Fenglei Huang

Spherical nanometer-sized diamond obtained from detonation

Abstract Ultrafine diamond (UFD) was synthesized under high pressure and high temperatures generated by explosive detonation. The structure, composition, surface and thermal stability of UFD were studied by use of XRD, TEM, Raman Spectroscopy, FTIR, etc. The influences of the synthesis conditions and purification conditions on the properties of UFD were analyzed. The UFD had an average size of 4–6 nm, commonly exhibiting a spherical shape. The highest yield was of up to 10 mass% of the explosive. Attempts were made to use UFD as an additive to metal–diamond sintering and as crystallite seeds of CVD diamond films. The results show that UFD can decrease the coefficient of friction of the composite by 30%, and raise the nucleation density in CVD diamond films by 2–3 times.

A Pore Collapse Model for Hot-spot Ignition in Shocked Multi-component Explosives

A new pore collapse model, in which the effect of the binder in Plastic Bonded Explosives (PBX) is taken into account, is developed and integrated into the so-called hot-spot ignition model of shocked explosives. A two-dimensional hydrocode DYNA2D is used to simulate the shock initiation of PBX, with a reaction rate model consisting of a hot-spot ignition term, a slow-burning term at low pressure and a high-pressure reaction term. The numerical results show that the model can successfully describe the effects of the strength and the content of the binder, particle size and porosity of explosives on the shock initiation.

Numerical simulations of oblique penetration into reinforced concrete targets

A dynamic constitutive model based on the tensile and the compressive damage models for concrete was developed and implemented into the three-dimensional finite element code, LS-DYNA. Numerical simulations of oblique penetration into reinforced concrete targets were performed using LS-DYNA. On the basis of the proposed model, the tensile and compressive damages of reinforced concrete after oblique penetration were observed and the deformation of reinforcing steel bars was obtained. Moreover, the depths of penetration for different oblique angles were obtained. The numerical results for the depth of penetration are in good agreement with existing experimental data.

Quasi-static tensile deformation and fracture behavior of a highly particle-filled composite using digital image correlation method

Polymer bonded explosives (PBXs) are highly particle-filled composite materials. This paper experimentally studies the tensile deformation and fracture behavior of a PBX simulation by using the semi-circular bending (SCB) test. The deformation and fracture process of a pre-notched SCB sample with a random speckle pattern is recorded by a charge coupled device camera. The displacement and strain fields on the observed surface during the loading process are obtained by using the digital image correlation method. The crack opening displacement is calculated from the displacement fields, the initiation and propagation of the crack are analyzed. In addition, the damage evolution and fracture mechanisms of the SCB sample are analyzed according to the strain fields and the correlation coefficient fields at different loading steps.

Foil-like manganin gauges for dynamic high pressure measurements

Foil-like manganin gauges with a variety of shapes used in different ranges of pressure for the one-dimensional strain mode and axisymmetric strain mode were designed for measuring the detonation pressures of explosives and high shock pressure in materials. In the stress range of 0–53.5 GPa, the pressure–piezoresistance relationships of the manganin gauges were calibrated by the light gas gun and the planar lens of explosive. The piezoresistance coefficients were obtained in different ranges of pressure. To verify the coefficients, the detonation pressure (CJ pressure) of TNT explosive was measured by the manganin gauges, which give similar CJ pressure values to those reported by Zhang et al (2009 Detonation Physics (Beijing: Ordnance Industry Press)) with the maximum relative deviation being less than 3%.

Measurement of Young's modulus and Poisson's ratio of Human Hair using Optical techniques

Human hair is a complex nanocomposite fiber whose physical appearance and mechanical strength are governed by a variety of factors like ethnicity, cleaning, grooming, chemical treatments and environment. Characterization of mechanical properties of hair is essential to develop better cosmetic products and advance biological and cosmetic science. Hence the behavior of hair under tension is of interest to beauty care science. Human hair fibers experience tensile forces as they are groomed and styled. Previous researches about tensile testing of human hair were seemingly focused on the longitudinal direction, such as elastic modulus, yield strength, breaking strength and strain at break after different treatment. In this research, experiment of evaluating the mechanical properties of human hair, such as Youngs modulus and Poissons ratio, was designed and conducted. The principle of the experimental instrument was presented. The system of testing instrument to evaluate the Youngs modulus and Poissons ratio was introduced. The range of Poissons ratio of the hair from the identical person was evaluated. Experiments were conducted for testing the mechanical properties after acid, aqueous alkali and neutral solution treatment of human hair. Explanation of Youngs modulus and Poissons ratio was conducted base on these results of experiments. These results can be useful to hair treatment and cosmetic product.

