Reduce Contact Stress Research Articles

Effect of Elevated Acetabular Cup on Contact and Failure Analysis in Hip Implants for Different Microseparations and Cup Inclinations Under Routine Gait Activities Using In Silico Approach.

The acetabular cup design plays a critical role in reducing contact stress between femur head acetabular cup. Many studies used ellipsoidal and spheroidal geometry in acetabular cup design to effectively reduce contact stress. The present study focuses on elevated acetabular cup rim with round corner design to reduce contact stress with round corner geometry. The cobalt chromium femur head and cup are considered for finite element (FE) model of hip resurfacing. The gait loads of routine activities of humans like normal walking, stair ascending and descending and sitting down and getting up gait activities are applied to the developed 3D FE model. Five microseparations of 0.5, 1, 1.5, 2 and 2.5mm are considered in the present study. The acetabular cup inclination angle considered for this study are 35°, 45°, 55°, 65° and 75°. The contact stress and von Mises stress plot for each gait activities under these microseparations are analyzed for betterment of longevity of implants. Overall elevated cup rim design helped in reducing contact stress to a greater extent than conventional cup with different geometries. Also, the predicted von Mises stress for all the parameters considered in the current study are well within the yield strength of CoCr material. Therefore, elevated cup rim could be used as a better alternative to spline and, ellipsoidal and circular geometries of cup.

Increasing the operational parameters of worm gears

An analysis of factors that reduce the operational parameters of worm gearboxes has been carried out. Equations for calculating the efficiency of a worm gear, contact pressure, and the residual service life are given. It is shown that the friction angle and friction coefficient depend on the material of the worm and wheel teeth, the roughness of the working surfaces of the worm pair matings, the quality of the lubrication, and the sliding speed. Significant contact pressures and friction losses in meshing lead to heat generation, a decrease in efficiency and service life of the worm gear. To produce a worm gear with a maximum radius of a conjugate globoid-cylindrical pair with an involute profile, it is proposed to use rotational turning of the globoid worm turns with a multi-blade forcedly rotating tool, and the wheel teeth with a hob cutter. A nickel antifriction solid lubricating coating containing carbon nanotubes has increased hardness and resistance to abrasion. A method for manufacturing a ZT-type worm gear is proposed, as well as methods that reduce contact stresses and the coefficient of friction during operation of a mating worm pair to increase the service life of worm gears.

Contact stress analysis of xylon coated spur gear using ANSYS workbench

One of the most crucial mechanical components of a mechanical power transmission system is the gear. To transfer torque, a spinning machine component with cut teeth meshes with another tooth component. Due to their great degree of versatility, gears are used in a broad variety of applications, from small wristwatches to massive heavy equipment like those used in the automotive and aerospace industries and marine engines. Contact stress and bending stress are therefore the two key factors that affect gear failures. In the current study, a static stress analysis is carriedout on the spur gear part to figure out the equivalent stress, total deformation, and stress intensity. Additionally, the component's possible fracture point is also located. Many materials, such as xylon, PTEF (polytetrafluoroethylene), and boron carbide, are used to increase the gear lifespan with the intention of reducing contact stress. Coated materials in gears are chosen because they are readily available and low-friction, and they are compared to conventional gear.

