scholarly journals Approximation of elastic-plastic local strains in surface-hardened notched components

2021 ◽  
Vol 349 ◽  
pp. 04008
Author(s):  
Patrick Yadegari ◽  
Teresa Schlitzer ◽  
Michael Vormwald
Keyword(s):  
Notch Root ◽  
Core Material ◽  
Plastic Strains ◽  
Local Strains ◽  
Elastic Plastic ◽  
Approximation Formulas ◽  
Potential Failure ◽  
Structural Failures ◽  
Step Algorithm ◽  
Notched Components

Elastic-plastic strains at points relevant for structural failures are usually approximated using formulas based on the stresses determined by elasticity theory. For this purpose, the Neuber approximation is a common method to estimate the local elastic-plastic strains in the notch root, although this is currently only approved for homogeneous components. For surfacehardened notched components, these approximation formulas need to be modified to cover two potential failure points: The notch root as well as the interface between the stronger surface layer and the weaker core material. In the following, a multi-step algorithm is shown that allows the estimation of elastic-plastic local strains at these two points, based on a single elasticitytheoretical solution. A comparison of the approximated values with those from finite element analyses (FEA) reveals that this results in only minor inaccuracies, while the usability is remarkable.

The Use of Strain Energy and Fracture Correlation to Determine Life Expectancy for Notched Components

2009 ◽  
Author(s):  
Onome Scott-Emuakpor ◽  
Tommy George ◽  
Charles Cross ◽  
M.-H. Herman Shen
Keyword(s):  
Fatigue Life ◽  
Stress Concentration ◽  
Cross Section ◽  
Strain Energy ◽  
Notch Root ◽  
Stress Gradient ◽  
Strain Curve ◽  
Experimental Results ◽  
Cyclic Process ◽  
Notched Components

An energy-based method for predicting fatigue life of half-circle notched specimens, based on the nominal applied stress amplitude, has been developed. This developed method is based on the understanding that the total strain energy dissipated during a monotonic fracture and a cyclic process is the same material property, where the density of each can be determined by measuring the area underneath the monotonic true stress-strain curve and measuring the sum of the area within each Hysteresis loop in the cyclic process, respectively. Using this understanding, the criterion for determining fatigue life prediction of half-circle notched components is constructed by incorporating the stress gradient effect through the notch root cross-section. Though fatigue at a notch root is a local phenomenon, evaluation of the stress gradient through the notch root cross-section is essential for incorporating this method into finite element analysis minimum potential energy process. The validation of this method was carried out by comparison with both notched and unnnotched experimental fatigue life of Aluminum 6061-T6 (Al 6061-T6) specimens under tension/compression loading at the theoretical notch fatigue stress concentration factor of 1.75. The comparison initially showed a slight deviation between prediction and experimental results. This led to the analysis of strain energy density per cycle up to failure, and an improved Hysteresis representation for the energy-based prediction analysis. With the newly developed Hysteresis representation, the energy-based prediction comparison shows encouraging agreement with unnotched experimental results and a theoretical notch stress concentration value.

Elastic-plastic strain distributions at fillet welds

1996 ◽  
Vol 31 (3) ◽  
pp. 215-230 ◽  
Author(s):  
K S Elliott ◽  
H Fessler
Keyword(s):  
Strain Range ◽  
Post Weld Heat Treatment ◽  
Steel Plates ◽  
Plastic Strains ◽  
Weld Toes ◽  
Thick Plates ◽  
Full Size ◽  
Elastic Plastic ◽  
Tensile Forces ◽  
Fringe Patterns

Steel plates 25 mm thick were fillet-welded to 50 mm thick plates according to good offshore welding practice. The thinner plates were inclined at 90° or 60° to the thicker ones to represent, at full size, the crown or saddle positions of a structural tubular T joint. Slices 4 mm or 10 mm thick were cut from these weldments and the elastic, elastic-plastic and residual plastic strains in the surfaces of these sections were measured using photoelastic coatings and moiré interferometry. The slices were loaded by tensile forces on the 25 mm wide parts, reacted at pin joints near the ends of the 50 mm wide part. The positions and directions of loading were arranged to load the welds in the same way as in a tubular T joint, loaded in tension. Yielding initiated at the weld toes and could be clearly identified in the moiré fringe patterns. It progressed into the plates, being inhibited by the heat-affected zone. Maximum plastic strains also occurred at the weld toes. Measurements of residual plastic strains showed that the actual strain range, which ‘drives’ fatigue failure, differs from predictions based on elastic analyses. Post-weld heat treatment is beneficial, but extending the weld along the plate reduces the strain concentrations much more.

