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The term “productivity” all too often has becomes a buzz-word, ultimately diminishing its perceived importance. However, productivity is the major concern of any team, and therefore must be defined to gain an appropriate understanding of how a system is actually working. Here, productivity means the level of contribution to the throughput of a system such as defined in the Theory of Constraints. In the field of space exploration, the throughput is the number of milestones of the mission accomplished as well as the potential survival during extreme events (due to failures or other unplanned events). For a time tasks were accomplished by expert individuals (e.g., an astronaut), but recently team structures have become the norm. It is clear that with increased mission complexity, “no single entity can have complete knowledge of or the abilities to handle all matters” [10].

Edge stretchability reduction induced by mechanical trimming is a critical issue in advanced high strength steel applications. In this study, the tooling effects on the trimmed edge damage were evaluated by the specially designed in-plane hole expansion test with the consideration of three punch geometries (flat, conical, and rooftop), three cutting clearances (6%, 14%, and 20%) and two materials grades (DP980 and DP1180). Two distinct fracture initiation modes were identified with different testing configurations, and the occurrence of each fracture mode depends on the tooling configurations and materials grades. Digital Image Correlations (DIC) measurements indicate the materials are subject to different deformation modes and the various stress conditions, which result in different fracture initiation locations.

Edge stretching performance was assessed with the conical-punch hole expansion test for a variety of automotive sheet steels. Included were: an ultra-low carbon IF steel, a dual-phase advanced high strength steel (DP 980), an austenitic stainless steel (204), an annealed martensitic stainless steel (410 AN), and a ferritic stainless steel (429 MOD). Various hole fabrication methods were considered: conventional piercing (shearing), water-jet cutting and laser cutting. With pierced holes, no effect of shearing clearance on the hole expansion ratio (HER) was observed. The dual-phase steel and the austenitic stainless steel exhibited relatively low hole expansion performance in the pierced-hole condition (HER ≤ 50%). However, these materials demonstrated tremendous potential for improvement with alternative edge preparation methods, and both benefitted more from laser cutting than from water-jet cutting.

In this study we consider the coordinated exploration of an unfamiliar Martian landscape by a swarm of small autonomous rovers, called Swarmies, simulated in a distributed setting. With a sustainable program of return missions to and from Mars in mind, the goal of said exploration is to efficiently prospect the terrain for water meant to be gathered and then utilized in the production of rocket fuel. The rovers are tasked with relaying relevant data to a home base that is responsible for maintaining a mining schedule for an arbitrarily large group of rovers extracting water-rich regolith. For this reason, it is crucial that the participants maintain a wireless connection with one another and with the base throughout the entire process. We describe the architecture of our simulation which is composed of HLA-compliant components that are visualized via the Distributed Observer Network tool developed by NASA.

This study introduces a new practical calibration approach of ductile fracture models by performing square punch tests on metal sheets. During square punch tests, ductile fracture occurs at either the corner of die or punch radius when applying different clamping loads and lubrication conditions. At the corner of die radius, in-plane pure shear is induced at the intersection between the side-walls and the flange by combined tension and compression. On the other hand, the material at the corner of the punch radius is under combined bending and biaxial tension. The material studied in this paper is advanced high strength steel (AHSS) DP780 from ArcelorMittal. Isotropic J2 plasticity model with mixed Swift-Voce hardening rule is calibrated from uniaxial tensile tests.

The application of Statistical Process Control and Design of Experiment methods in the research laboratory can lead to significant gains in the Powertrain development process. Empirical methods such as Design of Experiments, Regression, and Neural Network techniques can be applied to help researchers gain better understanding of the cause and effect relationships of emission, alternative fuel source, performance, fuel economy, and engine management system - calibration studies. The use of these empirical modeling techniques along with model based Genetic Algorithm, Gradient, or Constraint based solution search methods will help identify the “process settings” that improve fuel economy, improve performance, and reduce pollutants. Since empirical methods are fundamentally based on the acquired test data, it is vitally important that the laboratory measurements are repeatable, consistent, and void of sources of variance that have a significant effect on the acquired test data.

Twist spring-back would interfere with stamping or assembling procedures for advanced high strength steel. A “homeopathic” resolution for controlling the twist spring-back is proposed using unbalanced post-stretching configuration. Finite element forming simulation is applied to evaluate and compare the performance for each set of unbalanced post-stretching setup. The post-stretching is effectuated by stake bead application. The beads are separated into multiple independent segments, the height and radii of which can be adjusted individually and asymmetrically. Simulation results indicate that the twist spring-back can be effectively controlled by reducing the post-stretching proximate to the asymmetric part area. Its mechanism is qualitatively revealed by stress analyses, that an additional but acceptable cross-sectional spring-back re-balances the sprung asymmetrical geometry to counter the twist effect.

