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This study aims to resolve the problems of low precision, poor flexibility and unstable operation in the control performance of loading robots with long telescopic booms and heavy loads. Firstly, the kinematics and dynamics of long-arm heavy-duty robots are analyzed, and the dynamics model of a long-arm heavy-duty robot is established using the Lagrange method. A new power-hybrid sliding-mode approach law is proposed, and a hybrid force/position control strategy is used to control long-arm heavy-duty robots. The position control of long-arm heavy-duty robots uses a new sliding-mode adaptive control to improve the position accuracy of important joints, and PD control is used to force control the other joints. The two-stage telescopic arm is flexible and the long-arm heavy-load robot is simulated. The simulation results show that the long-arm heavy-load robot obtained using the improved sliding-mode adaptive control algorithm has good track-tracking and jitter-suppression effects. The new power-hybrid sliding-mode controller designed in this paper reduces the jitter amplitude of the end-effector of long-arm heavy-duty robots by 28.75%, 10.92% and 16.22%, respectively, compared with the existing new approach law sliding-mode controller. The simulation results show that the proposed power-hybrid reaching law sliding-mode controller can effectively reduce the amplitude difference of the end-effector. Finally, the force/position control strategy is combined with force-based impedance control, and the design process of impedance controller parameters is introduced, which provides a reference for the trajectory-tracking and vibration-suppression of end-effectors of long-arm heavy-duty robots.

Hydraulic fracturing is an essential technology for continuously developing non-renewable energy, such as oil and gas. The erosion of solid-liquid two-phase flow in hydraulic fracturing is a theoretical problem that needs to be solved urgently. In the current computational fluid dynamics-discrete element method (CFD-DEM) research, we present calculation methods for the collision restitution coefficients of quartz particle in Newtonian fluids (1 mPa⋅s) and non-Newtonian fluids (10 mPa⋅s and 20 mPa⋅s). The influence of power-law fluid is considered in the algorithm, and the problem of particle penetration in the CFD-DEM method is optimized. These experimentally obtained collision restitution coefficients are incorporated into the optimized CFD-DEM method to consider the influence of fluid viscous forces on particle collisions. The accuracy of the numerical simulation method in this paper is verified by particle settlement and erosion experiments. The elbow erosion experiment is then used to validate the correctness of the erosion simulation. Finally, the erosion behavior of the fracturing pipe (elbow and tee junction) under different conditions is analyzed. Nanyang Technological University This work was supported by Singapore Center for 3D Printing (SC3DP) [grant numbers 001163–00010], and State Key Laboratory of Robotics and Systems (HIT) [SKLRS-2023-KF-24].

In this study, pulse current electrodeposition (PC) was used to fabricate Ni-W-SiCthin films on mild steel plates, by utilizing a Watts-type Ni liquid that contained SiC nano-particles (NPs). The films deposited with 9 g/L SiC NP showed a smooth, finely granular, and remarkably homogeneous surface structure. All films showed SiC NPs equally distributed on the Ni-W-SiC-NPs surface regardless of the starting SiC NP content. The calculations revealed that the thicknesses of Ni-W-SiC-NPs films deposited at 9 and 12 g/L were ≈ 27.3 and ≈ 22.2 μm, respectively. Moreover, the crystallite sizes decreased as the SiC NPs’ level was changed up to 9 g/L. Film particles became smaller (≈66 nm) but enlarged to 85 nm when SiC NPs level was changed from 9 g/L to 12 g/L, respectively. The deposited layer demonstrated an increase in microhardness from 490.2 HV to 881.5 HV with the addition of SiC nanoparticles. However, the hardness values of the Ni-W-SiC-NPs films became lower as the SiC NPs levels were changed from 9 to 12 g/L. Additionally, films fabricated using 9 g/L of SiC NP level demonstrated a minimal corrosion current (equal to 1.536 ×10−6 μA/cm2). The corrosion resistance of the film deposited at 9 g/L was about 5.3 times that of the film obtained at 0 g/L, indicating an excellent corrosion resistance. The study can provide the corrosion protection for water or oil pipes, metal containers and agricultural machinery. Published version The research is supported by the National Natural Science Foundation of China (Granted no. 51974089), and the Daqing Guiding Science and Technology Project (Granted no. zd-2020-25).

