scholarly journals Femoroacetabular impingement: question-driven review of hip joint pathophysiology from asymptomatic skeletal deformity to end-stage osteoarthritis

2019 ◽  
Vol 20 (1) ◽  
Author(s):  
L. Pierannunzii
Keyword(s):  
Femoroacetabular Impingement ◽  
Contact Stress ◽  
Academic Research ◽  
Hip Osteoarthritis ◽  
Surgical Correction ◽  
Level Of Evidence ◽  
Skeletal Deformity ◽  
Normal Contact Stress ◽  
Normal Contact ◽  
Cartilage Wear

Abstract Femoroacetabular impingement (FAI), together with its two main pathomechanisms, cam and pincer, has become a trending topic since the end of the 1990s. Despite massive academic research, this hip disorder still conceals obscure aspects and unanswered questions that only a question-driven approach may settle. The pathway that leads a FAI asymptomatic morphology through a FAI syndrome to a FAI-related osteoarthritis is little known. Contact mechanics provides a shareable and persuasive perspective: cam FAI is based on shear contact stress at joint level with consequent cartilage wear; pincer FAI, contrariwise, determines normal contact stress between acetabular rim and femoral neck and squeezes the labrum in between, with no cartilage wear for many years from the onset. Pincer prognosis is then far better than cam. As a matter of fact, cartilage wear releases fragments of extracellular matrix which in turn trigger joint inflammation, with consequently worsening lubrication and further enhanced wear. Inflammation pathobiology feeds pathotribology through a vicious loop, finally leading to hip osteoarthritis. The association of cam and pincer, possibly overdiagnosed, is a synergic combination that may damage the joint rapidly and severely. The expectations after FAI surgical correction depend strictly on chondral layer imaging, on time elapsed from the onset of symptoms and on clinic-functional preoperative level. However, preemptive surgical correction is not recommended yet in asymptomatic FAI morphology. Level of evidence V.

scholarly journals New Numerical Solution of von Karman Equation of Lengthwise Rolling

2015 ◽  
Vol 2015 ◽  
pp. 1-20 ◽  
Author(s):  
Rudolf Pernis ◽  
Tibor Kvackaj
Keyword(s):  
Contact Stress ◽  
Rolling Force ◽  
Rolling Process ◽  
Normal Contact Stress ◽  
Normal Contact ◽  
Circular Arch ◽  
Relative Stress ◽  
Roll Flattening ◽  
Polygonal Curve ◽  
Rolling Torque

The calculation of average material contact pressure to rolls base on mathematical theory of rolling process given by Karman equation was solved by many authors. The solutions reported by authors are used simplifications for solution of Karman equation. The simplifications are based on two cases for approximation of the circular arch: (a) by polygonal curve and (b) by parabola. The contribution of the present paper for solution of two-dimensional differential equation of rolling is based on description of the circular arch by equation of a circle. The new term relative stress as nondimensional variable was defined. The result from derived mathematical models can be calculated following variables: normal contact stress distribution, front and back tensions, angle of neutral point, coefficient of the arm of rolling force, rolling force, and rolling torque during rolling process. Laboratory cold rolled experiment of CuZn30 brass material was performed. Work hardening during brass processing was calculated. Comparison of theoretical values of normal contact stress with values of normal contact stress obtained from cold rolling experiment was performed. The calculations were not concluded with roll flattening.

DYNAMIC ANALYSIS OF A ROTARY HOLLOW SHAFT WITH HOT-FIT PART USING CONTACT ELEMENTS WITH FRICTION

2011 ◽  
Vol 35 (3) ◽  
pp. 461-474 ◽  
Author(s):  
Shin-Yong Chen ◽  
Chieh Kung ◽  
Jung-Chun Hsu
Keyword(s):  
Natural Frequency ◽  
Contact Stress ◽  
High Speed ◽  
Modal Testing ◽  
Key Factors ◽  
Normal Contact Stress ◽  
Normal Contact ◽  
Hollow Shaft ◽  
Testing Experiment ◽  
Local Stiffness

One of the key factors in designing a motor built-in high speed spindle is to assemble the motor rotor and shaft by means of hot-fit. Presented in this paper is a study of the influence of a hot-fit rotor on the local stiffness of the hollow shaft. Dynamic analyses of the rotor-hollow shaft assembly using contact elements are conducted. The normal contact stress state between the rotor and the hollow shaft is obtained through the use of contact elements with friction effects included. The normal contact stress, considered as the pr-stress between the rotor and the hollow shaft, is then adopted for subsequent modal analyses. In this study, the modal analysis results are verified by a modal testing experiment. The percent errors of the first natural frequency and the second natural frequency are down to about 0.58% and 0.79%, respectively.

scholarly journals Experimental and Numerical Investigations of Fretting Fatigue Behavior for Steel Q235 Single-Lap Bolted Joints

