Contact Pressure Research Articles

Unraveling the complex interplay between elastic recovery, contact pressure, and friction on the flank face of the micro tools via plunging-type testing

A good understanding of the interplay between the cutting tool edge radius, elastic recovery, friction, and contact pressure is essential for better modeling of ploughing forces during micro-scale cutting. This study conducts plunging tests on an ultra-precision CNC with engineered tungsten carbide cutting tools on commercially pure titanium alloy. The cutting tool edge radius is prepared to be around 3.5–4 μm, which resembles those cutting tools used in micro scale machining. During plunging tests, the micro cutting tool is given a sinusoidal movement with an amplitude close to edge radius of the tool as the work material is rotated at a constant speed. The residual depth profiles of the webs corresponding to the commanded depths were investigated in detail to identify elastic recovery rate. The cutting and thrust force measurements during plunging experiments together with identified elastic recovery rate was employed in an analytical model of micro scale machining to obtain the variations of contact pressure and coefficient of friction as a function of commanded depth. Due to the scale of the experiments that were performed, the effects of surface topography of the cutting tool and possible alignment errors are also considered in the analytical model. A linear relationship between the contact pressure and elastic recovery has been identified during ploughing-dominated machining conditions for the work material and the cutting tool pair considered in this study. The proposed experimental technique is shown to be promising in terms of modeling ploughing forces during micro-scale cutting.

Computational framework for predicting friction law under mixed-boundary lubrication, and its application to sheet metal forming process

The role of friction in the forming of automotive parts composed of ultra-high-strength lightweight metals has become increasingly important as industry attempts to overcome inferior formability and springback against enhanced strength. At the tool-design stage, finite-element simulations should use more accurate and efficient friction models that account for complex friction behavior between the metal and tool surfaces. Complex friction behavior is commonly dependent on contact pressure, sliding velocity, microscale surface effects (or roughness), and lubrication, among other factors. This study presents a microscale, asperity-based friction model of mixed-boundary lubrication. The developed hydrodynamic friction model is based on the load-sharing concept, which considers the lubrication area and metal-to-metal contact separately. Lubricant film thickness is calculated to couple the existing boundary lubrication model, and film lubrication behavior is formulated using finite-element programming of the Reynolds equation to obtain the hydrodynamic pressure. The proposed computational framework is validated by simulating an in-line incremental die-forming process. The result shows that the predicted friction law with multi-scale, mixed-boundary lubrication can be efficiently applied to realistic sheet-metal-forming simulations with reasonable accuracy by accounting for complex frictional behavior.

Femtosecond laser darkened copper surfaces: Characterization for possible application as laser beam blocker

This study focuses on the optical and mechanical properties of copper surfaces darkened by femtosecond laser irradiation, with regard to their applicability as laser beam blockers. Copper surfaces were processed with a Ti-Sapphire laser (1 kHz repetition rate, ∼100–600 mJ/cm2 fluence), while scanning parameters were optimized for low reflectivity and processing speed. A total reflectivity below 6 % was obtained for the 250–2500 nm wavelength range. SEM imaging and ion beam etching showed submicron period structures covered with high density nanoparticles, with a total depth of ∼3–4 μm. Numerical reflectivity simulations suggest that besides the structures, the formation of oxides also contributes to the observed darkening. Thermal and mechanical stability, chemical resistance and laser damage threshold were studied. Temperatures above 200 °C caused surface degradation. Scratch tests showed that the nanostructured layers could withstand ∼60 MPa contact pressure. The surfaces could resist 48 h treatment with various acids at 10−3 M concentration. The laser damage threshold for the applied femtosecond laser showed that the surface could withstand the unfocused beam of most high-frequency femtosecond lasers. The results indicate that laser darkened copper can be a promising candidate for use in laser beam blockers.

