Magnitude Of Contact Pressure Research Articles

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.

Tribological properties of AlCoCrCuFeNi0.7 using tribometer in ANSYS

Tribological properties of AlCoCrCuFeNi0.7 alloys under dry condition impression against SHK hardened steel were explored. Here the tribological property based on the type of high entropy alloy(HEA) material used which have its own properties. The HEA show significantly minor friction coefficient and weight loss of the material by rubbing against SHK hardened steel. The AlCoCrCuFeNi0.7 have better sliding wear characteristics than many of HEA alloys as literature review data shows due to it high strength and high hardness. The finite element software ANSYS 2021 R2 is used for wear simulation. Wear depth was assumed to be insufficient to influence the magnitude of contact pressure. The Archad's linear wear law is used to calculate wear depth and contact pressure, using the Euler integration formulation absorbed in Ansys.

Vocal fold dynamics in a synthetic self-oscillating model: Contact pressure and dissipated-energy dose.

The energy dissipated during vocal fold (VF) contact is a predictor of phonotrauma. Difficulty measuring contact pressure has forced prior energy dissipation estimates to rely upon generalized approximations of the contact dynamics. To address this shortcoming, contact pressure was measured in a self-oscillating synthetic VF model with high spatiotemporal resolution using a hemilaryngeal configuration. The approach yields a temporal resolution of less than 0.26 ms and a spatial resolution of 0.254 mm in the inferior-superior direction. The average contact pressure was found to be 32% of the peak contact pressure, 60% higher than the ratio estimated in prior studies. It was found that 52% of the total power was dissipated due to collision. The power dissipated during contact was an order of magnitude higher than the power dissipated due to internal friction during the non-contact phase of oscillation. Both the contact pressure magnitude and dissipated power were found to be maximums at the mid anterior-posterior position, supporting the idea that collision is responsible for the formation of benign lesions, which normally appear at the middle third of the VF.

Design and numerical investigation of an adaptive intramedullary nail with a novel interlocking mechanism

Abstract Malalignment is a common complication in the treatment of distal fractures of the tibia. Numerous efforts have been made to reduce the malalignment ratio. However, the reported cases with this disorder are still high. This study aimed at investigating an adaptive design of an intramedullary nail with a novel interlocking mechanism (AINIM), as an alternative for the customary nailing, in reducing malalignment ratio. A verified finite element model was employed to compare the performance of AINIM with the customary nail. The finite element model of the tibia follows the exact shape of the medullary canal, and nonhomogeneous material properties were assigned to the bone from bone ash density. It was assumed that the nails were implanted and interlocked in the tibia according to surgical protocols, and physiological-like loading was applied to finite element models. The results of this study showed that AINIM reduces the mean shear interfragmentary strains by about 30%, and the axial interfragmentary strain by 55%, also it increases the uniformity in the interfragmentary movements, compared to the customary nail. It was also found that AINIM caused a reduction of the stress on the nail by 60%, and an increase of 25% on the bone, compared to the customary nail. Moreover, average compressive principal strains in the tibia fixed by AINIM increased by 40% from 485 to 678 με, compared to the tibia fixed by the customary nailing method. The results of this work also showed that AINIM causes an increase in the contact area with the intramedullary canal, particularly at the fracture site, and it also escalates the magnitude of contact pressure. Results of this work indicate that, from the biomechanical standpoint, the adaptive nail, i.e. AINIM, with an innovative interlocking mechanism, compared to the customary nailing, can lessen intra- and post-operative malalignment occurrence, and it also mitigates the side effects of stress shielding, and thus better conserves neighboring bone density in a long period.

An Intelligent Approach for Contact Pressure Optimization of PEM Fuel Cell Gas Diffusion Layers

The compression of the gas diffusion layer (GDL) greatly affects the electrochemical performance of proton exchange membrane fuel cells (PEMFCs) by means of both the equivalent value and distribution of contact pressure, which depends on the packing manner of the fuel cell. This work develops an intelligent approach for improving the uniformity and equivalent magnitude of contact pressure on GDLs through optimizing the clamping forces and positions on end plates. A finite element (FE) model of a full-size single fuel cell is developed and correlated against a direct measurement of pressure between the GDL and a bipolar plate. Datasets generated by FE simulations based on the optimal Latin hypercube design are used as a driving force for the training of a radial basis function neural network, so-called the agent model. Once the agent model is validated, iterations for optimization of contact pressure on GDLs are carried out without using the complicated physical model anymore. Optimal design of clamping force and position combination is achieved in terms of better contact pressure, with the designed equivalent magnitude and more uniform distribution. Results indicate the proposed agent-based intelligent optimization approach is available for the packing design of fuel cells, stacks in particular, with significantly higher efficiency.