The wetting properties of ALES (Ammonium lauryl ether sulfate), SLES (sodium lauryl ether sulfate), TD (dodecyl triethanolamine salfate) and SDS (sodium dodecyl sulfate) solutions and their adsorption capacities on coal dust surface were evaluated by surface tension, contact angle, sink time, wetting rate, and changes in the micromorphology and functional groups on coal surface. The results showed that the four surfactants share similar adhesion and spreading wettability, while they differ notably in immersion wetting. A water-surfactant-low rank coal (LRC) system was established using Materials Studio software and the Wender coal model; then quantum chemical calculations and molecular dynamics (MD) simulations were conducted. The results showed that ALES is of the widest relative concentration distribution range (25.25–60 Å), the largest overlap range (25 Å) and the largest diffusion coefficient (D = 0.318); NH4+ can easily penetrate the surfactant layer, which proves the strong modification ability of ALES to LRC. ALES/LRC/H2O has the lowest interaction energy and the most H-bonds, indicating that ALES is of a strong adsorption capacity. Based on the experimental data and simulation results, the integrated wettabilities of the four surfactants follow ALES＞SLES＞TD＞SDS, partially contributed by the hydrolytic cations and EO groups. This project was supported by the Key Program of the National Natural Science Foundation of China (Grant No. 52130411), the National Natural Science Foundation of China (Grant No. 51974299), and the Fundamental Research Funds for the Central Universities (2020CXNL10). Jian Gan was supported by the China Scholarship Council (Grant No. 202006420018).

Three-dimensional (3D) particles in composite materials often have sharp corners which cause complex stress singularities. In our current research, the 3D singular stress fields in the corner front vicinity of various revolution-shaped inclusions have been investigated using a specially developed novel singular inclusion corner element SICE. Numerical eigensolutions with both singular and non-singular terms for the 3D singular stress and displacement fields in the curvilinear coordinate system are transformed into the interpolation forms of the SICE. The robustness of the element stiffness matrix is reflected in the fact that it is established based on a local coordinate system attached to the rotation axis with arbitrary inclusion orientation. The singular stresses in the vicinities of revolution-shaped inclusions of various shapes, orientations and material properties are investigated. The benchmark examples show that the proposed SICE has excellent versatility and are very useful for micro-damage analysis of particle-reinforced composites. Agency for Science, Technology and Research (A*STAR) The authors acknowledge the support of the National Natural Science Foundation of China under Grant Nos.51975411 and 51365013, the Tianjin Natural Science Foundation of China under Grant No. 18JCYBJC88500, and the Personnel Training Plan for Young and Middle-aged Innovation Talents in Universities in Tianjin, China. The support of Singapore A*STAR SERC AME Programmatic Fund for the “Structural Metal Alloys Programme” (Project WBS 4070307.051) is acknowledged. Congman Wang acknowledges the support of Tianjin Graduate Research and Innovation Project under grant No. 2020YJSB072.

The discharge of industrial liquid waste continues to cause more and more environmental problems. The current research aims at developing a durable and highly efficient filter screen for oil-water separation. In this paper, hydrophobic nano-SiO

By considering the surface free energy effect, an analytical investigation on the fracture behaviors of nanoparticle-reinforced composites was performed in this study. The plastic zones ahead of the crack tips based on the Irwin model were introduced in our analysis, which has a significant influence on the fracture toughness of inelastic structures, especially for polymer and metal matrix composites. Take copper and aluminum nanoparticles as examples, comprehensive parametric studies were conducted to investigate the interaction between a Griffith crack and the nearby nanoparticle. It was found that for nanoparticles with the radius of less than 10 nm, apart from the mechanical property of the nanoparticle, the surface free energy effect plays a dominant role in determining the fracture behaviors of the nanoparticle-reinforced composites. Moreover, taking the surface free energy into account, a decrease in the plastic zone size is obtained, particularly for the crack tip nearer the nanoparticle.

