Dynamic Friction Coefficient Research Articles

Identification of lubricant viscosity to minimize the frictional impact of colonoscopy on colonic mucosa

Applying a lubricant to the colonic mucosa and reducing the dynamic friction coefficient (DFC) between the endoscopic shaft and colonic mucosa may reduce colonoscopy invasiveness. However, the ideal lubricant viscosity remains unknown. Here, we developed a DFC measurement model integrating samples of colonic mucosa from forensic autopsy specimens into a simulated bowel bend and determined the low-friction lubricant viscosity that minimizes the DFC. Carboxymethyl cellulose, xanthan gum, hydroxyethyl cellulose, sodium alginate, and sodium polyacrylate aqueous solutions of various concentrations were used as lubricants. Low-friction lubricants minimized the load on the colonic mucosa during colonoscope insertion and reduced the total endoscopy insertion time. The highest correlation was between the DFC and the lubricant viscosity at a shear rate of 100 1/s. The lowest DFC was almost constant at approximately 0.09, irrespective of the chemical composition of the lubricant, and the low-friction lubricant viscosity (100 1/s) was 0.031–0.086 (median: 0.059). The viscosities of conventional colonoscopic lubricants were suitable for lubricating the anorectal skin owing to their low DFC, but too high for lubricating the colonic mucosa because of their high DFC. The utilization of the low-friction lubricants with the optimal viscosity can reduce the stress on colonic mucosa during colonoscopy.

Improving mechanical and tribological properties of carbon fabric/resin laminated composites by carbon fiber powder

AbstractCarbon fabric/resin laminated composites (CFRC) are extensively used in aerospace, transportation, and other fields owing to their superiorities of lightweight, high strength, and convenient integral molding. Therefore, strong interlaminar binding and prominent wear resistance are urgent requirements for avoiding premature failure of laminated materials in harsh working environments. To elevate the superficial wear resistance and interlaminar bonding strength of composites simultaneously, the modified composites were obtained by introducing carbon fiber powder (CFP) with different densities on the surface of the composites and between layers. The experimental results indicate that CFP can be evenly distributed in the interlaminar resin enrichment zone of the sample (CFRC‐40) when the deposition density is 40 g/m2. Consequently, CFRC‐40 presents optimal thermal conductivity owing to better heat transfer bridges between layers of the composite established by CFP. At the same time, the mechanical properties such as the tensile, impact, and interlaminar shear strengths of CFRC‐40 are improved by 42.8%, 10.2%, and 8.5%, respectively, compared with the original CFRC, which are attributed to the absorption of crack propagation energy and the inhibition of crack propagation by CFP. Furthermore, the dynamic friction coefficient maintains at a high level after introducing CFP with a density of 40 g/m2, while the wear rate significantly decreases by 61.2% from 12.99 × 10−14 m3(N m)−1 to 5.04 × 10−14 m3(N m)−1. This study proposes an innovative strategy to improve the interlaminar bonding of carbon fabric/resin laminated composite, which is conducive to obtaining composite with excellent mechanical and tribological properties.Highlights A facile and effectual method was adopted to introduce carbon fiber powder (CFP) into the interlamination and surface of the composites simultaneously. The mechanical properties and abrasive resistance of the composites were obviously strengthened by regulating the content and distribution of CFP. CFP at a certain scale, could not only hinder the propagation of cracks but also alleviate the surface wear and extend the service life of composites.

Effect of prophylactic dressings to reduce pressure injuries: a polymer-based skin model.

