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Technical Paper

Fatigue Evaluation of a Nodular Cast Iron Component

1992-02-01
920669
A ferritic-pearlitic nodular iron automobile suspension knuckle was fatigue tested in the laboratory using a constant amplitude load level that simulated a severe service condition. It was found that cracks always initiated from surface casting defects and that the fatigue life could be extended significantly by machining away the as-cast surface in the fatigue sensitive locations. Both local strain and fracture mechanics approaches were used successfully to predict the fatigue life of the component.
Technical Paper

The Effect of Nitrogen on the Mechanical Properties of an SAE 1045 Steel

1992-02-01
920667
A cold worked and induction hardened SAE1045 steel component exhibited excessive distortion after cold working and straightening, as well as cracking during straightening after induction hardening. Since the problems occurred only in certain heats of electric furnace (EF) steel, in which nitrogen content can vary widely and in some cases be quite high, and never occurred for basic oxygen furnace (BOF) steel for which nitrogen contents are uniformly low it was suspected that the source of the problem was low temperature nitrogen strain aging in heats of EF steel with a high nitrogen content. The measured distortion and mechanical properties at various stages in the fabrication process showed that while nitrogen content had no significant effect on the hot rolled steel the component distortion and strength after cold working and after induction hardening increased with increasing nitrogen content.
Technical Paper

Effect of Bead Finish Orientation on Friction and Galling in the Drawbead Test

1992-02-01
920632
This study was undertaken to examine the role of tool finish orientation on the drawing of zinc-coated steel sheets. Beads of average roughnesses of 0.1 μm and 0.2 μm, finished parallel to and perpendicular to sliding, were used in the drawbead test. Lubrication was provided by unblended base oils of 4.5, 30, and 285 mm2/s @ 40°C, used neat and with a boundary additive, 1% stearic acid. Three types of coated sheet (galvannealed, electrogalvanized, and hot-dip galvanized) were compared to bare AKDQ steel sheet. Results show that lubricant viscosity had the greatest effect on friction, while bead finish orientation and coating type influenced the nature of metal transfer and the galling of the strip. Mixed-film lubrication dominated with the medium and heavy lubricants, here contact area and friction were reduced with increasing lubricant viscosity.
Technical Paper

Tribological Factors Affecting the LDH Test

1992-02-01
920434
The present work is aimed at investigating the tribological factors influencing the LDH test. The material used was AKDQ cold-rolled bare steel, 0.82mm thick. The investigated factors included: test speed (0.833, 4.167, 6.667, and 8.333 mm/s), lubricant viscosity (4.5, 7.0, and 12.5 mm2/s), punch roughness (0.033 and 0.144 μm Ra), and test temperature (25 and 50 °C). Test speed and lubricant viscosity form a variation of the numerator of the Stribeck curve's x-axis (ηV). With ηV increasing from 4 to 120 mm3/s2 friction decreased, resulting in a 0.5 mm higher LDH. Increasing the punch roughness decreased friction producing an increase of 0.25 mm in the LDH. There appears to be an optimum roughness -- at which the roughness features act as lubricant reservoirs but the asperities do not break through the lubricant film -- resulting in minimum friction, therefore, maximum LDH.
Technical Paper

Numerical Modeling of Rear Subframe Under Different Loading Conditions

2013-04-08
2013-01-0571
In this paper, finite element methods are used to analyze the rear subframe for Chevrolet Malibu. Plasticity based material model along with dynamic and static analysis is used. Commercial software LS-DYNA is used to model the subframe. Half model for the subframe is used with the corresponding boundary conditions for our simulations. A material model based on power law is used to account for the material behavior in all simulations. Different loading conditions are used to analyze the subframe under normal driving conditions while the crash results are used to analyze the subframe under vehicle crash. This data is used to compare the performance and safety of the original stock car. A parametric study is also conducted to analyze the effect of material response by changing the material hardening properties. Results show that 1018 mild steel is the most suitable material under crash and normal loading conditions.
Technical Paper

Edge Formability and Material Characterization of Hot-Rolled Multiphase Steels

2014-04-01
2014-01-0992
New innovations in the field of advanced high strength steels (AHSS) have led to the development of steels with improved stretch-flangeability known as hot-rolled multi-phase (HR) steels. To understand the performance of HR steels, hole expansion tests were conducted on five prototype HR steels and compared with their commercial dual-phase (DP) steel equivalent. A variety of hole edge conditions were considered to study the influence of the shear-affected-zone (SAZ), the surface roughness at the sheared edge and the shear burr orientation. The microstructure of each material was characterized and discussed in relation to its formability for the different edge conditions. It was observed that the bainitic-ferrite microstructure of the HR steels showed superior formability during sheared edge stretching compared to commercial dual-phase steels.
Technical Paper

