Past GDIS Presentations
Past GDIS Presentations
This presentation will summarize work of the Auto/Steel Partnership (A/SP) project, repairability of advanced high strength steels (AHSS). This project is focused on the evaluation of various weld repair processes and to provide joint test data for use by OEMs. The materials tested were MS1500, MS1700 and press-hardened steel (PHS). The team evaluated the following joining processes; resistance spot welding (RSW), metal inert gas (MIG) welding, MIG brazing and mechanical fastening. Production and service adhesives were also considered. The team utilized coupon test assemblies fabricated from various grades of AHSS. A variety of repair process joints were destructively tested. The test parameters included shear tension and cross tension quasi-static, shear tension fatigue, and cross-sections.
The resulting data can be used by OEMs to update repair process strategies using these advanced high-strength steels.
In conventional high strength steels niobium’s role is very evident: it provides grain refinement and precipitation hardening, both being the main mechanisms for strengthening such low-carbon HSLA steels. Advanced high strength steels, on the contrary, utilize a hard second phase being dispersed in a softer matrix for achieving an attractive combination of high strength and good ductility. Microstructural design on that basis has resulted in dual phase steels, complex phase steels and various forms of TRIP aided steels including 3rd generation steels. Despite that niobium initially has not been regularly alloyed to advanced high strength steels, it is nowadays widely used for optimizing their properties. Essentially, niobium is also refining the microstructure of advanced high strength steels resulting in a better homogeneity of phases, which improves bendability as well as the hole expansion ratio. Besides, niobium boosts the strength especially of the ferritic and bainitic phase by precipitation hardening. In ultra-high strength AHSS, the niobium carbide precipitates can also act as hydrogen traps and thus counteract delayed cracking. The presentation will give an overview of the so-far identified metallurgical effects of niobium in AHSS and will demonstrate the beneficial implications for processing in the mill and properties at the end user.
The Insurance Institute for Highway Safety (IIHS) has been conducting side impact crash tests since 2003. To understand how the side crashworthiness program can be enhanced, an ongoing research effort is focused on understanding the correlation between IIHS ratings and the driver death rate. In addition, the performance of good-rated late-model vehicles has been assessed in higher severity side crash tests. The objective of this study is to summarize the ongoing work and potential next steps toward developing a new crash test procedure or updating ratings criteria to further advance side crashworthiness. Analysis of real-world crashes indicates that tightening the rating criteria can potentially advance vehicle designs. Additionally, adopting a higher severity crash test may address additional real-world injury-causing crashes. Modifications to the IIHS MDB are needed for the 60 km/h test to be more representative of deformation and injury patterns caused by light truck vehicles (LTVs). This presentation will cover concluded research.
Vehicle lightweighting efforts to improve fuel economy require adequate material characterization and simulation tools to improve efficiency without compromising safety. With crash-induced deformation leading to complex stress states on the structural components, we focus the present investigation in the differences in fracture behavior of thin sheets under plane strain states of tension and bending. A numerical analysis is presented to compare the stress-strain response of VDA bending and in-plane notched tensile tests within the localized zone of deformation. The analysis suggests the significant stress state differences in bending and tension are mainly driven by the effects through the sheet’s thickness. These results offer an insight in the fundamental mechanisms contributing to the differences in fracture strain in bending and tension tests. As only one input value is possible for each triaxility level, the consequences of an apparent increase in ductility in bending (with respect to the in-plane tension) in the material characterization are discussed. The effects on the ability to reliably predict fracture in automotive crash and other large structures, commonly modelled using shell elements, are also mentioned.
Keywords: Ductile fracture modeling, material model, crash, shell mechanics, plane strain
Nearly all vehicles produced have front subframes, also referred to as engine cradles in front engine vehicles, which are considered a part of the vehicle suspension. Significant effort has been invested into reducing the mass of engine cradle assemblies. Many aluminum and aluminum/steel hybrid engine cradles are currently in production and carbon fiber prototypes have even been developed. Mass optimized steel engine cradles, on the other hand, receive less attention. Advanced high-strength steels (AHSS) are rarely used since engine cradles are primarily stiffness driven assemblies, and lightweighting manufacturing technologies, such as tailored blanks, are rarely employed. This presentation will take a closer look at mass reduction methods for optimized steel engine cradle designs and propose new lightweight steel designs with corresponding mass and cost estimates.
Use of press hardened parts in Body-In-White (BIW) structures has evolved in recent years to encompass wide range of part complexity, size and mechanical properties. In addition, the number of components per vehicle has also increased pushing demand for more capital investments. Suppliers of press hardened parts need to accommodate these changes while staying competitive. Advanced design of heat treatment furnace has to offer a unique furnace design that provides flexibility to handle future part sizes minimizes down time to increase line utilization and offers a unique solution to produce tailor tempered parts for crash performance.
