PSI - Issue 39

A.L. Pinto et al. / Procedia Structural Integrity 39 (2022) 409–418 Author name / Structural Integrity Procedia 00 (2019) 000–000

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structured but is formed by the same kind of elements. Plane strain elements are considered in all the analyses. Loading conditions considered in the FE model are as follows: firstly, a mean bulk, B, is prescribed on the right side of the specimen while its bottom and left sides have their appropriate movement constraints, Figure 4. Secondly, a constant normal load, P, is applied on the upper surface of the pad. Finally, a tangential fully reversed tangential load, Q, is prescribed on pad’s upper surface ensuring partial slip conditions. Multi-point constraints are enforced on the upper surface of the pad so that rotation is prevented. Regarding the contact conditions, the Lagrange multiplier approach was used to enforce frictional contact constraints. Specimen’s contact nodes were defined as the master ones, whereas, slave nodes were set on the pad contact surface.

Figure 4 – FE model for the fretting fatigue problem. In the Method 2, it is necessary to model the crack and calculate the stress intensity factors (SIF’s). In this case, ABAQUS’ interaction integral method was used to extract the individual SIF’s, and . Contact interactions between the crack faces were also considered in the analyses, where the friction coefficient adopted for the crack faces was the same as the one observed in the fretting contact. Crack propagation analyses were performed by redefining crack’s geometry and re-meshing the model for each crack propagation increment. 4. Experimental data In order to test the accuracy of the proposed methods, the experimental data provided by Almeida et al. (2020) was used in this work. The material considered was an aluminum 7050-T7451. The average size of the small grains of this material is 8 μm. Flat dog -bone specimens and cylindrical pads both made of AA7050- T7451 were used in the fretting tests. The specimens have a square cross section of 13 × 13 mm. Two sizes of cylindrical pads were considered in the tests: a smaller one with a radius of 30 mm and a larger one with a radius of 70 mm. The mechanical properties of the material are listed in Table 1. Table 2 reports the loading conditions in each fretting fatigue test, where represents the mean bulk load, the pad radius, the normal contact force, the tangential load amplitude and 0 the contact peak pressure. The loading history considered in all the tests is depicted in Figure 5. Firstly, a mean bulk, , is prescribed on the specimen. Secondly, a constant normal load, P, presses the cylindrical pad against the specimen. Finally, a tangential fully reversed tangential load with amplitude, , is prescribed on the pad ensuring partial slip conditions. Notice that the mean bulk stress is given by the ratio of the mean bulk stress, , to the cross-section area of the specimen.