A New Compression Test for Determining Free Surface Roughness Evolution in Thin Sheet Metals

Abstract

In sheet microforming processes, in-surface principal strain rates may be compressive such that the thickness of the sheet increases in the process of deformation. In general, the evolution of free surface roughness depends on the sense of the principal strain normal to the free surface. Therefore, in order to predict the evolution of free surface roughness in processes in which this normal principal strain is positive by means of empirical equations, it is necessary to carry out experiments in which the thickness of the sheet increases. Conventional experiments, such as the Marciniak test, do not provide such strain paths. In general, it is rather difficult to induce a sufficiently uniform state of strain in thin sheets of increasing thickness throughout the process of deformation because instability occurs at the very beginning of the process. The present paper proposes a compression test for thin sheets. Teflon sheets are placed between support jigs and the metallic sheet tested to prevent the occurrence of instability and significantly reduce the effect of the support jigs on the evolution of surface roughness. The test is used to determine the evolution of surface roughness in thin sheets made of C1220-O under three strain paths.

Constitutive Model of the Surface Roughening Behavior of Austenitic Stainless Steel

“…Micro-/meso-scaled parts have been widely used in electronics, automobiles, aerospace, and biomedicine in tandem with the ubiquitous trend of product miniaturization [1][2][3][4][5][6]. In this decade, the demand for micro parts has increased unabated.…”

“…Stainless steels such as SUS 304 and SUS 316 have wide applications in the micro-manufacturing industry. The estimated rise in turnover from USD 15 to 35 billion in the last seven years [1][2][3][4][5][6][7] shows a growing demand for micro technical products, which is mainly driven by the rising trend of the miniaturization of products. The demand for miniaturization comes not only from customers, who desire more handy electronic devices and more integrated functions, but also from technical applications such as medical equipment, sensor technology, and optoelectronics [3,4,8].…”

“…Mahmudi et al [18] concluded that surface roughening was caused by inhomogeneity of the material's microstructure. The degree of development in surface roughening also depended on the strain rate and the crystal structure [5][6][7][8][9][10][11][12][13][14][15]. The rotation of the crystal orientation caused by plastic strain was the factor of surface roughening in steel and aluminum sheets.…”

“…The rotation of the crystal orientation caused by plastic strain was the factor of surface roughening in steel and aluminum sheets. [6][7][8][9][10][11][12][13][14][15]. The deformation of interior crystal grains from the surface to the second layer could affect the surface unevenness in some kinds of metal [6][7][8][9][10][11][12][13][14][15].…”

“…[6][7][8][9][10][11][12][13][14][15]. The deformation of interior crystal grains from the surface to the second layer could affect the surface unevenness in some kinds of metal [6][7][8][9][10][11][12][13][14][15]. The previous studies concluded that the surface roughening should be expressed as a function of plastic strain as ∆Ra = Ce p , where ∆Ra is the increase in surface roughness, C is a constant, and e p is the plastic strain level [25][26][27][28][29][30][31][32][33][34].…”