Descriptions of Reversed Yielding in Internally Pressurized Tubes

Using Tresca's yield criterion and its associated flow rule, solutions are obtained for the stresses and strains when a thick-walled tube is subject to internal pressure and subsequent unloading. A bilinear hardening material model in which allowances are made for a Bauschinger effect is adopted. A variable elastic range and different rates under forward and reversed deformation are assumed. Prager's translation law is obtained as a particular case. The solutions are practically analytic. However, a numerical technique is necessary to solve transcendental equations. Conditions are expressed for which the release is purely elastic and elastic–plastic. The importance of verifying conditions under which the Tresca theory is valid is emphasized. Possible numerical difficulties with solving equations that express these conditions are highlighted. The effect of kinematic hardening law on the validity of the solutions found is demonstrated.

Low-Cycle Fatigue Test of Circular Concrete Filled Tubular Columns

During earthquake, the inelastic action in the plastic hinge regions of structures and bridges results in significant reversed deformation and failure of the critical components because of cumulative damage. To simulate seismic behavior of structure members and develop a simplicity damage criterion for circular concrete filled steel tubular (CFT) columns subjected to a series of earthquake excitations, an experimental study was undertaken to investigate the cumulative damage and relationship between low cycle fatigue life and displacement amplitude. Two types of large scale circular CFT columns with different kinds of seam weld and inner concrete compressive strength including nine specimens were tested under quasi static loading with constant and variable cyclic amplitudes. The test data were evaluated with the fatigue model relating deformation and fatigue life. Fatigue life expressions for application in damage-based seismic design are developed.

In situ reversed deformation of prefatigued aluminum single crystals in the HVEM

Utilizing a technique describe earlier by Wall et al., prefatigued aluminum single crystals oriented for single slip, were cyclically deformed in the HVEM operating at 1.5Mev by deforming in mutually perpendicular “X and Y” directions. Deforming in X and Y avoids foil buckling and allows for shear reversal (fatigue). Initial observations are reported here and will aid in the understanding of the micro-mechanisms of cyclic deformation.In situ specimens extracted from prefatigued single crystals (560 cycles, strain amplitude of 1.2 X 10−3 at 77K) were oriented in such a manner as to facilitate imaging primary dislocations, b=[0,l,-1], on the primary (111) slip plane. The (111) plane is inclined 25° about the [0,1,-1] direction to increase the projected length of these dislocations for viewing on the TEM screen. The [0,1,-1] direction is also contained in the plane of the specimen foil and is 45° to the tensile axes. The specimens are then tilted to a [1,1,-1] diffracting condition. Nonperforated specimens were prepared by a technique described by Kassner Specimens were then alternately deformed along mutually perpendicular tensile axis in the HVEM.

In situ reversed deformation of aluminum single crystals in the HVEM: a new X-Y straining stage

The metal fatigue phenomenon is poorly understood, partially because the dislocation dynamics of reversed deformation have not been well characterized. Little success has been realized with the direct observation of dislocations during in situ cyclic deformation. Problems associated with buckling of the specimen foil occur during applied shear, bending or compression. Buckling can preclude adequate imaging conditions and further complicate the thin foil stress-state. Recent experiments have shown that dislocation movement can be reversed by tensile stressing in alternate perpendicular directions (i.e. 90° rotation of the tensile stress to X and Y directions results in the reversal of the shear stress). Buckling of the specimen foil is also reduced in these experiments.Results from recent in situ reversed deformation experiments are presented here. The experiments were performed on a new straining stage which is a modification of the Sleeswyk- Kassner X-Y stage. The specimen design and preparation procedures have also been modified to facilitate better and more reproducible in situ experiments. The new X-Y straining stage is illustrated in figure 1.