The Influence of the Honeycomb Design Parameters on the Mechanical Behavior of Non-Pneumatic Tires

Non-Pneumatic Tires with honeycomb structure have complex design and their mechanical behavior is influenced by their geometry. As a result, deep understanding of the effect of various design parameters is very important for design optimization. In this numerical analysis, the effect of a wide range of internal geometrical parameters on the tire’s weight and mechanical behavior was quantified. For this purpose, a parametric finite element model was designed and subjected to vertical loading to assess its maximum stress, contact pressure, maximum vertical displacement and energy absorbed during loading. The analysis indicated that vertical stiffness is strongly affected by the density, thickness and internal angles of the honeycomb cells. The internal angles of the honeycomb also appeared capable of changing the tire’s vertical stiffness without changing its weight, which is associated with the tire’s fuel efficiency and dynamic properties. A decrease in cell length or an increase in cell density was capable of significantly reducing the internal stresses. Proper tuning of cell thickness or cell length could also significantly reduce the magnitude of contact pressure developed by producing a more even distribution of loading between the tread and the road.

Is there any advantage of using stand-alone cages? A numerical approach

BackgroundSegment fusion using interbody cages supplemented with pedicle screw fixation is the most common surgery for the treatment of low back pain. However, there is still much controversy regarding the use of cages in a stand-alone fashion. The goal of this work is to numerically compare the influence that each surgery has on lumbar biomechanics.MethodsA non-linear FE model of the whole lumbar spine was developed to compare between two types of cages (OLYS and NEOLIF) with and without supplementary fixation. The motion of the whole spine was analysed and the biomechanical environment of the adjacent segments to the operated one was studied. Moreover, the risk of subsidence of the cages was qualitatively evaluated.ResultsA great ROM reduction occurred when supplementary fixation was used. This stiffening increased the stresses at the adjacent levels. It might be hypothesised that the overloading of these segments could be related with the clinically observed adjacent disc degeneration. Meanwhile, the stand-alone cages allowed for a wider movement, and therefore, the influence of the surgery on adjacent discs was much lower. Regarding the risk of subsidence, the contact pressure magnitude was similar for both intervertebral cage designs and near the value of the maximum tolerable pressure of the endplates.ConclusionsA minimally invasive posterior insertion of an intervertebral cage (OLYS or NEOLIF) was compared using a stand-alone design or adding supplementary fixation. The outcomes of these two techniques were compared, and although stand-alone cage may diminish the risk of disease progression to the adjacent discs, the spinal movement in this case could compromise the vertebral fusion and might present a higher risk of cage subsidence.

Comparative tests of contact elements at current collectors in order to comprehensively assess their operational performance

We have studied the interaction between contact elements in the pantographs of electric transport under operation at the sections of railroads powered by direct and alternating current. In contrast to known techniques for bench tests, we investigated the mechanism of current collection and wear resistance at the new testing installation over a minimally narrow region of the sliding contact, simulating the phenomenon of a cut. This installation can be used both industrially when manufacturing new contact elements and under laboratory setting when studying wear resistance. The experimental research confirmed that the wear intensity of contact elements at pantographs depends on current load over a contact area, the magnitude of contact pressure, the area of a contact surface, and motion speed. We have practically proven a possibility to maintain a reliable contact connection in the sliding contact under extreme operating conditions when using a reliable contact material for the current collector pads. It has been proposed to use the powder composition BrIG based on bronze, iron, and graphite, for making contact elements for pantographs that could provide for reliable contact when interacting with the contact wire. Application of new and high-quality contact materials affects the tribology and stability of interaction between plates and the contact wire. Owing to our study, a possibility has been established to manufacture a reliable contact element BrIG, which would prolong the time of interaction in the contact pair pantograph at electric transport ‒ contact network. The practical significance of this research relates to the proven efficiency of utilizing the new contact material BrIG for electric railroad transport network, in trolley buses and trams. Thus, one can argue about the possibility to prolong the time of operation for the contact pair pad in a at electric transport ‒ contact network by applying the new contact material BrIG

Numerical investigation of crack initiation in rails and wheels affected by martensite spots

