Tangential Traction Research Articles

Idiopathic Macular Hole without Vitreomacular Separation

Purpose: This study aimed to investigate the clinical features and treatment outcomes of idiopathic full-thickness macular hole (FTMH) without vitreomacular separation (VMS). Methods: Consecutive cases of idiopathic FTMH at one tertiary center from January 2013 to April 2020 were retrospectively recruited. They were separated into two groups according to the findings in optical coherence tomography (OCT): FTMH with VMS and FTMH without VMS. Ophthalmic examinations and OCT were performed pre- and postoperatively. The clinical findings were compared between the two groups. Results: Of the total 124 cases, 15 (12.1%) were noted as FTMH without VMS with the presence of an attached posterior hyaloid (PH) at macula. The macular hole (MH) size was smaller (276.06 ± 170.10 μm) compared to those with VMS (492.83 ± 209.31 μm) (p < 0.001). The incidence of lamellar hole-associated epiretinal proliferation (LHEP) was much higher in this group (13/15, 86.7%) compared to FTMH with VMS (11/109, 10.1%) (p < 0.001). A higher rate of spontaneous closure of MH (13.3%) was also noted in FMTH without VMS (13.3% vs. 0.9% in FTMH with VMS, p = 0.040). After operation, the MH closure rate was 93.3%. The postoperative best-corrected visual acuity was not significantly different between the two groups (p = 0.098). Conclusions: A small percentage (12.1% in this series) of idiopathic FTMH had no VMS. The completely attached PH along with the high incidence of LHEP implied a tangential traction in FTMH without VMS. The MH size was usually small, and the postoperative outcomes were similar to those of conventional FTMH with VMS.

On the growth of rolling contact fatigue cracks using weight functions

The present paper discusses the estimation of the stress state of Rolling Contact Fatigue (RCF) cracks according to linear elastic fracture mechanics, by making use of the weight function to obtain the Stress Intensity Factors. The weight functions are considered for both the mode I and mode II Stress Intensity Factor and are based on existing formulations for an inclined edge crack in a finite width plate for which Green’s functions are derived by means of a numerical methods. The Stress Intensity Factors been predicted for a side crack having an inclination angle typical for RCF defects in a plate of finite width supported by an elastic foundation and subjected to a moving wheel load, modelled as a patch load. The Stress Intensity Factors are obtained by superimposing the bending moment due to the moving load, and local stresses due to normal pressure and tangential tractions resulting from the contact with the wheel. These local stresses are determined using theoretical solutions partially available in the literature. The Stress Intensity Factors obtained are compared with the results of numerical models presented in the literature regarding the RCF crack growth.

The contribution of plastic sink-in to the static friction of single asperity microscopic contacts

We report microscale friction experiments for diamond/metal and diamond/silica contacts under gigapascal contact pressures. Using a new nanoprobe technique that has a sufficient dynamic range of force and stiffness, we demonstrate the processes involved in the transition from purely interface sliding at the nanoscale to the situation where at least one of the sliding bodies undergoes some plastic deformation. For sliding of micrometre-sized tips on metallic substrates, additional local plastic yielding of the substrate resulting from tangential tractions causes the tip to sink into the surface, increasing the contact area in the direction of loading and resulting in a static friction coefficient higher than the kinetic during ploughing. This sink-in is largely absent in fused silica, and no friction drop is observed, along with lower friction in general. The transition from sink-in within the static friction regime to ploughing in the sliding friction regime is mediated by failure of the contact interface, indicated by a sharp increase in energy dissipation. At lower contact pressures, the elastic interfacial sliding behaviour characteristic of scanning probe or surface force apparatus experiments is recovered, bridging the gap between the exotic realm of nanotribology and plasticity-dominated macroscale friction.

