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Keywords = roll-press straightening

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19 pages, 7974 KiB  
Article
Effect of Constraint and Crack Contact Closure on Fatigue Crack Mechanical Behavior of Specimen under Negative Loading Ratio by Finite Element Method
by Xinting Miao, Haisheng Hong, Xinyi Hong, Jian Peng and Fengfeng Bie
Metals 2022, 12(11), 1858; https://doi.org/10.3390/met12111858 - 31 Oct 2022
Cited by 5 | Viewed by 1891
Abstract
Mechanical behaviors at fatigue crack tips of cracked specimens under negative loading ratios are studied in detail by the finite element method in this paper. Three factors induced by specimen type and loading type on fatigue crack field are discussed, including constraint, compressive [...] Read more.
Mechanical behaviors at fatigue crack tips of cracked specimens under negative loading ratios are studied in detail by the finite element method in this paper. Three factors induced by specimen type and loading type on fatigue crack field are discussed, including constraint, compressive loading effect (CL effect) and crack contact closure. For mode I crack under negative loading ratios, the effects of the CL effect and crack contact closure on plastic strain accumulations are dominant, with the constraint effect being minor. The constraint effect has effects on the monotonous plastic zone, while the CL effect and contact closure both have effects on the reversed plastic zone (RPZ) and residual tensile plastic zone (RTPZ). That is, the higher the constraint, the smaller the size of the monotonous plastic zone; the greater the CL effect, or the smaller the contact degree, the larger the size of RPZ and RTPZ. For mode II crack, there is only CL effect on the crack tip field without the effect of constraint and contact closure, so plastic strain accumulation at the mode II crack tip is much greater than that at the mode I crack tip when they are under the same loading level. Full article
(This article belongs to the Special Issue Studies on Fatigue Behavior of Engineering Material and Structures)
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17 pages, 4223 KiB  
Article
Pure-Bend and Over-Bend Straightening Theory for In-Plane Curved Beams with Symmetrical Section and Straightening Mechanism Analysis
by Chunge Wang, Gaochao Yu, Jun Zhao and Wen Liu
Metals 2022, 12(8), 1362; https://doi.org/10.3390/met12081362 - 16 Aug 2022
Cited by 1 | Viewed by 3440
Abstract
Straightening is an important process in the production and application of shafts, tubes, and various profiles. According to the springback theory of small curvature plane bending, the pure bending process and springback of in-plane curved beam with symmetrical section were analyzed, and the [...] Read more.
Straightening is an important process in the production and application of shafts, tubes, and various profiles. According to the springback theory of small curvature plane bending, the pure bending process and springback of in-plane curved beam with symmetrical section were analyzed, and the over-bend straightening theory was established. Based on this, the straightening mechanism of the existing over-bend straightening process was revealed; that is, a zigzag straightening moment was applied in the three-point multi-step straightening process to approximate the smooth curve of theoretical moment, while the multi-point one-time straightening technology was to discretize the theoretical curve using the broken line, so both of them needed a load correction coefficient to compensate the error between the actual load and theoretical calculation. In order to realize the complete loading of theoretical curve, a new technology of three-roll continuous straightening was further proposed and the experimental equipment for shafts and tubes was built. In order to match the characteristics of a pipe section, an accurate moment calculation equation was established. Three-roll continuous straightening experiments of the tube showed that the straightness of the straightened workpiece could be controlled within 1.5‰, which meets the standard requirements. Therefore, it is suggested that the over-bend straightening theory can predict the load required for straightening in-plane curved parts with any symmetrical cross-section, and the three-roller continuous straightening process is an efficient and highly accurate straightening technique. Full article
(This article belongs to the Special Issue Plastic Forming, Microstructure, and Property Optimization of Metals)
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