The Residual Stress State Generated by Single Point Incremental Forming of Aluminum Metal Sheets

2013 ◽  
Vol 371 ◽  
pp. 148-152 ◽  
Author(s):  
Crina Radu ◽  
Eugen Herghelegiu ◽  
Nicolae Catalin Tampu ◽  
Ion Cristea
Keyword(s):  
Residual Stresses ◽  
Incremental Forming ◽  
Single Point ◽  
Hole Drilling ◽  
Single Point Incremental Forming ◽  
Cnc Machine ◽  
Hole Drilling Method ◽  
Residual Stress State ◽  
Metal Sheets ◽  
Drilling Method

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.

scholarly journals Interaction of Process Parameters, Forming Mechanisms, and Residual Stresses in Single Point Incremental Forming

Metals ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 656 ◽  
Author(s):  
Fabian Maaß ◽  
Marlon Hahn ◽  
A. Erman Tekkaya
Keyword(s):  
Mechanical Properties ◽  
Residual Stress ◽  
Stress State ◽  
Residual Stresses ◽  
Process Parameters ◽  
Process Model ◽  
Incremental Forming ◽  
Single Point ◽  
Single Point Incremental Forming ◽  
Residual Stress State

The residual stress state of a sheet metal component manufactured by metal forming has a significant influence on the mechanical properties, and thus determines the time until the component fails, especially for dynamic loads. The origin of the resulting residual stress state of incrementally formed parts with regard to the forming mechanisms of shearing, bending, and the normal stress component is still under investigation. The relationship between the process parameters, the forming mechanisms, and the resulting residual stress state for a complex part geometry manufactured by single point incremental forming (SPIF) is presented in this publication. For this purpose, a validated numerical process model is used to analyze the influence of the step-down increment Δz for truncated cones on the characteristics of the forming mechanisms and the resulting residual stress state. For the first time the forming mechanisms are evaluated numerically on both sides of the formed component. A relationship between the process parameters, forming mechanisms, residual stresses, and the mechanical properties of an incrementally formed component is shown. Shearing-induced hardening is identified as a relevant influence on the residual stress state of cones.

scholarly journals The Effect of Fiber Waviness on the Residual Stress State and Its Prediction by the Hole Drilling Method in Fiber Metal Laminates: A Global-Local Finite Element Analysis

Metals ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 156
Author(s):  
Steffen Tinkloh ◽  
Tao Wu ◽  
Thomas Tröster ◽  
Thomas Niendorf
Keyword(s):  
Residual Stress ◽  
Stress State ◽  
Residual Stresses ◽  
Global Model ◽  
Hole Drilling ◽  
Fiber Waviness ◽  
Hole Drilling Method ◽  
Residual Stress State ◽  
Incremental Hole Drilling ◽  
Drilling Method

In this paper, fiber waviness, as one of the most frequently occurring defects in fiber reinforced composites, is numerically investigated with regard to the formation of residual stresses in fiber metal laminates. Furthermore, the prediction of the residual stress state in the thickness direction by means of the simulated hole drilling method is studied. To this regard, a global-local finite element analysis based on the submodel technique is presented. The submodel technique essentially consists of two governing steps: In the first step, a global model is first utilized to calculate and analyze the residual stress distribution and deformation in the intrinsically joined hybrid structure. Effective cure-dependent thermo–elastic properties predicted by a numerical homogenization procedure were used to simulate the curing-process and analyze the residual stresses state. However, the dimension of the intrinsically manufactured hybrid plate is large compared to the diameter of the drilled hole (2 mm), so that a local model is necessary, which provides only a geometric partial portion of the global model. The local model takes the global stress state into account and is subsequently used to simulate the incremental hole drilling method with a refined mesh discretization. The production-related fiber waviness is modeled by an element-wise orientation approximating a sinus function. In order to validate the global-local modeling approach, a comparison between numerical results and experimental data from literature is presented. The comparison between global residual stress state (global model) and the simulated hole drilling method (local model) is used to assess the applicability and reliability of the hole drilling method in case of fiber waviness. It is found that an in-plane fiber waviness leads to a rather low variance of residual stresses over thickness. In case of an out-of-plane fiber waviness, oscillating residual stress fields occur over the entire thickness along the fiber direction. Moreover, the current limits of the incremental hole drilling method could be pointed out by the presented investigations. It is seen that the simulated results of the incremental hole drilling method are sensitive to waviness, even if the amplitude-wavelength-ratio is small. Without further adjustment of the calibration coefficients the oscillating stress and strain fields lead, in particular fiber waviness in thickness direction, to unreliable predictions. For the experimental application it can be concluded that the specimens have to be carefully examined with regard to fiber waviness.