Adhesive behavior of transversely isotropic piezoelectric bimaterials

The adhesive contact behavior between two dissimilar transversely isotropic piezoelectric cylinders is investigated in this paper. The effect of adhesion on the contact behavior between piezoelectric bimaterials is considered within the framework of the non-slipping JKR model, which takes the coupling effect between the tangential and normal tractions inside the contact region into account. The explicit analytical solutions of stress and electric displacement fields within the contact region are obtained by solving the resulting coupling singular integral equations with the analytical function theory. The relationship between the contact size and external loadings are established by adopting the Griffith energy balance criterion at the edges of the contact zone. It is found that different types of piezoelectric bimaterials show the same adhesive contact behaviors, which is different from the case of a single layer piezoelectric material. The result obtained from the present paper should be helpful for the design of micro-electro-mechanical systems (MEMS) devices involving multi-layered smart structures.

Effects of Near-Surface Composites on Frictional Rolling Contact Solved by a Semi-Analytical Model

Abstract A semi-analytical model (SAM) to tackle the steady-state elastic frictional rolling contact problem involving composites is presented. Specifically, the frictional rolling contact is categorized into two subtypes, namely, normal and tangential problems, and the conjugate gradient method (CGM) is used to figure out the normal pressure and tangential traction. In SAM, the equivalent inclusion method (EIM) is applied to analyze the influence of composites on the matrix, and the displacement disturbance resulting from such composites is added to the total surface displacement, which implements the coupling between surface contact and composites. The accuracy of the proposed model is verified by the finite element (FE) model. The effects of composites on the frictional rolling contact behavior are investigated. The results indicate that Young’s modulus, as well as the size and location of the composites, are correlated with the distributions of tangential traction, subsurface stresses, and the sizes of stick and sliding zones.

A framework for the analysis of fully coupled normal and tangential contact problems with complex interfaces

An extension to the interface finite element with eMbedded Profile for Joint Roughness (MPJR interface finite element) is herein proposed for solving the frictional contact problem between a rigid indenter of any complex shape and an elastic body under generic oblique load histories. The actual shape of the indenter is accounted for as a correction of the gap function. A regularised version of the Coulomb friction law is employed for modeling the tangential contact response, while a penalty approach is introduced in the normal contact direction. The development of the finite element (FE) formulation stemming from its variational formalism is thoroughly derived and the model is validated in relation to challenging scenarios for standard (alternative) finite element procedures and analytical methods, such as the contact with multi-scale rough profiles. The present framework enables the comprehensive investigation of the system response due to the occurrence of tangential tractions, which are at the origin of important phenomena such as wear and fretting fatigue, together with the analysis of the effects of coupling between normal and tangential contact tractions. This scenario is herein investigated in relation to challenging physical problems involving arbitrary loading histories.

The influence of 2D periodic surface texture on the partial slip problem for elastic bodies

We consider contact interaction of elastic bodies, one of which has a 2D texture, described by a sinusoidal function of 2n power, in partial slip conditions within two material models. The first approach based on the Cattaneo-Mindlin theory for linear elastic half-plane, the second is an elastic foundation model (EFM) which takes into account normal and tangential compliances. Analytical expressions for determining the size of the contact zone and the stick and slip zones for both models are obtained, as well as the expressions for the normal and tangential tractions. It is shown that for relatively small profile heights, both models give close results for the stick and slip zones sizes when the parameters of the EFM are selected from the developed half-plane solution. We analyze the influence of the geometric parameters (shape, profile height, and distance between the grooves) of the texture profile on the stick zone size while the tangential force increases. The EFM model allows capturing the dependence of the stick zone width on the profile height.

Modelling tangential contact problem with surface stress

In this paper, we investigate the effects of surface stress on the spherical contact problem under combined normal and lateral loads. The boundary element method based on fast Fourier transform and conjugate gradient algorithm is employed to perform the contact analysis with partial slip. It is shown that as the size of contact reduces to the characteristic scale that surface stress dominates, the contact behavior will significantly deviate from the classical model. Under the same loading condition, the tangential traction within contact region tends to distribute more evenly and the width of slip zone would be relatively smaller due to the presence of surface stress. In addition, it is found that the variations of the total tangential force and the lateral contact stiffness with respect to the lateral displacement depend strongly on the contact scale. This work provides a theoretical basis for the study of contact and friction of some soft materials and biological systems.

