Final Report: Vibratory Residual Stress Relief and Modifications in Metals to Conserve Resources and Prevent PollutionEPA Grant Number: R828737C004
Subproject: this is subproject number 004 , established and managed by the Center Director under grant R830420
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: Center for Environmental and Energy Research (CEER)
Center Director: Earl, David A.
Title: Vibratory Residual Stress Relief and Modifications in Metals to Conserve Resources and Prevent Pollution
Investigators: Hahn, William F.
Institution: Alfred University
EPA Project Officer: Klieforth, Barbara I
Project Period: September 1, 2000 through August 31, 2002
RFA: Targeted Research Center (2000) Recipients Lists
Research Category: Targeted Research
Many manufacturing processes use large amounts of energy to make useful products. One such process is the thermal stress relief (TSR) process that is widely used to reduce/modify the internal or residual stresses in parts that are introduced by other manufacturing procedures such as fabrication, machining, or assembly. The TSR process typically is done in large furnaces and is heated by the combustion of fossil fuels. The large consumption of energy, the thermal influence, and air pollution affects on the environment are the biggest concerns of this process. As an alternative to the TSR, vibratory stress relief (VSR) has the advantages of low energy consumption and dramatic reduction of pollution to the environment.
The residual stresses in parts will cause them to distort either during the manufacturing process and/or later during the useful life of the part. The widely used traditional process of thermal stress relief involves raising the temperature of the part under carefully controlled conditions several hundred degrees, holding at the high temperature until the bulk of the stresses have been removed, and then slowly cooling the part to prevent introducing new residual stresses. For some parts, this may have to be done several times during the manufacturing process. Thermal heat treatment of stress relief always results in some loss of strength in the part, some distortion during the process, and oxidation of the surface of the part. Vibratory stress modification is an alternative method for altering and/or reducing residual stresses in parts so that they do not distort during subsequent manufacturing processes and during the life of the part. VSR is accomplished by vibrating the part at a particular frequency and amplitude for a short period of time thereby using a minute amount of energy and generating a minute amount of pollution compared to the traditional heat treatment process.
To implement an alternative process, a thorough understanding of how it works and why it works must be developed. Without this understanding, it is difficult for engineers and manufacturing managers to determine when, where, and how the VSR process can be effectively applied.
The objective of this research was to develop an analytical model using Finite Element techniques to show how vibration alters the residual stress in a part in a beneficial way. The results of the analytical modeling demonstrated the reduction in residual stress in a particular part as a result of vibration.
Mr. Paul Chilcott, Dr. Donald L. Roth, members of Ms. Lin Kuang’s thesis advisory committee, Ms. Lin Kuang and Ms. Lingyu Dong, who continues to do experimental work in this area, have contributed to this research effort.
A cantilever beam model was developed in ANSYS, commercial finite element analysis software, for VSR analysis. Because of the symmetry design of the cantilever beam specimen, only half of the beam requires modeling with ANSYS. A two-dimensional model was considered because the stress introduced across the thickness of the beam was assumed uniform.
To model plastic deformation, elastic-plastic material was employed in the ANSYS model database. Aluminum 6061-T6 was selected as the material for the model. For finite element analysis, the model was meshed with linear, four-node, quadrilateral elements.
To simulate the VSR, residual stress was first introduced into the model by applying and releasing an external force on the tip of the beam. Static non-linear analysis was conducted to introduce the residual stress and calculate the resulting internal stress distribution. The relationship between the external load and tip deflection also was obtained as information for later determining the vibration amplitude.
The controlling parameters for the VSR considered were existing residual stress level, driven frequency, and excitation amplitude. These parameters were obtained from static nonlinear, modal, and harmonic analyses.
To investigate the frequency range where vibration works to relieve residual stress in parts and the driven frequencies that maximize the relief of residual stress in parts, four cases were run to compare the effect of resonance frequency and sub-resonance frequency on VSR.
The results show that the frequency producing the greatest stress relief occurs at the resonant peak (natural frequency). The reduction of residual stress after resonant vibratory treatment can attain 97 percent. Sub-resonant VSR treatments get less or no residual stress relief, depending on the frequency level applied.
Another variable investigated for VSR was the excitation amplitude to observe the effect of excitation displacement amplitude on VSR. The results show that larger excitation amplitude will produce greater stress relief.
Initial residual stress level in parts also was investigated to see its effect on VSR. Two cases were compared with different initial residual stress in the sample. The comparison results show that the part that has less initial residual stress level will get greater stress relief under the same excitation frequency and displacement amplitude.
From the above analyses, the following conclusions can be drawn:
- Finite element modeling approach can be used to predict the vibratory treatment on residual stress relief.
- Both resonant and sub-resonant vibrations can relieve residual stresses in parts. Resonant VSR produces the greatest residual stress relief. Sub-resonant VSR can get stress relief, whose effect depends on the driven frequency employed. The larger tip deflection the driven frequency produces, the greater reduction of residual stresses.
- Larger excitation amplitude produces greater residual stress relief.
- Stress reduction is greater for parts with lower level of initial residual stresses.
The VSR analysis was done with commercial finite element analysis software, ANSYS; it is a reliable tool to use for analytical modeling. The data that were input in the analysis were all standard engineering data, which included the published ANSI standard material properties. Scripts of various ANSYS analyses were enclosed at the end of the thesis document for reference.
The research work enhanced our understanding of the conditions under which VSR can produce significant reduction of residual stresses in parts. With this understanding, engineers can get expected stress reduction with appropriate environmental friendly VSR treatment, hence reducing the use of environmentally hazardous heat treatment methods.
Journal Articles:No journal articles submitted with this report: View all 1 publications for this subproject
Supplemental Keywords:thermal stress relief, vibratory stress relief, residual stress, analytical modeling, finite element analysis, ANSYS, plastic deformation, static non-linear analysis,, RFA, Scientific Discipline, INTERNATIONAL COOPERATION, TREATMENT/CONTROL, Sustainable Industry/Business, POLLUTION PREVENTION, Sustainable Environment, Energy, Technology, Technology for Sustainable Environment, Chemistry and Materials Science, Environmental Engineering, energy conservation, cleaner production, environmentally conscious manufacturing, clean technologies, green design, vibratory visual stress relief, alternative materials, thermal stress relief alternative
Progress and Final Reports:Original Abstract
Main Center Abstract and Reports:R830420 Center for Environmental and Energy Research (CEER)
Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
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