Identification of material parameters to predict Single Point Incremental Forming forces

in International Journal of Material Forming (2008)

The purpose of this article is to develop an inverse method for adjusting the material parameters for single point incremental forming (SPIF). The main idea consists in FEM simulations of simple tests ... [more ▼]

The purpose of this article is to develop an inverse method for adjusting the material parameters for single point incremental forming (SPIF). The main idea consists in FEM simulations of simple tests involving the SPIF specificities (the “line test”) performed on the machine used for the process itself. This approach decreases the equipment cost. It has the advantage that the material parameters are fitted for heterogeneous stress and strain fields close to the ones occurring during the actual process. A first set of material parameters, adjusted for the aluminum alloy AA3103 with classical tests (tensile and cyclic shear tests), is compared with parameters adjusted by the line test. It is shown that the chosen tests and the strain state level have an important impact on the adjusted material data and on the accuracy of the tool force prediction reached during the SPIF process. [less ▲]

Elasto-plastic material parameter identification by inverse methods: sensitivity matrix calculation

in Proceedings of the SEM annual conference and exposition 2006 (2006)

Inverse methods offer a powerful tool for the determination of the elasto-plastic material properties. Contrary to standard tests, these methods can deal with heterogeneous stress and strain-fields which ... [more ▼]

Inverse methods offer a powerful tool for the determination of the elasto-plastic material properties. Contrary to standard tests, these methods can deal with heterogeneous stress and strain-fields which have a larger information contents and hence allow the simultaneous identification of several material parameters. Moreover, it is expected that the obtained material parameters are more accurate, since these heterogeneous deformation fields are much closer to those occurring in real (metal) forming operations. The principle of the inverse method for the identification of material parameters presented in this paper is to compare an experimentally measured strain field to that computed by a Finite Element (FE) model. The material parameters in the FE model are iteratively tuned in such a way that both strain fields match each other as close as possible. One of the building blocks in this identification procedure is the updating algorithm for the material parameters in the FE model. The key problem of this updating algorithm is the determination of the sensitivity matrix, which expresses the sensitivities of the strains with respect to the material parameters. This paper presents an analytical method for the calculation of this sensitivity matrix in case of simple tensile tests. [less ▲]

Quality assessment of speckle patterns for digital image correlation

in Optics & Lasers in Engineering (2006), 44(11), 1132-1145

Digital image correlation (DIC) is an optical–numerical full-field displacement measuring technique, which is nowadays widely used in the domain of experimental mechanics. The technique is based on a ... [more ▼]

Digital image correlation (DIC) is an optical–numerical full-field displacement measuring technique, which is nowadays widely used in the domain of experimental mechanics. The technique is based on a comparison between pictures taken during loading of an object. For an optimal use of the method, the object of interest has to be covered with painted speckles. In the present paper, a comparison is made between three different speckle patterns originated by the same reference speckle pattern. A method is presented for the determination of the speckle size distribution of the speckle patterns, using image morphology. The images of the speckle patterns are numerically deformed based on a finite element simulation. Subsequently, the displacements are measured with DIC-software and compared to the imposed ones. It is shown that the size of the speckles combined with the size of the used pixel subset clearly influences the accuracy of the measured displacements. [less ▲]