Null stress planes graphs through numerical simulations of a beam subjected to variable bending stress

In engineering, how solid materials behave to environment and external forces (such as tensile and compressive forces, torsion, bending and shear) must be known. The threats to structural elements can be categorized in time factor and failure models, such as: Time-dependent, time-independent, stable over time. Time-dependent threats (Stress Corrosion Cracking (SCC), corrosion and plastic deformation) and timeindependent threats (natural forces, damage caused by third parties, improper operations) are random events and their appearance is generally not predictable. Stable over time threats, such as both construction and manufacturing defects are possibly considered as time-dependent due to its potential growth generated by load cycles. However, potential failure of any defect can be increased by the effects of fatigue induced by load cycles. This paper shows how the magnesium alloy ZC71 reinforced with silicon carbide (SiC), when subjected to cyclic loading, can have two or three null stress zones which can lead to variations in the equilibrium equations of the Strength of Materials. Different tension and compression behaviors can accentuate the appearance of these areas in such a way that they are not necessarily symmetrical to a neutral axis, in the case of bending, which can result in not as predictable fracture behavior over time. Numerical simulations have been made of a homogeneous beam of rectangular section where alternating loads which are capable of plasticize the material have been applied. The material has different behavior in both tension and compression as it plasticizes in some compressive load magnitudes or in tensile and compressive load magnitudes. Numerical simulations of a homogeneous material with the same behavior in both tension and compression are also performed. In every case null stress graphs in the cross section of the beam are created. In these graphs, variations of the neutral axis can be seen once the beam has plasticized and loading and unloading of loads are being made.