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[Display omitted] • A completely non-assembly steerable grasper in titanium was fabricated by additive manufacturing. • Miniature lattice structures were used as compliant flexures. • Deflection tests of different lattice designs were performed as characterization. • Lattice flexures were applied in the design of rolling joints with different configurations. • The final grasper design is low-friction and does not require any post-processing steps. Metal additive manufacturing is a promising technology for the production of functional medical products, due to its high shape complexity and resolution, and ability to withstand sterilization temperatures. This study explores the possibility of designing a completely non-assembly steerable surgical instrument using Selective Laser Melting. Despite its advantages for medical devices, the rough surface quality of unfinished parts can be problematic for non-assembly designs, leading to increased friction and wear in rigid body mechanisms and tendon-actuated mechanisms. We investigated printing of rolling contact joints with crossed flexures as low-friction joints, adjusted for printing in titanium for the design of the instrument. Grid-based lattice structures were incorporated as miniature flexures, and we explored the influence of various grid sizes on the flexibility and bending stiffness of the lattices. Based on this exploration, we altered the rolling joint configuration from two crossed flexures to a single straight flexure for our design. The resulting steerable surgical instrument design is completely non-assembly, including its actuation, facilitates easy removal of support structures, and requires no surface finishing steps. It has a diameter of less than 20 mm, facilitates opening and closing of a grasper, and steering of the grasper by 20 degrees. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ultrasonic rolling and its finite element simulation on a bearing raceway was conducted. • Multi-objective process optimization for ultrasonic rolling on a bearing was performed. • Oriented martensitic grain stacking forms a flocculent plastic deformation layer. • Carbide particles are refined, and its size changes gradiently along the layer depth. For the first time, the ultrasonic surface rolling processing (USRP) technology was applied to a real bearing raceway, and a finite element simulation model for USRP on a bearing raceway was established. Practical tests were conducted to evaluate the surface integrity of the bearing raceway before and after USRP treatment. The USRP parameters were optimized using Taguchi-gray correlation analysis. The results show that the optimal process parameters for the 7224 bearing raceway are: an amplitude of 10 μm, a static pressure of 2400 N, a spindle speed of 45 rad/min, and rolling times of 7. In the process of USRP, residual compressive stress results from inhomogeneous elastic and plastic deformation. Adjacent tempered martensitic laths merge and deflect at a certain angle along the rolling direction to form directional grain stacks, resulting in a flocculent plastic deformation layer. The USRP based on the finishing mechanism of "peak-cutting and valley-filling" can improve the surface micro-morphology, reduce roughness value Ra to approximately 0.16 μm, and effectively eliminate microscopic cracks caused by grinding. The micro-hardness of the bearing raceway surface increased from 760 HV to 840 HV under the dual action of surface grain refinement and work hardening effect. [ABSTRACT FROM AUTHOR]

Wettability and stress concentration are the main challenges affecting the engineering application of copper/alumina dissimilar joints. In this paper, continuous drive friction welding of copper to alumina was conducted using 2.5 mm thick AA1100 aluminum as interlayer. The effects of friction pressure and friction time on the tensile strength of joints were evaluated, and the interface microstructure evolution and fracture morphologies were also analyzed. Obvious mutual diffusion occurred at the alumina/aluminum and aluminum/copper interfaces, enhancing wettability and proving metallurgical bonding. Microcracks formed in alumina base due to thermo-mechanical coupling effect in welding. As increasing friction pressure and friction time, the tensile strength increased till reaching a peak value of 35 MPa, and then decreased. The optimized parameters were determined as friction pressure of 12 MPa and friction time of 12 s. All samples failed at the aluminum/alumina interface, leaving a pit structure on alumina base. The application of pure aluminum interlayer is essential to obtain sound copper/alumina joints by diminishing stress concentration and wetting alumina, and the optimized residual aluminum layer is about 0.47 mm thick. The friction interface transferred from alumina/aluminum to inner plasticized aluminum layer, and then moved to aluminum/copper till the welding process finished. [ABSTRACT FROM AUTHOR]