This paper presents advanced innovative design of continuous roller furnace. These types of furnaces are generally used in hot forming lines. Design is focused on optimal heating layout, modern drives of rollers, new design and other items respecting the optimal technological and technical aspects. Also the technological functions like the dew point temperature regulation, oxygen rate regulation. All results are based on the theoretical background of heat and mass transfer, con-firmed by numerical Finite Element Method (FEM) analysis. Based on the long-time experiences with manufacturing and development of the machinery for the automotive industry, new roller furnaces were designed using modern methods including the FEM analyses for numerical simulations of heating processes and heating power distribution. The numerical solution of many mathematical problems involves the combination of external and internal conditions and different technological processes.
This presentation will summarize work of the Auto/Steel Partnership (A/SP) projects, Gas Metal Arc Welding (GMAW) of Advanced High Strength Steel (AHSS). This project is focused on the development and validation of 3rd Gen GMAW process for AHSS for use by the automakers. The Project Team identified (3) different AHSS grades for evaluation. Two GI coated materials were welded using gas metal arc welding techniques and the welds produced were tested using X-ray and quasi-static lap shear tensile tests. The other non-coated steels were welded using different fillers to evaluate differences in filler strength materials. Micro-hardness and metallurgical examinations were conducted to evaluate the welds. Lap tensile shear coupons for coated and uncoated steels were tested to determine tensile shear strength, fracture locations, and other weld metallurgical properties.
In general for 3rd Gen AHSS, coated steel is susceptible to Liquid Metal Embrittlement (LME). Based on observation, there is no concern under current welding procedures.
This presentation will summarize work of the Auto/Steel Partnership (A/SP) projects, gas metal arc welding (GMAW) of advanced high-strength steel (AHSS). This project is focused on the development and validation of 3rd Gen GMAW process for AHSS for use by the automakers. The project team identified (3) different AHSS grades for evaluation. Two GI coated materials were welded using GMAW techniques and the welds produced were tested using X-ray and quasi-static lap shear tensile tests. The other non-coated steels were welded using different fillers to evaluate differences in filler strength materials. Micro-hardness and metallurgical examinations were conducted to evaluate the welds. Lap tensile shear coupons for coated and uncoated steels were tested to determine tensile shear strength, fracture locations, and other weld metallurgical properties.
In general for 3rd Gen AHSS, coated steel is susceptible to liquid metal embrittlement (LME). Based on observation, there is no concern under current welding procedures.
This presentation describes a new method called generalized stress parameter (GSP) to predict fatigue life of gas metal arc weld joints (GMAW). GSP is based on the structural stress and the stress intensity factor and is based on a modified version of the Maddox equation. The structural stress accounts for the effect of global weldment geometry and the stress intensity factor captures the local effect of the weld angle and weld toe radius. Stress versus fatigue life (S-N) curve is developed using GSP and fatigue test results of various specimen configurations, material grades and thickness combinations. The developed S-N curve along with the GSP approach is used to predict the GMAW’s fatigue life of an actual OEM’s production control arm link subjected to variable amplitude loading. Laboratory tests of the above component subject to the same variable loading history are conducted. Comparison of the analysis results based on GSP and the test results revealed excellent correlation.
One of the driving principals of automotive engineering today is improving fuel efficiency thereby reducing carbon emissions. Many strategies have been implemented concurrently by the automotive OEMS such as improved aerodynamics and adopting alternative powertrains but the most widely implemented practice involves reducing vehicle mass. More than ever, innovative designs and light-weight materials are playing a significant role in enabling the engineering teams to design competitive vehicles that do not compromise performance. While offering various degrees of mass saving compared with traditional materials, rarely do these innovations integrate seamlessly into longstanding manufacturing and design practices. There are often headwinds associated with implementing new technologies. Examples of headwinds include complex manufacturing and assembly processes, additional equipment, new fastening schemes or unproven CAE modeling techniques.
MSC Smart Steel® is a new multilayer steel laminate engineered as a direct substitute for vehicle body parts stamped from low carbon steel. While offering up to a 35% mass save compared with same thickness standard steel, MSC Smart Steel® is produced as a coil, stamped in typical dies, spot welded with existing equipment and processed through standard electro-coat and paint systems – essentially minimal disruption to existing manufacturing systems. This is the first ever spot weldable low-density composite laminate to be used in a body application.
Following a five-year collaborative effort between Material Sciences Corporation and a strategic customer, MSC Smart Steel® is now validated for vehicle implementation and is going into production on multiple 2019 global platforms.
Non-Equilibrium Thermodynamic Modeling to Aid Materials Design for Quench and Partition (Q&P) Steels
In support of a scientific foundation for the predictive design of composition and processing of quench and partition (Q&P) martensite/austenite TRIP steels, theory of coupled diffusional/displacive transformation is experimentally calibrated to control austenite carbon content and its associated mechanical stability. The calibrations are based on highly accurate experimental measurements using electron microscopy, high- energy x-ray diffraction and 3D atom probe tomography to quantify the amount and carbon content of retained austenite as a function of Q&P treatment. Varying the initial quench temperature to vary the initial retained austenite amount, it is demonstrated that carbon partitioning is affected by the direction of motion of the interface, favoring greater C partitioning for BCC->FCC motion. The variation in partition temperature is shown to have the maximum effect the austenite carbon content and its stability. The influence of processing parameters and alloy composition on the final Q&P microstructural characteristics are predicted via the developed mechanistic models and validated with a new series of experimental alloys. The effect of change in the microstructural features (phase composition, phase stability) on the mechanical properties would be discussed.
