𝒓-Value Determination with Video Type Non-Contact Extensometer (ISO 10113:2020)

User Benefits

－Related standards include ISO 10113, ASTM E517, GB/T 5027, IS 11999, and JIS Z 2254. －The video-type non-contact extensometer enables simultaneous determination of other tensile test properties as well as the 𝑟-value. －The regression method is effective for materials that exhibit inhomogeneous behavior in the plastic region, such as Al-Mg alloys.

Introduction

Thin materials like high-tension steel have been gaining attention in terms of improving fuel efficiency by reducing vehicle weight, especially in the transportation equipment industry. However, high-tension steel is prone to shape defects after press forming, posing a significant challenge in terms of time and cost required for the production of press molds. Recent advancements in computer-aided engineering (CAE) analytical techniques and the computational speed of computers have improved high-precision simulation of press forming for high-tension steel. That has enabled the prediction of the ideal shape of press-formed products, leading to substantial reductions in the development time and cost of press molds. The realization of high-precision press forming simulation requires reliable determination of the Lankford value, referred to as the 𝑟-value, which is one of the indicators representing the formability of sheet metal. The 𝑟-value serves as a quantitative indicator of the ductility of a material in the thickness direction and corresponds to the material’s drawability, which contributes significantly to press formability. In ISO 10113, revised in 2020, three different 𝑟-value determination methods have been standardized (the manual method, the semi-automatic method, and the automatic method). The automatic method uses extensometers for the gauge length and width, enabling the 𝑟-value to be determined for any given plastic strain after completion of standard metal tensile testing in accordance with ISO 6892-1. Therefore, this method is very useful for determining other tensile property values (e.g., tensile strength) at the same time. Details of each determination method and a case study of 𝑟-value determination with contact extensometers are described in a previous Application News article 1. Measurements with contact extensometers involve attaching and removing the extensometers to a test piece for each test. In contrast, TRViewX video-type non-contact extensometers achieve more convenient testing by recognizing gauge length and width values in captured images. This article describes a case study of 𝑟-value determination in accordance with the automatic method specified in ISO 10113 by using the AGX-V2 universal testing machine and a TRViewX extensometer.

March 6, 2024 GMT