BEHAVIOR OF CONCRETE ROUND DOUBLE BEAM FRACTURE TOUGHNESS TEST SPECIMENS
Laboratory fracture toughness tests of concrete using wedge-loaded round double beam specimens with a length to diameter ratio of 2:1 show two distinctly different specimen behaviors. Either the crack remains in the plane of the notch, and a valid test result can be obtained, or there is lateral cracking around mid-length which invalidates the results. Results of a controlled study show that the behavior transitions from desired to lateral cracking as the maximum aggregate size in a particular concrete increases. Two theories are proposed to explain this behavior and transition: new crack branching and crack turning. To prevent the lateral cracking behavior, two alternate testing techniques have been developed for use with the RDB specimen.
A Review of Chevron-Notched Fracture Specimens
The historical development of chevron notched fracture specimens is reviewed. Stress intensity factors and load line displacement solutions proposed for some of these specimens are compared. The original bend bar configurations up to the present day short rod and bar specimens are reviewed. The results of an analytical round robin that was conducted on chevron-notched specimens are presented. In the round robin, stress-intensity factors for either the chevron notched round rod or square bar specimens were calculated. The consensus stress intensity factor (compliance) solution for these specimens is assessed. The stress intensity factor solutions proposed for three and four point bend chevron notched specimens are reviewed.
Research on Carbon-Based Electrode Materials for Supercapacitors
As a new type of energy storage device, supercapacitors with high specific capacitance, fast charge and discharge, and long cycle life have attracted significant attention in the energy storage field. Electrode materials are a crucial factor defining the electrochemical performance of supercapacitors. The standard supercapacitor electrode materials used can be classified into three types:carbon-based materials, metal oxides and hydroxide materials, and conductive polymers. This review introduces the principles of supercapacitors and summarizes recent research progress of carbon-based electrode materials, including pure carbon materials, and the binary and ternary complex materials with carbon.