Strength Of Rods Research Articles

Analysis of bond strength of CFRP cables with concrete using random forest model

The use of carbon fiber-reinforced polymer (CFRP) as an alternative to steel tendons in prestressed concrete is increasingly favored due to its non-corrosive properties. A critical aspect of this substitution is the bond strength required to effectively transfer pre-stressing force. This study investigates the bond strengths of CFRP rods, CFRP strands, and steel strands following ISO 10406 standards. The research comprehensively explores the influence of cable type, cable surface roughness, and concrete strength on bond-slip behavior. Experimental results were augmented using a data augmentation method to enrich the dataset, which facilitated the development of a robust random forest (RF)-based prediction model for bond strength. The RF model achieved strong performance metrics, including a mean absolute percentage error (MAE) of 17.9 % and an R-value of 0.97, underscoring its efficacy in predicting bond strength. Notably, the model highlighted the significant impact of cable surface roughness on bond strength relative to other parameters studied based on the feature importance analysis. This study contributes to advancing the understanding of CFRP's applicability as a steel tendon replacement in prestressed concrete structures. The findings emphasize the importance of surface characteristics in optimizing bond strength, providing valuable insights for structural engineers and material scientists.

Effects of stiffeners on anchor rod flexural strength in column base-plate connections

The present paper reports results of a numerical investigation of the mechanical behavior of a column base plate connection subjected to an axial compression force and a bending moment. A three-dimensional nonlinear model was developed, using the Cast3M software, and validated against experimental data. In addition, the material nonlinearity as well as contact conditions between the different components of the connection were thoughtfully considered. Based on the validated model, an extensive parametric analysis was conducted to investigate the effect of stiffeners on the forces in the anchor rods. The results clearly indicate that the design approaches that consider only the tensile strength of anchor rods while neglecting the bending moments can lead to a poor estimation of the forces applied to these rods. They also suggest that adding stiffeners provides additional strength and reduces the anchor rod bending in one direction. However, it is important to note that the stiffeners also induce an additional moment in the opposite direction. This could make the anchor rod more susceptible to biaxial bending with tension. Furthermore, this study proposes a new specific shape of stiffener is suggested (cbp5). It was concluded that the proposed shape of stiffeners allows a more uniform distribution of forces and avoids excessive stress concentrations, effectively prevents the biaxial bending in the anchor rod.

Investigating the effectiveness of concentric welded anchor rods in column base plate connections: A numerical and experimental study

This study presents a new strategy for column base plate connections, which involves the utilization of welded anchor rods positioned concentrically beneath the base plate, in alignment with the connected column. The objective was to remove the eccentricity between the anchor rods and the column, thereby excluding the base plate from the load-transferring chain. A numerical study was performed to compare the cyclic behavior and uplift response of the proposed connection with conventional column base connections. Additionally, different weld types were investigated to connect the anchor rods to the base plate, and their efficiency was evaluated based on a comprehensive dataset of nine tests on equivalent base-plate T-stub connections with different base-plate thicknesses, anchor-rod strengths, and anchor-rod diameters. The numerical results showed that using welded anchor rods could remove the pinching from the hysteresis loops, as the anchor rods can effectively resist cyclic loads in both compression and tension. Furthermore, removing the eccentricity between the anchor rods and the column enhanced the uplift stiffness by approximately 31 %. The experimental results indicated that the failure mode was the fracture of anchor rods for all specimens, while the other components remained elastic. The specimens with high-strength anchor rods showed a brittle failure accompanied by a sudden drop in load, which coincided with the fracture of anchor rod in the softened heat-affected zone. All developed weld types successfully withstood the ultimate tensile strength of anchor rods upon fracturing.

Experimental Study on Durability and Bond Properties of GFRP Resin Bolts.

