Why the Need to Extract the Gasket L-D Curve?
It is widely accepted that an accurate representation of the load versus displacement characteristics of the head gasket is of fundamental importance in attaining high-quality FEA predictions of displacements and stresses in cylinder head and cylinder block structures.
These characteristics are usually supplied by the gasket manufacturer based on their measurements (i.e. FUJI film).
Unfortunately, this data is expensive and time consuming to produce relying as it does on the limited availability of specialized high-precision machines.
Further, during the early design phase of a powertrain project a physical gasket may not even be available for testing.
As a result the information required for the FEA simulation is often not available.
Solution: Finite Element Simulation of the Gasket
As a consequence of the frequent lack of availability of measured data Caepro has developed an FEA simulation method for deriving the load versus displacement characteristics of various types of gasket.
Caepro’s methodology of L-D curve generation has been validated by correlating it with test results with an accuracy greater than 90%.
The methodology allows bead parameters such as height, width and material properties to be optimized based on its application. This can result in a significant reduction in gasket development time.
Caepro has extensive experience using this method for across many of the common types of head gaskets and recently applied it to a rather unusual combustion chamber gas seal based on a soft copper sheet and a stainless-steel wire O-ring with excellent results.
This example is used in the methodology description below.
Caepro Methodology
Step 1: Problem Definition
The individual gasket bead or wire O-ring can be represented as a 2D axisymmetric problem. The gasket and wire O-ring section and adjacent components such as cylinder head, block, liner etc. are considered for the simulation.
Step 2: Finite Element Mesh
All the components are represented using 2D axisymmetric, quadrilateral and triangular elements and fine element discretization is used to capture the behaviour accurately.
Node-to-node matching is used wherever possible, with rigid elements used to facilitate loads and boundary condition application.
Step 3: Model Setup
The nonlinear behaviour of the soft copper gasket is captured using the gasket material’s stress-strain curve.
Also, the geometric nonlinearity is taken into consideration. Interactions between various components are simulated using contact elements.
Frictional behaviour with finite sliding, surface-to-surface contact formulation is used.
If not done so already the model is orientated axisymmetrically.
Step 4: Loads and Boundary Conditions
Displacement controlled boundary conditions are used to start the gasket bead activation.
Step 5: Analysis
Static nonlinear axisymmetric analysis is performed using Abaqus solver.
Step 6: Outputs/Post-processing
Reactions are extracted to establish the loading behaviour in terms of Line Pressure versus Compression.
Similarly, unloading behaviour is also captured at 3 points on the loading curve by removing the applied loads.
This allows a derivation of the L-D curve for the gasket:
Conclusion
Using FEA to simulate the gasket is an effective way of deriving the L-D curve required for accurate powertrain thermal-structural analysis.
In addition, it can be used to optimise the bead characteristics of the gasket reducing development time and cost.
Caepro has extensive experience using this method for across many of the common types of head gaskets and recently applied it to a rather unusual combustion chamber gas seal based on a soft copper sheet and a stainless-steel wire O-ring with excellent results.
Here to Help You
If you would like to know more about Caepro’s approach to gasket simulation, powertrain thermo-structural analysis or any of our other design and simulation approach or capabilities, we’re here to help you.
Just call us on 01865 809 445 or send us an email and we’ll be happy to answer any questions you may have, or to discuss how we can help with your current project.
