ORAL REFERENCE: ICF100914OR HIGH TEMPERATURE CREEP DAMAGE OF FABRICATED STRUCTURES Frederick W. Brust Engineering Mechanics Group, Battelle Memorial Institute, 505 King Ave, Columbus, Ohio 43201 ABSTRACT The need for structural systems to perform reliably at high temperatures continues to increase. Improvements in energy production, pollution control, chemical processes (especially, engine propulsion), efficient micro-process devices, among other applications, are possible with higher temperature operations. Higher temperature operation means that creep damage must be managed over the life of the component. One of the important mechanisms of creep damage development, matter diffusion, is investigated here. In particular, the effect of elastic accommodation on the grain boundary diffusion-controlled void growth is analyzed using an axisymmetric unit cell model. An incremental form of the virtual work principle was used to formulate the boundary value problem involving grain boundary diffusion. The model accounts for material elasticity and void interaction effects. Analyses are performed for initially spherical voids spaced periodically along the grain boundary. The results of the analyses on void growth rates agree well with the Hull-Rimmer [1] model after the initial transient time. During the elastic transient, void growth rates can be several orders of magnitude higher than the steady state growth rate. Though the elastic transient time may occupy a small portion of the total rupture time, in metallic components experiencing cyclic loading conditions with short hold times, elasticity effects may be important. KEYWORDS Creep, damage, diffusion, fracture, high temperature, steel. INTRODUCTION Failure in metals exposed to high temperature creep conditions predominantly occurs by nucleation and growth of cavities along grain boundaries, thus resulting in intergranular fracture. Nucleation of such cavities is mainly driven by diffusion of atomic flux from the lattice or interfaces into grain boundaries. Further growth of these cavities is aided by diffusion of atomic flux primarily from cavity surface into grain boundaries. The nucleation of these intergranular cavities in many instances occurs during the primary creep stage. In addition to diffusion mechanisms, the creep deformation of the material also contributes to cavity growth. The purpose of this paper is to quantitatively examine the effect of elastic transient on growth of spherical cavities. The growth of the cavities was controlled by grain boundary diffusion as well as material elasticity.
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