No abstract

No abstract

No abstract

One-dimensional shock loading, attenuation, and recompression data from gas-gun experiments on mechanical mixtures of alumina powder and epoxy were used to develop model parameters for stress-wave propagation. Specimens with 0.42, 0.34, and 0.20 volume fractions of alumina were investigated. Calculations simulating the experiments were performed using an extension of a Maxwell rate-dependent model which requires definitions of the instantaneous, equilibrium, and relaxation functions as input. Experimental observations indicated the shock-loading behavior is identifiable with the equilibrium response, and the release wave behavior is closely related to the instantaneous response. To model these effects, for negative strain rates, indicative of expansion, a relaxation time of 0.25 μs was used; this value gave agreement between the calculated and measured release wave behavior. For positive strain rates, indicative of compression, the relaxation time was permitted to decrease to 0.03 μs, which caused the shock-loading response to be dominated by the equilibrium function. Hugoniot data determined from the stress-wave profiles were compared to effective modulus calculations. This comparison suggests a strength effect which can be interpreted as an interaction between the components. Analysis using a self-consistent scheme for spherical particles shows good correlation between calculated and measured ultrasonic and Hugoniot intercept wave velocities.

While numercus constitutive models have fceer. propose: for the lur*-cr.n' j-^',-.,;creep of salt, this work is the first to develop such a model v.'ir.hir. the-f•-••r-c- .- .-v>. of rate controlling mechanisms and the reformation-mechanism map. L'r.e cf t.hi.frejr.ework permittei unfolding of the rather ccxplicatej low temperature SW, ly-cta:.' creep bel-.nvior ir.t-i liter Siguier responses involving separate refiner •.. i',1: i;. : Lvi : > controlling mechanisms. The observed total creep rate obeys the rul-?. of a;::itivc processes. The creep model incorporates primary (trans i^ni,) creep t=s P. SLT.TO t7>\porameter modification to the steaey-s^a-e creep equation?. Application of the n-.oriel is through a formulation into proper stress an: strtin neasiirps f^r ui:e ir. u Ian?-strain finite element cede. Intensive analysis of available lev; ••.•:- .-:;rerr:f:i-.' ^riaxial creep data produced the appropriate material parameters, including p.^t-ivsti energies and stress dependencies for the separate refines. Material varir-.hions ::rv observed to produce changes in absolute creep rate, without change in controllinrmechanism. Numerous calculations demonstrate the adequacy of the ma:el nr.-i numeric?! nethod to simulate the results of triaxial creep experiments on Souths a st-m llev Mexico salt from the horizons proposed for the Waste-Isolati";-Pilot riant (.V.'TPP). ntSTR' Brrrww nr ™s nnawwt is WAITED

Three Epon 828 epoxy systems which had significant variation in glass transition temperatures were tested dynamically in plate impact experiments to obtain their pressure-volume response. The choice of hardener determines the transition temperature of the system through the degree of crosslinking and structural changes. For this study, the hardeners used were metaphenylenediamine, Z and D. The dynamic ``equilibrium'' compression curves for the three systems are identical within experimental uncertainty and are adequately represented by the Z system shock-velocity-particle-velocity results of U=2.64+1.66u(mm/μsec); ρ0=1.194 g/cm3. The dynamic results may be reduced to isothermal conditions through the use of the Gruneisen equation and appropriate thermodynamic quantities. These dynamic isotherms are compared to static compressibilities obtained by other investigations using piston apparatus. While the static results show marked variation of compressibility with processing conditions, this was not confirmed by the dynamic results. Possible reasons for this discrepancy are advanced.

No abstract

Creep damage in rock salt, which generally manifests in the form of microcracks, can be recovered or healed when subjected to sufficiently high pressures and temperatures. In this paper, the phenomena of damage recovery and healing in rock salt are treated using the continuum damage mechanics approach. A healing term is formulated and incorporated into an existing constitutive model for describing coupled creep, fracture, and healing in rock salt. The constitutive model is then evaluated against experimental data of rock salt from the Waste Isolation Pilot Plant (WIPP) site. Satisfactory results are obtained between model calculations and experimental measurements of axial, lateral, and volumetric strains, as well as acoustic wave velocity and attenuation recovered during damage healing. Furthermore, analyses of experimental data revealed that healing anisotropies exist in WIPP salt. Most, though not all, of the healing anisotropies can be modeled with an appropriate power-conjugate equivalent stress, kinetic equation, and evolution equation for damage healing based on a scalar damage variable. This work represents the first attempt to simulate healing of damaged intact WIPP salt; however, further evaluations and improvement of the model can be anticipated.