Search Results for crack test

This article describes the fracture mechanics in fatigue. It discusses the fatigue crack growth rate (FCGR) testing that consists of several steps, beginning with selecting the specimen size, geometry, and crack length measurement technique. The two major aspects of FCGR test analysis are to ensure suitability of the test data and to calculate growth rates from the data. The article presents an analysis of the crack growth data. Optical, compliance, and electric potential difference are the most common laboratory techniques, and the article reviews their merits and limitations. Forced-displacement, forced-vibration, rotational-bending, resonance, and servomechanical systems for various loading conditions are also discussed.

Testing and characterization of fatigue crack growth are used extensively to predict the rate at which subcritical cracks grow due to fatigue loading. ASTM standard E 647 is the accepted guideline for fatigue crack growth testing (FCGR) and is applicable to a wide variety of materials and growth rates. The two most widely used types of specimens are the middle-crack tension and compact-type specimens. This article describes the factors affecting the selection of appropriate geometries of these specimens: consideration of material availability and raw form, desired loading condition, and equipment limitations. Various crack measurement techniques, including optical, ultrasonic, acoustic emission, electrical, and compliance methods, are also reviewed. The article discusses the two major aspects of FCGR test analysis: to ensure suitability of the test data and to calculate growth rates from the data.

Predicting the service life of structural components involves creep-fatigue crack growth (CFCG) testing under pure creep conditions. This article provides a discussion on the loading condition and the type of ductile and brittle material showing creep behavior. It focuses on a description of the experimental method that should be followed in conducting tests of CFCG with various hold times. The article describes the testing conditions, definitions, and the necessary calculations of various crack-tip parameters considered during static and cyclic loading in time-dependent fracture mechanics. The parameters considered for static loading are C*, C(t), C*(t), C*h, Ct, and Cst(t). For cyclic loading, the parameters are delta Jc and (Ct)avg. An overview of life-prediction models is also provided.