Glass fiber-reinforced polymer (GFRP) anchor bolts are a new type of high-performance nonmetallic anchor with significantly higher tensile strength, a lighter weight, better corrosion resistance, and a lower cost than steel bars. Therefore, exploring the durability and bonding performance of GFRP anchor systems is of great importance for the structural design of protective engineering, especially in coastal environments. However, insufficient research has been conducted on the durability of GFRP resin bolts in seawater conditions, with no universal standard on the pullout testing of GFRP bolts. To study the durability and bonding performance of GFRP resin bolts, durability experiments were conducted in this work using artificial seawater, and the pullout tests were conducted using a large-scale concrete platform with different compressive strengths (21.2, 40.8, and 61.3 MPa). The results of the durability experiments indicated that the strength variations of the GFRP rods and epoxy resin materials in artificial seawater environments were less than 5%. Subsequently, indoor pullout tests using steel tubes filled with epoxy resin were conducted, and the test results indicated a critical anchor length value. Pullout tests of the GFRP resin bolts embedded in large-scale concrete blocks were also conducted with different strengths. According to the test results, all GFRP resin bolts embedded in the three concrete blocks with different compressive strengths exhibited rod fracture failure. The failure mode was not controlled via the compressive strength of the concrete blocks due to the high bonding strength between the resin and the rod, as well as between the resin and the concrete. Therefore, this GFRP resin anchor system could fully utilize the tensile strength of GFRP rods. This research offers significant practical value in verifying the safety and reliability of GFRP resin bolts in corrosive marine service environments, and it contributes to the application and development of GFRP materials in the engineering field, serving as a valuable reference for the structural design and further study of GFRP bolts.

XGBoost algorithm based estimation of near surface mounted FRP rod-to-concrete bond strength and failure mode

Using fiber-reinforced polymer (FRP) in reinforced concrete (RC) structures can mitigate the colossal repair costs due to reinforcing steel corrosion. Hence, FRP rod/bar is gaining wider applications in diverse RC structures as a partial or full replacement for steel rebar. The FRP rod-to-concrete interfacial bond is pivotal in transferring stresses from concrete to FRP rods. This study develops a novel prediction model to estimate the near surface mounted FRP rod-to-concrete bond strength as well as the failure type using five machine learning (ML) algorithms, namely, linear regression, decision tree, gradient boosting tree, random forest, and extreme gradient boosting (XGB). The performance of the developed models was compared with that of four bond strength design guidelines and one analytical model. A database comprising 416 experimental datasets was constructed and used for model training and validation. Based on statistical performance metrics, the precision of the XGB algorithm was superior to that of the other ML models, design guidelines, and analytical model. Feature importance analysis based on the SHapley Additive exPlanations theory and partial dependence plot was performed. The results show that the bond length had the most significant influence on the bond strength, followed by the tensile strength of the FRP composite, diameter of the FRP rod, compressive strength of concrete, and elastic modulus of the FRP composite. A graphical user interface was developed and offers a user friendly, free access, and simple tool for estimating the bond strength and failure type of FRP rods in concrete.

Evaluation of the strength performance of the steering system of hybrid off-road vehicles

In response to the strength performance requirements of the new energy Off road Vehicle steering system, this article analyzes and studies the strength performance and failure modes of the new energy Off road Vehicle steering rod based on a certain new energy Off road Vehicle model through simulation, bench experiments, and vehicle strength testing teams. Based on various vehicle misuse conditions, the force law of the steering rod under different vehicle driving conditions was analyzed, and a load spectrum for the steering rod strength bench test was developed to meet the actual vehicle usage conditions. The results indicate that the steering rod strength failure is mainly manifested as bending failure of the compression rod under alternating tension and compression conditions. Finally, based on the stability principle of the compression rod, the requirements for the strength performance index of the steering rod are proposed. The research results can provide certain technical support for the strength assessment of the vehicle steering rod.

