Steel Interfaces Research Articles

Experimental study of interface performance between calcareous sand and steel pile with different surface roughness and temperatures

The shear characteristics of calcareous sand, a typical deposit in the South China Sea, could significantly influence the safety and stability of marine structures. Previous studies showed that many factors, such as temperature and surface roughness, could affect the mobilized shear strength between the calcareous sand and steel surface. Therefore, studies on the shear behaviors of the steel-sand interface under various thermal conditions are necessary. In this study, a new multifunctional sediment shear system has been developed and employed to investigate the shear performance. For this purpose, steel plates with different surface roughness were tested under various normal stress values, shear displacement rates and temperatures. Shear strength and deformation were analyzed using test data to reveal the relationships between several factors and the shear strength of the steel-sand interface. Results from test demonstrate that the interfacial shear strength on rough steel interfaces will be 1.45–3.15 times higher than that on the smooth steel interface. Besides, the shear strength of the interface rises significantly with the roughness of the steel plate. The peak friction angle increases rapidly at the start and then tends to stabilize with the increase of normalized roughness. The interfacial shear strength could be enhanced in low-temperature environments but would reduce in high-temperature environments, e.g. the energy pile, particularly under low normal stress. The shear displacement rate also has a positive effect on the interface shear strength for most cases in this study. Finally, a new nonlinear function is proposed to describe the peak friction angle ratio of foundation interface to consider the effect of temperature and shear displacement rate reasonably.

Study on the Superlubricity Behavior of Ions under External Electric Fields at Steel Interfaces.

Realizing macroscopic superlubricity in the presence of external electric fields (EEFs) at the steel interfaces is still challenging. In this work, macroscopic superlubricity with a coefficient of friction value of approximately 0.008 was realized under EEFs with the lubrication of LiPF6-based ionic liquids at steel interfaces. The roles of cations and anions in the superlubricity realization under EEFs were studied. Based on the experimental results, the macroscopic superlubricity behavior of Li(PEG)PF6 under EEFs at steel interfaces is attributed to the strong hydration effect of Li+ cations and the complete reactions of anions that contributed to the formation of a boundary film on the appropriate surface. Moreover, the reduction in the number of iron oxides in the boundary film on the disc was beneficial for friction reduction. We also provide a calculation model to describe the relationship between the hydration effect and the optimal voltage position, at which the lowest friction might occur. Ultimately, this work proves that macroscopic superlubricity can be realized under EEFs at steel interfaces and provides a foundation for engineering applications of superlubricity in an electrical environment.

Experimental and theoretical study on mechanical behaviors of CFRP–steel interface

The performance of the CFRP–steel interface is crucial to the reinforcement efficiency of the steel structures strengthened by using externally pasted CFRP sheet method; while it is influenced significantly by adhesive properties and geometrical characteristics of joints. The present study aims to optimize the adhesive layer of the CFRP–steel interface and establish a theoretical model of predicting the interfacial behaviors of the optimized CFRP–steel joints. A commercially available adhesive was modified by addition of Nano-SiO2 ranged from 0 to 7wt% to ascertain the optimal content of Nano-SiO2. A series of tensile tests were carried out on dog-bone adhesive specimens, single-lap shear specimens and CFRP–steel double-lap joints to obtain the mechanical properties of the adhesive at different content of nanofiller and the corresponding bond–slip laws in the unmodified and modified CFRP–steel interfaces. Accordingly, theoretical models were derived to predict the load capacity of the joints and the bond stress distribution along the CFRP–steel interface during different loading phases. The results show that the mechanical properties of the adhesive are improved with the addition of nano-SiO2 up to 1.4 wt%. When the content of nano-SiO2 rises from 1.4 to 7 wt%, the tensile and shear strengths as well as the tensile modulus decline gradually whereas the ductility keeps growing with a lower growth rate. These indicate the nano-SiO2 content of 1.4 wt% is favorable. Both the peak stress and the load capacity of the CFRP–steel joint increase with the adhesive thickness varying from 0.5 to 1 mm. The bond–slip law of the unmodified CFRP–steel interface can be simplified to be bilinear, regardless of the adhesive thickness and curing duration. In contrast, the modified interface presents a trilinear curve due to the special plastic plateau caused by the filling of nano-SiO2. Consequently, a larger fracture toughness and a higher load capacity can be reached by the optimized joints. The theoretical results are in agreement with the experimental phenomena and results. The modified adhesive is beneficial to utilize the CFRP material better and improve the reinforcement efficiency.

