AISI Convenes Fracture Symposium II

April 13, 2020 -- Southfield, MI

Summary: Technical presentations from the symposium stimulated a dialogue emphasizing that fundamental research can only be accomplished through a collaborative effort among all industry partners, academic institutions, and government agencies. Real life examples underscored the marked improvement in proposed experimental and analytical techniques to allow automakers to fully leverage existing and emerging steel grades. There is clearly a need to validate methods, through real life component testing, to confirm accuracy and consistency.

The American Iron and Steel Institute (AISI) Automotive Program convened the second Advanced High Strength Steel (AHSS) Fracture Symposium in February of this year in Southfield, MI. The symposium was designed to share important research updates among the automotive supply and manufacturing community, supported by various Auto/Steel Partnership (A/SP) teams, namely: Fracture Prediction, Nonlinear Strain Paths, and Steel Testing and Harmonization. More than 50 engineers and scientists representing automakers, steel members, partnering universities and the National Institute of Standards and Technology (NIST) attended with a goal of stimulating an open dialogue aimed at collaboratively tackling challenges associated with testing and simulation of AHSS grades used in automotive body and chassis subsystems.

Reliable and repeatable formability and crash simulations aided by accurate material models will enable the design of AHSS automotive components with the desired properties, at minimum cost, and reduced development time. Additionally, more reliable crash simulations and formability predictions will encourage automakers to increase their use of AHSS grades in body and chassis components and assemblies by reducing the risk of forming and crash performance issues, thus enabling automakers to produce more mass-efficient, high-performance designs within the boundary of existing manufacturing processes.

Conventional analytical practices currently used to predict formability and crash performance rely on the interpretation of well-known standard testing to define material failure criteria and generate the necessary material constitutive and fracture characterizations used as input to commercially available analysis programs. Up until recent times, these established criteria were widely used to predict failure under forming and service loads, albeit conservatively. The shift within the industry towards incorporating more AHSS and ultra-high strength steel (UHSS) grades, including third generation steel grades, in order to engineer mass optimized, cost effective automotive body and chassis structures rendered these failure criteria inadequate and drove the need for updated material test procedures and material models to accurately predict the performance of these new and emerging steel grades.

The Symposium featured a collection of technical presentations that addressed a wide spectrum of topics including: fracture models for dual phase AHSS grades under nonlinear loading histories, formability and fracture characterization of 3rd Gen AHSS grades, effects of the initial microstructure and strain rate on fracture of hot stamped steels, prediction of failure within resistance spot weld groups under tensile and shear loading in press hardened steels, a comprehensive review of Digital Image Correlation (DIC) testing, and a discussion of local formability and fracture in tight radius bending for crash applications. The common focus among all speakers was on the development, implementation, and validation of more realistic constitutive and failure models for AHSS and UHSS grades expected to more reliably predict the outcome of the highly complex nonlinear deformations intrinsic to the manufacture and performance of automotive sheet metal components.

The presentations stimulated a productive dialogue around the viability of proposed test procedures and analytical models, and interpretation of their results to accurately characterize large deformation and fracture behavior of different steel grades. Real life examples underscored the marked improvement in these proposed experimental and analytical techniques to allow automakers to fully leverage the capability of existing and emerging steel grades. The dialogue also pointed to the considerable amount of work which remains ahead to be able to standardize these experimental and analytical methods and ensure their broad applicability across different grades and complex stress states. The need to validate such methods, through real life component testing, to confirm accuracy and consistency was also underscored during the general discussions.

A key take-away agreed upon by all attendees was that such fundamental research can only be accomplished through a collaborative effort among all industry partners, academic institutions, and government agencies.

Speakers representing A/SP along with General Motors, Honda R&D Americas, University of Waterloo, NIST who shared research updates and insights made it a successful day of productive conversation and collaboration.

For more information about this and other research please visit www.AutoSteel.org.