Mechanical Engineering ETDs

Publication Date

5-28-1965

Abstract

The investigation deals with certain aspects of wave propagation in a rod containing a penny-shaped cavity, particularly fracture related to the presence of the cavity. When a rod containing a cavity is subjected to a compressive stress pulse, part of the pulse is transmitted past the cavity and part is reflected. When the end of the rod is free, the cavity is subjected to a reflected tensile pulse which, if strong enough, can cause fracture. The existence of the cavity tends to weaken the rod since there is a reduction in the cross-sectional area and a stress concentration effect. Epoxy models were built to experimentally investigate the gross effects of the cavities (i.e., the reflected and transmitted pulses), and an analytical study, based upon Donnell's elementary theory, was developed to explain the observed phenomena The strain fields around the cavities were partially measured by the use of electrical resistance strain gages embedded in the vicinity of the cavities. The gross effects and strain fields were studied for three cavity sizes and three locations of the cavities relative to the free end. Nine fracture models were built (one for each cavity size and cavity location) and loaded to failure to determine the nominal in ident pulse required to produce fracture. In order to produce pulses of sufficient magnitude to produce fracture, an explosive loading technique was developed. The results of the gross effects study indicated that most (90% or more) of each pulse was transmitted past the cavities and little (less than 20%) was reflected. The study of the strain field indicated that very close to the corners of the cavities the principal direction of strain rotates 10° to 20° toward the axis of revolution. The fracture tests indicated that the location of the cavity relative to the free end had little effect on the fracture strength. With increasing cavity size, the incident peak strain necessary to produce fracture decreased. However, if the strain levels were corrected for the reduced area at the cavity section, most of this variation was eliminated.

Degree Name

Mechanical Engineering

Level of Degree

Masters

Department Name

Mechanical Engineering

First Committee Member (Chair)

Frederick Dsuin Ju

Second Committee Member

Richard Charles Dove

Third Committee Member

Unknown

Document Type

Thesis

Language

English

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