Deep Hole Drilling Method Research Articles

Analytical model for measurement of stresses using two-hole drilling

Residual stresses have a significant effect on the strength, deformation, plasticity, and fatigue properties of materials. In general, tensile residual stresses are adverse to material performance and component life, while compressive residual stresses can improve material fatigue strength. In this study, an analytical model employing two-hole drilling (THD) is proposed for the measurement of interior stresses. Firstly, the analytical solution for the distortion of the reference hole induced by drilling an adjacent hole is derived using the complex variable method. Based on the analytical solution, the reverse procedure is established to determine the original stress state. Then, the comparative validations of the THD method with the deep hole drilling (DHD) method are performed in conjunction with the finite element (FE) simulations for the beam subjected to bending, the unloaded elastoplastic beam, and the shrink fitted assembly. Finally, parametric analysis is conducted and the results show that: the influence of drilling an adjacent hole on the reference hole rises with the increase of the hole diameters or the decrease of the hole spacing; the THD method is able to give good estimations for the stresses with linear, parabolic, and sinusoidal distributions, although the accuracy is reduced for the prediction of the longitudinal residual stress in the cold-formed section; the uncertainties in evaluated stresses ascend linearly with the increase of the measurement error in the diameter of the reference hole. Relative to the DHD method, the THD method has the merits of less damage and less equipment required and can provide an effective approach for the measurement of stresses inside materials.

An Overview of Techniques for Measuring Residual Stress in Metal Matrix Composites

Measurement of residual stress is significant to ensure safety, reliability and the life of composites, and currently has been a hot issue in scientific research. The fabrication processes such as machining, and heat treatment inherit either kind of residual stress which had either positive consequences or negative ones, for example, the fatigue limit of a component enhances by compressive stress, whereas corrosion resistance gets reduced by tensile stress. This study is aimed at a brief overview of the recent advancement in this field to help researchers in the in-depth study of measuring residual stress. It helps them in selecting the most appropriate techniques among destructive methods i.e., mainly Contour, ring core, deep hole-drilling method, and non-destructive techniques i.e., diffraction, ultrasonic method, depending on their requirements and applications. For each available technique, working methodology, physical limitations, and applications are discussed. At the end of this paper, future trends regarding an assessment of residual stress have been forecasted.

Advances in analysis of total uncertainties in a semi‐invasive residual stress measurement method

AbstractThe ability to characterise residual stress distribution accurately and over different length scales, particularly deep into an engineering part, plays a significant role in assessing structural integrity. Two most commonly used techniques to measure residual stress fields deep into engineering components include neutron diffraction (ND) and deep‐hole drilling (DHD). As the measurements depend on several physical quantities, they are susceptible to error. The error or uncertainties may turn substantial and compromise the suitability of the results. Although noninvasive, the neutron diffraction technique is neither readily available nor portable and is limited to approximately 60‐mm‐thick specimen; errors associated with results become unacceptable at greater flight paths. Moreover, a mock‐up representing the engineering component is normally used in the ND technique. In contrast, the DHD technique is portable and measures residual stresses with high spatial resolution. An error propagation technique was applied to develop an error analysis procedure taking into consideration various stages of the DHD method and successfully applied to different DHD measurements. An essential feature comprising the effect of plasticity due to the creation of reference hole in the DHD procedure has not yet been taken into account in the error analysis procedure. This paper briefly describes how the uncertainties due to the creation of the initial reference hole can be determined. The effect of plasticity in the drilling procedure is quantified in this study. This error is combined with other sources of error and formulated to determine the total error. An incremental DHD technique was used to measure the complex triaxial residual stress field in an as‐welded circular disc, and the measured data were used to illustrate the total error using the error analysis method developed in the study.

Measurement of manufacture assembly stresses in thick composite components using a modified DHD method

Understanding of the through-thickness distribution of assembly stresses caused by manufacture process-induced distortion (PID) in thick composite components is essential for safety and reliability assessment. Inspired by deep-hole drilling (DHD) method which is widely used to reconstruct residual stresses in thick metallic components, current research attempts to extend and modify the DHD technique to measure the manufacture assembly stresses in composite components. It is observed that the modified DHD technique can capture the global deformation profiles induced by the assembly stresses, but the previous DHD stress calculation method produces large stress errors. An integrating stress calculation method is then proposed by combining the homogeneous global and the layer-wise antistrophic stress–strain solutions. It is demonstrated that the assembly stresses calculated by the proposed integrating calculation method are significantly improved and it is feasible to measure the manufacture assembly stresses of thick composite components with the modified DHD technique.

