Numerical Analysis of Experiments on Damage and Fracture Behavior of Differently Preloaded Aluminum Alloy Specimens

Abstract

A large amount of experimental studies have shown significant dependence of strength of ductile metals on stress state and stress history. These effects have to be taken into account in constitutive models and corresponding numerical analysis to be able to predict safety and lifetime of engineering structures in a realistic manner. In this context, the present paper deals with numerical analysis of the influence of the load path on damage and fracture behavior of aluminum alloys. A continuum damage model is discussed taking into account the effect of stress state and loading history on damage criteria and on evolution equations of damage strains. Experiments with the biaxially loaded H-specimen have been performed and different preloading histories have been taken into account. Evolution of strain fields is monitored by digital image correlation, and fracture modes are visualized by scanning electron microscopy (SEM). In addition, numerically predicted stress states are used to explain occurrence of different stress-state- and preloading-path-dependent localization behavior in critical specimens areas, as well as damage and fracture modes, revealed by SEM. The experiments with newly developed biaxially loaded specimens and corresponding numerical simulations show that the preloading history remarkably affects the occurrence of width and orientation of localized strain fields, as well as evolution of damage mechanisms and fracture modes. Therefore, characterization of materials must be based on an enhanced experimental program including biaxial tests with different loading histories. The observed damage and failure behavior can be predicted by the proposed continuum model taking into account stress-state-dependent damage criteria and damage strains.

Analysis of Damage and Failure in Anisotropic Ductile Metals Based on Biaxial Experiments with the H-Specimen

“…to occur [10,39]. In the case of the investigated anisotropic material the failure mode also depends on loading direction with more small sheared voids for loading in RD and more pronounced shear-crack mechanisms with marginal number of initial voids for loading in DD and TD.…”

“…11(c)). In this case in isotropic materials the mixed failure mode with simultaneous growth of voids and formation of micro-shear-cracks is expected to occur [10,39]. In the investigated anisotropic aluminum alloy the damage and fracture mode is also dependent on the F 1 -loading direction with more superimposed void growth for F 1 -loading in RD and more pronounced shear-crack mechanisms for F 1 -loading in DD and TD.…”

“…Fig. 6 Geometry, forces and displacements of the H-specimen (all dimensions in mm) [39] of 33Px with an overlap of 11Px in both directions leading to 2.5 evaluation points per mm. During the tests the displacements and the forces of the actuators are transferred and stored with the data sets of the digital image correlation system at a frequency of 1.0Hz.…”

Experiments on forming behaviour of the aluminium alloy AA6016

“…Gerke et al [5] applied the X0-specimen to determine the dependence of non-proportional loading paths on damage evolution and fracture behaviour of an aluminium alloy EN AW 6082 and indicated the significant influence of the strain history on the fracture behaviour. In continuation Brünig et al [6] confirmed these results with the H-specimen. Besides its influence on damage evolution and fracture behaviour the pre-loading history affects remarkably the load-displacement curves, while the IOP Publishing doi:10.1088/1757-899X/1238/1/012023 2 final stresses are almost unaffected.…”

Analysis of damage and fracture behavior in ductile metal sheets undergoing compression and shear preloading

“…A recently proposed approach is the use of biaxial specimens [12] made of sheets, in which the ratio of axis loading can be changed in defined ways, and thus the stress states in critical regions of the specimen can be varied sequentially and by superimposed loadings [33][34][35]. This method is characterized by a wide range of possible variations in the individual stress states as well as in the design of non-proportional load paths [36,37].…”