Overview on the Prediction Models for Sheet Metal Forming Failure: Necking and Ductile Fracture
37
Citation
146
Reference
10
Related Paper
Citation Trend
Keywords:
Necking
Forming limit diagram
Necking
Forming limit diagram
Tensile testing
Strain (injury)
Cite
Citations (22)
Forming limit diagram
Necking
Tola
Deep drawing
Cite
Citations (27)
Necking
Forming limit diagram
Cite
Citations (37)
This paper is concerned with the anisotropy effect on the stress-based fracture forming limit diagram using a modified Lou-Huh ductile fracture criterion. In sheet metal forming process, a usage of advanced high-strength steels (AHSSs) has been remarkably increasing for the lightweight car body and good formability. It is, however, unable to evaluate the formability of AHSS with the conventional forming limit diagram during complex forming processes since it is obtained by assuming the proportional loading path and AHSS shows sudden fracture involving little amount of necking. The stress-based fracture forming limit diagram was constructed using a modified Lou-Huh ductile fracture criterion in order to evaluate the formability of AHSS accurately. The anisotropy effect on the fracture strain is also evaluated to reflect the material behavior of sheet metals in constructing the criterion for the prediction of onset of the fracture. The constructed stress-based fracture forming limit diagrams deal with the stress state ranging from pure shear to equi-biaxial tension with the variation of orientation of sheet metals. It is clearly observed that the stress-based fracture forming limit diagrams are varied with the change of orientation of sheet metals.
Forming limit diagram
Necking
Cite
Citations (1)
: Sheet metal forming is defined as the ability of metal to deform plastically (deformation by Stretching or drawing) or changing the shape of the sheet into a new desirable shape with out necking or crack . To control the operation of sheet metal forming with out failure. A diagram is used in which the range accepted , failure and critical deformation range are shown . This diagram is known as the Forming limit diagram. It is considered as one of the important tool to determine the formability of sheet metals. Every sheet metal has its own forming limit diagram which determines its formability, strain limit and the forming regions. These diagrams can be assessed using theoretical and experimental approaches, In this paper, the FLD is determined using different yield criteria Hill1948, Hosford1979 and modified Hosford 1985. It is shown that the determination of forming limit curve using the modified Hosford 1985 criterion with the (M-K) analysis , gave the best results compared with the other used criteria .Using this criterion gave the closest forming limit curve to that obtained experimentally, but with different criterion index for different alloy . The value of the index (a=6) gave the best results for brass, while (a=8) gave the best results for aluminum alloy and mild steel.
Forming limit diagram
Necking
Brass
Tola
Cite
Citations (4)
One of the main issues in sheet metal forming operations design is the determination of formability limits in order to prevent necking and fracture. In fact, the ability to predict fracture represents a powerful tool to improve the production quality in mechanical industry. Many researchers investigated the problem here addressed, mainly studying forming limit diagrams (FLD) or developing fracture criteria which are able to foresee fracture defects for different processes. In this paper, the author present some early results of a research project focused on the application of artificial intelligence (AI) for ductile fracture prediction in sheet metal forming operations. The main advantage of the application of AI tools and in particular, of artificial neural networks (ANN), is the possibility to obtain a predictive tool with a wide applicability. The prediction results obtained in this paper fully demonstrate the usefulness of the proposed approach.
Necking
Forming limit diagram
Cite
Citations (2)
Necking
Forming limit diagram
Deep drawing
Incremental sheet forming
Tensile testing
Cite
Citations (4)
Abstract A forming limit diagram (FLD) illustrates the behavior of sheet metal under different levels of strain. The line describing the behavior of the metal is called forming limit curve (FLC). Forming limit diagram provides information on the maximum stress the metal can undergo before fracturing or necking. The diagrams are constructed by using forming limit test of sheet metal and measuring the deformation. In this study, formability of AISI 1020 sheet metal with different thickness were investigated using experimental data obtained from forming limit test. Forming limit diagram, strain hardening exponent (n) and height of cup values have been obtained for evaluating formability of the studied material. After each test, deformation of the grid was measured by using Mylar band and the true major and true minor strains were computed. Same formability results have been found from the FLD, strain hardening exponent and height of the cup for studied materials.
Forming limit diagram
Necking
Strain hardening exponent
Hardening (computing)
Cite
Citations (1)
The sheet metal forming process is the process of deforming the sheet metal into a desired shape without fracture or excessive localized necking. Variables in sheet metal forming process can be discussed together with formability and test methods. There are many defects occurring during sheet metal forming processes, such as cracking, wrinkling, local necking, buckling etc. The strain measurement in a deformed sheet metal is necessary for measurement comparison. As the thickness of sheet metal is very small as compare to other dimensions of the sheet metal, the sheet metal operation is usually considered as a plane stress problem. The Forming Limit Diagram (FLD) was also determined from surface strain measurement. The FLD is the graph between major strain (℮1) and minor strain (℮2). The Forming Limit Curve (FLC) or the Forming Limit Diagram (FLD) is useful concept for characterizing the formability of sheet metal, which reflects the maximum principal strains that can be sustained by sheet materials prior to the onset of localized necking. Generally there are three methods to establish FLD i.e. theoretical, numerical and experimental. In this paper experimental method is used to develop FLD. For experimental determination of FLD of Mild Carbon steel sheet Limit Dome Height testing is used according to the American Society of Testing Material (ASTM) as published in ASTM E 2218-02. In this paper the procedure of grid marking, punch stretching and strain measurement is used. For punch stretching operation the set up of spherical die and punch has developed on the hydraulic Universal Testing Machine (UTM). The material used for the die and punch is High Carbon High Chromium Steel (HCHCr). For printing the grids on sheet material chemical etching method is used. In this grid making process grids of 5 mm diameter circles printed. For trial experiment the sheet metal sample is stretched at the force of 23 KN. The deformed circles were converted into ellipse and from that deformed ellipse major and minor strains are to be calculated. After that the FLD will give the two different regions of safe and failure zone.
Necking
Forming limit diagram
Tola
Deep drawing
Plane stress
Carbon steel
Hydroforming
Cite
Citations (14)