Improvement of adhesion performance of mortar-repair interface with inducing crack path into repair

The most important performance for repair materials is adhesion to the substrate. The authors experimentally find out that high modulus fine aggregates in repair material enhance strength of it as well as the strength of the interface repaired with it, compared to the ordinary repair without fine aggregates. This paper elaborates the mechanisms for that with fractographic observation and FEM analysis based on the results of experiment. Also the authors discuss the ways for enhancing the strength and ductility of the repaired mortar.

Effects of Trace Pb on Creep and Fracture of 25Cr35Ni-Nb Alloy

The centrifugal casting 25Cr35Ni-Nb ethylene pyrolysis furnace tubes with different contents of Pb were selected to study the effects of Pb content on the creep and fracture properties. Both the high temperature rupture test at 1100 °C /17 MPa and the slow straining test at 850 °C with different loading rates show that the increase of Pb content significantly degrades the high temperature creep properties of centrifugal casting 25Cr35Ni-Nb alloy furnace tubes. The fractographic observation and the chemical composition analysis show that Pb segregates to the grain boundary at high temperature. It shows that the segregation of Pb to grain boundary occurs even when the content of Pb is several ppm, which leads to the reduction of grain boundary surface energy at high temperature. The initiation of creep cavities becomes easier. The creep cavities coalesce together under the local stress, forming cracks and finally causing the early failure of furnace tubes.

Theoretical and Experimental Investigation on Forming Limit for TNW700 Titanium Alloy

Forming limit is identified to evaluate the formability of sheet metal. The in-plane limit strains of sheets are plotted in a diagram with coordinates of major strain vs. minor strain. TNW700 titanium alloy is a high temperature resistant material. The products made of TNW700 can be used in a long serving period at 500°C, short time at 700°C. In this work, the forming limit of TNW700 will be investigated in theoretical and experimental ways. The experiment to test limit strains was carried out at 750°C under different loading paths. Marciniak – Kuczynski (M-K) model was calculated with Swift constitutive equations to predict the curves of limit strains. The effect of the groove angle on forming limit is that, the same angle on both sides of centerline determines the same FLC, and the limit points shift from left side to right side. The experiment shows that, the formability of TNW700 is not excellent, and it is lower than that of TC4 and TA15 at the same condition. The comparison shows that the curve predicted by M-K model is in a good agreement with that at plane strain, however higher than that in both sides. The fractographic observation shows that the fracture mode of TNW700 is dimple rupture.

Combined Cycle Fatigue of Ni-Base Superalloy

Fatigue life of a cast Ni-base superalloy IN 713LC under combined cycle loading consisting of a superposition of low- and high-cycle fatigue at 800 °C was experimentally determined. No measurable effect of combined cycle was found for studied loading conditions. High scatter of fatigue life related to the initiation of cracks on casting defects was observed. Size of the largest defect in a specimen was predicted by the largest extreme value distribution method. The predicted size was compared with fractographic observation of defects resulting in final fatigue failure.

Effect of Dicing Technique on the Fracture Strength of Si Dies With Emphasis on Multi-Modal Failure Distribution

The ball-on-ring (BOR) and 3-point bending (3PB) tests were used in this study to characterize the effect of dicing process on the fracture strength of Si dies. Dies prepared by a blade dicing process and a laser dicing process were studied. The edge-initiated fracture was distinguished from the surface-initiated fracture by the fractographic analysis. The fracture strength distributions related to surface flaws in the 3PB test as well as the BOR test were consistent regardless of dicing process. For the edge defect-induced failure mode, on the other hand, blade-sawn dies showed wider spread distribution than laser-sawn dies. It was due to the scattered nature in size and location of edge flaws induced by blade dicing. The laser-sawn dies showed a tighter distribution of the die strength although the average die strength was slightly lower than that of the blade-sawn dies. This work successfully demonstrated that the die failure caused by the edge defects can be deconvoluted from the 3PB test data by using the fractographic observation.

Low Cycle Fatigue Behavior of Zirconium Tube under the Cyclic Pressurization

Study was attempted to produce stress-life curve of the zirconium tube under the cyclic pressurization and to analyze its behavior. The internal pressurization machine was devised and the low cycle fatigue test at the zirconium cladding tube was carried out. The result showed that the O’Donnell and Langer relationship can be fitted to the fatigue behavior of the zirconium cladding under the cyclic pressurization, where the fatigue limit of the Zircaloy-4 at 350oC was shown at 341.6MPa. From the analysis of the diametral changes and the fractographic observation, a combined creep-fatigue interaction rather than a pure fatigue had an influence on the failure of the zirconium cladding under the cyclic pressurization at 350oC.

The Analysis on Causes of Rupture of a HP-Nb High Temperature Alloy Radiant Furnace Tube

An explosion accident occurred in a HP-Nb high temperature alloy radiant furnace tube. Twenty one lengths of furnace tubes were broken and cracked during this explosion. This paper investigates the explosion accident. The broken furnace tubes were investigated by fractographic observation and metallographic inspection and with mechanical performance test and analysis to determine the cause of the explosion. The results of the analysis indicated that the failure of the furnace tube was caused by high temperature creep. In order to determine the temperature of the furnace tube failure, some heat simulation tests from 900°C to 1200°C were carried out, the results of which confirmed that the failure of the furnace tube was primarily due to creep fracture because of the high temperature.