STP711: A Dynamic Photoelastic Study of Crack Propagation in a Ring Specimen

    Dally, JW
    Dean, College of Engineering, University of Rhode Island, Kingston, R.I.

    Shukla, A
    Research assistant and associate professor, Photomechanics Laboratory, Mechanical Engineering Department, University of Maryland, College Park, Md.

    Kobayashi, T
    Research assistant and associate professor, Photomechanics Laboratory, Mechanical Engineering Department, University of Maryland, College Park, Md.

    Pages: 17    Published: Jan 1980


    Abstract

    Crack propagation in a thick-walled ring specimen subjected to a mechanically simulated thermal stress was investigated by employing dynamic photoelasticity. Ring models fabricated from Homalite 100 were loaded with a specially designed mechanical deformeter which separated and rotated a slit cut into the ring to produce a combination of tension and bending that simulated a steady-state thermal stress.

    Short starter cracks were machined into a series of ring models and the deformeter adjusted to give KQ/K1m ranging from 1.2 to 3.0. The crack was initiated and high-speed photographs of the isochromatic fringe loops at the tip of the running crack were recorded. The data were analyzed to obtain the instantaneous stress-intensity factor K, the normalized crack position a/w, and the crack velocity ˙a.

    The relation between K and ˙a was established for Homalite 100 using the ring specimen. It was noted that this K-˙a relation compared well with those determined previously using single edge notch, rectangular double cantilever beam, contoured double cantilever beam, and modified compact tension specimens.

    A comparison of K, as a function of position a/w, was made between static and dynamic crack growth. A marked difference was noted. For static crack growth, K increases with a/w until a/w = 0.2 and then decreases with further crack extension. For dynamic crack growth, K decreased monotonically with increasing a/w.

    Keywords:

    dynamic photoelasticity, fracture, thermal stresses, mechanical deformeter, ring specimen, high-speed camera, stress-intensity factor, dynamic crack propagation


    Paper ID: STP27446S

    Committee/Subcommittee: E08.05

    DOI: 10.1520/STP27446S


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