Efficient Electro-Thermal Model for Lithium Iron Phosphate Batteries

2018-04-03
2018-01-0432
The development of a comprehensive battery simulator is essential for future improvements in the durability, performance and service life of lithium-ion batteries. Although simulations can never replace actual experimental data, they can still be used to provide valuable insights into the performance of the battery, especially under different operating conditions. In addition, a single-cell model can be easily extended to the pack level and can be used in the optimization of a battery pack. The first step in building a simulator is to create a model that can effectively capture both the voltage response and thermal behavior of the battery. Since these effects are coupled together, creating a robust simulator requires modeling both components. This paper will develop a battery simulator, where the entire battery model will be composed of four smaller submodels: a heat generation model, a thermal model, a battery parameter model and a voltage response model.
Technical Paper

Weldability Improvement Using Coated Electrodes for RSW of HDG Steel

2006-04-03
2006-01-0092
The increased use of zinc coatings on steels has led to a decrease in their weldability. Weld current and time need to be increased in order to achieve sound welds on these materials compared to uncoated steels, and electrode tip life suffers greatly due to rapid alloying and degradation. In this work, typical uncoated Class II electrodes were tested along with a TiC metal matrix composite (MMC) coated electrode. Tests were conducted to study the weldability and process of nugget formation for both electrodes on HDG (hot dipped galvanized) HSLA (high strength low alloys) steels. Current and time ranges were constructed for both types of electrodes by varying either the weld current or weld time while holding all other parameters constant. Analysis of weld microstructures was conducted on cross-sectioned welds using SEM (scanning electron microscopy). Using the coated electrodes reduced weld current and times needed to form MWS (minimum weld size) on the coated steels.
Technical Paper

Effect of End-feed in Hydroforming of Straight and Pre-bent High Strength and Advanced High Strength Steel Tubes

2006-04-03
2006-01-0544
One of the major concerns preventing wider utilization of high strength steels (HSS) and advanced high strength steels (AHSS) in hydroforming is their inherent lower formability, compared to conventional mild steels. The application of the axial forces on the tube ends during a hydroforming operation is often referred to as end-feed, and can facilitate deformation of the tube by postponing failure. This research examines the effect of end-feed on the formability of HSS and AHSS tubes during hydroforming. Through simulation, straight and pre-bent tubes are hydroformed at different levels of end-feed for three materials: DDQ, HSLA350 and DP600.
Technical Paper

Monitoring the Effect of RSW Pulsing on AHSS using FEA (SORPAS) Software

2007-04-16
2007-01-1370
In this study, a finite element software application (SORPAS®) is used to simulate the effect of pulsing on the expected weld thermal cycle during resistance spot welding (RSW). The predicted local cooling rates are used in combination with experimental observation to study the effect pulsing has on the microstructure and mechanical properties of Zn-coated DP600 AHSS (1.2mm thick) spot welds. Experimental observation of the weld microstructure was obtained by metallographic procedures and mechanical properties were determined by tensile shear testing. Microstructural changes in the weld metal and heat affect zone (HAZ) were characterized with respect to process parameters.
Technical Paper

Evaluation of Automobile Fluid Ignition on Hot Surfaces

2007-04-16
2007-01-1394
Automobile fires are a serious concern to manufacturers and consumers. However, understanding how the fires begin, in the confines of the engine compartment, is a difficult task. One known cause of fires is hot surface ignition (HSI) arising when engine fluids contact hot surfaces in the engine compartment or the exhaust train. In this study, the ignition of automotive gasoline on four hot surfaces: stainless and carbon steels from the heat shields, stainless steel from the exhaust manifold and cast iron cut from an intake manifold, was examined in a well-controlled, model study. Infra-red thermography and thermocouples were used to monitor surface temperatures prior to, during and after the fluid impacted the surface. This allowed evaluation and comparison of temperature evolution during fluid impact and the ignition event, resulting in an improved mechanistic understanding of the fluid/hot surface interaction.
Technical Paper

Effect of Endfeed on the Strains and Thickness During Bending and on the Subsequent Hydroformability of Steel Tubes

2003-10-27
2003-01-2837
This research examines the effect of endfeed on the thickness and strains during bending of steel tubes. The tubes were bent using an instrumented rotary draw tube bender and subsequently hydroformed into a diamond-profile outside corner fill die. DQAK tubes with an OD of 76.2 mm and a thickness of 1.55 mm were investigated. Endfeed during bending was found to have a significant effect on the thickness and strains within the tube after bending, and numerical models that were generated showed good agreement with the experimental data. It is shown how slight changes in thickness can cause localized failure during hydroforming, and how excessive die clearances can cause large strains in undesired areas.
Technical Paper

Static and Dynamic Denting of Paint Baked AA6111 Panels: Comparison of Finite Element Predictions and Experiments

