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Design For Six Sigma with Critical-To-Quality Metrics for Research Investments

Description: Design for Six Sigma (DFSS) has evolved as a worthy predecessor to the application of Six-Sigma principles to production, process control, and quality. At Livermore National Laboratory (LLNL), we are exploring the interrelation of our current research, development, and design safety standards as they would relate to the principles of DFSS and Six-Sigma. We have had success in prioritization of research and design using a quantitative scalar metric for value, so we further explore the use of scalar metrics to represent the outcome of our use of the DFSS process. We use the design of an automotive component as an example of combining DFSS metrics into a scalar decision quantity. We then extend this concept to a high-priority, personnel safety example representing work that is toward the mature end of DFSS, and begins the transition into Six-Sigma for safety assessments in a production process. This latter example and objective involves the balance of research investment, quality control, and system operation and maintenance of high explosive handling at LLNL and related production facilities. Assuring a sufficiently low probability of failure (reaction of a high explosive given an accidental impact) is a Critical-To-Quality (CTQ) component of our weapons and stockpile stewardship operation and cost. Our use of DFSS principles, with quantification and merging of CTQ metrics, provides ways to quantify clear (preliminary) paths forward for both the automotive example and the explosive safety example. The presentation of simple, scalar metrics to quantify the path forward then provides a focal point for qualitative caveats and discussion for inclusion of other metrics besides a single, provocative scalar. In this way, carrying a scalar decision metric along with the DFSS process motivates further discussion and ideas for process improvement from the DFSS into the Six-Sigma phase of the product. We end with an example of ...
Date: June 22, 2005
Creator: Logan, R W
Partner: UNT Libraries Government Documents Department

Implications of a {open_quotes}cross-rolled{close_quotes} yield surface approximation on deep drawing

Description: During deep-drawing, two issues manifest themselves that are due to normal and planar anisotropy in the sheet. These are a dependence of the Limiting Draw Ratio (LDR) on the average thinning ratio (R-value), and a dependence of ear formation and thinning around the circumference on the variation of R-value in the plane of the sheet. The quadratic (1948 Hill) yield surface has been applied to these issues and it has been demonstrated that there are numerous higher exponent yield criteria that may more closely duplicate experimental trends. These predict varying degrees of R-value dependencies of uniaxial yields and strength ratios in multiaxial loading paths. The result of this is that there are sometimes subtle and sometimes substantial differences in the predictions of the various yield surfaces on deep drawing regarding LDR and earing. Additional differences arise due to the way the shear term (45-degree yield) and the 0-degree vs. 90-degree strengths are treated in each criterion. These dependencies (in-plane strengths generated by the yield surfaces) are shown to affect the results of both LDR and earing during cupping. In particular, the 1979 Hosford and 1989 Barlat (Tricomponent) criteria, although identical for the normal anisotropy (planar isotropy) case, are strikingly different for cases where there are differences at 45 degrees and 90 degrees from the rolling direction.
Date: March 1, 1996
Creator: Logan, R.W.
Partner: UNT Libraries Government Documents Department

Finite-element analysis of earing using non-quadratic yield surfaces

Description: During deep draw cupping, the phenomenon known as earing may occur as the cup wall is formed, resulting in a periodic variation of cup wall height around the perimeter of the finished cup. This is generally due to planar anisotropy of flow in rolled sheet product. It is generally observed that the anisotropy parameter R will vary in the plane of the sheet when ears are observed in cupping, with a parameter {Delta}R describing the variation of R in the plane of the sheet. For many common textures in face-centered and body-centered materials, the ears form relative to the sheet rolling direction at 0{degrees} and 90{degrees} around the perimeter if {Delta}R>0, and at -45{degrees} and +45{degrees} if {Delta}R<0. There is extensive experimental evidence that ear height shows a linear correlation with {Delta}R/R, but attempts to duplicate this using the finite-element method are highly dependent on both the methodology and yield surface used. It was shown previously that using a coarse mesh and the quadratic Hill yield surface tends to greatly under predict earing. In this study, we have used two different finite-element codes developed at LLNL to examine the predicted earing using both quadratic Hill and alternative non-quadratic yield surfaces. These results are compared to experimental data and conclusions drawn about the most desirable closed-form yield surfaces to duplicate the observed earing phenomena.
Date: June 18, 1995
Creator: Logan, R. W.
Partner: UNT Libraries Government Documents Department

