Precise thermodynamic control of high pressure jet expansions

We describe an experimental setup for supersonic jet expansions of supercritical fluids. It is characterized by well-defined thermodynamic values to allow systematic investigations of pressure and temperature effects on molecular beam parameters. The design permits stagnation temperatures T(0)=225-425 K with a thermal stability DeltaT(0)<30 mK and stagnation pressures p(0)=0.2-12 MPa that are measured with 0.05% precision. For optimum stability, gas reservoir, pressure transducer, and gauge amplifier are temperature-controlled, and a feedback loop permits active pressure stabilization using a pulseless syringe pump. With this approach stagnation pressures can be reproduced and kept constant to Deltap(0)<2.9 kPa. As a result, flow velocity and kinetic energy of molecular beams can be controlled with maximum accuracy.     

Investigation of the tribological behavior of radial shaft rings and soft turned shafts under the influence of abrasive particles

Nowadays, radial shaft seals are more and more used in many products with a short or very short life cycle. As a consequence of the reduced durability, the demands on the sealing system decrease so that system components with a significantly lower resistance against wear can be used compared to conventional components. However, changing the resistance against wear of the radial shaft seals does not lead to any cost advantage. The situation in the production of the mating surface of the seal is quite different. Conventional manufactured shaft surfaces, for the use of dynamic radial seals have to be hardened and ground in a complex way, which increases the costs. By reducing these manufacturing processes to a pure turning procedure, a large part of the production costs can be saved.     

Simulation based optimization of the NC-shape grinding process with toroid grinding wheels

For achieving high material removal rates while grinding free formed surfaces, shape grinding with toroid grinding wheels is favored. The material removal is carried out line by line. The contact area between grinding wheel and workpiece is therefore complex and varying. Without detailed knowledge about the contact area, which is influenced by many factors, the shape grinding process can only be performed sub-optimally. To improve this flexible production process and in order to ensure a suitable process strategy a simulation-tool is being developed. The simulation comprises a geometric-kinematic process simulation and a finite elements simulation. This paper presents basic parts of the investigation, modelling and simulation of the NC-shape grinding process with toroid grinding wheels.     

Plasma biasing to control the growth conditions of diamond-like carbon

It is well known that the structure and properties of diamond-like carbon, and in particular the sp³/sp² ratio, can be controlled by the energy of the condensing carbon ions or atoms. In many practical cases, the energy of ions arriving at the surface of the growing film is determined by the bias applied to the substrate. The bias causes a sheath to form between substrate and plasma in which the potential difference between plasma potential and surface potential drops. In this contribution, we demonstrate that the same results can be obtained with grounded substrates by shifting the plasma potential. This “plasma biasing” (as opposed to “substrate biasing”) is shown to work well with pulsed cathodic carbon arcs, resulting in tetrahedral amorphous carbon (ta-C) films that are comparable to the films obtained with the conventional substrate bias. To verify the plasma bias approach, ta-C films were deposited by both conventional and plasma bias and characterized by transmission electron microscopy (TEM) and electron energy loss spectrometry (EELS). Detailed data for comparison of these films are provided.     

Haptic controlled three-axis MEMS gripper system

In this work, we describe the development and testing of a three degree of freedom meso/micromanipulation system for handling micro-objects, including biological cells and microbeads. Three-axis control is obtained using stepper motors coupled to micromanipulators. The test specimen is placed on a linear X-stage, which is coupled to one stepper motor. The remaining two stepper motors are coupled to the Y and Z axes of a micromanipulator. The stepper motor-micromanipulator arrangement in the Y and Z axes has a minimum step resolution of ～0.4?μm with a total travel of 12 mm and the stepper motor-X stage arrangement has a minimum resolution of ～0.3?μm with a total travel of 10 mm. Mechanical backlash error is ～0.8?μm for ～750?μm of travel. A MEMS microgripper from Femtotools? acts as an end-effector in the shaft end of the micromanipulator. The gripping ranges of the grippers used are 0-100?μm (for FT-G100) and 0-60?μm (for FT-G60). As the gripping action is performed, the force sense circuit of FT-G100 measures the handling force. This force feedback is integrated to a commercially available three degree of freedom haptic device (Novint Falcon) allowing the user to receive tactile feedback during the microscale handling. Both mesoscale and microscale controls are important, as mesoscale control is required for the travel motion of the test object whereas microscale control is required for the gripping action. The haptic device is used to control the position of the microgripper, control the actuation of the microgripper, and provide force feedback. A LABVIEW program was developed to interlink communication and control among hardware used in the system. Micro-objects such as SF-9 cells and polystyrene beads (～45?μm) are handled and handling forces of ～50?μN were experienced.     