Residual Stress Measurements in an Autofrettage Tube Using Hole Drilling Method

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Hamid Jahed ◽  
Mohammad Reza Faritus ◽  
Zeinab Jahed
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Hoop Stress ◽  
Test Method ◽  
Test Material ◽  
Hole Drilling ◽  
Hole Drilling Method ◽  
Ring Sample ◽  
Drilling Method ◽  
American Society

Relieved strains due to drilling hole in a ring sample cut from an autofrettage cylinder are measured. Measured strains are then transformed to residual stresses using calibration constants and mathematical relations of elasticity based on ASTM standard recommendations (American Society for Testing and Materials, ASTM E 837-08, 2008, “Standard Test Method for Determining Residual Stresses by the Hole-Drilling Strain-Gage Method,” American Society for Testing and Materials). The hydraulic autofrettage is pressurizing a closed-end long cylinder beyond its elastic limits and subsequently removing the pressure. In contrast to three-dimensional stress state in the autofrettage tube, the stress measurement in hole drilling method is performed on a traction free surface formed from cutting the ring sample. The process of cutting the ring sample from a long autofrettaged tube is simulated using finite element method (FEM) and the redistribution of the residual stress due to the cut is discussed. Hence, transformation of the hole drilling measurements on the ring slice to the autofrettage residual stresses is revealed. The residual stresses are also predicted by variable material properties (VMP) method (Jahed, H., and Dubey, R. N., 1997, “An Axisymmetric Method of Elastic-Plastic Analysis Capable of Predicting Residual Stress Field,” Trans. ASME J. Pressure Vessel Technol., 119, pp. 264–273) using real loading and unloading behavior of the test material. Prediction results for residual hoop stress agree very well with the measurements. However, radial stress predictions are less than measured values particularly in the middle of the ring. To remove the discrepancy in radial residual stresses, the measured residual hoop stress that shows a self-balanced distribution was taken as the basis for calculating residual radial stresses using field equations of elasticity. The obtained residual stresses were improved a lot and were in good agreement with the VMP solution.

scholarly journals Incremental Hole-Drilling Method Vs. Thin Components: A Simple Correction Approach

2014 ◽  
Vol 996 ◽  
pp. 283-288 ◽  
Author(s):  
Esther Held ◽  
Simone Schuster ◽  
Jens Gibmeier
Keyword(s):  
Residual Stress ◽  
Thin Metal ◽  
Hole Drilling ◽  
Depth Profiles ◽  
Hole Drilling Method ◽  
Incremental Hole Drilling ◽  
Metal Sheets ◽  
Drilling Method ◽  
Measured Strain ◽  
The Impact

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.

scholarly journals The Effect of Specimen Size on Residual Stresses in Friction Stir Welded Aluminum Components

2014 ◽  
Vol 996 ◽  
pp. 445-450 ◽  
Author(s):  
Wulf Pfeiffer ◽  
Eduard Reisacher ◽  
Michael Windisch ◽  
Markus Kahnert
Keyword(s):  
Residual Stresses ◽  
Specimen Size ◽  
Hole Drilling ◽  
X Ray Diffraction ◽  
X Ray ◽  
Friction Stir ◽  
Metal Parts ◽  
Hole Drilling Method ◽  
Incremental Hole Drilling ◽  
Drilling Method

Friction stir welding (FSW) is a well-known technique which allows joining of metal parts without severe distortion. Because FSW involves less heat input relative to conventional welding, it may be assumed that cutting specimens from larger friction stir welded components results in a negligible redistribution of residual stresses. The aim of the investigations was to verify these assumptions for a welded aluminum plate and a circumferentially-welded aluminum cylinder. Strain gage measurements, X-ray diffraction and the incremental hole drilling method were used.

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