DIRECT MEASUREMENT OF MICROSCOPIC STRAIN DISTRIBUTION NEAR A CRACK-TIP

A dot map method was used for direct measurement of the microscopic st rain field near a crack tip in a rubber-toughened epoxy, Results indic ate that very large viscoelastic strains (37 percent) are present at t he crack tip, though elongation in a tensile test is only 5.1 percent, Most of the strain is recovered immediately on unloading, and all of the remaining strain is recovered after annealing above the glass tran sition temperature.