Mechanics of Contact Fatigue

1994 ◽  
Vol 47 (6S) ◽  
pp. S194-S198
Author(s):  
Leon M. Keer
Keyword(s):  
Mechanical Properties ◽  
Crack Propagation ◽  
Material Properties ◽  
Contact Fatigue ◽  
Repeated Loading ◽  
Analytical Prediction ◽  
Griffith’S Criterion ◽  
Machine Elements ◽  
Prediction Techniques ◽  
Interacting Features

Contact fatigue between typical machine elements such as gears, roller followers, bearings and other components involves many complex interacting features. There are the effects of geometry, mechanical properties, material properties and surface chemistry. The present discussion will center around analytical prediction techniques that are concerned only with the mechanical aspects of contact fatigue between two elements. Aspects related to the initiation of a crack under repeated loading will be discussed. The application of an approach developed by Mura, analogous to Griffith’s criterion for fracture, will be used to show how estimates of initiation life can be made and how these estimates are related to currently used ones. Once a crack has been initiated, then issues related to crack propagation become important. Some fracture mechanics based methods developed to calculate crack growth will be described along with estimates of crack propagation life.

Cytocompatibility and Material Properties of Poly-carbonate Urethane/Carbon Nanofiber Composites for Neural Applications

2003 ◽  
Vol 774 ◽  
Author(s):  
Janice L. McKenzie ◽  
Michael C. Waid ◽  
Riyi Shi ◽  
Thomas J. Webster
Keyword(s):  
Mechanical Properties ◽  
Carbon Nanofibers ◽  
Material Properties ◽  
Carbon Nanofiber ◽  
Scar Tissue ◽  
Tissue Response ◽  
Positive Interactions ◽  
Weight Percentage ◽  
Poly Carbonate

AbstractCarbon nanofibers possess excellent conductivity properties, which may be beneficial in the design of more effective neural prostheses, however, limited evidence on their cytocompatibility properties exists. The objective of the present in vitro study was to determine cytocompatibility and material properties of formulations containing carbon nanofibers to predict the gliotic scar tissue response. Poly-carbonate urethane was combined with carbon nanofibers in varying weight percentages to provide a supportive matrix with beneficial bulk electrical and mechanical properties. The substrates were tested for mechanical properties and conductivity. Astrocytes (glial scar tissue-forming cells) were seeded onto the substrates for adhesion. Results provided the first evidence that astrocytes preferentially adhered to the composite material that contained the lowest weight percentage of carbon nanofibers. Positive interactions with neurons, and, at the same time, limited astrocyte functions leading to decreased gliotic scar tissue formation are essential for increased neuronal implant efficacy.

The Effect of Heat Treatment on Mechanical Properties of Car Interior Fabric Used for Injection Molding

2012 ◽  
Vol 532-533 ◽  
pp. 234-237
Author(s):  
Wei Lai Chen ◽  
Ding Hong Yi ◽  
Jian Fu Zhang
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
High Temperature ◽  
Injection Molding ◽  
High Temperatures ◽  
Material Properties ◽  
Injection Molding Process ◽  
Molding Process ◽  
Composite Fabrics

The purpose of this paper is to study the effect of high temperature in injection molding process on mechanical properties of the warp-knitted and nonwoven composite fabrics (WNC)used in car interior. Tensile, tearing and peeling properties of WNC fabrics were tested after heat treatment under120, 140,160,180°C respectively. It was found that, after 140°C heat treatment, the breaking and tearing value of these WNC fabrics are lower than others. The results of this study show that this phenomenon is due to the material properties of fabrics. These high temperatures have no much effect on peeling properties of these WNC fabrics. It is concluded that in order to preserve the mechanical properties of these WNC fabrics, the temperature near 140°C should be avoided possibly during injection molding process.