Calculation of Fuel Rod Strength Under Steady-State Operating Condition

Calculation of Fuel Rod Strength Under Steady-State Operating Condition

Experimental and machine learning study on a novel high-performance hybrid steel-grout connector for cross-laminated timber panels under pre-yield cyclic loads

This work presents the results from quasi-static cyclic tests on a novel hybrid steel-grout connector for cross-laminated timber (CLT) panels. These test series are part of an experimental, analytical, and numerical research program to develop reliable and resilient connections for hybrid CLT mass timber structural assemblies. Each designated connector arrangement’s cyclic loading step path has been anchored to the yield point; this latter was obtained as the average of the seven replicates of monotonic tests. From the cyclic test results, mechanical characteristics, namely, the secant stiffness and the residual slip, have been evaluated and discussed. Furthermore, machine learning (ML) models based on deep neural networks have been developed to predict the mechanical characteristics of connectors in the function of the mechanical and geometrical properties of each material used. The developed ML models proved to be able to predict the connector’s stiffness and residual slip and were used to infer the effects of experimental variables on these performance parameters. It was shown that the steel rod and grout diameters are the most influencing parameters regarding the secant stiffness of connectors. As for the residual slip, it was found that the grout diameter and the steel rod strength class are the most influencing parameters. Furthermore, it was observed that a grout-to-rod diameter ratio of about 3.6 enables maximization of the secant stiffness while minimizing the residual slip. Lastly, polynomial equations were developed and found to be able to predict the secant stiffness and residual slip of connectors with a coefficient of determination of 0.99 and 0.98, respectively.

Improving Bond Performance of Near-Surface Mounted Steel Ribbed and Threated Rods in the Concrete

In this study, the experimental findings of twenty pull-out tests on the bond efficiency of threaded/ribbed steel rods used in near-surface mounting (NSM) are presented. On a groove (20 × 20 mm) that was slotted in one of the sides of a concrete block measuring 250 × 250 × 200 mm, a pull-out experiment was performed. The primary factors are the slot-filling materials (substrate concrete and epoxy paste), bonded length (equal to 5, 7, 10, and 15 times the rod diameter), surface pattern conditions (conventional ribbed reinforcing rebar and threaded bolt), use of nuts or rings welded at the free end of the bonded length, and use of straight or spiral wire welded along the length of the bonded length. The tested specimens' ultimate bond strength, slip, bond stress–slip response, failure patterns, stiffness, and ductility are recorded and assessed. The results showed that the ultimate bond strength and corresponding slip of ribbed rods cemented with epoxy were higher by 11.11% and 199%, respectively, than those of ribbed rods submerged in the substrate. Over the controls, all NSM epoxy-rods exhibited a greater ductility. As the bonded length increased, the ultimate bond strength of NSM rods fell by 12–32%. As the bonded length increased, the stiffness decreased. On the other hand, the ductility of NSM epoxy-rods increased as the bonded length increased. All applied schemes such as nuts, rings, longitudinal bars, and spiral bars significantly improved the ultimate bond strength (maximum = 25.93%) and corresponding slip (maximum = 166.67%) of NSM threaded rods as compared to the control ones.

Industrial testing of sand-oil mixtures based on natural oils.

Rods made of sand-oil mixtures have high strength and gas permeability, pliability, non-hygroscopicity, good fluidity, are easily knocked out of castings, and do not require more binder. The optimal addition of oil to sand-oil rod mixtures is 1,3‒1,5%. To increase the strength in the raw state, up to 2% of clay is added, and for the unhindered exit of the rod from the rod box, an addition of water in an amount of 2,5% is provided. Drying of these rods is carried out at a temperature of 200‒230 °C. Sand-oil rod mixtures are used in the manufacture of rods for critical castings in conditions of small-scale and large-scale production of castings. The technological disadvantage of sand-oil mixtures is the low strength in the raw state, and hence the need to use drivers, that is, they are laid out on special core plates, on which they enter the dryer. The low strength of sand-oil rods in the wet state is explained by the low surface tension of the oil. Due to the scarcity of cotton and linseed oils, it became necessary to replace them with more affordable and cheaper oils that have the ability to form strong films, and which will be competitive with sand-oil mixtures based on pure linseed binders. The aim of the work is to replace cotton and linseed oils with more affordable natural oils (sun-flower and rapeseed) without reducing the physical and mechanical properties in sand-oil core mixtures. The work was carried out by comparing it with a workshop core mixture, and a lignosulfonate-based core mix. The ultimate goal of the research was the possible introduction of a core composition based on sunflower and rapeseed oils into the produc-tion cycle

