TECHNOLOGY AREA(S): Materials/Processes

ACQUISITION PROGRAM: Naval Ordnance Safety and Security Activity (NOSSA)

OBJECTIVE: Develop a fast running model (FRM) for hardened structure debris prediction by using reliability analysis and adopting a stochastic procedure that can provide practical fundamentals for site planning of the hardened structures such as the magazine.

DESCRIPTION: Analysis of reinforced concrete and other forms of structural component cementations affected by weapons effects have been performed using a variety of deterministic analysis tools/methods, such as finite element methods, FRMs, pressure-impulse (PI) curves, and single-degree-of-freedom models. Such analyses have a critical limitation related to the manner in which such tools handle the inherent stochastic nature of the weapons effects problem. The modeling and simulation (M&S) technology is not standardized, thus no reliable procedure for evaluation has been developed. Currently the required time and effort for the evaluation is a measurement taking weeks or months for just one specific case. A new FRM will provide reliable and accurate predictions in the scale of minutes for all the magazine and related hardened structures.

The present approach to weapons effects analysis should be revised to improve its consideration of the actual uncertainties presented by targeting problems and weapons effects responses. The methodology was developed in 1943 and since then it has not been changed or improved seriously. The only advantage of the methodology is that it is a simple hand calculation process, and because of this advantage, it is traceable to check validity. The analysis method far beyond finite element method is being used as a proven technology. However, the non-traceable nature, huge Computer Processing Unit (CPU) time and technical complicacy prevents the use of advanced methods such as mesh-free analysis, even though it is the most reliable method. The proposed R&D pursuing the development of FRM can solve three problems to keep the reliability and accuracy: no need to be traced for validation because it is already validated by this proposed R&D; week-level CPU time can be reduced to minute level thanks to FRM nature; and easy access by user-friendly Graphical User Interface (GUI).

More reliable prediction of the structural damage due to fragment and secondary debris in case of detonation shall specify required resistance of the structural components of a specific area to enhance the structural soundness evaluation, and eventually to reduce cost and efforts for the maintenance of the magazine structures. Generally, maintenance of the structure is conducted by three levels: visual inspection; non-destructive test (NDT); and computer simulation or test for validation by acquired inspection data and NDT data. More reliable prediction of the structural damage due to fragment and secondary debris in case of detonation can specify required resistance of the structural components of specific area.� It can enhance the efficiency of the structural health monitoring and eventually can reduce cost and efforts for the maintenance of the magazine structures.

Functional change of the ammunition structures requires stopping all the operations related to the designated structure. The development shall pursue accurate and reliable prediction of the structural response to expedite the evaluation process, which drives the minimization of the operational discontinuity. Functional change of the ammunition structures requires stopping all the operations related to the designated structure. Accurate and reliable prediction of the structural response can expedite the evaluation process, which drives the minimization of the operational discontinuity.

The statistical characteristics of the debris or fragmentation prediction cause two major difficulties in the application of deterministic analysis procedures for analysis: the high statistical variance of the loading and the variance in response that it engenders. For example, mesh size is not sufficiently considered in performing an analysis concerning the influence of smaller particle fragments on the results. The influence of the small size fragment (e.g., one smaller than the mesh size) cannot be adequately predicted by a conventional finite element or mesh-free analysis method.� Cracks and break-up simulation requires the mesh to be as small as possible.� Even tenth of an inch is not sufficiently small enough to simulate discontinuity.� Normally, analysis should accept the error from the mesh size, which cannot be ignored.

Since the physical reduction of mesh size in the model is limited based on the response information computed during the analysis, less physical analysis techniques or indirect analysis methods, such as FRM or database concepts, should be incorporated in the analysis procedure. For example, multi-layer analysis schemes could be applied to get the behaviors caused by smaller size fragments into standard size meshes. Non-structural analysis techniques are needed to capture these multi-scale stochastic features of weapons effects analyses. A combination of structural, non-structural, and intermediate approaches is needed to capture such characteristics of the fragment loading, and similar features would be needed for other aspects of such response predictions. For example, response to contact and embedded munitions, where the standard analysis methodologies cannot effectively operate even by high-fidelity physics-based (HFPB) analyses methodologies. This research would result in a new form of analysis method, such as a hybrid method combining HFPB modeling with reliability modeling. This combination will address problems where refinement alone is inadequate for considering the intense environment generated by many forms of weapons effects and the corresponding extreme distortions introduced in the structural component struck.