Study on the tribological performance at the interface between a steel wire rope and groove during a twisting process

In actual use, a steel wire rope is often stretched and twisted around a groove, increasing the risks of contact fatigue, friction and wear at the rope-groove interface under a long-term service condition. With the consideration of influence factors such as the nonlinear contact and wear between the rope and groove, the tribological performance at the rope-groove interface during a twisting process is analyzed in this study. A winding rope-groove model is first established in order to obtain the contact and sliding solutions at the interface between the rope and groove, which are then used as the load conditions of a simplified local model that is built for wear solution using a modified Archard's wear theory. Based on the finite element simulation software ABAQUS, the ALE adaptive mesh technology and UMESHMOTION subroutine secondary development are adopted to analyze the evolutions of wear topography and contact behavior between the rope and the groove. The results show that the twisting movement of the steel wire rope around the groove causes an interfacial wear between them. The wear scars occur on the outside wire of the steel wire rope and the bottom area of the groove, and the wear scar on the groove is smaller but deeper. A ring-shaped region of stress concentration happens near the edge of wear region. As the wear process proceeds, the depths and dimensions of the wear scars increase, while the contact pressure decreases. The contact performance and wear change dramatically at the beginning of wear process and tend to be stable subsequently. An increment of lay angle of the outside wire aggravates the wear and contact between the steel wire rope and the groove.

Tribological behavior of PEEK based composites with alternating layered structure fabricated via fused deposition modeling

In the present study, novel polyether ether ketone (PEEK) based composites were fabricated by multi-material fused deposition modeling (FDM), which were composed of alternating short carbon fiber reinforced PEEK and silicon dioxide filled PEEK layers. And the composites’ tribological properties were evaluated in order to guide their application in industrial parts where friction and wear are of special importance. It is revealed that the tribological properties of the composite were highly dependent on the contact pressure. The low friction and wear occurred at high contact pressure was found to be associated with the combined contribution of rolling of nanoparticles and graphitized self-lubricating transfer films. This work provides a simple strategy for manufacturing highly customized tribo-components with required functions to replace conventional hybrid materials.

Effect of corrosion on fretting wear morphology and mechanical behaviors of wires

Corrosion and fretting wear inevitably occur in wires, which are important parts of cables. To study the wear morphology and surface mechanical behavior of wires for different fretting and corrosion times, a numerical model of fretting wear of wire with different corrosion conditions is established using MATLAB and ABAQUS software’s. Firstly, according to the surface roughness of wires under different corrosion times, the node coordinates in the numerical model are modified to simulate different rough surfaces. Secondly, the wear characteristics of wires under different fretting cycles are obtained by using a cycle jump concept and an ABAQUS user subroutine. Finally, the numerical model is validated using experimental data. The results show that when the corrosion time is 0 h, the wear area has a regular oval shape. The wear volumes of wires with corrosion times of 120 h and 480 h are the largest and the smallest, respectively. As wear volume increases, both residual surface contact pressure and stress decrease. When the corrosion time is 0 h and 120 h, the residual surface contact pressure is maximum and minimum, respectively.

A pressure-triggered isobaric sequential liquid sampling system for full-ocean-depth: Design and field deployment

Collecting pressure-retaining deep-sea liquid samples is important for the research on in-situ environment and life. A pressure-triggered isobaric sequential liquid sampling system (PTISLSS) was developed for the collection of seawater at target depths. The sampling system comprises six independent seawater collection modules, each containing a titanium sample container and a pre-charged accumulator. A motor-driven sampling mechanism was designed to open and close the fluid channels at depth. Theoretical studies have indicated that the mechanism can generate a contact pressures of up to 160 MPa to ensure the sealing of the samples. The relationship between the pressure of pre-charged gas and the volume of fluid sample has been derived considering the effects of seal friction. The sampling system was built for full-ocean-depth sampling operation and the reliability of the system was tested at a pressure of 120 MPa. The field test was conducted in the West Philippine Basin on a recent scientific research cruise. Pressurized seawater from depths of 2000 to 4500 meters was recovered, and the pressure-retaining rate exceeded 93.5%. The developed sampling system presents satisfactory performance and high operational efficiency, and it will have a wide range of applications in the field of large-scale deep-sea sampling.