Since our first application of inline robotic laser cutting on the 2019 RAM 1500 hot stamped door ring, the industry is now focused on next generation advancements in overall equipment effectiveness. New process innovations combined with robust automation solutions allow for next generation door ring laser cutting machines to have increased performance, throughput, part to part quality and process robustness. We will explore the current obstacles of laser cutting in relation to upstream and downstream processes such as the blank trimming, furnace variables, hot forming press, die changes, and touch base on theoretical solutions to overcome these process variables. There are many laser cutting avenues that compliment other value added trim processes such as near net shape, in-die trim and predeveloped holes. Finding the right balance will ensure industry best practices are used in future light weight cost effective hot stamp door ring solutions.
Steel content for automotive applications represent the fundamental building blocks that OEMs and their tier 1’s suppliers continue to rely on to meet the evolving needs of the North American auto landscape. Advanced grades of steel show no signs of slowing down with innovation in its production, forming, and applications within the vehicle. The Ducker Study builds on several past iterations to determine current content (demand Pounds per Vehicle) by grade of steel for all NA produced light vehicles as well as scenario based forecasts for materials thru 2025.
There is a growing need to efficiently and accurately characterize next generation advanced high-strength steels (AHSS) for virtual prototyping and to predict the response of automotive structural components in crash events. The focus of the present study is to consider two next generation steels of 980 and 1180 MPa strength to develop the experimental test methodology to characterize and predict the material behavior for forming and crash applications. Advances have been made in the determination of the hardening response to large strains and to predict the formability and fracture curves in stress states ranging from shear to biaxial tension with an emphasis on plane strain bending. This project is a collaboration with SMDI and Honda Research Americas and will detail the fracture characterization and methodology used in the virtual design and tooling try-outs for a full-scale 3rd Gen B-pillar for a mid-size SUV.
Three failures can be found on drawn parts in the stamping productions. One is the necking and split on the walls of the drawn part that can be predicted with the Forming Limit Diagram (FLD), another one is the necking at the tangent point of a drawn part radius that is controlled by the material n value. These two failures are all caused by the material plastic instability. The third one is the fractures of advanced high-strength steel (AHSS) on part radii when the materials are subjected to an excessive bending under tension load. The failure criterion has yet to be developed to control the issues in stamping productions. In the current study, the fracture limits of four grades of AHSS, i.e. DP590, DP780, DP980 and DP1180, were studied with a simulative 90 degree stretch bending tests and various tool radii (from 1.0mm to 14.0mm). The DIC equipment was used to measure the surface strains and determine the fracture limits. On the basis of test results, the failure criterion has been developed for the four AHSS grades in terms of the permissible tensile strains of materials when they are on different tooling radii (R/t).
AISI’s Hesham Ezzat discussed the role of steel in future mobility.
NEXMET® 1000 is a commercialized 3rd Generation AHSS innovatively developed by AK Steel. With significantly improved elongation at higher ultimate tensile strength, NEXMET® 1000 offers OEM customers a promising solution for the lightweighting goals. To demonstrate stamping formability with NEXMET® 1000, a systematic experimental analysis was conducted to generate the forming limit curves at various thicknesses. The formability was then verified with finite element simulations and through actual component stamping. Edge stretchability and its sensitivity to hole punching configurations (punch profile, cutting clearance, etc.) was evaluated with both in-plane and out-of-plane hole expansion tests. In order to understand deformation induced plasticity phenomena in NEXMET® 1000, neutron diffraction and 3D digital image correlation (DIC) techniques were utilized to measure the evolution of constituent phase transformation at different stain paths.
The continuing expansion in the application and use of advanced high-strength steels (AHSS) in automotive vehicle structures requires increased attention relative to engineering, design and manufacturing to effectively take advantage of the superior performance characteristics of these steels. Additionally, the needs for both local and global formability must be properly balanced for efficient component manufacturing along with the added consideration of in-vehicle structural performance. It has become increasingly evident that the focus on a select group of mechanical properties and manufacturing performance metrics, e.g., yield strength, tensile strength, elongation, n-value, FLD, etc., has proven inadequate for an increasing number of applications. This talk will examine the continued development direction of selected advanced steel classes, namely press hardened steel and multi-phase steels, with a focus on property optimization via microalloying techniques and associated process strategies. Novel grade classifications with improved properties for applications are proposed for adoption within the global automotive industry.
If you have feedback about the GDIS past presentation tool, please email Sarah Burns at sburns@steel.org.