This study evaluated the effect of pressure injury (PI) prophylactic dressings used for patients at high risk of PI development to reduce friction, shear force and pressure, and their combined force, in an original polymer-based skin model. A low-friction outer-layer hydrocolloid (LFH) dressing and a multilayered silicone foam (MSF) dressing were used. Before application, compression and friction properties were measured. Our original experimental model-the 'simulated skin-shearing test'-consisted of: a weight; a polyurethane-based skin model containing a three-axis tactile sensor; dressings; a table covered with bedsheets; and a mechanical tester, by which the interface friction force, internal shear force and pressure were measured continuously during skin model movements. An estimated combined force generated by internal shear and pressure was represented as a vector. A model with no dressing was used as a control. The LFH dressing had significantly higher compression strength versus the MSF dressing. In contrast, the dynamic coefficient of friction was lower for the LFH dressing versus the MSF dressing (p<0.05). In simulated skin-shearing test results, shear forces were 0.45N and 0.42N for LFH and MSF dressings, respectively, with no significant difference. The estimated combined force was lower for the MSF dressing compared with that of the LFH dressing and control. The shear force-reducing effect in the skin model was equivalent between the LFH and MSF dressings. However, the MSF dressing significantly reduced the force generated by a combination of internal shear force and pressure compared with the LFH dressing.

Comparison of reality and illusion of wetness on soft materials and the multisensory perceptual space of wetness illusion

Skin contact with cold objects can induce the perception of wetness, known as the wetness illusion, even in the absence of actual moisture. However, the differences between wetness perceived from moisture and cooled-dry soft materials and how the material parameters affect the wetness illusion from cooled-dry soft materials remain unclear. This study recruited 12 women and 12 men to touch paired moisture and dry fabrics to compare the prescription and intensity of wetness, suggesting that the wetness illusion focused more on roughness and stickiness while the wetness of moisture fabrics sensed more on coldness. Another 12 women touched cooled-dry materials with different temperatures (10°C and 15°C), thicknesses (0.75/0.73 and 1.99/1.96 mm), and dynamic friction coefficients (mean coefficient of friction) (0.17 and 1.88), rating on wetness dissimilarity and intensity of wetness, coldness, softness, and roughness. Data were illustrated in a two-dimensional space by multidimensional scaling, in which dimension 1 represented the haptic perception in wetness, most related to the mean coefficient of friction, and dimension 2 represented the coldness perception in wetness, most related to temperature. Overall, the mean coefficient of friction and the temperature of the material had a strong influence on the wetness illusion, while the thickness had less impact. This study improves the understanding of wetness illusion and sheds light on the reproduction of wetness perception in multisensory augmented virtual reality, such as immersive gaming and virtual dress fitting.

Study of mechanical and technological properties of seed fruits of vegetable and melon crops

The analysis of literature sources shows that the production of seed material for vegetable and melon crops is one of the most important problems that exists in the field of agricultural processing. The production of cucumber and melon seeds is an urgent issue in view of the volume of their cultivation in Ukraine. To study the processes of fruit grinding and seed production in agriculture, the key parameters are the dynamic friction coefficient, the volume deformation coefficient and the static load coefficient, but existing methods and equipment are limited to determining the limit values of the indicators, not allowing a full study of the dynamics of changes in properties at different stages of the technological process. To solve this, it is proposed to develop new methods, in particular, the use of computer modelling, which will allow a more detailed study and optimisation of physical and mechanical properties and their changes. The aim of the article was to study the physical and mechanical properties of vegetable fruits, which have the greatest impact on the quality of the technological process of fruit seed grinding and preliminary seed extraction. The study was conducted in the problematic research laboratory of the Faculty of Engineering and Energy of Mykolaiv National Agrarian University. Experimental setups were used to determine the dynamic coefficient of friction of melon and cucumber seeds, a device for determining the initial density of seed fruits, and a device for determining the dependence of seed deformation on compressive load. Experimental data show that the most optimal values of the static coefficient of friction, depending on the type of surface, for cucumber and melon seeds are perforated sieves, the values of which are 0.75 and 0.85, respectively. Optimal values of dynamic friction coefficients for cucumber have a surface made of perforated sieve – 0.69 and for melon made of aluminium – 0.88. The dependence of the linear deformation of seed fruits on the specific pressure increases from 0.9 to 3.6. The values of fruit deformation from compressive load vary from 4.1 to 24.6. The research presented in the article is of practical importance and can be used in the field of agricultural production and in the development of new engineering solutions

