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Computational Software Development
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Under our strategic alliances and business partnership with Prof. Ted Belytschko at Northwestern University, the development of computational software product is one of core technology areas. At present, we are developing an automatic software tool for residual strength and life prediction of composite structure using the extended finite element method (XFEM). This tool will for the first time be able to model arbitrary crack growth without user intervention or remeshing and thus provide a user-friendly, reliable tool for predicting component life.
XFEM Based Delamination Failure Prediction Tool – INTRODUCTION
The delamination failure mode is particularly significant in the damage tolerance of advanced composite, since manufacturing flaws and in-service damage most often manifest themselves as interlaminar cracks. Given the escalating costs associated with the test-driven certification and qualification procedures, there is an immediate need for verified computational software to accurately and efficiently predict delamination onset and growth under monotonic and cyclic loading.
GEM along with our team members (LM Aero, Bell Helicopter, ABAQUS, Inc.) and our consultant (Prof. Ted Belytschko) is developing XFEM toolkit for residual strength and life prediction of a composite structure with a given set of initial multiple delamination areas. This tool will for the first time be able to model arbitrary 2D/3D delamination crack growth without remeshing. This automated delamination onset and growth prediction tool will be implemented within the ABAQUS implicit solver. It will not only capture the commonly accepted and understood failure physics but be consistent with current damage tolerance and residual strength assessment requirements and testing procedures. The unique features of the Phase II software product are: 1) the capability for arbitrary insertion of multiple initial delamination cracks into any finite element mesh at either element boundaries or within elements via a PATRAN GUI; 2) simulation of arbitrary crack growth without remeshing; 3) accurate extraction of strain energy release (SERR) rate along an arbitrary crack front with or without closure via a modified VCCT technique; and 4) characterization of delamination onset and growth results via PATRAN and ABAQUS’s CAE.
Figure1: Representation of a Crack by Mesh Independent Nodal Enrichment
XFEM Approach to Shear Band Evolution in Metallic Structures under Impact Loading
Shear bands are material instabilities, localized in narrow regions of high strains that are formed in materials under intense thermo-plastic shear deformations. Understanding their mechanical behavior is important for predicting material failure. They are observed in many physical processes, including impact and penetration, and high speed machining. They develop in different material types, for example in metals, sand and concrete. Figure 1 illustrates several pictures of shear bands formed in different materials.
Figure 2: Shear band formation in various materials
Study of the solution behavior is difficult both analytically and numerically due to the rapid growth of temperature, strain and strain rate within the band relative to these prosperities outside the band.
Considerable progress has been achieved in the past decades in understanding shear banding; nonetheless, an efficient numerical simulation of localization problems still poses a great challenge. It is well known that standard finite element schemes are mesh dependent and thus require very fine meshes, in particular across the localization bands, to properly resolve band features.
We study a strong discontinuity approach for tracking shear band progression in metals under various loading rates. Strong discontinuity is the assumption of zero
band thickness, where information within the band is neglected. This approach simplifies the numerics by employing XFEM approach to track the propagation of
shear bands without re-meshing. To achieve accurate behavior, a concurrent micro/macro multiscale method is formulated. In essence we extract rate dependent, normal and tangential, cohesive laws from a simplified micro model and inject them to the macro XFEM simulations. We employ an elastic-thermo-viscoplastic constitutive model to simulate material softening. Specifically, we explore the response of 4340 steel modeled by a Johnson-Cook model and C-300 steel. The discontinuity line continues to propagate only if the material stability of an adjacent element is lost. The behavior of the strong discontinuity,
micro/macro approach is examined through a series of force-deflection curves. We show that XFEM enhanced by these cohesive rate dependent laws, is
able to capture both the material response and the shear band path accurately, on relatively coarse meshes without the need to re-mesh.
Figure 4: Steel plate under tension shear band in 45 degrees
Figure 5: discontinuity propagation in XFEM. Circles indicate elements enriched with jump functions
Figure 6: Force-deflection response of C-300 steel subjected to tension shear band in 45 degress
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Demo
Creating an Internal Crack
Creating an Interface Crack
Generating Enriched Nodes
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