An irreversible bilinear cohesive law considering the effects of strain rate and plastic strain and enabling reciprocating load

The commonly used bilinear cohesive law doesn’t consider the effects of strain rate and plastic strain, but it is well known that strain rate and plastic strain can greatly affect materials’ mechanical response. In this paper a new bilinear cohesive law is proposed that can handle these two effects and enables reciprocating load. Compared with the commonly used bilinear cohesive law, one difference in the new bilinear cohesive law is that normal traction and tangential traction are always coupled even when normal traction is negative. And after combined with finite thickness modeling method of cohesive element, this new bilinear cohesive law can solve problems like penetration, force discontinuity and increase of compliance. For damage evolution model, the difference between monotonically increasing effective separation and monotonically increasing damage factor is explained. The influence of strain rate (or opening speed) on stiffness, fracture strength and critical energy release rate is referred from literature. Based on zero plastic strain damage factor model, a Generalized Damage Factor Model (GDFM) is proposed that can cover all materials from zero plastic strain to full plastic strain by changing only one parameter. A Bilinear Cohesive Law Update Method (BCLUM) is proposed to make this new bilinear cohesive law handle reciprocating load, which includes the update of local coordinate system and bilinear cohesive law parameters. A single cohesive element analysis is presented first to show some basic differences among different bilinear cohesive laws, and then Tapered Double Cantilever Beam (TDCB) and Mixed Mode Bending (MMB) analyses are used to verify the proposed law.

Energy release rate, the crack closure integral and admissible singular fields in fracture mechanics

One of the assumptions of Linear Elastic Fracture Mechanics is that the crack faces are traction-free or, at most, loaded by bounded tractions. The standard Irwin’s crack closure integral, widely used for the computation of the Energy Release Rate, also relies upon this assumption. However, there are practical situations where the load acting on the crack boundaries is singular. This is the case, for instance, in hydraulic fracturing, where the fluid inside the crack exerts singular tangential tractions at its front. Another example of unbounded tractions is the case of a rigid line inclusion (anticrack) embedded into an elastic body. In such situations, the classical Irwin’s crack closure integral fails to provide the correct value of the Energy Release Rate. In this paper, we address the effects occurring when square-root singular tractions act at the boundary of a line defect in an elastic solid and provide a generalisation of Irwin’s crack closure integral. The latter yields the correct Energy Release Rate and allows broad applications, including, among others, hydraulic fracturing, soft materials containing stiff inclusions, rigid inclusions, shear bands and cracks characterized by the Gurtin-Murdoch surface stress elasticity. We present the results in the most general form, where six Stress Intensity Factors are present: three of them are classical SIFs corresponding to the Modes I-II-III and computed under the assumption of homogeneous boundary conditions at the defect surfaces, while the other three SIFs are associated with singular admissible tractions (those that lead to a finite ERR value). It is demonstrated that this approach resolves an ambiguity in using the same SIF’s terminology in the cases of open cracks and rigid inclusions, among other benefits.

Теоретические исследования производительности форвардеров при ограничениях воздействия на почвогрунты

Wheeled forest machines currently dominate the logging industry in Russia and in the world. Every year in Russia, the share of machine-made wood harvesting using Scandinavian technology increases, which involves felling trees, delimbing, and bucking them at a swath. Moreover, this technology is used not only for conventional two-machine systems with harvester and forwarder. In some regions of Siberia three-machine systems are gaining popularity. They consist of a feller-buncher, a swath processor, and a forwarder for skidding obtained logs. The issue of increasing the efficiency of forwarders is relevant for the timber industry. Its solving is possible on the basis of a comprehensive assessment of design solutions with the use of modern modeling and process optimization tools at the stage of development design. This approach requires deep theoretical and experimental research and is of great scientific and practical interest. When determining the maximum volume of skidded wood, the following machine limitations are considered: by bearing capacity; by tangential traction force; by the traction of the mover with the soil (tangential traction force should not exceed the traction force of the mover with the driving surface – the soil of the logging site). Besides this, there are recommendations to limit the weight of the skidder with the load, based on the permissible track depth after the first pass of the machine; it is believed that this figure should not exceed 20 cm. This statement is supported by the results of studies of the track development under the cyclic influence of the wheel mover (that is when the forwarder repeatedly passes the same section of the portage). This raises the question of forwarder productivity in the skidding operation with the regard to the track depth limitation. For citation: Burmistrova O.N., Prosuzhih A.A., Khitrov E.G., Kunitskaya O.A., Luneva E.N. Theoretical Studies of Forwarder Productivity with Limited Impact on Soils. Lesnoy Zhurnal [Russian Forestry Journal], 2021, no. 3, pp. 101–116. DOI: 10.37482/0536-1036-2021-3-101-116