Triaxial experimental study of mechanical behavior of non-persistent jointed granite subjected to slight cyclic dynamic disturbances

A slight disturbance can induce fault-slip burst failure in deep rock masses. In this paper, a series of triaxial tests were conducted to investigate the strength, deformation characteristics, and failure behavior of non-persistent jointed granite specimens subjected to slight cyclic loading. A representative stress–strain curve for non-persistent jointed rock was generated and used to study the crack evolution process (initiation → propagation → coalescence). The effects of varying the joint angle and frequency and amplitude of the disturbance were then analyzed. A theoretical (fracture mechanics) model for a non-persistent joint subject to triaxial cyclic loading was also established and used to investigate the combined effects of static confining stress and slight disturbances. Finally, the mechanical mechanism by which a slight dynamic disturbance induces fault-slip burst was discussed. Our results show that the failure mode of a non-persistent jointed rock mass depends more on the joint angle than the amplitude and frequency of the slight disturbance. The disturbance induces the initiation and extension of cracks. It can also induce fracture-slip bursting once the disturbance exceeds a certain threshold. The value of this threshold depends on the initial stress state, joint angle, length, dynamic and static friction coefficients, and fracture toughness of the rock. The study thus enriches our mechanistic understanding of the crucial ingredients involved in the triggering of fault-slip rock bursts in deep rock masses by slight disturbances.

Comparison of Superhydrophilic, Liquid-Like, Liquid-Infused, and Superhydrophobic Surfaces in Preventing Catheter-Associated Urinary Tract Infection and Encrustation.

Over the past decade, superhydrophilic zwitterionic surfaces, slippery liquid-infused porous surfaces, covalently attached liquid-like surfaces, and superhydrophobic surfaces have emerged as the most promising strategies to prevent biofouling on biomedical devices. Despite working through different mechanisms, they have demonstrated superior efficacy in preventing the adhesion of biomolecules (e.g., proteins and bacteria) compared with conventional material surfaces. However, their potential in combating catheter-associated urinary tract infection (CAUTI) remains uncertain. In this research, we present the fabrication of these four coatings for urinary catheters and conduct a comparative assessment of their antifouling properties through a stepwise approach. Notably, the superhydrophilic zwitterionic coating demonstrated the highest antifouling activity, reducing 72.3% of fibrinogen deposition and over 75% of bacterial adhesion (Escherichia coli and Staphylococcus aureus) when compared with an uncoated polyvinyl chloride (PVC) surface. The zwitterionic coating also exhibited robust repellence against blood and improved surface lubricity, decreasing the dynamic coefficient of friction from 0.63 to 0.35 as compared with the PVC surface. Despite the fact that the superhydrophilic zwitterionic and hydrophobic liquid-like surfaces showed great promise in retarding crystalline biofilm formation in the presence of Proteus mirabilis, it is worth noting that their long-term antifouling efficacy may be compromised by the proliferation and migration of colonized bacteria as they are unable to kill them or inhibit their swarming. These findings underscore both the potential and limitations of these ultralow fouling materials as urinary catheter coatings for preventing CAUTI.

New database for the estimation of dynamic coefficient of friction of snow

New database for the estimation of dynamic coefficient of friction of snow

Additive manufacturing of high-performance Ni-Co coatings for micro/nanomold applications using an advanced gradient ultrasonic electrochemical deposition process

