposited metal was achieved, the highest yield strength of 1038 MPa was attained, and the yield-to-tensile ratio was more than 0.88, while the highest Charpy absorbed energy of 55.7 J at − 40 °C and the lowest yield strength of 915 MPa were obtained when the deposited metal contains 0.078 wt.% C, and the yield-to-tensile ratio was less than 0.85. It is concluded that bainite fraction and fine effective grain size were the dominant factors to achieve good comprehensive mechanical properties (the required strength and an acceptable toughness) of deposited metals with various carbon contents.

Recent research advances of high strength steel welded hollow section joints

High strength steel (HSS) with acceptable toughness and ductility has been produced due to advances in steel manufacturing technologies. The application of HSS in tubular structures could significantly reduce construction costs and lower carbon footprints. Welded hollow section joints are critical components in tubular structures. This paper aims to provide a review of recent research advances of HSS welded hollow sections joints. Current design rules and their research background for welded hollow section joints under static and fatigue loadings are firstly described. Recent investigations on the static design and fatigue performance of HSS welded hollow section joints are summarised, and further research work is discussed. The preliminary results indicate that suitability of current design rules for the HSS welded joints under static loading depends on the loading type, failure mode, steel yield stress, geometric parameters, chord preload ratio and welding. High-cycle fatigue performance of the HSS welded joints is comparable or even higher when compared with normal strength steel counterparts. More research is highly desirable for comprehensive assessment of current design provisions and proposing appropriate design rules for the HSS welded joints.

Microstructure and mechanical properties of high-strength steel welding consumables with a minimum yield strength of 1100\xa0MPa

Welded high-strength steel components have great potential for use in lightweight constructions or highly loaded structures. Welding of steels with a yield strength of more than 1100 MPa is particularly challenging because of the toughness requirements for the weld metal. Currently, a new generation of welding consumables with a minimum yield strength of 1100 MPa has been developed. Based on electron backscatter diffraction and atom probe tomography, a concept for toughening and strengthening of all-weld metal samples was deployed. Starting from a martensitic all-weld metal sample with an approximate yield strength of 1000 MPa, a reduction in manganese and silicon content resulted in a refined microstructure with a lower prior austenite grain size and effective grain size. Furthermore, a higher average grain boundary misorientation was measured, which influences the toughness positively. An addition of vanadium caused the formation of vanadium-rich clusters, which increased the strength of the all-weld metal significantly. With a combination of these two mechanisms, it was possible to produce an all-weld metal sample with the required yield strength of more than 1100 MPa and an acceptable toughness.

MECHANICAL CHARACTERIZATION OF ANCIENT PORTUGUESE RIVETED BRIDGES STEELS

In repairing and retrofitting processes of ancient riveted steel bridges is crucial to assess the structural state of old metals to guaranty structural safety. Metals under long-time operations (mild, rimmed low carbon steels <0.1% C, puddle irons) and cyclic loading present a tendency for degradation processes. The case-studies of this work are five metallic bridges existing in Portugal (Luiz I, Eiffel, Fao, Pinhao and Trezoi). This work presents the study of some characteristics of materials extracted from the five case-studies, such as: monotonic tensile strength, chemical composition, microstructures, hardness, notch toughness and fatigue crack propagation. In terms of monotonic tensile tests, the materials from Luiz I, Eiffel and Fao bridges are similar to puddle steel and the materials from Pinhao and Trezoi bridges are similar to mild steel. In terms of toughness only the material from the Pinhao bridge exhibits acceptable toughness properties, considering current design requirements. The materials from the other bridges exhibit relatively low toughness properties. The fatigue crack propagation data from the old Portuguese riveted steel bridges were correlated using the Paris’s law and the possibility for a design crack growth rate was discussed.

Manufacturing and Properties of Tungsten Carbide-Oxide Composites

Conventional WC-Co hardmetals are widely used in various applications due to their excellent properties. High hardness can be achieved using compositions with little to no content of cobalt or nickel. These binder metals are hazardous to health, making a substitution not only desirable because of availability and cost reasons. A new possibility to manufacture such hard materials is the combination of tungsten carbide with oxides such as Al2O3 and ZrO2. In this way the binder metal content can be replaced. Furthermore the content of the also expensive WC can be reduced. Such metal carbide – oxide composites with oxide contents between 16 vol% and 40 vol% were manufactured. The completely dense composites feature high hardness values of 2000 HV10 to 2400 HV10 while also having an acceptable fracture toughness of up to 7 MPa⋅m1/2. The improved mechanical properties make the replacement of WC-Co hardmetals and binder free WC ceramics in special areas possible.