Comprehensive analysis of electro-mechanical characteristics and new regression models of a novel slanted groove electrical connector

Electrical connectors are crucial electro-mechanical components, with insertion, withdrawal, and electrical contact characteristics serving as key indicators of their reliability. Studying the electro-mechanical characteristics and regression models of electrical connectors is vital to enhance their reliability. This work focuses on the M2-type electrical connector, investigating its electro-mechanical characteristics and developing a regression model. A withdrawal force calculation model is established using cantilever beam theory. Simulation and analysis provide data on insertion force, contact pressure, and contact resistance. Experiments on insertion, withdrawal, and electrical contact are conducted using an insertion force tester and a DC low-resistance instrument, comparing experimental results with simulations. The study reveals the fitting relationship between contact pressure and contact resistance for the M2-type connector. Key findings include a stable fluctuation in contact pressure with a relative error of 1.72% between simulated and tested values, an average discrepancy of 3.81% for insertion force, and 2.38% for withdrawal force, with insertion force slightly higher than withdrawal force. Contact resistance shows a U-shaped trend with pin displacement, with an average experimental error 3.70% and 1.16% lower than theoretical values (4.86%). The new regression model (quadratic polynomial fitting) demonstrates mean absolute percentage errors of 0.1458% for simulation values and 0.2219% for experimental values, significantly lower than those obtained using theoretical formulas (0.7046% and 0.3451%). These results provide theoretical guidance for studying electro-mechanical characteristics and designing experiments for electrical connectors, offering valuable insights for designing and ensuring the reliability of new types of electrical connectors.

Modeling and characterization of contact behavior of asperities with irregular shapes

This paper introduces a model for characterizing the contact behavior of irregular asperities, transforming it into a superposition of sinusoidal asperity contact behaviors. A new sinusoidal asperity model is developed for bilinear hardening under plane strain conditions. Empirical equations are proposed, considering geometric shapes, tangent modulus, and Young’s modulus. The frequency of asperity height is extracted through Fourier transform for irregular asperities. Contact area and pressure are predicted using the sinusoidal asperity model, and the behavior of irregular asperities is obtained by superimposing those with the first three frequencies. Experimental validation is conducted with milling and knurling-formed asperities, showing good alignment between the model and experimental results. In rough surface models, the proposed irregular asperity model exhibits greater accuracy in predicting contact behavior than a single sinusoidal asperity when interference exceeds 10% of the amplitude.

INVESTIGATION OF STRUCTURAL AND MECHANICAL PROPERTIES OF TUBING STEELS

The study of the structural and mechanical properties of tubing steels used in wells at oil and gas condensate fields is of particular interest due to the resource intensity of these systems and the high cost of their repair and restoration. Tubing is operated under conditions of increased loads under the influence of its own weight, internal pressure and constant contact with highly aggressive media. As a result of simultaneous exposure to corrosive media and operational loads, tubing is the most consumable downhole material. The destruction and, as a result, the breakage of the tubing suspension occurs as a result of mechanical abrasion and cracking of the pipe body, the development of fatigue cracks in the thread, etc. Contact with aggressive agents of the extracted fluid and reservoir waters leads to various types of corrosion damage: ulcerative, pitting, corrosion fatigue, corrosion cracking, meza corrosion, biocorrosion, etc. Corrosion foci are localized on the inner and outer surfaces of pipes. The problem is complicated by the increased content of carbon dioxide (CO2), hydrogen sulfide (H2S), as well as the presence of various bacteria in oil and gas fields.This article is devoted to the study of the mechanical characteristics and microstructure of tubing steels that were in operation under conditions of complicating factors and highly aggressive corrosive environment. Tubing pipes Ø73x5.5 of strength group E. were tested. The following research methods were carried out: visual inspection; determination of the chemical composition of steel; determination of hardness; uniaxial tensile test; optical microscopy.As a result of the tests, quantitative characteristics of the mechanical properties of the steels were obtained. A significant decrease in the hardness, tensile strength and yield strength of steel has been established under prolonged exposure to complicated operating conditions. Metallographic studies have established the contamination of steels with silicates of various shapes, amounting to 3 and 2 points according to GOST 1778. Microstructural studies have been carried out. The fine-grained ferrite-carbide structure of steels has been revealed. This structure corresponds to the heat treatment mode: quenching followed by tempering.