The mass production of polymeric microdevices using microinjection molding or nanoimprinting necessitates high-performance micro/nano Ni-Co molds. However, the achievement of a synergistic enhancement of the mechanical and lubricating properties of Ni-Co mold through general electrodeposition process remains challenging. This study for the first time proposes a gradient ultrasonic-assisted electrodeposition process to investigate its impact on the microstructural, mechanical, and tribological properties of Ni-Co coatings. Meanwhile, wear simulations are also conducted to elucidate the deterministic relationship of microstructure-process-properties by integrating surface topography and dynamically changing the coefficient of friction (COF) in the wear model. Our findings show that a high Co content (Ni:Co = 5:5) along with gradient-increased ultrasonic power (30–100 W) achieves maximum hardness (approximately 489 HV) and minimum COF (approximately 0.17), indicating a 1.73-fold hardness increase and 72% COF decrease relative to Ni coating. Such improvements result from grain refinement, reduced lattice distortion, and increased hydrophobicity, driven by the synergistic enhancement of high Co content and gradient ultrasonic power. Wear simulations highlight the undeniable impact of surface roughness and dynamic COF, which is vitally important for micro/nanomolds applications. This study realizes the integration of wear model–ultrasonic-process–microstructure–properties of Ni-Co coatings, offering valuable insights into the development of high-performance micro/nano Ni-Co molds based on gradient ultrasonic-assisted electrodeposition process.

Foot Bionics Research Based on Reindeer Hoof Attachment Mechanism and Macro/Microstructures.

The attachment performances of mechanical feet are significant in improving the trafficability and mobility of robots on the extreme ground. In the future, frozen-ground robots can be used to replace human soldiers in scouting and deep space exploration. In this study, the influence factors on the attachment function of the bionic feet were analyzed. Soft frozen soil and tight frozen soil close to natural frozen soil were prepared, and the friction between ungula and frozen soil ground was simulated together with the plantar pressures of reindeer under trotting. The major attachment parts were the ungula cusp, outer edges, and ungula capsules, and the stress on the ungula was mainly 4.56-24.72 MPa. According to the microstructures of plantar fur and ungula, the corresponding ratio of the rib width and length was 0.65:1, and the corresponding ratio of the rib width and distance was 3:1. In addition, the scales of the plantar fur were very tightly arranged and had large ripples. Based on typical curves, an ungula capsule-curved surface, and a nonsmooth plantar fur surface, four types of bionic feet and the corresponding ordinary multidamboard foot were designed. On the frozen soil, the bionic foot with ribs and an ungula capsule showed the best attachment performance. Compared with the multidamboard foot, the dynamic coefficient of friction of the bionic foot with ribs and ungula capsules increased by 11.43-31.75%. The attachment mechanism of the bionic feet is as follows: under the action of pressure, the fine patterns of the bionic convex-crown generate friction with the nonsmooth structure of the frozen soil surface, which improves the attachment performance.

Stick–Slip Vibration Characteristics Study of the Drill String Based on PID Controller

In order to address the issue of drill string stick–slip vibration, which leads to drill bit wear and reduces the drilling velocity, we conducted a study on the characteristics of stick–slip vibration using a proportional-integral-derivative (PID) controller. By applying the principles of rigid body mechanics, we established a two-degree-of-freedom torsional dynamics equation and derived the first-order differential dynamics equation for the drill string. Subsequently, we designed a PID controller and obtained an equation for the control of stick–slip vibration. The research findings indicate that variations in the difference between the static and dynamic friction coefficients directly impact the nature of the limit cycles in the phase plane. As this difference decreases, the limit cycle narrows and the stick–slip vibrations weaken progressively. When the static and dynamic friction coefficients are equalized, no stick–slip vibrations occur within the drill string. The implementation of PID control effectively manages stick–slip vibrations in the drill string, with greater efficiency observed in controlling the turntable velocity compared to the drill bit velocity. This research provides valuable insights for the development of control strategies aimed at mitigating stick–slip vibrations in drilling engineering applications, thereby facilitating the efficient and safe extraction of oil and gas resources.

