Showing papers on "Slip line field published in 1976"

Slip-line field theory and large-scale continental tectonics

Abstract: A simple analogy is made between the tectonics of Asia and deformation in a rigidly indented rigid–plastic solid. India is analogous to the indenter and the great strike-slip faults correspond to slip lines. For various indentation geometries, the sense and linearity (or curvature) of strike-slip faults, convergence at the Burma arc and the existence of the Himalayan Burman Syntax, the conjugate strike-slip faults in Mongolia and the extension at the Baikal and Shansi graben can be predicted. Given the horizontal force necessary to support Tibet, an average shear stress of a few to several hundred bars along faults in Asia is predicted, corresponding to the yield stress of rigid–plastic material.

A two-dimensional analysis of surface deformation due to dip-slip faulting

Abstract: A two-dimensional model of dip-slip faulting is developed on the basis of elastic dislocation theory. General relationships among the fault-slip distribution, the stress-drop distribution, and the crustal surface deformation are derived for this model for arbitrary dip angle. The relationships are valid for arbitrary distribution of slip on the fault plane, except for the requirement that all stress components be finite at the boundaries of the slip zone. In order to illustrate some of the features of the derived relationships, a sample calculation based on surface deformation data obtained following the 1964 Alaska earthquake is performed, and the calculated values of various fault parameters appear to fall within accepted limits. For purposes of direct comparison, the same calculations are performed assuming the slip distribution to be uniform over the slip zone.

The mechanism of brittle fracture in notched impact tests on polycarbonate

Abstract: The impact testing of notched polycarbonate bars that are thick enough to yield in plane strain has been investigated. Shear bands occur in the plastic zone that resemble the slip line field for yielding from a circular notch. Eventually, an internal craze nucleates at the tip of the plastic zone, where the stresses are highest, and a crack forms in the thickest part of the craze. Above −15‡ C the stress for the craze to nucleate is a nearly constant multiple of the yield stress. It is shown that previous observations that annealing polycarbonate causes a ductile to brittle transition is a consequence of testing bars of thickness less than 5 mm.

Slip processes in the deformation of polystyrene

Abstract: Two slip processes are characterized in the deformation of atactic polystyrene by compression. In the optical microscope, one appears as intensive shear bands and the other as diffuse shear zones. But in the electron microscope, the latter reveals itself in the form of two sets of numerous, fine, discontinuous shear bands intersecting at nearly right angles. In addition to their differences in appearance, the coarse slip band propagates fast along a localized path, inclines at less than 45‡ with the compression axis, and invariably produces shear fracture when it extends across the specimen. On the other hand, the fine slip bands spread slowly by multiplication mainly along the maximum shear stress direction, contribute to almost all the macroscopic strain and cause shape changes of the specimen. Hence the coarse band process is a brittle mode and the fine band process a ductile mode. The relative abundance of these bands depends on the thermal history of the specimen, the loading condition, and the deformation temperature. The average shear strain inside either band is about 1.5 and is recoverable upon annealing.

Pressure and normal stress effects in shear yielding

Abstract: The classical yielding theory of Tresca is generalized to include the effects of both hydrostatic pressure and normal stress in the slip plane. The three-parameter theory is the most general for polyhedral yield surfaces. The new theory is applied to the yielding of polystyrene. Two modes of slip: a brittle mode in the form of coarse slip bands, and a ductile mode in the form of fine slip bands, are studied separately. All three parameters are determined for each mode.

On the nature of superplastic deformation

Abstract: The peculiarities of dislocation slip, grain-boundary slip and boundary migration are studied at superplastic deformation of the Zn—0.4% Al alloy. The nature, interconnection, and role of these processes are investigated. Dislocation slip at the deformation of the alloy which is the primary deformation mechanism is found to be of great importance. At the same time the importance of grain boundary sliding (GBS) consists in the fact that it is not only a deformation mechanism but a recovery mechanism as well. Grain-boundary migration is a process concurrent to sliding. [Russian Text Ignored]

Computer simulation of plastic deformation through planar glide in an idealized crystal

Abstract: The behavior of the plastic deformation of an idealized crystal made by stacking parallel slip planes is reported. Each slip plane is assumed to contain active sources of dislocations leading to a constant density of non-interacting dislocations in the plane which glide through randomly distributed localized point obstacles, representing small precipitates. The dislocation is assumed to have a constant line tension and the dislocation-obstacle interaction is taken to have a simple step form. Using results of computer simulation of thermally activated glide through random arrays of point obstacles, deformation was modeled as a function of temperature and applied stress, determining the strain rate and the morphological characteristics of slip.

Deformation and Solid Solution Strengthening of Titanium-Aluminum Single Crystals.

Abstract: : Solid solution strengthening and deformation behavior of titanium-aluminum single crystals has been studied over the range of temperature 77-1100K and from 0 to 6.6 w/o Al. Crystal orientations have been chosen to promote prism slip, basal slip and c+a slip, and the temperature and composition dependence of the critical resolved shear stress (CRSS) for each of these slip systems has been determined. Although prism slip has the lowest CRSS of all the slip systems studied, both increasing temperature and Al concentration make the stresses for prism and basal slip converge. Deformation with a c+a slip vector is always more difficult to activate than either basal or prism slip with an a slip vector, and this resulted in fracture of crystals oriented for c+a slip by unstable shear, under certain conditions. In addition to the work on the deformation of Ti-Al crystals in compression, some studies were conducted on both creep and cyclic deformation (fatigue) of single crystals. The impact of these studies on understanding of deformation texture development and the use of textured titanium alloys in structures is briefly discussed. (Author)

Slip Deformation and Low-Cycle Fatigue Damage of an Aluminium Alloy

Abstract: Plastic strain is mainly due to the crystallographic slip in grains. The slip quantity Δλes reversed in individual slip bands is more important than the macroscopically observed plastic strain Δep as the criterion of a crack initiation along a slip band. In the present work, it was investigated on the basis of microscopic observation how the macroscopic plastic strain was distributed in the individual slip bands. Manson-Coffin type relation was expressed by using the slip quantity Δλes reversed in the individual slip band. The material used was an anti-corrosion aluminium alloy.