The temperature variation of hardness of olivine and its implication for polycrystalline yield stress

Abstract

The variation of hardness with temperature was measured for olivine on a number of crystal faces by the Vickers diamond pyramid technique (up to 800øC) and by a mutual indentation technique (for temperatures up to 1500øC). A comparative review of hardness data and compressive creep measurements obtained under large confining pressures confirms the hypothesis of Rice [1971] that single-crystal hardness measurements, corrected for elastic effects, can be correlated to the fully ductile yielding of a polycrystal by intragranular dislocation mechanisms, including dislocation climb and glide. The computed differential yield stresses, o (in gigapascals), which empirically correspond to a bility problems attendant with high temperatures • = • [1 + in (• tan •)] (4) tion scheme designed to reduce chemical incompati-• is the angle between the surface of the cone and the test surface. As the parameter E/o in-Hardness of Olivine becomes much smaller than the strain accommodated by ductile flow; in the limit of vanishingly small elastic strain the constraint factor

Strength and water weakening of mantle minerals, olivine, wadsleyite and ringwoodite

“…This would suggest that water would play a major role in the hightemperature, low-stress regime characterized by power-law creep. In our study, we see significant effects in the lowtemperature, high-stress regime, where flow is probably dominated by dislocation glide (Evans and Goetze, 1979). While the detailed microstructural processes are poorly defined, it is clear that water affects these processes.…”

Stress evolution and associated microstructure during transient creep of olivine at 1000–1200 °C

“…The stress surpasses steady state estimations from the single crystal flow laws from Evans & Götze (1979) and Demouchy et al (2013), but is in good agreement with the flow law based only on [001](100) glide from deformation experiments in shear from Tielke et al (2016), as seen in Figure 12. The higher strength of our samples can at least partly be attributed to the lack of sufficient independent slip systems in polycrystalline olivine samples (the so called olivine paradox) and the difference between single crystal and polycrystal rheology (e.g., Evans and Goetze, 1979, their Fig 14). The deformation curves of samples CMT16-13 and CMT16-9 obtained at 1200 °C (Figure 12b) show a quasi-steady-state mechanical behavior.…”

Quartz Rheology and Short-time-scale Crustal Instabilities

“…If the hardness and the elastic modulus are known at a given temperature the constraint factor C and the yield stress can be computed (EVANS and GOETZE, 1979;JOHNSON, 1970). The hardness data for quartz suggest that at temperatures below 600°C, the ratio of Young's modulus to the yield is very low, probably less than 25.…”

“…We have attempted to derive the Peierls stress flow law from the quartz indentation data (EVANS, 1984) using the same approach as proposed for the olivine case (EVANS and GOETZE, 1979). We find that we cannot use the elastic contact formulae because of the polymer-like behavior of quartz.…”

“…Indentation experiments on olivine (EVANS and GOETZE, 1979) and quartz (EVANS, 1984) suggest that quartz yields when it has stored a substantial amount of elastic energy. It is thus best compared to a polymer.…”