2016 ◽  
Vol 2016 ◽  
pp. 1-10 ◽  
Author(s):  
Yazhou Xu ◽  
Zhen Sun ◽  
Yuqing Zhang
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Crack Initiation ◽  
Failure Mode ◽  
Contact Stress ◽  
Fatigue Cracks ◽  
Fretting Fatigue ◽  
Bolted Joints ◽  
Normal Contact Stress ◽  
Normal Contact

This work aims to investigate the fretting fatigue life and failure mode of steel Q235B plates in single-lap bolted joints. Ten specimens were prepared and tested to fit theS-Ncurve. SEM (scanning electron microscope) was then employed to observe fatigue crack surfaces and identify crack initiation, crack propagation, and transient fracture zones. Moreover, a FEM model was established to simulate the stress and displacement fields. The normal contact stress, tangential contact stress, and relative slipping displacement at the critical fretting zone were used to calculate FFD values and assess fretting fatigue crack initiation sites, which were in good agreement with SEM observations. Experimental results confirmed the fretting fatigue failure mode for these specimens. It was found that the crack initiation resulted from wear regions at the contact surfaces between plates, and fretting fatigue cracks occurred at a certain distance away from hole edges. The proposed FFD-Nrelationship is an alternative approach to evaluate fretting fatigue life of steel plates in bolted joints.

Cytoskeleton-Membrane Interactions in Neuronal Growth Cones: A Finite Analysis Study

2008 ◽  
Vol 131 (2) ◽  
Author(s):  
Kathleen B. Allen ◽  
F. Mert Sasoglu ◽  
Bradley E. Layton
Keyword(s):  
Mechanical Properties ◽  
Cell Membrane ◽  
Actin Filament ◽  
Contact Stress ◽  
Cell Membranes ◽  
Cytoskeletal Proteins ◽  
Neuronal Growth ◽  
Normal Contact Stress ◽  
Normal Contact ◽  
Membrane Rupture

Revealing the molecular events of neuronal growth is critical to obtaining a deeper understanding of nervous system development, neural injury response, and neural tissue engineering. Central to this is the need to understand the mechanical interactions between the cytoskeleton and the cell membrane, and how these interactions affect the overall growth mechanics of neurons. Using finite element analysis, the stress in the membrane produced by an actin filament or a microtubule acting against a deformable membrane was modeled, and the deformation, stress, and strain were computed for the membrane. Parameters to represent the flexural rigidities of the well-studied actin and tubulin cytoskeletal proteins, as well as the mechanical properties of cell membranes, were used in the simulations. Our model predicts that a single actin filament is able to produce a normal contact stress on the cell membrane that is sufficient to cause membrane deformation but not growth. Our model also predicts that under clamped boundary conditions a filament with a buckling strength equal to or smaller than an actin filament would not cause the areal strain in the membrane to exceed 3%, and therefore the filament is incapable of causing membrane rupture or puncture to a safety factor of ∼15–25. Decreasing the radius of the membrane upon which the normal contact stress is acting allows an increase in the amount of normal contact stress that the membrane can withstand before rupture. The model predicts that a 50nm radius membrane can withstand ∼4MPa of normal contact stress before membrane rupture whereas a 250nm radius membrane can withstand ∼2.5MPa. Understanding how the mechanical properties of cytoskeletal elements have coevolved with their respective cell membranes may yield insights into the events that gave rise to the sequences and superquaternary structures of the major cytoskeletal proteins. Additionally, numerical modeling of membranes can be used to analyze the forces and stresses generated by nanoscale biological probes during cellular injection.

scholarly journals Standard of Crushing Value of Coarse Aggregates for Permeable Asphalt Mixture Based on Contact Stress between Aggregates

2020 ◽  
Vol 2020 ◽  
pp. 1-7
Author(s):  
Tian Xiaoge ◽  
Wang Xiaofei ◽  
Yuan Huitong
Keyword(s):  
Contact Stress ◽  
Coarse Aggregate ◽  
Asphalt Mixture ◽  
Compression Tests ◽  
Normal Contact Stress ◽  
Normal Contact ◽  
Deformation Curves ◽  
Coarse Aggregates ◽  
Technical Requirements ◽  
The Stability

Crushing resistance of coarse aggregate is the key to the stability and durability of the skeleton structure of permeable asphalt (PA) mixture. To determine the technical requirements of crushing value of coarse aggregate used in PA mixture, step-loading compression tests were conducted on the mixtures of PA-13 and a control asphalt mixture AC-13, respectively. Virtual compression tests under the same loading conditions were simulated on the corresponding digital specimens with PFC2D®. By comparing the load-deformation curves obtained from the actual tests and virtual simulation, the values of the microscopic parameters of the two graded mixtures were obtained through trial calculation and adjustment. Then, the states of contact stress between aggregates in PA-13 and AC-13 mixtures under the standard crushing pressure (400 kN) were analyzed with PFC2D®. It was found that the average normal contact stress and the maximum normal contact stress between aggregates in PA-13 were 1.71 times and 1.28 times larger than those in AC-13, respectively. The crushing values of two different lithologic coarse aggregates were measured under different pressures, 400 kN or 600 kN, respectively. The crushing value criterion of coarse aggregates used in the PA mixture was suggested to be no greater than 16% after comparative analysis.

