Research on Finite Element Calibration Technology of Calibration Coefficients in Hole-drilling Method

2011 ◽  
Vol 47 (14) ◽  
pp. 26 ◽  
Author(s):  
Jianyi ZHENG
Keyword(s):  
Finite Element ◽  
Hole Drilling ◽  
Hole Drilling Method ◽  
Drilling Method ◽  
Finite Element Calibration ◽  
Calibration Coefficients

Thermal Stress Measurement in Continuous Welded Rails Using the Hole-Drilling Method

2016 ◽  
Author(s):  
Xuan Zhu ◽  
Francesco Lanza di Scalea ◽  
Mahmood Fateh
Keyword(s):  
Thermal Stress ◽  
Stress Relaxation ◽  
Residual Stresses ◽  
Thermal Stresses ◽  
Stress Measurement ◽  
Test Procedure ◽  
Hole Drilling ◽  
Hole Drilling Method ◽  
Drilling Method ◽  
Calibration Coefficients

Continuous Welded Rail (CWR) has been widely used in modern railway system for it provides smooth ride, higher freight speed, and less maintenance. A major safety concern with this type of structure is the absence of the expansion joints and the potential of buckling in hot weather. According to the FRA safety statistics, the track alignment irregularity is one of the leading factors responsible for the accidents and the most economic/environmental damages, among all the railway accident causes. However, the thermal stress measurement in the CWR for buckling prevention has been an unresolved problem in railroad maintenance. In this study, a method is introduced to determine the in-situ thermal stress of the in-service CWR by using the Hole-Drilling method. The ASTM Hole-Drilling test procedure, as one type of stress relaxation methods, was originally developed to measure the in-plane residual stresses close to the specimen surfaces. The residual stresses are typically computed based on the relieved strains with the calibration coefficients. Inspired by the stress relaxation philosophy, an investigation on the thermal stress measurement of the CWR using the Hole-Drilling test procedure is conducted in this paper. First, the feasibility of using the Hole-Drilling method of the thermal stress measurement is examined via a 3-D finite element model. The stress relaxation computed from the Hole-Drilling test is compared with the applied uniaxial thermal stress. To facilitate the implementation on the CWR, a new set of calibration coefficients with finer depth increment is computed with a novel three-dimensional finite element model for more realistic simulation. The updated coefficients are experimentally validated with an aluminum column specimen under uniaxial load. For the experimental studies, a roadside prototype is developed and two sets of tests are carried out on free-to-expand rail tracks and on rails subjected to controlled thermal loads at UCSD Powell Laboratories. The relieved stresses are computed using the updated calibration coefficients, and a linear relationship between the axial and vertical residual stresses at the neutral axis is observed for both 136RE and 141RE rails. Furthermore, the in-situ thermal stresses are estimated with the residual stress compensation and the neutral temperatures are predicted according to linear thermal expansion theory. These tests illustrate that the determination of the thermal stresses by the Hole-Drilling method is in principle possible, once ways are developed to compensate for the residual stress relaxation. One such compensation is proposed in this paper. A statistical interpretation on the proposed method is also given to provide a reference for railroad applications.

Measurement of Non-Uniform Residual Stresses Using the Hole-Drilling Method. Part II—Practical Application of the Integral Method

1988 ◽  
Vol 110 (4) ◽  
pp. 344-349 ◽  
Author(s):  
G. S. Schajer
Keyword(s):  
Integral Method ◽  
Strain Relaxation ◽  
Hole Drilling ◽  
Calibration Data ◽  
Depth Limit ◽  
Practical Applications ◽  
Hole Drilling Method ◽  
Incremental Hole Drilling ◽  
Drilling Method ◽  
Calibration Coefficients

The Integral Method for calculating non-uniform residual stress fields using strain relaxation data from the incremental hole-drilling method is examined in detail. Finite element calculations are described which evaluate the calibration coefficients required for practical applications of the method. These calibration data are tabulated for a range of hole sizes and depths. It is found that the hole drilling method is not well adapted to measuring stresses remote from the surface, and a theoretical depth limit for stress measurements of 0.5 of the mean radius of the strain gauge rosette, rm, is identified. A practical depth limit is in the range 0.3–0.4 rm.

On the Improvement of Calibration Coefficients for Hole-Drilling Integral Method: Part II—Experimental Validation of Calibration Coefficients

2003 ◽  
Vol 125 (2) ◽  
pp. 107-115 ◽  
Author(s):  
Jong-Ning Aoh ◽  
Chung-Sheng Wei
Keyword(s):  
Experimental Validation ◽  
Three Dimensional ◽  
Bending Test ◽  
Hole Drilling ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
Fem Model ◽  
Hole Drilling Method ◽  
Drilling Method ◽  
Calibration Coefficients

Experimental validation of the calibration coefficients for integral hole-drilling method obtained from an improved three-dimensional FEM model was achieved using bending test of a cantilever beam. The experimental setup is a simple yet accurate method to validate the calibration coefficients obtained by a three-dimensional FEM model. With this experiment, we also validate the adequacy of the criterion applied for thin or thick plates in a previous work. The relieved stresses calculated from the calibration coefficients of the three-dimensional FEM model were compared with those calculated from two-dimensional model calibration coefficients. The results show that the accuracy of relieved stress calculation has been greatly improved as the calibration coefficients based on a three-dimensional model are used for integral hole-drilling method. Significant error in the residual stress measurement and calculation could be arisen if calibration coefficients for integral hole-drilling method were not chosen correctly for corresponding thin plate or thick plate cases according the results of the bending test of cantilever beam. A transitional dimensionless thickness was proposed by examining the calculated relieved stresses obtained from the calibration coefficients for different plate thickness. The probability bounds of relieved stress corresponding to both cases were also calculated to further reveal the improvement of the calibration coefficients obtained from the three-dimensional model.

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