Experimental and numerical investigation of fracture in a cast aluminium alloy

Abstract

a b s t r a c tThis paper describes an experimental and numerical investigation on the fracture behaviour of a cast AlSi9MgMn aluminium alloy. In the experiments, a modified Arcan test set-up was used to study mixed-mode fracture. During testing, the tension load and the displacement of the actuator of the test machine were recorded, simultaneously as a high-resolution digital camera was used to record a speckle-patterned surface of the specimen. The recorded images were post-processed using an in-house digital image correlation (DIC) software to obtain information of the displacement and strain fields in the specimen during the test. In addition, some newly implemented features in the DIC software allowed us to detect and follow the crack propagation in the material. The numerical calculations were carried out with a user-defined material model implemented in an explicit finite element code. In the model, the material behaviour is described by the classical J 2 flow theory, while fracture was modelled by the Cockcroft-Latham criterion, assuming the fracture parameter to follow a modified weakest-link Weibull distribution. With the proposed probabilistic fracture modelling approach, the fracture parameter can be introduced as a random variable in the finite element simulations. Crack propagation was modelled by element erosion, and a non-local damage formulation was used to reduce mesh-size sensitivity. To reveal the effect of mesh density and meshing technique on the force-displacement curves and the crack propagation, several different meshes were used in the numerical simulations of the modified Arcan tests. The numerical results were finally compared to the experimental data and the agreement between the measured and predicted response was evaluated.

The effects of local variations in mechanical behaviour – Numerical investigation of a ductile iron component

“…using a fracture criteria [18] or a damage evolution model [19]. Homogeneous material behaviour with local values in amount and effect of defects have typically been used to simulate local variations in material performance [20,21] and stochastic methods have been applied to consider the effect of defects on damage [22] or failure [23] of cast components. Previous investigations regarding the effect of local variations in mechanical behaviour on the mechanical behaviour of components, however, have not been found in the literature.…”

Characterisation and investigation of local variations in mechanical behaviour in cast aluminium using gradient solidification, Digital Image Correlation and finite element simulation

“…Regarding cast materials, DIC has e.g. been applied on a microstructural level to study the distribution of strain over different phases during tensile loading of cast irons [26] and on a macroscopic level to study the fracture of a HPDC aluminium alloy [27]. However, the use of DIC to characterise or investigate the macroscopic effects of local variations in microstructure caused by local variations in solidification conditions has not, to the authors' knowledge, been reported in the literature.…”

Simulation of mechanical behaviour of cast aluminium components

“…The Cockcroft-Latham fracture criterion is convenient to use since it is based on only one parameter, Wc, that can be determined from a single test. 57 The fracture criterion is rewritten as an ISV damage evolution law for the damage variable D according to 58 …”

“…The FC method has been used to study the effect of statistical variations of mechanical behaviour in a component. 58 The probability of particle fracture, ppf(W), was assumed to follow a Weibull distribution as 58,59 …”