Based on the numerical simulation method of the virtual crack closure technique (VCCT), an interference model was established to investigate the physical problem of two interacting cracks of different sizes in the welding zone of oil and gas pipelines. The obtained results of the current interference problem were compared with those of single crack case. Various crack configurations, such as different crack spacing and different crack sizes, were analyzed. The characteristic quantity fluid pressure load P during the crack propagation process, the peak value of the von Mises stress distribution field of the crack growth path, as well as the difference ∆Bx between the peak value of the magnetic induction intensity component at the crack and the value of the magnetic induction intensity component at its symmetrical position were calculated. The crack interaction scale factors, including γP, γMises, and γΔBx, were compared and analyzed. The numerical modeling results show that when the unequal-length double cracks interfere with each other, the cracks are more likely to propagate toward each other. The tendency of the double-cracks to propagate toward each other gradually weakens as the distance between the crack tips increases and is finally the same as that of single-crack cases. It was also found that the effect of large-sized cracks on small-sized cracks is greater than that of small-sized ones on large-sized ones. The numerical modeling results could be applied for the prediction and analysis of multicrack damage in oil and gas pipeline welds. Published version This research was funded by the Natural Science Foundation of Heilongjiang province, grant number LH2021E020.

Hip replacement femoral implants are made of substantial materials that all have stiffness considerably higher than that of bone, which can cause significant bone resorption secondary to stress shielding and lead to severe complications. The topology optimization design method based on the uniform distribution of material micro-structure density can form a continuous mechanical transmission route, which can better solve the problem of reducing the stress shielding effect. A multi-scale parallel topology optimization method is proposed in this paper and a topological structure of type B femoral stem is derived. Using the traditional topology optimization method (Solid Isotropic Material with Penalization, SIMP), a topological structure of type A femoral stem is also derived. The sensitivity of the two kinds of femoral stems to the change of load direction is compared with the variation amplitude of the structural flexibility of the femoral stem. Furthermore, the finite element method is used to analyze the stress of type A and type B femoral stem under multiple conditions. Simulation and experimental results show that the average stress of type A and type B femoral stem on the femur are 14.80 MPa, 23.55 MPa, 16.94 MPa and 10.89 MPa, 20.92 MPa, 16.50 MPa, respectively. For type B femoral stem, the average error of strain is −1682με and the average relative error is 20.3% at the test points on the medial side and the mean error of strain is 1281με and the mean relative error is 19.5% at the test points on the outside.

Fluctuated loadings from currents, waves and sea ground motions are observed on offshore steel pipelines, and they will result in small cracks to propagate continuously and cause unexpected damage to offshore/geotechnical infrastructures. In spite of the availability of efficient techniques and high-power computers for solving crack problems, investigations on the fatigue life of offshore pipelines with 3D interacting cracks are still rarely found in open literature. In the current study, systematic numerical investigations are performed on fatigue crack growth behaviours of offshore pipelines containing coplanar and non-coplanar cracks. Extended finite element method (XFEM) is adopted to simulate the fatigue crack growth. The qualitative validations of numerical results are made for certain cases with available experimental results. Parametric studies are conducted to investigate the influences of various important parameters on fatigue crack growth. The results will be helpful to assess the fatigue behaviours of steel pipeline with 3D interacting cracks. Ministry of Education (MOE) Nanyang Technological University Published version The authors would like to acknowledge the financial support for this project under Nanyang Technological University, Singapore’s Academic Research Fund (AcRF) Tier 1 Grant No. RG 168/16.

When cracks are initiated in a helical gear pair, the mesh stiffness and vibration response of the gear pair will be affected. Unlike previous studies on gear crack, in which only the transverse gear stiffnesses are calculated due to gear crack, or purely uniformly distributed gear crack are modelled, however, in the current study, an improved model is proposed for the calculation of mesh stiffness of helical gear system due to gear crack, in which the gear tooth stiffness, and gear foundation stiffness in both transverse and axial direction have been comprehensively considered. Two typical cracking cases, namely, the addendum extended crack and end face extended crack have been investigated. Furthermore, the analytical mesh stiffness calculation results are validated with the simulated results that obtained from finite-element method, both results show acceptable coincidence. Based on the proposed method, the dynamic model of the cracked helical gear system has been established to analyze the vibration response of the system with the propagation of gear cracks. The obtained results indicate that cracks in gear could cause substantial mesh stiffness reduction. The vibration response in time-domain experience sudden change when the cracked gear tooth is engaged in mesh, and the spectrum shows that the side frequency components become more abundant with higher amplitude under more severe crack conditions. The findings in our study have wide applications in vibration-based fault diagnosis of helical gear systems. This work is supported by the National Natural Science Foundation of China (Grant No. 51775265, 51775277), and the China Scholarship Council (202006830075).

