Abstract: By finding stress states which are consistent both with any existing experimental measurements and with elasticity theory, residual stress fields can often be reconstructed from incomplete measurement data. We discuss such methods of residual stress reconstruction, their implementation using finite element analysis, and the measurement strategies which enable them. In general, reconstruction of residual stress fields must be formulated as an inverse problem, which can usually be solved using stress basis functions. However, prior knowledge of the form of the residual stress field and/or underlying eigenstrain distribution often allows the problem to be reduced such that inverse methods become unnecessary, greatly simplifying the analysis. Two examples of when residual stress field reconstruction can be simplified in this way are given.
Abstract: Two common problems of mechanical strain relaxation(MSR) residual stress measurement methods are investigated in this work:(1) assumption of stress uniformity and (2) the effect of plasticity at relaxation. A new MSR technique, designed specifically for highly non-uniformin-plane residual stress fields, is applied in this work to measure the residual stress field resulted from pure bending of an Al7075 alloy.The method involves introducing a straight cut across the whole part in a single increment, and collecting full field displacement fields from the side surface. Application of a 2D high resolution digital image correlation (DIC) method proved successful in this work.The reconstructed residual stress agrees well with that predicted by FE modelling. It is shown that the direction of the propagation of the slit has a major influence on plastic flow during relaxation.The major conclusion from this work is that it is possible to substantially reduce, or completely eliminate, plastic flow on relaxation by careful planning of the slit orientation and the cutting schedule.
Abstract: A new approach in hole-drilling residual stress analysis is described, applying a laser for quasi non-destructive material removal by laser ablation and measuring simultaneously the residual deformation around the hole by means of high-resolution, digital holographic interferometry. To evaluate this technology, experiments measuring well-defined in-plane stresses in curved strip specimen, on experimental bending device based on the European Standard for four-point bending tests, were carried out with the conventional hole drilling and milling technique and the laser-optical technique described.
Abstract: The incremental hole-drilling method was adapted for the measurement of residual stresses in polymer based composite materials. The parameters of the hole drilling process and the strain measurement in non-reinforced and 70 weight-percent glass-fiber-reinforced polypropylene were investigated. Calibration coefficients for the calculation of the residual stresses in the orthotropic material systems were determined by Finite Element Analysis. By means of application of the method to unidirectional and cross-ply glass-fiber reinforced composites the residual stresses, maximum measurable depths and measurement uncertainties could be derived.
Abstract: 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.
Abstract: LLocalized laser hardening of steel surfaces performed with optimal parameters not only hardens the surface layer, but is also capable of generating advantageous hook-like shape of residual stress depth distribution. Upon combining two most common methods of XRD and hole-drilling, the residual stresses up to the depth of 3 mm were analysed for two widths of high-powered diode laser beam. Narrower laser beam generates wider area with compressive stresses and the diffraction technique as compared with hole-drilling method always indicates higher values of compressive residual stress maxima.
Abstract: The incremental hole-drilling method is a widely used technique to determine residual stress depth profiles in technical components. Its application is limited in respect to the components geometry, for instance the components thickness. In this paper, a direct correction of the measured strain relaxations is proposed to consider the impact of deviant geometries, here the component thickness, on the residual stress evaluation that moreover, allows the application of commercially available evaluation software. The herein proposed approach is based on finite element simulation of the incremental hole drilling. The simulated strain relaxations for thin metal sheets are evaluated with an algorithm as used in commercially available evaluation software (i) for uncorrected data as well as (ii) for strain data corrected by the proposed correction procedure. It is shown that the correction approach leads to a significant improvement of the measurement accuracy. Further, by means of the approach residual stress depth profiles in thin metal sheets can be as usual determined using commercial evaluation software for the incremental hole-drilling method regardless of the algorithm used, i.e. differential or integral.
Abstract: Metal forming processes often involve large strain gradients which results in heterogeneous deformation and consequently residual stresses. Furthermore the strain gradients also generate variations in the deformation texture and related properties. For materials with a significant crystallographic elastic anisotropy such as ferritic steel, these textures may have a substantial effect on the reliability of the determination of residual stresses. In the present investigation this influence is examined for the hole drilling method by a combination of experiments and finite element simulations.
Abstract: The review and some experiences are given from measurement and evaluations of residual stresses on large shaft forgings and rail axles using the hole-drilling and ring-core strain-gauge methods, provided by Pilsner Research and Testing Institute, Czech Republic.
Abstract: The hole drilling technique is probably the most widely used residual stress measurement technique. The ASTM E837 standard covers hole drilling measurements for thin and thick specimens. VEQTER have encountered several cases when the specimen was between the thick and thin specification. In order to gain a greater understanding of the sensitivity of the analyses and accurately measure the residual stresses using the hole drilling technique within intermediate thickness specimens and within thin specimens containing non-uniform residual stresses a study was performed.