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SBIR Topic no AF01-137

SBIR Topic Number AF01-137

Strain Rate Effects In Ballistic Analysis Of Bonded & Co-Cured Composite Structures

Abstract:

The aim of our Phase II activity is to incorporate the Cohesive Volumetric Plate and Shell Finite Elements(CVFE ) into LS-Dyna, thereby enhancing its capabilities in modeling HRAM(Hydro Dynamic Gun, Figure 1) loading and damage in composite structures. In Phase I, we reported interlaminar failure criteria and modes, based on fracture mechanics. A damage-dependent bilinear cohesive element is used to capture the crack initiation, propagation, and arrest, while accounting for inertial effects. An algorithm was developed to compute essential toughness parameters (strain energy release rate G and stress intensity factor K) and the variations thereof, with crack length and adhesive effects. Experimental testing of double cantilever beam (DCB) specimens at various stroke rates, using an electronic circuit to measure crack propogation relative to the crack-opening displacement, yielded data which enabled the calculation of material parameters used in the explicit CVFE/LS-Dyna formulation. As the next step, we developed a rate-dependent cohesive volumetric element, and used this technique to analyze failure in un z-pinned, z-pinned and other joint type specimens. We have been working on incorporating CVFE algorithms in LS-Dyna with filtering and damping.

Experimental work focuses on hydrodynamic pulse tests, using the impact machine developed at the 46th test wing, thus simulating high-rate fracture dynamical scenarios. The material property data obtained in these tests is being incorporated into the LS-Dyna code with CVFE formulation, thus achieving the desired objectives of the SBIR. Both static and ballistic tests on double cantilever beam, T-Joints and end notch flexure specimens are considered.

HydroDynamic Ram Gun

Cracktrack Electronics System
Fig. 1(HydroDynamic Ram Gun)
Fig. 2(Cracktrack Electronics System)
 
In the process, we have developed a Cracktrack Electronics System for accurately measuring crack propagation and strain rate parameters in DCB specimens at different strain rates.(Figure 2 and Figure 3).
PreProcessor for Dyna3D
High Strain Rate Testing
Fig. 3 (Pre Processor for Dyna3D)
Fig. 4 (High Strain Rate Testing)
A mechanical system attached to a MTS machine is developed to simulate high strain rate conditions using tension springs with different stiffness (Figure 4 and Figure 5). A trigger mechanism is developed to provide ballistic loads through spring extensions (Figure 6).
We have used the same concept to develop a system for testing T-joints under ballistic loads. Dyna3D Pre processor is being developed to compute the response of three specimen geometries using the Dyna3D package
High strain rate fixture
Fig. 5( High Strain Rate Fixture)
Trigger mechanism
Fig 6 (Trigger mechanism)

Benefits:

The proposed Cohesive Volume Finite Element (CVFE) High Strain Rate Module for incorporation into established FEA codes has potential applications in composites and any other adhesively bonded materials. Thus it has high potential use by the Federal Government, particularly DoD, as well as numerous commercial applications across a number of industries. The module was designed to address dynamic (high strain rate) issues; however, it is also applicable to quasi-static (low strain rate) issues. Industry segments that will have definite needs for this software enhancement include aerospace, automotive, shipbuilding and boat building to name a few. Actually any design engineers designing products or components made of composites or any other material systems that are being adhesively bonded, will have need for this module.

Partners
Adtech Systems Research Inc
46th test wing
RHAMM Inc.

UIUC
Lockheed Martin

 
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