Measurement of assembly stress in composite structures using the deep-hole drilling technique

The deep-hole drilling (DHD) method is a residual stress measurement method that is widely used for measurements in thick metallic components. In the DHD method a reference hole is first drilled through the thickness of the component. The diameter of the hole is measured accurately and then a cylindrical core of material around the hole is trepanned from the component, relaxing the residual stresses in the core. Finally, the diameter of the reference hole is re-measured and the change in diameter used to calculate the residual stress. In this work the method is used to attempt the measurement of cure and assembly stress in thick AS4/8552 composite laminates. The results indicate that although the DHD method cannot measure cure stress, it is able to measure assembly stress. Futhermore, a modification to the standard DHD method allows the through-thickness component of assembly stress to be measured in angle components.

Finite element validation of the deep hole drilling method for measuring residual stresses

The influence of free surfaces, local geometry and plasticity on the residual stress analysis by the deep-hole drilling (DHD) method is addressed in this paper. A finite element (FE) analysis using the commercial software ABAQUS was used to model a number of selected specimens that had been subjected to thermal process conditions that create initial residual stress fields. The essential steps of the DHD method were then simulated at a selected number of locations through the specimens. Two sets of analyses were conducted; one set assumed only that the process of simulating the DHD method was entirely elastic. The second set assumed that the DHD process was elastic–plastic. In the majority of the test cases the conventional DHD method is shown to provide reconstructed in-plane residual stresses that agreed well with the initial residual stresses and did not suffer from expected near free-surface or geometric effects. The results for the out-of-plane residual stresses were however dependent on the assumed state of stress and the interpretation of the axial distortions. The reconstructed out-of-plane residual stresses were shown to have limited agreement with the initial stresses. For the elastic–plastic study, results from a ring welded cylinder were successfully mapped on to a DHD model. A new incremental technique was shown to reconstruct the initial in-plane residual stresses with reasonable accuracy with only limited success for the out-of-plane stress.

Uncertainties in Triaxial Residual Stress Measurements

Residual stress measurement techniques using mechanical strain relaxation depend on a number of physical quantities and are therefore sensitive to errors associated with the measured data. The resulting stress uncertainties can easily become significant and compromise the usefulness of the results or lead to misinterpretation of the behaviour of the residual stress distributions. It is therefore essential to develop an error analysis procedure for the measurements undertaken. Error analysis procedures for the deep hole drilling (DHD) method are developed to consider triaxial residual stresses. A modified deep hole drilling method, called the incremental deep-hole drilling (iDHD), was applied to measure the near yield residual stress distributions in a cold water quenched aluminium 7010 alloy forged block. The experimental results are used to illustrate the errors.

A Method of Measuring Through‐Thickness Internal Strains and Stresses in Graphite

Abstract: Currently, the structural integrity of the nuclear graphite reactor components is evaluated using irradiated material properties data obtained from test reactors. These data are applied to numerical or mathematical models to assess the integrity of the graphite components. On the other hand, there is a need to measure internal strains and stresses in reactor core graphite and to explore the potential for in‐situ measurement. The deep hole drilling (DHD) technique is a semi‐destructive method for measurement of the through thickness residual strains or stresses. Previously the technique has been applied successfully to metallic and composite materials. In this paper, the method for internal strain and stress measurement in polygranular graphite is examined particularly when a significant volume fraction of porosity is present. Finite element simulation shows that the method can be used to measure internal stresses generated by a thermal gradient. On the basis of this a series of experiments have been conducted using Pile Grade ‘A’ (PGA) and PG25 filter graphite; with the latter being a surrogate for service exposed material. Tests were conducted to illustrate that the bulk mechanical response was linear elastic for both graphites and elastic moduli were measured. The DHD method was then used to determine internal strain and stress profiles through the materials. The results were compared with the strain data obtained from strain gauges bonded to the samples. Overall, there was an excellent agreement between the measured through‐thickness internal strains and stresses and the surface strains and stresses determined from the applied loading.

S71 Residual Stresses in a Machined and Shrink Fitted Assemblies

A shrink-fit is a semi-permanent assembly system, widely used in industry, which is designed to resist the relative movement or transmit torque between two components. This done by creating high radial pressures at the interface of the constituent parts. Examples include fitting of gears to shafts to transmit torque and shrink fitted hard wearing sleeves to shafts for steel rolling mills. This paper presents measured and predicted residual stresses from a variety of shrink fitted assemblies, including aluminium alloys, stainless steel and cast irons. In a number of cases the sleeves shrink fitted to the shaft were subjected to prior machining or prior quenching to introduce initial residual stresses in the sleeve. Residual stresses were measured using a combination of deep-hole drilling (DHD) and incremental centre hole drilling (ICHD) techniques. The ICHD method provided near surface residual stress measurements to depths up to about 1mm. The DHD method measured through thickness residual stresses along radial lines through the outer sleeve and into the shaft up to depths of 400mm. Results are shown for a variety of assemblies and reveal residual stress that are significantly different from both simple analysis and finite element studies. For example, prior machining introduced near surface compressive residual stresses, that is then expected to be counteracted by the near surface tensile shrink fit residual stresses. However, measurements reveal that this is not the case.