Influence of the geometric shape of the nickel-sulfide inclusion on the stress-strain state caused by phase transformation

Abstract

The presence of nickel sulphide inclusions in tempered glass is a serious problem related to the reliability of products, due to the tendency in this case to spontaneous breakage. Despite taken activities, the prevention of such type of defects in the flat glass production process is impossible for now. One characteristic of these impurities, which usually have a spherical or slightly elliptical shape, is that they can change their phase state during operation. As a consequence of this change, they undergo a significant increase in volume. The resulting tension stresses are sufficient to generate micro cracks and breakage of the glass. This work presents a study of the stress-strain state around a nickel sulfide inclusion with a geometric inhomogeneity. The stress state and probability of crack formation were investigated using a computer simulation by temperature-deformation analogy. The conditions of crack propagation are evaluated by stress intensity. The change in volume during allotropic transformation was modeled using different coefficients of temperature expansion for the alpha and beta phases.