The following is an excerpt.

Wrinkles can be found on the surface of largely compressed areas of metallic materials. Researcher Borja Erice knows how they can evolve.

Researcher Borja Erice at SFI CASA
Before joining SFI-CASA in 2018, Borja Erice was a researcher at the Department of Engineering Science at the University of Oxford (UK). (Photos: Sølvi W. Normannsen)

Borja Erice works as a researcher at SFI CASA and is also an Academic Visitor at the University of Oxford. His primary research lines are:

  • The development of experimentally-validated numerical models and techniques for the prediction of the mechanical behaviour of advanced engineering materials under extreme conditions
  • The design and development of experimental devices and tools that allow the testing and measuring of relevant magnitudes in materials subjected to high strain rate or impact loading scenarios.

Relevant for the automotive and offshore industries

Recently, Erice gave a short lecture on his work in one of CASA´s internal seminars. The topic was wrinkles and creases, and the following is a summary in his own words:

«On the surface of largely compressed areas of metallic materials, one often finds wrinkles. This particular type of instabilities can be observed in structural elements that are relevant for the automotive and offshore industries, such as bent pipes, pressure vessels or die formed sheet metal pieces.

Wrinkles can evolve into creases by an unstable growth of self-contact when such structural elements are increasingly strained remotely.

(a) Compressed block up to a maximum of 60 % engineering strain showing contour plots of equivalent plastic strain. (b) Normalised crease length evolution for maximum compressed levels from 40 to 80 %. An x indicates when positive maximum principal stress is detected at the tip of the crease.

A Surface Crack That Might Lead to Catastrophic Failure

The onset of a crease can be detected when the self-contact length grows unsteadily, which can develop into a surface crack that might lead to catastrophic failure. Hence, this phenomenon is critical to consider in industrial applications when surface imperfections such as wrinkles are detected. Typically, for materials that present elastic-plastic mechanical responses, such as metallic materials, the critical strain at which the onset of crease occurs is quite significant

Therefore, one might need to consider that the material can develop other forms of instabilities created by inhomogeneous states. These are typically assessed performing bifurcation or imperfection analysis. In order to ascertain the underlying phenomena that might create either form of plastic instability, a finite element model of a crease formation is analysed in detail.

The Crease Formation Scenario

The crease formation scenario is simulated by compressing a rectangular solid under plane strain conditions that contains a rounded defect. The bifurcation criterion is implemented directly in a material level user subroutine allowing the detection of inhomogeneous states within a single finite element.

Results indicate that the detection of the critical strain is far from being trivial. However, the strain ranges for which instabilities are detected follow the trends observed experimentally».

From Spain to France, Switzerland, England and Norway

Before joining SFI-CASA in 2018, Borja Erice was a researcher at the Department of Engineering Science at the University of Oxford (UK). There he performed research activities related to the experimental and computational modelling development of fibre-reinforced polymers under extreme conditions

Until 2015, he worked as Postdoctoral Research Associate at the Laboratoire de Mecánique des Solides (LMS) at École Polytechnique (France). At the Department of Mechanical and Process Engineering at ETH Zürich (Switzerland), he investigated the mechanical behaviour and ductile fracture of metallic materials under high strain rates and impact loadings.

Before moving to France, he completed his PhD in 2012 at the Universidad Politécnica de Madrid (UPM, Spain) after being awarded an FPI fellowship from the Spanish government in 2008. He holds a B.Sc. in Aeronautical Engineering and M.Sc. in Materials Engineering, both from UPM.