DESIGN PARAMETERS AND OPERATION CHARACTERISTICS OF BALL-TYPE SAFETY-OVERRUNNING CLUTCH WITH MODIFIED GROOVES

The article investigates the force interaction of the elements and operation characteristics of a ball-type safety-overrunning clutch with modified semi-clutch grooves. Grooves modification provided through grooves sides to the semi-couplings radius inclination. Through balls with other clutch parts force interaction consideration, taking into account inertia and friction forces, obtained expressions for calculating of clutch parts loadings, main moments of the clutch: rating, operation beginning and ending. Those make possibility to evaluate main clutch operation characteristics - coefficients of accuracy, sensitivity, and rating torque exceeding. Influence of main design parameters on clutch operation characteristics is studied. Particularly it is shown that grooves to clutch axe inclination angle exerts a great influence on parts load and clutch operation characteristics in overload mode. It is shown that in highly loaded high-speed drives it is advisable to install clutches with inclined to the radius grooves sides. It is shown that from the point of view of increasing clutch operation characteristics, it is more advantageous to make the grooves at smaller angles to the clutch axe. It is established that characteristics of clutch with inclined to the radius grooves sides are not very sensitive to changes in operation rotating frequency. Reducing the balls diameter makes a positive effect on the clutch operation characteristics in overload mode through inertia and friction forces impact decreasing and reducing contact stresses in balls with grooves contact zone. Practically significant ratios for the design and verification calculations of presented clutch parts loads and stresses are obtained. Presented results are useful for engineers dealing with mechanical driving design. Keywords: clutch, torque, overload, gearing, stress, operation accuracy, contact strength, operation characteristics

PPARδ Agonist Promotes Type II Cartilage Formation in a Rabbit Osteochondral Defect Model.

Osteoarthritis (OA) is a chronic degenerative joint disease accompanied by an inflammatory milieu that results in painful joints. The pathogenesis of OA is multifactorial, with genetic predisposition, environmental factors, and traumatic injury resulting in the direct or indirect loss of cartilage. The articular cartilage can also be damaged by direct focal traumatic injury. Articular cartilage provides a smooth, deformable bearing surface with a low coefficient of friction, increased contact area, and reduced contact stress. Articular type II hyaline cartilage lines the synovial joints and, when injured, has a limited ability for repair, except for the most superficial layers via diffusion from the synovial fluid, secondary to no blood supply, a complex structure, and a low metabolic rate. Restoring the articular surface can relieve pain and restore function. Although many strategies have been developed to regenerate type II collagen based on the extent of the lesion, surgical treatments are still evolving. The peroxisome proliferator-activated receptor delta (PPARδ) agonist and collagen treatment of mesenchymal stem cells (MSCs) enhance the chondrogenic capacity in vitro. We present a novel technique for cartilage restoration in a rabbit cartilage osteochondral defect model using a PPARδ agonist (GW0742)-infused 3D collagen scaffold to induce type II cartilage from MSCs.

Contact stress and sliding wear damage tolerance of hydroxyapatite and carbon nanotube reinforced polyethylene cup liner against zirconia femoral head

A finite element modeling (FEM) approach is carried out to estimate the contact stresses such as von-Mises and shear stress on the acetabular cup liner, made up of ultra-high molecular weight polyethylene (UHMWPE)-hydroxyapatite (HAp)-carbon nanotubes (CNT) based composites. The highlights of this work include the effects of liners' material (UHMWPE-HAp-CNT composites), radial clearance (0.05 to 1 mm), and liners' wall thickness (3 to 8 mm) on contact stresses. The thick liner (thickness: 8 mm) with conformal geometry (radial clearance 0.05 mm) produced the lowest contact stresses (von-Mises: 13.8–17.5 MPa and shear stress: 2.3–3.3 MPa). In contrast, the thin liner (thickness: 3 mm) with higher radial clearance (1 mm) showed the highest von-Mises stress (78.6–131.0 MPa) and shear stress (17.0–23.3 MPa). According to ISO 7206–1, nearly 6–7 times reduced contact stresses were observed because of the wider articulating contact area provided by thick cup liner and its conformity with respect to the femoral head. The UHMWPE-2 wt % CNT composite (UC) showed low von-Mises stress (16.1 MPa) and lowest shear stress (2.3 MPa); thus, it is the most damage tolerant material (wear rate: 2.6 × 10-7 mm3/Nm). The excellent mechanical properties such as hardness (165 MPa), elastic modulus (2.28 GPa), and tensile strength (36.7 MPa) are reasoned to elicit an increased sliding-wear resistance of UC. Thus, CNT-based UHMWPE composite can be the potential acetabular cup liner with a thickness of 8 mm and clearance of 0.05 mm without plastic deformation.

Biomechanical guidance can improve accuracy of reduction for intra-articular tibia plafond fractures and reduce joint contact stress.