Competition between bead boundary fusion and crystallization kinetics in material extrusion-based additive manufacturing

Assembling polymer beads into well-defined 3D geometries through a layer by layer deposition process, such as material extrusion additive manufacturing, remains challenging due to the complex interplay between the several kinetics involved (flow, inter-beads diffusion/fusion, cooling, solidification, etc). Here, we explore the influence of physical parameters like bead cross section geometry, partial bead fusion (also called bead coalescence or bead welding) and crystallization kinetics on the 3D printing of isotactic polypropylene as a model semi-crystalline polymer. New methods for the characterization of printed stacks cross sections, interlayer cohesion and viscoelastic coalescence are introduced. Our results demonstrate how printing conditions, through input parameters like layer height and nozzle temperature, can greatly affect interlayer cohesion in relation to polymer interdiffusion at the interface. We show that the relevant timescale for fusion is mainly driven by the polymer’s rheology, and that fusion is many-fold faster under Hertzian compression, i.e. due to the effect of contact pressure. Quantitative description of the influence of the extrusion nozzle and build platform temperatures on the crystallization time of printed beads highlights how the processability window is defined by the competition between fusion and crystallization. Our approach therefore provides a framework for the optimization of process parameters based on the physical processes involved during the production run of semi-crystalline polymers.

Poster 365: Impact of Graft Type and Meniscal Status on Patellofemoral Cartilage Early after ACL Reconstruction

Objectives: Anterior cruciate ligament reconstruction (ACLR) restores passive knee stability but does not reduce the rate of osteoarthritis (OA). Meniscal status, requiring repair or meniscectomy, is a known component of degenerative progression. Regarding the patellofemoral joint (PFJ) specifically, traditional imaging modalities have shown some evidence that patellar tendon autograft (BPTB) is associated with an increased risk of OA. T2 relaxation time using quantitative MRI (qMRI) is an established method to identify early cartilage changes. However, T2 relaxation in the PFJ as a function of graft type and meniscal status has not been previously evaluated. We aimed to evaluate the effect of autograft type (BPTB, hamstring [HT] and quadriceps tendon [QT]) as well as concomitant meniscal surgery (repair or meniscectomy) at the time of ACLR on T2 relaxation time in PFJ cartilage. We hypothesized that BPTB grafts, concomitant meniscal repair, and meniscectomy would result in higher (worse) T2 relaxation times at 6 months after ACLR. We also evaluated the effect of abnormal joint loading during gait on the PFJ cartilage. We hypothesized that T2 relaxation times would not differ in any group after controlling for knee joint loading during walking. Methods: Thirty-four participants aged 15-35 years were enrolled prospectively within 1 month of ACL injury. Exclusion criteria included prior knee injury or surgery, concomitant grade III tear to other knee ligaments that was symptomatic or required surgical intervention and presence of chondral damage. Sagittal qMRIs were obtained within 1 month of injury (but prior to ACLR) and 6 months after ACLR. Articular cartilage of the PFJ was manually segmented using ITK-SNAP software (Penn Image Computing and Science Laboratory, University of Pennsylvania) and was confirmed for accuracy by a board-certified, fellowship-trained musculoskeletal radiologist (Figure 1). Mean T2 relaxation times were extracted from the trochlear and patellar cartilage. Non-physiological T2 relaxation times less than 10 ms and greater than 90 ms were excluded. Gait biomechanics were captured using two in-ground force plates (Bertec Corporation, Columbus, OH) sampled at 1,080 Hz and retroreflective markers with an 8-camera motion capture system (Qualisys, Göteborg, Sweden) sampled at 120 Hz. Data was processed using Visual 3D software (C-motion, Bethesda, MD). Using an inverse dynamic approach, joint angle and force plate data were used to calculate the knee flexion moment (KFM) impulse normalized to mass and height during the stance phase. Separate one-way ANOVAs were used to evaluate the relationship between graft type and concomitant meniscus surgery with the percent change in T2 relaxation time in PFJ cartilage from baseline to 6 months after ACLR. To determine the influence of gait biomechanics on T2 relaxation time across groups, general linear models were used with the interlimb ratio (involved/uninvolved) of KFM impulse as a covariate. Results: The 34 participants had a mean age of 19.0±4.7 years, and 21 (61.8%) were female. Grafts used during ACLR included 22 BPTB, 4 HT and 8 QT. Seventeen participants (50.0%) had a concomitant meniscus repair and 3 (8.8%) had a meniscectomy. Overall, T2 relaxation time increased 8.7±7.3% in the patellar cartilage (pre-ACLR: 39.1±2.6 ms, 6 months: 42.4±3.6 ms, p<0.001) and 7.1±7.3% in the trochlear cartilage (pre-ACLR: 46.3±2.6 ms, 6 months: 49.5±2.7 ms, p<0.001). The change in T2 relaxation time 6 months after ACLR did not differ based on graft type in either the patellar (p=0.729) or trochlear cartilage (p=0.525) (Figure 2). Group differences remained insignificant after controlling for knee loading (KFM impulse) during gait (patellar: p=0.594; trochlear: p=0.222). Meniscal status was also not associated with a change in T2 relaxation time in either the patellar (p=0.392) or trochlear cartilage (p=0.190) (Figure 3) although there was a trend toward higher T2 relaxation times in those with a concomitant meniscus repair or meniscectomy. Group differences remained statistically insignificant after controlling for the KFM impulse during gait (patellar: p=0.400; trochlear: p=0.197). Conclusions: Our findings provide insufficient evidence that graft type is associated with worse quantitative chondral changes within the PFJ at 6 months following ACLR. While meniscal status is a known risk factor for increased contact pressure in the involved compartment and subsequent degenerative progression, our data does not demonstrate statistically significant changes to the PFJ cartilage when meniscal tears were present, likely due to the limited sample size and large variation within groups. Future work with larger cohorts is needed to confirm our findings and further investigate the role that graft type and meniscal status may play within the PFJ after ACLR. [Figure: see text][Figure: see text][Figure: see text]