Assessment of industrial nitriding processes for fusion steel applications

The 9Cr steels EUROFER and F82H-mod are the candidate materials for future fusion reactors. The extension of the operation limits including temperature, strength and toughness are still the scope of ongoing research. In a pulsed reactor operation, fatigue lifetime is one of the major properties for the steels. While the oxide dispersion strengthened EUROFER-ODS variant showed significant improvements in this area, the production costs and availability of large quantities of materials drastically limits its applications.In the present study, different surface nitriding treatments of EUROFER972 have been performed and the impact on microstructure, dynamic fracture toughness and high temperature fatigue has been analysed. Four different states of EUROFER including different heat treatments, nitriding of the surface and the ODS variant are tested and compared in this work.Low cycle fatigue tests show the improvements after certain treatments. Charpy impact tests and microstructural investigation by scanning electron microscopy and analytical transmission electron microscopy are also performed to compare the materials against the reference (EUROFER97).While conventional gas nitriding showed no beneficial effect on the material, the Hard-Inox-P treatment showed a significant improvement in the cycles to failure while retaining an acceptable toughness. Microstructural investigations showed the presence of very small chromium- and nitrogen-rich precipitates in the area close to the surface.

Hybrid Welding of 45 mm High Strength Steel Sections

Thick section welding has significant importance for oil and gas industry in low temperature regions. Arc welding is usually employed providing suitable quality joints with acceptable toughness at low temperatures with very limited productivity compared to modern high power laser systems. Laser-arc hybrid welding (LAHW) can enhance the productivity by several times due to higher penetration depth from laser beam and combined advantages of both heat sources. LAHW was applied to join 45mm high strength steel with double-sided technique and application of metal cored wire. The process was captured by high speed camera, allowing process observation in order to identify the relation of the process stability on weld imperfections and efficiency. Among the results, it was found that both arc power and presence of a gap increased penetration depth, and that higher welding speeds cause unstable processing and limits penetration depth. Over a wide range of heat inputs, the welds where found to consist of large amounts of fine-grained acicular ferrite in the upper 60-75% part of welds. At the root filler wire mixing was less and cooling faster, and thus found to have bainitic transformation. Toughness of deposited welds provided acceptable toughness at -50°C with some scattering.

Influence of Solution Annealing on Microstructure and Mechanical Properties of Maraging 300 Steel

Maraging 300 belongs to a family of metallic materials with extremely high mechanical strength and good toughness. Some works have been published about aging temperatures that improve ultimate strength resistance with acceptable toughness levels in this steel family, where the prior austenite grain size obtained by different solution annealing temperature influence in the final mechanical properties. Solution annealing temperatures ranging from 860 °C to 1150 ºC and were kept constant until the aging temperature. These treatments were used in order to investigate their influence on the microstructure and mechanical properties of maraging steel 300, especially with regard to toughness. The characterization of the microstructure was performed by optical microscopy, scanning electron microscope (SEM) and X-ray diffraction (XRD). Mechanical properties were evaluated by Rockwell C hardness and Charpy impact tests. The results showed that there is a temperature range where one can get some improvement in toughness without a large loss of mechanical strength.

Polymer matrix hybrid composites: The efficient way of improved performance

and innovative subject in the field of materials science. Hybrid systems by definition contain at least two, structurally different, units performing the same task, but which together exhibit some synergy with respect to a simple combination of these units. What is the main difference between a commonly used micro fibre reinforced polymer composite and a hybrid one? In the former one usually two separated phases are present namely the matrix (responsible for reinforcement’s embedding and toughness) and the reinforcing material (providing the desired strength). The result of this combination is a high strength engineering material with acceptable toughness. At hybrid composites a third phase is also present therefore three basic types of hybrid systems can be envisioned. One is when the matrix is hybridised. For instance there is an intensive research on rubber filled thermoset resins (DOI: 10.1007/s10853-012-6564-2); but the combination of two resins could also be effective (DOI: 10.3311/PPme.7237). At this combination the purpose is usually to increase the mentioned moderate toughness. The second way of hybridization is when there are at least two kinds of reinforcing materials (e.g. DOI: 10.1177/0731684413516393) and the third one when both the matrix and the reinforcing material are hybridised (DOI: 10.1016/j.radphyschem.2011.11.015). What are the main difficulties that obstruct the extensive use of this type of materials? One is that hybrid structures contain at least three phases, which makes the correlation between the structure and the mechanical properties much more complex compared to the well-known two phase systems. Additionally in case of hybrid matrix, the formed morphology depends on several parameters and also the reinforcing material has to be considered. The cost of hybrid composite production due to their complexity is also higher compared to general purpose composites, as typically additional technological steps are necessary. As hybrid composites are relatively new group of materials their long term performance and cyclic behaviour have to be examined, too. It should also be mentioned that at the end of the life cycle the recycling of the hybrid parts can be carried out usually on low level (energy recovery) as the separation of constituent materials is not easy. Only one exception is available, when all of the components are from bio degradable materials. These materials will have great future in the field of biotechnology especially as human implants. Significant part of the research has to address solving of the above mentioned problems in order to make these hybrid materials available for everyday use. In the near future detailed investigation is needed on their structural and mechanical behaviour and it is also relevant to manage their reproducible production and recycling.