Tuesday, September 18, 2007

Micro Crack Density Prediction of Continuous Fiber Reinforced Polymeric Composites


Software Suite for Durability, Damage Tolerance, and Life Prediction
Augments FEA Solvers MSC Nastran*, ABAQUS, ANSYS & LS-DYNA

* Best Performance and Verified Solutions with MSC Nastran



This Week's Feature Composite Example

Micro Crack Density Prediction of Continuous Fiber Reinforced Polymeric Composites

Figure 1 - Typical micro cracks in polymer matrix composites
Cryogenic polymer composite propellant tanks are widely employed in Reusable Space Vehicles due to their lightweight. However, micro crack can cause loss of stiffness, stress re-distribution, material degradation due to moisture and oxidation, and leakage when micro-damages exceed tolerable levels which may cause catastrophic tank failure. Micro-cracks (Figure 1), formed in the polymer matrix during manufacturing and service, significantly contribute to the leakage of composite propellant tanks. Therefore, predicting micro-crack formation and development in cryogenic tanks is of great importance to tank design.
Figure 2 - Comparison between the simulated crack densities and test data in 90-degree plies of two IM600/Q1334 laminates under monotonic tension.
GENOA's prediction of the crack density in a polymer composite structure includes three parts: 1) onset of cracks in the structure, 2) multiplication of cracks through the entire structure, and 3) degradation of composite properties due to the existence of cracks at each location. Crack density is obtained at the ply level in the laminate at each location of the structure.
Figure 3 - Crack density development in the 90 degree plies of the IM7/977-2 laminate under tension fatigue in the 0 degree direction. Laminate configuration is [0/45/90/-45]
  
Figure 2 illustrates the micro crack initiation and propagation in two IM600/Q1334 laminates under monotonic tension [1]. The crack density developments in an IM7/977-2 quasi-isotropic laminate under isothermal fatigue loads (room and cryogenic temperatures) were predicted and verified against Air Force test results (Figure 3) [2].

Click here to receive demo and presentation of Micro Crack Density.

References:
1. Su, X., Abdi, F. and J. Andre Lavoie, "Prediction of Micro-crack Densities in Cryogenic IM7/977-2 Propellant Tanks", 45rd AIAA Structures, Structural Dynamics, and Materials Conference, AIAA-2006-1933. Click here to read technical publication.

2. Su, X., Abdi, F. and Kim, R.Y., "Prediction of Micro-crack Densities in IM7/977-2 Polymer Composite Laminates under Mechanical Loading at Room and Cryogenic Temperatures," 46rd AIAA Structures, Structural Dynamics, and Materials Conference, AIAA-2005-2226. Click here to read technical publication. 
 

Did You Know?

Modeling Multiple Plies Using a Single Shell Element

imageUnlike many Finite Element Solvers, GENOA is able to model multiple plies (laminate) using a single shell element layer. In many FE solvers, the analyst has to model several layers of shell elements to assign plies in a laminate to each layer which increases the computation time significantly.  GENOA's single shell element modeling of plies offers easier assignment and faster performance.  For more information on trying out GENOA through our demos, please contact our sales at sales@ascgenoa.com.
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Wednesday, September 5, 2007

Impacted Composite Sandwich Panel


Software Suite for Durability, Damage Tolerance, and Life Prediction
Augments FEA Solvers MSC Nastran*, ABAQUS, ANSYS & LS-DYNA

* Best Performance and Verified Solutions with MSC Nastran



This Week's Feature Composite Example

Impacted Composite Sandwich Panels

Simulation of impacted foam core composite panels and calculation of residual strength after impact is a complex and challenging computational process. Accurate prediction requires the integration of material modeling capability with finite element dynamic explicit solution and damage tracking and fracture algorithms. A new computational methodology for assessing impact related damage and determination of residual strength after impact is presented. The analytical procedure relies on both implicit and explicit computational schemes. The degraded damaged properties are progressively updated at every time step of the analysis process.
Table 1: Comparison between Test and Simulation Results for Impact and Post-Impact Compression Analysis of a Foam Core Composite Sandwich Panel
A rigid body impacting a composite sandwich panel with a foam core with high velocity in the center of the panel was simulated. The simulation results indicated local delamination in the panel. The local damage due to impact was then included in the compression analysis. The numerical results obtained from the analytical approach predicted residual strength that is 6% higher than the one from the tests. In all, the analysis predicted that the strength of the sandwich panel in compression was reduced by a factor of 2.25 due to impact. 
Figure 1: Damage Accumulation at the End of Impact Simulation (Left) Damaged Foam (Right) Isolated Ply Damage View of the Foam, Adhesive, and the Face-sheets. Note that both figures show that the adhesive and the face sheets did not accumulate any damage
 
Figure 2: Comparison of Tests and Simulation Results (Left) Load versus Time and (Right) Impact Energy versus Time
 
Figure 3: Failure of the Composite Sandwich Panel during the Post-Impact Compression Simulation (Left) Damaged Panel after Impact Analysis (Right) Failure of the Composite Panel due to In-plane Compression at 24.78 kips
 
Figure 4: Load versus Displacement Curve obtained from Post-Impact Compression Analysis to Assess the Residual Strength
The results validated that the novel progressive failure dynamic approach in GENOA can be reliably used to assess damage growth and residual strength of impacted composite panels.


References:
Garg, M. and Abumeri, G., 2007. Assessment of Residual Strength in Impacted Composite Panels. JEC Composites Magazine (Pending Paper)

 
 

Did You Know?

Faster and Smaller Native .GEN File Format

imageDid you know that GENOA introduced a new native binary file format as of version 4.2? This format is identified with the file extension of ".gen" and supports a highly compressed binary format to allow fast reading and writing of project and data files.  On average, the file size is usually less than 1/10th the size of the previous text format.  For more information on trying out GENOA through our demos, please contact our sales atsales@ascgenoa.com.
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