The imbibition of water with surfactants, including spontaneous imbibition and forced imbibition, is of great significance for enhanced oil recovery (EOR) in tight sandstone reservoirs. Up to now, the migration behaviors of the water and the oil in pores of different sizes, as well as the mechanisms of both spontaneous imbibition and forced imbibition with different surfactants, have not been comprehensively addressed yet. This work first measured the oil-water interfacial tensions (IFTs) and the contact angles in oil-water-rock system with two types of surfactants, namely medium-IFT (0.1–10 mN/m) and low-IFT (0.001–0.1 mN/m) surfactants, at different concentrations to comprehend the functionalities of surfactants on oil recovery. Secondly, the pore size distributions of tight sandstones were determined by the high-pressure mercury intrusion (HPMI) and the nuclear magnetic resonance (NMR) technology to characterized the pores into three types (micropores, mesopores, and macropores) according to the pore sizes. Eventually, this work presented the oil recovery results in these three types of pores for spontaneous and forced imbibition using the two types of surfactants in water-wet tight core samples. Both spontaneous and forced imbibition results showed that the oil recoveries with surfactants were higher than those with brine, which was primarily attributed to the increased oil in the mesopores and the macropores. However, the addition of low-IFT surfactants apparently reduced the oil recovery in micropores, hence resulted in a lower oil recovery in comparison with the medium-IFT surfactants. It was also found that the oil in micropores contributed more than 50% of the oil recovery in the imbibition, except for the imbibition with low IFT, due to the high initial oil volume ratios in micropores; there could be a moderate IFT value (e.g., 0.1–1 mN/m) with the use of surfactants to obtain the highest oil recovery. Moreover, in comparison with the spontaneous imbibition, the forced imbibition could enhance the imbibition of water into the micropores but prevent the oil from being extracted from the mesopores and the macropores, which consequently led to a higher contribution of the micropores on oil recovery than that of the larger pores, especially the mesopores. This work was supported by National Major Science and Technology Projects of China (2016 ZX05058-003-010), National Postdoctoral Program for Innovative Talents (BX20190065), SPE Nico van Wingen Memorial Fellowship, National Natural Science Foundation of China (No. 51574086), Open Fund of Xi’an Key Laboratory of Tight Oil (Shale Oil) Development (XSTS-202001).

High-concentration solid-liquid two-phase flow causes particle erosion or accumulation at the sudden change positions of flow channels, resulting in pipe leakage and tool failure. In existing CFD-DEM methods, since the particle time sub steps cannot be infinitely small, local high-speed particles may penetrate each other. In the current study, the CFD-DEM method is optimized by adding the judgment condition of particle collision forces so that the DEM can automatically reduce and restore the particle time sub steps to obtain a precise solution, which avoids the penetration caused by the high-speed collision of particles. The fracturing fluid and quartz particles were used to conduct sedimentation experiments to verify the simulation results. The research on the two-phase flow in the reduced-diameter pipe that the newly proposed simulation model could predict the distribution, retention, and erosion of the dense high-speed particles, whose movement mechanism in high-speed two-phase flow have been logically explained. Agency for Science, Technology and Research (A*STAR) Funding for this work was provided by A*STAR SERC AME Programmatic Fund for the “Structural Metal Alloys Programme” (A18B1b0061), the National Natural Science Foundation of China (11972114) and the Natural Science Foundation of Heilongjiang Province in China (LH2020A001)

The high-speed flow of sand-carrying fracturing fluid through tee junctions causes severe erosion and affects the safety of the fracturing operation. This study improves the traditional computational fluid dynamics-discrete element method (CFD-DEM) to avoid the (dense particles) collision-leading abnormal penetration but also considers the influence of fracturing fluid viscosity on particle collisions. Then the tee junction erosion model under fracturing conditions is established and verified by experiments. The simulation analysis shows that with the increase of two-phase flow velocity and Stokes number, the dominant effect of particle motion and collision changes from viscous force to inertial force, and then the tee junction erosion position also changes. Nanyang Technological University This work was supported by Singapore Centre for 3D Printing (SC3DP) under the project “Acquisition and reconstruction of 3D CAD models for repair and re-engineering [grant numbers 001163-00010]; the National Natural Science Foundation of China [grant number 11972114]; and the Natural Science Foundation of Heilongjiang Province in China [grant number LH2020A00].