Tribological behavior of shape-specific microplate-enriched synovial fluids on a linear two-axis tribometer

Nano- and micro-particles are being increasingly used to tune interfacial frictional properties in diverse applications, from friction modifiers in industrial lubrication to enhanced biological fluids in human osteoarthritic joints. Here, we assessed the tribological properties of a simulated synovial fluid enriched with non-spherical, poly lactic-co-glycolic acid (PLGA) microparticles (µPL) that have been previously demonstrated for the pharmacological management of osteoarthritis (OA). Three different µPL configurations were fabricated presenting a 20 µm × 20 µm square base and a thickness of 5 µm (thin, 5H µPL), 10 µm (10H µPL), and 20 µm (cubical, 20H µPL). After extensive morphological and physicochemical characterizations, the apparent Young’s modulus of the µPL was quantified under compressive loading returning an average value of ∼ 6 kPa, independently of the particle morphology. Then, using a linear two-axis tribometer, the static (µs) and dynamic (µd) friction coefficients of the µPL-enriched simulated synovial fluid were determined in terms of particle configuration and concentration, varying from 0 (fluid only) to 6µ105 µPL/mL. The particle morphology had a modest influence on friction, possibly because the µPL were fully squeezed between two mating surfaces by a 5.8 N normal load realizing boundary-like lubrication conditions. Differently, friction was observed to depend on the dimensionless parameter Ω, defined as the ratio between the total volume of the µPL enriching the simulated synovial fluid and the volume of the fluid itself. Both coefficients of friction were documented to grow with Ω reaching a plateau of µs ∼ 0.4 and µd ∼ 0.15, already at Ω ∼ 2×10−3. Future investigations will have to systematically analyze the effect of sliding velocity, normal load, and rigidity of the mating surfaces to elucidate in full the tribological behavior of µPL in the context of osteoarthritis.

Early-stage modeling and analysis of continuum compliant structure for multi-DOF endoluminal forceps using pseudo-rigid-body model

Early detection and treatment of intraluminal diseases enable minimally invasive surgery and can lead to a high cure rate. Advanced devices with multiple degrees of freedom (DOFs) make narrow intraluminal procedures easier and safer. In a previous study, we developed a multi-DOF compliant endoluminal forceps with a tendon-sheath mechanism. The maximum bending stress of this design was reduced by changing the thickness of a compliant hinge in each segment, and the forceps achieved a wide range of motion. However, its deformed shapes with a non-constant curvature, due to a compliant inhomogeneous-thickness hinge structure, hinder fine manipulation in a narrow lumen. Here, we construct an accurate model of this compliant inhomogeneous-thickness hinge structure using pseudo-rigid-body model. In the proposed method, each compliant hinge is represented by a torsion spring and rotational joint, and the deformed shape is estimated from the bending angle caused by the tensile force. We derive the coefficient of dynamic friction by considering the friction between the wire and compliant joint based on a belt friction model. These novel calculations allow to consider individual differences in material properties and surface roughness. We experimentally confirm the feasibility of constructing a highly accurate model with a lower calculation cost than the finite element method. Our proposal seems suitable for developing dexterous forceps and other endoluminal devices, such as catheters, which mitigate operation errors and help approach lesions in narrow lumens.

CHARACTERISTICS OF THE INERTIAL PROPERTIES OF THE DISPERSED MATERIAL

It is noted that in the strength calculations of structural elements of aircraft, among other things, the modes of forced and natural vibrations are taken into account. In this regard, the dynamic properties of the transported cargo are taken into account, which are significantly different for solid and dispersed materials. Considered is a dispersed material located on a platform that performs harmonic oscillations. The main problem in establishing the dynamic properties of a dispersed material is the impossibility of calculating the average coefficient of dynamic friction, since its value is influenced by the interaction of dispersed particles with each other in the entire mass of the material, and not only with the surface of the platform. The description of the dynamic status of a dispersed material in the form of a composition of its unstable and stable statuses provides the key to solving this and similar problems.

