Showing papers on "Deformation (meteorology) published in 1979"

Hardness, Toughness, and Brittleness: An Indentation Analysis

Abstract: The ratio H/Kc, wjere His hardness (resistance to deformation) and Kc. is toughness (resistance to fracture), is proposed as an index of brittleness. Indentation mechanics provides the scientific basis for this proposal. The analysis, developed in terms of a model contact system, indicates that all materials are more susceptible to deformation in small-scale loading events and to fracture in large-scale events. By normalizing the characteristic dimensions of the two competing processes and the contact load in terms of appropriate functions of H and Kc a universal deformation/fracture diagram can be constructed. From this diagram the mechanical response of any material of known hardness and toughness may be predicted for any prospective in-service contact loading conditions. The concept offers a simple approach to materials classification for design purposes.

Indentation deformation/fracture of normal and anomalous glasses

Abstract: Vickers deformation/fracture indentations have been investigated in six silicate glasses. The characteristic damage patterns fall into two distinct groups, according to whether the glass shows “normal” or “anomalous” mechanical behaviour. Observations of the damage morphology during and after contact, of the scales of the deformation and fracture zones, and of the residual stress intensity about the impressions, all point to a basic difference in the local stress/strain micromechanics. This difference is discussed in relation to the factors which control the brittleness of glass.

Micromechanics of crack nucleation during indentations

Abstract: An analysis for the nucleation of microcracks from the inhomogeneous flow lines in soda-lime glass under Vickers indentations is considered. The minimum loads for crack nucleation are shown to depend on the hardness,H, and the critical stress intensity factor,K IC. Unlike the Lawn and Evans analysis, the present model does not require the presence of any fortuitous flaws of critical dimensions in the material, since the flaws are nucleated by the deformation in the deformed zone.

Experimental electron density distribution of molecular chlorine

Abstract: The electron density distribution of solid chlorine is determined from high resolution X-ray diffraction intensity measurements at 90 K. Deformation densities are calculated from the observed X-ray data and parameters obtained from a high order refinement of data with sin ϑ/λ > 0·65 A-1. Refinements including the population of multipole density functions are used to calculate model deformation densities and the asymmetry of the electric field gradient. Inclusion of third and fourth cumulant thermal parameters results in a significant improvement in the fit to the experimental data. The deformation density reveals a torus of non-bonding density at 0·31–0·37 e/A3 encircling the Cl-Cl bond somewhat in the back of each of the Cl atoms. A double peak of 0·22 e/A3 is found in the bonding region of the experimental deformation density similar to the bonding density found in S8. This feature is not properly reproduced in density maps based on the atom-centred multipole functions. The calculated distribution of er...

Studies on Droplet Deformation and Breakup. I. Droplet Deformation in Extensional Flow

Abstract: The extensional deformation of a viscoelastic droplet suspended in a viscoelastic medium was investigated, both theoretically and experimentally. A theoretical analysis was carried out on the deformation of a droplet suspended in a steady extensional flow field, where both fluids may be represented by the second‐order fluid model. The study took into account the effects of the elasticity, viscosity, and interfacial tension of the fluids concerned. The shape of a deformed droplet is determined by solving the equations of motion for both fluids (droplet phase and medium). A perturbation technique was employed and the iteration method was used to determine the shape of the droplet undergoing extensional deformation. Series solutions of stream function inside and outside the droplet, pressure distribution around the droplet, and the deformation of the droplet were obtained. For the experimental study, a transparent flow channel consisting of a conical section and a straight cylindrical tube was constructed. A...

Analysis of adaptive optical elements made from piezolectric bimorphs

Abstract: The deformation properties of an adaptive optical element made from a piezoelectric bimorph plate are analyzed. The fundamental relationship between the deformation of the optical surface and the voltage distribution applied across the thickness of the plate is derived and the general solution for an infinite plate is presented. A particular solution for a finite rectangular plate is also presented.

Thermal deformation record device with bleachable dye

Abstract: In accordance with the present invention, the optical characteristics of a thermal deformation record device are so altered that the device can be read back using the same beam as was used for recording. Moreover, the read beam can be used for playback at an arbitrarily high power level to enhance the signal-to-noise ratio of the recovered signal and yet not damage the deformation recording.

Discontinuous Deformation Gradients in Plane Finite Elastostatics of Incompressible Materials. (I) General Considerations. (II) An Example

Abstract: This investigation is concerned with the possibility of the change of type of the differential equations governing finite plane elastostatics for incompressible elastic materials, and the related is sue of the existence of equilibrium fields with discontinuous deformation gradients. Explicit necessary and sufficient conditions on the deformation invariants and the material for the ellipticity of the plane displacement equations of equilibrium are established. The issue of the existence, locally, of "elastostatic shocks" -- elastostatic fields with continuous displacements and discontinuous deformation gradients -- is then investigated. It is shown that an elastostatic shock exists only if the governing field equations suffer a loss of ellipticity at some deformation. Conversely, if the governing field equations have lost ellipticity at a given deformation at some point, an elastostatic shock can exist, locally, at that point. The results obtained are valid for an arbitrary homogeneous, isotropic, incompressible, elastic material. In order to illustrate the occurrence of elastostatic shocks in a physical problem, a specific displacement boundary value problem is studied. Here, a particular class of isotropic, incompressible, elastic materials which allow for a loss of ellipticity is considered. It is shown that no solution which is smooth in the classical sense exists to this problem for certain ranges of the applied loading. Next, we admit solutions involving elastostatic shocks into the discussion and find that the problem may then be solved completely. When this is done, however, there results a lack of uniqueness of solutions to the boundary value problem. In order to resolve this non-uniqueness, dissipativity and stability are investigated.

Ab initio calculations of the deformation of polyethylene

Abstract: Ab initio H‐F SCF quantum‐mechanical calculations have been done to evaluate the energy of covalent bond deformation of a –CH2CH2– ethylene repeat unit at strains up to e=0.6. The computational scheme involves subtracting energies of axially strained normal paraffins (n‐C3H8, n‐C5H12, and n‐C7H16) differing in length by one ethylene unit. At small strains it is found that the deformation is contributed to equally by C–C bond stretch and by CCC bond angle opening. At higher strains the majority of the deformation is accomplished by C–C stretch. The calculated elastic modulus is 405 GPa and the tensile strength of the polymer in the chain direction is 66 GPa. While both of these values are higher than previous estimates, it is believed that these quantities are the most reliable which have been calculated.