Blind Hole Drilling Technique Research Articles

Numerical and experimental investigation on distribution of residual stress and the influence of heat treatment in multi-pass dissimilar welded rotor joint of alloy 617/10Cr steel

In the present study, numerical and experimental investigation of stress distribution pattern has been performed for thick walled nuclear rotor pipe joint of Alloy 617 and 10Cr steel. Hot wire Tungsten Inert Gas (HW-TIG) welding process has been adopted for multipass narrow groove welding since it yields better mechanical properties at low heat input than manual TIG welding and decreases the accumulation of residual stress significantly. The residual stress generated at the surface of the welded joint was evaluated experimentally using the Blind hole drilling technique (BHD), and consequently, the distribution of stresses along the thickness of the welded joint was masured using the Deep hole drilling (DHD) method. According to the findings, shrinkage at the HAZ area of the weld influences the stresses generated at the cylinder outer surface. The distribution of residual stresses in the weld region is driven mostly by the bending effect produced during the welding process. The influence of post weld heat treatment (PWHT) on residual stress distribution has also been investigated using both experimental and numerical approaches. Numerical investigations have been performed using ABAQUS finite element method. A 2D finite element model has been developed to simulate the welding process and the subsequent heat treatment, using coupled thermo-mechanical analysis. The residual stress results obtained from the numerical approach were validated with the experimentally obtained results and a good correlation has been found. The lumped pass model along with an equal density heat source has been implemented to minimize the computation complexity without affecting the accuracy of the simulated results. The obtained findings revealed that apart from weld centerline, hoop tensile residual stresses were higher around the buttered layer of Alloy 617 and 10Cr steel in an as-welded state. It has been found that nearly 80% of the stresses generated along the weld section have been released after PWHT.

Significance of Finite Element Models and Solid-State Phase Transformation on the Evaluation of Weld Induced Residual Stresses

In the present study, different finite element (FE) models were prepared to investigate weld induced residual stresses in thick multi-pass butt welded joint of SA516 Gr. 70 plates. Both 3D and 2D full geometry models and their axisymmetric half models were taken into consideration. The competence of these FE models on the accuracy of predicting residual stress distribution across the weld cross-section was investigated by comparing it with the experimental results. Blind hole drilling technique and deep hole drilling technique were employed to evaluate the surface and through-thickness residual stress distributions, respectively. In addition, the change in volume and yield strength of weld material due to austenitic phase transformation was also incorporated in the material modeling to observe the effect of solid-state phase transformation (SSPT) on the evaluation of residual stresses. Computed residual stresses obtained from different FE models indicate that the 3D FE models procured the best accuracy compared with the experimental results. On the other hand, 2D models can save a significant amount of computational time with reasonable accuracy. Incorporation of SSPT in the 3D FE full model exhibited a better agreement of predicted results with the experimental measurements.

A comparative study of transverse shrinkage stresses and residual stresses in P91 welded pipe including plasticity error

The paper deals with the measurement of the residual stresses in P91 welded pipe using the blind hole drilling technique. The P91 pipe weld joints were prepared using gas tungsten arc welding process. The residual stress measurement was carried out using the strain gauge rosette that was associated with the plastic deformation of material and stress concentration effect of multi-point cutting tool. Strain gauge response was estimated experimentally using the tensile testing for the uniaxial loading while finite element analysis was performed for biaxial loading. Gas tungsten arc welds joint was prepared for conventional V-groove and narrow groove design. The corrective formulation was developed for calculating the corrected value of residual stresses from the experimentally obtained strain value. The corrected and experimental induced residual stresses values as per ASTM E837-13 were calculated for both V-groove and narrow groove design. Post weld heat treatment (PWHT) of P91 welded pipe was also conducted to study their effect on residual stresses.

A study on the effect of weld groove designs on residual stresses in SS 304LN thick multipass pipe welds

Present research describes the effect of weld groove designs on residual stresses of thick SS 304LN pipe welds which are commonly utilized for applications such as boiling water reactor system, oil and steam piping. The faying surfaces of the pipe joints were machined to generate conventional and narrow groove geometries for welding. Circumferential multipass pipe welding was carried out without applying preheat and post weld heat treatment. Blind hole drilling technique was employed for measuring hoop and axial residual stresses in narrow and conventional grooved SS 304LN pipe welds considering plasticity and stress concentration effects of hole drilling process. The result exhibited 20 to 30 percent reduction in residual stresses in narrow grooved pipe welds. A finite element model was developed for estimating the pass by pass peak temperature distributions in the pipe welds. Sequentially coupled thermomechanical elastic-plastic analysis of both conventional and narrow groove pipe welds indicated close agreement between the predicted and experimentally determined hoop and axial residual stresses.