2001-10-16
2001-01-3047
This work presents comparisons of finite element model predictions of static and dynamic denting with experimental results. Panels were stamped from 0.81, 0.93 and 1.00mm AA6111-T4 and then paint-baked to produce representative automotive outer body panels. Each type of panel was statically and dynamically dented at three locations using a 25.4mm steel ball. Static denting was accomplished with incremental loading of 22.24N loads up to a maximum of 244.48N. Dynamic denting was accomplished by dropping the steel ball from heights ranging from 200mm to 1200mm. Multi-stage finite element analysis was performed using LS-DYNA1 and ABAQUS2 to predict the entire process of forming, spring-back, denting and final spring-back of the dented panels. The predicted results show good correlation with the experiments, but also highlight the sensitivity of the predictions to formulation of the finite element problem.
Technical Paper

Damage and Formability of AKDQ and High Strength DP600 Steel Tubes

2005-04-11
2005-01-0092
Using standard tensile testing methods, the material properties of AKDQ and DP600 steels tubes along the axial direction were determined. A novel in-situ optical strain mapping system ARAMIS® was utilized to evaluate the strain distribution during tensile testing along the axial direction. Microstructural and damage characterization was carried out using microscopy and image analysis techniques to compare the damage evolution and formability of both materials. Failure in both steels was observed to occur via a ductile failure mode. AKDQ was found to be the more formable material as it can achieve higher strains, total elongations and thinning prior to failure than the higher strength DP600.
Technical Paper

Fatigue Life Prediction for Variable Amplitude Strain Histories

1993-03-01
930400
This paper presents a model for fatigue life prediction for metals subjected to variable amplitude service loading. The model, which is based on crack growth and crack closure mechanisms for short fatigue cracks, incorporates a strain-based damage parameter, EΔε*, determined from the effective or open part of a strain cycle along with a fatigue resistance curve that takes the form: EΔε* = A(Nf)b, where E is the elastic modulus, Nf is the number of cycles to failure, and A and b are experimentally determined material constants. The fatigue resistance curve is generated for a SAE 1045 steel and the model is used successfully to predict the fatigue lives of smooth axial specimens subjected to two variable amplitude strain histories. The model is also used to predict the magnitude of non-damaging cycles that can be omitted from the strain histories to accelerate fatigue testing.
Journal Article

Predicting Failure during Sheared Edge Stretching Using a Damage-Based Model for the Shear-Affected Zone

2013-04-08
2013-01-1166
Hole expansion of a dual phase steel, DP600, was numerically investigated using a damage-based constitutive law to predict failure. The parameters governing void nucleation and coalescence were identified from an extensive review of the x-ray micro-tomography data available in the literature to ensure physically-sound predictions of damage evolution. A recently proposed technique to experimentally quantify work-hardening and damage in the shear-affected zone is incorporated into the damage model to enable fracture predictions of holes with sheared edges. Finite-element simulations of a hole expansion test with a conical punch were performed for both a punched and milled hole edge condition and the predicted hole expansion ratios are in very good agreement with the experiment values reported by several researchers.
Journal Article

The Influence of the Through-Thickness Strain Gradients on the Fracture Characterization of Advanced High-Strength Steels

2018-04-03
2018-01-0627
The development and calibration of stress state-dependent failure criteria for advanced high-strength steel (AHSS) and aluminum alloys requires characterization under proportional loading conditions. Traditional tests to construct a forming limit diagram (FLD), such as Marciniak or Nakazima tests, are based upon identifying the onset of strain localization or a tensile instability (neck). However, the onset of localization is strongly dependent on the through-thickness strain gradient that can delay or suppress the formation of a tensile instability so that cracking may occur before localization. As a result, the material fracture limit becomes the effective forming limit in deformation modes with severe through-thickness strain gradients, and this is not considered in the traditional FLD. In this study, a novel bending test apparatus was developed based upon the VDA 238-100 specification to characterize fracture in plane strain bending using digital image correlation (DIC).
Technical Paper

Crack Initiation and Propagation Fatigue Life Prediction for an A36 Steel Welded Plate Specimen

2019-04-02
2019-01-0538
Fatigue crack initiation and propagation models predict the fatigue life of welded "T" specimens tested by the Fatigue Design and Evaluation (FDE) Committee of SAE under constant and variable amplitude load histories. The crack propagation equations stipulated by British Standard BS-7910 have been incorporated in a material memory model for cyclic deformation. The simulations begin with the crack initiation model and show how it is used to account for cyclic mean stress relaxation and the effects of periodic overloads. After the cracks initiate the BS-7910 model is applied to predict the crack advance due to either constant or variable amplitude histories. Simulation results correspond to the experimental results with good accuracy.
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