Articular fracture malreduction increases posttraumatic osteoarthritis (PTOA) risk by elevating joint contact stress. A new biomechanical guidance system (BGS) that provides intraoperative assessment of articular fracture reduction and joint contact stress based solely on a preoperativecomputed tomography(CT) and intraoperative fluoroscopy may facilitate better fracture reduction. The objective of this proof-of-concept cadaveric study was to test this premise while characterizing BGS performance. Articular tibia plafond fractures were created in fivecadaveric ankles. CT scans were obtained to provide digital models. Indirect reduction was performed in a simulated operating room once with and once without BGS guidance. CTscans after fixation provided models of the reduced ankles for assessing reduction accuracy, joint contact stresses, and BGS accuracy. BGSwas utilized 4.8 ± 1.3 (mean ± SD) times per procedure, increasing operative time by 10 min (39%), and the number of fluoroscopy images by 31 (17%). Errors in BGS reduction assessment compared to CT-derived models were 0.45 ± 0.57 mm in translation and 2.0 ± 2.5°in rotation. For the fourankles that were successfully reduced and fixed, associated absolute errors in computed mean and maximum contact stress were 0.40 ± 0.40and 0.96 ± 1.12 MPa, respectively. BGS reduced mean and maximum contact stress by 1.1 and 2.6 MPa, respectively. BGSthus improved the accuracy of articular fracture reduction and significantly reduced contact stress. Statement of Clinical Significance: Malreduction of articular fractures is known to lead to PTOA. The BGS described in this work has potential to improve quality of articular fracture reduction and clinical outcomes for patients with a tibia plafond fracture.

Investigations on the Performance of Shotcrete Using Artificial Lightweight Shale Ceramsite as Coarse Aggregate.

In this study, a type of artificial lightweight shale ceramsite (ALSC) was used as the coarse lightweight aggregate for shotcrete (LAS), of which the mechanical properties, chloride penetration ion resistance, and rebound behavior were investigated. Based on the experimental results on compressive, tensile, and bond strength, LAS meet the strength requirements, and the replacement rate of fly ash (FA) and silica fume (SF) are suggested to be kept at ~15% and 10%, respectively, to result in the best mechanical properties of LAS. Adding FA and SF to the mixture significantly improved the chloride ion penetration resistance (CPR) of LAS because of morphology effects and secondary hydration of FA and SF that lead to a denser microstructure of the mixture. The electric flux and chloride ion migration coefficient (DRCM) of LAS decreased by 56% and 67%, respectively, with FA increasing from 0 to 10%. The electric flux and DRCM further decreased by 71% (153C) and 66% (3.24 m2/s), respectively, with FA increasing from 10 to 20%. As 5–10% SF was further added, the electric flux and DRCM of LAS decreased to extremely low levels; for instance, with FA = 10% and SF = 10%, DRCM = 1.61 m2/s, and the electric flux was too small and could be ignored. The contact stresses between aggregate and shotcrete mixtures were measured to investigate the rebound trend of ALSC in shotcrete. According to the analyses of the theoretical model of the rebound behavior of aggregate in shotcrete proposed by Armelin and Banthia, because of the reduced contact stresses between ALSC and mortar and the smaller density of LAS compared with normal-weight aggregate, the rebound rate of ALSC was about half of that of normal-weight aggregate in the shooting process of the shotcrete.

Structural design for planetary roller screw mechanism based on the developed contact modelling

The structural design of planetary roller screw mechanism (PRSM) with lower contact stress is beneficial to delay the fatigue failure and prolong the service life. However, few studies focused on this field and a reasonable contact model is therefore required due to its complexity structure. In this paper, a developed contact model is established for PRSM, and a process-based parameterization method is proposed to precisely calculate the contact characteristics along with the change of parameters. Based on the in-depth study of the parameter sensitivities of contact characteristics, the structure design to reduce contact stress for PRSM is realized through the multi-objective optimization under the proposed geometric constraints. The validity of this model is well verified by finite element method.

