Hello all,
I have been trying to simulate a 4-point bending test of a multi-layer bar with a geometrically simple 2-d model on COMSOL 4.3a.
For the better understanding of the case,
The bar consists of 3 horizontal layers, the nethermost one consists of a 5 mm thick Ni-base superalloy PWA 1484, the middle layer is an intermetallic compound NiAl with 80 micrometer thickness and the uppermost is Al2O3 with 5 micrometer thickness.
In order to simplify the 4 point bending test, I have adjusted two points on the top of the bar and assigned point loads in the negative y-direction, since the case is a bending under compressional load. 2 other points were also assigned for this stationary case at the netherrmost surface of the bar in order to fix the bar in the y-direction, in other words to contribute the deformation and bending of the bar. The model is quite simple, even for a beginner like me, but efficient indeed. As attached you might find this quite simple model, in order to understand the problem.
Now, I would like to take another step and couple this model with a time-dependent concentration change. Since my middle layer is a diffusional coating which would break down with time due to the Al depletion and instead of NiAl, in the middle layer Ni3Al would form with proceeding time. This case effects also the mechanical properties, therefore the 4-point bending mechanics, since the Elastic Modulus of my 2nd layer should be concentration and time dependent. Therefore the attached model should be somehow modified to compute a time-dependent and isothermal concentrational change and couple it with the initial 4 point bending under constant load.
More accurately, the concentration of the 2nd layer at the beginning should be pure 100 % NiAl, but as the time proceeds the NiAl should be completely consumed and the concentration should drop linearly (for simplification) to 0 % at the end, while the concentration of Ni3Al should start from 0% and increase to 100% linearly. Time dependence of the concentration and this phase transformation causes the elastic modulus of my second layer to be also time and concentration dependent.
Unfortunately, I couldnt achieve the so-called concentrational gradient with a time dependent study of transport of diluted species under the chemical species transport module.
Can someone suggest me a real beginner-friendly and simple approach to this problem? In reality the case is much more struggling since the growth rate of Ni3Al is not linear and affected by the deformation also. As a start, I thought that it would be much more simple for me to try a linear approach. Every idea for a better approach is welcome and appreciated.
With sincere regards,
Ceyhun