Impact dynamic response of large aperture space deployable antenna supporting structures based on a dual-scale model

This study investigates the joint damage patterns and changes in shape accuracy of large aperture space deployable antenna supporting structures subject to hypervelocity impacts from micro space debris. Based on the dual-scale method, a joint scale model is constructed for a hexagonal prismatic space deployable truss antenna supporting structure with an aperture of six meters and 37 modules. ANSYS/AUTODYN is used for the impact damage analysis, with an equivalent model of impact force integrating the structure's actual damage characteristics in the structure scale model. The dynamic response and deformation performance of the antenna supporting structure under impact velocities from 2.5 to 15.0 km/s, with spherical space debris of 2.5 mm and 5.0 mm diameters, impacting modular central points in both positive and negative directions, are analyzed. The results show that the primary damage to the joint scale model after impact includes cratering, perforation, punch failure, and joint failure. The debris diameter significantly influences joint damage and deformation of the bolt hole diameter. Additionally, the debris cloud post-impact significantly affects the vertical bar's inner wall, spalling the wall and reducing the rod's strength. As the impact point moves towards the structure's centroid, the antenna's overall response increases. With higher impact velocities, the antenna supporting structure's overall deformation first increases, then decreases. At an impact velocity of 12.5 km/s, the impact area of the structure gradually reduces post-impact. Our proposed joint damage forms and three-case damage classification (no effect, repairable, and joint failure) may serve as a valuable reference for designing structural protection and impact identification for space deployable antennas.

Development of PSS-bolt with high load and large deformation capacities

As mining migrates to deep levels, engineering disasters such as excessive deformation, rockburst and massive roof collapse occur frequently. It is important to develop rockbolts that have high load and large deformation capacities, which translates into high energy-absorption capacity, for ground support. This paper presents a piston self-swelling bolt (abbreviated as PSS-bolt) that utilizes steel stretching and frictional sliding to maximize the bolt’s energy absorption capacity. The structure design and working mechanism of the PSS-bolt are introduced. The influence of rod strength, piston length and tube shape on the load–displacement curves of the PSS-bolt was investigated. Laboratory and field static pull-out tests were carried out to optimize the piston length of the PSS-bolt. The test results show that when the piston length is 1350 mm, the load varies between 180 and 210 kN, the displacement can reach 500 mm, and the energy absorption capacity is 95 kJ. In addition, the bolt can reach 71.4% and 100% of its ultimate strength 12 h and 24 h after installation, respectively. The PSS-bolt presented in this paper has high force and large deformation capacities, which can provide a large energy capacity for ground support in high stress and large deformation conditions.

Hydrothermal aging of carbon fiber reinforced polymer rods intended for cable applications in civil engineering

Carbon fiber reinforced polymer (CFRP) composites have become increasingly popular due to their high strength-to-weight ratio and excellent mechanical properties. However, CFRP composites are susceptible to hydrothermal aging when used as cable applications in civil engineering, which can cause irreversible damage to their service performance. In this study, the effects of water immersion (water@60 °C), constant temperature and humidity exposure (95%RH@60 °C), and alternating hydrothermal environment (12h_60 °C&12h_25 °C@95%RH) were investigated on the property degradation of the CFRP rods. In addition, the water absorption behavior, and thermal and mechanical properties of the CFRP rods were systematically analyzed and compared. We found that elevated temperature and humidity accelerated the water absorption process, resulting in to the higher equilibrium moisture content and diffusion coefficient. Hydrothermal exposure led to maximum degradation in the tensile strength, three-point bending strength and short-beam shear strength of CFRP rods, with values reaching 4.8%, 17.4% and 24.3% in the water@60 °C, 95%RH@60 °C, and 12h_60 °C&12h_25 °C@95%RH conditions, respectively. Among the three mechanical performance properties analyzed, the tensile strength degradation of the CFRP rods was least affected by the three environmental conditions, primarily due to the tensile direction along the carbon fibers. In addition, the three-point bending and short-beam shear strength values of the CFRP rods showed the greatest degradation in the 12h_60 °C&12h_25 °C@95%RH environment. The long-term effects of the water molecules against the CFRP rods in the hydrothermal environment caused resin hydrolysis and debonding of the fiber-matrix interface, leading to degradation in three-point bending and short-beam shear strength. Additionally, the temperature alternating factor accelerated the degradation of the mechanical properties of the CFRP rods, and the mechanical properties of the CFRP rods declined most noticeably with alternating temperatures under the same moisture content conditions.

