Effect Of Mechanical Degradation Research Articles

304 力学的な予損傷を与えられた CrMoV 鋼におけるクリープ, 疲労き裂進展速度

The effect of mechanical degradation in a long-term-operated component on the creep-and fatigue-crack growth rates was studied. Creep-crack-growth tests and fatigue-crack growth tests were performed on creep-pre-strained and cyclic-strained CrMoV rotor-steel specimens. It was found that under constant load, creep-crack growth rates, da/dt, of the creep-pre-damaged specimens were higher than those of virgin specimens. Another result showed that fatigue-crack growth rates, da/dn, of fatigue-pre-damaged specimens were higher than those of virgin specimens. The results suggest that the creep remaining lives and fatigue remaining lives of the mechanically damaged CrMoV rotor steel can be estimated by using C^*&ΔJ of the damaged material and the da/dt and da/dn values of the virgin material.

The effect of mechanical degradation on the pyrolysis of poly(methyl methacrylate) and its copolymers

The effect of mechanical degradation in air on the thermal degradation of poly(methyl methacrylate) and its copolymers with methacrylamide and hydroxymethyl methacrylamide has been studied by pyrolysis—evolved gas—infrared analysis. It has been shown that degradation results in reduced zip length, decreased yield of monomer, and evolution of carbon dioxide, carbon monoxide, methanol and methane. These latter gaseous products can lead to erroneous interpretation and to postulation of incorrect degradation mechanisms. The results demonstrate that the effects of mechanical degradation must be considered when preparing samples for thermal degradation studies.

The Effects of Mechanical Degradation and Viscoelastic Behavior on Injectivity of Polyacrylamide Solutions

AbstractResults of recent experiments that clarify the effects of mechanical degradation and viscoelastic behavior on the flow of partially hydrolyzed polyacrylamide solutions through porous media are presented. From these results, a simple model that may be used to predict injectivity of polyacrylamide solutions is developed.Injection pressures for linear corefloods are shown to be separable into two components: (1) an initial pressure drop associated with the entrance of polymer into the sandstone and (2) a constant pressure gradient throughout the remainder of the core. Entrance pressure drop is zero until the polymer solution flux increases to the rate where mechanical degradation takes place. Thereafter, entrance pressure drop and the degree of polymer mechanical degradation increase with increasing flux. In addition, polymer solutions that undergo a large entrance pressure drop and a high degree of mechanical degradation when first injected into a core show no entrance pressure drop and no further degradation after reinjection into the same core at the same flux. These observations suggest that the entrance pressure drop is associated closely with the process of polymer mechanical degradation.A new correlation is developed that may be used to determine entrance pressure drop and the level of mechanical degradation directly as a function of sand-face flux, permeability, and porosity. This correlation is more convenient to apply and less dependent on flow geometry than previous correlations.Based on these observations, a model is developed that may be used to estimate injectivity of polyacrylamide solutions in linear or radial flow geometries. This model takes into account the entrance pressure drop and the dilatant nature of the polymer near the wellbore. Predictions made with this model are compared with experimental results.

The Effects of Mechanical Degradation on Rheological Properties of Elastomers

Abstract Several anomalies are observed in the flow of the melts of many elastomers which are not commonly observed with melts of plastics. A stress-oscillation at high rates of shear and a tendency to reach a constant level of stress at lower rates of shear are two of the more commonly encountered anomalies. Both anomalies occasionally occur in the flow of a single melt. The role of molecular weight, molecular weight distribution and branching in producing anomalous flow is demonstrated. The presence of supermolecular flow units is invoked to explain certain anomalies and supporting evidence is presented. The data strongly suggest changes in the rheological flow units take place as the conditions of shear are changed. The flow properties of many elastomers are complicated by the severe mechanical degradation taking place under these conditions of shear. Anomalous flow patterns can be either produced or removed by mechanical degradation depending upon the specific elastomer system. The extent of degradation appears to be dependent upon the flow unit governing the flow process and independent of the shearing stress or work input per unit volume of polymer sheared. The complexity and distribution of entanglements play a major role in the flow processes as well as in the mechanical degradation process of certain elastomers.