1. Principle of the test

This test includes only one model where one of the non-linear resolutions of test case SSLL105D is used.

When calling STAT_NON_LINE, buckling instability occurs and we will check here that the associated exception is properly caught and that the test finishes properly: the database being properly closed and would therefore be usable further.

This mode of stopping on instability, whether in STAT_NON_LINE or DYNA_NON_LINE, is triggered by declaring in DEFI_LIST_INST an event of type “INSTABILITE” associated with the action “ARRET”. Without this specific argument, the code, in its mode by default, will attempt to continue the calculation even in the presence of instability: the non-linear algorithm then follows a branch of solution.

In practice, we will test the three possible instability criteria, which are defined via the value associated with the keyword SIGNE under CRIT_STAB in STAT_NON_LINE [U4.51.03].

The critical load, during the non-linear calculation, is initially greater than 2 and decreases to become less than 1: we therefore have an instability by positive values.

So if the stopping criterion considers any value calculated between -1 and 1 to be unstable (SIGNE = “POSITIF_NEGATIF”) then the calculation must stop because of the event “INSTABILITE” of DEFI_LIST_INST.

If this criterion considers critical loads between 0 and 1 to be unstable (SIGNE = “POSITIF”), we will also have the same type of stop.

On the other hand, we test that if the stopping criterion is based on the instability interval -1 to 0 (SIGNE = “NEGATIF”), then the non-linear calculation must continue until the end of its list of moments.