Research and Optimization of Machining Technology of Hammer Rod Subjected to Frequent Impact

In the oil exploration work, the hammer rod as the main component, due to the insufficient strength of the hammer rod, the hammer head falling off, the hammer body bending deformation and copper layer falling off and other problems often occur in the work, which not only affects the exploration progress but also causes huge economic losses. Aiming at the problem of insufficient strength of the hammer rod, through the analysis of the processing technology of the hammer rod and the working environment of the hammer rod, it is concluded that there are problems in the design of the hammer head, the material selection of the hammer body, and the processing technology of the copper layer. In this regard, the design of the hammer head is optimized, the depth of the inner hole of the hammer head is deepened, and the inner hole of the hammer head is changed to a taper hole; replace the 2CrMo alloy steel with higher strength as the main material of the hammer body, and add a heat treatment process after the rough turning to release the residual stress inside the hammer body; the processing process scheme for replacing the copper layer is attached to the surface of the hammer body by means of a hot-mounted copper sleeve. The improved hammer rod strength fully meets the needs of high-intensity impact work, shortens the exploration time, saves exploration costs, and makes great contributions to the exploration work.

Numerical modeling investigation of cross-laminated timber connections consisting of multiple glued-in rods

Glued-in rods are stiff and high-capacity connections that are used in timber structures. Regardless of the many advantages of glued-in rods, research on the glued-in rods in CLT is limited, especially on numerical modeling. This paper provides the numerical modeling principles, validation details, and parametric studies of glued-in rods embedded on the edge of CLT. The numerical modeling was performed on a 3D finite element basis, and the cohesive surface method was used to define the bond lines along the rods. To validate the numerical models, 24 replica experiments were performed and investigated the effect of the rod diameter and of the embedment length on the pull-out strength of rods embedded perpendicular, parallel, and on the boundary of two cross-wised layers. The numerical models were validated according to the maximum load, stiffness, as well as the failure mode of the glued-in rods. The numerical models showed high reliability in simulating the experiments and predicted the strength of the glued-in rods with a maximum of 4% difference. After validation of the numerical models, the parametric study covered the pull-out strength investigation of rods with 20, 24, and 30 mm diameter and anchorage lengths of 250, 350, and 450 mm embedded in the perpendicular, parallel, and on the boundary of cross-wised layers on the edge of 5 and 7 layer CLT panels. The findings showed that increasing the embedment length and rod diameter enhanced the pull-out strength of the glued-in rods, regardless of where the rod was positioned on the CLT's edge. Rods embedded perpendicular to the grain showed the highest pull-out strength, and two rods with 30 mm diameter and 450 mm embedment lengths reached 961 kN pull-out strength. Numerical models showed that for the same diameter and embedment length of two rods embedded on the parallel and on the boundary of two cross-wised layers reached 836 and 738 kN pull-out strength, respectively. Finally, A design equation is provided to determine the pull-out strength of the glued-in rods embedded in CLT based on the shear strength of the bondline.

Detection in RC Beams Damaged and Strengthened with NSM CFRP/GFRP Rods by Free Vibration Monitoring

This paper intends to deepen the topic of damage detection based on non-destructive tests (NDT) for the assessment of the dynamic behavior of RC beams damaged and strengthened both with near-surface mounted (NSM) Carbon and GlassFRP rods. The NSM strengthening with fiber-reinforced polymer (FRP) rods of damaged reinforced concrete (RC) beams is a viable alternative to the traditional strengthening with externally bonded (EB) FRP strips or sheets. In this paper, static tests were foreseen on RC beams to create cracking, and successively, the RC beams strengthened with NSM CFRP and GFRP rods were still investigated using free vibration tests at different loading levels until failure. The purpose of this research is to compare the response of two different types of strengthening of damaged RC beams based on the strength of CFRP and GFRP rods until failure modes. At different steps of loading, the behavior of beams under experimental vibrations has been monitored by frequency response function (FRF) diagrams. Finally, a discussion of the results is presented.

