Incremental Hole Drilling Technique Research Articles

Influence of laser shock peening on the residual stresses in additively manufactured 316L by Laser Powder Bed Fusion: A combined experimental–numerical study

Detrimental subsurface tensile residual stresses occur in laser powder bed fusion (LPBF) due to significant temperature gradients during the process. Besides heat treatments, laser shock peening (LSP) is a promising technology for tailoring residual stress profiles of additively manufactured components. A multi step process simulation is applied aiming at predicting the residual stress state after applying LSP to a cuboid shaped specimen manufactured by LPBF in two different building directions as well as comparing it with a post-build heat treatment. The validity of the numerical simulation is evaluated based on comparisons of residual stresses determined by incremental hole drilling technique within different stages of the multi step process: in the as-build condition, after subsequent heat treatment as well as after applying LSP to the as-build and heat treated specimens, showing overall a good experimental-numerical agreement throughout each of the process stages. Applying a heat treatment to the as-build LPBF sample at 700 °C for 6 h showed not to be effective in eliminating the surface tensile stress entirely, reducing the tensile residual stresses by 40%. However, the application of LSP on LPBF components showed promising results: LSP was able even to convert the detrimental near surface tensile residual stresses in the LPBF component into compressive residual stresses next to the surface, which is known to be beneficial for the fatigue performance.

Numerical and experimental investigation on the residual stresses generated by scanning induction hardening

Induction hardening is widely used in the industry as a surface heat treatment that improves the surface and the subsurface hardness of components greatly. The hardened case, which usually is a few mm, highly impacts the surface and structural integrity of the component. In this work, we simulate the scanning induction hardening process by means of finite element modeling. The computed hardness, microstructure, and residual stress profile are compared with experimentally measured data using several surface and subsurface characterization techniques. A very good agreement is found between the simulated and experimentally measured residual stresses, which were characterized by the incremental hole drilling technique.

Experimental and analytical investigation of the effects of laser shock peening processing strategy on fatigue crack growth in thin 2024 aluminium alloy panels

The focus of this paper is on the use of the Laser Shock Peening (LSP) process, and the strategy with which it is employed, to retard fatigue cracks in thin metallic airframe structural panels. This approach allows for the extension of component life in both design and maintenance applications. LSP was carried out without an ablative coating. Various compressive residual stress fields were created by using different laser parameter sets, through the variation of power intensity and coverage. These were quantified using X-Ray Diffraction and Incremental Hole Drilling techniques. The size and position of the peened region was considered in order to balance induced compressive residual stresses and the resulting tensile residual stresses to obtain improved fatigue life and damage tolerance. The investigation was carried out using analytical fracture mechanics code AFGROW and validated through experimentation. Applying LSP to a pre-cracked aluminium panel provided clear retardation of the crack front as it propagated through the processed region. Decreasing the offset of the LSP region from the centre of the panel and increasing the width of the LSP region improved the results. The best configuration, a 15 mm wide LSP region with a 15 mm offset from the crack tip, yielded a fatigue life of more than 6 times the baseline fatigue value.

Use of Power Series Expansion for Residual Stress Determination by the Incremental Hole-Drilling Technique

The integral method of incremental hole-drilling is used extensively to determine the residual stress distribution in isotropic materials. When used with Tikhonov regularization, the method is robust and produces accurate results with minimal uncertainty. Alternatively, an optimal hole depth distribution can be found using the method of Zuccarello to improve the conditioning of the calibration matrices. If substantial measurement noise or a steep variation in stress exists, however, considerable uncertainty in, or distortion of, the calculated residual stress distribution can occur. Series expansion offers an alternative solution, but it has been reported to become unstable before meaningful accuracy can be achieved. Investigate the use of series expansion to determine a rapidly changing throughthickness residual stress distribution in an aluminium alloy 7075 plate subjected to laser shock peening treatment. Power series expansion of eigenstrains is used in finite element modelling to calculate the calibration coefficients. Monte Carlo simulation is used to determine robust uncertainties in the residual stress distributions. This allows the series order with the lowest RMS uncertainty in stress to be selected from those series orders that have converged. The best estimate of the residual stress distribution is thereby obtained. Series expansion is shown to be stable up to 8th order and convergence to a stress solution can be found before instability dominates. The method is insensitive to measurement errors due to the least-squares approach employed by the inverse solution. The use of series expansion reduces the RMS uncertainty in stress when compared to the regularized integral and Zuccarello methods.

