Simulation of the Kitagawa-Takahashi diagram using a probabilistic approach for cast Al-Si alloys under different multiaxial loads

Abstract

This article describes a microstructural-based high cycle fatigue strength modelling approach applied to different cast Al-Si alloys used in an automotive context. Thank to different casting processes (gravity die casting and lost foam casting), associated with several heat treatment (T7 and Hot Isostatic Pressing-HIP), three alloys with very different microstructures have been obtained. In a vast experimental campaign undertaken to investigate the fatigue damage mechanisms governing these alloys under different multiaxial loading conditions, it was shown that the principal crack initiation mechanisms for the porosity-free alloy are either the formation of persistent slip bands (PSB) or the rupture and/or debonding of eutectic particles. For the porosity-containing alloys, the fatigue damage is always controlled by crack growth from pores. In order to take into account these fatigue damage mechanisms, a probabilistic model using a combination of the Dang Van and a modified LEFM criteria is proposed. The modified LEFM criterion is able to take into account the influence of the grain size on the threshold of the stress intensity factor. It is shown that for the porosity-free alloy, the predictions are good for combined tension-torsion loads with R ¼ À1. However, because the crack initiation mechanisms are not the same depending on the hydrostatic stress, the predictions are non-conservative for the uniaxial and equibiaxial tension loads with R ¼ 0:1. For the porosity-containing alloys, the predictions are very good for the uniaxial, combined tension-torsion and equibiaxial tension loads with both R ¼ À1 and R ¼ 0:1. As observed experimentally, the proposed model can also predict a more pronounced effect of casting porosity for the uniaxial and combined tension-torsion loads, when compared to pure torsion loads.

Investigation of the effect of porosity on the high cycle fatigue behaviour of cast Al-Si alloy by X-ray micro-tomography

“…It can be seen in Fig. 15(a) that the proposed approach predicts a decrease in the fatigue strength with an increase in the equivalent pore size V 1/3 that is in agreement with approaches at the macroscopic scale [2,6,11]. The difference between the numerical predictions and the experimental data is generally less than 15% (Fig.…”

“…In two previous publications [10,11], the authors have presented the results of experimental work investigating the high cycle multiaxial fatigue behaviour of three cast aluminium alloys, referred to as alloys A, B and C. The fabrication steps of the three alloys are as follows.…”

“…The effect of the pore size on the fatigue strength of cast aluminium alloys has been widely studied in the literature [4][5][6][7][8][9][10][11]. In this body of work the pore size has been typically measured via the observation of polished samples or by the inspection of fatigue failure surfaces.…”

Interpretation of the fatigue anisotropy of additively manufactured TA6V alloys via a fracture mechanics approach

“…7 as the linear regression lines of the non-zero experimental points. Greater details concerning this methodology can be found in references [31,32].…”

On the Statistical Size Effect of Cast Aluminium

“…In order to assess the decrease in fatigue strength with elevated probabilities of critical defects, the EVIR methodology of Murakami [68] is invoked, as utilized in various preliminary studies [83,84,85]. Hereby, a reduced variate yj is calculated and plotted in a Gumbel probability paper—see Figure 12.…”