UWE Bristol Engineering showcase 2015

David R Irvine
Bsc Engineering
Project Supervisor
Rui Cardosso
The M-K Analysis and its Accuracy at Determining Sheet Metal Ductility
Limits via Forming Limit Diagrams.
Introduction
The Forming Limit Diagram (FLD) outlines the ductility limits of a specific sheet metal in reference to the principle in plane strain
directions . These diagrams allow for designer and manufacturers alike to determine if a material or process is capable of being made.
The report for this project details the various methods of procuring the necessary data to create these diagrams along with methods to
construct the curve. A series of ABAQUS models were used to carry out numerical analysis to determine its effectiveness.
Theoretical modelling
The Marciniak-Kuczynski Model is a broadly excepted way of modelling inhomogeneity
in sheet metal it does this by creating a groove (seen right) through the model with a
different thickness to the rest of the model usually between 90% and 99% of the
original thickness . If this sheet is then subjected to a critical load the necking will
originated in this new groove area.
FLC
The forming limit curve (FLC) seen left, consists of three main sections:
• The mono axial extension where minor strain is 0 this is usual the lowest point on
the diagram
• Tensile extension the area to the left of the y axis depicting the sheet under a
stretching process and is mainly straight .
• The biaxial extension the area to the right of the y axis consists of many different
strain rates causing it to curve and depicts such things as stamping.
Project summary
This project compare d the capabilities,
accuracy and ease of creating FLDs with a
variety of methods including simulations and
physical experiment
Project Objectives
The project set out to observe the pros and
cons of each analytical method, outline the
methodology behind these processes
Project Conclusion
This project found while there are many
methods to create forming limit diagrams
some are better suited to certain situations
like deep drawing in useful when dealing
with highly plastic metals and hemispherical
punch is well suited to thin brittle sheets. FEA
solutions are great but definitely need some
kind of physical experiment behind them to
validate the strain localization location. And
assist in geometry decisions.
Press testing
The main testing method for deriving FLDs is via press testing consisting of deep
drawing experiments and punch testing. The premise of theses tests is subject a
series of test blanks of the sheet metal in question to a pressing force until the
fail. The blanks vary in shape giving the different strain paths needed to create
the forming limit curve.