Evaluating Non-Uniform Residual Stress by the Hole-Drilling Method With Concentric and Eccentric Holes. Part II: Application of the Influence Functions to the Inverse Problem

Strain ◽  
2010 ◽  
Vol 46 (4) ◽  
pp. 337-346 ◽  
Author(s):  
M. Beghini ◽  
L. Bertini ◽  
L. F. Mori
2000 ◽  
Vol 35 (2) ◽  
pp. 125-135 ◽  
Author(s):  
M Beghini ◽  
L Bertini

Analytical expressions of the influence functions suitable for obtaining variable through-thickness residual stresses by the hole-drilling method are proposed. They were determined by interpolating the results of accurate finite element simulations of the experimental arrangement as prescribed by the ASTM standard. The effects of the geometrical parameters and material properties were included. The influence functions allow the relaxed strain measured by the strain gauge rosette to be directly calculated for a general residual stress distribution. With no interpolation of tabular values, they can be employed to evaluate the coefficients required for the application of the integral method. It is also shown how the influence functions can be used to obtain residual stress distribution on the basis of a fully general series expansion.


2017 ◽  
Vol 52 (3) ◽  
pp. 137-151 ◽  
Author(s):  
Sergey Chupakhin ◽  
Nikolai Kashaev ◽  
Benjamin Klusemann ◽  
Norbert Huber

The hole drilling method is a widely known technique for the determination of non-uniform residual stresses in metallic structures by measuring strain relaxations at the material surface caused through the stress redistribution during drilling of the hole. The integral method is a popular procedure for solving the inverse problem of determining the residual stresses from the measured surface strain. It assumes that the residual stress can be approximated by step-wise constant values, and the material behaves elastically so that the superposition principle can be applied. Required calibration data are obtained from finite element simulations, assuming linear elastic material behavior. That limits the method to the measurement of residual stresses well below the yield strength. There is a lack of research regarding effects caused by residual stresses approaching the yield strength and high through-thickness stress gradients as well as the correction of the resulting errors. However, such high residual stresses are often introduced in various materials by processes such as laser shock peening, for example, to obtain life extension of safety relevant components. The aim of this work is to investigate the limitations of the hole drilling method related to the effects of plasticity and to develop an applicable and efficient method for stress correction, capable of covering a wide range of stress levels. For this reason, an axisymmetric model was used for simulating the hole drilling process in ABAQUS involving plasticity. Afterward, the integral method was applied to the relaxation strain data for determining the equibiaxial stress field. An artificial neural network has been used for solving the inverse problem of stress profile correction. Finally, AA2024-T3 specimens were laser peened and the measured stress fields were corrected by means of the trained network. To quantify the stress overestimation in the hole drilling measurement, an error evaluation has been conducted.


2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Hamid Jahed ◽  
Mohammad Reza Faritus ◽  
Zeinab Jahed

Relieved strains due to drilling hole in a ring sample cut from an autofrettage cylinder are measured. Measured strains are then transformed to residual stresses using calibration constants and mathematical relations of elasticity based on ASTM standard recommendations (American Society for Testing and Materials, ASTM E 837-08, 2008, “Standard Test Method for Determining Residual Stresses by the Hole-Drilling Strain-Gage Method,” American Society for Testing and Materials). The hydraulic autofrettage is pressurizing a closed-end long cylinder beyond its elastic limits and subsequently removing the pressure. In contrast to three-dimensional stress state in the autofrettage tube, the stress measurement in hole drilling method is performed on a traction free surface formed from cutting the ring sample. The process of cutting the ring sample from a long autofrettaged tube is simulated using finite element method (FEM) and the redistribution of the residual stress due to the cut is discussed. Hence, transformation of the hole drilling measurements on the ring slice to the autofrettage residual stresses is revealed. The residual stresses are also predicted by variable material properties (VMP) method (Jahed, H., and Dubey, R. N., 1997, “An Axisymmetric Method of Elastic-Plastic Analysis Capable of Predicting Residual Stress Field,” Trans. ASME J. Pressure Vessel Technol., 119, pp. 264–273) using real loading and unloading behavior of the test material. Prediction results for residual hoop stress agree very well with the measurements. However, radial stress predictions are less than measured values particularly in the middle of the ring. To remove the discrepancy in radial residual stresses, the measured residual hoop stress that shows a self-balanced distribution was taken as the basis for calculating residual radial stresses using field equations of elasticity. The obtained residual stresses were improved a lot and were in good agreement with the VMP solution.


2014 ◽  
Vol 996 ◽  
pp. 283-288 ◽  
Author(s):  
Esther Held ◽  
Simone Schuster ◽  
Jens Gibmeier

The incremental hole-drilling method is a widely used technique to determine residual stress depth profiles in technical components. Its application is limited in respect to the components geometry, for instance the components thickness. In this paper, a direct correction of the measured strain relaxations is proposed to consider the impact of deviant geometries, here the component thickness, on the residual stress evaluation that moreover, allows the application of commercially available evaluation software. The herein proposed approach is based on finite element simulation of the incremental hole drilling. The simulated strain relaxations for thin metal sheets are evaluated with an algorithm as used in commercially available evaluation software (i) for uncorrected data as well as (ii) for strain data corrected by the proposed correction procedure. It is shown that the correction approach leads to a significant improvement of the measurement accuracy. Further, by means of the approach residual stress depth profiles in thin metal sheets can be as usual determined using commercial evaluation software for the incremental hole-drilling method regardless of the algorithm used, i.e. differential or integral.


2020 ◽  
Vol 20 (1) ◽  
pp. 16-55 ◽  
Author(s):  
M. F. de Campos

AbstractThe investigation of plastic deformation and residual stress by non-destructive methods is a subject of large relevance for the industry. In this article, the difference between plastic and elastic deformation is discussed, as well as their effects on magnetic measurements, as hysteresis curve and Magnetic Barkhausen Noise. The residual stress data can be obtained with magnetic measurements and also by the hole drilling method and x-ray diffraction measurements. The residual stress level obtained by these three different methods is different, because these three techniques evaluate the sample in different depths. Effects of crystallographic texture on residual stress are also discussed. The magnetoelastic term should be included in micromagnetic methods for residual stress evaluation. It is discussed how the micromagnetic energy Hamiltonian should be expressed in order to evaluate elastic deformation. Plastic deformation can be accounted in micromagnetic models as a term that increases the coercive field in soft magnetic materials as the steels are.


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