Fluid-driven slow slip and earthquake nucleation on a slip-weakening circular fault

We investigate the propagation of fluid-driven fault slip on a slip-weakening frictional interface separating two identical half-spaces of a three-dimensional elastic solid. Our focus is on axisymmetric circular shear ruptures as they capture the most essential aspects of the dynamics of unbounded ruptures in three dimensions. In our model, fluid-driven aseismic slip occurs in two modes: as an interfacial rupture that is unconditionally stable, or as the quasi-static nucleation phase of an otherwise dynamic rupture. Unconditionally stable ruptures progress through four stages. Initially, ruptures are diffusively self-similar and the interface behaves as if it were governed by a constant friction coefficient equal to the static friction value. Slip then accelerates due to frictional weakening while the cohesive zone develops. Once the latter gets properly localized, a finite amount of fracture energy emerges along the interface. The rupture dynamics is then governed by an energy balance of the Griffith’s type. In this stage, fault slip transitions from a large-toughness to a small-toughness regime due to the diminishing effect of the fracture energy in the near-front energy balance. Ultimately, self-similarity is recovered and the fault behaves again as having a constant friction coefficient, but this time equal to the dynamic friction value. This condition is equivalent to a fault interface operating to leading order with zero fracture energy. When slow slip is the result of a frustrated dynamic instability, slip also initiates self-similarly at a constant peak friction coefficient. The maximum size that aseismic ruptures can reach before becoming unstable can be as small as a critical nucleation radius (shear modulus divided by the slip-weakening rate) and as large as infinity when faults are close to a well-defined limit that separates the two modes of aseismic sliding. In the former case, earthquake nucleation occurs unaffected by the dynamic friction coefficient. In contrast, the latter case exhibits fracture-mechanics behavior, characterized by a finite influx of elastic strain energy being supplied to and dissipated at the rupture front. We provide analytical and numerical solutions for the problem solved over its full dimensionless parameter space, including expressions for relevant length and time scales characterizing the transition between different stages and regimes. Due to its three-dimensional nature, the model enables quantitative comparisons with field observations as well as preliminary engineering design of hydraulic stimulation operations. Existing laboratory and in-situ experiments of fluid injection into simulated and natural faults are briefly discussed in light of our results.

Research on nonlinear dynamic characteristics of high-speed gear in two-speed transmission system

The working performance and service life of the two-speed transmission system directly affects the performance and service life of helicopters and other equipment. One of the main tasks of the two-speed transmission system research is to improve its dynamic characteristics. For the two-speed transmission system in high-speed gear, a purely torsional nonlinear dynamic differential equation set considering the number of planetary gears, backlash, and clutch dynamic load is established by using the lumped parameter method, and the equations are dimensionless. Then the dimensionless differential equation set is solved by using the variable step-size fourth-order Runge–Kutta method, and the phase diagram and Poincare diagram of high-speed gear are obtained. By changing the dynamic friction coefficient of the friction clutch and the backlash of the gear pair, the influence of parameter change on the nonlinear dynamic characteristics of the system is analyzed. The results show that, with the increase of excitation frequency, the system has experienced single cycle, quasi-cycle, chaos, and double cycle, then changed from double cycle to chaotic motion, and then changed from chaotic motion to double cycle and single cycle motion in turn, and found the path to chaos. In the low-frequency band, reducing the friction coefficient of the friction clutch can reduce vibration amplitude; In the middle-frequency band, reducing the friction coefficient will make the system tend to unstable vibration. In the high-frequency band, it is a single-cycle movement, which is not affected by friction coefficient.