LONGITUDINAL CHANGE IN QUANTITATIVE 3D MEDIAL MENISCUS MEASURES PRECEDING TO AND CONCURRENT WITH STRUCTURAL KNEE OSTEOARTHRITIS PROGRESSION - DATA FROM THE OAI FNIH BIOMARKER STUDY

Purpose: The menisci of the knee joint play an important role in distributing joint loads, reducing contact stress between femorotibial cartilages, and guiding knee joint movement. Meniscal pathology such as extrusion and tears are very common and associated with incidence and progression of radiographic knee osteoarthritis (KOA). The meniscus position and integrity are also known to affect the minimum radiographic JSW (minJSW). We previously observed 3D quantitative measurements of meniscus position and morphology to be associated with subsequent structural progression, defined as both loss in radiographic minJSW and cartilage thickness and observed change in 3D quantitative meniscus measures concurrent with minJSW loss.

Anatomsko-morfološke karakteristike acetabuluma

The acetabulum forms the pelvic bones, together with the head of the femur forms the hip joint, which is the link between the upper part of the body and the lower extremities. The morphology of the acetabulum determines and influences the quality and function of the hip joint. All anatomical and morphological changes of the acetabulum directly affect the development of many diseases of the hip joint. Its anatomical structure and morphological orientation play a major role in the transfer of body weight through the femur to the foot. The acetabulum labrum has the role of increasing the surface of the acetabulum, increasing its depth, reducing contact stress, and preventing direct con-tact between the acetabulum cartilage and the femoral head.

Особливості зносу пар тертя канат-блок і канат-барабан за умов роботи підйомно-тягових пристроїв

The features of wear of rope-block and rope-drum friction pairs of lifting and traction devices operating in the conditions of a hot manufactory of the metallurgical plant and also the mining and beneficiation plant were studied. It is shown that the causes of wear of the elements of the rope-block and rope-drum friction pairs are the interaction in their contact zones, which occurs in the surface layers under the influence of high contact stresses, friction, cyclic loads, abrasive particles, active atmospheric and industrial environments. It was found that these actions lead to irreversible processes of accumulation of stresses and plastic shifts, which have a periodic and heterogeneous character. It is shown that the strength of the lifting or traction rope is determined by the degree of wear of the wires, primarily those in contact with the block and the drum. The structural changes in the surface layers of the wires and the mechanisms of the formation of wear particles were analyzed, which confirm the heterogeneous nature of the wear of the wires in the strands of the rope. Areas of abrasive wear were also observed on the worn surface of the wires, where under the action of solid foreign particles of contamination with sharp corners falling between the wires, the surface of the wires was undercut. It is shown that the presence of non-metallic inclusions leads to the formation of wear particles and fatigue cracks. It was established that the wear of friction pairs of rope-block and rope-drum of hoisting and traction devices has a fatigue-corrosive nature, and the main mechanism of the formation of wear particles is the development of plastic shifts in the surface layers of friction pairs and their separation by plastic exfoliation and abrasive and corrosive destruction. The shape of the wear particles depends on the type of material and the conditions of their formation. It is proposed to take measures regarding structural approaches to friction pairs, taking into account their working conditions, in order to reduce contact stresses and increase their wear resistance, reliability and durability.

Failure analysis and improvement measures of airplane actuator seals

Hydraulic actuators are an important executive component of modern aircraft and are typically characterized by a reciprocating sealing form. Sealing failure affects the implementation of aircraft missions and flight safety. To determine the main cause for sealing failure of the ACGT-HP combined rod seal in an aircraft actuator, taking the new seal as the control group, compare and analyze the failure and non-failure combined rod seals under the same working conditions for approximately the same time. By means of microscopic examination, physical performance testing and chemical composition analysis, eight ACGT-HP seal failure reasons that act synergistically are summarized and preventive improvement measures are proposed. It is concluded that the main reason for the failure of the combined seal is that the wear of the seal is exacerbated by various inappropriate coupling factors, resulting in the rapid reduction of contact stress and seal failure. By putting forward the key points of seal design and assembly, a universal failure analysis method from macro to micro is found, which can be used for various types of combined seals to guide the design and application of the ACGT-HP seals.