Arbitrarily loaded circular crack in a piezoelectric solid of the symmetry class 6

The paper focuses on the problem of evaluating analytically the electric and elastic fields in a piezoelectric material of the symmetry class 6 containing a penny-shaped crack loaded by both normal and tangential tractions and by electric charges. A solution of this kind has been developed for symmetry class 6 mm by Karapetian et al. (Arch. Appl. Mech. 70: 201–229, 2000). To the best of our knowledge, it has never been derived for a material of class 6. The research is motivated by needs in evaluation of damage accumulated in bone tissue, which possesses such a symmetry. The problem is solved by the method of potential functions developed by Fabrikant (Applications of Potential Theory in Mechanics: Selection of New Results. Kluwer, Dordrecht,1989). Closed form solutions are obtained for the full electric and elastic fields. The approach is first verified by comparison with the results of Karapetian et al. (Arch. Appl. Mech. 70: 201–229, 2000) for the limiting case of piezoceramic of class 6 mm (PZT-6B) and then applied to calculation of the electroelastic fields associated with a penny-shaped crack in cortical bone (material of class 6).

Tribological Analysis of Engineering Plastics/Steel Friction Pairs

This study involves the case of polymer–metal contact, where deformation and strain behavior play a significant role. In present work, a section of polymer gear is mated against steel gear, and the friction behaviors for different groups of polymer materials of PA 6G, PA 6G Mg, POM-C, PETP/PTFE, PA 66 GF 30 and Bakelite were experimentally studied. From the results obtained, all the materials coefficient of friction decreased significantly at the pitch point. This was attributed to the pure rolling at the pitch point and tangential traction, which was the dominant mechanism for resistance to motion. An unstable friction characteristic from flank tooth to the pitch point was evident in the low load conditions.

Numerical study on the ratcheting performance of rail flash butt welds in heavy haul operations

The ratcheting performance of a new R400HT rail flash butt weld was numerically evaluated under a typical heavy haul in-service condition. Due to varying mechanical properties across the rail weld, the weld region was divided into 23 zones in the numerical study. A dynamic finite element simulation of wheel–rail weld rolling contact was first carried out to obtain the total vertical contact force and its variation along rolling distance. Multiple quasi-static wheel–rail weld contact simulations were then performed by applying the total vertical contact force to determine the non-Hertzian contact pressure distribution when the wheel was located at different positions across the weld in the rolling direction. Based on each normal contact pressure distribution, the Haines and Ollerton's strip theory and Carter's theory were employed to estimate the corresponding longitudinal surface tangential traction distribution. Finally, a cyclic loading simulation was conducted to evaluate the ratcheting performance of the rail weld in terms of RCF initiation life by repeatedly translating these normal contact pressure and longitudinal tangential traction distributions on the running surface. The results reveal that the subzone with the lowest hardness in the softened zone has the shortest RCF initiation life among the weld region, followed by the region around the bond line. The parent rail provides the longest RCF initiation life and therefore has the best resistance to RCF. Additionally, the existence of the softened zone can shorten the RCF initiation life of the parent rail and the bond line section, particularly the regions located adjacent to the softened zone. The possible location of RCF initiation in the softened zone of the rail head can reach deeper than those in the parent rail and the region around the bond line. The results can help us understand the failure of flash butt rail welds in heavy haul operations and the numerical method can be applied to study different rail welds and rail welds under different conditions such as in a curved track.