White etching layers (WELs) in the form of thermally induced martensite spots are often associated to so-called stud defects on rail surfaces and so-called rolling contact fatigue clusters on wheel treads. These defects might promote further material deterioration of rails and wheels and it is thus of importance to deepen the knowledge regarding their initiation mechanisms. The aim of this study is to gain insight into the problem by making qualitative assessments of different operational scenarios, involving various axle loads and amount of friction. To this end, this paper considers crack initiation, quantified through the Jiang–Sehitoglu low cycle fatigue criterion, in the vicinity of pre-existing WELs (in the form of martensite spots) subjected to varying contact load conditions. Three-dimensional finite element analyses are conducted to model phase transformations as well as the resulting residual stresses. It is seen that the contact pressure magnitude and WEL thickness affect the results only moderately, while the traction coefficient has a significant detrimental influence. It is furthermore seen that occasional wheel passages that are off-set in the lateral direction with respect to the WEL spot’s centre might be responsible for crack initiation on the gauge corner side of the rail surface.

Smart pressure distribution estimation in biological joints for mechanical bio-inspired design

Designing new mechanical links using bio-inspiration requires the knowledge of operating contact pressure in biological joints. However, the contact pressure magnitude and distribution are difficult to measure experimentally without disrupting the functioning of the articulation. In this paper, a new methodology to estimate the pressure distribution in biological joints is presented. A robust finite element model was developed based on in-vitro precise measurements of shapes, relative positions and loads in order to get accurate results. Furthermore, the envelope of the contact area was obtained through thermal imaging for comparison with the numerical results and qualitative validation of the FE model.

Investigation of the process of thread extrusion using the ultrasound

We investigated and modelled the process of ultrasonic extrusion of a thread when imposing the ultrasonic oscillations. Based on the rheological model of deformation of the perfect elastic-plastic body, we constructed dependences for the calculation of contact pressures and specific friction force. In carrying out the present research, in order to simplify a mathematical model, the assumption was made on that the phenomenon of surface strengthening exerts little effect on the magnitude of contact pressure and friction force at plastic deformation. This mathematical model describes complex motion of the tool (rotational and oscillatory motion of the tap). The system of the derived dependences, which describes the influence of oscillation amplitude, oscillation direction, deformation rate, and mechanical properties of the machined material on the magnitude of contact pressure, makes it possible to estimate parameters of the process of plastic deformation when imposing the ultrasound. By employing such a description, it is possible to derive the value of contact pressure and friction forces for each region of the load chart. During analysis of the obtained results it was established that an increase in the amplitude of oscillations leads to a decrease in the time of contact between a tool and the machined surface, which is why contact pressure, specific friction of axial and torsional oscillations over a period decrease accordingly within a change in the examined factors. The benefit of the present study is a detailed analysis of the contact interaction between a tool and a part, as well as consideration of mechanical properties of the machined material, which makes it possible to choose the modes of treatment and to provide maximum operational performance

Medial knee loading is altered in subjects with early osteoarthritis during gait but not during step-up-and-over task.

This study evaluates knee joint loading during gait and step-up-and-over tasks in control subjects, subjects with early knee OA and those with established knee OA. Thirty-seven subjects with varying degrees of medial compartment knee OA severity (eighteen with early OA and sixteen with established OA), and nineteen healthy controls performed gait and step-up-and-over tasks. Knee joint moments, contact forces (KCF), the magnitude of contact pressures and center of pressure (CoP) location were analyzed for the three groups for both activities using a multi-body knee model with articular cartilage contact, 14 ligaments, and six degrees of freedom tibiofemoral and patellofemoral joints. During gait, the first peak of the medial KCF was significantly higher for patients with early knee OA (p = 0.048) and established knee OA (p = 0.001) compared to control subjects. Furthermore, the medial contact pressure magnitudes and CoP location were significantly different in both groups of patients compared to controls. Knee rotation moments (KRMs) and external rotation angles were significantly higher during early stance in both patient groups (p < 0.0001) compared to controls. During step-up-and-over, there was a high variability between the participants and no significant differences in KCF were observed between the groups. Knee joint loading and kinematics were found to be altered in patients with early knee OA only during gait. This is an indication that an excessive medial KCF and altered loading location, observed in these patients, is a contributor to early progression of knee OA.

Numerical Simulation & Experimental study of wear depth and Contact pressure distribution Of Aluminum MMC Pin on Disc Tribometer.

