Uniform Contact Pressure Distribution Research Articles

Bio-inspired Generative Design for Contact Interfaces

Synovial joints are known by their resistance to wear as they can withstand millions of load cycles. Such performance is attributed to the development process where joints are adapted to the loading environment. In engineering applications, wear is frequently a cause of failure. Classical joint design usually leads to uneven pressure distribution, accelerating wear in concentrated regions. In this work, we use a bio-inspired design methodology to generate contact interfaces. The key point of this methodology is the use of the growth rules of synovial joint during development. Specifically, hydrostatic stress promotes growth and high shear stress inhibits it. We apply these rules in an iterative algorithm to generate contact interfaces adapted to the loading environment. We present a case study to generate the shape of body in frictionless contact with an elastic half space using the bio-inspired approach. We compare the pressure and wear distribution between the bio-inspired and classical designs. The results highlight that the bio-inspired methodology produces almost uniform contact pressure and wear distribution, in contrast to the concentration inherent in classical designs. Thus, this study accentuates the potential advantages of this bio-inspired methodology, offering a compelling avenue for achieving high-performance contact interfaces.

Long-term bolt preload relaxation and contact pressure distribution in clamping anchorages for CFRP plates

Clamping anchorages are commonly used to anchor carbon fiber reinforced polymer (CFRP) plates, and the anchoring performance is significantly impacted by bolt preload. This research presents experimental and numerical investigations of long-term bolt preload relaxation in clamping anchorages for CFRP plates. First, a compression test was conducted to obtain the elastic modulus in the thickness direction of CFRP plates. Subsequently, four types of relaxation tests (single bolt, planar and curved anchorage, external load effect, and thickened anchorage) were conducted, considering the effects of the number of CFRP plates, anchorage type, external load, and initial preload. The elastic interaction during the tightening process was also investigated. The contact pressure distribution was simulated through the finite element method, which is in good agreement with the experimental results obtained from pressure papers. To fit relaxation test results and predict million-hour relaxation, different theoretical models were employed. The results indicate that the number of CFRP plates is crucial to preload relaxation, and the presence of CFRP plates introduces strong elastic interactions between bolts in the anchorage. Preload relaxation also increases under external loads and with the increase in initial preload. Curved anchorage has less bolt preload relaxation in the long term under external loads. Additionally, thickened anchorages have a more uniform contact pressure distribution due to the improved pressure diffusion mechanism.

Study of Contact Pressure Distribution in Bolted Encapsulated Proton Exchange Membrane Fuel Cell Membrane Electrode Assembly

The distribution of contact pressure on the Membrane Electrode Assembly (MEA) significantly affects the performance of a Proton Exchange Membrane Fuel Cell (PEMFC). This paper establishes a PEM fuel cell model to investigate the impact of bolt load and its distribution, sealing gasket hardness, and size on the magnitude and distribution of contact pressure on the MEA during assembly. Thermal–mechanical coupling is employed to simulate the thermal effects resulting from chemical reactions under operational conditions. The findings reveal that there is an extremum of pressure uniformity in the range of 5000 to 6250 N for bolt loads. When the average bolt load is lower than this extremum, altering the distribution of the load can effectively enhance the uniform distribution of contact pressure. Stiffer gaskets reduce the contact pressure on the MEA while increasing the pressure on the gasket itself, resulting in reduced deformation. A rational matching relationship among gaskets, Gas Diffusion Layers (GDLs), and seal grooves is proposed. During operational conditions, thermal effects decrease the sealing performance and also impact the magnitude and distribution of contact pressure on the MEA. These outcomes provide significant guidance for the assembly and performance evaluation of PEMFCs.

Dynamic Characteristics of a Rotating Blade with a Dovetail Fixture

Considering rotation-induced centrifugal stiffening, spin softening, and Coriolis effects, the reduced dynamic model of a rotating blade with a dovetail fixture is established in the ANSYS environment via the fixed-interface method for higher computational efficiency and lower memory consumption. Then some parameters such as rotating speed, friction factor, and stator blade number affecting the nonlinear vibration responses of the system under the combined actions of aerodynamic force, centrifugal force, and gravity are elaborately discussed. The results show that: (1) the contact-induced nonlinearity between the tenon and the mortise mainly results in the frequency multiplications of the aerodynamic excitation frequency; (2) a larger friction factor results in a lower magnitude of contact pressure and a higher resonance frequency, while a larger stator blade number results in a lower magnitude of the uniform and continuous contact pressure distribution; (3) the excitation of the resonant mode caused by the aerodynamic force is primarily characterized by the first-order bending mode of the system.

