- Online only
- New
Due to the electrification in the automotive industry pure aluminum like EN AW-1050A H24 with good conductivity experiences increased interest. The reason is the usage of pure aluminum in cell contacting systems for EVs while the cyclic transient material behavior remains challenging especially due to the non-stabilizing cyclic softening as well as pronounced strain localization.
The non-stabilizing cyclic softening leads to significant differences between the hysteresis curves from the experiments and the simulation using the Chaboche material model [1]. The Damage-Dependent Modified Material Model (DD3M) has already been proposed as a solution [2]. For this, kinematic parameters are calibrated to 100 hysteresis curves, which are taken equidistantly from the test data as a…
Datenschutzbedingungen (bearbeiten im Modul "Kundenvorteile")
Lieferbedingungen (bearbeiten im Modul "Kundenvorteile")
Rücksendebedingungen (bearbeiten im Modul "Kundenvorteile")
Due to the electrification in the automotive industry pure aluminum like EN AW-1050A H24 with good conductivity experiences increased interest. The reason is the usage of pure aluminum in cell contacting systems for EVs while the cyclic transient material behavior remains challenging especially due to the non-stabilizing cyclic softening as well as pronounced strain localization.
The non-stabilizing cyclic softening leads to significant differences between the hysteresis curves from the experiments and the simulation using the Chaboche material model [1]. The Damage-Dependent Modified Material Model (DD3M) has already been proposed as a solution [2]. For this, kinematic parameters are calibrated to 100 hysteresis curves, which are taken equidistantly from the test data as a function of damage, i. e. percentage value of normalized cycles to crack initiation. With the help of these kinematic parameters, a loop is run in the simulation, which calculates the current total damage after each hysteresis. Based on the current total damage, the parameters for the subsequent simulation are determined until accumulated damage of 100 %, a theoretical damage sum of 1, is reached.
While the DD3M is capable of significantly improving the calculation of the fatigue life of the unnotched specimens, a very conservative result is reached when the method is applied on other specimen geometries. In ongoing research, strain localization effects were identified as the main challenges causing the mismatch between calculated and actual fatigue life for notched specimens and whole parts.
Using a DIC system for tracking the local strain of a LCF-test while using a clip-on extensometer for the strain control, significant differences reveal between the strain controlled between the two edges of the extensometer and the actual local strains after just a few cycles, as shown in Figure 1.
When further evaluating the local strain using the data from the DIC system and plotting the maximum local strain over cycles, the self-reinforcing effect of the localization and the resulting high strains can be observed, as shown in Figure 2. With this observation the very conservative results can be explained when the DD3M is applied to notched specimens and parts. The strain-controlled cyclic tests are used to define the strain-life curve and therefore the loading capacity of the material. While the state-of-the-art strain-life curves for EN AW-1050A H24 material relate ~ 300 cycles to failure to the total strain amplitude of 0.6 % for a volume controlled of 10 x 1.2 x 6 mm³, significantly higher local strains of up to ~ 40 % are derived using DIC analysis. Consequently, the strain-life curve considering strain localization would need to be shifted significantly up the y-axis, which translates to less conservative results.
The challenge of the ongoing research is that the local strains from the LCF-tests are no longer of constant amplitude loading. Therefore, an approach to calculate equivalent constant amplitude loading from the local variable amplitude loading using energies is currently applied in ongoing research. The aspired solution is defining an alternative to the current state-of-the-art damage-parameter S-N curves. In combination with the cyclic transient material description using the DD3M a significantly better fatigue life estimation for pure aluminum can be expected.