The discharge of industrial liquid waste continues to cause more and more environmental problems. The current research aims at developing a durable and highly efficient filter screen for oil-water separation. In this paper, hydrophobic nano-SiO2 and phenolic resin were used as raw materials. Hydrophobic SiO2 particles were fixed on the surface of the coated filter screen by heating and curing the anchored particles. The surface morphology, element composition, surface roughness and water contact angle of the prepared super hydrophobic SiO2/phenolic resin-coated filter screen were analyzed and discussed by using SEM, EDS, AFM, OCA and other instruments. The results showed that the prepared filter screen contained Si, O, C elements, which proved that the resin coating film had adhered to the filter screen surface. When the aperture of the phenolic resin-coated filter screen was 400 meshes, the drainage angle reached a maximum value of 153.8° ± 0.8°. When two layers of hydrophobic SiO2 phenolic resin were coated on the screen, the surface of the filter screen had a sufficient nano-porous structure and high roughness. The tests showed that the minimum water contact angle of the filter screen exceeded 150°, which indicated excellent chemical resistance. Through the analysis of oil-water separation efficiency of isooctane, gasoline, n-hexane, dodecane, edible oil, dichloromethane and trichloromethane, it was concluded that the lowest separation efficiency for edible oil was 97.2%, and the highest separation efficiency for n-hexane was 99.4%. After 50 cycles of separation, the oil-water separation efficiency for n-hexane was still at 99%.

Based on the virtual crack closure technique for finite element numerical simulation, a new magnetic structural algorithm is proposed to analyze fracture signals from nondestructive testing. As an example of solving engineering problems, this algorithm is employed to investigate the circumferential symmetric double-crack propagation in an X80 oil and gas pipeline welding zone. The material property of the welding zone is treated as bilinear kinematic hardening elastic–plastic, and the fluid pressure load on the inner wall of the pipeline weld is dynamically applied. In our magnetic structural multi-physics field model, every time when the incremental crack propagation is completed, the mesh is reconstructed. As a result, the crack propagation and magnetic field is analyzed cyclically. Six characteristic quantities (P, GI, Lg, CTOA, Bxᴾ, Msᴾ) in the process of crack propagation are computed, forming the magnetic structural algorithm for circumferential symmetric double-crack propagation. The results show that using the algorithm can judge the damage location and damage degree of the pipeline weld by calculating the crack growth process. The algorithm has high sensitivity which can distinguish the double cracks whose circumferential spacing is greater than or equal to 0.05 times of the circumferential arc length of the weld. When the circumferential spacing of double cracks is less than or equal to 0.4 times of the circumferential arc length of the weld seam, the single crack grows faster than the double crack due to the interference effect of double cracks, and the existence of double cracks inhibits the crack growth. Through this practical example, it is proved that the implementation of the proposed algorithm can provide a theoretical basis for guiding the actual safety assessment of engineering materials and structures containing microcracks. Agency for Science, Technology and Research (A*STAR) This work was sponsored by the National Natural Science Foundation of China (51607035, 11502051, 51774091) and China Postdoctoral Science Foundation (2018M641804, 2018T110268) and China Scholarship Council and Heilongjiang Youth Innovation Talents of Ordinary Undergraduate Colleges and Universities (UNPYSCT-2018046) and Heilongjiang Postdoctoral Research Foundation (LBH-Q18029) and Heilongjiang Postdoctoral Foundation (LBH-Z16040) and Science and Technology Project of China Petroleum and Chemical Industry Association (2017-11-04) and Research start-up fund of Northeast Petroleum University (rc201732) and Natural Science Foundation of Heilongjiang province (LH2019E018). The authors acknowledge the support of Singapore A*STAR SERC AME Programmatic Fund for the “Structural Metal Alloys Programme” (Project WBS M4070307.051).

