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Neutron diffraction measurements of residual stresses in a thermoelastically coupled AA6082 alloy system
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Radiat. Phys. Chem. Vol. 51, No. 4±6, pp. 525±526, 1998 # 1998 Elsevier Science Ltd. All rights reserved Printed in Great Britain S0969-806X(97)00192-8 0969-806X/98 $19.00 + 0.00
NEUTRON DIFFRACTION MEASUREMENTS OF RESIDUAL STRESSES IN A THERMOELASTICALLY COUPLED AA6082 ALLOY SYSTEM G. ALBERTINI,1,5 G. CAGLIOTI,2,6 M. CERETTI,3 F. FIORI,4,5 F. OGGIONI,2 F. RUSTICHELLI4,5 and L. VIVIANI2 Univ. di Ancona, Dip. Scienze dei Materiali e della Terra, 60131 Ancona, Italy, 2Politecnico di Milano, Dip. Ingegneria Nucleare (CESNEF), 20133 Milano , Italy, 3LLB (Lab. Comm. CEA-CNRS), CEN Saclay, 91191 Gif-Sur-Yvette, France, 4Univ. di Ancona, Istituto di Scienze Fisiche, 60131 Ancona, Italy, 5Istituto Nazionale per la Fisica della Materia, U.d.R. Ancona, Italy and 6Istituto Nazionale per la Fisica della Materia, U.d.R. Milano, Italy
1
The residual stress ®eld induced by a thermoelastic shrink-®tting procedure in a disc-ring system of AA6082 aluminium alloy was investigated by neutron diraction. The shrunk-®t sample is built of a ring and a disc, joined together by means of a thermoelastic coupling procedure (Viviani, 1995). The two parts are worked in such a way that the disc diameter is slightly wider than the inner diameter of the ring. The latter is held at a temperature of 2208C for 30 min, and then the disc is inserted inside it. The subsequent cooling of the system to room temperature gives rise to an elastic strain ®eld, and thus to a residual stress ®eld. In such a system, the highest stress level is found in the hoop direction, and in applications this component should be kept below the yielding limit. Experiments were performed at the LLB, Saclay (F) and at the Risù National Laboratory (DK). In both cases the 200 re¯ex was used (d20012.024 AÊ). At the LLB the neutron wavelength was l = 2.84 AÊ, and 13 gauge points were investigated (six in the disc, seven in the ring). In each of them the gauge volume, de®ned by two slits situated on the incident and on the diffracted beam, respectively, was a 1.1 mm diameter basis 3 mm height cylinder. At Risù the neutron wavelength was l = 3.02 AÊ, and the gauge volume was a 1 1 10 mm3 parallelepiped. By Bragg's law (l = 2dsinY) the diraction peak position was converted into the interplanar distance d, and then the strain, de®ned as E = (d ÿ d0)/d0 (where d0 is the unstrained interplanar distance), was calculated. d0 was determined by imposing the plane-stress condition (axial stress = 0), which is likely to be full®lled for the sample geometry, at least in the region of the disc far from the disc-ring interface. The three principal strain directions were investigated (radial-r, hoop-ù, axial-z), assuming that no shear strains were present. Finally, the 525
residual stresses sr, sf and sz were calculated by Hooke's law, using the elastic constant values known in the literature for AA6082 alloy (E = 69 GPa, v = 0.383). As remarked above, for the system studied in the present work the most important stress level is obtained in the hoop direction. Figure 1 shows the hoop stress as a function of the radial distance from the disc centre, as measured at the two used neutron sources, and compared to results of numerical calculations which take into account plastic deformations. The agreement between the two experiments is good, as is that between experimental data and numerical calculations. A discrepancy can be noted in the disc where, according to calculations, a low hoop compressive stress ®eld should be found, while experiments detected a tensile ®eld. This fact was ascribed to the presence of a stress state, both in the disc and in the ring, already existing before the coupling procedure, probably due to the extrusion process from which they were obtained. The eect is more visible in the disc, where stress levels are vey low. In order to verify this hypothesis, measurements were carried out at the LLB on uncoupled samples (a disc and a
Fig. 1. Measured hoop stresses, compared to results from numerical calculations.
526
G. Albertini et al.
ring), in the same experimental conditions as for the shrunk-®t sample. As expected, the presence of a low tensile state in the hoop and radial directions was found.
of the LIP and HCM programs of the European Community.
AcknowledgementsÐExperiments at Risù and LLB were possible thanks to the support received in the framework
Viviani, L. (1995) Ph.D. thesis, Politecnico di Milano, Italy.