An Investigation Into Effect of Train Curving on Wear and Contact Stresses of Wheel and Rail

2008 ◽  
Author(s):  
Xuesong Jin ◽  
Jun Guo ◽  
Xinbiao Xiao ◽  
Zefeng Wen
Keyword(s):  
Numerical Method ◽  
Contact Stress ◽  
Great Influence ◽  
Contact Stresses ◽  
Rolling Contact ◽  
Railway Vehicle ◽  
Normal Contact Stress ◽  
Normal Contact ◽  
Rail Wear ◽  
Curved Track

Some important papers concerning the studies on rail wear and wheel/rail contact stresses are reviewed. The present paper utilizes a numerical method to analyze the effect of railway vehicle curving on the wear and contact stresses of wheel/rail. The numerical method considers a combination of Kalker’s non-Hertzian rolling contact theory, a material wear model and a vertical and lateral coupling dynamics model of a half vehicle and a curved track. The present analysis investigates the influence of the curving speed, the curved track super-elevation and the rail cant on the wear and the contact stresses. Through the detailed numerical analysis, it is found that the maximum contact stress depends greatly not only on the curving speed but also on the profiles of the wheel/rail. The curving speed increasing leads to increase the normal load of the wheel rolling over the high curved rail, but, decrease the normal contact stress level under the condition of the optimum match of wheel/rail profiles. The track super elevation increasing efficiently lowers the contact stresses and the wear at a constant curving speed. The rail cant has a great influence on the low rail wear of the curved track. Increasing the rail cant leads to the great growth of the low curved rail wear, the reduction in the high rail wear. The results are very useful in the maintenance of the track.

scholarly journals Influence of Cutting Tool Wear on Contact Stresses and Temperature Distribution in Titanium Alloy Machining

2017 ◽  
Vol 743 ◽  
pp. 252-257 ◽  
Author(s):  
Victor Kozlov ◽  
Jia Yu Zhang ◽  
Ekaterina Letshiner ◽  
Wen Ze Zhao
Keyword(s):  
Titanium Alloy ◽  
Temperature Distribution ◽  
Experimental Research ◽  
Contact Stress ◽  
Cutting Tool ◽  
Flank Wear ◽  
Contact Stresses ◽  
Cutting Edge ◽  
Normal Contact Stress ◽  
Normal Contact

This paper analyses the results of experimental research of contact stresses distribution over an artificial flank wear-land and temperature distribution in a cutting wedge in a free orthogonal turning of the disk made from titanium alloy (Ti-6Al-2Mo-2Cr) by a cutter with a sharp-cornered edge and with a rounded cutting edge. The investigation was carried out by the method of “split cutter” (sectional tool) and method of variable length of an artificial flank wear land. Experiments with variable feed rate and cutting speed show that in titanium alloy machining with a sharp-cornered cutting edge, the highest normal contact stress over the flank land (σh max = 3400…2200 MPa) is observed immediately at the cutting edge, and the curve has a horizontal region with a length of 0.2…0.6 mm. At larger distance from the cutting edge, the value of normal contact stress is dramatically reduced to 1100…500 MPa. The character of normal contact stresses for a rounded cutting edge is different: it is uniform and its value is approximately 2 times smaller as compared to machining with sharp-cornered cutting edge. In author’s opinion it is connected with generation of a seizure zone in chip formation region and explains working capacity of very worn-out cutting tools in machining titanium alloys. The results of experimental research of temperature distribution in the cutting tool wedge show that temperature reaches 1000 °С at essential wear over the flank surface. Such high value of temperature on the contact surface causes softening of work material, and explains the small value of tangential contact stresses (τh = 800…200 MPa) and reduction of normal contact stresses σh far from the cutting edge for a sharp-cornered cutting edge.

Axisymmetric contact analysis of piezoelectric materials with surface effect

2021 ◽  
pp. 1045389X2098388
Author(s):  
Hong-Xia Song ◽  
Jie Su ◽  
Liao-Liang Ke
Keyword(s):  
Contact Stress ◽  
Radial Stress ◽  
Integral Transform ◽  
Surface Effect ◽  
Piezoelectric Materials ◽  
Influencing Factor ◽  
Electric Displacement ◽  
Surface Residual Stress ◽  
Normal Contact Stress ◽  
Normal Contact

Based on the surface piezoelectricity theory, this article predicts the axisymmetric smooth contact of a piezoelectric half-space indented by a rigid insulated punch. In this theory, the surface effect is characterized with four material parameters: the surface elastic constant, surface residual stress, surface piezoelectric constant and surface dielectric constant. By applying Hankel integral transform, the fundamental solution for this axisymmetric contact problem is derived with the surface effect. Then, the normal contact stress, radial electric displacement and radial stress of the contact surface are solved numerically. Finally, the surface effects on the normal contact stress, radial electric displacement and radial stress are analyzed. It is found that the surface effect is a significant influencing factor on the axisymmetric contact behaviors of micro-/nano-scale piezoelectric materials.

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