Influence of Surface Discharge on Resin Degradation in Decay-like Fracture of Composite Insulators

Composite insulators have gradually become the preferred approach for electrical insulation in power systems, especially in polluted areas. Composite insulators consist of three main components: the shed, rod, and end fitting. Insulators withstand mechanical stresses via rods that are composed of glass-fiber-reinforced epoxy (GFRE). However, regardless of the high tensile strength of GFRE rods, in real-life operation, abnormal fractures have frequently been reported all over the world, which substantially increase the risk of major accidents in power systems. Fractural accidents mainly consist of brittle and decay-like fractures, which exhibit rather different morphologies at the cross sections. Brittle fracture has been effectively eliminated, while the mechanism of decay-like fracture has still not been clearly revealed. In this study, surface discharge tests were applied to investigate the discharge influence on the degradation of GFRE. The test successfully simulated the composition variation of the rods in real-life composite insulators with decay-like fractures. Moreover, it confirmed that the distinction between the characteristics of brittle fracture and decay-like fracture stems from epoxy degradation due to hydrolysis and carbonization. In addition, the respective influences of the resin type, glass fiber type, and acid liquid immersion on the degradation process were probed, and the degradation mechanism proposed in this research was verified. Based on the results, measures for preventing the development of decay-like fractures in real-life operations were determined.

Joining different grades of low carbon steel to develop unsymmetrical rod to plate joints using rotary friction welding for automotive applications

The main objective of this investigation is to optimize the rotary friction welding (RFW) parameters for maximizing the tensile strength (TS) and weld interface hardness (WIH) of rod to plate joints of different grades of low carbon steel and analyze the effect of RFW parameters on TS and WIH of joints. AISI 1018 and AISI 1020 grades of low carbon steel are joined to develop unsymmetrical rod to plate joint using RFW for automotive applications. RFW being a solid-state welding (SSW) was employed to avoid the problems in fusion welding and development of unsymmetrical joints such as solidification cracking, wider heat affected zone (HAZ) and distortion. The RFW parameters specifically friction pressure/friction time (FRNP/FNRT), forging pressure/forging time (FRGP/FRGT) and rotational speed (rps) were optimized using response surface methodology (RSM) to maximize the strength and hardness of rod to plate joints. The three factor – five level central composite design (3 × 5 - CCD) consisting of less experiments was employed for designing experimental matrix. The tensile strength and microhardness tests were performed to evaluate mechanical performance of rod to plate joints. The numerical and graphical optimization techniques of RSM were employed to optimize the RFW parameters. The 3D response surfaces were developed which show the optimum conditions of RFW parameters. The effect of RFW parameters on TS and WIH of rod to plate joints was analyzed from 3D response surfaces. The microstructural features of optimized rod to plate joint were analyzed using optical microscopy. The fractured surfaces of rod to plate joints were analyzed using scanning electron microscopy. Results showed that rod to plate joints developed using FRNP/FRNT of 3.71 MPa/s, FRGP/FRGT of 3.71 MPa/s and RTSP of 19.99 rps exhibited higher TS and WIH of 452 MPa and 252 HV0.5 respectively. The higher TS and WIH of rod to plate joints is attributed to the evolution of finer grain structure in weld zone and narrower HAZ. The RTSP revealed greater effect on TS and WIH of rod to plate joints followed by FRGP/FRGT and FRNP/FRNT.

