Study, Evaluate, Measure, and Calculate the Thermal Cracking of Rocks.
Abstract
Changes of longitudinal-wave velocity (VL), porosity, and Q, together with optical and scanning electron microscopic observations, demonstrate unequivocally that appreciable thermal cracking occurs during slow thermal cycling of Sioux Quartzite. Thermally-induced cracks develop primarily along grain boundaries and secondarily as intragranular cracks. Intragranular cracks are preferentially oriented and appear to be influenced by the preheating residual strain state locked-in the rock. Acoustic emission reveals that thermal cracking occurs only upon exceeding a threshold temperature, which for the Sioux Quartzite ranges between 200 C and 250 C. Thermal cracking increases progressively with increasing temperature, with the largest fraction of cracking occurring prior to the alpha-beta transition of quartz (573 C). In the temperature interval 200-573 C, VL decreased 40% and porosity increases 130%; new porosity is associated with low aspect-ratio cracks. Fracture intensifies during the alpha-beta transition as reflected by an abrupt decrease in Vl, a rapid porosity increase and intense acoustic emission. Above 573 C, thermal cracking continues but at a reduced rate. Porosity continues to increase but is associated primarily with high aspect-ratio cracks. Cooling induces little additional structural damage.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 01, 1977
- Accession Number
- ADA044238
Entities
People
- C. Branning Johnson
- John Handin
- Melvin Friedman
Organizations
- Texas A&M University