Abstract
The hole expansion ratio (HER) is an important material property which defines the extent of edge formability of sheet metals. The stress states observed at the hole edge after the hole expansion test are similar to those seen during traditional uniaxial tensile deformation. This observation has provoked research, directed at ascertaining a correlation between the HER and tensile properties. In order to account for the forming behaviour of complex materials like titanium, a highly robust model that takes into account the material formability in all sheet-processing directions must be considered. The R programming language was used in this research to build a model fitting expression capable of predicting the HER as well as generating a regression model equation for titanium alloys, based on their thickness and Erichsen index number. The proposed regression model equation for predicting HER of titanium alloys exhibited an excellent statistical significance (p= 0.00076), indicating the robustness of the model fitting expression to predict HER values of titanium alloys. An accompanying adjusted R squared value of 0.9987 for the generated regression model equation also shows how well the regression line fits the data for accurate prediction of the HER of titanium alloys. A numerical validation analysis of the strength of the relationship derived between the predicted and the experimental HERs gave a correlation coefficient of 0.9884. This result shows a strong linear relationship between the experimental and predicted HER values of the titanium alloys with an average absolute error of 8.8%.
Highlights
The manufacture of components for aerospace application sometimes involves the integration of hole flanging parts with other segments
The varied formability performance of the titanium grades suggests that apart from the influence of machining induced edge surface defects on the hole expansion ratio (HER), the material microstructures played an important role in the edge formability of the titanium alloys
The stress state observed at the hole edge of sheet metals after hole expansion test (HET) are synonymous to those observed during conventional uniaxial tensile testing
Summary
The manufacture of components for aerospace application sometimes involves the integration of hole flanging parts with other segments. During forming operations, the pre-fabricated holes are often exposed to different processes including stretching, bending or even wrinkling. Sheet metal edge formability is a material property which defines the ability of a sheet metal to oppose edge failure during edge forming processes. The hole expansion test (HET) is the standard experimental testing technique used to quantify the edge formability of sheet metals according to ISO 16630:2017. The hole expansion ratio (HER) defines the extent of edge formability of a sheet material. The higher the HER, the higher the edge formability of materials. For a given sheet metal with an initial fabricated hole diameter D0 prior to HET, and a final hole diameter Df at fracture after HET, the HER can be expressed as; HHHHHH
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