Oxidation damage and interfacial failure of dissimilar metal welds containing ferritic heat resistant steels

The ex-service steam tubes containing dissimilar metal weld (DMW) between high Cr ferritic steel T91 and austenitic stainless steel TP347H and the ex-service steam tubes containing DMW between low Cr ferritic steel G102 and austenitic stainless steel TP347H were obtained from coal-fired thermal power plants in China, and their microstructures at the nickel-based weld metal (WM)/ferritic steel interfaces and oxidation characteristics were investigated. After operating for 15,000 h at steam temperature of 541 °C and steam pressure of 17.5 MPa, a G102/TP347H DMW failed along the WM/G102 steel interface, which was a dangerous premature failure mode without obvious plastic deformation. This interfacial failure was attributed to the interaction between oxidation and cracking along the interface, where fracture appeared to be related with the strain concentration at the interface. Oxide notch along the WM/G102 steel interface was the precursor of premature interfacial failure of DMW involving G102. For the DMW involving high Cr ferritic steel T91, ferritic steel side could form a Cr-rich passive film during service and thus would not be further oxidized after operating for 67,000 h at steam temperature of 541 °C and steam pressure of 3.5 MPa. It was concluded that oxidation played a more important role in failure of these DMWs, and retarding the development of oxidation and avoiding the interfacial oxide notch would dramatically improve the service performance of steam tubes containing DMWs.

Influence of surface texture on sand–steel interface strength response

The surface texture of the interface material plays a significant role in the shear behaviour of soil–continuum interface. This study investigates the influence of surface texture of steel on the shear behaviour of sand–steel interface using different types of steel counterfaces with distinct texturing patterns. The patterns include concentric circular asperities, square-tiled surfaces with equally spaced individual asperities and ruled ribbed asperities oriented parallel, perpendicular and at an angle to the shear direction. The results show that the texturing pattern of the steel counterface significantly affects the shear strength of the sand–steel interface. The peak and residual interface friction angles for the sand–steel interfaces with different texturing patterns (with identical asperity height and spacing) varied from 26·6° to 37·5° and 14·2° to 28·7°, respectively. Moreover, the surface with ruled ribs/asperities inclined at right angle to the shear direction shows the maximum interface shear strength among all the texturing patterns tested. The findings presented herein are imperative for a realistic assessment of the performance of geotechnical structures involving soil–steel interaction.

Influence of Dilation on the Strength of Sand – Steel Interfaces

In this paper the sand-steel interface behaviour is analysed on the basis of frictional state theory. It is shown that for a small stress level the influence of dilatancy is fundamentally similar for sand-steel and sand-sand behaviour for a direct shear test. The use of the new parameter describes the influence of surface roughness on stress-dilatancy relationship. The peak strength of sand-steel is analysed. Values of the new parameter grow with normalised roughness for smooth surface and are constant for intermediate and rough surfaces. It is also shown that values of normalised friction coefficient obtained theoretically are similar with those shown in literature.

Chalk–steel interface testing for marine energy foundations

To aid deployment and recovery of tidal stream generators, gravity-based foundations rather than fixed-foundation alternatives are being considered in areas where the foundation may be placed directly onto an exposed rock seabed. Horizontal loading is usually critical in such applications, therefore specific knowledge of the interface friction between the foundation (made of steel or concrete) and seabed is important for design. This paper presents results of an interface testing programme of chalk–steel interfaces carried out utilising a computer-controlled interface shear tester under constant normal stress conditions against steel of different roughness. Results indicate that interface strength is significantly affected by the normal stress applied, as interface strength degrades for normal stress levels in excess of 30% of the chalk's tensile strength (∼300 kPa). Large-displacement tests revealed a tendency of the ultimate interface frictional resistance to drop to values very similar to that of the basic chalk–chalk interface at normal stresses up to 300 kPa, whereas substantial additional degradation was noticed for normal stresses above 700 kPa. At low normal stresses and displacements the behaviour of the chalk–steel interface was captured by an alpha type approach related to the rock unconfined compressive strength, which has been developed for other higher strength rock types.

