scholarly journals Determination of Critical Hydrogen Concentration and Its Effect on Mechanical Performance of 2200 MPa and 600 HBW Martensitic Ultra-High-Strength Steel

Metals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 984
Author(s):  
Eric Fangnon ◽  
Yuriy Yagodzinskyy ◽  
Evgenii Malictki ◽  
Saara Mehtonen ◽  
Esa Virolainen ◽  
...  
Keyword(s):  
Tensile Strength ◽  
Hydrogen Concentration ◽  
Mechanical Performance ◽  
Thermal Desorption Spectroscopy ◽  
Local Stress ◽  
High Strength ◽  
Constant Load ◽  
Strength Degradation ◽  
Load Test ◽  
Extension Rate

The influence of hydrogen on the mechanical performance of a hot-rolled martensitic steel was studied by means of constant extension rate test (CERT) and constant load test (CLT) followed with thermal desorption spectroscopy measurements. The steel shows a reduction in tensile strength up to 25% of ultimate tensile strength (UTS) at critical hydrogen concentrations determined to be about 1.1 wt.ppm and 50% of UTS at hydrogen concentrations of 2 wt.ppm. No further strength degradation was observed up to hydrogen concentrations of 4.8 wt.ppm. It was observed that the interplay between local hydrogen concentrations and local stress states, accompanied with the presence of total average hydrogen reducing the general plasticity of the specimen are responsible for the observed strength degradation of the steel at the critical concentrations of hydrogen. Under CLT, the steel does not show sensitivity to hydrogen at applied loads below 50% of UTS under continuous electrochemical hydrogen charging up to 85 h. Hydrogen enhanced creep rates during constant load increased linearly with increasing hydrogen concentration in the steel.

Hydrogen effects on fracture of high-strength steels with different micro-alloying

2015 ◽  
Vol 33 (6) ◽  
pp. 515-527 ◽  
Author(s):  
Olga Todoshchenko ◽  
Yuriy Yagodzinskyy ◽  
Valentina Yagodzinska ◽  
Tapio Saukkonen ◽  
Hannu Hänninen
Keyword(s):  
Chemical Composition ◽  
Electron Backscatter Diffraction ◽  
High Strength Steels ◽  
Thermal Desorption Spectroscopy ◽  
High Strength ◽  
Constant Load ◽  
Carbon Steels ◽  
Hydrogen Induced Cracking ◽  
Load Tests ◽  
Backscatter Diffraction

AbstractConstant load tests of high-strength carbon steels with different micro-alloying using strengths in the range of 1000–1400 MPa were performed at ambient temperature under continuous electrochemical hydrogen charging. Hydrogen markedly affects delayed fracture of all the studied steels. Fractography of the studied steels shows that fracture mechanism depends on the chemical composition of the studied steels and hydrogen-induced cracking exhibits intergranular or transgranular character occurring often in the form of hydrogen flakes. The size and chemical composition of non-metallic inclusions are analyzed by scanning electron microscopy and energy-dispersive X-ray spectroscopy. Hydrogen-induced cracking initiates at TiN/TiC particles in steels with Ti alloying. Crack paths are studied with electron backscatter diffraction mapping to analyze crack initiation and growth. The thermal desorption spectroscopy method is used to analyze the distribution of hydrogen in the trapping sites. The mechanisms of hydrogen effects on fracture of high-strength steels are discussed.

scholarly journals The influence of the opening size on the shear performance of the cross-laminated timber (CLT) walls

BioResources ◽  
2021 ◽  
Vol 16 (4) ◽  
pp. 7071-7085
Author(s):  
Daiyuan Zhang ◽  
Liming Shen ◽  
Xudong Zhu ◽  
Sujun Zhang ◽  
Meng Gong
Keyword(s):  
Shear Strength ◽  
Mechanical Performance ◽  
Shear Stiffness ◽  
High Strength ◽  
Load Test ◽  
Static Load Test ◽  
Cross Laminated Timber ◽  
Wall Panels ◽  
Shear Performance ◽  
The Cross