Multiscale modeling of friction hysteresis at bolted joint interfaces

Friction at connection interfaces plays an important role in understanding the nonlinear vibration response of jointed structures. A reliable friction contact model capable of reproducing nonlinear behaviors at the friction interface is critical in the design and optimization of jointed structures. In this paper, a multiscale friction model is proposed. This approach provides a novel perspective for improving prediction accuracy by combining the predictability offered by a physics-based model and the convenience of a phenomenological model. Specifically, this method considers the actual topography of joint interfaces by measuring the three-dimensional (3D) topography data with high-resolution instruments. The surface topography data is then processed to obtain the geometry data at different scales, and the finite element method is used to determine the physics-based multiscale contact pressure distribution of surfaces. The twofold Weibull mixture model is used to represent the contact pressure distribution and further determine the Iwan density function. The effectiveness of the proposed approach is validated by comparing the model predictions with the experiment results of a new as-built structure. Moreover, the effects of the surface roughness and waviness on the friction behavior are discussed.

ANALYTICAL STUDY OF DURABILITY AND CONTACT CHARACTERISTICS OF METAL-POLYMER COMPOSITE SLIDING BEARINGS FOR MEANS OF TRANSPORT

The field of application of metal-polymer bearings is vast: transport of various types, processing industry equipment, medical equipment, various types of maintenance equipment, etc. With the use of the developed generalized author's analytical method of metal-polymer plain bearings on the basis of which it is laid the author's research methodology of materials wear kinetics at sliding friction (dry, lubricated), calculation of their durability is carried out. Contact parameters are also determined. Metal-polymer bearings with a bushing made of PA6, PA66 polyamide and PA6 based composites filled with glass (PA6 + 30GF) and carbon (PA6 + 30CF) dispersed fibres, molybdenum disulphide (PA6 + MoS2) and oil filled cast polyamide (PA6 + oil) are considered. These polyamides (unfilled and filled), as self-lubricating materials, are widely used in this type of dry friction sliding bearings. The predictive estimation of durability of investigated bearings depending on loading, polymer materials Young's modulus, their wear resistance and sliding friction coefficient is executed. Regularities of change from the specified factors of bearing's durability and the maximum contact pressures are established. Experimental indicators, diagrams, and wear resistance characteristics of the specified polymeric materials are presented. The results of researches of sliding friction coefficient and modulus of elasticity for carbon steel (0.45%C) – polyamides tribocouples are presented.

