A Method for Evaluating the Stress Corrosion Characteristics of Brittle Materials

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  • ぜい性材料の応力腐食特性を評価するための一方法
  • ゼイセイ ザイリョウ ノ オウリョク フショク トクセイ オ ヒョウカスル タ

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Abstract

A simple method for measuring the relation of stress intensity factor (KI) -crack velocity (v) of the brittle materials was studied. Pyrex glass specimens with chevron notch angle of 120° were fractured by three-point bending technique with test span of 90mm. The fracture tests were carried out under a constant cross-head speed from 0.2 to 0.001mm/min. in air with relative humidity of 50-58% or in toluene at room temperature. KI were calculated from the compliance analysis of the load-time curves of the stable fracture, and the corresponding v were measured by using a video camera with zoom up lens. The plot for logKI vs. logv in air showed the behavior of the region I that the crack growth was attributable to a stress-enhanced chemical reaction between water and glass. On the other hand, the plot in toluene showed a transition from the regions I to II that the crack growth was controlled by the rate of transport of water to the crack tip. This method has the following advantages to measure KI-v relation by three-point bending technique of ceramic samples with chevron notch: (1) the simplicity of specimen geometry, (2) small, inexpensive test specimens, (3) no precracking required for stable fracture, (4) easy measurement at high temperature because of simple compressive loading, and (5) easy environmental control. This should be, therefore, an easier method to obtain KI-v relation than Double-Torsion method etc. and serve to consider the stress corrosion and fatigue problem for ceramics at elevated temperature.

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