How do I lock a spring element?

Enrico_21967

Hi,

I have a model with a dummy positioned on a seat. I need the belt to be snug to the dummy and also lock in the event of a front impact. To do so I connected the belt to the seat frame with a spring2 element to which I associated the property /PROP/TYPE32 (SPR_PRE). Inside the property Ilock=1 was set, as well the slide length D1, as sensor a nodal distance sensor was used between the two nodes of the spring2 element. The slide length D1 is smaller than the actual distance the spring shortens during the first part of the analysis (the first fase while, due to gravity, the dummy lowers itself on the seat, deforming it) so I would expect the spring to lock when it shortens by D1 and never extend afterward. Sadly, during the second part of the analysis (a front impact) that doesn't happen and the spring2 elongates.

Does any of you know why is that? Am I using the wrong property? Every help is much appreciated

PaulAltair

/SPR_PRE should work for your application, provided you use the correct combination of options

From your description, I have some questions:

How are you defining the preload in the spring? Using Fct ID 1 or Fct ID 2?

What is the purpose of the sensor? normally you would use the sensor to delay the onset of the loading beyond the start of the run, but it sounds like that may not be required here (having no sensor is ok, it isn't mandatory), when you say it shortens by more than D1 in the 1st phase, it makes me think it is never activated?

What is your Stif0 set as?, even after locking, the spring acts as a spring, with stiffness = Stif0, so even if everything is working 'correctly' you may still see elongation of the spring if it is loaded within that stiffness definition.

If you can share your model (or even just the spring property and associated function) I can maybe comment further?