Design of welds under dynamic (shock) loads

[FEAnalyst]

TL;DR Summary

How can we account for dynamic (shock) loads when designing welded connections ?

Hi,

in the books about the design of welded connection, we can find detailed description of calculations for static and fatigue loads. But what about the other type of dynamic behavior - shock ? As an example consider welded parts of the tow hitch used to free vehicles stuck in mud. Of course, numerical analyses can include such dynamic effects but is it possible to account for them in analytical calculations ? If yes then how to do it or where can I find some examples ?

Thanks in advance for your help

 

[Baluncore]

The members being welded together also need to withstand the shock load.
I would expect the weld to have the same or greater strength than the members being joined, so there should not be a problem.

 

[FEAnalyst]

That seems legit but is it possible to account for these shock loads when designing welds and members ? Other than numerical analyses, of course.

 

[Baluncore]

You can think of welds as being physical impedance matching between members. Incident energy must enter one member, then flow through welds into another member, and so be directed to flow to some compliant termination or restraint. Follow the energy flow through the weldment making sure that the impedance is matched. Any point of mismatch at a weld will magnify the strain difference and so magnify the stress at that mismatch.

If the weld is too heavy, or is poorly oriented, it will focus energy onto the HAZ of the members. It is possible to design welds that are stronger than the members because the weld can be distributed over a greater contact area than the section of the members, and the weld metal can be composed of higher tensile material than the parent metal being welded.

Impact or shock loads should not be reflected in phase from a line across a member. Avoid resonant sections. Avoid butt joints, instead use longer tapered scarf joints, so energy flows between members over a greater sectional area, so shock loads are rapidly diffused. Think of a scarf as a tapered transformer that does not reduce the available section of the members.

Preheat the material before welding. Then allow it to cool slowly and evenly to reduce accumulated stress.