Feasibillity Study

Feasibility study of atomic/molecular process

associated with precursory fracture phenomena

Yuuji Enomoto

■Object

This feasibility study aims to establish methods of measurements and computer and statistical analyses to understand physiochemical phenomena associated with precursory fracture process of solids including earthquake.Since this is interdisciplinary area,5 groups has joined from 3 AIST laboratories;Mechanical Engineering Laboratory (MEL),Geological Survey of Japan (GSJ),Chugoku National Industrial Research Institute(CNIRI).

■Results in Fiscal Year

1)Modeling of molecular dynamics of fracture process(Tezuka and Hirano Group of MEL)

Using a molecular dynamic computer analysis,the fracture probability per unit time for classical atomic system was characterized in terms of activation energy,rate constant,temperature and number of atoms.The present model can estimate the activation energy and rate constant for the fracture.

2)Characterization of mechanical properties using Lateral force modulation atomic force microscope (Yamanaka and Sato Group of MEL)

Using the lateral force modulation atomic force microscope (LM-AFM),thatwe have developed,the mechanical properties of a Langmuir-Blodgett (LB) film was characterized in water.It was found that,during loading,the friction force was rapidly increased at the load above 14 nN and was reversibly decreased during unloading cycle. This suggests that a tip was penetrated into the LB film and then the penetrated hole was recovered by the LB film during unloading.

3)Fractoemission (Kawaguchi,Takatsubo and Yamamoto Group of CNIRI)

We have investigated excitation and relaxation processes of fracto-luminesence associated with fracture of silica glasses.Spectra of the luminescence showed that its origins are attributed to oxygen deficient centers and oxygen hole centers generated and excited during breaking of Is-O bonds. The rigidity of the network structure affected the fractoluminescence spectra in silica glasses.

4)Investigation of electromagnetic phenomena in precursor period of fracturing solids (Enomoto and Kano Group of MEL)

Thermally stimulated exo-electron emission (TSEE)is detected at temperature above the critical temperature 250-350 degree C during heating of granite at constant rising rate to temperature. We found that the critical temperature for the TSEE decreased drastically under uniaxial compressing of the granite sample.

5)Statistical analysis of seismic phenomena (Nishizawa and Masumoto Group of GSJ)

Time series analysis was made for ground water level changes obtained at Kusanagi and Haibara of Shizuoka prefecture.Effects of atmospheric pressure,earth tide and precipitation on ground water level were eliminated in this analysis.Remarkable coseismic changes of ground water level were observed for two large earthquakes at distant points and one earthquake of magnitude 5.1 occurred at a near by point,26km.

Fig.1 Time-resolved fractoluminescence spectra of silica glass at 1.3×10-5 Pa (Kawaguchi)	Fig.2 Thermally stimulated electrical signal from granite with and without uniaxial compression(Enomoto and Kano)