Residual Stresses In Glass Research Articles

HYBRID MECHANICS FOR AXISYMMETRIC THERMOELASTICITY PROBLEMS

The present article extends the integrated photoelasticity technique for the case where stresses are due to an unknown axisymmetric temperature field. Relationships that express radial and circumferential stresses through the axial and shear stresses are derived. Since residual stresses in glass can be described by the equations of thermoelasticity, the results of this article offer a means for complete determination of the residual stresses in axisymmetric glass articles using integrated photoelasticity. The results are verified by numerical and physical experiments.

Determination of the residual stresses in the welded joints of glass structures

We propose a computational model for determining the residual stresses in a welded glass structure taking account of the properties of the formation of residual stresses in glass. The problem is solved in displacements using Galerkin's method in conjunction with a finite-element model. A numerical solution is obtained for the axisymmetric case.

Use of Crack Branching Data for Measuring Near‐Surface Residual Stresses in Tempered Glass

An analytical procedure based on fracture mechanics is used to obtain the amount of residual stress in glass from measurements on the fracture surface. The technique utilizes the measurement of microcrack branching distances, known as the mirror — mist boundary, which occur at a critical crack branching stress intensity (Km) value. This procedurre shows that σArm1/2YF(θ) =σRr1/2m+Ψ0, where σA is the applied stress, rm is the microcrack branching radius, σR is the residual stress, YF (θ) is the crack‐border correction factor, and Ψ0 is a material constant based on Km. Thus, the equation is that of a straight line with the slope equal to the magnitude of the residual stress. Data for tempered glass from the literature are used to demonstrate the applicability of the technique.

Determination of residual stresses in glass and glass crystal materials

Determination of residual stresses in glass and glass crystal materials

On the studies of residual stresses in glass plates

The theoretical foundation of the photoelastic methods being presently used for measuring and analyzing residual stresses in glass is insufficient for studying development of transient viscoelastic stress states in glass plates during tempering process and for an explanation of the actual material behavior. It is shown that the basic knowledge of photoviscoelastic effect in glass over a wide range of electromagnetic radiation and temperature is necessary for such on analysis. Some photoelastic properties of plate glass are presented.

Stress and Volume Relaxation in Annealing Flat Glass

Laboratory simulation of the industrial process of annealing sheet glass has yielded data on the genesis of stresses in initially stress‐free glass. The experimental results differed from expectations based on classical annealing theory in that stresses began to develop in the annealing range even when the glass was being cooled at a constant rate, i.e. even in the absence of any changes of temperature gradients within the glass. Typically, these stresses account for 40% of the total residual stress in glass annealed according to a linear schedule. The remaining 60% are the well‐known thermoelastic stresses that arise later in the annealing process from the decay of temperature gradients in the glass. The stresses observed to arise in glass as it is being cooled at a constant rate are attributed to volume relaxation effects which, in parts of the annealing range, generate stresses rapidly enough that they are not dissipated by stress relaxation. A mathematical model of annealing is proposed that takes account of both stress and structural relaxation. The model fits the experimentally observed evolution of stresses during linear cooling. It also suggests that (with the activation energies of stress and structural relaxation about the same) the actual rate, at any given temperature, of structural relaxation is about 4 times lower than that of stress relaxation.

Calculation of Residual Stresses in Glass

Lee, Rogers, and Woo presented a theory for calculating the stresses produced in glass by tempering. Unlike earlier treatments, theirs takes account of the viscoelastic properties of glass. The purpose of this paper is to evaluate this theory by comparison with experimental data. Discrepancies were found to exist between calculated and observed stress distributions. For cases in which glass is quenched from initial temperatures well above the strain point, these discrepancies result from the numerical formulation of the theory, not from any shortcomings of the theory itself. A modification of this formulation brought calculated and observed stresses into good agreement. For quenching from lower initial temperatures, the present theory could not be brought into agreement with experimental data. The reasons for this are briefly considered in the context of the structural heterogeneity of tempered glass and its possible effects on residual stresses.