Evidence of dilatant and non-dilatant damage processes in oolitic iron ore:P-wave velocity and acoustic emission analyses

Abstract

S U M M A R YUniaxial and triaxial compression experiments were performed on oolitic iron ores to investigate damage processes. Most of these experiments included four indirect measurements of damage evolution, that is, P-wave velocity and maximum amplitude received during pulse transmission experiments, elastic properties (apparent Young´s modulus and apparent Poisson´s ratio) and acoustic emission (AE) monitoring. The mechanical behaviour deduced from strain measurements is dilatant for some samples and non-dilatant for the other samples. However, variations in elastic properties indicate damage processes for all samples. AE source mechanism analysis shows two different microscopic damage processes: (1) for dilatant rock, the development of axial extensive microcracks as well as their interaction and coalescence lead to the formation of shear macroscopic discontinuities; (2) for non-dilatant oolitic iron ore, both compressive and shear micromechanisms take place and interact with macroscopic fractures. A particular consistency between the four types of measurements employed was observed.

Strength Failure and Crack Evolution Behavior of Rock Materials Containing Pre-existing Fissures

“…The results reveal clearly the failure processes of rock including initiation, nucleation, and propagation of micro-fractures when the axial stress is close to the peak strength of rock. But up to now, AE technique has been less used to explore the initiation, propagation, and coalescence of brittle rock containing fissures (Jouniaux et al 2001;Wassermann et al 2009;Van De Steen et al 2005;Lei et al 2004). Van De Steen et al (2005) investigated the effect of a tensile stress gradient on fracture initiation and growth in Brazilian disk rock specimen containing a hole by AE technique, which showed that the maximum local tensile stresses the material was able to withstand increase as the stress gradient increases.…”

Strength failure and crack coalescence behavior of brittle sandstone samples containing a single fissure under uniaxial compression

“…The results reveal clearly the failure processes of rock including initiation, nucleation and propagation of micro-fractures when the axial stress is close to the peak strength of rock. But up to now, AE technique was less used to explore the initiation, propagation and coalescence of brittle rock containing fissures (Jouniaux et al 2001;Wassermann et al 2009;Van De Steen et al 2005;Lei et al 2004). Van De Steen et al (2005) investigated the effect of a tensile stress gradient on fracture initiation and growth in Brazilian disc rock sample containing a hole by AE technique, which showed that the maximum local tensile stresses the material was able to withstand increase as the stress gradient increases.…”

Damage and Changes in Mechanical Properties of a Gabbro Thermally Loaded up to 1,000°C

“…Two of these processes are particularly relevant: thermal loading and tectonic stress. Stress damage has been widely investigated during the last decades (FORTIN et al, 2007), including its time dependency (FABRE and PELLET, 2006;WASSERMANN et al, 2009). DAVID et al (1999) summarized some laboratory studies that clearly showed how thermal cracking modifies elastic moduli (BARBISH and GARDNER, 1969;HEARD and PAGE, 1982;NASSERI et al, 2007), permeability (DAROT et al, 1992;MENÉNDEZ et al, 1999), and mechanical strength (HOMAND and TROALEN, 1984;HOMAND and HOUPERT, 1989).…”