Structure of the tip region of a crack in an unstable material during low-cycle loading

Abstract Several technical difficulties diminish the usefulness of serum triglyceride estimation by the method of Stone and Thorp [Clin. Chim. Acta 14, 812 (1966)]. An artificial and somewhat unstable material is used in the standardization. Falsely elevated readings caused by scratched cuvettes are a frequent problem. Conventional quality-control procedures cannot be used because stable preparations are not available. Specimen stability is a greater problem than with conventional chemical methods. In spite of these difficulties, the method can be useful, if its limitations are recognized, in measurements made on nonfasting individuals.

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The Interface Microstructure and Shear Strength of Sn2.5Ag0.7Cu0.1RExNi/Cu Solder Joints under Thermal-Cycle Loading

Metals ◽

10.3390/met9050518 ◽

2019 ◽

Vol 9 (5) ◽

pp. 518 ◽

Cited By ~ 1

Author(s):

Congcong Cao ◽

Keke Zhang ◽

Baojin Shi ◽

Huigai Wang ◽

Di Zhao ◽

...

Keyword(s):

Shear Strength ◽

Fracture Mechanism ◽

Thermal Cycle ◽

Solder Joints ◽

Joint Interface ◽

Interface Microstructure ◽

Average Thickness ◽

Thermal Cycles ◽

Initial State ◽

Cycle Loading

The interface microstructure and shear strength of Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints under thermal-cycle loading were investigated with scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and physical and chemical tests. The results show that an intermetallic compound (IMC) layer of Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints evolved gradually from the scalloped into larger wavy forms with increasing number of thermal cycles. The roughness and average thickness of IMC increased with thermal-cycle loading. However, at longer thermal-cycle loading, the shear strength of the joints was reduced by about 40%. The fracture pathway of solder joints was initiated in the solder seam with ductile fracture mechanism and propagated to the solder seam/IMC layer with ductile-brittle mixed-type fracture mechanism, when the number of thermal cycles increased from 100 to 500 cycles. By adding 0.05 wt.% Ni, the growth of the joint interface IMC could be controlled, and the roughness and average thickness of the interfacial IMC layer reduced. As a result, the shear strength of joints is higher than those without Ni. When compared to joint without Ni, the roughness and average thickness of 0.05 wt.% Ni solder joint interface IMC layer reached the minimum after 500 thermal cycles. The shear strength of that joint was reduced to a minimum of 36.4% of the initial state, to a value of 18.2 MPa.

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Advanced First Core Design for the Westinghouse AP1000

Volume 5: Fuel Cycle and High and Low Level Waste Management and Decommissioning; Computational Fluid Dynamics (CFD), Neutronics Methods and Coupled Codes; Instrumentation and Control ◽

10.1115/icone17-75806 ◽

2009 ◽

Cited By ~ 4

Author(s):

Robert J. Fetterman

Keyword(s):

Fuel Cycle ◽

The United States ◽

Pressurized Water ◽

Loading Pattern ◽

The Core ◽

Low Leakage ◽

Fuel Assemblies ◽

Cycle Loading ◽

Water Reactors ◽

Under Construction

As the nuclear renaissance is now upon us and new plants are either under construction or being ordered, a considerable amount of attention has also turned to the design of the first fuel cycle. Requirements for core designs originate in the Utilities Requirements Document (URD) for the United States and the European Utilities Requirements (EUR) for Europe. First core designs created during the development of these documents were based on core design technology dating back to the 1970’s, where the first cycle core loading pattern placed the highest enrichment fuel on the core periphery and two other lower enrichments in the core interior. While this sort of core design provided acceptable performance, it underutilized the higher enriched fuel assemblies and tended to make transition to the first reload cycle challenging, especially considering that reload core designs are now almost entirely of the Low Leakage Loading Pattern (LLLP) design. The demands placed on today’s existing fleet of pressurized water reactors for improved fuel performance and economy are also desired for the upcoming Generation III+ fleet of plants. As a result of these demands, Westinghouse has developed an Advanced First Core (AFCPP) design for the initial cycle loading pattern. This loading pattern design simulates the reactivity distribution of an 18 month low leakage reload cycle design by placing the higher enriched assemblies in the core interior which results in improved uranium utilization for those fuel assemblies carried through the first and second reload cycles. Another feature of the advanced first core design is radial zoning of the high enriched assemblies, which allows these assemblies to be located in the core interior while still maintaining margin to peaking factor limits throughout the cycle. Finally, the advanced first core loading pattern also employs a variety of burnable absorber designs and lengths to yield radial and axial power distributions very similar to those found in typical low leakage reload cycle designs. This paper will describe each of these key features and demonstrate the operating margins of the AFC design and the ability of the AFC design to allow easy transition into 18 month low leakage reload cycles. The fuel economics of the AFC design will also be compared to those of a more traditional first core loading pattern.

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