IMPACT OF LOADS ON LOCOMOTIVE MOTOR AXLE BEARINGS ON THE CONDITIONS OF FORMATION OF OIL FILM ON FRICTION SURFACES

During the active operation of locomotives, a significant portion of failures (up to 20 %) is attributed to the malfunction of motor-axial bearings. This is due to the imperfection of the lubrication system of the motor-axial bearings, the proper functioning of which largely depends on various factors such as climatic conditions, the level of wear of lubricating oil, and lubrication devices, among others. There is a need to improve the existing lubrication systems for motor-axial sliding bearings. One of the methods to address this issue involves examining the factors influencing the lubrication process of the friction surfaces of motor-axial bearings and the conditions of lubricant material supply. The article provides calculations of the loading forces on the motor-axial bearings, their action vectors, and analyzes the impact of these parameters on the ability to form an oil film on the friction surfaces of motor-axial bearings. To determine the magnitude of the load, technical specifications of the locomotive were used, and the relationship between power usage and locomotive speed was analyzed. The study involved an analysis of recent publications regarding the generation of contact pressure force between the contact surfaces of friction pairs, the magnitude of which exceeds permissible limits, considered one of the primary factors leading to bearing failure. Additionally, the existing bearing lubrication system used on the locomotive was analyzed, its shortcomings were identified, and methods for addressing these issues were discussed. The calculations were performed for the 2TE116 locomotive with traction electric motors ED-118B, based on the operational characteristics of the locomotive in the speed range of 0-80 km/h.

Saliva-derived secondary DNA transfer on fabric: The impact of varying conditions

This study explored secondary DNA transfer involving saliva, a body fluid often encountered in forensic investigations. Various factors were examined to investigate their potential impact on the transfer of DNA from saliva stains deposited onto common types of fabric (cotton, nylon, and towel). We examined varying types of saliva moisture (wet, dry, and rehydrated) and different types of contact (controlled pressure and active/friction pressure) to quantitatively evaluate how such variables could impact transfer and possible conclusions surrounding saliva-derived DNA deposits. The transfer of DNA was generally least pronounced with more absorbent primary fabrics (cotton and towel materials) while a less absorbent primary fabric (nylon) exhibited a greater propensity for DNA transfer. There were significantly higher amounts of transferred DNA (p < 0.05) observed in wet saliva samples compared to dry and rehydrated saliva samples. Further, the use of active pressure (friction) appeared to result in more DNA transfer overall as compared to controlled pressure contact. Experiments conducted with wet saliva and active pressure (friction) demonstrated the highest likelihood of transfer, with the primary nylon and secondary towel fabric combination demonstrating the greatest average transfer percentage of 94.74 %. The variables explored in this study presented multiple combinations wherein a sufficient amount of DNA (≥ 240 pg total) was transferred to the secondary fabric, making it potentially suitable for STR-PCR amplification in our laboratory. The findings from this study indicate that the type of primary fabric receiving the saliva deposit, the type of saliva moisture, the type of secondary fabric and its moisture type, and the type of contact all have the potential to affect the quantity of DNA transferred and recovered. This study provides empirical data on the ease, and to what extent, DNA from saliva transfers between fabrics and aids DNA activity level evaluations. The significance of this research lies in its contribution to expanding our current understanding of DNA transfer involving saliva within forensic science and criminal investigations.

