Appropriate design loads
It is important to choose an appropriate design load so that the maximum amount of load that a vehicle has been designed to carry can be calculated. A good design load should be quick to evaluate so that the process of evaluation can be optimized. It should be easy to understand so that finding a remedy in case of issues related to withstanding a design load is easy. It should be appropriate so that the structure can be designed to withstand the design load and customer use.
For Fatigue Design there are no accepted standards for commercial vehicles. So each EOM has unique methods to find the design load. It could be a quasi-static design load, a distributed body force, a random load or transient.
Our main aim for our vehicles is finding the appropriate design load appropriate design load. How do we know if what we apply to our components is appropriate or not?
There are three ways of generating Fatigue Design loads.
1. Measure loads on existing products
2. Simulate vehicles on the test track in the design phase
3. Use simulations to derive development loads
Let us look at the Static Inverse Force Method. What we see in the first figure is a fuel tank bracket that is used to attach a fuel tank. In the old days, a pulley was used to apply a known force on the bracket at a known point and at the same time measure the strain. We then get to know the correlation between the strain and the applied force. Inversely, if we know the strain, we also know the force.
Now we use the simulation model where we measure the strain in the model and we calibrate our sensors in the model. This really has empowered us to apply very different loads. We can easily use distributed loads or a combination of loads difficult to simulate in a laboratory with a pulley. So this is what the process looks like today.