Cross-laminated timber is a wood product with excellent fire resistance and mechanical performance that is often used in tiny houses. Using the ASTM standard E564, the shear performance of cross-laminated timber wall panels, with and without openings, were investigated in this study. The specimens were made of spruce-pine-fir IIc lumber and installed on a test platform using high-strength bolts passing through them. This connection mode limited the displacements obtained in the test, primarily the shear displacements and rocking displacements. By comparing the static load test data of the three specimens with openings and the one without an opening, it was found that openings reduced the shear strength and shear stiffness. For the same sized rectangular opening, the shear stiffness of the cross-laminated timber panel was less when the wider side was horizontal (normal to the direction of the applied force). The shear stiffness of the cross-laminated timber wall panels can be effectively improved by reinforcing the areas near the openings with metal sheets. With reinforcement, the shear strength did not change drastically, but the damage to the cross-laminated timber wall panels was significantly reduced.

scholarly journals Strength Degradation in Curved FRP bars as Concrete Reinforcement

2020 ◽  
Author(s):  
Thanongsak Imjai ◽  
Reyes Garcia ◽  
Maurizio Guadagnini ◽  
Kypros Pilakoutas
Keyword(s):  
Tensile Strength ◽  
Structural Damage ◽  
Mechanical Performance ◽  
Failure Criteria ◽  
Strength Degradation ◽  
Future Research ◽  
Frp Composites ◽  
Current Design ◽  
Frp Reinforcement ◽  
Superior Corrosion Resistance

Steel reinforcement in concrete has the tendency to corrode and this process can lead to structural damage. FRP reinforcement represents a viable alternative for structures exposed to aggressive environments and has many possible applications where superior corrosion resistance properties are required. The use of FRP rebars as internal reinforcements for concrete, however, is limited to specific structural elements and does not yet extend to the whole structure. The reasons for this relate to the limited availability of curved or shaped reinforcing elements on the market and their reduced structural performance. Various studies, in fact, have shown that the mechanical performance of bent portions of composite bars is reduced significantly under a multiaxial combination of stresses and that the tensile strength can be as low as 25% of the maximum tensile strength that can be developed in the straight part. In a significant number of cases, the current design recommendations for concrete structures reinforced with FRP, however, were found to overestimate the bend capacity of FRP rebar. This paper presents the state-of-the art review of the research works on the strength degradation in curved FRP composites and highlighted the performance of exiting predictive models for the bend capacity of FRP reinforcement. Recent practical predictive model based on the Tsai-Hill failure criteria by considering the material at marcromechanical level is also discussed and highlighted. The review also identifies the challenges and highlights the future directions of research to explore the use of shaped FRP composites in civil engineering applications and the trends for future research in this area.

Studies of SCC and Hydrogen Embrittlement of High Strength Alloys Using Fracture Mechanics Methods

2005 ◽  
Vol 482 ◽  
pp. 11-16 ◽  
Author(s):  
Wolfgang Dietzel ◽  
Michael Pfuff ◽  
Guido G. Juilfs
Keyword(s):  
Plastic Deformation ◽  
Fracture Mechanics ◽  
Hydrogen Embrittlement ◽  
Hydrogen Diffusion ◽  
High Strength Steels ◽  
High Strength ◽  
Constant Load ◽  
Rate Of Change ◽  
Extension Rate ◽  
Hydrogen Atoms

Fracture mechanics based test and evaluation techniques are used to gain insight into the phenomenon of stress corrosion cracking (SCC) and to develop guidance for avoiding or controlling SCC. Complementary to well known constant load and constant deflection test methods experiments that are based on rising load or rising displacement situations and are specified in the new ISO standard 7539 – Part 9 may be applied to achieve these goals. These are particularly suitable to study cases of SCC and hydrogen embrittlement of high strength steels, aluminium and titanium alloys and to characterise the susceptibility of these materials to environmentally assisted cracking. In addition, the data generated in such R-curve tests can be used to model the degradation of the material caused by the uptake of atomic hydrogen from the environment. This is shown for the case of a high strength structural steel (FeE 690T) where in fracture mechanics SCC tests on pre-cracked C(T) specimens a correlation between the rate of change in plastic deformation and the crack extension rate due to hydrogen embrittlement was established. The influence of plastic strain on the hydrogen diffusion was additionally studied by electrochemical permeation experiments. By modelling this diffusion based on the assumption that trapping of the hydrogen atoms takes place at trap sites which are generated by the plastic deformation, a good agreement was achieved between experimentally obtained data and model predictions.

scholarly journals Effect of Relative Humidity on Mechanical Degradation of Medium Mn Steels

