Incremental Hole-drilling Method Research Articles

Residual stresses in laser welded aluminium plate by use of ultrasonic and optical methods

Abstract With the wide application of aluminium alloys to the automotive, aerospace and other industries, laser welding has become a critical joining technique for aluminium alloys. In this paper, two techniques have been used to measure the non-uniform residual stresses in laser-welded aluminium alloys, i.e. the Lcr ultrasonic technique and the moire interferometry incremental hole-drilling (MIIHD) method. The non-uniform residual stress distribution in the transverse direction in a laser welded sample was obtained using the Lcr ultrasonic method. The non-uniform in-depth and in-plane residual stresses in the weld center and heat-affected zone were measured using MIIHD. The experimental results showed that these two methods are effective for non-uniform residual stresses problems such as welding.

Influence of experimental parameters on determination of residual stress using the incremental hole-drilling method

The incremental hole-drilling method is an effective semi-destructive technique for determining the profile and magnitude of residual stresses in composite laminates. This method provides access to the residual stress profile of the intra and inter plies in the through thickness of the laminate. Correct application of the method requires optimisation of the relevant experimental parameters. Tests were performed to investigate the influence of two experimental parameters—the depth of each drilled increment and the influence of the relative position of the strain gages compared with the radius of the hole drilled. The development of a rapid automatic method for numerical calculation of the calibration coefficients enhanced the interest of the method while extending the experimental data range being investigated. The results clearly show that these parameters have an appreciable effect on determination of the residual stress gradient, and especially the magnitude and stability of the residual stress.

Determination of Residual Stress in Composite Laminates Using the Incremental Hole-drilling Method

The cooling conditions used in the forming process of composite materials play an important role in the creation ofresidual stress. In this study, a new method for measuring residual stress in composite laminates is presented. Three cooling conditions were used to produce different residual stress levels. Residual stresses in [02/902]s and [08] laminate have been measured by the incremental holedrilling method combined with 3-D finite element modelling. A software which quickly calculates all the coefficients for each increment was developed. The automatic procedure can be used to calculate the calibration coefficient for any type oflaminate (ply number, mechanic characteristics,...) and whatever the number of increments and their depths. The different results show that this method provides access to the in-depth distribution and through thickness ofresidual stress in the laminate with a good accuracy and practicality.

Study of Nonuniform In-Plane and In-Depth Residual Stress of Friction Stir Welding

Friction stir welding (FSW) is a newly developed welding technique that can join aluminum alloys of low fusion weldability. The conventional hole-drilling method does not consider the nonuniform in-plane stress around the drilled hole, it is no longer valid for the residual stress of FSW which has high stress gradient. However, assuming the relaxation of in-plane nonuniform residual stress to be uniform on a small increment of the boundary of the hole, the recently developed Moire´ interferometry incremental hole-drilling (MIIHD) method can be used. Residual stress of a thin plate of friction stir welded aluminum alloy was studied by MIIHD. The longitudinal residual stress distribution in the transversal direction and through the thickness was obtained and compared with results by strain gage method.

Determination of residual stresses by an optical correlative hole-drilling method

In conjunction with the incremental hole-drilling method, a new evaluation procedure is presented for determining the residual stress state in components. In contrast to the classical method, the whole displacement field around the drilled hole is measured using the electronic speckle pattern interferometry technique. The displacement patterns, measured without contact to the surface, are then correlated with those obtained by finite-element simulations using statistical methods. The simulated displacement patterns, used for calibration purposes, result from the application of properly defined basic loads. In this way, the values and the orientation of the residual stresses can be determined by superposition of these properly scaled and shifted basic loads. Even complex states of stress can be evaluated. The theoretical background and experimental results are presented.

Study of Residual Stresses in Composite Laminates by the Finite Element Method and Experimental Analysis

High-performance composite are fabricated by hot isostatic pressing of matrix and fibers. The cooling conditions in the forming process (Resin Transfer Molding, Structural Resin Injection Molding, Laying-up) play an important part in the thermal residual stress distribution. The existence of residual stresses, combined with mechanical loads, could considerably decrease the durability of laminate structures by leading matrix cracking, fibres breaking and interface delamination initiation. The objective of this study is to investigate the influence of residual stresses on the mechanical behavior of composite laminates. Incremental hole-drilling method combined with 3D FE analysis is used to performed the internal strains in laminate plates [0 2 /90 2 ] s polymerized with different cooling conditions (fast, normal and slow). The emission acoustic events system was used during static tensile tests and the signal interpretations are given by a schematic classification in order to estimated the damage initiation between interfaces. The results of this study show that the general level of the residual stresses changes appreciably with the conditions processing and prove that this new method gives a new prospect for the study of the residual stresses distribution in advanced composites parts.

