Dynamic Fracture Mechanics
Covering a wide variety of topics in dynamic fracture mechanics, this volume presents state-of-the-art experimental techniques and theoretical analysis on dynamic fracture in standard and exotic materials.
TABLE OF CONTENTS Dynamic Fracture Mechanics
Chapter 4: Optical Methods For Dynamic Fracture Mechanics
Hareesh V. Tippur,
Dept of Mechanical Engineering, Auburn University,
Dept of Mechanical Engineering, Auburn University,
AL, 36849. htippur@eng.auburn.edu
In this Chapter, prominent optical interferometers that have contributed to the advancement of dynamic fracture mechanics in the recent past are reviewed. Specifically, the methods of 2-D photoelasticty, Coherent Gradient Sensing (CGS) and moire interferometry are discussed. Following a brief introduction of each method, sections on typical experimental set up, working principle and a few prominent examples of applications to dynamic fracture investigation are provided for each of these three methods.
1 Photoelasticity
Several milestones in the field of fracture mechanics in general and dynamic fracture mechanics in particular are attributed to photoelasticity. From the classical work of Post and Wells [1] that raised questions on crack tip K-dominance, Dally and coworkers' observations on K 1 ?v, v relationship [2-4], Kobayashi and Ramulu [5]'s works on dynamic crack curving to the recent Shukla and Singh's [6] observation of Mach waves near dynamically growing interfacial cracks have all one thing in common. They all have used 2-D transmission photoelasticity as the investigative tool.
The method of transmission light photoelasticity uses transparent amorphous model materials which are optically isotropic in unstressed state and become anisotropic when stressed. This optical effect, first observed by Sir David Brewster (1816), is referred to as temporary optical birefringence and is similar to permanent double refraction observed in some naturally occurring crystals. The interference fringes, commonly referred to as isochromatics, observed by this method are proportional to the maximum in-plane shear stress at...
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