Increasing the load capacity of a gear transmission under skew conditions by reducing contact stresses by means of longitudinal modification of the teeth

A method was developed and dependencies were obtained for determining the parameters of the longitudinal modification of the gear wheels teeth. Longitudinal modification is an effective way to reduce contact stresses in case of misalignment of axes in gear mechanisms, increases the load capacity of the gear transmission. Examples of calculation are given. Keywords: gear transmission, contact spot, axle misalignment, uneven load distribution, longitudinal modification, barrel shape. filnahat7@mail.ru

Study of Wear and Redistribution Dynamic Forces of Wheel Pairs Restored by a Wear-Resistant Coating 15Cr17Ni12V3F

The relevance of this study lies in the need to research the wear process of the elements of dynamic systems and to establish the dependence of the geometric and structural characteristics of wheels restored by plasma surfacing with a coating of 15Cr17Ni12V3F on dynamic, cyclically varying loads. The study was aimed to establish the dependencies between the deviation of the wear area, the formation of contact and fatigue stresses, and the change in the phase structure of the wheel defect. It is important to justify the permissible limits of wear of the transverse profile in the contact zone of a wheel and ridge. The object of the study was the dynamic interaction of the “wheel–ridge–rail contact surface” system. To achieve the goal, the following methodology was adopted: kinematic analysis, strength calculation, the use of mathematical analysis in dynamic system modelling, virtual modelling in the SOLIDWORKS software environment of the GearTrax application, experiment planning, and model correction through the results of metallographic studies. The results of the study are presented as reasonable prediction criteria that consider contact cycles during the formation of fatigue stresses at the stage of defect origin. The process of the dynamic interaction of the contact worn profile of a wheel with a railway rail is explored. Polynomial equations are proposed to substantiate the optimal design and technological parameters of designing a railway carriage wheel. The permissible limits of wear of the transverse profile in the contact zone of the wheel and the ridge are justified while taking the coefficient of the reduction of contact stresses in the metal into account. The dependences of the change in static load on the utilization factor of the railway carriage load capacity are established. The dependences of changes in fatigue stresses on the design deviation of the contact area of wheel wear are established. It is confirmed that the stress concentration under cyclic loads is formed in the ferritic layers of the material structure before the appearance of wear.

Research on advances in roller bearing manufacturing

In general the manufacturing of bearing require strict technological step that are performed on highly specialized equipments that require timely adjustments at batch changes. The process of forging and heat treatment stages consume the most amount of energy but the most expensive stage is the grinding operation. An alternative to grinding and honing processes is hybrid machining by combined hard turning and rolling process. One main development directions of all major roller bearing manufacturers is improving durability of bearings by reducing the roughness by inducing high residual stresses in the surface layers of bearing rings and improving the profile of roller for reduced contact stress. Rolling can induce higher surface stresses and reduce roughness with benefits to the durability of the bearings. The present paper presents and analysis of the technological route for bearing ring and bearing roller and focuses on the research direction on the advances in manufacturing / machining methods for bearing rings and rollers.

Reducing Contact Stress of the Surface by Modifying Different Hardness of Femoral Head and Cup in Hip Prosthesis

The wear of hip prosthesis due to applied load and sliding distance during the patient's daily activity cannot be avoided. Wear causes osteolysis or metallosis due to the wear debris produced by the wear process. Several methods were used to reduce wear in metal-on-metal hip prostheses. One of the efforts performed to reduce wear was the differential-hardness concept. Based on the literature, the fine surface roughness of the femoral head are the reason why the hip prosthesis with differential-hardness reduces wear. Besides, the differential-hardness will contribute to the difference of modulus elasticity then influenced the contact stress on the surface contact. According to Archard's wear law, wear on the material pair is affected by contact stress. Therefore, the analysis of contact stress on the hip prosthesis with differential-hardness is important to investigate. The investigation performed by the static contact of two-dimensional axisymmetric with frictionless by using finite element simulation. The simulated models are the alumina vs. alumina, alumina vs. SS316L, CoCr vs. CoCr, CoCr vs. SS316L, and SS316L vs. UHMWPE. The purpose of this study is to determine the contact stress on the surface contact due to differential-hardness of the femoral head and cup. The results of simulations show that the differential-hardness marked by differences in the modulus of elasticity can reduce the contact stress on the surface contact if compare with the similar hardness.