Volatile Lubricants Injected Through Laser Drilled Micro Holes Enable Efficiently Hydrocarbon-Free Lubrication for Deep Drawing Processes

In order to reduce the use of classic lubricants such as synthetic or mineral oils, emulsions or waxes in the deep drawing process, a new tribological system based on volatile lubricants was investigated. In this system, a volatile medium is injected under high pressure through laser drilled micro holes directly into the contact zone between the tool and the sheet metal and serves as a temporary lubricant. In order to investigate this tribological system under realistic conditions, strip drawing experiments with different volatile lubricants (air, nitrogen, carbon dioxide and argon) were performed on galvanized sheets. Therefore, a new generation of strip drawing tools was designed and numerically calculated for low elastic deformations to ensure a uniform contact pressure distribution over the entire friction contact area. To obtain a homogeneous distribution of the volatile lubricants, a number of micro holes with a depth of several millimeters were drilled into the hardened strip drawing jaws using ultrashort pulsed laser radiation. Taking into account the capabilities of this laser drilling technique in terms of size and shape of the micro holes, computational fluid dynamics simulations were performed to predict the flow behavior of the lubricant within the micro hole as well as the contact zone and were compared with observable effects in outflow tests. The chemical composition of the acting tribological layers was characterized by means of X-ray photoelectron spectroscopy and their changes during the deep drawing process were correlated with the lubricants used as well as the measured wear and friction values.

Design and Performance Evaluation of a Novel Spiral Head-Stem Trunnion for Hip Implants Using Finite Element Analysis

With an expectation of an increased number of revision surgeries and patients receiving orthopedic implants in the coming years, the focus of joint replacement research needs to be on improving the mechanical properties of implants. Head-stem trunnion fixation provides superior load support and implant stability. Fretting wear is formed at the trunnion because of the dynamic load activities of patients, and this eventually causes the total hip implant system to fail. To optimize the design, multiple experiments with various trunnion geometries have been performed by researchers to examine the wear rate and associated mechanical performance characteristics of the existing head-stem trunnion. The objective of this work is to quantify and evaluate the performance parameters of smooth and novel spiral head-stem trunnion types under dynamic loading situations. This study proposes a finite element method for estimating head-stem trunnion performance characteristics, namely contact pressure and sliding distance, for both trunnion types under walking and jogging dynamic loading conditions. The wear rate for both trunnion types was computed using the Archard wear model for a standard number of gait cycles. The experimental results indicated that the spiral trunnion with a uniform contact pressure distribution achieved more fixation than the smooth trunnion. However, the average contact pressure distribution was nearly the same for both trunnion types. The maximum and average sliding distances were both shorter for the spiral trunnion; hence, the summed sliding distance was approximately 10% shorter for spiral trunnions than that of the smooth trunnion over a complete gait cycle. Owing to a lower sliding ability, hip implants with spiral trunnions achieved more stability than those with smooth trunnions. The anticipated wear rate for spiral trunnions was 0.039 mm3, which was approximately 10% lower than the smooth trunnion wear rate of 0.048 mm3 per million loading cycles. The spiral trunnion achieved superior fixation stability with a shorter sliding distance and a lower wear rate than the smooth trunnion; therefore, the spiral trunnion can be recommended for future hip implant systems.