Use of non-quadratic yield surfaces in design of optimal deep-draw blank geometry

Description: Planar anisotropy in the deep-drawing of sheet can lead to the formation of ears in cylindrical cups and to undesirable metal flow in the blankholder in the general case. For design analysis purposes in non-linear finite-element codes, this anisotropy is characterized by the use of an appropriate yield surface which is then implemented into codes such as DYNA3D . The quadratic Hill yield surface offers a relatively straightforward implementation and can be formulated to be invariant to the coordinate system. Non-quadratic yield surfaces can provide more realistic strength or strain increment ratios, but they may not provide invariance and thus demand certain approximations. Forms due to Hosford and Badat et al. have been shown to more accurately address the earning phenomenon. in this work, use is made of these non-quadratic yield surfaces in order to determine the optimal blank shape for cups and other shapes using ferrous and other metal blank materials with planar anisotropy. The analyses are compared to previous experimental studies on non-uniform blank motion due to anisotropy and asymmetric geometry.
Date: December 1, 1995
Creator: Logan, R.W.
Partner: UNT Libraries Government Documents Department

Solution Verification Linked to Model Validation, Reliability, and Confidence

Description: The concepts of Verification and Validation (V&amp;V) can be oversimplified in a succinct manner by saying that 'verification is doing things right' and 'validation is doing the right thing'. In the world of the Finite Element Method (FEM) and computational analysis, it is sometimes said that 'verification means solving the equations right' and 'validation means solving the right equations'. In other words, if one intends to give an answer to the equation '2+2=', then one must run the resulting code to assure that the answer '4' results. However, if the nature of the physics or engineering problem being addressed with this code is multiplicative rather than additive, then even though Verification may succeed (2+2=4 etc), Validation may fail because the equations coded are not those needed to address the real world (multiplicative) problem. We have previously provided a 4-step 'ABCD' quantitative implementation for a quantitative V&amp;V process: (A) Plan the analyses and validation testing that may be needed along the way. Assure that the code[s] chosen have sufficient documentation of software quality and Code Verification (i.e., does 2+2=4?). Perform some calibration analyses and calibration based sensitivity studies (these are not validated sensitivities but are useful for planning purposes). Outline the data and validation analyses that will be needed to turn the calibrated model (and calibrated sensitivities) into validated quantities. (B) Solution Verification: For the system or component being modeled, quantify the uncertainty and error estimates due to spatial, temporal, and iterative discretization during solution. (C) Validation over the data domain: Perform a quantitative validation to provide confidence-bounded uncertainties on the quantity of interest over the domain of available data. (D) Predictive Adequacy: Extend the model validation process of 'C' out to the application domain of interest, which may be outside the domain of available data in one or more planes ...
Date: June 16, 2004
Creator: Logan, R W & Nitta, C K
Partner: UNT Libraries Government Documents Department

Relative sensitivity of formability to anisotropy

Description: This work compares the relative importance of material anisotropy in sheet forming as compared to other material and process variables. The comparison is made quantitative by the use of normalized dependencies of depth to failure (forming limit is reached) on various measures of anisotropy, as well as strain and rate sensitivity, friction, and tooling. Comparisons are made for a variety of forming processes examined previously in the literature as well as two examples of complex stampings in this work. 7 The examples rover a range from nearly pure draw to nearly pure stretch situations, and show that for materials following a quadratic yield criterion, anisotropy is among the most sensitive parameters influencing formability. For materials following higher-exponent yield criteria, the dependency is milder but is still of the order of most other process parameters. However, depending on the particular forming operation, it is shown that in some cases anisotropy may be ignored, whereas in others its consideration is crucial to a good quality analysis.
Date: January 1, 1997
Creator: Logan, R.W. & Maker, B.N.
Partner: UNT Libraries Government Documents Department

