Dear Rashi,

Frictional contact is an example of a path dependent nonlinearity.

For example, if a thermal expansion was followed by a bolt pretension to engage the frictional contact surface, that creates a different result than a bolt pretension followed by a thermal expansion.

When a model has only linear effects in the model, the order of application of loads doesn't matter and the result is the same. The order of application of loads over time is considered the "path" to the final load condition.