Arrangement of Belleville Springs on Endplates Combined with Optimal Cross-Sectional Shape in PEMFC Stack Using Equivalent Beam Modeling and FEA

A set of Belleville springs integrated into an endplate plays a key role in a proton exchange membrane fuel cell (PEMFC) stack, which makes the applied assembly force smoother, resulting from the absorbed vibration and thermal expansion. The appropriate arrangement of Belleville springs is important in PEMFC stack design. The aim of this study is to establish an equivalent beam model to optimize the numbers and positions of Belleville springs to minimize endplate deformation. Based on this, a finite element analysis (FEA) model of the PEMFC stack is proposed to further optimize the cross-sectional shape of the endplate. For the endplate with two, three and four groups of Belleville springs, its optimal positions correspond to 0.17lin, 0.27lin and 0.5lin (lin is the equal distance between steel belts). In addition, the low thickness should be 2/3 of the high thickness of the curved endplate for a uniform contact pressure distribution as well as the high-volume-specific power. However, the curvature radius of the endplate arc is negative to the uniformity of the contact pressure distribution, and particularly the internal cells of the PEMFC stack. This study provides a design direction for endplates combined with Belleville springs in large fuel cell stacks clamped with steel belts.

An equivalent mechanical model investigating endplates deflection for PEM fuel cell stack

The aim of this study is to obtain the deflection curve equations of endplates with one to five clamping belts which allows investigating endplates deflection for uniform contact pressure distribution. Based on an equivalent mechanical model for a large fuel cell stack, the effects of the thicknesses of endplates, numbers, and positions of clamping belts are discussed, and the optimal thickness of endplate with different clamping belts is obtained, and moreover the optimal position of intermediate and outer clamping belts on the endplates. Finally, a three-dimensional finite element analysis (FEA) of a fuel cell stack clamping with steel belts and nonlinear contact elements is compared to what the equivalent mechanical beam model predicts. The result of this study shows that the equivalent mechanical model gives good prediction accuracy for the deflection behavior of endplates and the clamping force of the fuel cell stack, which is effective and helpful for the design of a large fuel cell stack assembly.

3D printed deformable product handle material for improved ergonomics

In product handle ergonomic design optimisation researchers focused mainly on the size and shape of the handles; however, interface handle materials have been neglected despite showing potential to improve ergonomics. Deformable elastic cellular meta-materials with pre-engineered mechanical response based on the biomechanical evaluation of human hand soft tissue during grasping were designed and manufactured using commercial 3D printing technology. A sawing task has been utilized for the evaluation of subjective comfort rating. Based on distinct mechanical behaviour of cellular solids, 3D printed handle interface material stays stiff at the low grasping forces and deforms only when certain amount of contact pressure is reached. Cellular density can be easily adjusted to meet the desired biomechanical response. Hereby stability of the handle in hands is maximised while providing more uniform contact pressure distribution on the soft tissue at higher grasping forces. By this means comfort rating is also increased compared to stiff handle interface materials such as plastic. Results also suggest the handle material has greater influence on the comfort rating than the handle size and shape. Relevance to industryApplication of this research includes the utilization of this methodology and design techniques in development of handles for powered and non-powered tools and handheld products for improved comfort and also ergonomics.

The effects of the friction block shape on the tribological and dynamical behaviours of high-speed train brakes

Drag brake experiments using hexagonal, pentagonal, and circular friction blocks are conducted using a self-designed small-scale brake dynamometer to investigate the influence of the friction block shape on the tribological and dynamical behaviours of high-speed train brakes. A four-degree-of-freedom model that considers the interface contact behaviour is established to investigate the influence of the contact stiffness at the friction interface on the stability and vibration characteristics of the braking system. The experimental results show that the surface of the hexagonal friction block is slightly worn, and the contact plateaus is relatively uniform in size, whereas the pentagonal and circular friction blocks show visible ploughing and exfoliation and a significant proportion of large contact plateaus. Accordingly, the hexagonal friction block produces considerably less friction-induced vibration and noise than the pentagonal block and the circular block. Moreover, analysis of the vibration characteristics of the friction system indicates that the interface of the hexagonal friction block is mainly subjected to normal impact, whereas the interfaces of the other two blocks exhibit significantly more ploughing and shearing action in the tangential direction. In general, higher contact stiffness results in stronger friction-induced vibration, thereby enhancing the instability of the friction system. In this work, it is found that the friction block shape has a significant effect on the contact pressure distribution. The hexagonal friction block exhibits a more uniform distribution of contact pressure than the pentagonal and circular friction blocks, resulting in the lowest contact stiffness, as well as the least wear, vibration, and noise.

