Werner Riedel

DEVELOPMENT OF MATERIAL MODELS FOR NEXTEL AND KEVLAR-EPOXY FOR HIGH PRESSURES AND STRAIN RATES

Abstract Material models suitable for Nextel cloth and Kavlar-epoxy in bumper shield systems are being developed. The paper describes the current status of a project aimed at developing such material models for usage in hydrocode simulations. The starting assumption was that the model should be suitable for implementation in existing hydrocodes and it should aim to simulate the main system phenomena rather than the detailed microscopic response of the material under hypervelocity impact loading. It is shown how the anisotropic behaviour, of these materials, leads to a coupling of the volumetric and deviatoric response. This creates a difficulty in combining conventional equation of state behaviour with the anisotropic constitutive model. We have implemented an approach based on that by Anderson [1] to overcome this difficulty. Further development of this approach, to include non-linear constitutive behaviour and in particular porous compaction effects, is in progress. An overview of the material characterisation tests being conducted is given with details, and results, presented for confined static compression, inverse flyer plate and hypervelocity impact tests. The confined static compression tests have enabled the definition of a porous compaction model. This compaction model has been used in simulations of the inverse flyer plate tests and has led to much improved correlation. Results of micro- and meso- mechanical simulations of Nextel cloth under confined compressive loading are also presented. Finally, we show details of three preliminary simulations of a hypervelocity impact test on a multi-shock shield. The results of these simulations emphasise the importance of compaction and anisotropic response to the system behaviour.

Dynamic Progressive Collapse of an RC Assemblage Induced by Contact Detonation

The nature of progressive collapse is a dynamic event caused by accidental or intentional extraordinary loading. Most published experimental programs are conducted statically, without any consideration of the accidental loading and treating progressive collapse as threat independent. This paper demonstrates the more realistic process of progressive collapse in an experimental program on reinforced concrete subassemblages collapsed by a combination of dead weight loading and contact detonation. The dynamic results are represented systematically at different aspects and compared with previous published quasi-static experiments in terms of structural mechanisms, crack patterns and local failure modes. Moreover, the dynamic increase factor (DIF) of reinforcing bars and the dynamic load amplification factor (DLAF) are investigated and discussed. Following the above comparisons and the findings in the dynamic tests, previous quasi-static test results can be linked to actual progressive collapse behavior more convincingly. Finally, the dynamic tests also highlight the effect of contact detonation on structures, which are often not considered in quasi-static tests and design guidelines. The test results indicate that contact detonation causes uplift and out-of-plane actions to the subassemblage before their downward movement under gravity load, in which the strain rate of reinforcement is between 10⁻² and 10⁻¹/s. Moreover, the structural mechanisms are similar in both quasi-static and dynamic tests.

Susceptibility, vulnerability, and averaged risk analysis for resilience enhancement of urban areas

The dynamic growth and evolution of urban areas generate new challenges for safety and security driving societal, economic, and ecological developments at local and worldwide levels. Cities comprise a high degree of critical infrastructure with an increasing complexity and interdependency. In addition, modified and new threats ranging from natural to man-made and malicious hazards ask for more robust and sustainable cities. This work combines and extends existing empirical, engineering, and simulative methods to define and determine quantities for resilience assessment of urban areas in a comprehensive approach. Based on a multitude of possible events in a city quarter with a larger number of infrastructures, susceptibilities, vulnerabilities, and averaged risks are analyzed in a systematic and quantitative way. The use of an established empirical-historical database gives first insights to identify susceptible elements or endangered areas in the considered urban environments. It is coupled to an approach for consequences where state-of-the-art physical-engineering hazard and damage propagation and quantification models are integrated for vulnerability assessment. The consideration of multiple threats and multiple possible locations cumulates in an object- and location-dependent quantification of averaged risks to visualize the most critical regions and infrastructure aspects in densely populated areas. In this article, the approach is exemplarily applied to terroristic threats. The integration of the three-dimensional visualized approach into existing risk assessment and management processes will help to create cities that are more resilient.