Degradation Processes of Two Compound Layers on Nitrided Surfaces During the Wear Test by “Block on Hot Al Cylinder”

The results obtained in the study help to explain the degradation process of the nitrided steel compound layer. Compound layers with different properties on gas-nitrided H10 tool steel blocks were tested for wear with “block on hot Al cylinder”. Degradation processes were observed on both compound layers with different properties and at three contact pressures. In order to observe the degradation processes in the compound layers, the wear tests were interrupted at various fixed time intervals and the resulting changes were closely monitored. The comprehensive analysis highlighted the complexity of the degradation process in the compound layers and emphasized the existence of complex relationships between the above-mentioned parameters. The reaction of the nitrided steel surface with hot Al is more pronounced in areas with lower contact pressure, while adhesive removal and furrow formation are pronounced in areas with low and medium contact pressure. This process begins with a sufficient density of the areas where islands of adhesive removal are located, their enlargement during the test, the breaking up of the walls between them, and finally the removal of the compound layer in the sliding direction, which appears as furrowing in the final phase of wear.

Evaluation framework of digital characteristics (DC) enhanced lubricant: Consideration of essential geometric features for hot-stamped components

Innovative digitally enhanced technologies are revolutionising the manufacturing systems, including the metal forming sector, at an unprecedented speed and scale. By utilising voluminous metadata collected through sensing networks and experimentally verified simulations during daily production and academic activities, profound insights can be provided to facilitate the ongoing efforts on understanding metal forming processes from the perspective of data. Data science in metal forming has emerged as an interdisciplinary research challenge that requires the knowledge of both manufacturing and data science. To unveil the distinctive thermo-mechanical characteristics of metal forming processes, for example the hot stamping process, the Digital Characteristics (DC), defined as the metadata visualisation that contains essential information spanning over the design, manufacturing and application of the manufactured products, were developed for different geometric features based on a vast number of hot stamping metadata. The analysis on distinctive hot stamping DC led to the development of a digitally enhanced interactive friction model considering complex, transient contact conditions incorporating evolutionary interfacial thermo-mechanical characteristics, such as interfacial temperature, contact pressure and sliding speed. The lubricant limit diagram (LLD) was developed demonstrated by coefficient of friction (COF) and performance grade (PG) to enable the quantitative evaluation of different lubricants considering different geometric features of hot-stamped components. The results advanced the understanding of lubricant performance and further demonstrated a novel methodology that integrates the development of DC in the hot stamping process, data-guided LLD, and a quantitative evaluation of lubricant performance. With the advancements in DC and LLD, a new framework can be established to characterise alternative applications in other forming processes that demand rigorous lubricant evaluation.

Polymer transfer film formation from cryogenic to elevated temperatures

This study reports on the tribological performance of aromatic thermosetting co-polyester (ATSP) and polyether ether ketone (PEEK)-based polymer composite coatings mixed with PTFE filler. The coatings were tested across a wide temperature range from −180 to 110 °C to simulate the environmental temperatures on Titan, Moon, and Mars, which are of particular interest for NASA’s future exploratory missions. An experimental setup was developed to conduct the pin-on-disk experiments under dry sliding conditions and extreme temperature and contact pressure. Transfer film formation and its characteristics were found to play significant roles in the tribological performance, and the characteristics of the film were temperature-dependent. The XPS and SEM analysis indicated the increase of the PTFE content in the transfer film as the temperature decreased to cryogenic conditions. The coefficient of friction did not follow a linear trend with temperature and was minimum at 110 °C and maximum at −180 °C. ATSP coating showed superior performance with lower friction and unmeasurable wear at all temperatures, whereas PEEK coating exhibited maximum wear at 25 °C followed by −180, and 110 °C.

Failure analysis and structural improvement of helicopter landing gear seals based on experiments and three-dimensional numerical simulation

The utilization of O-ring seal structures in landing gears has historically been associated with high rates of failure. Therefore, this study analyzes helicopter landing gear friction failures based on experimental and numerical simulations. The model is designed to replicate the failure phenomena including “seal extrusion”, “seal leakage”, “seal wear”, and “seal distortion”, and to further investigate causes of failure. Corresponding failure criteria are also presented. Addressing the deficiencies inherent in the original O-ring structure, three composite seal structures—namely, the VL seal, double triangle seal, and T-seal—are introduced to enhance the respective seal structure of the buffer pillar. The findings exhibit that, following the transition to the composite seal structure, the strain peaks are optimized. Finally, this paper offers optimal contact pressure ranges for the optimized seals.