A Bi-Axial Quantum State That Controls Molecular Collisions Like a Double-Slit Interferometer

To control molecular scattering, we consider hydrogen molecules prepared in a coherent superposition of m states within a single rovibrational (v, j) energy eigenstate using Stark-induced adiabatic Raman passage (SARP). Specifically, SARP can prepare a bi-axial state of the HD molecule in which the HD bond axis exists simultaneously in two possible alignments at right angles to one another with a well-defined relative phase. We show that scattering from this biaxial state will interfere, resulting in a φ -dependent scattering intensity distribution, where φ is the azimuthal angle about the collision velocity direction. Using the scattering matrix extracted from our experiments on the rotationally inelastic collisions of quantum state prepared HD at low temperatures, we calculate the differential scattering cross-section dσ/dΩ, which shows an interference pattern as function of θ and φ in the image plane perpendicular to the collision velocity. The calculated scattering image shows that scattering from the bi-axial state directs molecules along well-defined angles, corresponding to interference maxima. Thus, the bi-axial state behaves like a double slit for molecular scattering. Moreover, by rotating the polarizations of the SARP preparation lasers, we can control the interference thereby altering the scattering angular distribution. This molecular interferometer, which experimentally measures the relative phases of the scattering matrix elements, allows a direct test of theoretical calculations on important, fundamental collision processes.

Some Remarks on the Equilibrium of Granular Materials Described by Constitutive Relations That Depend on the Gradients of the Density or Volume Fraction

One of the ways of determining the properties of granular materials is to subject the material to a tri-axial state of stress with three distinct eigenvalues, in a cubical tri-axial testing equipment, the material tested being in a static state. A constitutive relation for granular materials that does not allow the body to be in tri-axial static equilibrium would not be a reasonable model as experiments clearly show that granular materials can exist in such tri-axial states. In this short note, we observe that a large class of models that have been developed and used to describe the response of granular materials will not allow them to be in a static tri-axial state of stress with three different principal stresses.

Predictions of the Mechanical Response of Sintered FGH96 Powder Compacts

This paper presents predictions of the mechanical response of sintered FGH96 Ni-based superalloy powder compacts at high temperatures, obtained by the analysis of 3D representative volume elements generated by both X-ray tomography and a virtual technique. The response of the material to a multi-axial state of stress/strain for porosities as large as 0.3 is explored, obtaining the yield surfaces and their evolution as well as scaling laws for both elastic and plastic properties. The two modeling approaches are found in good agreement. The sensitivity of the predictions to particle size, inter-particle friction, applied strain rate, and boundary conditions is also examined.

High Cycle Fatigue Life Assessment of Compressor Blades Under Multi-Axial Fatigue Mode

Stringent mission requirements of Aero Gas Turbine engines result in severe aerodynamic loads on engine components. Structural integrity and durability of blades is an important aspect with fatigue being a major failure mode and especially High Cycle Fatigue being a critical design concern. HCF failures in blades are mainly attributed to resonant excitations where the dynamic stress amplitude in the blade increases as the exciting frequency approaches the resonant speed. These excitations could be due to integral orders, i.e. as multiples of rotational speeds and also due to nozzle or blade pass frequencies. The frequency of these excitations is very high and under these excitations, the blades are subjected to highly complex modes or deformation patterns resulting in a multi-axial state of stress. Other causes for multi-axial state of stress may be attributed to anisotropy in material, presence of stress raisers and end fixity/ support mechanism of the blade in context. Assessing the severity of this multi-axial stress state in the blade from HCF is very important from the designer’s perspective. This paper describes the methodology employed in a compressor stator blade to assess the HCF damage by distortion energy based multi-axial fatigue failure criteria with a modification to include the mean static stresses. Based on this method, safe operating strain limits are established and are used as guide lines to monitor the stator blades during engine testing. When this methodology is checked for a pure bending mode of a compressor stator blade, i.e. for a state of stress which is predominantly unidirectional, both the Goodman approach and the distortion energy based multi-axial method yield the same assessment under HCF, whereas for a complex mode with a multi-axial state of stress, considerable difference in results is observed.

Permeability Changes of Coal Cores and Briquettes under Tri-Axial Stress Conditions

The paper is dealing with the permeability of coal in triaxial state of stress. The permeability of coal, besides coal’s methane capacity, is the main parameter determining the quantity of methane inflow into underground excavations. The stress in a coal seam is one of the most important factors influencing coal permeability therefore the permeability measurements were performed in tri-axial state of stress. The hydrostatic three-axial state of stress was gradually increased from 5 MPa with steps of 5 MPa up to a maximum of 30 MPa. Nitrogen was applied as a gas medium in all experiments. The results of the permeability measurements of coal cores from the “Zofiówka” mine, Poland, and three mines from the Czech Republic are presented in this paper. As a “reference”, permeability measurements were also taken for coal briquettes prepared from coal dust with defined porosity. It was confirmed that the decreasing porosity of coal briquettes affects the decreasing permeability. The advantage of experimentation on coal briquettes is its good repeatability. From the experimental results, an empirical relation between gas permeability and confining pressure has also been identified. The empirical relation for coal briquettes is in good correspondence with published results. However, for coal cores, the character of change differs. The influence of confining pressure has a different character and the decrease in permeability is stronger due to the increasing confining pressure

Analysis of Bi-Axial and Tri-Axial State of Stresses in Plastically Deformed Solid Cylindrical Specimens under Dry Lubrication

This paper explains the type of stresses induced in the AA2014 solid cylindrical specimens when deformed plastically between a set of rigid dies. The solid cylindrical specimens machined to different height(h) to the diameter(d) ratios namely h/d=1, h/d=0.75 and h/d=0.5 were compressed between the dies using a 100 ton capacity UTM. These billets were deformed to different strains. At each and every stage of the incremental strain, the various elements of the geometry such as contact diameter at the die/billet interface, bulged diameter at the equatorial region and the height after deformation were noted down. The significance of measuring the various elements of the geometry is to predict the value of stresses namely axial stress, hoop stress, hydrostatic stress and effective stress which influence the ductility or formability of the material. The stresses induced in the billets were predicted using the empirical equations and a comparison has been made for uni-axial, bi-axial and tri-axial state of stresses for different aspect ratios. A notified behavior in the value of stresses has been observed for all the aspect ratios and for different state of stresses