Potentialities of Ultrasonics for Evaluating Residual Stresses: Influence of Microstructure

The good control of residual stress level in mechanical components is an important factor, particularly for a good fatigue strength of these components. This paper presents advances obtained at the technical center for mechanical engineering industries (CETIM) in the field of development of an ultrasonic method for stress measurements. This method is potentially advantageous because it is nondestructive, has good portability, and is easy to use. In the paper are discussed the results obtained with ultrasonics on steel welded plate, and a comparison is made with stress measurement obtained by incremental hole-drilling method, and X-ray diffraction. These results are also validated by thermal relaxation of the plates. The paper discusses also the microstructure influence on ultrasonic measurements and methods for adjusting the ultrasonic measurements to improve the agreement with results obtained from other techniques. In conclusion is emphasized the interest for studying the ability of the ultrasonic residual stress measurement method in different industrial cases.

High sensitivity moiré interferometry and incremental hole-drilling method for residual stress measurement

The theoretical development of a combined method of moiré interferometry, Twyman–Green interferometry and incremental hole-drilling method is presented. The relationship between the three-dimensional surface displacements produced by introducing a blind hole and the corresponding residual stress is established by employing the existing theoretical solution containing a set of undetermined coefficients. The in-plane surface displacements U x and U y and out of plane surface displacement U z produced by the relaxation of residual stresses are obtained from moiré interferometry and Twyman–Green interferometry respectively. The accuracy of the method and the experimental procedure to determine the signs of residual stresses are described. A typical examp1e is presented.

Experimental Study of Residual Stress Distributions in Quenched Parts by the Incremental Large Hole Drilling Method and by the Neutron Diffraction Method

Abstract The incremental hole-drilling method has been used to measure the residual stress field in a quenched part. In quenched parts, there is great compressive residual stress at the surface and tensile residual stress in the middle of the part, so in this case we used an unusually large hole diameter. The classical rosette system cannot be used. The rosette we studied is made up of six strain gages that are placed in a circle with a diameter two times the hole diameter. This system can be adapted to any chosen hole diameter. An error estimation about the positions of the gages has been developed. This procedure is based on a statistical study of measured strains by the six gages. To learn the validity of the incremental large hole drilling and to obtain the complete residual stress field through the thickness of the part, the neutron diffraction method has been used as well. This second method, however, is time consuming and expensive. The aim of this study is to integrate the residual stress field due to quenching into a fatigue life calculation. As is known, only the compressive residual stress field influences the fatigue life, so in the case of quenched parts only the part depth with compressive residual stress need be studied. The quenching of the studied part has been modeled by the finite element method. All the experimental results have been compared to numerical results.

Comparative Analysis of Shot-Peening Residual Stresses Using Hole-Drilling and X-Ray Diffraction Methods

An identical shot-peening treatment was applied to steel samples with different mechanical properties. The in-depth distributions of the residual stresses were analysed by the incremental hole-drilling (IHD) method and compared to X-ray diffraction (XRD) results. The strain hardening of the near surface layers was quantified by microhardness measurements, allowing to estimate a local yield strength. Due to the shot-peening treatment, the local yield strength increased thus reducing the influence of the plasticity effect on IHD results. In some cases, IHD can still give satisfactory results even though residual stresses exceed by far 60% of the bulk material's yield strength, normally limiting the application range of this method. Taking the local yield strength into account, a simple criterion for the assessment of IHD measurements is proposed to predict the influence of the plasticity effect in the case of shot-peening residual stress analysis.

Optimal calculation steps for the evaluation of residual stress by the incremental hole-drilling method

The integral method is a suitable calculation procedure for the determination of nonuniform residual stresses by semidestructive mechanical methods such as the hole-drilling method and the ring-core method. However, the high sensitivity to strain measurement errors due to the ill conditioning of the equations has hindered its practical use. the analysis of the influence of the strain measurment error on the computed stresses carried out in the present work has showed that, given both maximum hole depth and number of total steps, the error sensitivity depends on the particular depth increment distribution used. By means of the matrix formulation, the depth increment distribution that optimizes the numerical conditioning is investigated. Numerical simulations and an experimental test have corroborated the best performance of the proposed step distribution with respect to the constant or increasing distributions commonly used.

Study of Residual Stress Distribution by a Combined Method of Moire´ Interferometry and Incremental Hole Drilling, Part I: Theory

A new method combining Moire´ interferometry and the incremental hole-drilling method is developed to determine both uniform and nonuniform residual stress distribution in depth. The study is reported in two parts. In this first part, the theoretical development of the moire´ interferometry hole-drilling method is presented. The relationship between the in-plane surface displacements produced by introducing a blind hole and the corresponding residual stresses is established by employing the existing theoretical solution containing a set of undetermined coefficients. The coefficients are calibrated by the three-dimensional finite element method and they are processed nondimensionally for general use. The whole field in-plane surface displacements data Ux and Uy produced by the relaxation of residual stresses are obtained from moire´ interferometry after each increment of hole drilling. The high signal-to-noise ratio provided by moire´ interferometry allows accurate determination of fringe orders near the hole boundary which is essential for enhancing fidelity of residual stress determination. The experimental procedure to determine the signs of residual stresses is described and the accuracy of the method is also discussed.