Investigation into the fate of mercury in bituminous coal during mild pyrolysis

Two high-volatile bituminous coal (Lower Freeport #6A and Pittsburgh #8), used primarily for electricity production, were tested to determine the fate of their mercury content during mild pyrolysis. Mono-sized samples of the well characterized coals were tested under nitrogen in a horizontal tube furnace at different residence times at different temperatures throughout the range 275–600°C. The resulting char was analyzed for mercury, and compared to the original parent coal concentration. The percent Hg removal was found to be a function of both residence time and temperature. The data for both coals have shown two distinct regimes; a low temperature chemical evolution mechanism which follows an Arrhenius form (apparent activation energies for the Lower Freeport #6A and the Pittsburgh #8 coals are 25.6±1.5 and 21.7±1.9 kcal/mol respectively), and a higher temperature regime where the Hg evolution dramatically decreases. This can be attributed to the changing structure of the coal at these higher temperatures. The results of bomb calorimetry analysis performed on the Lower Freeport #6A coal samples verify that the overall heating value of the coal is essentially unaffected by mild pyrolysis at temperatures lower than 400°C.     

轮胎有限元研究(FEA)进展及应用成果

从非线性有限元的实验设计获得在低应变条件下门尼里夫林（ＭｏｏｎｅｙＲｉｖｌｉｎ）方程的常数解,成功地预测了轮胎的充气尺寸,从绘制的负荷条件下轮胎应力场色谱图分析,预报花纹沟并拢情况,并找出设计的薄弱环节,优化轮胎结构设计。     

Absolute calibration method for laser megajoule neutron yield measurement by activation diagnostics

The laser megajoule (LMJ) and the National Ignition Facility (NIF) plan to demonstrate thermonuclear ignition using inertial confinement fusion (ICF). The neutron yield is one of the most important parameters to characterize ICF experiment performance. For decades, the activation diagnostic was chosen as a reference at ICF facilities and is now planned to be the first nuclear diagnostic on LMJ, measuring both 2.45 MeV and 14.1 MeV neutron yields. Challenges for the activation diagnostic development are absolute calibration, accuracy, range requirement, and harsh environment. At this time, copper and zirconium material are identified for 14.1 MeV neutron yield measurement and indium material for 2.45 MeV neutrons. A series of calibrations were performed at Commissariat a? l'Energie Atomique (CEA) on a Van de Graff facility to determine activation diagnostics efficiencies and to compare them with results from calculations. The CEA copper activation diagnostic was tested on the OMEGA facility during DT implosion. Experiments showed that CEA and Laboratory for Laser Energetics (LLE) diagnostics agree to better than 1% on the neutron yield measurement, with an independent calibration for each system. Also, experimental sensitivities are in good agreement with simulations and allow us to scale activation diagnostics for the LMJ measurement range.     

Resonant ultrasound spectroscopy of cylinders over the full range of Poisson's ratio

Mode structure maps for freely vibrating cylinders over a range of Poisson's ratio, ν, are desirable for the design and interpretation of experiments using resonant ultrasound spectroscopy (RUS). The full range of isotropic ν (-1 to +0.5) is analyzed here using a finite element method to accommodate materials with a negative Poisson's ratio. The fundamental torsional mode has the lowest frequency provided ν is between about -0.24 and +0.5. For any ν, the torsional mode can be identified utilizing the polarization sensitivity of the shear transducers. RUS experimental results for materials with Poisson's ratio +0.3, +0.16, and -0.3 and a previous numerical study for ν = 0.33 are compared with the present analysis. Interpretation of results is easiest if the length∕diameter ratio of the cylinder is close to 1. Slight material anisotropy leads to splitting of the higher modes but not of the fundamental torsion mode.     

Particle Size and the Mechanical Properties of Uganda Clay

This paper describes a study of the effects of particle size on the porosity, microstructure, and mechanical properties of compacts fabricated under uniaxial compression with a rectangular die. Four ranges of different particle sizes were investigated to determine the dependence of fracture toughness; porosity and strength of the compacts on particle size. Thermal shock effects on the compacts were also investigated by determining the number of cycles to failure, when the compacts were cold shocked at four different temperatures. Compacts made from powders of larger particle size tended to have larger number of cycles to failure than those made of finer particle sizes. Contrary to this, compacts made from smaller particles size exhibited higher fracture toughness compared to those made from larger particle size.