Elastic punching of material during flattening of a spherical asperity and restoration of the imprint in unloading

The development of the methodology previously proposed by the authors for determining the displacements of half-space points under the action of an axisymmetric load described by a parabola is presented. It is shown that when the sphere is flattened, the pressure distribution on the contact area is a function of complex shape, which can be represented by a combination of several equations for description in adjacent sections. The knowledge and description of the contact pressure distribution function is of practical importance in solving the issues of elastic punching of the material, the magnitude of the elastic recovery of the contact print during unloading, and determining the curvature of its profile. Equations are proposed for determining displacements inside and outside the contact area when describing the distribution of contact pressure by analytical functions and when using a discrete distribution of contact pressure. The accuracy of the obtained results depends on the rate of the approximating functions to the actual pressure distribution at the contact area. At the same time, the goals of the problems to be solved should be considered. When determining elastic recovery in the center of the contact area, it is sufficient to use a uniform distribution of contact pressure. When determining the profile of the restored contact print and its curvature, increased accuracy of approximating functions is required.

The Sealing Technology in Pipeline Repair Clamp

Zhao, B.J.; Zhang, S.L.; Li, T.; Hao, J.L., and Wang, T.Y., 2020. The sealing technology in pipeline repair clamp. In: Guido Aldana, P.A. and Kantamaneni, K. (eds.), Advances in Water Resources, Coastal Management, and Marine Science Technology. Journal of Coastal Research, Special Issue No. 104, pp. 872–881. Coconut Creek (Florida), ISSN 0749-0208.In order to meet the repair requirements in the subsea pipeline, the present study envisages the design for the sealing structure of the subsea oil and gas pipeline repair clamp. Based on the uniform contact pressure distribution theory and the thick-walled cylinder theory, a theoretical calculation formula was established to calculate the contact pressure between the sealing ring and the pipeline. With a goal of employing a φ219 subsea oil and gas pipeline repair clamp, the finite element models were established and the finite element simulation calculations were carried out for different pressure and thickness sealing rings. Meanwhile, the models were calculated based on the theoretical calculation formula. Subsequently, the results of finite element simulation and the theoretical calculation formula were analysed. Based on the theoretical calculation and the finite element calculations, the acceptance criterion of the theoretical calculation was proposed. The study lays a reliable basis for the sealing design and manufacturing of subsea oil and gas pipeline clamp.

Modeling and design of tuned mass dampers using sliding variable friction pendulum bearings

An effective vibration control device, the pendulum tuned mass damper (P-TMD), can be easily realized as a mass supported on rolling or sliding pendulum bearings. While the bearings’ concavity provides the desired gravitational restoring force, the necessary dissipative force can be obtained either from additional dampers installed in parallel with the bearings or from the same friction resistance developing within each bearing between the roller/slider and the rolling/sliding surface. The latter solution may prove cheaper and more compact but implies that the P-TMD effectiveness will be amplitude dependent if the friction coefficient is kept uniform along the rolling/sliding surface, as in conventional friction bearings. In this case, the friction P-TMD will be as efficient as a viscous P-TMD only at a given vibration level, with large performance reductions at other levels. To avoid this inconvenience, this paper proposes a new type of sliding variable friction pendulum (VFP) TMD, called the VFP-TMD, in which the sliding surface is divided into two concentric regions: a circular inner region, having the lowest possible friction coefficient and the same dimensions of the slider, and an annular outer region, having a friction coefficient set to an optimal value. A similar arrangement has been recently proposed to realize adaptive seismic isolation devices, but no specific application to TMDs is reported. To assess the VFP-TMD performance, first its analytical model is derived, rigorously accounting for geometric nonlinearities as well as for the variable (in time and space) pressure distribution along the contact area, and then, an optimal design methodology is presented. Finally, numerical simulations show the influence of the main design parameters on the device behavior and demonstrate that the VFP-TMD can achieve nearly the same effectiveness of viscous P-TMDs, while considerably outperforming conventional uniform-friction P-TMDs. The proposed analytical model can be used to enhance or validate existing models of VFP isolators that assume a constant and uniform contact pressure distribution.

