Experimental and numerical analyses of mean stress relaxation in cold expanded plate of Al‐alloy 2024‐T3 in double shear lap joints

Abstract

In this paper, the mean stress relaxation behavior of simple Al‐alloy 2024‐T3 specimens and also the mean stress relaxation around the hole of cold expanded specimen are studied. The analyses are performed through the combination of the nonlinear isotropic hardening and Chaboche nonlinear kinematic hardening model accompanied by the results of experimental tests. The strain‐controlled axial tests are performed at two different strain amplitudes, while the stress‐controlled tests of cold expanded specimens are performed for three different imposed load amplitudes. The constitutive equations of the hardening model are coded as a UMAT subroutine in FORTRAN programming language and implemented in the commercial finite element code of ABAQUS. The accuracy of the hardening model has been proved in two steps: first by simulations of mean stress relaxation during the uniaxial strain‐controlled cyclic tests and second by simulation of strain ratcheting during the stress‐controlled cyclic loading. The stress and strain distributions after cold expansion process are examined as well as the mean stress relaxation due to cyclic loading. The results show the influences of imposed stress amplitude on increasing mean stress relaxation and also the effect of cold expansion level on reducing the mean stress relaxation.

Residual stress/strain evolution due to low‐cycle fatigue by removing local material volume and optical interferometric data

“…Thus significant contradiction between experimental and numerical data, presented in Ref . and Ref ,. is evident.…”

“…In order to illustrate the effect of point position x (see Figure 3) with respect to the weld line centre on residual stress evolution in more detail, relaxation parameters could be defined as it has been proposed in Ref. 29 :…”

“…The results of both approaches show that the evolution of residual stress at the weld proximity is of complex character and cannot be uniquely qualified as a gradual relaxation. In order to illustrate the effect of point position x (see Figure ) with respect to the weld line centre on residual stress evolution in more detail, relaxation parameters could be defined as it has been proposed in Ref where σ 2 N is the value of σ 2 residual stress component after N cycles applying; σ 2( N = 0) is the initial level of σ 2 residual stress component; is the value of SIF K I after N cycles applying; is the initial level of SIF K I .…”

“…A numerical approach to a quantitative description of residual stress relaxation near cold-expanded hole, based on FEM simulation, is presented in Abdollahi and Chakherlou. 29 Cyclic loading of double shear lap joints of thin plates with holes of initial diameter 5.9 mm and cold expansion level 1.5% and 4.7% is considered. Specimens are made from 2024-T3 aluminium alloy with the yield stress and ultimate tensile strengths equal to 353 and 535 MPa, respectively.…”

Identification of Chaboche–Lemaitre combined isotropic–kinematic hardening model parameters assisted by the fuzzy logic analysis

“…For constant strain amplitude, the plastic deformation would also result in the vertical shift of the stress-strain curves towards the zero-mean stress position. This shift in the vertical direction is associated with the mean-stress shift and is equivalent to the reduction of the residual stress [66]. Both ratcheting and mean stress relaxation phenomenon are characterized by unclosed hysteresis loops.…”