Influence of Matric Suction and Counterface Roughness on Shearing Behavior of Completely Decomposed Granitic Soil and Steel Interface

The interface can be defined as the zone in which the transfer of stresses occurs between soil and structure. The behavior interface is significantly influenced by stress state variables. In this paper, the influence of matric suction and counterface roughness on the interface shearing behavior was examined by conducting a series of suction controlled direct shear test on the interface formed between completely decomposed granite soil and steel specimens. Experimental tests were performed on two different types of soil–steel interfaces under different stress state variables. Test results show that matric suction has a significant influence on the interface shear behavior. The counterface roughness influences the dilative-contractive behavior of the interface. The critical interface shear strength at specific counterface roughness and net normal stress is controlled by the matric suction. The experimental results are compared with an analytical model that considers the influence of suction and dilation on apparent interface friction angle. The analytical model works reasonably well for predicting the unsaturated soil–steel interface shear strength under different stress state variables.

Numerical–experimental assessment of roughness-induced metal–polymer interface failure

A numerical–experimental method is presented to study the initiation and growth of interface damage in polymer–steel interfaces subjected to deformation-induced steel surface roughening. The experimentally determined displacement field of an evolving steel surface is applied to a numerical model consisting of a polymer coating and interface layer. The measured displacement field is obtained with a Finite Element based Digital Image Correlation method.The resulting simulations provide novel insights into the mechanical behaviour of the polymer–steel interface during interface roughening. The appearance of local hills and valleys on the evolving steel surface results in local bands of intensified stress in the polymer layer. These localized deformation bands trigger interface damage, which grows as the surface deformation increases. Polymer ageing initially delays the initiation of interface damage. However, for increased polymer ages the average interface damage increases. Likewise, the critical strain, at which the interface integrity is locally compromised, decreases.The presented method allows for a detailed study of the interface integrity during deformation-induced steel surface roughening. With properly identified material parameters, it becomes possible to tailor the polymer–steel material properties to minimize interface damage during production and storage of cans or canisters, e.g. for food and beverages.

Cathodic delamination: Quantification of ionic transport rates along coating–steel interfaces

So-called cathodic delamination is one of the major modes of failure for organic coatings immersed in electrolyte solutions (e.g. seawater). Cathodic delamination occurs as a result of the electrochemical reactions, which takes place on a corroding steel surface. This means that reactants must continuously be transported from the bulk solution to the cathodic areas. The transport of sodium ions from a defect in the coating to the cathodic areas is generally considered the rate-determining step for cathodic delamination because the transport of oxygen and water through the coating is sufficient for the corrosion processes. In this work, a novel practical method, which allows direct estimation of the apparent diffusion coefficient of sodium ions in the ultrathin aqueous layer at the coating–steel interface, is described. The apparent diffusion coefficients estimated are of similar magnitude as previously reported values and show an acceptable repeatability. The method was used to obtain the apparent diffusion coefficients of sodium ions in the coating–steel interface for three commercial inert-pigmented epoxy coatings. The delamination rates predicted using the apparent interfacial diffusion coefficients and Fick's second law, under the assumption of a transport-controlled mechanism, show qualitative agreement with the observed delamination rates in 0.5 M sodium chloride. This confirms that the rate-determining step of cathodic delamination is the transport of sodium ions along the coating–steel interface.

Cathodic delamination: Quantification of ionic transport rates along coating–steel interfaces

So-called cathodic delamination is one of the major modes of failure for organic coatings immersed in electrolyte solutions (e.g. seawater). Cathodic delamination occurs as a result of the electrochemical reactions, which takes place on a corroding steel surface. This means that reactants must continuously be transported from the bulk solution to the cathodic areas. The transport of sodium ions from a defect in the coating to the cathodic areas is generally considered the rate-determining step for cathodic delamination because the transport of oxygen and water through the coating is sufficient for the corrosion processes. In this work, a novel practical method, which allows direct estimation of the apparent diffusion coefficient of sodium ions in the ultrathin aqueous layer at the coating–steel interface, is described. The apparent diffusion coefficients estimated are of similar magnitude as previously reported values and show an acceptable repeatability. The method was used to obtain the apparent diffusion coefficients of sodium ions in the coating–steel interface for three commercial inert-pigmented epoxy coatings. The delamination rates predicted using the apparent interfacial diffusion coefficients and Fick's second law, under the assumption of a transport controlled mechanism, show qualitative agreement with the observed delamination rates in 0.5 M sodium chloride. This confirms that the rate-determining step of cathodic delamination is the transport of sodium ions along the coating–steel interface.

