Plane Strain Creep Research Articles

Grain‐Boundary Sliding and Grain Interlocking in the Creep Deformation of Two‐Phase Ceramics

Grain‐boundary sliding and grain interlocking of two‐phase ceramics during creep are examined on the basis of the Dryden–Kucerovsky–Wilkinson–Watt theory. That theory is extended to the plane–strain creep deformation of model arrays of square and hexagonal grains embedded in a continuous grain‐boundary melt phase to develop consti‐tutive equations for their universal creep. Superposition is derived for the “time‐applied stress” and the “time–temperature” relations during creep. The “shift factor” for the time–temperature superposition characterizes the temperature dependence of the apparent viscosity of the ceramic. A two‐phase ceramic during creep acts as a non‐Newtonian fluid, the viscosity of which is dependent on the creep strain. The constitutive relation between the creep strain rate and the creep strain is then utilized to estimate the viscosity and the volume fraction of the intergranular melt phase. The equilibrium creep strain to achieve grain interlocking is considered through the rotational motion of grains. Creep tests for a β‐spodumene glass‐ceramic are conducted under simple shear to generate experimental results for scrutinizing the theoretical predictions. Satisfactory agreement is observed, giving important rheological information on the creep process.

Prediction of Plane-Strain Creep-Crack Growth Using Continuum Damage Mechanics

The paper examines the possibility of using creep Continuum Damage Mechanics to predict plane strain creep crack growth in compact tension specimens using finite element based numerical methods, coupled with uni-axial and multi-axial stress laboratory creep data, and with mechanisms-based constitutive equations. The predictions of the behaviour of the compact tension specimens made using the single state damage variable equations due to Hayhurst, Dimmer, and Morrison (1984) are shown to be unable to predict that zones of damage do not grow in discrete planar regions as observed in laboratory experiments. To overcome the deficiencies of this approach, new constitutive equations have been developed, which combine the equations of Hayhurst et al. (1984) with those of Cocks and Ashby (1982), to describe the stress-state dependence of the physical mechanisms. The behaviour of the compact tension specimen determined using these new equations predicts lifetimes of the correct order and evolution of damage zones which reflect the growth of discrete cracks as observed experimentally. The paper shows that creep Continuum Damage Mechanics can be used with finite element based numerical procedures to predict creep crack growth, provided that mechanisms-based constitutive equations are used which describe the appropriate stress-state behaviour for each mechanism zone, and that continuity of mechanical properties are achieved across all mechanism boundaries.

Plane Strain Creep Behaviour of Spun-bonded Non-woven Fabrics

The creep characteristics of spun-bonded non-woven fabrics were investigated using a plane strain creep test.200mm wide samples were used. Several light weight hinged rods were spaced on the sample. These rods are fitted with pins which pierce the fabric and resist contraction during the test. The test temperature was maintained at 20±2°C.According to the test results, creep deformation characteristics varies largely with the type of fabrics. In the case of fabrics made from polypropylene, creep deformations increase rapidly as the applied stress level increase above 10 to 20 percent of the maximum tensile strength, but in the case of fabrics made from polyester, creep deformations do not increase largely below 60 percent of the maximum tensile strength.

Triaxial and plane strain creep rupture of an undisturbed clay : Campanella, RG Univ. British Columbia. Vancouver, CDN Vaid, YP Univ. British Columbia. Vancouver, CDN 10F, 25R Can. Geotech. J. V11, N1, Feb. 1974, P1–10

Triaxial and plane strain creep rupture of an undisturbed clay : Campanella, RG Univ. British Columbia. Vancouver, CDN Vaid, YP Univ. British Columbia. Vancouver, CDN 10F, 25R Can. Geotech. J. V11, N1, Feb. 1974, P1–10

Triaxial and Plane Strain Creep Rupture of an Undisturbed Clay

A comparative study of the undrained creep rupture characteristics of a saturated, normally consolidated, undisturbed marine clay has been carried out under triaxial and plane strain conditions. Creep rupture tests were performed on samples which were consolidated both isotropically and under K0 conditions to the same vertical effective stress. It is shown that for a given minimum creep rate or creep stress, large differences in rupture life are observed between conventional isotropically consolidated triaxial samples and K0 consolidated triaxial or plane strain samples. Similar discrepancies are introduced when conventional triaxial results are used to estimate remaining rupture life during tertiary creep stage when the real situation corresponds to either K0 consolidation or plane strain. Effective stress failure in creep rupture for a given type of test is governed by the same linear failure envelope which is obtained during constant rate of shear testing.

Plane strain creep behaviour of thick-walled cylinders

A range of thick-walled tubes ( 1·11⩽ diameter ratio ⩽ 10 ) operating under creep conditions is analysed for loading conditions which include internal pressure, external surface loading and inertia loading. The analysis incorporates the effects of initial elastic loading followed by stress redistribution due to creep leading to a stationary stress state. By using so-called reference stress techniques it has been possible to present all the results in compact graphical form for direct use in design for loadings applied singly and in combination. These loads may be steady or varying in proportion.

Plane strain creep and plastic deformation analysis of a composite tube

A method of analysis and associated computer program is described for the generalized plane strain analysis of transient creep and plastic deformations of composite cylinders. The material properties are permitted to vary with temperature and the axisymmetric loading conditions may vary with time. The loading may include any combination of internal pressure, external pressure, axial load and radial variation of thermal strains. Several forms of creep law are permitted including an iso-curve plastic strain law for use in obtaining certain plasticity solutions from the creep solutions.