Tool and pin geometries play significant roles in material flow, stirring and weld quality in friction stir spot welding (FSSW) process. The present work investigates the influence of tool pin length (0 mm i.e. pinless, 0.2 mm and 0.4 mm) and pin diameter (3.3 mm and 4.95 mm) on lap shear strength during the FSSW of similar and dissimilar aluminum and copper alloy. Pinless tools are differently designed from H13 die steel single material and embedded aluminum and/or copper rods in H13. Results indicate that the maximum lap shear strength is achieved with pinless tools (single material). However, when tools with pins are used lap shear strength decreases with increase in tool plunge depth but increases with pin diameter. For pinless tool obscure hook formation is noted and crack is initiated from the joint interface. Asymmetric strain distributions as observed from the finite element analysis and hook formation observed during microscopic analysis may be responsible for quick failure when higher plunge depth of pin is used. Shear fracture in presence of micro-voids/dimples elongated along the loading direction are observed in similar FSSW whereas in case of Cu-Al dissimilar joints, formation of intermetallic compounds and quasi-cleavage fracture is observed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Comparable hardness is obtained for WEL produced in laboratory and the one from field conditions. • Similar microstructural features are observed between WEL from field and after a single cycle of fast heating and quenching. • Grain refinement observed in WEL produced during wheel/rail contact is not reproducible by thermal heating only. • Mn homogeneization is obtained after 5 minutes soaking at high temperatures. The influence of soaking and cooling rates on the final microstructure of a R260Mn pearlitic railway steel subjected to fast heating is investigated. Fast-heating experiments followed or not by soaking and cooling at different rates were performed using quenching dilatometry on railway steel specimens obtained from the rail head. Additional cyclic heating and quenching experiments were done to investigate the evolution of the microstructure during thermal cycling, which is relevant for railway applications. The final microstructure is characterized via microhardness measurements, optical microscopy and scanning electron microscopy. The microstructural features are distinguished and the influence of each condition is detailed. The study allows the construction of transformation diagrams during cooling after fast heating. Furthermore, comparison between the final microstructures obtained in controlled laboratory conditions and field White Etching Layers is presented. The obtained results can serve as a guideline for future reproduction of White Etching Layers in laboratory conditions and interpretation of field conditions. [ABSTRACT FROM AUTHOR]

Abstract: Flaking failure in rolling contact fatigue (RCF) of hardened bearing steels under well-controlled lubrication is known to originate from the non-metallic inclusion present in the material’s subsurface region. Many researchers stress the importance of the inclusion size as an important factor in RCF life. The RCF performance of steels has been improved through the development of a steelmaking technology that allows reducing the inclusion size. However, due to the limits in visualization of crack initiation and propagation during RCF testing, the issue regarding the number of factors involved in the process remains unsolved. In our prior research, we observed and analyzed cracks initiating from internal defects. The obtained results suggested that the inclusion/matrix interface condition might play an important role in RCF life. In this study, we investigated the effect of inclusion/matrix interface cavities on RCF life through close observation of fatigue cracks. Hot Isostatic Pressing (HIP) treatment was conducted in order to close the cavities and it was found that closing the inclusion/matrix cavities is a very valuable technique for improving RCF life of bearing steels. [Copyright &y& Elsevier]

Abstract: Flaking failure of rolling contact fatigue is known to originate from non-metallic inclusions, where fatigue cracks occur at subsurface region of materials. It is fundamental to understand the main factors governing the rolling contact fatigue life. Steel samples with different size and chemical composition of oxide inclusions were evaluated on rolling contact fatigue life. As a result, [(i)] Rolling contact fatigue life was improved by reducing the oxide size. [(ii)] Rolling contact fatigue life varied depending on the oxides composition. It has been concluded that the chemical composition of the inclusions is an important factor of the rolling contact fatigue life, in addition to the inclusion size. [ABSTRACT FROM AUTHOR]

Abstract: Fatigue life investigations have been made for cylindrical hollow rollers in pure rolling contact. In addition to normal loading, the rollers have been subjected to tangential loading of 1/3rd the normal load value. Sufficient coefficient of friction has been used to ensure no slipping occurs. Two main models were built with different hollowness percentages to investigate the hollowness percentage that gives the longest fatigue life. The first model consists of two cylindrical rollers of same size, while the second model consists of two rollers of different sizes. Two cases have been studied, when both rollers are hollow and when only one roller is hollow. The stress distribution in the roller body and the resulting deformation has been investigated using the finite element package, ABAQUS. Then the Ioannides–Harris (IH) theory was used to predict the fatigue life of the hollow rollers in pure rolling contact. Investigations have been made for five different materials, CVD 52100, Carburized steel, VIMVAR M50, M50NiL and Induction-hardened steel. It has been found that the optimum hollowness percentage with the longest fatigue life ranges is around 50%. Many factors affect the optimum hollowness percentage, like the kind of the material used for the cylindrical roller, whether the rollers in contact are of the same size or different size and whether the hollow roller is in contact with another hollow roller or in contact with solid roller. [Copyright &y& Elsevier]