Development of a Three-Dimensional Semi-Analytical Elastic-Plastic Contact Code

2002 ◽  
Vol 124 (4) ◽  
pp. 653-667 ◽  
Author(s):  
C. Jacq ◽  
D. Ne´lias ◽  
G. Lormand ◽  
D. Girodin
Keyword(s):  
Three Dimensional ◽  
Indentation Test ◽  
Closed Form Expression ◽  
Reciprocal Theorem ◽  
Plastic Strains ◽  
Surface Geometry ◽  
Fe Method ◽  
Elastic Plastic ◽  
Fine Mesh ◽  
The Reciprocal Theorem

A three-dimensional elastic-plastic contact code based on semi-analytical method is presented and validated. The contact is solved within a Hertz framework. The reciprocal theorem with initial strains is then introduced, to express the surface geometry as a function of contact pressure and plastic strains. The irreversible nature of plasticity leads to an incremental formulation of the elastic-plastic contact problem, and an algorithm to solve this problem is set up. Closed form expression, which give residual stresses and surface displacements from plastic strains, are obtained by integration of the reciprocal theorem. The resolution of the elastic-plastic contact using the finite element (FE) method is discussed, and the semi-analytical code presented in this paper is validated by comparing results with experimental data from the nano-indentation test. Finally, the resolution of the rolling elastic-plastic contact is presented for smooth and dented surfaces and for a vertical or rolling loading. The main advantage of this code over classical FE codes is that the calculation time makes the transient analysis of three-dimensional contact problems affordable, including when a fine mesh is required.

Numerical Simulation and Analysis for 3D Elastic-Plastic Rough Contacts

Tribology ◽  
2006 ◽  
Author(s):  
Fan Wang ◽  
Leon M. Keer ◽  
Q. Jane Wang
Keyword(s):  
Real Contact Area ◽  
Plastic Strains ◽  
Normal Contact ◽  
Elastic Plastic ◽  
Hardening Behavior ◽  
Real Contact ◽  
Residual Displacements ◽  
Surface Deflection ◽  
Plastic Hardening ◽  
Contact Field

A 3D elastic-plastic rough contact (EPC) solution and code is developed using a modified semi-analytical method. The total surface deflection is induced by the contact pressure and plastic strain. A purely elastic contact field and a residual field arising from the plastic deformation are simulated iteratively to gain the final approximate solution for the elastic-plastic rough contact. Frictionless normal contact between a rigid ball and an elastic-plastic half space with polished, turned, and honed rough surfaces was numerically simulated using the developed EPC code. The distributions of surface pressures, real contact area, total stresses, residual stresses, residual displacements, and plastic strains are obtained through simulation. The effects of surface roughness, wavelength, and plastic hardening behavior upon the calculated results are analyzed.

Elastoplastic Plane Strain Analysis of Stresses and Strains at the Notch Root

1988 ◽  
Vol 110 (3) ◽  
pp. 195-204 ◽  
Author(s):  
G. Glinka ◽  
W. Ott ◽  
H. Nowack
Keyword(s):  
Energy Density ◽  
Plane Strain ◽  
Strain Energy Density ◽  
Strain Energy ◽  
Notch Root ◽  
Equivalent Strain ◽  
Element Analysis ◽  
Elastic Plastic ◽  
Energy Concept ◽  
Notch Tip

For the evaluation of the local elastoplastic strains and stresses at the notch root suitable approximation formulas of sufficient accuracy are often used. In the present study the “equivalent strain energy density” concept for elastic-plastic notch strain-stress analysis has been developed. It was found that the evaluation of the strain energy density in the notch tip plastic zones does not require any input data other than the material stress-strain relation and the elastic stress concentration factor. The concept was verified on the basis of the results obtained from plane strain elastic-plastic finite element analysis using the material model after Mro´z. Comparison of the two sets of results revealed satisfactory accuracy of the equivalent strain energy concept. It was also shown that all stress and strain components in the notch tip can be calculated by complementing the method with Hencky’s equations. Neuber-based calculations were also included in the study. It was found that the energy concept was superior to Neuber’s rule, especially in the presence of high inelastic strains in the notch tip.

Sign in / Sign up

Export Citation Format

Share Document