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Session 1547

APPLIED FATIGUE AND FRACTURE MECHANICS: A MECHANICS COURSE FOR MECHANICAL ENGINEERING TECHNOLOGY

Michael A. Magill Purdue University

ABSTRACT The purpose of this paper is to provide an overview of a new course at Purdue University. The course is entitled “Applied Fatigue and Fracture Mechanics” and is offered by the School of Technology. This course emphasizes applied principles such as predicting failure loads on flawed structures, brittle fracture, predicting time to failure due to fatigue loading on cracked and uncracked structures, designing to prevent failure, analyzing stress corrosion cracking, and conducting ASTM standard tests. An outline of course topics and laboratory projects is included in this paper along with detailed highlights of effective course activities. This paper demonstrates that the topics of fatigue and fracture mechanics fit well with the mechanical engineering technology (MET) curriculum and the MET student.

BACKGROUND The course has two primary components: fatigue and fracture mechanics. This section provides a brief description of these two topics.

The term fatigue, in the engineering sense, means the mechanical fatigue of materials. All structural materials (i.e. metals, timber, concrete, plastic, etc.) have an inherent strength to resist loading. Under static loading these materials are very strong. Yet, much like the human body, structural materials become “tired” or fatigued from repeated loading and ultimately will fail at much lower loads. An excellent illustration of this is a coat hanger. The static force required to break a coat hanger is large but if we repeatedly bend the coat hanger back and forth it easily breaks due to material fatigue.

The other topic, fracture mechanics, is that segment of solid mechanics concerned with the failure of flawed and brittle materials. Most MET students’ understanding of mechanics is based entirely on the principles of strength of materials. Often, however, strength of materials does not accurately describe a material’s failure. Frequently, a structure will fail in a brittle manner or because of crack formation. Using the strength of materials approach for predicting structural failures, the applied stress is compared to the yield or tensile strength of the material. The fracture mechanics approach for predicting failure is similar. This approach requires quantifying the relationship between the applied stress and the flaw size. Then the result is compared with the fracture toughness of the material. In fracture mechanics the applied stress and flaw size together constitute the “loading” while the fracture toughness is the material “strength”.

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Magill, M. A. (1998, June), Applied Fatigue And Fracture Mechanics: A Mechanics Course For Mechanical Engineering Technology Paper presented at 1998 Annual Conference, Seattle, Washington. 10.18260/1-2--6922