advances in mechanical engineering research volume 2 pdf
At National Institute for Materials Science Japan long time creep rupture data including
longer than 100,000h have been obtained on several heats of principal heat resistant materials.
The long time creep rupture life and ductility show a considerable amount of scattering
among several heats of a same kind of steels, and it was thought that the scattering might
include new effects of microelements on long time creep rupture properties, since the
scattering is difficult to explain by using well-known effects.
Experimental results showed
that main cause of the scattering is difference in microelements. It was indicated that very
small amount of Mo and N in solid solution causes the scattering for carbon steels, and also
trace of Al content in austenitic stainless steels causes long time creep rupture strength drop.
Mo and soluble N atoms in the steels diffuse to dislocations, and the segregated pairs of the
elements immobilizes dislocations. The Al in 12Cr and austenitic stainless steels precipitates
as AlN at grain boundaries and accelerates nucleation and growth of creep cavities.
It is found that very small amount of B and N in austenitic stainless steels diffuse to creep cavity surface and cover creep cavity surface by segregation of B or precipitation of BN when S is removed almost completely. The segregated B and precipitated BN decrease surface diffusion rate of creep cavity and also creep cavity growth rateremarkably. The B segregates and also BN precipitates to creep cavity surface autonomously during creep exposure and provide the steels with self-healing function for the creep damage. The self-healing of creep cavity by B segregation and BN precipitation is a new and promising research area for improving creep rupture properties.
Chapter 5 – The mitigation of seismic damage to masonry housing structures is considered in this study. Traditional high-damping rubber bearings (HDRBs), two hybrid systems involving the use of HDRBs and shape memory alloy (SMA) wire, and fiberreinforced bearings (FRBs) are numerically modeled as base isolators for a typical confined masonry, two-family house. The house is elastically modeled using multiple degrees-offreedom (MDOF) that are based on experimental data collected through ambient vibration testing. Fuzzy logic is utilized to numerically model dynamic behavior of the HDRBs, SMA wire, and FRBs based on experimental and analytical data.
The earthquake used for optimization of each isolation system is generated to match the design spectrum based on Chilean code through means of RSPMatch2005, an algorithm thatmodifies historic ground motions in the time domain through incorporation of wavelets. A suite of ground motions is used to evaluate seismic performance of the structure that is augmented with each of the isolation systems mentioned; results are compared to the performance of the traditionallyconstructed structure. Simulations indicate that each of the isolation systems can be effective in reducing the structural shear, interstory drift, and floor acceleration of the structure compared to the fixed-base case, although the HDRB-only system exhibits superior performance overall.