On the estimation of error in measuring the residual stress by strain gauge rosette

The blind hole drilling technique, utilized for measuring residual stress by using strain gauge rosette, is associated with plastic deformation of material that is removed from the hole and also with stress concentration effect of multi point cutting tool. Further, the plasticity effect is also induced in presence of high applied stress which may lead to local yielding of the hole boundary. The present paper describes the plasticity and stress concentration effects of blind hole drilling technique on the calculation of residual stresses for SS 304L and modified Cr–Mo Grade 91 alloys. For uniaxial loading, the responses of strain gauge rosettes were investigated experimentally through tensile testing and for biaxial loading through numerical modeling. Correlations were developed to directly calculate the corrected values of residual stresses from the experimental strain data obtained through the strain gauge rosette and from stress values as per ASTM E837-13.

Study of End Cracking during One-Sided Submerged Arc Welding with Flux-Copper Backing

Longitudinal hot tearing, popularly called as end cracking, frequently takes place in the end portions of large steel panels’ butt joints, using one-sided, submerged-arc welding with flux copper backing welding process (FCB welding). The study was to look for the possibility to improve and/or prevent the end cracking issue during FCB welding, center blind-hole drilling technique was used to measure the welding residual stress for five different cases, considering hot tearing mechanism, its influence factors and the relevant reported prevention measures. Unpredictable result was observed subsequently that transverse compressive stress is found on the shallow surface of weld seams, which could give supplementary information to the common assumption for conventional low heat input welding method that cracks initiation is caused by tensile stresses across the welded joints. The study concluded that FCB welding end cracking issue is caused by the comprehensive function of different stresses, and also properly use tack welding practice, suitable elastic run-off plate and relatively low heat input energy which will reduce the end cracking susceptibility for the tested materials.

Influence of residual stresses on the mechanical behavior of composite laminate materials

Residual stresses occur during most manufacturing processes (from shrinkage of the resin, difference of thermal expansion coefficients, etc.). Residual stresses may cause local yielding and damage initiation and propagation, and can severely affect performances of a composite structure component. The aim of this work is to investigate the influence of residual stresses on the mechanical behavior of carbon/epoxy cross-ply laminates under tensile and torsion loading. The residual stresses field was determined using the incremental blind-hole drilling technique combined with the finite element analysis. The effect of various cure cycles on the residual stress level is analysed. The quantitative effect of the residual stresses on the mechanical behaviour and the damage initiation and growth is studied by using acoustic emission technique.

Extension to the blind hole drilling technique for residual stress determination with airabrasive hole forming

For an austenitic clad ferritic steel plate it was necessary to determine the residual stress state between the austenitic surface and a region below the austenitic/ferritic interface.The thickness of claddings was 6 mm and to determine the stress variation between the surface and 8 mm an incremental analysis is required. Any material removal en masse in conjunction with small hole residual stress measurements would have resulted in a stress redistribution and hence a distortion in the stress field being measured. In conjunction with strain change measurements on the other face the sensitivity would not have been sufficient. These two options assume that a thin layer of material over relatively large areas can be removed by a non‐stress inducing technique.A blind hole residual stress measurement using a 13 mm diameter hole 13 mm deep will facilitate accurate incremental analysis to a depth of 8 mm.The end mill method of hole forming cannot be used with stainless steels because of the random damage effect which is induced in the readings. The airabrasive method which induces no damage effect was used.The standard airabrasive method of hole forming produces a 2 mm diameter and a 2 mm deep hole.The modification of the standard airabrasive system is discussed which enables 13 mm diameter and 13 mm deep holes to be formed.A deviation from the standard hole/gauge layout geometry has been investigated due to non‐availability of suitable standard rosettes, and a significant increase in sensitivity has been obtained.The incremental stress results for the austenitic layer and the austenitic/ferritic interface are discussed using the results from 1.6 mm, 3.2 mm and 13 mm diameter/deep holes.

Blind hole drilling technique for residual stress measurement: application in ndt

Blind hole drilling technique for residual stress measurement: application in ndt

Blind hole drilling technique for residual stress measurement: application in ndt

An incremental analysis of the hole drilling technique for determining the variation of residual stress with depth is described. Recent trends on the miniaturisation of the technique and the very short time required to make measurements render the technique preferable to X-rays when used in certain applications as a ndt tool.

Surface stresses induced by grit blasting

Summary Stress measurements using the blind hole drilling technique with electrical resistance strain gauges have been made on surfaces of an aluminium alloy which have been subjected to a variety of grit blasting treatments. Relationships between the induced stress and depth were determined for each treatment. It is shown that the magnitude and the depth of the induced compressive stress are particularly sensitive to variations in grit size and, to a much lesser extent, to changes in the nozzle air pressure, the angle of impact and the duration of the treatment. Discussion of the results is centred on the need for control of the operating variables in particular applications. (c) Copyright H.M.S.O. London 1979