A Novel Analytical Solution for the Brazilian Test with Loading Arcs

This research study presents a new theoretical model to calculate the indirect tensile strength for the Brazilian disk with loading arcs, based on numerical simulations, two-dimensional elasticity theory, and Griffith failure criterion. The new expression incorporates a no uniform contact pressure distribution determined by the results of the simulations with the finite element method. A computational experiment design has been developed to test the accuracy of the predictions made with the proposed model. This study demonstrates that the stresses predicted with the new model are closer to those determined by the finite element models than other theoretical solutions available in the literature. Additionally, a comparative analysis with experimental results obtained by other authors also indicates that the new model provides a more accurate magnitude of the indirect tensile strength.

Investigation of contact pressure distribution on gas diffusion layer of fuel cell with pneumatic endplate

Polymer electrolyte membrane fuel cell is a promising energy conversion device because of its high energy density, high efficiency and low emissions. Contact pressure on gas diffusion layers plays an important role in the performance improvement of polymer electrolyte membrane fuel cells by optimizing the ohmic and concentration losses. In this paper, geometric parameters of a pneumatic clamping system are optimized using a central composite design method and finite element simulations to obtain the most uniform contact pressure distribution on gas diffusion layers. The experimental data obtained by the pressure mapping system have been employed to validate the results of the optimized clamping system. The embedded pressure measurement films are placed in the designed polymer electrolyte membrane fuel cell with an active area of 400 cm2. The results reveal that the maximum difference between numerical and experimental results is less than 8%. Moreover, the contact pressure distributions over the gas diffusion layer for the clamping systems of pneumatic and conventional endplates are compared. The results demonstrate that the weight and efficiency of the clamping system with optimized pneumatic endplate is significantly better than the clamping system with conventional endplates.

X-ray tomography and modelling study on the mechanical behaviour and performance of metal foam flow-fields for polymer electrolyte fuel cells

Porous metal foams have been used as alternative flow-fields in proton exchange membrane fuel cells (PEMFCs), exhibiting improved performance compared to conventional ‘land and channel’ designs. In the current work, the mechanical behaviour of PEMFCs using metal foam flow-fields is investigated across different length scales using a combination of electrochemical testing, X-ray computed tomography (CT), compression tests, and finite element analysis (FEA) numerical modelling.Fuel cell peak power was seen to improve by 42% when foam compression was increased from 20% to 70% due to a reduction in the interfacial contact resistance between the foam and GDL. X-ray CT scans at varying compression levels reveal high levels of interaction between the metal foam and gas diffusion layer (GDL), with foam ligaments penetrating over 50% of the GDL thickness under 25% cell compression. The interfacial contact area between the foam and GDL were seen to be 10 times higher than between the foam and a stainless-steel plate. Modelling results demonstrate highly uniform contact pressure distribution across the cell due to plastic deformation of the foam. The effect of stack over-tightening and operating conditions are investigated, demonstrating only small changes in load distribution when paired with a suitable sealing gasket material.

Improvement of Rolling Dynamics to Increase Roller Life in Ball Rolling

The downtime of ball-rolling mills is largely associated with the replacement of worn rollers. In the present work, the degree and location of critical roller wear are studied: the greatest wear is observed at the flanges in the billet-capture zone. The conditions required for billet capture and successful rolling are determined analytically. Variation in roller speed during billet supply is proposed. Tests are conducted with linear and quadratic variation in roller speed. The familiar formulas for the mean deformation rate are modified for linear and quadratic variation in roller speed. Experiments are conducted on the ball-rolling mill of AO EVRAZ Nizhnetagil’skii Metallurgicheskii Kombinat (NTMK), in rolling 60-mm ШЗГsteel grinding balls on a 40–80 rolling mill. In the experiments, the roller speed is varied manually according to a specified program, with billet capture by the rollers. It is found that speed variation significantly affects the mean pressure at the instant of billet capture. Time dependences of the torque and the mean contact pressure are plotted on the basis of calculation results and experimental data. Empirical characteristics with linear and quadratic variation in roller speed are presented. The permissible agreement of the calculated and empirical results is determined. The installation of a thyristor converter is proposed, so as to decrease the roller speed before billet capture and restore the speed to the rated value in specified fashion after capture. That yields a uniform distribution of the mean contact pressure over the roller length during automatic operation of the mill in different conditions. As a result, the roller wear is decreased, without loss of mill productivity. That reduces roller consumption and the mill downtime for roller replacement.