Incremental Hole Drilling Residual Stress Measurement in Thin Aluminum Alloy Plates Subjected to Laser Shock Peening

The American standard ASTM E837 presents a standard procedure to determine residual stresses in isotropic materials using the incremental hole drilling technique (IHD). The standard, however, presents limitations regarding its applicability, such as those related with the thin thickness of the samples. According to this standard, in depth non uniform residual stresses can only be determined, roughly, in plates where the thickness is greater than the mean diameter of the strain gage rosette used. This limitation excludes important experimental cases and, therefore, deserves to be investigated. In this work this limitation is numerically and experimentally investigated in detail, considering the case of residual stresses induced by laser shock peening (LSP) in aluminum alloy 7075-T651 plates. The obtained results using the incremental hole drilling technique (IHD), based on the integral method, are benchmarked against the results of several diffraction techniques, used as reference, and a procedure to correct the experimentally determined strain-depth relaxation curves, to accurately still apply the ASTM E837 standard procedure is discussed and validated.

Residual stress measurement on 3-D printed blocks of Ti-6Al-4V using incremental hole drilling technique

3-D printing is envisaged to be a futuristic alternative for rapid and low-cost production of structural components. The major drawback in such fabrication processes is the occurrence of large magnitude of residual stresses (RS). RS are detrimental for the structural integrity of any component if it amplifies the service stresses beyond a limit. In this paper, RS measured using incremental hole drilling strain gauge technique on Direct Metal Laser Sintering (DMLS) 3-D printed prismatic blocks of Ti-6Al-4V has been reported in both non-heat treated and heat treated conditions. The results indicate that large tensile RS inherent in the non-heat treated blocks vanish after annealing. The extension of such mitigation plans to real-life structures and components must be planned so that the remaining service life is enhanced without any significant distortions and warpage.

Plasticity Effects in the Hole-Drilling Residual Stress Measurement in Peened Surfaces

The incremental hole-drilling technique (IHD) is a widely established and accepted technique to determine residual stresses in peened surfaces. However, high residual stresses can lead to local yielding, due to the stress concentration around the drilled hole, affecting the standard residual stress evaluation, which is based on linear elastic equations. This so-called plasticity effect can be quantified by means of a plasticity factor, which measures the residual stress magnitude with respect to the approximate onset of plasticity. The observed resultant overestimation of IHD residual stresses depends on various factors, such as the residual stress state, the stress gradients and the material’s strain hardening. In peened surfaces, equibiaxial stresses are often found. For this case, the combined effect of the local yielding and stress gradients is numerically and experimentally analyzed in detail in this work. In addition, a new plasticity factor is proposed for the evaluation of the onset of yielding around drilled holes in peened surface layers. This new factor is able to explain the agreement and disagreement found between the IHD residual stresses and those determined by X-ray diffraction in shot-peened steel surfaces.

Experimental Evaluation of Residual Stresses in Pipes Manufactured by UOE and ERW Processes

Pipes are basic elements used in the construction of pipelines for the long-distance transportation of oil and gas and their derivatives. They can be manufactured by cold forming processes such as UOE and ERW, both widely used in the oil and gas industry. These processes produce high levels of non-uniform plastic deformation, which introduce a new state of residual stress into the material. In some cases, these stresses combine with mechanical stresses generated by external loads leading to service failures, interrupting the transmission line and increasing the risk of accidents. Therefore, determining in advance the residual stress distribution in pipes is an important task which involves the evaluation of the structural integrity. Six pipe samples obtained by the UOE and ERW processes were measured and evaluated using a portable optical device that combines radial in-plane digital speckle pattern interferometer (DSPI) with the incremental hole-drilling technique to measure residual stresses. The experimental results indicate a distinct residual stress distribution for each manufacturing process, while the measured residual stress distributions in the longitudinal and circumferential directions were similar at all measurement locations along an individual pipe.

