Selection of the rational geometry of specimen for compression test

Abstract

The object of study in this article is the conditions during the compression test. The subject matter is the models that simulate the physical processes during the compression test. The goal is to obtain models, which allow obtaining real information about stress-strain dependence during compression. The tasks to solve are to develop a three-dimensional computer model of a specimen subjected to compression that geometry allows to avoid the nonuniform distribution of stress-strain state. The upsetting of cylindrical specimens is one of the most commonly used methods for compression tests. However, due to the frictional force on both ends of the specimen, a barreling shape is likely to appear in the middle of the cylinder during the compression process, resulting in inaccurate mechanical properties of the final measured specimens. Therefore, this paper conducts qualitative and quantitative research on the physical parameters that affect the degree of barreling during the upsetting process of cylindrical specimens. The following results were obtained. The Concave End Face (CEF)-Upsetting and Headed Specimen (HS)-Upsetting methods have a significant effect on reducing the barreling degree. The smallest difference in the barreling degree is almost close to 101.8 % that appears in the CEF-Upsetting. Further analysis shows that the above two methods have similar principles for reducing the barreling degree, and both reduce the barreling degree in the middle by increasing the deformation of the workpiece ends. Then, the influence of the deformation of the workpiece head zone on the deformation of the non-end (gauge length) zone is analyzed. The rounded corners of the transition zone between the workpiece end zone and the non-end zones of HS-Upsetting have a great influence on the generation of forming defects. The end face groove size of CEF-Upsetting has a significant effect on the barreling degree after upsetting. Under the same other conditions, the barreling degree is the smallest when the ratio of the concave depth (a/D) is 0.12, when the ratio of the concave diameter(Dc/D) doesn’t exceed 0.6, the smaller the ratio of the concave diameter(Dc/D), the smaller the barreling degree. Finally, through the design of the orthogonal test, the functional relationship between the barreling degree and the dimension parameters of the workpiece ends zone is established. Conclusions: It doesn’t prove the feasibility of barreling-less upsetting only, but also provides theoretical support for actual production in the future.

Keywords

• upsetting
• barreling degree
• compression test
• stress-strain state
• computer model
• simulation