Open Call case studies

Provision of innovative fracture toughness characterisation tests to European companies in the metal sector

Within the framework of the Open Call of the ToughSteel project, five European companies within the metal industry were selected as beneficiaries to receive complimentary services for characterizing metals’ fracture properties. The primary goal was to predict and prevent production losses, addressing challenges related to formability and part quality assessment.

Open Call beneficiaries included Benteler Automotive Vigo (Spain), MW Italia srl, Marcegaglia Ravenna (Italy), SSAB (Sweden), and Forvia Faurecia (France). These companies served as case studies for the ToughSteel project, showcasing how an analysis of fracture toughness can significantly improve fracture prediction during early design stages and forecast part performance. 

 

 Moreover, it empowered them to predict and manage in-service crack-related problems that conventional ductility criteria could not adequately address, as well as helped assess coil quality and make better material selections for specific components.

The selected companies received state-of-the-art fracture toughness testing services based on the Essential Work of Fracture (EWF) methodology. This approach proved highly effective in addressing cracking issues, such as edge-cracking in cold forming or crack formation during crash loading. The utilization of this approach marked significant advancements in the field of metal characterization and its practical application to industrial challenges.

 

Case studies developed

BENTELER Automotive Vigo

Fracture toughness assessment of TRIP800 coils to rationalise edge-cracking.

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Forvia Faurecia

Investigation of the Fracture Toughness of a component made of a Dual Phase steel with edge-cracking.

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Marcegaglia

Study of the correlation between material flangeability and other parameters and fracture toughness in carbon steels.

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MW Italy

Establishment of a correlation between fracture toughness and fatigue resistance automotive wheels’ Dual-Phase600 steel.

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SSAB

Investigation of the fracture toughness of hot-rolled steel grades for fine blanking applications-correlation with blanking behaviour.

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About the methodology used

Fracture toughness is a critical measure of a material’s ability to resist crack propagation and is typically evaluated using the J-integral and Crack Tip Opening Displacement (CTOD) measurements, as per the ASTM E1820 standard. While these traditional tests are suitable for assessing the fracture toughness of ductile engineering materials like advanced high strength steels (AHSSs), a simpler alternative known as the Essential Work of Fracture (EWF) methodology has gained popularity for thin metal sheets, including polymers, aluminium alloys, and steel.

Eurecat Technology Center has been actively exploring the application of the EWF method to assess fracture toughness in thin AHSS sheets and high-strength aluminium alloys. This technique has proven effective in measuring the fracture toughness of these materials, providing valuable insights into their behaviour during forming and crash situations.

The EWF methodology involves dividing the total work required to cause a fracture into two components:

  • The essential work of fracture responsible for creating two new crack surfaces
  • The non-essential plastic work, dissipated in an outer region of the fracture process zone and related to material’s plasticity.

To conduct this test on sheet metals, a set of pre-cracked double-edge notched tension (DENT) specimens are prepared. As an alternative to conventional fatigue pre-cracking procedures, Eurecat has developed an innovative tool to accelerate the process of creating these notches, streamlining specimen preparation.

Once the specimens are ready, they are tested up to fracture in tension mode, and load- displacement curves are obtained. By analysing these curves for different ligament lengths (distances between the notches), the EWF can be determined using a simple linear dataregression analysis. This calculation yields two important parameters that help assess the fracture toughness of the materials, the specific essential work of fracture (we) and the non-essential plastic work (wp), multiplied by a shape factor that depend on specimen geometry (β).

The assessment of fracture toughness holds significant value for various sectors, including transportation and companies involved in materials development, stamping, and automotive manufacturing. Understanding a material’s fracture behaviour is crucial in dealing with potential issues during various processes and along the service life of high-performance metallic products. Traditional mechanical properties may not fully describe material behaviour, but with the introduction of fracture toughness as a new parameter, the industry gains deeper insights into the behaviour of emerging materials.