Evaluating Mechanical Properties of Ceramics by Relative Methods

2007 ◽  
Vol 336-338 ◽  
pp. 2406-2410
Author(s):  
Yi Wang Bao ◽  
Xiao Xue Bu ◽  
Yan Chun Zhou ◽  
Li Zhong Liu
Keyword(s):  
Mechanical Properties ◽  
Material Properties ◽  
Ceramic Coatings ◽  
Relative Method ◽  
Tempered Glass ◽  
Theoretic Analysis ◽  
Surface Strength ◽  
Indirect Approach ◽  
Before And After ◽  
The Relationship

A relative method, defined as indirect approach to evaluate the material properties via the relationship between unknown properties and a known property, is proposed to estimate some properties that could not be measured by the traditional methods for ceramics. Experiments and theoretic analysis based on the relative method were carried out in this study to estimate the properties in following aspects: determining the temperature dependence of elastic modulus of some machineable ceramics by comparing the deflections; obtaining the modulus and strength of ceramic coatings supported by substrates, from the variation in properties of the rectangular beam samples before and after coating; estimating the residual stresses in tempered glass by comparing the change in the surface strength after strengthening.

The Effect of Cross-Linking on Nano-Mechanical Properties of Polyamide

2016 ◽  
Vol 699 ◽  
pp. 37-42 ◽  
Author(s):  
Martin Ovsik ◽  
David Manas ◽  
Miroslav Manas ◽  
Michal Stanek ◽  
Martin Reznicek
Keyword(s):  
Mechanical Properties ◽  
Surface Layer ◽  
Material Properties ◽  
Basic Material ◽  
Nanoindentation Test ◽  
Cross Linking ◽  
Indentation Hardness ◽  
Depth Sensing ◽  
Nanomechanical Properties ◽  
Radiation Crosslinking

Radiation crosslinking of polyamidu 6 (PA 6) is a well-recognized modification of improving basic material characteristics. Radiation, which penetrated through specimens and reacted with the cross-linking agent, gradually formed cross-linking (3D net), first in the surface layer and then in the total volume, which resulted in considerable changes in specimen behaviour. This research paper deals with the possible utilization of irradiated PA6. The material already contained a special cross-linking agent TAIC (5 volume %), which should enable subsequent cross-linking by ionizing β – radiation (15, 30 and 45 kGy). The effect of the irradiation on mechanical behavior of the tested PA 6 was investigated. Material properties created by β – radiation are measured by nanoindentation test using the DSI method (Depth Sensing Indentation). Hardness increased with increasing dose of irradiation at everything samples; however results of nanoindentation test shows increasing in nanomechanical properties of surface layer. The highest values of nanomechanical properties were reached radiation dose of 45 kGy, when the nanomechanical values increased by about 95%. These results indicate advantage cross-linking of the improved mechanical properties.

Hydrogen’s Peculiar Effect on Material Properties: Do We Need to Be Concerned About Hydrogen Transport in Pipelines?

2021 ◽  
Author(s):  
Erling Østby ◽  
Bjørn-Andreas Hugaas ◽  
Agnes Marie Horn
Keyword(s):  
Mechanical Properties ◽  
Material Properties ◽  
Reliable Data ◽  
Hydrogen Gas ◽  
Decision Makers ◽  
Hydrogen Transport ◽  
Offshore Pipelines ◽  
Vast Number ◽  
Technical Aspects ◽  
Controversial Topic

Abstract Considering the vast number of articles that have been published during the last 150 years related to hydrogen embrittlement and the multiple attempts to explain the governing mechanisms, it is evident that hydrogen’s effect on mechanical properties in steel is still a controversial topic. This little atom has even by some authors been referred to as the “little devil”. We do not intend to explore this particular description of hydrogen any further. However, we would like to shed some light on the key technical aspects we believe need to be further scrutinized and understood to ensure that the decision-makers have sufficiently reliable data available to decide whether hydrogen gas can be safely transported in new or existing offshore pipelines at an acceptable cost.

Micro-mechanical modeling using DEM to study the effect of mechanical properties on crack propagation for snow slab avalanches

2021 ◽  
Author(s):  
Bobillier Gregoire ◽  
Bergfled Bastian ◽  
Gaume Johan ◽  
van Herwijnen Alec ◽  
Schweizer Jürg
Keyword(s):  
Mechanical Properties ◽  
Steady State ◽  
Crack Propagation ◽  
Sensitivity Study ◽  
Tensile Fracture ◽  
Crack Speed ◽  
Stress Concentrations ◽  
Snow Layer ◽  
Stress Regime ◽  
Weak Layer