Parametric mathematical modeling and 3D response surface analysis for rod to plate friction welding of AISI 1020 steel/AISI 1018 steel

PurposeRotary friction welding (RFW) was used to solve the issues in fusion welding of rod to plate joints of low carbon steel (AISI 1020 steel/AISI 1018 steel) such solidification cracking, wider heat affected zone (HAZ), lower HAZ hardness, high residual stresses and distortion. The main objective of this investigation is to develop parametric mathematic models (PMMs), 3D response surface analysis to predict tensile strength (TS) and weld interface hardness (WIH) of rod to plate joints and correlate microstructure with TS and WIH of rod to plate joints.Design/methodology/approachThe three-factor x five-level central composite design (CCD) consisting fewer experiments was employed for designing experimental matrix. The tensile and microhardness tests were performed to evaluate mechanical performance of joints. The PMMs of TS and WIH of rod to plate joints were developed using polynomial regression equations incorporating the RFW parameters. The 3D response surfaces were developed using response surface methodology (RSM) to optimize RFW parameters for joining AISI 1020/AISI 1018 rod to plate.FindingsThe joints made using friction pressure/friction time (FRNP/FRNT) of 3.71 MPa/s, forging pressure/forging time (FRGP/FRGT) of 3.71 MPa/s and rotational speed (RTSP) of 19.99 rps exhibited higher TS and WIH of 452 MPa and 252 HV0.5. The PMMs accurately predicted TS and WIH of rod to plate joints at less than 1.5% error and 95% confidence. The RTSP revealed greater effect on TS and WIH of rod to plate joints followed by FRGP/FRGT and FRNP/FRNT. The superior TS and WIH of joints developed using optimized process parameters is correlated to the evolution of finer bainitic microstructure in weld interface due to the dynamic recrystallization of grains ensued by optimum frictional heating and plastic deformation.Originality/valueThe PMMs were developed for predicting TS and WIH of joints. The RFW parameters were optimized to enhance TS and WIH of joints. Low carbon steel rod to plates joints were developed using RFW for automotive applications without fusion welding defects. The microstructural features of low strength and high strength rod to plate joints were correlated to the TS and WIH of rod to plate joints.

Analysis of corrosion fatigue steel strength of pump rods for oil wells

Purpose is to perform analysis of corrosion durability (fatigue) of pump rod materials in terms of various chemically active simulation environments, and study influence of economically modified rare-earth impurity on corrosion fatigue strength of pump rod materials. Methods. 40 and 20N2M steel grades have been applied as well as experimental steel (ES). Steel of the conditinal ES grade has been melted within a pilot site of Institute of Electric Welding Named after E.O. Paton of the National Academy of Sciences of Ukraine. The steel was alloyed economically by means of a micro impurity of a rare-earth element (REE) being 0.03% of cerium; in addition, it contained comparatively low concentration of sulfur and phosphorus as well as minor concentration of dissolved hydrogen. The following has been used as simulation environments: 1) NACE environment (i.e. 5% NaCl solution which contained 0.5% СН3СООН, and saturated H2S; t = 22 ± 2°C; pH = 3.8-4.0); 2) 3% NaCl solution without hydrogen sulphide. Once every day, the environment was replaced to oxygenate it up to 8-10 mg/l concentration. Findings. Stability against sulfide stress-corrosion cracking (SSCC), hydrogen initiated cracking (HIC), and corrosion fatigue of steel of deep pump rods for oil industry has been studied. It has been defined that the experimental steel, modified economically by means of micro impurities of a REE, meets NACE MR0175-96 standard in terms of chemical composition as well as strength; in turn, 20N2M and 40 steel grades have high resistance neither to SSCC (threshold stresses are < 0.8 s) nor to corrosion fatigue attack; moreover, steel grade 40 has demonstrated low resistance to HIC (CLR > 6% and CTR > 3%). Originality. It has been identified that corrosion fatigue attack results from hydrogen penetration of steel initiating its cracking and hence destruction under the effect of alternating loads accelerated by the action of corrosive environment. Further, surface micro destructions, influenced by micro stresses, transform into large discontinuities and cracks with following macro destructions. Practical implications. It has been proved that high resistance to corrosion cracking can be achieved by means of refining of pump-rod steel of ferrite and perlite type using metallurgical methods, i.e. 0.01-0.03% REE microalloying.