REFERENCES
Radiat. Phys. Chem. Vol. 51, No. 4±6, pp. 525±526, 1998 # 1998 Elsevier Science Ltd. All rights reserved Printed in Great Britain S0969-806X(97)00192-8 0969-806X/98 $19.00 + 0.00
NEUTRON DIFFRACTION MEASUREMENTS OF RESIDUAL STRESSES IN A THERMOELASTICALLY COUPLED AA6082 ALLOY SYSTEM G. ALBERTINI,1,5 G. CAGLIOTI,2,6 M. CERETTI,3 F. FIORI,4,5 F. OGGIONI,2 F. RUSTICHELLI4,5 and L. VIVIANI2 Univ. di Ancona, Dip. Scienze dei Materiali e della Terra, 60131 Ancona, Italy, 2Politecnico di Milano, Dip. Ingegneria Nucleare (CESNEF), 20133 Milano , Italy, 3LLB (Lab. Comm. CEA-CNRS), CEN Saclay, 91191 Gif-Sur-Yvette, France, 4Univ. di Ancona, Istituto di Scienze Fisiche, 60131 Ancona, Italy, 5Istituto Nazionale per la Fisica della Materia, U.d.R. Ancona, Italy and 6Istituto Nazionale per la Fisica della Materia, U.d.R. Milano, Italy
1
The residual stress ®eld induced by a thermoelastic shrink-®tting procedure in a disc-ring system of AA6082 aluminium alloy was investigated by neutron diraction. The shrunk-®t sample is built of a ring and a disc, joined together by means of a thermoelastic coupling procedure (Viviani, 1995). The two parts are worked in such a way that the disc diameter is slightly wider than the inner diameter of the ring. The latter is held at a temperature of 2208C for 30 min, and then the disc is inserted inside it. The subsequent cooling of the system to room temperature gives rise to an elastic strain ®eld, and thus to a residual stress ®eld. In such a system, the highest stress level is found in the hoop direction, and in applications this component should be kept below the yielding limit. Experiments were performed at the LLB, Saclay (F) and at the Risù National Laboratory (DK). In both cases the 200 re¯ex was used (d20012.024 AÊ). At the LLB the neutron wavelength was l = 2.84 AÊ, and 13 gauge points were investigated (six in the disc, seven in the ring). In each of them the gauge volume, de®ned by two slits situated on the incident and on the diffracted beam, respectively, was a 1.1 mm diameter basis 3 mm height cylinder. At Risù the neutron wavelength was l = 3.02 AÊ, and the gauge volume was a 1 1 10 mm3 parallelepiped. By Bragg's law (l = 2dsinY) the diraction peak position was converted into the interplanar distance d, and then the strain, de®ned as E = (d ÿ d0)/d0 (where d0 is the unstrained interplanar distance), was calculated. d0 was determined by imposing the plane-stress condition (axial stress = 0), which is likely to be full®lled for the sample geometry, at least in the region of the disc far from the disc-ring interface. The three principal strain directions were investigated (radial-r, hoop-ù, axial-z), assuming that no shear strains were present. Finally, the 525
residual stresses sr, sf and sz were calculated by Hooke's law, using the elastic constant values known in the literature for AA6082 alloy (E = 69 GPa, v = 0.383). As remarked above, for the system studied in the present work the most important stress level is obtained in the hoop direction. Figure 1 shows the hoop stress as a function of the radial distance from the disc centre, as measured at the two used neutron sources, and compared to results of numerical calculations which take into account plastic deformations. The agreement between the two experiments is good, as is that between experimental data and numerical calculations. A discrepancy can be noted in the disc where, according to calculations, a low hoop compressive stress ®eld should be found, while experiments detected a tensile ®eld. This fact was ascribed to the presence of a stress state, both in the disc and in the ring, already existing before the coupling procedure, probably due to the extrusion process from which they were obtained. The eect is more visible in the disc, where stress levels are vey low. In order to verify this hypothesis, measurements were carried out at the LLB on uncoupled samples (a disc and a
Fig. 1. Measured hoop stresses, compared to results from numerical calculations.
526
G. Albertini et al.
ring), in the same experimental conditions as for the shrunk-®t sample. As expected, the presence of a low tensile state in the hoop and radial directions was found.
of the LIP and HCM programs of the European Community.
AcknowledgementsÐExperiments at Risù and LLB were possible thanks to the support received in the framework
Viviani, L. (1995) Ph.D. thesis, Politecnico di Milano, Italy.
REFERENCES