Matthew Abrams - Glass Research (This Site Under Construction)

Engineered-Stress-Profile (ESP) glass is a modification of conventional chemical tempering procedures. It involves the use of multiple, carefully controlled ion exchange steps to develop specific stress profiles in the final glass. This process induces a compressive stress which rises to a maximum well below the surface. In the current work, as well as prior research by Green, Sglavo, and others, this type of subsurface compressive stress profile has shown a number of beneficial effects in terms of strength, reliability, and flaw-tolerance.

An experimental stress measurement method involving differential optical retardation has been developed and used to measure the stress profile in the glass surface under a variety of ion-exchange conditions. Based on the measured stress profiles, apparent fracture toughness curves were generated and used to predict fracture strength, strength distribution, crack stability, and the potential for multiple surface cracking. In addition, a weight function approach was used to predict stress intensity factors as a function of crack geometry, and thus determine crack propagation paths for a given residual stress profile and applied stress. Predicted values were compared to experimental observations of crack growth and fracture behavior, and with measured fracture strength distributions.

Ion Exchange Process

Resulting Compressive Stress Profile