Residual Stress Evaluation by the Hole-Drilling Method With Off-Center Hole: An Extension of the Integral Method

With the incremental hole-drilling method, it is possible to evaluate residual stress variations with depth, acquiring strain values for each step by strain gages. These data can be processed by the integral method. Usually strain gages are not spaced equidistant from the hole center nor arranged in the radial direction, due to practical difficulties in drilling a centered hole. In this study we present a development of the integral method for evaluating stress variations with depth in the specimen for eccentric blind hole cases. The results can be extended and adopted for use with a non-conventional strain gage array.

Stress Calculation Error Analysis for Incremental Hole-Drilling Residual Stress Measurements

The incremental hole-drilling method for measuring non-uniform residual stresses gives stress results that are very sensitive to errors in the measured data. The resulting stress errors can easily become large enough to compromise seriously the usefulness of the calculated stress results. This paper describes a straightforward method for calculating the stress range that has a specified probability of containing the actual residual stresses. Knowledge of this range allows informed interpretations of the stress results to be made. The four measurement error sources considered are: strain errors, hole depth errors, uniform hole diameter errors, and material constant errors. Both the Integral and Power Series stress calculation methods are investigated, and their different responses to measurement errors are described.

Data Management for the Evaluation of Residual Stresses by the Incremental Hole-Drilling Method

The semidestructive incremental hole-drilling method commonly used to evaluate residual stresses is exceedingly sensitive to experimental errors, with sensitivity increasing as hole depth increases. To determine stress variations through the engine thickness, it is necessary to use accurate drilling methods, as well as suitable mathematical models and procedures to minimize the errors associated with residual stress measurement. This work examines the effects of measurement errors on the evaluation of residual stresses with the integral method. An enhanced procedure for managing the experimental data is proposed that allows evaluation of the residual stresses with thickness variations.

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

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.

Measurement of residual-stress distribution by the incremental hole-drilling method

The hole-drilling method is widely used to measure residual stresses in mechanical components. Recent developments have shown that strains measured on the surface during an incremental drilling can be related to residual-stress distribution. Researchers throughout the world have proposed different calibration methods which lead to more or less accurate results. The present paper discusses different approaches used. A new calibration method is proposed. We also show how finite-element analysis can be used to determine the correlation coefficients. The variation of the strains measured on the surface for each increment is due to, first, the residual stresses in the layer and, second, the change of the hole geometry. Most authors do not consider the latter aspect. Our results show that this causes a significant error in the experimental data. The finite-element method has been used to compute the coefficients for all types of strain-gage rosettes when the hole diameter is predetermined. Another problem of the hole-drilling method is the selection of the drilling tool. Two systems have been studied: ultra-high-speed air turbine and conventional milling machine. The method has been applied on both shot-peened and water-quenched test specimens. The results are successfully compared with the bending-deflection and the X-ray method.

Measurement of residual-stress distribution by the incremental hole-drilling method

The hole-drilling method is widely used for the measurement of residual stresses in mechanical components. Recent developments have shown that strains measured on the surface during an incremental drilling can be related to residual-stress distribution. Researches, internationally, have proposed different methods of calibration which lead to results of varying degrees of accuracy. The present paper discusses the different approaches used. A new method of calibration is proposed and it is shown how the finite element analysis can be used for the determination of the correlation coefficients. The variation of the strains measured on the surface for each increment is due, firstly to the residual stresses in the layer and secondly, to the change of the hole geometry. Most authors do not consider the latter aspect, but the presently reported results show that this causes a significant error in the experimental data. The finite-element method has been used for the computation of the coefficients for all types of strain-gauge rosettes when the hole diameter is pre-determinated. Another problem of the hole-drilling method is the selection of the drilling tool. Two systems have been studied: the use of a ultra high-speed air-turbine and the use of a conventional milling machine. The incremental hole drilling method has been applied to both shot-peened and water-quenched test specimens, and results have been successfully compared with those of the bending deflection and the X-ray method.

Récents développements de la mesure des contraintes résiduelles par perçage incrémental

The hole-drilling method is widely used for the measurement of residual stresses in mechanical components. Until recent years, the experimental procedure and its theoretical background were not enough developed to allow the use of the method for the measurement of residual stress distribution in the depth of a part. The method could only be used in the case of uniform stress state. New developments have shown that strains measured on the surface during an incremental drilling can be related to residual stress distribution.A finite element software has been developed by CETIM for the calculation of the coefficients of calibration of the hole drilling method. It is applicable to all isotropic materials, including multilayer materials.Another problem of the method is the selection of the drilling technique. Two systems have been studied: ultra high-speed air-turbine and conventional milling machine.The sensitivity of the incremental hole-drilling method will be discussed. The new hole-drilling method has been applied to shot-peened as well as to water-quenched steel specimens. The results have been successfully compared with those of the bending-deflection and the X-ray diffraction methods.