In cemented total hip prostheses, the role of creep of the occurred with all three bonding conditions, allowing addiacrylic cement (polymethyl methacrylate, [PMMA]) in intional subsidence of the stem and a decrease in the stress creasing or decreasing the chance of failure of the cement components within the cement. During the unloaded period mantle is a subject of ongoing controversy. In the present the full recovery of the preload conditions could be reached study we used a three-dimensional finite-element model of with the completely bonded and with the frictionless intera cemented stem to assess the influence of cement creep on faces. With the frictional interface there was residual cement subsidence of the stem, and on the stress and strain in the creep, residual stresses within the cement, and residual subsicement under cyclic load, both in the short and long term.dence of the stem during the unloaded period; however, the The cement layer was assigned the shear and bulk creep reduction of the stress was at most 13% and the subsidence moduli of Zimmer regular PMMA cement, which were obwas about 0.46 mm. The much larger subsidence of debonded tained experimentally. The stem-cement interface was stems that is often observed clinically might be attributed to modeled either as (1) completely MATERIALS AND METHODS INTRODUCTIONTo represent a total hip prosthesis, a three-dimensional, finite-element model (Fig. 1) was generated usIt has long been recognized that polymethyl methacing the PATRAN Plus modeling software (PDA Engirylate (PMMA) surgical cement undergoes both elastic neering, Costa Mesa, CA; version 2.5), and analyzed and viscoelastic (creep) deformation under load, as, for using the ABAQUS program (Hibbitt, Karlsson & example, in bench tests of unconstrained specimens. 1,2Sorenson, Inc., Pawtucket, RI; version 4.9). The stem Nevertheless, the clinical significance of this property was represented by 594 eight-node brick elements and has been a subject of controversy. For example, Harris 66 six-node wedge elements; the cement, by 432 eightand colleagues 3 have stated that creep of the cement node brick elements; and the cortical bone, by 608 mantle surrounding a hip prosthesis may be negligible eight-node brick elements. Thus, the model contained under cyclic physiological loading. At the other exa total of 1700 first-order interpolation isoparametric treme, Ling and colleagues 4,5 have concluded, at least solid elements. for smooth tapered stems, that substantial hoop andThe stem-cement interface was modeled either: radial creep of the cement not only occurs, but is essen-(1) completely bonded, (2) debonded, with a metaltial for the optimum clinical performance of the proscement frictional coefficient of 0.22, 6 or (3) debonded thesis. In the present study we used a nonlinear finiteand frictionless. The debonded interfaces were modelement model and cyclic loading to assess both the eled using 243 slide-line interface elements. These are a short-and long-term contribution of cement creep to type of Coulo...

The recent argument about nucleation phase of earthquakes reminds us to completely study the concept of earthquake nucleation. The original meaning of nucleation includes concentration, nucleation and initiation of the eruptive processes. Thus, it is needed to discuss how to exactly translate the word "nucleation" into Chinese in different fields. The basic concept of earthquake nucleation refers to microcrack concentration in rock. It causes local weakening and instability of the rock. The narrow sense of nucleation theory of friction constitutive is significant in friction of fault surfaces, but should not abuse everywhere unconditionally. In terms of thermodynamics, nucleation actually means the variety processes of multiple state parameters of rock. The nucleation is a project that covers multiple courses. In this paper, the studies of damage theory, fracture, earthquake rupture dynamics and constitutive of friction and their implication to earthquake nucleation are remarked. The recently developments are introduced, including the influence of tectonic on the earthquake nucleation process, the method of measuring medium anisotropy, especially shear wave splitting led by concentration and orientation ofmicrocracks, and the experimental study of remote sensing of infrared and microwave radiation related to the nucleation, etc. This paper also discusses the characteristic of large earthquake nucleation, and the implication of above studies to precursors of strong earthquakes.

1'4)(~) TENG Chun-kai 2~0]~) LU Zhen-ye 3~ (ff~) LIU Xiao-hong lm (~0J I~y_) LIU Qi-liang ~'4) (~lJ ~) HE Xue-song ]'4) (~ -~(~) AbstractThe evolution and nucleation of microcracks in typical tectonics are investigated in the experiment of fracture of marble specimen. The change of state during nucleation of microcracks is observed. The controlling effect of tectonics on evolution of microcracks is analyzed by using the damage mechanics theol')'. These characteristics can be analogized to kilometer meters as the first effect of earthquake precursors. These studies may be helpful to interpret.the foreshock or general foreshock in the moderate or short stage before strong earthquakes. The other physical precursors are second or third effect. The local density of microcracks increasing abruptly may be helpful to interpret the phenomenon that part precursor records appear catastrophic jump. The part out of nucleation where some microcracks heal and the density change reversibly may be helpful to interpret the phenomenon that some precursors records appear reverse change. The area difference of microcracks accumulation and evolution in different part of typical tectonics is studied. This difference may be helpful to interpret the characteristics (including the area) of earthquake preparation of different tectonics, and further to interpret the difference of the precursors between plate edge and intraplate. These differences may be introduced by the scholars with different points of view as to discuss about the existence of precursors before earthquakes. However, when the precursor records are studied, one must notice the geology background in different areas. key words: earthquake source physics; experiment; damage theory; nucleation of microcracks; earthquake precursors CLC number: P315,8 Document code: A "