Residual stress measurement of fiber metal laminates using incremental hole-drilling technique in consideration of the integral method

In this manuscript, integral method was used for the approximation of residual stresses field in fiber-metal laminates (FMLs). Initially, calibration coefficients matrix for the integral method were determined numerically by the finite element program using ANSYS software. The calibration coefficients were used to relate the measured strains relaxation field with the existing residual stresses prior to the IHD process. Subsequently, FML specimens with symmetric stacking sequence of [AL/02°/902°]S were manufactured. Next, the IHD experiment by high speed drilling machine were performed and released strains caused by the change in hole-geometry have been obtained. Finally, experimental results from IHD experiment were compared with the theoretical predictions from classical lamination theory. Very good agreements with the experimental and theoretical results show that, the IHD technique can be successfully applied for measuring residual stresses in FML composites.

USE OF THE HOLE DRILLING METHOD TO DETERMINE RESIDUAL WELD STRESSES IN BRIDGE CONSTRUCTIONS

Complex welding operations in orthotropic steel bridge decks introduce residual stresses near the weld region. To estimate fatigue failure of this type of bridge deck, tensile residual yield stresses are usually assumed around the weld region. However, to estimate the residual stress distribution near a weld connection more precisely, a test setup is developed. The weld connection of a closed longitudinal trapezoidal stiffener with the deck plate of an orthotropic bridge deck is investigated. The incremental hole-drilling technique is used to measure the residual stresses with strain gauge rosettes. Strain gauge rosettes are positioned on the deck plate and on a longitudinal stiffener of the orthotropic steel deck. A small hole is drilled through the center of the strain gauge rosettes and strains are measured at incremental depths. The residual stresses are calculated and based on these experimental measurements a distribution of the residual stresses is obtained. Compressive residual stresses exist near the longitudinal stiffener-to-deck plate weld. On the deck plate, the compressive residual stresses are equal to 60% of the yield strength while the compressive residual stresses on the stiffener are 42% of the yield strength. There are tensile residual stresses on both sides of the weld region. However, more research is necessary to confirm this distribution since it is contradictory to expected stresses in literature.

Incremental Hole Drilling for Residual Stress Analysis of Strongly Textured Material States – A New Calibration Approach

Technical components produced via sheet metal forming often obtain characteristic crystallographic textures and process induced residual stress distributions. Knowledge of the local residual stress states is essential for the proper components’ dimensioning. We report about the expansion of the incremental hole drilling technique for residual stress analysis to highly textured material states. A new evaluation approach using the differential evaluation algorithm is proposed, which bases on the calculation of multiple case specific calibration functions under consideration of the local orientation distribution function of the textured material. Systematic finite element (FE) simulations of incremental hole-drilling experiments are conducted regarding defined ideal nickel single crystal orientations (cube, Goss and brass). Multiple case-specific calibration functions, which consider the materials elastic anisotropy, are calculated and applied for stress calculation. In addition, the influence of a rosette misorientation between stress measurement and FE calibration is investigated. Using this new evaluation strategy a significant improvement of (residual) stress calculation on strongly textured materials is achieved. Finally, the capability of the proposed evaluation approach is experimentally validated for an uniaxially loaded CMSX-4 (nickel base super alloy) single crystal. The investigation clearly proved that in case of strongly anisotropic materials the evaluation using multiple case-specific calibration functions leads to a significant improvement in stress analysis compared to a conventional evaluation.