Modeling the dynamic crush of impact mitigating materials

Description: Crushable materials are commonly utilized in the design of structural components to absorb energy and mitigate shock during the dynamic impact of a complex structure, such as an automobile chassis or drum-type shipping container. The development and application of several finite-element material models which have been developed at various times at LLNL for DYNA3D will be discussed. Between the models, they are able to account for several of the predominant mechanisms which typically influence the dynamic mechanical behavior of crushable materials. One issue we addressed was that no single existing model would account for the entire gambit of constitutive features which are important for crushable materials. Thus, we describe the implementation and use of an additional material model which attempts to provide a more comprehensive model of the mechanics of crushable material behavior. This model combines features of the pre-existing DYNA models and incorporates some new features as well in an invariant large-strain formulation. In addition to examining the behavior of a unit cell in uniaxial compression, two cases were chosen to evaluate the capabilities and accuracy of the various material models in DYNA. In the first case, a model for foam filled box beams was developed and compared to test data from a 4-point bend test. The model was subsequently used to study its effectiveness in energy absorption in an aluminum extrusion, spaceframe, vehicle chassis. The second case examined the response of the AT-400A shipping container and the performance of the overpack material during accident environments selected from 10CFR71 and IAEA regulations.
Date: May 12, 1995
Creator: Logan, R.W. & McMichael, L.D.
Partner: UNT Libraries Government Documents Department

DYNA3D analysis of the DT-20 shipping container

Description: A DYNA3D model of the DT-20 shipping container was constructed. Impact onto a rigid steel surface at a velocity of 44 ft/sec (30 foot gravity drop) was studied. The orientation of most interest was a side-drop, but end and corner drops were also studied briefly. The assembly for the baseline side impact contained a 150 lb. payload. During this drop, the outer drum sustains plastic strains of up to 0.15, with most the deformation near the rim. The plywood/Celotex packing is crushed about 3 inches. The inner sealed can sees significant stresses, but barely reaches the onset of yielding in some local areas. Based on hand calculations, the bolts joining the can halves could see stresses near 50 ksi. It is felt that overall, the container should survive this drop. However, detailed modeling of the rim closure and the center bolted joint was not possible due to time constraints. Furthermore, better material models and properties are needed for the Celotex, plywood, and honeycomb in particular. 39 figs., 1 tab.
Date: August 22, 1991
Creator: Logan, R.W. & Lovejoy, S.C.
Partner: UNT Libraries Government Documents Department

Overview of crash and impact analysis at Lawrence Livermore National Laboratory

Description: This work provides a brief overview of past and ongoing efforts at Lawrence Livermore National Laboratory (LLNL) in the area of finite-element modeling of crash and impact problems. The process has been one of evolution in several respects. One aspect of the evolution has been the continual upgrading and refinement of the DYNA, NIKE, and TOPAZ family of finite-element codes. The major missions of these codes involve problems where the dominant factors are high-rate dynamics, quasi-statics, and heat transfer, respectively. However, analysis of a total event, whether it be a shipping container drop or an automobile/barrier collision, may require use or coupling or two or more of these codes. Along with refinements in speed, contact capability, and element technology, material model complexity continues to evolve as more detail is demanded from the analyses. A more recent evolution has involved the mix of problems addressed at LLNL and the direction of the technology thrusts. A pronounced increase in collaborative efforts with the civilian and private sector has resulted in a mix of complex problems involving synergism between weapons applications (shipping container, earth penetrator, missile carrier, ship hull damage) and a more broad base of problems such as vehicle impacts as discussed herein.
Date: August 5, 1993
Creator: Logan, R. W. & Tokarz, F. J.
Partner: UNT Libraries Government Documents Department

Estimating Parametric, Model Form, and Solution Contributions Using Integral Validation Uncertainty Quantification

Description: One of the final steps in building a numerical model of a physical, mechanical, thermal, or chemical process, is to assess its accuracy as well as its sensitivity to input parameters and modeling technique. In this work, we demonstrate one simple process to take a top-down or integral view of the model, one which can implicitly reflect any couplings between parameters, to assess the importance of each aspect of modeling technique. We illustrate with an example of a comparison of a finite element model with data for violent reaction of explosives in accident scenarios. We show the relative importance of each of the main parametric inputs, and the contributions of model form and grid convergence. These can be directly related to the importance factors for the system being analyzed as a whole, and help determine which factors need more attention in future analyses and tests.
Date: February 28, 2006
Creator: Logan, R W; Nitta, C K & Chidester, S K
Partner: UNT Libraries Government Documents Department