Materials ◽  
2020 ◽  
Vol 13 (6) ◽  
pp. 1304 ◽  
Author(s):  
Qingyang Liu ◽  
Juanping Xu ◽  
Liancheng Shen ◽  
Qingjun Zhou ◽  
Yanjing Su ◽  
...  
Keyword(s):  
Tensile Strength ◽  
Relative Humidity ◽  
Hydrogen Embrittlement ◽  
Hydrogen Concentration ◽  
High Strength Steels ◽  
Threshold Value ◽  
Tensile Tests ◽  
Constant Load ◽  
Mechanical Degradation ◽  
Delayed Cracking

Medium Mn steels have been considered as the next-generation materials for use in the automotive industry due to their excellent strength and ductility balance. To reduce the total weight and improve the safety of vehicles, medium Mn steels look forward to a highly promising future. However, hydrogen-induced delayed cracking is a concern for the use of high strength steels. This work is focused on the service characteristics of two kinds of medium Mn steels under different relative humidity conditions (40%, 60%, 80% and 100%). Under normal relative humidity (about 40%) at 25 °C, the hydrogen concentration in steel is 0.4 ppm. When exposed to higher relative humidity, the hydrogen concentration in steel increases slowly and reaches a stable value, about 0.8 ppm. In slow strain rate tensile tests under different relative humidity conditions, the tensile strength changed, the hydrogen concentration increased and the elongation decreased as well, thereby increasing the hydrogen embrittlement sensitivity. In other words, the smaller the tensile rate applied, the greater the hydrogen embrittlement sensitivity. In constant load tests under different relative humidity conditions, the threshold value of the delayed cracking of M7B (‘M’ referring to Mn, ‘7’ meaning the content of Mn, ‘B’ denoting batch annealing) steel maintains a steady value of 0.82 σb (tensile strength). The threshold value of the delayed cracking of M10B significantly changed along with relative humidity. When relative humidity increased from 60% to 80%, the threshold dropped sharply from 0.63 σb to 0.52 σb. We define 80% relative humidity as the ‘threshold humidity’ for M10B.

scholarly journals Improved Accuracy of Thermal Desorption Spectroscopy by Specimen Cooling during Measurement of Hydrogen Concentration in a High-Strength Steel

Materials ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1252 ◽  
Author(s):  
Eric Fangnon ◽  
Evgenii Malitckii ◽  
Yuriy Yagodzinskyy ◽  
Pedro Vilaça
Keyword(s):  
Thermal Desorption ◽  
Hydrogen Concentration ◽  
High Strength Steel ◽  
Vacuum Chamber ◽  
Thermal Desorption Spectroscopy ◽  
High Strength ◽  
Steel Sample ◽  
Martensitic Steels ◽  
Hydrogen Flux ◽  
Redistribution Of Hydrogen

Thermal desorption spectroscopy (TDS) is a powerful method for the measurement of hydrogen concentration in metallic materials. However, hydrogen loss from metallic samples during the preparation of the measurement poses a challenge to the accuracy of the results, especially in materials with high diffusivity of hydrogen, like ferritic and ferritic-martensitic steels. In the present paper, the effect of specimen cooling during the experimental procedure, as a tentative to reduce the loss of hydrogen during air-lock vacuum pumping for one high-strength steel of 1400 MPa, is evaluated. The results show, at room temperature, the presence of a continuous outward hydrogen flux accompanied with the redistribution of hydrogen within the measured steel during its exposure to the air-lock vacuum chamber under continuous pumping. Cooling of the steel samples to 213 K during pumping in the air-lock vacuum chamber before TDS measurement results in an increase in the measured total hydrogen concentration at about 14%. A significant reduction in hydrogen loss and redistribution within the steel sample improves the accuracy of hydrogen concentration measurement and trapping analysis in ferritic and martensitic steels.

scholarly journals Correlation between Microstructure and Mechanical Properties of Heat-Treated Ti–6Al–4V with Fe Alloying

Metals ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 854 ◽  
Author(s):  
Yongwei Liu ◽  
Fuwen Chen ◽  
Guanglong Xu ◽  
Yuwen Cui ◽  
Hui Chang
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Tensile Strength ◽  
Mechanical Performance ◽  
Volume Fraction ◽  
Phase Interface ◽  
High Strength ◽  
High Plasticity ◽  
High Aging Temperature ◽  
Microstructure And Mechanical Properties