Spontaneous Conversion of Lamellar Macular Holes to Full-Thickness Macular Holes: Clinical Features and Surgical Outcomes

To describe the clinical features and surgical outcomes of patients experiencing a spontaneous conversion of a lamellar macular hole (LMH) to a full-thickness macular hole (FTMH). Retrospective, multicenter, observational case series. Patients with LMH who experienced a spontaneous conversion to FTMH and underwent FTMH surgery. Clinical charts and OCT features of 20 eyes of 20 patients were reviewed. OCT features and surgical outcomes of FTMH derived from LMH. The mean baseline visual acuity (VA) was 0.21 ± 0.19 logarithm of the minimum angle of resolution (logMAR) (20/32 Snellen equivalent [SE]). Epiretinal proliferation was noted in 18 eyes (90%), and 14 eyes (75%) had an epiretinal membrane. At the diagnosis of FTMH, the mean VA decreased to 0.61 ± 0.50 logMAR (20/81 SE) (P= 0.001). The mean FTMH diameter was 224.4 ± 194.8 μm, with 15 (75%) small (≤250 μm), 2 (10%) medium (>250-≤400 μm), and 3 (15%) large (>400 μm) FTMHs. Eighteen (90%) FTMHs were sealed after 1 surgery, and 2 (10%) required an additional procedure. At the last follow-up, the mean VA was increased to 0.29 ± 0.23 logMAR (20/38 SE) (P= 0.003), but did not significantly differ from the baseline VA (P= 0.071). Patients with LMH may develop an FTMH with no evidence of vitreomacular traction. A tangential traction from an epiretinal membrane may contribute to its genesis, but a progressive loss of retinal tissue and an inherent weakness of the foveal architecture in LMH eyes could be sufficient. Most FTMHs derived from LMH had a small diameter, showed epiretinal proliferation, showed limited retinal hydration, and were associated with relatively poor surgical outcomes compared with idiopathic FTMH.

Combined Hamartoma of the Retina and Retinal Pigment Epithelium (CHR-RPE) in a Baby

Combined hamartoma of the retina and retinal pigment epithelium (RPE) is a rare, congenital, and benign tumour that may be mistaken with a choroid melanoma or retinoblastoma. These tumours often show an epiretinal membrane, tangential traction, disorganization of the retinal layers, and underlying uniform choroidal thinning. Our case report aims to describe the clinic and its correlation with MRI imaging on the evolution of a combined hamartoma of the retina and retinal pigment epithelium in a 5-month-old baby with six years of follow up.

Reducing the soil structure destruction along the rut and increasing the traction properties of the tractor by using the rear grouser of the track link

The traditionally used mixed grouser of the metal track link causes a decrease in the traction qualities of the agricultural tractor. The use of a rear grouser on the track link, in our opinion, will significantly improve the traction properties of an agricultural tractor with a metal track and reduce the soil destruction. When the rear grouser is immersed in the soil, an additional horizontal deformation of the soil occurs, which changes the law of horizontal deformation distribution along the support surface of the trackdrive, which ensures the alignment of the link shares in the implementation of the tangential traction force. This leads not only to a reduction in the trackdrive skidding, but also to a reduction in tractor rolling losses. Comparative tests of the T-4A tractor with a serial track, and a track on which links the front grousers were removed showed that the maximum traction power increases from 59 to 65 kW, the skidding with a hook load of 40 kN decreases from 14.6 to 9.4%, the rolling resistance coefficient decreases from 0.093 to 0.072, eliminates the “scissors” effect, which will reduce the number of erosive-dangerous particles in the track trace to 30...40%, which is 5.6...4.25 times less than in agricultural tractors with a mixed grouser, which confirms the effectiveness of their use.

Correlation between Visual Acuity and Optical Coherence Tomography Angiography Parameters in Unilateral Idiopathic Epiretinal Membrane.