The heterogeneous electrochemical characteristics of mild steel in the presence of local glucose oxidase—A study by the wire beam electrode method

The influence of glucose oxidase (GOD) activity on the heterogeneous electrochemistry at artificial biofilm/mild steel interface was first characterized by the wire beam electrode (WBE) method. Potential/current distribution maps show that a cathodic zone can be formed at the GOD capsule site. The cathodic zone is gradually weakened due to the gluconic acid production in seawater. When GOD capsule is confined on rusted WBE surfaces, the formerly formed anodic zone is gradually changed into cathodic zone, in the presence of glucose. The novel device developed in our laboratory demonstrates powerful applications in heterogeneous electrochemistry measurements at the biofilm/mild steel interfaces.

Ferrite transformation from oxide–steel interface in HAZ-simulated C–Mn steel

Abstract In steel weld metals and their heat affected zones, acicular ferrite or intragranular ferrite developed on selected oxide inclusions within prior austenite is a key to refining the microstructure and hence improving the toughness. In this study, to obtain a better understanding of the mechanism of the intragranular ferrite formation, different oxides were deposited onto C – Mn steel by a physical vapor deposition process, and ferrite formation was examined at the different oxide – steel interfaces after an HAZ-simulated thermal cycle. TiO, MgO, CaO and Al2O3 were deposited on C – Mn steel containing 0.16% C and 1.4% Mn and then they were heated up to 1623 K and cooled down at a cooling rate of 20 K s−1. Allotriomorphic ferrite was found to develop from TiO and MgO, while no allotriomorphic ferrite but Widmanstätten ferrite formed from CaO and Al2O3. Electron backscatter diffraction pattern analysis indicates that the allotriomorphic ferrite growing from the oxide has a specific orientation relationship either with the oxide or with prior-austenite. In the former case, the ferrite seems to be aligned so as to minimize the misfit against the oxide, implying that the likelihood of ferrite formation can be increased by the oxides having a good lattice match with ferrite. Manganese depletion was identified in the vicinity of TiO, but it is concluded that, although it encourages ferrite formation from the oxide, it is not a critical factor for the ferrite formation because of the fact that the ferrite formation was even found from TiO in manganese-free steel. First principles calculation indicates that the interfacial energy between oxide and steel is reduced when the magnesium in MgO is replaced by titanium, which suggests that the ferrite formation from TiO is also affected by the chemical effect of titanium.

Cyclic shear stress degradation and post-cyclic behaviour from sand–steel interface direct shear tests

The sliding interaction between sand and structural materials is involved in many geotechnical applications and is particularly important for the derivation of the shaft capacity of piles. Such interaction develops principally at the interface between the sand mass and the structural surface, and the comprehension of such interaction can be analysed through soil–structure interface tests. In particular, by using a modified version of the interface direct shear apparatus, that is, the constant normal stiffness direct shear apparatus, the friction characteristics of the interface and the role of the soil deformability on the experimental results can be studied. This paper focuses on the stress degradation occurring in these types of tests when cyclic loading is applied on sand–steel interfaces. Also, the post-cyclic response is analysed and compared to the response under monotonic conditions.Key words: interface, sand, shear stress, cyclic loading, stress degradation.

Enhancement of TiC/stainless steel interfaces by N+-implantation

TiC films were deposited on stainless-steel substrates by the reactive radio-frequency magnetron sputtering technique, and N+ implantation were performed to enhance the quality of the TiC/stainless steel interface. The deposition rate of the TiC film increased linearly with increasing applied radio-frequency power, and it decreased with increasing partial-pressure ratio of the sputtering gas to the reactive gas. The stoichiometry of the TiC films and the interfacial depth profiles of the TiC/stainless steel heterostructures were investigated by Auger electron spectroscopy measurements. Removal of the oxygen at the TiC/stainless steel interface due to N+-implantation and annealing were observed. These results indicate that the N+-implanted TiC thin films grown on stainless-steel substrates can be used for advanced engineering ceramic applications.

