Novel Ring Compression Test Method to Determine the Stress-Strain Relations and Mechanical Properties of Metallic Materials

Although there are methods for testing the stress-strain relation and strength, which are the most fundamental and important properties of metallic materials, their application to small-volume materials and tube components is limited. In this study, based on energy density equivalence, a new dimensionless elastoplastic load-displacement model for compressed metal rings with isotropy and constitutive power law is proposed to describe the relations among the geometric dimensions, Hollomon law parameters, load, and displacement. Furthermore, a novel test method was developed to determine the elastic modulus, stress-strain relation, yield and tensile strength via ring compression test. The universality and accuracy of the method were verified within a wide range of imaginary materials using finite element analysis (FEA), and the results show that the stress-strain curves obtained by this method are consistent with those inputted in the FEA program. Additionally, a series of ring compression tests were performed for seven metallic materials. It was found that the stress-strain curves and mechanical properties predicted by the method agreed with the uniaxial tensile results. With its low material consumption, the ring compression test has the potential to be as an alternative to traditional tensile test when direct tension method is limited.

Studies on friction behaviour of aluminium AA4032 alloy during forging using ring compression test

In metal forming, friction has a negative effect on the deformation load & energy requirements, homogeneity of metal flow, quality of formed surfaces, etc.; however, its effect can be reduced through the use of proper lubricants. Mostly, in industrial applications, selection of proper lubricant for specific material is challenging and quantification of magnitude of friction at diework piece interface is essential. Hence, for metallic alloys, a realistic friction factor is needed to be known and used at the diework piece interface for better control of deformation process. Thus, this research, generally, aims at experimental investigation of the friction behavior of aluminum AA4032 alloy and selection of suitable lubricant for its effective processing using ring compression test and finite element (FE) simulations. Meanwhile, the effect of metal surface conditions and different lubricants namely palm oil, grease, emulsion oil and dry conditions on the friction behaviour has been evaluated. A commercial FEM software, DEFORM 3D, is used to analyze the flow of metal, determine the geometry changes of the specimen and generate friction calibration curves. The results revealed that the nature of metal surface and lubricating conditions have significantly affected the metal flow pattern, deformation load requirement, induced effective stress and strain, and geometry of the metal. The friction factor at die-work piece is determined for different lubricating conditions. Among lubricants employed, palm oil is found to be suitable and effective for industrial processing of aluminium AA4032 alloy, specifically for forging. The FE simulation results are in a good agreement with the experimental one.

A comprehensive damage criterion in tube hydroforming

In the present study, the Johnson-Cook damage model is proposed as a comprehensive damage criterion to predict all types of probable failures in tube hydroforming process. Also, the Johnson-Cook material model is used to predict the profile of hydroformed tubes and their dimensions. The validity of numerical results was verified using experimental results obtained in this study. Moreover, because of the importance of friction force in this process, existing between the tube and die, the friction coefficient is determined using the ring compression test, separately. The comparison of experimental and numerical results shows that Johnson-Cook damage model can predict all of the possible failures in tube hydroforming process correctly, both in terms of location and loading conditions. And this model does not predict any failure if, the tube is hydroformed perfectly. Additionally, it was cleared that the Johnson-Cook material model is a proper model to predict the profile of hydroformed tubes with remarkable accuracy. Also, it was found that the loading path and creation of a proper wrinkling have a determinative and vital role in the prosperity of the process.

FEM Simulation Analysis of Ring Compression Test Using Stationary and Rotating Die under Constant Shear Friction

The main objective of this research was to investigate the effect of friction on the behaviour of the metal flow and ring geometry, using comparisons from a stationary and rotating bottom die. This was carried out using friction calibration curves, compressive force analysis, stress and strain relationships and the reduction ratio of the ring specimen. The ring compression test (RCT) is considered one of the most reliable ways to obtain the friction factor existing in a plastic deformation process. This technique utilizes the dimensional changes of a test specimen to determine the magnitude of the friction factor. The variation of the calibration curve for the stationary die, with a range of m=0.0 to 0.9, and for the rotating die a range of m=0.1, 0.5 and 0.9. The frictional factor is calculated using FEM analysis, friction calibration and reduction ratio curves were generated from the compressive force using the DEFORM software package. The results indicated that the change in the inner diameter is related to the friction conditions and angular velocities at the die-workpiece interface.