Two of the main tests required by most vibration test specifications to confirm product qualification, durability, and reliability are the half-sine shock and the sine sweep test.
A shock test is a short duration and non-periodic acceleration impulse defined by a certain shape, duration and amplitude, used to test a system’s capability to survive transient vibrations. These pulses do not necessarily represent real field environments, but they are still used throughout industry to test equipment robustness for convenience.
A simple but useful card to create these types of time-dependent dynamic loads is TLOAD2.
The excitation generated by TLOAD2 follows the following formula:
Which is represented in OptiStruct by the following fields:
Where,
f(t) - Time-dependent dynamic load.
A - Amplitude of the dynamic excitation referenced by the EXCITEID field.
τ -Time delay defined in the DELAY field.
T1 and T2 - Time constants defined in the T1 and T2 fields.
f – Frequency in cycles per unit time defined in F field.
φ – Phase angle in degrees defined in P field.
C - Exponential coefficient defined in C field.
B - Growth coefficient defined in B field.
Below you can find a few examples of loading curves created by TLOAD2. Attached to this article, there is a simple model with all the loads as well.
A 20ms half-sine is equivalent to a 40ms full sine, thus:
F = 1/0.04s = 25 Hz
The OptiStruct definition will be:
TLOAD2 | SID 11 | EXCITEID | DELAY | TYPE | T1 | T2 | F | P |
TLOAD2 | SID 12 | EXCITEID | DELAY | TYPE | T1 | T2 | F | P |
or
TLOAD2 | SID 12 | EXCITEID | DELAY | TYPE | T1 | T2 | F | P |
TLOAD2 | SID 13 | EXCITEID | DELAY | TYPE | T1 | T2 | F | P |
TLOAD2 | SID 14 | EXCITEID | DELAY | TYPE | T1 | T2 | F | P |
TLOAD2 in OptiStruct Documentation
Response Spectrum Analysis Overview