The microstructure and mechanical properties of a newly developed Fe-microalloyed Ti–6Al–4V titanium alloy were investigated after different heat treatments. The volume fraction and the morphological features of the lamellar α phase had significant effects on the alloy’s mechanical performance. A dataset showing the relationship between microstructural features and tensile strength, elongation, and fracture toughness was developed. A high aging temperature resulted in high plasticity and fracture toughness, but relatively low strength. The high strength favored the fine α and the slender β. The high aspect ratio of lamellar α led to high strength but low fracture toughness. The alloy with ~84 vol % α exhibited the highest strength and lowest fracture toughness because the area of its α/β-phase interface was the highest. Optimal comprehensive mechanical performance and heat-treatment procedures were thus obtained from the dataset. Optimal tensile strength, yield strength, elongation, and fracture toughness were 999 and 919 MPa, 10.4%, and 94.4 MPa·m1/2, respectively.

Mechanical Performance of Paper Pulp and Wood Glue Composite

2017 ◽  
Author(s):  
Daniel M. Madyira ◽  
Takalani Mabirimisa ◽  
Tien-Chien Jen
Keyword(s):  
Tensile Strength ◽  
Composite Material ◽  
Ultimate Tensile Strength ◽  
Mechanical Performance ◽  
High Strength ◽  
Fiber Content ◽  
Pulp Fiber ◽  
Paper Pulp ◽  
Recycled Paper ◽  
Future Work

Due to depleting natural resources, it is necessary to develop eco-composite materials that are fabricated from sustainable and inexpensive materials such as recycled paper or cellulose-based materials. Such materials are required to meet the mechanical performance at par with traditional materials. The main aim of this study was to investigate the mechanical performance of a composite material fabricated from paper pulp and polyvinyl acetate (wood glue). It is expected that a high strength composite material may be achieved by varying the amount of paper-pulp fiber fraction from 7.5%, 10%, 20%, 30%, 40%, 50% to 60% weight. A tensile test was conducted and it was found that an increase in fiber content on the fabricated composite resulted in an increase in ultimate tensile strength and a decrease in corresponding strain. Furthermore, the material becomes more brittle at higher fiber content and conversely, more ductile at lower fiber content. The ultimate tensile strength was found to be 7.69 MPa at 60% w.t fiber and the minimum tensile strength was 0.12 MPa at 0% w.t fiber. There were no signs of fiber content limit observed in the obtained results. It was concluded that a composite of moderate strength was produced and future work is required in order to fully understand how the composite behaves at different loading conditions. However, an optimum fiber content limit will have to be determined.

Structure, property and knittability of polyimide filaments with various strength and modulus

2018 ◽  
Vol 89 (5) ◽  
pp. 771-781 ◽  
Author(s):  
Fangbing Lin ◽  
Wei Li ◽  
Xiaodong Du ◽  
Jinhua Jiang ◽  
Nanliang Chen
Keyword(s):  
Experimental Investigation ◽  
Tensile Strength ◽  
Young’S Modulus ◽  
Mechanical Performance ◽  
High Strength ◽  
Chemical Compositions ◽  
Structure Property ◽  
Mechanical Behaviors ◽  
Performance Differences ◽  
Low Strength

This paper presents an experimental investigation on the knittability of various polyimide (PI) filaments, namely PI-H (high strength and modulus), PI-M (moderate strength and modulus) and PI-L (low strength and modulus) filaments. The tensile strength of the PI-H, PI-M and PI-L filaments is 3.41, 1.65 and 0.88 GPa, and the Young’s modulus is 92.94, 40.71 and 9.43 GPa, respectively. The chemical compositions and structures of various PI filaments were characterized to explain the mechanical performance differences. The results show that the imidization degree, structural crystallinity and orientation have significant effects on the mechanical behaviors of PI monofilaments. The filament forces during the knitting process are simplified into straight tensile, loop tensile and abrasion actions, which have been tested and analyzed on PI monofilaments. A home-made simulative knittability analyzer was designed to test the knittability of the PI filaments. A hand flat knitting machine was used to verify the validity of the simulating methods and the constructed knittability analyzer. The PI-H, PI-M and PI-L filaments have poor, moderate and excellent knittability, respectively. The results also demonstrate that the simulating methods and the constructed simulative knittability analyzer are reasonable and efficient to evaluate the knittability of PI filaments.

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