| There are several basic forming modes of stamping. Among them stretching is an important one. The desired formability levels should be specified so that the quality control of materials and products can be made. In stretching, formability depends on forming limit strains and strain distribution uniformity. The limit strains are sensitive to stress state and are represented best by a forming limit curve (FLC) which indicates the onset of plastic instability over all possible combinations of strains in the sheet plane and is a diagnostic tool of failure analysis in the press shop. This, in turn, makes the understanding of strain distribution the key to realistic studies.;To determine the strain distribution, a common used method was incremental loading and unloading tests which could show the development of strain concentration and eventual instability and fracture. The approach was however tedious and time consuming. Also the specimens were susceptible to strain aging. The experimental methodologies of material characterization for formability were not developed far enough to catch up with the advances in sheet forming technology. In addition, through an intensive review of literature it was found that the generally accepted theories which completely describe the way in which the sheet metal ruptures under biaxial tension are needed. The existed ones were not satisfactory.;Improvement of the test methodologies and the analysis is essential so that an additional work is needed, especially for the materials widely used such as aluminum alloys.;This program was carried out to update the tedious approaches of obtaining strain distribution in punch stretching to a computerized, non-interrupted and fast testing system using an optical sensing of the deformation in the previously imposed grid lines. With the monitoring and controlling of the computer, FLC's were constructed. Besides the experimental work, a model to compute the strain distribution and to relate it to the die load was developed. The computational strain distribution will be a helpful tool for formability analysis.;The experimental and computational studies were used to predict the failure of products by determining the critical values of strains of aluminum alloys and mild steel. Test result proved that the experimental setup is an efficient and accurate tool for studying and determining the important parameters controlling the formability of materials. Analytical results were in good agreement with the experiment ones. |