Analysis of oxide film on stainless steel via position-sensitive atom probe

Thermal oxide films formed on the surface of a type 316 stainless steel were atomically characterized by a recently built position-sensitive atom probe (POSAP). Oxidation on the clean field evaporated surface was performed at temperatures of 350 °C for 5 min, 475 °C for 1, 5, and 15 min, and 600 °C for 5 min in oxygen at a pressure of 10−4 Torr. The POSAP analysis has clarified that the oxide–steel interfaces at 350 °C for 5 min, and 475 °C for 1 and 5 min are very sharp, while the interfaces at 475 °C for 15 min and 600 °C for 5 min have subnanometer level roughness. In spite of the difference in oxidation temperature and time, the oxygen concentration in the oxide films is in the range from 35 to 50%, and Ni and Mo tend to segregate to the oxide–steel interface. Furthermore at 475 °C for 15 min and at 600 °C for 5 min, Ni and Mo segregate to the top surface region as well as to the interface. The oxide film has a triplex structure consisting of the top surface region being chromium rich oxide, the inner region being iron rich oxide, and the interface being chromium rich oxide. The Mo segregation is localized in a few nanometers in size and appears to inhibit the oxide formation in those segregated regions.

NEUTRON RADIOGRAPHY OF COMPOSITE MATERIALS-A COMPARISON STUDY OF ADVANCED NDE IMAGING TECHNIQUES

A comparison study of advanced nondestructive evaluation (NDE) imaging techniques demonstrates the merits of using neutron radiographs to characterize defects, particularly cracks, in fiberglass epoxy composites with stainless steel interfaces. Neutron radiographs of mockups of the arm pivot sockets used on the Hard Upper Torso of the Extravehicular Mobility Unit Spacesuits showed hairline cracks not detectable by x-ray radiography, x-ray computed tomography or ultrasonic C-scan images. The ultrasonic C-scans were more effective for detecting disbond and delamination defects associated with the composite material and stainless steel interface. A conceptual method of integrating nondestructive evaluation images from various techniques to generate mosaic images is introduced for enhancing detectability of flaws by using the optimum features of each NDE imaging technique

Analytical Model for Sliding Behavior of Teflon‐Stainless Steel Interfaces

An analytical model is proposed to describe the interfacial sliding characteristics of Teflon and stainless steel based on experimentally observed quasi‐static and dynamic sliding characteristics. The effects of normal pressure, sliding distance, normal pressure history, sliding velocity, sliding velocity history, normal pressure rate, sliding work, etc., are included. The dependence of the dynamic friction force on both the normal pressure and the sliding velocity is uncoupled in this formulation. The dynamic friction force is determined by multiplying the quasi‐static friction force by an amplification factor. The amplification factor is a pure function of sliding velocity. The proposed model is validated by a quasi‐static test and a dynamic sliding test. In the quasi‐static verification test, the applied normal contact pressures are changing during sliding. For the dynamic validation test, the Teflon‐stainless‐steel interfaces are subjected to varied normal pressures and sliding velocities. Very good agreement between the predicted and the experimental results is obtained.

Quasi‐Static and Dynamic Sliding Characteristics of Teflon—Stainless Steel Interfaces

This paper describes an experimental program of study on the sliding characteristics of Teflon‐stainless steel interfaces. The effects of normal pressure, sliding distance, normal pressure history, sliding velocity, sliding velocity history, normal pressure rate, and sliding work are identified and interpreted. Test results show that the friction force is independent of the normal pressure history and the sliding velocity history, and is also irrelevant to the normal pressure rate. In addition, the dependence of dynamic friction force on the normal contact pressure and the sliding velocity can be uncoupled. The dynamic friction force can be determined by multiplying the quasi‐static friction force by an amplification factor. The reciprocal of the quasi‐static friction coefficient is linearly dependent on the normal pressure only, and the amplification factor is solely a function of velocity. Moreover, the dynamic friction force decays during sliding, and the decaying is a function of excess dynamic slidin...

The Division of Heat and Surface Temperatures at Sliding Steel Interfaces and Their Relation to Oxidational Wear

Experiments are described in which a pin-and-disk wear machine has been used to measure the division of heat (δexpt) at the interface between the pin and disk, together with the temperature of the surface of the pin (T8), for low-alloy, medium-carbon steel specimens sliding against each other, without lubrication, at a speed of 5.11 m s−1 and under various loads (5.8 to 29.4 N). The equilibrium mild wear rates (wexpt) and frictional forces (F) were also measured. An analytical expression is deduced for the division of heat (δtheory) in terms of a surface model consisting of N asperities of approximately the same individual area of contact upon which an oxide film of thicknessζis situated. The various combinations of N andζwhich provide good correlation betweenδtheory andδexpt, and the values of the temperature of the real areas of contact (T0) which are associated with N,ζand T8, have been fed into a computer program designed to produce the Oxidational Activation Energy from an expression for the wear rat...