New correction terms concerning three-point and four-point bending tests

Lü

Advances in Mechanical Engineering

et al. 2018

The applied straightening moment and the springback after unloading with respect to the straightening process of rectangle-section metal bars have a direct influence on the straightening accuracy and efficiency. In this article, an asymmetrical hardening material model is first proposed to describe the stress-strain curves considering the asymmetrical features of yield stress and plastic hardening stage in tension and compression, and it is also compared with the traditional linear hardening material model. To accurately evaluate the elasto-plastic bending deformation and the springback in the straightening process, an analytical model for the loading and unloading moments is then established. The strain and stress distributions in elastic and plastic regions during the straightening process are also discussed in this article. Finally, the straightening experiments of rectangle-section metal bars under different heat-treated conditions are conducted on the ROSE-JZ50 straightening machine with displacement sensors, force sensors and strain gauges to validate the proposed analytical straightening model.

“…As shown in equations (10) and 12 According to the theory of stress equilibrium, the relationship between z 0 and A can be established by the following equation…”

Section: Straightening Momentsmentioning

confidence: 99%

Section: The Analytical Model Based On Straightening Pressure and Deflectionmentioning

confidence: 99%

A novel analytical model for straightening process of rectangle-section metal bars considering asymmetrical hardening features

Lü

Advances in Mechanical Engineering

et al. 2018

“…Hou et al [12] revealed the influence of punch radius on the elastic modulus, contact length and peak load of 6061 aluminum alloy. Mujika et al [13] proposed the load-displacement models of the three-point and four-point straightening processes considering the variation of contact points between the workpiece and supports. Sofuoğlu et al [14] investigated the springback behavior of the AA6082T6 tubes, including the springback level and acceleration in a three-point bending operation, considering indenter travel distance and wall thickness.…”

Section: Introductionmentioning

confidence: 99%

Variable Span Multistep Straightening Process for Long/Extra-Long Linear Guideways

et al. 2019

This paper presents a variable span multistep straightening process (VSMSP) to improve straightening accuracy and reduce the number of straightening steps for the multistep straightening of long linear guideways. It can also efficiently deal with the ineffectiveness caused by the single-step straightening process. The VSMSP adopts a sequence of three-point straightening processes with variable spans at different straightening positions. The paper presents the modeling of the behaviors of linear guideways in a straightening step and explains the use of the model to calculate the variables of the VSMSP. Key variables including span size, straightening position and straightening moment and stoke are optimized. The VSMSP and the model are validated experimentally on a straightening machine.

“…In the existing research of precise straightening, predictive models are mainly focused on the single straightening process, which is based on the assumption that the straightness of a workpiece can meet the requirement through a one-step straightening process [1][2][3][4]. The theoretical modelling approaches of the cold-straightening process include the following three aspects: bending models based on straightening curvature, bending models based on load and deflection, and analytical models based on elasto-plastic theory [5][6][7].…”

Section: Introductionmentioning

confidence: 99%

Analytical Model of a Multi-Step Straightening Process for Linear Guideways Considering Neutral Axis Deviation

et al. 2018

Abstract:The cross-sectional shape of a linear guideway has been processed before the straightening process. The cross-section features influence not only the position of the neutral axis, but also the applied and residual stresses along the longitudinal direction, especially in a multi-step straightening process. This paper aims to present an analytical model based on elasto-plastic theory and three-point reverse bending theory to predict straightening stroke and longitudinal stress distribution during the multi-step straightening process of linear guideways. The deviation of the neutral axis is first analyzed considering the asymmetrical features of the cross-section. Owing to the cyclic loading during the multi-step straightening process, the longitudinal stress curves are then calculated using the linear superposition of stresses. Based on the cross-section features and the superposition of stresses, the bending moment is corrected to improve the predictive accuracy of the multi-step straightening process. Finite element analysis, as well as straightening experiments, have been performed to verify the applicability of the analytical model. The proposed approach can be implemented in the multi-step straightening process of linear guideways with similar cross-sectional shape to improve the straightening accuracy.