The problem entailed investigation of a fractured separator sieve for one of Komptech separation machines. We were tasked with the investigation of the failure.
The biggest challenge of a failure investigation lies in the fact that any single malfunction or design discrepancy may cause the failure and many times these failures can surface after years of operation.
So we had to look at every possibility. We chose to work with FEM (Finite Element Method) to conduct our analysis.
Accurate boundary conditions for representing an actual operation or a process are of the utmost importance.
In our case we were looking at a fully dynamic high speed vibration equipment. We had to think of not only the static loads but also the dynamic inertial loads of the machine.
One of the machines at work
It is very important to evaluate the worst case loading conditions so all analysis and tests can be run on those conditions, if it fails, it will surely fail at the peak loads and the failure regions can be identified for redesign.
Best steps for conducting a comprehensive analysis
It is always important to start with defining the boundary conditions for your problem. Identify the peak loads and accurate representation of the fixtures and contacts in question. Efficient meshing is very important in reading accurate results with lesser computational resources.
If you are going for analysis of a complex machine with multiple parts, and make accurate mesh for all parts, your analysis will quickly become hardware intensive and eat up your RAM and computing power. Ideally you would want to divide your approach into three steps.
- Run the dynamic analysis with basic mesh detail. At this point the mesh need not be accurate, however you need to put the accurate boundary conditions. The aim of this step is to get the dynamic reaction forces at the fixtures.
- Once the reaction forces are generated, break the model into individual parts or sub-assemblies as per the reaction forces read from the global analysis.
- Generate detailed high resolution mesh for these sub-assemblies and analyze them using the dynamic reaction forces received from the global model.
- Read results and analyze for further analysis or redesign in-case of identification of failure.
Images below are for reference and not relevant to the case being discussed.
Example of a good mesh for evaluating dynamic reaction forces
How analysis results vary with the quality definition of the mesh
Example of an efficient mesh
Types of analysis to investigate failure?
This would entirely depend on the problem at hand. In our case for this particular scenario we started with the basic dynamic analysis on coarse mesh, calculated the reaction forces, applied them onto the refined meshed sub-assemblies and gathered results for signs of yield stress in the assembly. Once we exhausted that option, we then went on to calculate fatigue analysis for the fracture.
Fatigue analysis is calculated by applying cyclic loads on the structure for the material lifetime.
Even of that does not reveal the cause of failure, there could be reasons other than design failure that may have caused the failure.
These failures may include mishandling, low quality materials or low standard off the shelf parts which do not meet the specifications they boast.
Our report on the analysis was received with a lot of confidence as the reasons pin pointed not only seemed probable but were also the main probables for cause of failure at Komptech’s engineering team based on their decades of experience manufacturing and running these machines.