Recently, hydroforming has paid dividends in composite forming due to its uniform pressure distribution, which helps in reducing the delamination defects. Considering the need to develop an appropriate criterion for evaluating the formability of FMLs, inspired by sheet metal forming and testing, the uniform pressure loading test was adopted to characterize the formability of semi-cured FMLs by forming limit curve ( FLC). In this paper, both theoretical analysis models considering and ignoring the tangential cohesive effect were established, and the stress expression of the critical zone was given. The results show that the tangential cohesive stress demonstrates a non-negligible influence on the FLC. A new form of comprehensive FLC was given by defining global equivalent strain and global strain ratio and analyzed by the finite element method. In addition, the numerical simulation model and the experimental parameters were verified. A simplified Hashin criterion was proposed and developed into the numerical simulation as a subroutine based on theoretical analysis. Parameters such as blank holder pressure, pressure rate, and temperature were considered both in experiments and simulation. Only fiber stretching damage was distinguished in the cross, single, and arc crack but no wrinkling. As predicted theoretically, a lower forming limit is expected when FMLs are subjected to greater tangential cohesive stress. Finally, with the help of numerical simulation, the influence of different boundary conditions on the comprehensive FLC was studied. Instead of a simple evaluation of FMLs, this comprehensive FLC could be used directly to optimize hydroforming processes in the engineering field.
Excellent physical and mechanical properties of fiber metal laminates (FMLs) have made them a very popular and most suitable material to make high strength and lightweight products in different industries for example automobile, military, and aerospace. Glass fiber aluminum reinforced epoxy (GLARE) is one of the most used fiber metal laminate among the family of fiber metal laminates, but there are some challenges in its formability. Our study mainly focuses on the formability of the GLARE cup parts by using hydromechanical deep drawing. Forming depth with good quality (without any wrinkling, delamination, or fracture), failure mode analysis and wall thinning rate (%) distribution of the parts are the main criteria in the formability. The influence of variable cavity pressure (VCP) with respect to punch strokes had been investigated by using numerical simulations and experiments. Results showed that the variable cavity pressure in case of increasing or decreasing the cavity pressure had very much effect on the formability. Stepwise increasing the VCP with respect to punch strokes resulted in a maximum forming depth of 29.00mm as well as good quality whereas in the case of stepwise decreasing the variable cavity pressure, results were not encouraging.Commercially available code ABAQUS explicit was used for finite element analysis simulation which had shown close agreement with the experimental results.
Excellent physical and mechanical properties of fiber metal laminates (FMLs) have made them a very popular and most suitable material to make high strength and lightweight products in different industries for example automobile, military, and aerospace. Glass fiber aluminum reinforced epoxy (GLARE) is one of the most used fiber metal laminate among the family of fiber metal laminates, but there are some challenges in its formability. Our study mainly focuses on the formability of the GLARE cup parts by using hydromechanical deep drawing. Forming depth with good quality (without any wrinkling, delamination, or fracture), failure mode analysis and wall thinning rate (%) distribution of the parts are the main criteria in the formability. The influence of variable cavity pressure (VCP) with respect to punch strokes had been investigated by using numerical simulations and experiments. Results showed that the variable cavity pressure in case of increasing or decreasing the cavity pressure had very much effect on the formability. Stepwise increasing the VCP with respect to punch strokes resulted in a maximum forming depth of 29.00mm as well as good quality whereas in the case of stepwise decreasing the variable cavity pressure, results were not encouraging. Commercially available code ABAQUS explicit was used for finite element analysis simulation which had shown close agreement with the experimental results.
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