This paper investigates the influence of material non-linearity on load carrying mechanism and strain path in stiffened panel. First, clamped stiffened panel with dimensions of 1.2 x 1.2 m was penetrated with rigid indenter until fracture took place. Second, panel material was characterized with standard tensile tests using flat test coupons extracted from the face sheet of the panel. Failure strain for different element lengths was calibrated using iterative state-of-the-art procedure. Numerical finite element simulations were performed using failure strain calibrated with tensile tests. Comparison of numerical and experimental force-displacement curves of panel clearly shows that this widely used approach is not sufficient for reliable element size independent numerical simulations. The reason is that failure strain scaling depends on the element size as well as stress state. The stress state in the structural component however, can considerably vary from that observed in tensile test. (C) 2017 The Authors.Published by Elsevier B.V.