<p>Dry-snow slab avalanche release is a multi-scale process starting with the formation of localized failure in a highly porous weak snow layer below a cohesive snow slab, which can be followed by rapid crack propagation within the weak layer. Finally, a tensile fracture through the slab leads to its detachment. About 15 years ago, the propagation saw test (PST) was developed. The PST is a fracture mechanical field test that provides information on crack propagation propensity in weak snowpack layers. It has become a valuable research tool to investigate the processes involved in crack propagation. While this has led to a better understanding of the onset of crack propagation, much less is known about the ensuing propagation dynamics. Here, we use the discrete element method to numerically simulate PSTs in 3D and analyze the fracture dynamics using a micro-mechanical approach. Our DEM model reproduced the observed PST behavior extracted from experimental analysis. We developed different indicators to define the crack tip that allowed deriving crack speed. Our results show that crack propagation in level terrain reaches a stationary speed if the snow column is long enough. Moreover, we define stress concentration sections. Their length evolution during crack propagation suggests the development of a steady-state stress regime. Slab and weak layer elastic modulus, as well as weak layer shear strength, are the key input parameters for modeling crack propagation; they affect stress concentrations, crack speed, and the critical length for the onset of crack propagation. The results of our sensitivity study highlight the effect of these mechanical parameters on the emergence of a steady-state propagation regime and consequences for dry-snow slab avalanche release. Our DEM approach opens the possibility for a comprehensive study on the influence of the snowpack mechanical properties on the fundamental processes for avalanche release.</p>

Effect of defect length on rolling contact fatigue crack propagation in high strength steel

2015 ◽  
Author(s):  
T. Makino ◽  
Y. Neishi ◽  
D. Shiozawa ◽  
Y. Neishi ◽  
D. Shiozawa ◽  
...  
Keyword(s):  
Crack Propagation ◽  
High Strength Steel ◽  
Rolling Contact Fatigue ◽  
Contact Fatigue ◽  
High Strength ◽  
Rolling Contact ◽  
Micro Ct ◽  
Middle Line ◽  
Micro Computed Tomography ◽  
Depth Direction

 The objective of the present paper is to clarify the effect of defect length in depth direction on rolling contact fatigue (RCF) crack propagation in high strength steel. RCF test and synchrotron radiation micro computed tomography (SR micro CT) imaging were conducted. In the case of the defect with the 15 ?m diameter, flaking life decreased with increasing defect length. In a comparison of the CT image and the SEM view, the shapes of defects and the locations of the horizontal cracks were almost the same respectively. The mechanism of RCF crack propagation was discussed by finite element (FE) analysis. Defects led to higher tensile residual stress than that without defects in the region where the defect exists. The shear stress range at 0.1 mm in depth on the middle line of the defect and the range of mode II stress intensity factor at the bottom of a vertical crack increased with increasing defect length.

scholarly journals Influence of Microstructure on Mechanical Properties of Bainitic Steels in Railway Applications

Metals ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 778 ◽  
Author(s):  
Omid Hajizad ◽  
Ankit Kumar ◽  
Zili Li ◽  
Roumen H. Petrov ◽  
Jilt Sietsma ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Mechanical Behavior ◽  
Mechanical Performance ◽  
Electron Backscatter Diffraction ◽  
Bainitic Ferrite ◽  
Contact Fatigue ◽  
Rolling Contact ◽  
Uniaxial Tensile ◽  
Isothermal Heat Treatment

Wheel–rail contact creates high stresses in both rails and wheels, which can lead to different damage, such as plastic deformation, wear and rolling contact fatigue (RCF). It is important to use high-quality steels that are resistant to these damages. Mechanical properties and failure of steels are determined by various microstructural features, such as grain size, phase fraction, as well as spatial distribution and morphology of these phases in the microstructure. To quantify the mechanical behavior of bainitic rail steels, uniaxial tensile experiments and hardness measurements were performed. In order to characterize the influence of microstructure on the mechanical behavior, various microscopy techniques, such as light optical microscopy (LOM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD), were used. Three bainitic grades industrially known as B360, B1400 plus and Cr-Bainitic together with commonly used R350HT pearlitic grade were studied. Influence of isothermal bainitic heat treatment on the microstructure and mechanical properties of the bainitic grades was investigated and compared with B360, B1400 plus, Cr-Bainitic and R350HT in as-received (AR) condition from the industry. The results show that the carbide-free bainitic steel (B360) after an isothermal heat treatment offers the best mechanical performance among these steels due to a very fine, carbide-free bainitic microstructure consisting of bainitic ferrite and retained austenite laths.

Sign in / Sign up

Export Citation Format

Share Document