Application of the Incremental Hole-Drilling Method on Thick Film Systems—An Approximate Evaluation Approach

A new evaluation procedure is presented regarding the application of the incremental hole-drilling technique to determine in-depth residual stress distribution in thick film systems. Using a direct correction of the measured strain relaxation, obtained after each incremental depth, to take into account the effect of the layered structure of the material, the standard evaluation procedures can still be used without any further modification. For example, the standardized integral method uses specific geometrical calibration constants, which are only valid for isotropic, homogeneous and linear elastic materials. Using artificial neural networks, for the prediction of the correction function to be applied to the measured strain relaxation in thick layered systems, the standard integral method can still be applied. The validation of the proposed approach is shown using finite element (FE-) simulations. In addition, the new evaluation strategy is applied for residual stress determination in a thermally sprayed Aluminum oxide coating on a steel (S690QL) substrate.

Assessing Shot-Peening Residual Stresses by Using the Incremental Hole-Drilling Technique and Laser Interferometry (DSPI)

The incremental hole-drilling technique was applied to determine residual stress profiles in shot-peened steel layers. The accuracy of using an enhanced Digital Speckle Pattern Interferometry technique for measuring the strain relaxation arising around the drilled holes and, consequently, the in-depth residual stress distribution induced by shot-peening, was evaluated. The experimental results were systematically compared with those determined using standard electric strain-gauges. The X-ray diffraction technique was chosen as reference due to its high accuracy to determine shot-peening residual stresses.

Investigation of Residual Stresses in Flame Sprayed Ni-Based Wear Resistant Coatings by the Hole-Drilling and X-Ray Methods

The present investigation was carried out in order to determine residual stresses inNi-based self-fluxing alloy based high velocity oxy-fuel (HVOF) coatings with different wearresistant additives. The main components of the alloy were Ni, Cr, Si and B. To increase the wearresistance of self-fluxing NiCrSiB alloy based coatings, different ceramics and hard metals(WC-Co, TiC-NiMo and Cr2C3-Ni) were added. Residual stresses were measured by the holedrillingmethod and the X-ray method. The incremental hole-drilling technique combined with theintegral method was applied. This combined method allows to analyse non-uniform throughthicknessresidual stresses. The results obtained with the incremental hole-drilling method indicatethat through-thickness residual stress distribution is non-uniform. The determined residual stresseswere tensile on the surface of the coating and became compressive toward the interface.The values of the modulus of elasticity and microhardness of the coatings were obtained byinstrumented indentation. The microstructures of the studied coatings were investigated with theSEM technique.

Residual Stresses Evaluation in Equal Channel Angular Rolled Al 5083 by IHD Technique: Investigation of Two Calculation Methods

Equal channel angular rolling (ECAR) method is one of the severe plastic deformation (SPD) processes which can develop a shear deformation causing considerable residual stress into a sheet metal. In this work, the incremental hole-drilling (IHD) method was applied to determine the through-thickness residual stress distribution. The ECAR was first carried out on a 2 mm Al 5083 sheet for three passes through the channels. The residual stress field was then evaluated using the IHD method. The calibration coefficients A n and B n were obtained by finite element method. It was observed that the residual stress profile through the material thickness was non-uniform and it changed from compressive at the top surface to tensile at the bottom surface in rolling direction. Also, the integral method as an alternative method of calculation was used to determine the residual stresses. There was a good agreement between the results of two calculation methods. It is shown the equal channel angular rolled sample can reveal a maximum residual stress of nearly 45% of its yield strength.

The Contour Method for Residual Stress Determination Applied to an AA6082-T6 Friction Stir Butt Weld

Residual stresses parallel to the welding direction on a cross-section of a 3 mm thick friction stir butt-welded aluminum alloy AA6082-T6 plate were determined using the contour method. A full contour map of longitudinal residual stresses on a weld cross section was determined in this way, revealing detailed information on the residual stress distribution in the inside of a friction stir weld, especially in the nugget zone. The typical M-shape, usually described for the residual stress distribution in friction stir welds, was found. The maximum residual stresses are below the yield strength of the material in the shoulder region and, outside of the welding region, low tensile and compressive residual stresses are responsible for the necessary stress equilibrium on the plane of interest. A comparison was made with the established incremental hole drilling technique on an equivalent plate for validation and good agreement of both techniques was obtained. The distribution, as well as the magnitude of the residual stresses measured by both techniques, is very similar, thus validating both the experimental and numerical procedures used for the contour method application, presented and discussed in the present paper.

