Defect Mechanisms in a Noncrystalline Solid

It is proposed that spiral defects originate at torque stress fields in glass and represent variations in localized bond energy. By postulating shear stress couples across flaw lines, extension and annihilation of flaws from neighboring spiral sources were tentatively explained. Distortion or movement within a spiral was indicated on samples subjected to localized stress before etching. Experimentally it was shown that substitution of lead and bismuth for silica in a nonspiral glass produced a rigid, brittle network which ultimately disclosed spirals originating at minute nuclei. Details of structure were quantitatively studied by using the dynamic spherical indenter. Flaw loops were also discovered which originated at random etch pit sources and increased in diameter with applied stress. Rows of etch pits were observed on samples stressed in torque. The conjecture was introduced that the torsion stress caused collapse of flaws into point defect rows. The etch pit rows appeared to be more stable than linear flaws. The minimum length of stability of a void derived from dislocation theory was in agreement with experimental measurements from the point defect rows.