Determination of Uniaxial Residual Stress and Mechanical Properties by Instrumented Indentation

We propose an improved technique to determine the uniaxial residual stress, elastic modulus, and yield stress of a linear elastic, perfectly plastic bulk material from the force–displacement curve of one conical indentation test. Explicit relationships between the indentation loading–unloading parameters, material properties, and residual stress are established through extensive finite element analyses. Good agreement is found between the input material parameters used in numerical indentation tests and the properties identified from the reverse analysis, with an error of less than 10% in most cases. The technique is applied to a nanoindentation experiment on the crosssection of a thermal barrier system, to measure the elastic–plastic behavior and the residual stress in the bond coat. Likewise, the improved method may be used to measure effectively the material properties and uniaxial residual stress of a multilayer system

Determination of Uniaxial Residual Stress and Mechanical Properties by Instrumented Indentation

We propose an improved technique to determine the uniaxial residual stress, elastic modulus, and yield stress of a linear elastic, perfectly plastic bulk material from the force–displacement curve of one conical indentation test. Explicit relationships between the indentation loading–unloading parameters, material properties, and residual stress are established through extensive finite element analyses. Good agreement is found between the input material parameters used in numerical indentation tests and the properties identified from the reverse analysis, with an error of less than 10% in most cases. The technique is applied to a nanoindentation experiment on the crosssection of a thermal barrier system, to measure the elastic–plastic behavior and the residual stress in the bond coat. Likewise, the improved method may be used to measure effectively the material properties and uniaxial residual stress of a multilayer system

Dominance of HIV-1 Subtype CRF01_AE in Sexually Acquired Cases Leads to a New Epidemic in Yunnan Province of China

BACKGROUND: Dating back to the first epidemic among injection drug users in 1989, the Yunnan province has had the highest number of human immunodeficiency virus type 1 (HIV-1) infections in China. However, the molecular epidemiology of HIV-1 in Yunnan has not been fully characterized. METHODS AND FINDINGS: Using immunoassays, we identified 103,015 accumulated cases of HIV-1 infections in Yunnan between 1989 and 2004. We studied 321 patients representing Yunnan's 16 prefectures from four risk groups, 11 ethnic populations, and ten occupations. We identified three major circulating subtypes: C/CRF07_BC/CRF08_BC (53%), CRF01_AE (40.5%), and B (6.5%) by analyzing the sequence of p17, which is part of the gag gene. For patients with known risk factors, 90.9% of injection drug users had C/CRF07_BC/CRF08_BC viruses, whereas 85.4% of CRF01_AE infections were acquired through sexual transmission. No distinct segregation of CRF01_AE viruses was found among the Dai ethnic group. Geographically, C/CRF07_BC/CRF08_BC was found throughout the province, while CRF01_AE was largely confined to the prefectures bordering Myanmar. Furthermore, C/CRF07_BC/CRF08_BC viruses were found to consist of a group of viruses, including C, CRF08_BC, CRF07_BC, and new BC recombinants, based on the characterization of their reverse transcriptase genes. CONCLUSIONS: This is the first report of a province-wide HIV-1 molecular epidemiological study in Yunnan. While C/CRF07_BC/CRF08_BC and CRF01_AE are codominant, the discovery of many sexually transmitted CRF01_AE cases is new and suggests that this subtype may lead to a new epidemic in the general Chinese population. We discuss implications of our results for understanding the evolution of the HIV-1 pandemic and for vaccine development

Failure Mechanism Researches of Material Surface and Interface in Micro-Scratch Test

ABSTRACTIn the present research, the adhesion properties and failure mechanisms for a ductile thin film on a silicon substrate (Ni/Si) are studied experimentally, and are simulated theoretically. In the experimental research, the relations of the horizontal driving force, vertical displacement and the frictional coefficients with horizontal displacement are measured. Furthermore, the variation of the total energy release rate and the frictional coefficient between contact surfaces are measured through obtaining a frictional effect law. The law displays that the frictional influences on the energy release rate of the total system weakly depend on the thin film thickness. This conclusion leads to that the frictional effect can be eliminated in the toughness ratio relation approximately. So that one can directly obtain the interfacial adhesion toughness from measurements in the micro-scratching test. In addition, the micro-scratching process for the ductile thin film/brittle substrate systems is simulated using the double cohesive zone model. Prediction results of the energy release rate are obtained, and are compared with the experimental results obtained in the present research.</jats:p