Abstract: To analyse the off-road tyre–road contact pressure distribution as a function of inflation pressure and normal load, a non-linear multi-laminated model of a tractor tyre was developed. The modelling process is based on the 3D pressure fields obtained through the non-linear static stress analysis of a finite element (FE) tyre model, which considers the structural geometry, the anisotropic material properties of the multiple layers and the nearly incompressible property of the tread rubber block. Increased levels of tyre–road interface stress were found near the centre of the tyre–road model when inflation pressure was increased and near the edge when load was increased. The peak interface pressure results showed that the greatest ratio of peak interface pressure to inflation pressure was 2.5 and the lowest ratio was 0.21. The computed tyre–road contact lengths are qualitatively compared with the measured data to examine the validity of the model. It is concluded that the proposed model can provide reliable predictions for the three-dimensional stress field in the multi-laminated system and the contact pressure distribution throughout the tractor tyre–road interface. [Copyright &y& Elsevier]

Abstract: Rolling element bearings experience fretting wear type of failures due to small relative oscillatory motion existing between races and rolling elements of the bearing. Small oscillatory motion between contacting surfaces that occur due to overall machine or system vibration and unexpected loads in service causes accumulation of wear debris in the contact zone and accelerate the wear process. A fretting wear test rig is designed and developed in the laboratory for understanding the fretting wear behavior of bearing materials. The test rig is designed for testing at slip amplitudes ranging from 20 to 200 μm and test frequencies ranging from 1 to 30 Hz. Preliminary studies for understanding the fretting wear characteristics were conducted on hardened and tempered bearing steel, En31 and widely employed hardened and tempered structural steel, En24 at various normal loads. Coefficient of friction during fretting tests was high during the initial stages of fretting tests and reached a steady state. The coefficient of friction depends on the normal load. Wear scar morphology reveals the nature of contact exhibited by the fretting contacts. [Copyright &y& Elsevier]

Abstract: A novel pressurised chamber was designed to construct a special purpose test rig to achieve saturated liquid state of refrigerants for lubricated rolling contact fatigue experiments. Traditional bench testing using refrigerants as the lubricant is difficult due to the gaseous phase at standard atmospheric conditions. Pressurising the concentrated contact test chamber is therefore necessary to evaluate at a liquid state and therefore simulate practical applications. The gas/liquid phase transitions have a significant influence on the lubricant properties and hence wear mechanisms. It is necessary to modify the wear test conditions for the Hydrocarbon (HC) and Hydrofluorocarbon refrigerants to obtain realistic simulation of refrigerator compressor tests. The chamber design and test rig are described in this paper. A preliminary experimental study of the influence of the HC (R600a) on rolling wear of the silicon nitride (Si3N4)/steel elements using the pressurised chamber is presented. Rolling fatigue test methods are adopted to measure the wear performance of silicon nitride/steel bearing materials. In this case the rolling wear mechanisms of Si3N4 were measured using R600a refrigerant lubrication. [Copyright &y& Elsevier]

The fracture behavior of a white etching layer formed on the rail surface in pearlitic steels during the rail-wheel contact is investigated using indentation-based microcantilever fracture tests. The sample thickness is in the order of 5 μm. The local fracture toughness of the white etching layer, its neighboring brown etching layer, martensite and pearlite with similar chemical composition are determined and compared to ferritic steels. All samples show stable crack growth accompanied by significant plasticity at the crack tip. The toughnesses scale inversely with the microhardness. The white etching layer exhibits a toughness of 16.0 ± 1.2 MPa m1/2 which is in the same range as the fully martensitic steel. It is shown that the local fracture toughness can be roughly estimated based on the Vickers hardness of the white etching layer. Also, an estimation of a critical defect size in white etching layers which considerably furthers the understanding of crack initiation is made in this study. Furthermore, various criteria for analyzing the elasto plastic fracture toughness are compared. Unlabelled Image • The fracture toughness of WELs and comparable microstructures were obtained using elasto-plastic micro fracture experiments • The fracture toughness of WELs is comparable to martensite • The fracture toughness of WELs can be estimated from the hardness via a proposed empirical relation. • Various criteria for interpreting the J-integral at small scales are quantitatively compared and discussed. • We determined critical defect size in WELs. [ABSTRACT FROM AUTHOR]