The rooftop punch is proposed to reduce the maximum cutting force during the trimming operation for advanced high strength steels (AHSS), by introducing a shearing angle at the tool edge. However, such non-simultaneous shearing mechanism results in the inconsistent deformation around the hole perimeter, and consequently affects the dimensional accuracy of the trimmed hole. A numerical study was conducted to investigate the effects of punch tipping angle and tipping heights on the force reduction and dimensional discrepancies. The 60mm hole punching operation for DP 1180 (1.2mm) material was simulated with finite element analysis. The tipping height was reduced by introducing flat portions to the rooftop punch and it can mitigate the material deformation difference before trimming. The results showed tipping height played a significant role of dimensional accuracy control by adopting small tipping angle and broad flat portions.

To meet the automotive industry's increasing demand for lighter, more cost efficient products, AK Steel Corporation sees stainless steel as an effective material for structural components, including many light-weight body applications. With this in mind, AK Steel commissioned Troy, MI based Altair Engineering Inc. to design a lightweight tailgate using stainless steel that was easier to open and more resistant to dent and corrosion damage. The concept was designed to meet or exceed the performance of a current production carbon steel tailgate. This stainless steel design resulted in a 38% weight reduction over the carbon steel tailgate and can be a more cost-effective solution to aluminum or other alternative light-weight materials.

The die wear up to 80,800 hits on a prog-die setup for bare DP1180 steel was investigated in real production condition. In total, 31 die inserts with the combination of 11 die materials and 9 coatings were evaluated. The analytical results of die service life for each insert were provided by examining the evolution of surface wear on inserts and formed parts. The moments of appearance of die defects, propagation of die defects, and catastrophic failure were determined. Moreover, the surface roughness of the formed parts for each die insert was characterized using Wyko NT110 machine. The objectives of the current study are to evaluate the die durability of various tooling materials and coatings for flange operations on bare DP 1180 steel and update OEM tooling standards based on the experimental results. The current study provides the guidance for the die material and coating selections in large volume production for next generation AHSSs.

Dimensional accuracy of punched hole is an essential consideration for high-quality sheet metal forming. An out-of-shape hole can give rise to manufacturing issues in the subsequent production processes thus inducing quality defects on a vehicle body. To understand the effects of punch shapes and cutting configurations on punched hole diameter deviations, a systematical experimental study was conducted for multiple types of AHSS (DP1180, DP980, DP590) and one mild steel. Flat, conical and rooftop punches were tested respectively with three cutting clearances on each material. The measurement results indicated different diameter enlargement modes based on the punch profiles, and dimensional discrepancies were found to be more significant with the stronger materials and higher cutting clearance. To uncover the mechanism of punched hole enlargement, a series of finite element simulations were established for numerical investigation.

As an engineering approach of balanced complexity and accuracy, the Generalized Incremental Stress-State dependent damage Model (GISSMO) in LS-DYNA® has now been widely adopted by the automotive industry to predict metallic materials’ fracture occurrences in both forming and crashworthiness simulations. Calibration of the nominal GISSMO is typically based on material characterization data along a certain representative material orientation. Nevertheless, many rolled or extruded metallic materials, such as advanced high-strength steel (AHSS) sheets, exhibit accentuated anisotropic fracture behavior, even though, notably, some of these materials show comparatively weak anisotropic plasticity in the meantime. Accordingly, in this work, the deformation and fracture behavior of a selected AHSS grade, Q&P980 steel, was first characterized based on a series of mechanical experiments under simple shear, uniaxial tension, plane strain, and equi-biaxial tension conditions.

The lightweighting potential brought by advanced high strength steels (AHSS) was studied on automotive exterior panels. The dent resistance was selected as a measure to quantify the lightweighting since it is the most crucial for exterior panels. NEXMET® 440EX and 490EX, which possess both the surface quality and high strength, are evaluated and compared with BH210 and BH240. The denting analysis was conducted first on representative plates with different curvatures to simulate the dented areas on door outer, roof and hood panels. In addition, both 1% and 2% pre-strain and baking scenarios are considered for this plate, which represent the most common situations for exterior panels. The maximal dent load that the plates can sustain was calculated and compared for all those steel grades. Then the dent resistance analysis was conducted on a selected door outer panel. The minimum gauge required to meet the dent resistance performance was obtained.

The front bumper of a current production vehicle, which is made of hot-stamped 15B21 aluminized steel, was studied for mass and cost reductions using the Advanced High Strength Stainless Steel product NITRONIC® 30 (UNS Designation S20400) manufactured by AK Steel Corporation. This grade of stainless steel offers a combination of high ductility and strength, which was utilized to significantly modify the design of the bumper beam to incorporate geometry changes that improved its stiffness and strength. The structural performance of the bumper assembly was evaluated using LS-Dyna-based CAE simulations of the IIHS 40% Offset Full-Vehicle Impact at 40 mph with a deformable barrier, and the IIHS Full Width Centerline 6 mph Low-Speed Impact. Optimization of the bumper beam shape and gauge was performed using a combination of manual design iterations and a multi-objective optimization methodology using LS-Opt.