Improved Integrated Robotic Intraocular Snake: Analyses of the Kinematics and Drive Mechanism of the Dexterous Distal Unit.

Retinal surgery can be performed only by surgeons possessing advanced surgical skills because of the small, confined intraocular space, and the restricted free motion of the instruments in contact with the sclera. Snake-like robots may be essential for use in retinal surgery to overcome this problem. Such robots can approach the target site from suitable directions and operate on delicate tissues during retinal vein cannulation, epiretinal membrane peeling, and so on. We propose an improved integrated robotic intraocular snake (I2RIS), which is a new version of our previous IRIS. This study focused on the analyses of the kinematics and drive mechanism of the dexterous distal unit. This unit consists of small elements with reduced contact stress achieved by changing wire-hole positions. The kinematic analysis of the dexterous distal unit shows that it is possible to control the bending angle and direction of the unit by using two pairs of drive wires. The proposed drive mechanism includes a new pull-and-release wire mechanism in which the drive pulley is mounted at a right angle relative to the actuation direction (also, relative to the conventional direction). Analysis of the drive mechanism shows that compared to the previous drive mechanism, the proposed mechanism is simpler and easier to assemble and yields higher accuracy and resolution. Furthermore, considering clinical use, the instrument of the I2RIS is detachable from the motor unit easily for cleaning, sterilization, and attachment of various surgical tools. Analyses of the kinematics and drive mechanism and the basic functions of the proposed mechanism were verified experimentally on actual-size prototypes of the instrument and motor units.

Kontaktni napon kod helikoidnih konusnih zupčanika

Helical bevel gears have inclined or twisted teeth on a conical surface and the common types are skew, spiral, zerol, and hypoid bevel gears. However, this study does not include hypoid bevel gears. Due to the geometric complexities of bevel gears, commonly used methods in their design are based on the concept of equivalent or virtual spur gear. The approach in this paper is based on the following assumptions, a) the helix angle of helical bevel gears is equal to mean spiral angle, b) the pitch diameter at the backend is defined as that of a helical gear, and c) the Tredgold's approximation is applied to the helical gear. Upon these premises, the contact stress capacity of helical bevel gears is formulated in explicit design parameters. The new contact stress capacity model is used to estimate the contact stress in three gear systems for three application examples and compared with previous solutions. Differences between the new estimated results and the previous solutions vary from -3% and -11%, with the new estimates being consistently but marginally or slightly lower than the previous solution values. Though the differences appear to be small, they are significant because the durability of gears is strongly influenced by the contact stress. For example, a 5% reduction in contact stress may result in almost 50% increase in durability in some steel materials. The equations developed do not apply to bevel crown gears.

Improved Integrated Robotic Intraocular Snake.

Retinal surgery can be performed only by surgeons possessing advanced surgical skills because of the small, confined intraocular space, and the restricted free motion of instruments in contact with the sclera. Snake-like robots could be essential for use in retinal surgery to overcome this problem. Such robots can approach from suitable directions and operate delicate tissues when performing retinal vein cannulation, epiretinal membrane peeling and so on. In this study, we propose an improved integrated robotic intraocular snake (I2RIS), which is a new version of our previous IRIS. This update focuses on the dexterous distal unit design and the drive unit design. The proposed dexterous distal unit consists of small elements with reduced contact stress. The proposed drive unit includes a new wire drive mechanism where the drive pulley is mounted at a right angle relative to the actuation direction (also, relative to the conventional direction). A geometric analysis and mechanical design show that the proposed drive mechanism is simpler and easier to assemble and yields higher accuracy than the conventional drive mechanism. Furthermore, considering clinical use, the instrument of the I2RIS is detachable from the motor unit for cleaning, sterilization, and attachment of various surgical tools. Weighing merely 31.3 g, the proposed mechanism is only one third of the weight of the conventional IRIS. The basic functions and effectiveness of the proposed mechanism are verified by experiments on 5:1 scaled-up models of the dexterous distal unit and actual-size models of the instrument and motor units.