Background: The tangential traction by idiopathic epiretinal membrane (iERM) may alter the hemodynamics of the macula. We investigated the correlation between visual acuity and the optical coherence tomography angiography (OCTA) parameters in unilateral iERM. Methods: We included 61 eyes of 61 consecutive patients with unilateral iERM between January 2018 and December 2018. The flow area of the retinal superficial capillary plexus (SCP), deep capillary plexus (DCP), and choroidal capillary plexus (CCP) were measured using OCTA. The normal fellow eyes were used for comparison. The iERM patients were divided into those with a presence of foveal concavity and those with a loss of foveal concavity. Results: When compared with fellow eyes, the flow areas showed a statistically significant decrease in the SCP and CCP of those with iERM (p = 0.037 and p = 0.011, respectively). In the DCP, no significant reduction in flow area was found in iERM (p = 0.054). The flow area of the CCP was the only factor significantly associated with best vision (p = 0.012). No significant differences in the flow areas of the SCP, DCP, and CCP were found between the presence and loss of foveal concavity. Conclusions: The flow area of the CCP is an important determinant of vision, emphasizing the crucial role of choroidal circulation in iERM. Moreover, mechanical stretch by iERM is not the only mechanism affecting the flow area.

Different modes of full-thickness macular hole formation

Full-thickness macular holes (FTMH) are an important cause of visual deterioration. However, different modes of FTMH formation are less investigated. It is also not clear whether the development of edematous cysts contributes to FTMH formation. In this retrospective case series of 30 eyes of 30 patients, we describe using spectral-domain optical coherence tomography different modes of FTMH formation. Morphological alterations of established FTMH are shown in 5 eyes of 5 patients. We found in 2 of 30 eyes investigated that anterior hyaloidal traction induced a hyperreflectivity of the inner Müller cell layer of the foveola prior to FTMH formation. In 3 eyes, FTMH were caused by anterior hyaloidal traction which produced foveal pseudocysts that developed to an outer lamellar hole (OLH) characterized by a disruption of the central outer retina. The OLH developed to a FTMH by the disruption of the inner layer of the foveola. FTMH formation from an OLH by hyaloidal traction was observed also in further 7 eyes. In 2 eyes, the OLH, which preceded FTMH formation, was generated by a serous retinal detachment. In 3 eyes, anterior hyaloidal traction caused a detachment of the fovea from the retinal pigment epithelium (RPE); the subsequent disruption of the foveola resulted in a FTMH. Six eyes showed the development of a FTMH from a degenerative lamellar hole (DLH). In 5 eyes with macular pucker, FTMH were formed by traction of epiretinal membranes (ERM) or hyaloidal traction. Two eyes showed the development of a FTMH by anterior or tangential hyaloidal traction likely without a formation of an OLH. FTMH formation from an OLH proceeded with or without an enlargement of cystic cavities in the foveal walls. The formation of FTMH from a DLH, after a detachment of the fovea, and in macular pucker eyes was associated with a formation of cystic cavities in the foveal walls. The best-corrected visual acuity (BCVA) of eyes with an OLH or FTMH was inversely correlated to the base and minimum diameters of the holes, and with the height of the foveal walls; the highest correlation coefficients were found between the BCVA and the base diameter. The data show that FTMH may be formed via different modes by hyaloidal traction and/or traction of ERM, or after a serous retinal detachment. It is suggested that, after FTMH formation, the impaired fluid clearance through the RPE after detachment of the central outer retina causes the development of edematous cysts in the foveal walls which enlarges the FTMH. The BCVA of eyes with an OLH or FTMH mainly depends on the size of the central photoreceptor-free area.

Effect of Impedance Boundary on the Reflection of Plane Waves in Fraction-Order Thermoelasticity in an Initially Stressed Rotating Half-Space with a Magnetic Field

In this research article, the propagation of the plane waves in an initially stressed rotating magneto-thermoelastic solid half-space in the context of fractional-order derivative thermoelasticity is studied. The governing equations in the x–z plane are formulated and solved to obtain a cubic velocity equation that indicates the existence of three coupled plane waves. A reflection phenomenon for the incidence of a coupled plane wave for thermally insulated/isothermal surface is studied. The plane surface of the half-space is subjected to impedance boundary conditions, where normal and tangential tractions are proportional to the product of normal and tangential displacement components and frequency, respectively. The reflection coefficients and energy ratios of various reflected waves are computed numerically for a particular material and the effects of rotation, initial stress, magnetic field, fractional-order, and impedance parameters on the reflection coefficients and energy ratios are shown graphically.