Forming rectangular tubes into complicated 3D shapes by combining three-roll push bending, twisting and rotary draw bending: the role of the fabrication loading history on the mechanical response
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Tubular structures find wide application in the automotive context. In particular, rectangular cross-section tubes are used to fabricate structural frames via different techniques, such as Three-Roll-Push-Bending with the addition of twisting component (TRPBT) and the Rotary Draw Bending (RDB). However, whether the accumulated plastic strains, hardening and residual stresses influence the load capacity of the tubular component is still unclear. This paper is intended to shed light on this issue. The load capacity of a tubular mock-up obtained by sequential combination of TRPBT and RDB has been empirically assessed by a destructive compression test. A finite element (FE) model has been devised and validated to analyse the manufacturing processes. This work puts in light the need to correctly model the compliance of the tool set-up for Roll Bending in the numerical calculations. The final shape of the mock-up obtained by FE analysis is the input of the numerical simulation of the compression test. The present modelling has shown clearly that the global resistance of a tubular component is sensitive to plastic strains, hardening and residual stresses resulting from the previous forming processes. Taking into account these three factors greatly improves the capability of the FE to model the mechanical response of the structural part.
KeywordsThree-roll-push-bending Twisting Rotary draw bending Rectangular tubes Compression test FEM Hardening Plastic strains Residual stresses;
This work was financially supported by the Autonomous Region of Trento (Italy), within the research project SOLCO under the supervision of CRF (Centro Ricerche Fiat). The authors gratefully acknowledge BLM Group s.p.a (Cantù, CO, Italy) for performing bending tests. Furthermore we express our gratitude to Dr. Nicolò Corsentino (University of Trento) for CMM measurements and to Daniel Stimpfl for his precious contribute to the development of the FE model.
Compliance with ethical standards
This study was founded by the Autonomous Region of Trento (Italy), within the research project SOLCO. Each author declares that they have no conflict of interest and all investigations were conducted in conformity with ethical principles of research. The present work is the result of collaboration with CRF within the aforementioned research project. The company CRF has allowed this publication.
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