Strain ratcheting and stress relaxation around interference‐fitted single‐holed plates under cyclic loading: experimental and numerical investigations

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.

mentioning

confidence: 99%

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

Abdollahi

Chakherlou

2018

“…A comprehensive plasticity model should be able to predict the following phenomena: Bauschinger effect, hardening/softening behaviour, mean stress relaxation, strain ratcheting, and load history memory. Considering the importance of strain ratcheting in fatigue life of mechanical joints, special emphases have been given to this issue, and many constitutive equations have been developed for ratcheting response simulations. In this study the Chaboche kinematic hardening models 1986 (3 decomposed rules) and 1991 (fourth rule with a threshold) used for analysing the strain ratcheting behaviour of Al‐alloy 2024‐T3 sheets.…”

Section: Constitutive Modelling: Cyclic Plasticitymentioning

confidence: 99%

Numerical and experimental study of ratcheting in cold expanded plate ofAl‐alloy 2024‐T3 in double shear lap joints

Abdollahi

Chakherlou

2017

Self Cite

In this paper strain ratcheting in cold expanded flat plate of Al-alloy 2024-T3 in double shear lap joints was studied both experimentally and numerically. In the experimental part, two types of symmetric strain-controlled and asymmetric stress-controlled cyclic tests were performed. Also, the cold expanded double shear lap joints subjected to cyclic stress-controlled tests. The required parameters for simulating the cyclic plastic behaviour of Al-alloy 2024-T3 were obtained on the basis of the experimental responses. In the numerical part, a combination of nonlinear isotropic and nonlinear kinematic hardening model (Chaboche) was implemented in the commercial finite element code of ABAQUS, using the subroutine UMAT written in FORTRAN. The results of simulations give an accurate prediction of ratcheting for all types of loading. The obtained results show that increasing the mean stress increases the strain ratcheting. It is clearly shown that the cold expansion process decreases the magnitude of strain ratcheting remarkably compared with "as drilled" specimens and the decrease is bigger for larger cold expansion sizes.Also, it is shown that the middle plane has the highest amount of ratcheting compared to the pin entrance plane and exit plane of the plate hole.

“…Chakherlou and Ajri performed experiments and numerical analysis to evaluate the longitudinal ratcheting and stress relaxation in interference‐fitted single‐holed plates. They reported larger magnitudes of ratcheting strains as cyclic load level increased.…”

Section: Introductionmentioning

confidence: 99%

Ratcheting progress at notch root of 1045 steel samples over asymmetric loading cycles: Experiments and analyses

Khayat

Mahmood

Farhangdoost

et al. 2018

The present study examines ratcheting response of steel samples with various notch diameters through conducting several cyclic tests. Ratcheting strain values were measured through strain gauges mounted at different distances from the notch root. Local ratcheting at the notch region was highly influenced by notch diameter, notch shape, distance from the notch root, and magnitude of the nominal mean/amplitude of loading cycles. Nominal force‐controlled cycles were kept below the yield point and the Neuber's rule accommodated for the maximum/minimum local stress components along those local strains measured through the strain gauges at the notch region. Plastic strains at the vicinity of notch root over loading cycles were further accumulated by means of the Chaboche hardening model. The local ratcheting strain while progressed at the notch root plastic zone over loading cycles resulted in mean stress relaxation controlled by the model.