Influence of pressure distribution and friction on determining mechanical properties in the Brazilian test: Theory and experiment

The improved Brazilian test is a popular method for indirectly measuring rock mechanical parameters, in which the current assumption of a uniform contact pressure distribution on the disc-jaw interface would result in measurement deviations because the real distribution is non-uniform. This investigation examines the influence of pressure distribution and friction on the determination of mechanical properties such as tensile strength σt and Young's modulus E by both theoretical analyses and experiments. For a Brazilian disc under arbitrary distributions of normal and tangential loads, the power series expansion technique is used to find the analytical solutions of the full-field displacements and stresses. The related formulae for calculating the tensile strength σt and Young's modulus E are derived. Eight load distributions with identical resultant forces are considered. The results show that the series solution converges in the form of a negative power law. Based on the Griffith failure criterion, the minimum contact angles that make the crack initiate at the center of the disc are given for different load distributions. The analysis indicates that these distributions have a significant influence on Young's modulus E and, if the contact angle is smaller, on tensile strength σt. The deviation caused by ignoring friction is also discussed. The Brazilian test is implemented for shale disc samples. The tensile strength σt and Young's modulus E of shale are determined indirectly using the theoretical formulae discussed here and experimental data.

Design and optimization of the shape of the roller generatrix of double-row railway roller bearing

The paper considers constructing a parametric model of the double-row railway roller bearing and determining the optimal shape of its roller to reduce contact pressure. Solution of problems of one-and two-parameter roller shape optimization, ensuring maximum uniform contact pressure distribution, is achieved by forming the roller geometry by varying the radius of curvature of the roller generatrix, or by varying the two radii that describe the change in the generatrix curvature. The level of maximum contact pressure was considered as the objective function. To determine the contact pressures, finite element method in the formulation of the contact problem of elasticity theory was used. Numerical solution of the contact problem was performed by expanding Lagrange's method; ANSYS software package was used. Solution of problems of one-and two-parameter roller surface shape optimization was carried out by applying the penalty function method in combination with the alternating-variable descent method and the golden section search method. Optimal radii of curvature of roller generatrix of double-row railway roller bearing CRU 150x250 in the formulation of one-and two-parameter optimization problem were obtained. It was revealed that the roller generatrix geometry in the form of two conjugated radii of curvature ensures maximum contact pressure level by 8% lower than in forming the roller surface curvature by a single radius of curvature. The results show the possibility of a significant reduction of the contact pressure for a pair of roller - bearing race due to the optimal profiling of roller generatrix, which will allow proportionally increase the durability and life of the product.

Coupled thermal/structural contact analyses of shrink-fit tool holder

Design of shrink-fit tool holders requires fast reliable stress analysis (from operational point of view). However, such an analysis exhibits difficulties due to its nonlinear nature. This article shows how to execute a complete cycle of design analysis iteration utilizing finite element analysis approach. Each finite element analysis cycle of iteration requires both transient thermal and structural coupled analyses. For a particular initial design, the transient heating of shrink-fit holder is first simulated, that is, the tool inner diameter hole expands due to inductive heating from its nominal value, so that cutting tool is easily inserted. Following this, both tool holder and cutting tool are allowed to cool down so that shrink-fit design forms a uniform contact pressure distribution. Finally, cutting tool is fixed at the contact interface. Then, the tool assembly is rotated (for testing) up to a cutting speed of 40,000 r/min, where transmission torque is also calculated to assess design limits for safe/efficient torque transmission. All of these analyses complete a single design cycle of iteration of the shrink-fit tool holder. Results presented include the calculation of change in shrink-fit pressure values over preload and preload + spin cases. Further assessment is also made to make sure overall elastic equivalent stresses at maximum operating speed are below yield limit of the tool holder material used in the design.