The Stress Field Generated in an Elastic Layer by Normally Loaded, Periodically Spaced Circular Contacts

1974 ◽  
Vol 96 (3) ◽  
pp. 376-380 ◽  
Author(s):  
T. G. Johns
Keyword(s):  
Shear Stress ◽  
Stress Field ◽  
Layer Thickness ◽  
Elastic Layer ◽  
Substrate Material ◽  
Contact Spot ◽  
Thin Layers ◽  
State Of Stress ◽  
Octahedral Shear Stress ◽  
Contact Surfaces

The stress field generated in an elastic layer by normally loaded, periodically spaced circular contacts is analyzed. It is intended that this model represent a pair of rough, plated contact surfaces whose plating is much more compliant than the substrate material. The effect of plating thickness and spacing of load-bearing asperities upon the state of stress within the layer is studied. It is shown that there exist values of layer thickness and contact-spot spacing such that the octahedral shear stress within the layer is maximized. Further, for very thin layers, the maximum octahedral shear occurs at the surface of the layer as in tangentially loaded contacts.

Flexural motion due to laser ablation: Influence of force location on the flexural motion

2004 ◽  
Vol 218 (12) ◽  
pp. 1411-1420 ◽  
Author(s):  
B S Yilbas ◽  
J Hyder
Keyword(s):  
Shear Stress ◽  
Laser Ablation ◽  
Maximum Shear Stress ◽  
Substrate Material ◽  
Thin Layers ◽  
Stress Fields ◽  
Pressure Force ◽  
Ablation Process ◽  
Maximum Displacement ◽  
Recoil Pressure

The flexural motion of a multilayer assembly subjected to laser ablation is studied. The assembly consists of thin layers of Inconel alloy (top and bottom layers) and a steel layer (intermediate layer). The assembly resembles a stainless steel sheet with both surfaces coated. The recoil pressure generated during the ablation process results in a loading pressure force acting normal to the assembly surface. The pressure force causes flexural motion in the assembly. In order to secure a sufficiently large flexural displacement, a cantilever arrangement of the assembly is considered. The recoil pressure and the resulting force are formulated and the flexural displacement as well as the resulting stress fields are computed. The influence of the pressure force location at the assembly surface on the flexural motion is examined. It is found that the time occurrence of maximum flexural displacement is the same for all the load locations and the maximum displacement occurs at the free end of the cantilever assembly. The magnitude of normal stresses and shear stress is less than the yielding limit of the substrate material. Moreover, the maximum shear stress is almost three times the maximum normal stress in the assembly.

scholarly journals Spreadability Testing of Powder for Additive Manufacturing

2021 ◽  
Vol 166 (1) ◽  
pp. 9-13
Author(s):  
Christopher Neil Hulme-Smith ◽  
Vignesh Hari ◽  
Pelle Mellin
Keyword(s):  
Additive Manufacturing ◽  
Layer Thickness ◽  
Measurement Procedure ◽  
Quantitative Information ◽  
Thin Layers ◽  
Spreading Speed ◽  
Powder Bed ◽  
Critical Step ◽  
Robust Image

AbstractThe spreading of powders into thin layers is a critical step in powder bed additive manufacturing, but there is no accepted technique to test it. There is not even a metric that can be used to describe spreading behaviour. A robust, image-based measurement procedure has been developed and can be implemented at modest cost and with minimal training. The analysis is automated to derive quantitative information about the characteristics of the spread layer. The technique has been demonstrated for three powders to quantify their spreading behaviour as a function of layer thickness and spreading speed.

Analysis of the Elastic Contact of a Hollow Ball With a Flat Plate

1970 ◽  
Vol 92 (1) ◽  
pp. 138-142 ◽  
Author(s):  
J. H. Rumbarger ◽  
R. C. Herrick ◽  
P. R. Eklund
Keyword(s):  
Shear Stress ◽  
Stress Field ◽  
Flat Plate ◽  
Normal Load ◽  
Thick Wall ◽  
Elastic Contact ◽  
Solid Ball ◽  
Ball Contact ◽  
Contact Life ◽  
Hollow Ball

