PSI - Issue 18

A.P. Zakharov et al. / Procedia Structural Integrity 18 (2019) 749–756 A.P. Zakharov / Structural Integrity Procedia 00 (2019) 000 – 000

754

6

Fig. 4. Plastic SIF distributions for both small-scale yielding ( K ssy ) and large-scale yielding ( K p ).

Note, that numerical results of small-scale and large-scale yielding plastic SIF were obtained for infinite sized central cracked plate. However, in the case of real structures or test specimens under complex stress state, when the plastic zone is no longer small compared to the crack length, the numerical difference between small- and large-scale yielding plastic SIF may be more significant. 4. Mixed Mode Crack Behavior by Plastic Stress Intensity Factor In this section special emphasis is put on the behaviour of the plastic SIF as a function of mixed mode loading and elastic-plastic material properties for specified test specimen geometries. For this purpose an elastic – plastic FE analysis was performed for cruciform specimens of two configurations and a compact tension – shear specimen subjected to mixed Mode I/II loading. Different degrees of mode mixity from pure Mode I to pure Mode II were obtained in all specimens by combinations of the nominal stress level σ n , remote biaxial stress ratio η=σ xx /σ yy and the initial crack angle α with respect to the loading direction. FE meshes of the flat cruciform specimen (CS-1), cruciform specimen with thinned working area (CS-2) and compact tension – shear specimen (CTS) are presented in Fig. 5.

Fig. 5. FEM meshes of flat the CS-1 (a) and CTS (b) geometries and (c) 3D FEM mesh of the CS-2 specimen.

Two-dimensional (2D) plane strain eightnode isoparametric elements have been used for the 2D flat CTS and CS-1 configurations, and twenty-node quadrilateral brick isoparametric three-dimensional (3D) solid elements have been used to model the 3D biaxially loaded CS-2 specimen. The principal feature of this study is the evaluation of coupling mode mixity and solid nonlinearity effects. To this end, two types of steels, titanium and aluminium alloys were considered in numerical calculations. The main mechanical properties of the considered materials are listed in Table 1, where E is Young’s modulus, σ 0 is the yield stress, σ u is the ultimate tensile stress, and α and n are strain hardening coefficient and the strain hardening exponent