Vulnerability Identification and Resilience Enhancements of Urban Environments

Steadily increasing number of the world’s population is living in urban centres. The issue of security and citizen safety in densely populated areas is a growing concern. Considering terrorism and large scale accident scenarios, natural disasters and crime, urban planning practice must be complemented with vulnerability identification and resilience enhancements methods.

A general concrete model in hydrocodes: Verification and validation of the Riedel–Hiermaier–Thoma model in LS-DYNA:

The Riedel–Hiermaier–Thoma model, which is available in ANSYS Autodyn since 2000 as a description of concrete and similar geological materials in highly dynamic loading situations, has recently been implemented in the multi-purpose Finite Element code LS-DYNA. This article gives a brief overview of the physical details and verifies the new implementation by comparing single element test results with the established Autodyn code. Four real cases, ranging from low to very high pressure loading by impact, penetration and blast, are used to demonstrate thereafter the validity of the model in a wide range of applications. Simulation results from both codes are compared to experimental data at several occasions. Although slight differences between the implementations are observed, the overall agreement, both between the codes and with experiments, is very good. The systematic work in this publication demonstrates that the Riedel–Hiermaier–Thoma model is a useful addition to the LS-DYNA material library and shall motivate research to apply the model over a wide range of applications. A comprehensive, physically derived dataset is provided for a C70/85 high-strength concrete used in one validation case.

A Combined Experimental/Computational Approach for Assessing the High Strain Rate Response of High Explosive Simulants and Other Viscoelastic Particulate Composite Materials

The quasistatic and dynamic mechanical properties of a viscoelastic particulate composite employed as a surrogate, cast‐cure high explosive were determined from uniaxial compression experiments at strain rates up to 107 sec−1. The results from these experiments were used to obtain parameters for a non‐linear viscoelastic material model. The viscoelasticity described by the macroscopic material model introduced in this paper affects not only the deviatoric components of stress and strain but the volumetric components as well. The material description is adequate for reproducing experimentally observed responses at loading rates ranging from quasistatic to shock levels with a single set of material parameters. Parameters for an HTPB‐sugar composite are provided.

Protection Capabilities of HHA and UHA Steels against Long-Rod Kinetic Energy Penetrators

The protective capabilities of three different armor steels of the HHA and UHA class against a long rod penetrator (LRP) were examined. Due to the lack of commercial availability of thick armor plates, the specific ballistic behavior under overmatch conditions, and unavoidable experimental scatter, we were unable to confirm any performance differences among the steels in ballistic testing, even when compared to standard RHA. In a second approach, numerical simulations of the ballistic behavior of the armor steels based on material testing (tensile tests and planar-plate-impact tests) were performed. The simulations provided the possibility to examine the steels in unavailable configurations, i.e. thickness. With this combined approach it could be shown that UHA steels may give a considerable protection increase against LRP in diminishing their maximum effective range by at least several hundred meters compared to HHA steel.

Application of the RHT Concrete Model for Predictive Simulations of the Penetration into Adobe Targets

In the present paper, we review and extend our results concerning predictive numerical simulations of the penetration into adobe on the basis of the RHT concrete model [C. Sauer et al., Int. J. Impact Engng., 104 (2017) 164-176]. We apply this model to the theoretical description of adobe in a hydrocode. For this purpose a set of material parameters is derived on the basis of published data, own material tests, and engineering assumptions. Available ballistic results for the penetration of spherical steel projectiles into semi-infinite and finitethickness adobe targets are used for validating our approach. As a result, we obtain a hydrocode model which is expected to predict a wide range of penetration scenarios into adobe. The predictive character is exemplarily demonstrated by the successful reproduction of the instability within the penetration process and residual velocities of differently shaped tungsten heavy alloy projectiles.

New Building Concepts Protecting against Aircraft Impact

Aircraft impact is a decisive load case for critical infrastructure as high-rise buildings in prestigious large-scale urban developments or nuclear power plants. The proposed paper introduces new concepts based on high performance concretes (HPC, UHPC) for the example of the ‘Security Scraper’[1,2] and an innovative superstructure for existing power plants [3,4]. Key analysis steps using Two-Degree-of-Freedom (TDOF) and finite element (FEM) methods and their experimental validation [5] are used to predict dynamic response on local and global levels to maintain structural integrity under impact and to keep the fire outside the security zone.