Spalling is one common defect generally observed in railway wheels. The spalling phenomenon usually starts from the white etching layer (WEL) of the wheel due to cyclic loading. So far, the research work has not been systematically done on how the crack orientation influences the spalling behaviour. In our current study, the fatigue behaviours of the wheel steel with a surface crack under cyclic loading are investigated using extended finite element method. The significant parameters affecting the spalling behaviours such as the crack orientation and loadings are studied. Two key indices are used: the number of cycles required for the crack to reach the interface between the WEL and wheel steel material, and the crack propagation rate. The fatigue propagation trend in the WEL is validated by relevant experimental studies. Moreover, it is concluded from our results that a crack vertical to the surface has a greater propagation rate compared to other crack orientations.

Buckling of rods with cylindrical constraints is an essential problem in engineering and medical fields. Completely different to the buckling of classical Euler rods, the post-buckling modes for rods with cylindrical constraints involve highly complicated deformations and geometric configurations. In this paper, the rods are discretized into beam elements by finite element method, and the constraint relation between the rods and cylinders is described by gap element. A dynamic relaxation method for static buckling of compressed rods in cylinders is introduced. Numerical simulations have been carried out to investigate the effects of damping, element length, initial contact stiffness and penetration on post-buckling, etc. The characteristic buckling modes include deflection curves with single point, two points, three points and point-line-point contact. For the helical buckling, it is found that the transition section consists of two noncontact sections only, while the perturbed-helix section does not exist. Except the critical load and shear force of helical buckling, numerical simulation results are in good agreement with the analytical solution. By using the dynamic relaxation method, stable helical buckling modes can be obtained directly without undergoing sinusoidal buckling deformation under given compressive loads.

In this paper, we investigate the numerical simulation of the whole buckling transition process during unloading and loading of the compression load with quasi-static method. By using a smaller load increment step, longer calculation time and appropriate damping, this buckling transition is calculated. We find that the tubular deformation evolves from continue-line contact to bottom-top-point, continuous-point, spatial two-point, spatial one-point, planar one-point contact, and finally back to vertical configuration during unloading. This deformation sequence is reversed during loading. During the transition from planar one-point contact to spatial two-point contact deformation, the buckling shape and related physical quantities change abruptly. During unloading and loading, the dimensionless critical loads of the first three buckling deformations are basically the same. For the buckling deformations with spatial two-point and planar one-point contact, and for spatial one-point contact deformation, the critical loads of loading are about 5% and 50% larger than that of unloading, respectively. For the spatial one-point contact deformation with dimensionless length greater than 40 and other buckling deformations with dimensionless length greater than 20, the critical loads obtained in the buckling process remain almost unchanged. It is noted that since the friction effect is not considered in our numerical simulation, the critical loads obtained are the minimum values in the process of buckling transition. The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China (11502051, 51607035, 51674088), China Postdoctoral Science Foundation (2018M641804), Heilongjiang Youth Innovation Talents of Ordinary Undergraduate Colleges and Universities (UNPYSCT-2018046), Heilongjiang Postdoctoral Research Foundation (LBH-Q18029) and Postgraduate Innovative Research Project of Northeast Petroleum University (JYCX_CX04_2018).

The failure of thickeners at high temperature results in gelled acid acidification fracturing. To solve the problem, 8 kinds of polymers were synthesized by free radical polymerization of aqueous solution using AM, AMPS, NaAMPS, MAPTAC, DTAB and NVP as raw materials. The polymer was characterized by infrared spectroscopy and viscosity-average molecular weight, and the temperature resistance, rheology, salt resistance and shear resistance of the polymer solution were compared, and the mechanism was analyzed. The results show that the viscosity of GTY−2 is 181.52 mPa·s, and the viscosity loss rate is 56.89% at 180 °C and 100 s−1, and its temperature resistance is the best. Meanwhile, the viscosity retention rate of GTY−2 is 84.58% after 160 min shear, showing the strongest shear resistance. The viscosity loss rate of GTY−1 in 20% hydrochloric acid solution is 80.88%, and its acid resistance is stronger than that of GTY−2. Moreover, due to the amphiphilicity of DTAB, the molecular hydration film becomes thicker, and the salt resistance of GTY−2 is lower than that of GTY−1. The experimental results show that GTY−1 and GTY−2 have good temperature resistance, salt resistance, acid resistance and shear resistance, and can be used as thickeners for acid fracturing with thickened acid to improve the effect of acid fracturing under high temperature conditions. Published version The authors are grateful for the National Natural Science Foundation of China (No. 51574089).