This paper presents the analysis of the stress field in a hollow sphere in the vicinity of the contact area. The sphere is subjected to a normal load applied through a flat plate. The elastic contact shape and extent are developed for a load of 1000 lb applied to a 1-in-dia hollow ball with a 0.08-in-thick wall. Hollow ball shell bending stresses have a significant effect upon the subsurface stress field. Fatigue life estimates for the hollow ball vary significantly depending upon the selection of decisive stress amplitude. Comparison of the maximum value and location of the reversing orthogonal subsurface shear stress with solid ball data according to the Lundberg-Palmgren dynamic life theory predicts a 91.6 percent life reduction for the hollow ball contact. The use of the unidirectional subsurface shear stress results in a prediction of hollow ball contact life over 30 times the solid ball contact life.

scholarly journals The Contact Mechanics of Novikov’s Surface-Hardened Gearing during Running-in Process

2018 ◽  
Vol 2018 ◽  
pp. 1-8 ◽  
Author(s):  
Alexey Beskopylny ◽  
Nikolay Onishkov ◽  
Viktor Korotkin
Keyword(s):  
Cold Deformation ◽  
Contact Fatigue ◽  
High Hardness ◽  
Contact Spot ◽  
The State ◽  
Contact Strength ◽  
Friction Forces ◽  
Contact Surfaces ◽  
Defective Surface ◽  
The Impact

The article is devoted to the analysis of the state of the contact surfaces of the higher kinematic pair in the general case of relative motion, that is, in the presence of rolling, sliding, and twisting, which is characteristic of Novikov’s circular-screw gears. The purpose of the work is to assess the impact of friction forces, the state of contact surfaces after tool processing, and the localization of the instantaneous contact spot on the level of contact—fatigue durability of gears. Power contact in the presence of geometric slippage of the mating surfaces leads to a significant change in the initial geometry and the mechanical properties of surface layers. In the existing methods of calculations of contact strength, the effect of running-in is investigated insufficiently, which leads to an incorrect result, especially for gear with high hardness of the teeth. In this work, the conditions of contact interaction close to the real requirements are studied on the basis of experimental material, numerical solution of the contact problem, determination of the terms of the contact areas of slip, and adhesion within the instantaneous spot. The shape of the instant contact spot has asymmetry and can be approximated by an ellipse with the introduction of a correction factor. The running-in period is of a plastic nature with cold deformation and reduction of the roughness of surfaces. As a result of the run-in period, the area of actual contact (tooth height) is increased by 2 or more times. It is not desirable to spread the area of contact at the area of adhesion that initiates the formation of pitting. The presence of defective surface area on the level of contact strength does not have significant influence, because of the running-in period, but increases the risk of spalling and brittle fracture.

A critical look at the Wallace-Bott hypothesis in fault-slip analysis

2013 ◽  
Vol 184 (4-5) ◽  
pp. 299-306 ◽  
Author(s):  
Richard J. Lisle
Keyword(s):  
Shear Stress ◽  
Maximum Shear Stress ◽  
Fault Slip ◽  
Shear Stresses ◽  
Homogeneous State ◽  
Slip Direction ◽  
Fault Surface ◽  
State Of Stress ◽  
Simultaneous Movement

AbstractThe assumption is widely made that slip on faults occurs in the direction of maximum resolved shear stress, an assumption known as the Wallace-Bott hypothesis. This assumption is used to theoretically predict slip directions from known in situ stresses, and also as the basis of palaeostress inversion from fault-slip data. This paper examines different situations in relation to the appropriateness of this assumption. Firstly, it is shown that the magnitude of the shear stress resolved within a plane is a function with a poorly defined maximum direction, so that shear stress values greater than 90% of the maximum occur within a wide angular range (± 26°) degrees. The situation of simultaneous movement on pairs of faults requires slip on each fault to be parallel to their mutual line of intersection. However, the resolved shear stresses arising from a homogeneous state of stress do not accord with such a slip arrangement except in the case of pairs of perpendicular faults. Where fault surfaces are non-planar, the directions of resolved shear stress in general give, according to the Wallace-Bott hypothesis, a set of slip directions of rigid fault blocks, which is generally kinematically incompatible. Finally, a simple model of a corrugated fault suggests that any anisotropy of the shear strength of the fault such as that arising from fault surface topography, can lead to a significant angular difference between the directions of maximum shear stress and the slip direction.These findings have relevance to the design of procedures used to estimate palaeostresses and the amount of data required for this type of analysis.

