Xinjian Zhang

Bio: Xinjian Zhang is an academic researcher from Old Dominion University. The author has contributed to research in topics: Materials science & Amorphous solid. The author has an hindex of 2, co-authored 2 publications receiving 542 citations.

Characterizations the deposition behavior and mechanical properties of detonation sprayed Fe-based amorphous coatings

Abstract: In this study, the spreading morphologies and deposition behaviors of molten droplet in a single detonation sprayed shot under different oxygen-fuel ratio conditions are characterized in detail to reveal the formation mechanism of Fe-based amorphous coatings. Additionally, the porosities, micro-hardness, amorphous phase content and wear behavior of the coatings were also carefully evaluated to correlate the relationship between preparation process parameters, particle deposition behavior, spreading morphology, and mechanical properties. The results indicate that the spraying oxygen-fuel ratio (OF) parameter can determine the microstructure change of the coating, which is considered to be a reflection of the molten state of the sprayed particles. The low OF reduces the combustion efficiency, making the coating particles deposited in a form similar to cold spraying, resulting in uneven coating structure. In the case of medium OF (2.00), amorphous particles can form completely melted droplets and spread well on the substrate, and produce a good metallurgical bond with the substrate. Thanks to the good spread of the amorphous droplets, the OF-2.00 coating displays a very uniform and dense structure and uniformly distributed microhardness, which also makes its wear resistance (0.63 × 10 −6 mm 3 N −1 m −1 ) increased by about 8 times compared with OF-1.43 coating.

Rate-dependent nanoindentation creep behavior of a Fe-based amorphous coating

Abstract: A very thick (∼1 mm) coating of Fe-based amorphous material was applied to a Q235 steel substrate by detonation spraying. The rate-dependent anelastic and viscoplastic deformations of the coating were investigated through nanoindentation creep experiments with loading rates of 0.1∼5 mN s−1; the results were analyzed using the Maxwell-Voigt model with two Kelvin units. Creep deformation in the Fe-based amorphous coating was found to be sensitive to loading rate; the nanohardness, creep-stress exponent, and viscosity lessened with increased loading rate during viscoplastic deformation. The presence of two characteristic peaks in the relaxation-time spectrum shows that the anelastic deformation was related to the activation of two types of defects. Low loading rates promoted the activation of defects in the soft region with long relaxation times; larger loading rates promoted the activation of defects in the hard region with shorter structural relaxation times, allowing plastic deformation. This resulted in lower creep resistance at higher loading rates.

NGA Ground Motion Model for the Geometric Mean Horizontal Component of PGA, PGV, PGD and 5% Damped Linear Elastic Response Spectra for Periods Ranging from 0.01 to 10 s

Abstract: We present a new empirical ground motion model for PGA, PGV, PGD and 5% damped linear elastic response spectra for periods ranging from 0.01– 10 s. The model was developed as part of the PEER Next Generation Attenuation (NGA) project. We used a subset of the PEER NGA database for which we excluded recordings and earthquakes that were believed to be inappropriate for estimating free-field ground motions from shallow earthquake mainshocks in active tectonic regimes. We developed relations for both the median and standard deviation of the geometric mean horizontal component of ground motion that we consider to be valid for magnitudes ranging from 4.0 up to 7.5–8.5 (depending on fault mechanism) and distances ranging from 0 – 200 km. The model explicitly includes the effects of magnitude saturation, magnitude-dependent attenuation, style of faulting, rupture depth, hanging-wall geometry, linear and nonlinear site response, 3-D basin response, and inter-event and intra-event variability. Soil nonlinearity causes the intra-event standard deviation to depend on the amplitude of PGA on reference rock rather than on magnitude, which leads to a decrease in aleatory uncertainty at high levels of ground shaking for sites located on soil. DOI: 10.1193/1.2857546

Assessment of the Liquefaction Susceptibility of Fine-Grained Soils

Abstract: Observations from recent earthquakes and the results of cyclic tests indicate that the Chinese criteria are not reliable for determining the liquefaction susceptibility of fine-grained soils. Fine-grained soils that liquefied during the 1994 Northridge, 1999 Kocaeli, and 1999 Chi-Chi earthquakes often did not meet the clay-size criterion of the Chinese criteria. Cyclic testing of a wide range of soils found to liquefy in Adapazari during the Kocaeli earthquake confirmed that these fine-grained soils were susceptible to liquefaction. It is not the amount of “clay-size” particles in the soil; rather, it is the amount and type of clay minerals in the soil that best indicate liquefaction susceptibility. Thus plasticity index (PI) is a better indicator of liquefaction susceptibility. Loose soils with PI 0.85 were susceptible to liquefaction, and loose soils with 12 0.8 were systematically more resistant to liquefaction. Soils with PI>18 tested at low effective confining stresses ...

Normalized shear modulus and material damping ratio relationships

Abstract: Predictive equations for estimating normalized shear modulus and material damping ratio of Quaternary, Tertiary and older, and residual/saprolite soils are presented in this paper. The equations are based on a modified hyperbolic model and a statistical analysis of existing Resonant Column and Torsional Shear test results for 122 specimens obtained from South Carolina, North Carolina, and Alabama. Variables used in the equations for normalized shear modulus are: shear-strain amplitude, confining stress, and plasticity index (PI). The equations for damping ratio are expressed in terms of a polynomial function of normalized shear modulus plus a minimum damping ratio. It is found that the Quaternary soils exhibit more linearity than soils of the other two groups. Also, it is found that the effect of PI on dynamic soil behavior is not as significant as previously thought. Data from all three groups exhibit significant variations with confining stress, similar to the variations determined by Stokoe et al. The uncertainties associated with the equations for PI of 0 and mean effective confining stress of 100 kPa are quantified using the point estimate method. A case study from Charleston, S.C. is provided to illustrate an application of the equations to seismic response analysis and the importance of considering confining stress and geologic age.