Energy absorption in aluminum extrusions for a spaceframe chassis

Description: This work describes the design, finite-element analysis, and verifications performed by LLNL and Kaiser Aluminum for the prototype design of the CALSTART Running Chassis purpose-built electric vehicle. Component level studies, along with our previous experimental and finite-element works, provided the confidence to study the crashworthiness of a complete aluminum spaceframe. Effects of rail geometry, size, and thickness were studied in order to achieve a controlled crush of the front end structure. These included the performance of the spaceframe itself, and the additive effects of the powertrain cradle and powertrain (motor/controller in this case) as well as suspension. Various design iterations for frontal impact at moderate and high speed are explored.
Date: September 19, 1994
Creator: Logan, R.W.; Perfect, S.A. & Parkinson, R.D.
Partner: UNT Libraries Government Documents Department

Selection of candidate canister materials for high-level nuclear waste containment in a tuff repository

Description: A repository located at Yucca Mountain at the Nevada Test Site is a potential site for permanent geological disposal of high-level nuclear waste. The repository can be located in a horizon in welded tuff, a volcanic rock, which is above the static water level at this site. The environmental conditions in this unsaturated zone are expected to be air and water vapor dominated for much of the containment period. Type 304L stainless steel is the reference material for fabricating canisters to contain the solid high-level wastes. Alternative stainless alloys are considered because of possible susceptibility of 304L to localized and stress forms of corrosion. For the reprocessed glass wastes, the canisters serve as the recipient for pouring the glass with the result that a sensitized microstructure may develop because of the times at elevated temperatures. Corrosion testing of the reference and alternative materials has begun in tuff-conditioned water and steam environments. 21 references, 8 figures, 8 tables.
Date: November 1, 1983
Creator: McCright, R.D.; Weiss, H.; Juhas, M.C. & Logan, R.W.
Partner: UNT Libraries Government Documents Department

Implementation of a pressure and rate dependent Forming Limit Diagram model into NIKE and DYNA

Description: The Forming Limit Diagram (FLD) has been used for decades as an aid to successful sheet metal forming. In this work, we describe the incorporation of the FLD technique into the DYNA and NIKE codes at LLNL along with applications that led to the developments. The algorithm is currently available in the public version of DYNA3D. Several augmentations of the basic technique have been made available due to the necessity of their incorporation to solve programmatic problems of interest at LLNL. Illustration of the use of the FLD model is shown for a dome geometry similar to that used in the Limiting Dome Height (LDH) test. This early example uses the simplest FLD option (analogous to circle grid) and shows the relative merits of this method versus scalar plastic work in prediction of tearing. In a phenomenological extension of the method, a pressure-dependent (FLD+P) method is used to successfully predict the relative design merits of stainless steel forgings. A final application to sheet stamping of a Boeing 757 door frame shows how the scatter plot circle grid option and strain path plots can be used to predict when preforms and intermediate anneals are necessary. The phenomenological nature of the FLD model as implemented is discussed relative to alternative approaches of calculating the FLD and its path dependence.
Date: June 1, 1995
Creator: Logan, R.W.; Thomas, D.B. & Young, G.K.
Partner: UNT Libraries Government Documents Department

Design study of fiber-composite penetrator cases

Description: A design study was conducted to demonstrate the viability of carbon-fiber reinforced epoxy composites as structural case materials for penetrating warheads. The objective was to conduct well-instrumented experimental studies of composite-body penetrators perforating mild steel plates and quantitatively model these plate penetrations using two- and three-dimensional finite element codes over a wide range of velocities and impact conditions in order to develop predictive capability for composite design and for use in tradeoff studies with existing case materials. Understanding of the failure of composite-body penetrators would be demonstrated by a rational design iteration which significantly improved performance. Initial studies utilized existing 1-degree tapered cylindrical carbon fiber/epoxy composite cases fabricated by wet-filament winding. These sharp-tipped, steel-nose, composite penetrators were strain-gaged, piggy-backed with 57 kilograms, and impacted into steel plates in a velocity-boosted droptower at impact velocities ranging from 3 to 18 meters per second. Load, time, and position data were recorded during the impact event as well as the axial and hoop strains in the composite case. Monolithic 4340 hardened steel penetrators with both sharp- and flat-tip 3-caliber ogive noses were also impacted into mild steel plates. Data from the composite-case and steel penetrators were used to calibrate a multiaxial, rate-dependent, flow and failure model for the mild steel plates in NIKE2D. The authors were then able to successfully predict survival and failure of the composite-case penetrators in normal-incidence droptower tests for different target thickness and velocity combinations.
Date: October 22, 1993
Creator: Logan, R. W.; Groves, S. E. & Lyon, R. E.
Partner: UNT Libraries Government Documents Department