Variable speed limit in foggy conditions considering dynamic sight distance and friction

Fog is a weather condition that can significantly threaten expressway safety and efficiency by reducing natural visibility and the road friction coefficient. The variable speed limit (VSL) strategy is an effective traffic-management method for harmonising vehicle speed and reducing rear-end crash potential under foggy conditions. Two key inputs – driver sight distance and the road friction coefficient – determine the reliability of VSL calculation. However, a driver's sight distance in a running vehicle (i.e. the dynamic sight distance (DSD)) is significantly lower than that at rest. Additionally, a dust–water coupled film on the expressway surface will also affect the dynamic friction coefficient (DFC). Based on a stopping sight distance model, a new VSL strategy that considers the DSD, DFC, alignment and slope is proposed. The results obtained from simulations based on the CarSim software program and the Simulink programming environment showed that, in foggy conditions with a natural visibility of 200 m, the speeds calculated by the proposed VSL strategy in straight and curved road segments were 70 km/h and 67 km/h, respectively, 16% and 11% higher than China's legal speed limit. A braking experiment on Wentai expressway in Zhejiang province, China confirmed that these speeds are safe and could improve efficiency. The research results provide a theoretical basis and support for the management of expressways in foggy conditions.

Research on the bidirectional sliding phenomena of a toppling rod under frictional situations

In this work, we investigated the phenomenon of spontaneous bidirectional sliding on a toppling rod under a frictional situation. We explained the reasons for sliding is the friction force from the table is not sufficient to support the horizontal acceleration of the mass center when toppling, so the rod itself has to obtain a horizontal acceleration and apply the inertia force to play the role of supporting the acceleration of the mass center. This phenomenon and converted the question into a mathematical model. We pick the contacting point between the rod and the horizontal surface as the reference point for our computing of physical quantity, therefore the torque caused by friction and normal force can be ignored. With this model, we finished the theoretical analysis of the effects of varying static friction and dynamic friction coefficients on the phenomenon, with computer simulations verified.

Inverse estimation of mode I fracture energies for structural adhesives from impact wedge peel tests

This work presents a practical approach to estimate mode I fracture energy of structural adhesives at high strain rates from impact wedge peel (IWP) tests. For this purpose, an inverse estimation approach is used which requires relevant input quantities for the associated IWP simulations, e.g., primarily the dynamic friction coefficient between the wedge and the fractured adhesive and the adhesive strength. We describe two new impact-pendulum-based test devices to measure these unknown parameters. These parameters serve as input for the IWP simulation from which the remaining unknown fracture energy of the structural adhesive is estimated by an efficient regression scheme. An uncertainty quantification approach is used to approximate the statistical deviation of the generated material parameters based on the deviation of the measured input parameters. Experimental IWP test results are matched to IWP simulation results for three different substrates. The entire workflow is tested and validated for two different structural adhesives.

Use of repeated indenter sliding coupled with finite element computations to investigate the tribological response of nano-twinned 316L stainless steel

The wear response of dynamically deformed 316 L austenitic stainless steels with varying percentages of compressive strain has been investigated. A relatively high strain rate of 80 s−1 has been used while compressing 316 L at engineering strains of 20 % and 80 %. Nano-indentation coupled with inverse algorithm approaches were used to extract the yield strength and strain hardening exponent of all the specimens. The strain hardening exponent decreased with deformation percentage while the strength enhanced, and these properties have been used in the finite element model (FEM) to find out the stresses and strains during repeated sliding to make scratches. A depth-sensing instrumented nano-indenter with a conical tip was used to make multiple scratches on all the specimens, and the damage in the form of scratch groove depth and width was characterized using a combination of profilometry and scanning electron microscopy. The results showed that the 80 %deformed sample exhibited the least wear damage evident in the form of thinnest scratch profiles, shallowest scratch depths and hence the least specific wear rate. However, after multiple cycles of sliding, undeformed and 20 % deformed samples showed similar wear rates. The friction coefficient decreased with an increase in the percentage deformation, but the dynamic friction coefficient for all the specimens saturated after about 30 passes of sliding. Cross-sectional scanning electron microscopic (SEM) imaging of the scratches revealed refinement and alignment of the microstructure along the shape of the bottom of the groove after repeated sliding. We discovered through the utilization of transmission electron microscopy imaging and selected area diffraction pattern that the region affected by scratching exhibited partial transformation of the initial austenitic phase into martensitic phase.