For successful fabrication of components using additive manufacturing techniques such as powder bed fusion (PBF), directed energy deposition, and laser cladding of an alloy on to a substrate of a dissimilar one, an interpenetrating interface morphology is essential for a good interface strength. The physical mechanisms behind the formation of different solidified interface morphologies after single track laser PBF of Inconel 718 powders on to the 316L austenitic stainless stress substrate were investigated by recourse to numerical simulations, which combine micron-scale fluid dynamics and solidification protocols with nanosecond-level thermal diffusion processes. These were complemented with parametric experiments to verify the simulations. Results show that an interface with the “fish scale” morphology can occur under certain combinations of process parameters, and because of the combined actions of recoil pressure, Marangoni forces, surface tension and melt pool shape. Three distinct morphologies that depend on the melt pool width and depth are identified and the interfacial areas for each of them are computed. The influence of the processing conditions that not only dictate the geometric parameters of the melt pool but also the degree of alloying and the resulting grain morphology within the interface microstructure were elucidated. Agency for Science, Technology and Research (A*STAR) Funding for this work was provided by A∗STAR SERC AME Programmatic Fund for the “Structural Metal Alloys Programme” (A18B1b0061).

A lot of research work has been done on the buckling of compressed rods with connectors in cylinders. However, very limited investigations on the buckling of a twisted sucker rod with centralizers in the progressing cavity pump well has been carried out so far. In our present study, a numerical computational strategy is proposed to investigate this highly important buckling problem. Firstly, a twisted sucker rod with or without centralizers is selected for finite element simulation and calculation, which verifies our solution method. Following that, the effects of centralizer number, centralizer spacing, sucker rod diameter and tubing diameter on the critical torque are analyzed. It is found that the clearance ratio, i.e., the ratio of the clearance between the centralizer and the tubing to the clearance between the sucker rod and the tubing, is the only factor that affects the dimensionless critical torque. With a centralizer, the critical rod length is usually reduced by 25% compared to the case of a rod with hinged restraint. The authors would like to acknowledge that the work described in this paper was funded by National Natural Science Foundation of China (No. 51774093, 51904075, 11502051), Natural Science Foundation of Heilongjiang Province of China (No. LH 2020A001), China Postdoctoral Science Foundation (No. 2019M661248) and Postdoctoral Foundation of Heilongjiang Province of China (No. LBH-Z19124).

Three-dimensional diamond-like defects with circumferential V-shape corner fronts are often contained in engineering materials. In this paper, generalized stress intensity factors are calculated for this type of defect using a modified advanced finite element method. A super corner front element model in the global coordinates is established to capture the stress singularities along the circumferential corner front. Three-dimensional numerical series eigen-solutions in the element have been transformed from asymptotic expressions in the local curvilinear coordinates. The element is suitable for a sharp V-shape corner with arbitrary opening and inclination angle. Singular stress fields near various shapes of diamond-like defects are systematically investigated. The interaction of an embedded defect with free surface or another identical defect is also investigated. The numerical results can be used as stress intensity parameters to predict fatigue strength at circumferential corner front of a diamond-like defect. Agency for Science, Technology and Research (A*STAR) The authors acknowledge the support of National Natu-ral Science Foundation of China under grantno. 51975411 and 51365013, the Natural Foundation of Tianjin, China, under grantno. 18JCYBJC88500, and the Personnel Training Plan forYoung and Middle-aged Innovation Talents in Universi-ties in Tianjin, China. The work was finished when X. CPing visited Prof. Z.M. Xiao at School of Mechanical andAerospace Engineering in Nanyang Technological Uni-versity as a visiting Scholar. The support of SingaporeA*STAR SERC AME Programmatic Fund for the“Struc-tural Metal Alloys Programme”(project WBSM4070307.051) is also acknowledged.