Spring-back phenomena are critical in stamping procedures for advanced high strength steel. An analytical model is developed to predict the spring-back effect for a U-channel part with post-stretching process. The stress distribution is obtained by direct application of material constitutive relationship. The subjected loading conditions are sequentially bending, (un-bending), and uniform stretching, based on different zones in the part. Both the loading history and the friction effects are considered in the model. The bending moments are obtained to generate a theoretical spring-back shape. Great performance in spring-back control is achieved by applying certain high level of external forces. FE simulation is conducted for the identical stamping process with post-stretching. Good correlation is observed between the analytical and numerical solutions/experimental results under various scenarios.

Utilizing the tailor welded blanks (TWBs) design along with the latest AHSS grades for the front rails on a sedan was studied to reduce the weight of the vehicle and improve the crash safety performance. To find the most efficient material usage, the front rail parts were tailored into multiple blanks with varying thickness. A structural thickness optimization study of the tailored front rails was conducted for IIHS moderate overlap frontal crash, and the tailored blank thickness was set as design variable. The equivalent static loads (ESL) method was adopted for the thickness optimization, which allows many design variables to be optimized simultaneously. The torsion and bending stiffness of the sedan body in prime were set as design constraints, and would not be compromised. The optimal thickness configurations of the TWB designs by ESL optimization suggest that the weight of the frontal rails can be reduced by more than 30% while still maintaining the crash safety performance.

A fully modularized framework was established to combine isotropic, kinematic, and cross hardening behaviors under non-monotonic loading conditions for advanced high strength steels. Experiments under the following types of non-proportional loading conditions were conducted, 1) uniaxial tension-compression-tension/compression-tension-compression full cycle reversal loading, 2) uniaxial reversal loading with multiple cycles, and 3) reversal shear. The calibrated new model is decoupled between isotropic and kinematic hardening behaviors, and independent on both anisotropic yield criterion and fracture model. Nine materials were calibrated using the model, include: DP590, DP600, DP780, TRIP780, DP980LY, QP980, AK Steel DP980, TBF1180, and AK Steel DP1180. Good correlation was observed between experimental and modeled results.

While Advanced High Strength Steels (AHSS) and the next generation AHSS grades offer improved crash safety and reduced weight for vehicles, the global stiffness and NVH performance are often compromised due to reduced material thickness. This paper discusses an advanced method of evaluating the joint effectiveness on contribution to global stiffness and NVH performance of vehicles. A stiffness contribution ratio is proposed initiatively in this research, which evaluates the current contribution of the joints to the global stiffness and NVH performance of vehicles. Another parameter, joint effectiveness factor, has been used to study the potential of each joint on enhancing the global stiffness. The critical joints to enhance the vehicle stiffness and NVH performance can be identified based on above two parameters, and design changes be made to those critical joints to improve the vehicle performance.

While offering improved crash worthiness and significant lightweighting opportunities, the increased use of advanced high strength steels (AHSS) may compromise the stiffness and NVH performance of vehicles due to reduced part thickness. Different methods to improve the torsional rigidity were studied on a pickup chassis frame. These methods include adding bulkhead pairs as reinforcement, increasing the thicknes of frame parts, and enlarging the closed sections on the rails. Structural optimization was conducted for each stiffness improvement method and the minimal mass increase required to reach the improvement targets was obtained. A material efficiency ratio μ is proposed in this research and used as a criterion to evaluate the efficiency of a mass increase to improve the structural stiffness and NVH characteristics of vehicles. Based on this parameter, the methods to improve the torsional rigidity of the pickup frame in all design spaces were evaluated.

In this paper, we address the thermal management issues which limit the lifespan, specific power and overall efficiency of an air-cooled rotary Wankel engine used in Unmanned Air Vehicles (UAVs). Our goal is to eliminate the hot spots and reduce the temperature gradients in the engine housing and side plates by aggressive heat spreading using heat pipes. We demonstrate by simulation that, for a specific power requirement, with heat spreading and more effective heat dissipation, thermal stress and distortion can be significantly reduced, even with air cooling. The maximum temperature drop was substantial, from 231°C to 129°C. The temperature difference (measure of temperature uniformity) decreased by 8.8 times (from 159°C to 18°C) for a typical UAV engine. Our heat spreaders would not change the frontal area of the engine and should have a negligible impact on the installed weight of the propulsion assembly.