Texture Evolution and Residual Stress Relaxation in a Cold-Rolled Al-Mg-Si-Cu Alloy Using Vibratory Stress Relief Techni
- PDF / 1,606,010 Bytes
- 13 Pages / 593.972 x 792 pts Page_size
- 94 Downloads / 182 Views
TRODUCTION
VIBRATORY stress relief (VSR) is a newly developed technology. The cost of a stimulator, the energy charge (the expense of energy consumption), and the work hours are low; the mechanical properties of the component parts are not damaged, the macro-residual stress does not reappear in later service, and VSR does not contaminate the environment.[1] VSR technique is a general term used to refer to the reduction of residual stress by means of cyclic loading treatments. Industries have employed the VSR method for reducing residual stresses.[2,3] Kwofie[4] reported that VSR may be described as a cycle-dependent stress relaxation/redistribution phenomenon occurring under vibratory loads and a nonuniform deformation phenomenon whereby different sections or regions of the material experience different cyclic stresses/strains during vibration. The question of how to optimize VSR performance has remained unanswered because of the difficulties in measuring residual stress and the unknown effects of vibration. Thus far, three theories[5–7] have been set JIA-SIANG WANG and CHI-MING LIN, Ph.D. Graduate Students, CHIH-CHUN HSIEH and CHE-WEI KUO, Postdoctoral Researchers, and WEITE WU, Professor, are with the Department of Materials Science and Engineering, National Chung Hsing University, 250 Kuo Kuang Road, Taichung 402, Taiwan, R.O.C. Contact e-mail: [email protected] Manuscript submitted May 14, 2012. Article published online October 17, 2012 806—VOLUME 44A, FEBRUARY 2013
forth: First, the use of resonant frequencies was considered most effective.[5] Then, Dawson and Moffat[6] proved that stress relief was not related to the vibrational frequency but to the amplitude. Then, Hebel[7] suggested the use of subresonant frequencies, which found commercial application in the product Meta-Lax. All the theories were based on the vibrational amplitude that can be obtained in the work piece, and amplitude was deservedly treated as the most crucial factor. The material plastic deformation theory shows the most identification. Many researchers agree that the most important parameter of VSR, the vibrational amplitude, must reach a threshold value. If vibrational amplitude is lower than the threshold value, the residual stress will not decrease. There must be microstrain on the component during VSR. Therefore, a higher shear stress will have a good effect. Then, a simple theory of bulk plastic flow, because of the combination of the residual stress with the applied stress, is often cited[8]; hereafter, this is referred to as the ‘‘standard model.’’ The standard model postulates that the stress is relieved when the combination of the residual stress and the vibrating stress exceeds the yield strength of the material; the assumption is that the subsequent plastic flow is such that when the vibrational amplitude is removed, the previously stressed area can return to a low level of residual stress. This is because the plastic deformation processes in metals are indicative of a process of dislocation movement. It has been postulated that the
Data Loading...
