Cummins: Exhaust Aftertreatment System – New Methodology Reduces Testing Costs By 85%



>85% cheaper than physical testing

future design validation

Design iterations in @20% of the time

SUMMARY

Our client develops industry-leading exhaust after-treatment technology. They asked us to investigate significant fatigue failures associated with the compact box mounting brackets, believed to be due to a combination of dynamic effects and thermal effects. We combined thermo-mechanical and random vibration (Power Spectral Density) fatigue analysis to assess the mounting brackets. Our analysis methodology and model cut the time for creating design iterations by 20% and reduced the costs of physical testing by 85%.

SITUATION

Cummins Emissions Solutions, a division of Cummins, develops industry-leading exhaust after-treatment technology for light to heavy-duty and high horsepower commercial on and off-highway vehicle markets to meet current and future emissions legislation across the globe. This case study focusses on their new Euro VI compact box design, which incorporates all after-treatment requirements into one structure (Diesel Oxidation Catalysts, Diesel Particulate Filters, Selective Catalyst Reduction filters, etc.) for a multitude of different vehicles.

CHALLENGE

Cummins had significant fatigue failures associated with the compact box mounting brackets, believed to be due to a combination of dynamic effects and thermal effects. The fatigue analysis investigated the damage and therefore the life of the bracket and welds consistent with multi-axis shaker table tests, with the inclusion of the effects to mean stress due to thermal expansion and fatigue strength reduction due to the high temperatures involved. We were called in due to our capabilities and extensive experience to develop such analysis methodologies. 

SOLUTION

Our aim was to combine the thermo-mechanical and random vibration (Power Spectral Density) fatigue analysis to produce an assessment that resulted in an appropriate assessment of the mounting brackets. This involved:

  • We developed an FEA model that matches the modes seen in real data from the truck (and therefore correct dynamic action in Power Spectral Density analysis).
  • From this FEA model, produce a thermal structural analysis to represent thermal pre-stress effects from thermal point cloud data.
  • We created a post-processing APDL deck to combine the results from the thermal and PSD models to calculate fatigue effects, incorporating thermal mean stress effects and fatigue strength reduction:

                      - Goodman correction applied with respect to thermal stress at each node

                      - Fatigue strength reduction due to the temperature at each node

                      - The assessment then uses the Dirlik method for fatigue assessment of random vibration effects, considering mean stress effects and strength reduction mentioned above

Due to the nature of the project, we were based on site carrying out the assessments as well as providing additional analysis support and knowledge to the wider team. A Cummins functional excellence procedure was completed to document the methodology and process to be utilised on future design validation.

BENEFITS
  • We developed a functional excellence procedure for Cummins so they can use this coupled thermal fatigue assessment approach for future design validation.
  • The analysis approach increases the accuracy and confidence of design, therefore, reducing the risk of failure during test or operation.
  • Analysis methodology and model built to carry out design iterations in approximately 20% of the time compared to carrying out physical tests.
  • Our development of analysis methodology and design iterations are more than 85% cheaper compared to carrying out physical multi-axis shaker table tests


Our client develops industry-leading exhaust after-treatment technology. They asked us to investigate significant fatigue failures associated with the compact box mounting brackets, believed to be due to a combination of dynamic effects and thermal effects. We combined thermo-mechanical and random vibration (Power Spectral Density) fatigue analysis to assess the mounting brackets. Our analysis methodology and model cut the time for creating design iterations by 20% and reduced the costs of physical testing by 85%.



Cummins Emissions Solutions, a division of Cummins, develops industry-leading exhaust after-treatment technology for light to heavy-duty and high horsepower commercial on and off-highway vehicle markets to meet current and future emissions legislation across the globe. This case study focusses on their new Euro VI compact box design, which incorporates all after-treatment requirements into one structure (Diesel Oxidation Catalysts, Diesel Particulate Filters, Selective Catalyst Reduction filters, etc.) for a multitude of different vehicles.



Cummins had significant fatigue failures associated with the compact box mounting brackets, believed to be due to a combination of dynamic effects and thermal effects. The fatigue analysis investigated the damage and therefore the life of the bracket and welds consistent with multi-axis shaker table tests, with the inclusion of the effects to mean stress due to thermal expansion and fatigue strength reduction due to the high temperatures involved. We were called in due to our capabilities and extensive experience to develop such analysis methodologies. 



Our aim was to combine the thermo-mechanical and random vibration (Power Spectral Density) fatigue analysis to produce an assessment that resulted in an appropriate assessment of the mounting brackets. This involved:

  • We developed an FEA model that matches the modes seen in real data from the truck (and therefore correct dynamic action in Power Spectral Density analysis).
  • From this FEA model, produce a thermal structural analysis to represent thermal pre-stress effects from thermal point cloud data.
  • We created a post-processing APDL deck to combine the results from the thermal and PSD models to calculate fatigue effects, incorporating thermal mean stress effects and fatigue strength reduction:

                      - Goodman correction applied with respect to thermal stress at each node

                      - Fatigue strength reduction due to the temperature at each node

                      - The assessment then uses the Dirlik method for fatigue assessment of random vibration effects, considering mean stress effects and strength reduction mentioned above

Due to the nature of the project, we were based on site carrying out the assessments as well as providing additional analysis support and knowledge to the wider team. A Cummins functional excellence procedure was completed to document the methodology and process to be utilised on future design validation.



  • We developed a functional excellence procedure for Cummins so they can use this coupled thermal fatigue assessment approach for future design validation.
  • The analysis approach increases the accuracy and confidence of design, therefore, reducing the risk of failure during test or operation.
  • Analysis methodology and model built to carry out design iterations in approximately 20% of the time compared to carrying out physical tests.
  • Our development of analysis methodology and design iterations are more than 85% cheaper compared to carrying out physical multi-axis shaker table tests
After-treatment System Bracket Spectral Stress vs Frequency Results
After-treatment System Equivalent Stress Result
After-treatment System Model
After-treatment System Model Displacement Result

SECTOR

PROJECT ATTRIBUTES

ANSYS Parametric Design Language (APDL)

ANSYS Workbench environment

Thermal-fatigue analysis methodology

Power Spectral Density (random vibration) analysis

Fatigue assessment for random vibration and thermal effects


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Cummins had significant fatigue failures associated with the compact box mounting brackets, believed to be due to a combination of dynamic effects and thermal effects

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