This paper is focused on Simulation and analysis of a simple tribo system confirming to ASTM G99, constituted by a deformable cylindrical pin that rotates around a rigid disc surface with friction. Aluminum6061 Metal Matrix Composite samples have been experimentally analyzed to investigate the Tribological characteristics of wear for various loading conditions with a constant sliding rotational velocity. The finite element software ANSYS 15 is used for this wear simulation. Assumptions were made that wear depth is not enough to change the contact pressure magnitude. The wear depth and contact pressure are being evaluated by the Archad’s linear wear law with the Euler integration formulation absorbed in Ansys. The wear coefficient (k) obtained from the experimental results which also accounted the effect of oxide formation & debris during dry slide wear. Simulation of wear involves solution of a general contact problem, which is highly non-linear due to the contact boundary conditions between the interfaces. The prediction of wear depth is evaluated from contact pressure, which is obtained from finite element simulation results & it is an input into Archard’s wear equation. It is found that simulation results are confirming in line with the experimental results.

Influence of step rate and quadriceps load distribution on patellofemoral cartilage contact pressures during running

Interventions used to treat patellofemoral pain in runners are often designed to alter patellofemoral mechanics. This study used a computational model to investigate the influence of two interventions, step rate manipulation and quadriceps strengthening, on patellofemoral contact pressures during running. Running mechanics were analyzed using a lower extremity musculoskeletal model that included a knee with six degree-of-freedom tibiofemoral and patellofemoral joints. An elastic foundation model was used to compute articular contact pressures. The lower extremity model was scaled to anthropometric dimensions of 22 healthy adults, who ran on an instrumented treadmill at 90%, 100% and 110% of their preferred step rate. Numerical optimization was then used to predict the muscle forces, secondary tibiofemoral kinematics and all patellofemoral kinematics that would generate the measured primary hip, knee and ankle joint accelerations. Mean and peak patella contact pressures reached 5.0 and 9.7MPa during the midstance phase of running. Increasing step rate by 10% significantly reduced mean contact pressures by 10.4% and contact area by 7.4%, but had small effects on lateral patellar translation and tilt. Enhancing vastus medialis strength did not substantially affect pressure magnitudes or lateral patellar translation, but did shift contact pressure medially toward the patellar median ridge. Thus, the model suggests that step rate tends to primarily modulate the magnitude of contact pressure and contact area, while vastus medialis strengthening has the potential to alter mediolateral pressure locations. These results are relevant to consider in the design of interventions used to prevent or treat patellofemoral pain in runners.

Computational biomechanics of articular cartilage of human knee joint: Effect of osteochondral defects

Articular cartilage and its supporting bone functional conditions are tightly coupled as injuries of either adversely affects joint mechanical environment. The objective of this study was set to quantitatively investigate the extent of alterations in the mechanical environment of cartilage and knee joint in presence of commonly observed osteochondral defects. An existing validated finite element model of a knee joint was used to construct a refined model of the tibial lateral compartment including proximal tibial bony structures. The response was computed under compression forces up to 2000 N while simulating localized bone damage, cartilage–bone horizontal split, bone overgrowth and absence of deep vertical collagen fibrils. Localized tibial bone damage increased overall joint compliance and substantially altered pattern and magnitude of contact pressures and cartilage strains in both tibia and femur. These alterations were further exacerbated when bone damage was combined with base cartilage split and absence of deep vertical collagen fibrils. Local bone boss markedly changed contact pressures and strain patterns in neighbouring cartilage. Bone bruise/fracture and overgrowth adversely perturbed the homeostatic balance in the mechanical environment of articulate cartilage surrounding and opposing the lesion as well as the joint compliance. As such, they potentially contribute to the initiation and development of post-traumatic osteoarthritis.

Mechanical Responses of the Rabbit Patello-Femoral Joint to Blunt Impact

Various studies suggest impact trauma may initially soften cartilage, damage subchondral bone, or a combination thereof. The initial damages are commonly thought due to excessive contact pressure generated on cartilage and the underlying bone. The objective of this research was to develop a small animal model for studying post-traumatic OA and to correlate contact pressure with tissue damage. Blunt insult was graded by dropping a rigid mass onto the hyperflexed hind limb of rabbits. Contact pressure in the patello-femoral joint was measured with pressure sensitive film. One, 3, 6, and 14 days later the animals were euthanized. Damage to cartilage and the underlying bone was assessed visually and in microscopic sections. Indentation experiments were performed on the patellar cartilage with a rigid, flat probe. Contact pressures were nonuniform over the articular surfaces and a high frequency of surface fissures were generated on the lateral facet in severe insults. The appearance of surface fissures correlated better with the magnitude of contact pressure gradients in the damage zone than the magnitude of contact pressures on the facet, per se. Blunt trauma causing surface fissures resulted in a measurable degree of softening in the patellar cartilage, especially close to the defects. Surgical intervention of the joint to insert pressure sensitive film, however, also resulted in significant softening of the cartilage.