Plastic deformation, or just cracks?

[MJCfromCT]

Hi everyone,

I'm having a bit of difficulty interperting the results of an ANSYS model I'm currently running. This is of a small, thin piece of metal (0.018" in thickness, ~1"x1" length x width), that I am fixing at one end and displacing the other end ~0.015". Essentially this is a cantiliver plate. On the plate, near the fixed end, are a series of small holes. ANSYS reports that at the boundary of one of the holes, there will be a peak stress concentration of 180ksi. This is when plotting von mises stress. This is about 150ksi higher than what I think this piece can handle.

Is there any way to determine if this piece will plastically deform in the area of the stress concentration, making the stress concentration a non-issue? On the other hand, is there some sort of rule-of-thumb to determine if initiating a crack could be a concern?

Thanks in advance, and I'd be happy to provide any additional information.

 

[PerennialII]

For both of your questions I'd start by asking what you know about the material in question with respect to mechanical properties (anything about tensile and fracture mechanical would be a start along with some sort of a "classification" what it is in general). The judgment would have to be done on the basis of stress-strain behavior / limit load and then progress towards a fracture mechanical approach with respect to the crack initiation & propagation part (and under what sort of conditions these might occur ... starting with temperature and such). And also would need to know how you arrived at your stress value, elastic analysis imagine?

 

[oswaler]

Hello,

Based on the information provided, it is difficult to determine whether the stress concentration will result in plastic deformation or the initiation of a crack. However, there are a few factors to consider that may help in your analysis.

First, the material properties of the metal in question will play a significant role in determining its behavior under stress. Some materials are more ductile and can withstand higher stress levels before undergoing plastic deformation, while others may be more brittle and prone to cracking.

In addition, the geometry and size of the holes near the fixed end of the plate can also affect its response to stress. If the holes are too close together or too large, they may weaken the overall structure and increase the likelihood of plastic deformation or crack initiation.

One potential approach to determining the likelihood of plastic deformation or crack initiation is to perform a finite element analysis, similar to the ANSYS model you are currently running. This can help you visualize the distribution of stresses and strains within the plate and identify any potential areas of concern.

Additionally, you may want to consider conducting physical testing on a similar sample to validate the results of your model and gain a better understanding of the material's behavior under stress.

In summary, it is important to carefully consider the material properties, geometry, and potential failure modes when analyzing the stress concentration in your plate. Further analysis and testing may be necessary to determine the most likely outcome.