Advanced numerical simulation of tubes and plates hydroforming

Know to use, then know to influence. A good understanding of material behavior enables us to design high-performance mechanical structures using the right materials in the right quantities. In forming, a good understanding of materials requires the development of mechanical models capable of describing, as accurately as possible and on the relevant scale, the phenomena observed metallurgically and physically (crystallographic texture, anisotropy, elasticity, plasticity, work hardening, damage, effect of temperature). These models are intended to be implemented in calculation codes to simulate part shaping processes involving large non-reversible deformations. What's more, once the parts have been manufactured, we need to guarantee their performance and service life under complex loading.

Processes for shaping parts in metallic or composite materials have evolved considerably in recent years, boosting their use in the automotive, aerospace and other sectors. Quality, reliability and cost have become key criteria in product design.

During the shaping of solid or thin parts, materials are subjected to large irreversible deformations, with evolving frictional contact and heat transfer between parts and tools. These thermo-elasto-visco-plastic deformations often generate surface or volume micro-defects, which are born and develop in the part. The evolution of these defects leads to the creation of detectable macroscopic cracks, causing the part to be scrapped before use. They can also generate internal micro-cracks that are not easily detectable, thus jeopardizing the integrity of the part, which can lead to failure in service. It is therefore important for the designer to have an indicator capable of predicting when and where significant damage will develop during part shaping. In this way, damage can be postponed (hydroforming or forging) or, on the contrary, encouraged to appear and propagate (cutting or machining).

In order to design the optimum manufacturing range, and given the limited possibilities for experimentation (high material costs, small number of blanks, etc.), numerical simulation is essential. It enables the engineer to virtually predict the possibility of damaged areas appearing in the part during shaping, and to act on the relevant parameters to obtain a damage-free part.

In this article, following a literature review of the state-of-the-art in hydroforming processes, a damageable elastoplastic formulation is proposed to describe material behavior during finite element simulation of thin part hydroforming. As the quality of the finished part is highly dependent on the geometric and mechanical evolution of the part, there is a need to continuously update the self-adaptive discretization as a function...