A study on the mechanical properties of beagle femoral head using the digital speckle correlation method.

The mechanical properties of the femoral head are known to play an important role in the athletic performance of animals. In this paper, the full-field displacement and strain distributions of beagle femoral head samples in the U and V fields under loading were measured using the digital speckle correlation method (DSCM), and some deformation characteristics were analyzed. Youngs modulus and Poissons ratio were calculated to demonstrate the notable axial anisotropy of the femoral head. The axial compressive Youngs modulus varies from 361MPa to 583MPa, and the transverse one is 213MPa. The Poissons ratio in the axial-transverse direction ranges from 0.14 to 0.29, and the one in the transverse-axial direction is 0.07. Experimental results validated the accuracy of this measurement, providing a potential reference for investigating the deformation performance of the femoral head.

Theoretical model for plasma expansion generated by hypervelocity impact

The hypervelocity impact experiments of spherical LY12 aluminum projectile diameter of 6.4 mm on LY12 aluminum target thickness of 23 mm have been conducted using a two-stage light gas gun. The impact velocity of the projectile is 5.2, 5.7, and 6.3 km/s, respectively. The experimental results show that the plasma phase transition appears under the current experiment conditions, and the plasma expansion consists of accumulation, equilibrium, and attenuation. The plasma characteristic parameters decrease as the plasma expands outward and are proportional with the third power of the impact velocity, i.e., (Te, ne) ∝ vp3. Based on the experimental results, a theoretical model on the plasma expansion is developed and the theoretical results are consistent with the experimental data.

Study on dynamic fracture and mechanical properties of a PBX simulant by using dic and SHPB method

The deformation and fracture of a PBX simulant were studied in this work. A pre-cracked semi-circular bending sample was loaded using a SHPB. The failure process of the sample was recorded in situ using a high speed camera. Based on the recorded images corresponding to the loading steps, the displacement and strain fields were determined using digital image correlation method. The crack opening displacement was determined. The correlation coefficient distribution was used to predict the initiation and propagation of the crack initiated from the tip of the pre-crack. In addition, the dynamic fracture toughness of the specimen was measured. The KIC values were approximately 1.39 ± 0.02, 1.51 ± 0.01 and 1.87 ± 0.03 MPa·m1/2 corresponding to strain rates about 382 ± 13, 455 ± 8 and 621 ± 23 s-1, respectively. The fracture toughness results show strong strain rate dependence.

Ignition and Growth Modeling of Shock Initiation of Different Particle Size Formulations of PBXC03 Explosive

The change in shock sensitivity of explosives having various explosive grain sizes is discussed. Along with other parameters, explosive grain size is one of the key parameters controlling the macroscopic behavior of shocked pressed explosives. Ignition and growth reactive flow modeling is performed for the shock initiation experiments carried out by using the in situ manganin piezoresistive pressure gauge technique to investigate the influences of the octahydro-1,3,5,7–tetranitro-1,3,5,7-tetrazocine (HMX) particle size on the shock initiation and the subsequent detonation growth process for the three explosive formulations of pressed PBXC03 (87% HMX, 7% 1,3,5-trichloro-2,4,6-trinitrobenzene (TATB), 6% Viton by weight). All of the formulation studied had the same density but different explosive grain sizes. A set of ignition and growth parameters was obtained for all three formulations. Only the coefficient G1 of the first growth term in the reaction rate equation was varied with the grain size; all other parameters were kept the same for all formulations. It was found that G1 decreases almost linearly with HMX particle size for PBXC03. However, the equation of state (EOS) for solid explosive had to be adjusted to fit the experimental data. Both experimental and numerical simulation results show that the shock sensitivity of PBXC03 decreases with increasing HMX particle size for the sustained pressure pulses (around 4 GPa) as obtained in the experiment. This result is in accordance with the results reported elsewhere in literature. For future work, a better approach may be to find standard solid Grüneisen EOS and product Jones-Wilkins-Lee (JWL) EOS for each formulation for the best fit to the experimental data.