Date of Award
Spring 2011
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Mechanical Engineering
First Advisor
Weber, Ralph
Second Advisor
Fournelle, Raymond A.
Third Advisor
Stango, Robert J.
Abstract
The purpose of this dissertation is to explore the effect of cryogenic treatment on the fatigue life of compression springs. Product manufacturers are constantly searching for ways to make their products last longer. This dissertation addresses three questions: (1) What is the effect of cryogenic treatment on the fatigue life of chrome silicon steel compression springs? Does the life increase, decrease, or remain the same? (2) What is the effect of cryogenic treatment on the Percent Load Loss (Stress Relaxation) of chrome silicon steel compression springs? (3) What are the possible changes in the material that cause these effects?
The following tests were carried out; wire tensile test, hardness test, chemical analysis, residual stress, retained austenite, lattice parameter, force vs. deflection, percent load loss (stress relaxation), fatigue, microstructures, and eta carbides.
This research produced a number of key findings: (1) The cryogenically treated springs had a longer cycle life and a higher endurance limit than the untreated springs. (2) The percent load loss (stress relaxation) of the cryogenically treated springs was similar to the untreated springs. (3) The cryogenically treated springs had a higher compressive residual stress at the surface than the untreated springs.
The conclusions of this research are that the cryogenic treatment of chrome silicon steel compression springs led to an increase in compressive residual stress on the wire surface, which in turn led to an increase in fatigue life and a higher endurance limit. A recommended future study would be to compare cryogenically treated springs to shot peened springs.