PHASE I: Provide a concept for new forms of analytic models that incorporates hybrid HFPB and reliability-based on formulations that are intended for very intense weapons effects analyses. Identify the viable candidates for such a hybrid approach and the feasibility of their development. Highlight the limitations of conventional weapon effects analyses using HFPB models to identify the problems to be addressed and how the proposer recommends mitigating these problems.

The Phase I Option, if exercised, will include the initial design specifications and capabilities description to build a prototype solution in Phase II.

PHASE II: Develop, and validate theoretically, analysis methods for both structural and weapons effects characterizations. Ensure that one or more of these analysis methods is realized sufficiently to perform some weapons effects analysis for validation against test data. The test results from the Navy ESKIMO series are available to use for the validation. Produce a final report of findings of all the issues described above and a prototype form of FRM software that has the capability to analyze a structure developed to display the technology. For example, the software should comprehensively incorporate the physics-based and stochastic-based modeling of the weapons effects and, in particular, modeling the casing fragment characterization and structural response induced by fragment impacts/perforation. Normally FRM is composed by scientific computing software such as MATLab or Python for standalone program or linked to the integration software.� Scope of this development is to setup theoretical approaches and compose standalone program for current use and future integration, if it is required.

Ensure that the developed FRM shall have functions of magazine structure debris prediction under the given conditions such as construction materials, design facts, or surrounding structures.

PHASE III DUAL USE APPLICATIONS: Support the Navy in transitioning the FRM for Navy use in improving design regulations and standard designs for hardened structures. In the new design or when the modification or new design is required, predict the response for the safety estimation of the surrounding structures. Support the approval procedure conducted with interagency cooperation including Naval Ordnance Safety and Security Activity (NOSSA) and the Department of Defense Explosive Safety Board (DDESB). Validate the results of this effort by full scale tests whether simplified or full scale to be used as a part of the approval procedure.

REFERENCES:

1. Rinehart, Eric J., Henny, Robert W., Thomsen, Jeffrey M., and Duray,� Jeffery P. �DTRA weapons effects testing: a thirty-year perspective.� 21st International Symposium on Military and Blast, Israel, 2010. https://www.hsdl.org/?view&did=714840

2. Malvar, L. Javier. �Response of Robust Munitions to Secondary Fragmentation.� Twenty-Seventh DOD Explosives Safety Seminar, Las Vegas, NV, 20-22 August 1996. https://pdfs.semanticscholar.org/34fa/e164bbc4f82ac98b318d9aa96cbba1515303.pdf?_ga=2.30674301.396162968.1566487041-183382745.1565270410

3. Knight Jr., Norman F., Jaunky, Navin, Lawson, Robin E. and Ambur, Damodar R. �Penetration simulation for uncontained engine debris impact on fuselage-like panels using LS-DYNA.� Finite Elements in Analysis and Design, Volume 36, Issue 2, September 2000, pp. 99-133. https://www.sciencedirect.com/science/article/pii/S0168874X00000111

4. Wu, Youcai, Magallanes, Joseph M., Choi, Hyung-Jin and Crawford, John E. �Evolutionarily Coupled Finite-Element Mesh-Free Formulation for Modeling Concrete Behaviors under Blast and Impact Loadings.� 10.1061, Journal of Mechanical Engineering, ASCE, 2013. https://ascelibrary.org/doi/abs/10.1061/%28ASCE%29EM.1943-7889.0000497

5. Wu, Youcai, Choi, Hyung-Jin and Crawford, John E. �Concrete Fragmentation Modeling using Coupled Finite Element - Meshfree Formulations.� Interaction and Multiscale Mechanics, Vol. 6, No. 2, 2013, pp. 173-195.
http://www.techno-press.org/download.php?journal=imm&volume=6&num=2&ordernum=7

KEYWORDS: Debris and Fragmentation; Hardened Structure; Magazine Structure; Meshfree Method; Stochastic Analysis; Fast Running Model