Ultimate fracture toughness through thickness engineering
The design of critical structural metallic components in the aeronautic, biomedical, nuclear or pipeline fields is often dictated by a fail-safe criterion established in the context of fracture mechanics.
The design must prevent any pre-existing crack to propagate under nominal but also sometimes accidental loads. In this context, the primary material property is the fracture toughness quantifying the resistance to crack initiation.
In ductile metals, the fracture toughness depends on plate thickness with a peak value attained at an intermediate thickness in the range of a fraction of a millimetre up to ten millimetres or more.
Although this thickness dependence is known since the 60’s, the literature is very silent regarding the peak fracture toughness value, about what sets its magnitude and about the corresponding optimum thickness.
Hence, there is no definitive rational about how to use or account for such an optimum fracture toughness in structural design. The vision of HAPI is that the fracture resistance of critical metallic structural components can be significantly enhanced by selecting and/or controlling the plate thickness for thin-walled applications and the constituent plate thickness for thick laminates.
In particular, metal laminates with optimum thickness of the constituents, selected for their high strain hardening capacity will lead to unattained levels of cracking resistance. This will require generating a range of new experimental fracture data, performing complex 3D finite element simulations relying on a rich micromechanical model with new enhancements, extending the materials selection approach, exploring the processing/assembling of novel ultra-tough metal laminates up to a radically new concept of laminate pressure vessel.
Major gains are expected on the weight of structures, potentially up to a factor five if fracture toughness is the dominating design factor, and this, without changing the chemistry or inventing new microstructures.
This project has received funding from the European Research Council (ERC) under the European Union's Horizon Europe research and innovation programme under the grant agreement number 101097433.