Showing 3 results for Ductile Fracture Criteria
Yaghoub Dadgar Asl, Mohammad Morad Sheikhi, Ali Pourkamali Anaraki, Vali Ollah Panahizadeh Rahimloo, Mohammad Hosseinpour Gollo,
Volume 16, Issue 5 (7-2016)
Abstract
Today, with the development of technology, industries such as automotive and construction require products with variable cross section. Multiplicity of steps, dimensional limitation and high production costs of the components caused flexible roll forming process used to produce these products. One of the main defects in this process is the fracture phenomenon. The fracture is observed on the bending edges at transition zone that sheet thickness is large compared to the bending radius. In this research the fracture phenomenon is investigated on flexible roll forming process of channel section using ductile fracture criteria. For this purpose finite element simulation of the process using Abaqus software is done. The fracture defect in this process is investigated using six ductile fracture criteria by developing a subroutine. Experimental tests are performed on 27 specimens precut sheet of AL6061-T6, using flexible roll forming machine built in Shahid Rajaee University. By comparing simulation results with experimental results, numerical results were validated. In addition, by comparing the results of ductile fracture criteria with experimental results, the Argon ductile fracture criteria, was chosen as the most appropriate criterion to predict fracture. Also the effects of parameters as sheet thickness, bending radius and bending angle on fracture with argon selected criterion is studied.
S.j. Hashemi, F. Rahmani, S.m.h. Seyedkashi,
Volume 20, Issue 6 (6-2020)
Abstract
Incremental tube forming process is capable of manufacturing tubes with different cross sections and dimensions using simple and inexpensive forming tools. In the current study, seven different ductile failure criteria are used in finite element simulations in order to obtain the forming limit diagram (FLD) of Al6063 aluminium tubes at high temperatures. The predicted FLD using these criteria are compared with experimental data to select the optimum criterion. Standard universal tensile tests in different temperatures and strain rates along with Zener-holloman parameter are performed to calibrate the failure criteria. The effects of process parameters including temperature, forming depth and forming feed are considered. The results showed that failure criteria can predict the time and location of rupture in incremental tube forming process with a good accuracy. In high temperatures, Cockroft-Latham and normalized Cockroft-Latham criteria which consider the effect of the largest tensile stress had the best prediction. Investigation of temperature and strain rate showed that by increasing temperature, the forming limit goes higher but increasing strain rate causes to decrease it.
Hossein Mamusi, Mohammad Bakhshi Jooybari, Hamid Gorji, Ramin Hashemi,
Volume 21, Issue 4 (3-2021)
Abstract
Forming Limit Diagrams (FLDs) are very useful measures for safe forming of sheet metals without failure due to necking or fracture under different loading conditions. This paper uses ductile fracture criteria to predict the formability of low carbon steel sheets to evaluate their accuracy in predicting the FLDs. In addition, the fracture forming limit curves (FFLD) and necking forming limit curves (NFLD) for St12 low-carbon steel have been extracted experimentally and numerically. In the experimental procedure, the Nakazima stretching test was used. In the numerical procedure, by defining six phenomenological ductile fracture criteria in ABAQUS / Explicit finite element software, the failure is predicted and compared with the experimental results. These criteria were calibrated using 6 tests namely as In-plane shear, uniaxial tensile test, circle hole test, notched tension test, plane stress test, and Nakazima stretching test. The results showed that the criteria, which include both the stress triaxiality (η) and Lode parameter (L), provide a more accurate prediction of failure. Also to predict necking during numerical simulation of Nakazima test and also to extract the NFLD, three criteria of the second derivative of major strain, the second derivative of thickness strain and the second derivative of equivalent plastic strain have been used.