scholarly journals Evaluating Mechanical Properties of Thin Layers using Nanoindentation and Finite-Element Modeling: Implanted Metals and Deposited Layers

1996 ◽  
Vol 438 ◽  
Author(s):  
J. A. Knapp ◽  
D. M. Follstaedt ◽  
J. C. Barbour ◽  
S. M. Myers ◽  
J. W. Ager ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Finite Element ◽  
Finite Element Modeling ◽  
Yield Stress ◽  
Young’S Modulus ◽  
Layer Thickness ◽  
Young's Modulus ◽  
Thin Layers ◽  
Element Modeling ◽  
Surface Modified

AbstractWe present a methodology based on finite-element modeling of nanoindentation data to extract reliable and accurate mechanical properties from thin, hard films and surface-modified layers on softer substrates. The method deduces the yield stress, Young's modulus, and hardness from indentations as deep as 50% of the layer thickness.

Cell adhesion on gaseous plasma modified poly-(l-lactide) surface under shear stress field

Biomaterials ◽  
2003 ◽  
Vol 24 (21) ◽  
pp. 3757-3764 ◽  
Author(s):  
Yuqing Wan ◽  
Jian Yang ◽  
Junlin Yang ◽  
Jianzhong Bei ◽  
Shenguo Wang
Keyword(s):  
Shear Stress ◽  
Cell Adhesion ◽  
Stress Field ◽  
Gaseous Plasma ◽  
Shear Stress Field

The Influence of Boundary Conditions and Surface Layer Thickness on Dielectric Relaxation of Liquid Crystals Confined in Cylindrical Pores

2000 ◽  
Vol 651 ◽  
Author(s):  
Z. Nazario ◽  
G. P. Sinha ◽  
F.M. Aliev
Keyword(s):  
Liquid Crystal ◽  
Boundary Conditions ◽  
Temperature Dependence ◽  
Layer Thickness ◽  
Dielectric Spectroscopy ◽  
Relaxation Times ◽  
Thin Layers ◽  
Short Axis ◽  
Librational Mode ◽  
Cylindrical Pores

AbstractDielectric spectroscopy was applied to investigate the dynamic properties of liquid crystal octylcyanobiphenyl (8CB) confined in 2000 Å cylindrical pores of Anopore membranes with homeotropic and axial (planar) boundary conditions on the pore walls. Homeotropic boundary conditions allow the investigation of the librational mode in 8CB by dielectric spectroscopy. We found that the dynamics of the librational mode is totally different from the behavior observed in investigations of relaxation due to reorientation of molecules around their short axis. The interpretation of the temperature dependence of relaxation times and of the dielectric strength of the librational mode needs the involvement of the temperature dependence of orientational order parameter. For samples with axial boundary conditions, layers of LCs with different thickness were obtained on the pore walls as a result of controlled impregnation of porous matrices with 8CB from solutions of different liquid crystal concentration. The process due to rotation of molecules around their short axis with single relaxation time observed for bulk 8CB is replaced by a process with a distribution of relaxation times in thin layers. This relaxation process broadens with decreasing layer thickness.

Interfacial Thermal Stresses in Layered Structures: The Stepped Edge Problem

1995 ◽  
Vol 117 (2) ◽  
pp. 153-158 ◽  
Author(s):  
Wan-Lee Yin
Keyword(s):  
Stress Field ◽  
Elastic Layer ◽  
Thermal Stresses ◽  
Free Edge ◽  
Multilayered Structure ◽  
Local Geometry ◽  
Temperature Load ◽  
Edge Problem ◽  
Stress Functions ◽  
Multilayer Substrate

The intense, localized stress field produced by a temperature load in a multilayered structure may be significantly affected by the local geometry of the free edge. We examine here the stepped edge problem associated with bonding an elastic layer (silicon chip) to a single or multilayer substrate with a slightly larger length. Stress functions are introduced in various rectangular regions and the continuity of tractions are enforced across all inter-region boundaries. Furthermore, continuity of displacements is enforced across the junction of the two segments of the base laminate. The analysis results indicate that even a minute protrusion of the edge of the base laminate relative to the attached chip may cause significant changes in the peeling and shearing stresses in the end region of the interface.

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