Quantifying the Drilling Effect during the Application of Incremental Hole-Drilling Technique in Laminate Composites

In this work, a methodology to quantify the effect of the drilling operation, during the application of the incremental hole-drilling technique (IHD) for measuring residual stresses in laminate composites, in particular, the polymer matrix composites (PMC), is presented. This technique will allow the optimization of the drilling procedures and its parameters, enabling the quantification of the drilling effect. This quantification is obtained by using an experimental calibration procedure followed by a numerical simulation of the whole process. The direct comparison of the experimental and numerical results will allow quantifying the effect of the drilling operation. As example, the methodology was applied to the case of carbon/epoxy cross-ply laminate [0°/90°]5s. The holes have been made by using two different drilling procedures, but the same tool geometry. High speed milling powered by air compression, a process usually employed in the case of the application of hole-drilling technique to metal alloys and a conventional computer numerically controlled (CNC) milling machine, were used. The results seem to show that incremental hole-drilling could be a reliable technique to determine residual stresses in fibre-reinforced polymers.

A Windows‐based software package to evaluate residual stresses by the incremental hole‐drilling technique

AbstractA new software package for the incremental hole‐drilling technique (IHD) is presented in connection with undergraduate mechanical engineering education. The main available technical residual stresses evaluation procedures for applying IHD in isotropic materials are reviewed and have been included in the package. It has an easy‐to‐use, friendly interface, and can be used as a tool to teach the IHD technique or as a laboratory to study its applicability to real world problems. A set of exercises have been prepared, which are freely distributed to our students, in order to show the full potential of the package, but the students can also do simulations and experiments with their own data. © 2009 Wiley Periodicals, Inc. Comput Appl Eng Educ 17: 351–362, 2009; Published online in Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae.20225

Residual stresses analysis of ND-YAG laser welded joints

Laser deposit welding based on modern ND-YAG lasers is a new mould repair process with advantages relatively to the traditional methods (micro-plasma and TIG methods), namely deposition of small volumes of the filler material without distortion. Residual stresses play a major role on the fatigue and thermal–mechanical fatigue behaviour of welds. This paper presents the experimental results and numerical predictions of the residual stresses in joints manufactured with two hot-working tool steels: X.40.CrMoV.5.1 and 40.CrMnNiMo.8.6.4, in the laser-deposited layer and in the heat-affected zone. Welded specimens were prepared with U notches and filled with ND-YAG laser welding deposits. Trough-depth residual stresses evaluation after laser deposit welding were performed in order to analyse the influence of the residual stress state on fatigue behaviour of mould steels. Both X-ray diffraction sin 2γ method (XRD) and incremental hole-drilling technique (IHD) were used in residual stress measurement. Numerical predictions of the residual stress distributions were obtained for several values of the technologic parameters, compared with experimental results and discussed based on the assumptions stated.

Characterization and residual stresses of WC–Co thermally sprayed coatings

The present investigation has been conducted in order to determine the residual stresses of an as-ground WC–12Co coating of two different thicknesses, by means of two different methods. Firstly, X-ray diffraction techniques, which allowed the determination of the surface residual stresses of the coating by means of the method called “sin 2 ψ” method. Secondly, an incremental hole drilling technique together with the integral method, which allowed the analysis of the non-uniform through-thickness residual stresses present in the coatings. It has been determined that the surface residual stresses are of a compressive nature, which could be due to the grinding that was applied to the coatings in order to achieve the desired thicknesses. On the contrary, the results of the incremental hole drilling tests indicated that the through-thickness residual stress distributions are not uniform and are characterized by the presence of tensile peak stresses, at depths in the range of ~ 50–125 μm. Such stresses were observed to decrease towards the coating–substrate interface where the compressive component of the stress state becomes greater than the tensile component. It has been found that the mean residual von Mises stress is higher in the thinner coating than in the thicker one, of approximately 180 and 107 MPa, respectively.