Papers by Keyword: Hole Drilling Method

Abstract: In scope of the investigation of residual stresses the hole drilling method is an accepted method. The method is though not applicable for materials with high anisotropic behavior. Therefore a new algorithm is derived which allows the calculation of residual stresses in laminates made of unidirectional layers. Also the strain gauges deliver only strains on the areas where the strain gauges are applied. With the use of a high resolution imaging system and digital image correlation this area and the informational output can be widely improved. First, the derivation of the residual stress analysis algorithm is presented. For this an adequate finite element model, which is modeling the cooldown process as well as the drilling process, is set up and the surface strains are extracted. Based on this information an algorithm is derived and presented. Within the derivation a change of the layup, a possible change of the cooldown process and a variation of the drilling steps can be investigated. In consequence the input parameters of the algorithm can vary dependent on these factors. Second, the new optical testing setup with refinements to be able to measure the small deformations within micro-strains on the specimen’s surface is prepared and the concept presented. To solve the problem of casting shadows of the drill a special camera setup is being used.

Abstract: In this work, a computational method dedicates to realize the residual stress calculation for multi depths with incremental hole-drilling method. An optimized finite element model is determined with proper size compared to the experiment. By invaliding the mechanical properties of the drilled section in the model, the step-by-step drilling procedure is simulated for incremental hole-drilling method. As the practical application of such computational method, a bulk metallic glass (BMG) sample being mechanically treated by severe plastic process is used to demonstrate the distribution of residual stresses along thickness direction.

Abstract: The paper deals in hole drilling residual stress measurement method. The basic principles of measurement and evaluation by the uniform stress and Integral methods are described. The uncertainties of the residual stress evaluation procedure based on the ASTM E837 standard are analyzed. Examples of residual stress evaluation and comparison of different ASTM E837 standard editions are presented.

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 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 hole-drilling method (HDM) and ring core method (RCM) are limited to low residual stresses under 60% of the yield stress. This issue will experimentally analyze the method of adaptive calculation function, presented by the author on the ICRS9. With a four-point-bending test machine, a defined stress can be triggered between the middle bending. In this defined loading area, the strains in two load cases with the HDM and the RCM configuration were measured. With these measured strains the residual stress calculation will be analysed.

Abstract: This paper shows a large validation activity of the strain gage Hole Drilling Method. The residual stress measurements can not be validated easily, unless with Round Robin activity and/or comparison with other residual stress measurements such as X-ray diffraction. An accurate validation procedure is reported in the present paper, using abending test rig. The bending stress experimentally simulated a residual stress (known with uncertainty lower than 1%) that was considered as the reference stress distribution. The results showed very accurate measurement in terms of relaxed strain distributions, that were compared with the prediction obtained with the Influence Function technique. The differences were in the order of 0.5 microepsilon as standard deviation on a large number of tests. The bending stress prediction was consequently very accurate and the stress differences were as small as 1 MPa showing the accuracy potentiality of the method.

Abstract: The in-plane residual stresses in laser cladded specimens, made of 12-nickel precipitation hardening maraging hot-working tool steel 1.2799 (SIST EN 10027-2) are analyzed using the hole drilling method. The CO2 laser was used to deposit the alloy NiCoMo-1 with significantly higher content of nickel and cobalt with austenitic microstructure at room temperature. The Nd:YAG laser was used to deposit the maraging alloy designated NiCoMo-2, with similar chemical composition as the base material. The comparison of residual stress field showed the sign and the magnitude of residual stresses depends on the chemical composition of the clad being deposited. The high tensile residual stresses were found in NiCoMo-1 layers and favorable compressive residual stresses were found in NiCoMo-2 layers. The metallurgical aspects of residual stress generation are discussed.

Abstract: Single point incremental forming (SPIF) is a process during which at any moment a very small part of the sample is actually being formed. This progressive highly localised deformation is performed by a simple tool, whose trajectory is numerical controlled by a CNC machine. Since no support for the metal sheet is used during forming, large levels of deformation occur, which in turn, induce highly non-uniform residual stresses that affect the accuracy of the processed parts. The aim of the present paper was to inspect, experimentally and by simulation, the state of the residual stresses induced in SPIFed double frustums of pyramids made by A1050. The hole drilling method was used for the experimental measurements and the LS-Dyna software for simulation.

Abstract: Hole drilling strain gage method is a semi-destructive measurement. The method is most commonly used to measure residual stresses. The relieved strains are measured around the drilled hole, and the residual stresses are estimated by the mechanical relationship between relieved strains and residual stresses as well calibration coefficients. The calibration coefficients indicate the relieved strains due to unit stresses within the hole depth. Finite element method is always used to determine the calibration coefficients, and the analytical model is based on the infinite plate. But the geometrical shape and size of cylindrical part are different from the infinite plate. The relieved strains around the drilled hole are different too. Finite element model of the cylindrical part is constructed to obtain the hole drilling calibration coefficients. The measurement of residual stresses in a cylindrical part subject to axial loading calculated by calibration coefficients of both infinite plate and cylindrical part model are compared to show the difference.