Mississippi State University
Progressive failure modeling of composite components under crush load is a challenging task due to complexity of the failure mechanisms involved. Researchers at the Center for Advanced Vehicular Systems at Mississippi State University studied the progressive failure of circular tubes made of fiber-reinforced polymer composite materials.
Crush simulations were performed using the explicit finite element analysis capabilities of MD Nastran SOL 700 coupled with a micromechanics-based progressive failure analysis constitutive model, GENOA  implemented as a material library (MATM). The micromechanics based material stiffness at the ply level was used in stress analysis with results compared with the micromechanics-based strength predictions. Damage was described by the gradual deterioration of the elastic properties of material based on the effective stress assumption , and the damage affected stiffness and strength properties were used to represent the physical behavior of the damaged material.
Simulation Model and Results
A 90-mm long circular tube of 50.8 mm diameter was modeled using different laminate configurations. The material and layup configurations included carbon fiber tape [45/0/-45/0/-45/0/45], and fabric [±45/±45/±45/±45/±45/±45/±45/±45], and two hybrid laminates made of the same materials in tape and fabric combinations. The tube was held fixed against a rigid wall at one end and pressed at the other end by a moving rigid wall. Contact friction was defined to prevent slippage between surfaces as well as to prevent element-element inter-penetration due to excessive deformation. Hughes-Liu shell element formulation including an hourglass control option was used in this analysis. The material coordinate system was automatically updated during the solution process following the rotation of the element coordinate system. The orientation of the material coordinate system and, therefore, the response of orthotropic shells can be very sensitive to in-plane shear and hourglass deformations depending on how the element coordinate system is established through the nodal connectivity or local coordinate system. To minimize this sensitivity, Invariant Node Numbering option was invoked .
The fiber and matrix properties along with the fiber volume fraction and failure properties were defined. For this analysis, the only criterion that was active for element removal was fiber tensile failure, S11T. The maximum failure criteria used to identify damaged plies were S11C, S22C, S22T, S33T, S33C, S12S, S23S, S13S, with C, T, and S denoting compression, tension, and shear, respectively. Moreover, modified distortion energy (MDE), relative rotation (RROT), fiber crushing (CRSH), delamination criteria (DELM) and fiber microbuckling (FMBK) were also used. In order to obtain a stable crush response, a trigger mechanism in the form of small axisymmetric conical groove with a length of 5.13 mm was placed at the loaded edge of the tube. The trigger was modeled by gradual reduction of the number of layers.
The normalized crush force-displacement curves are compared with the experimental data for two different material systems. The deformation plot for a specific ply pattern is also shown indicating that brittle damage and the formation of fronds seen in the experiments is accurately predicted by this model. Generally, the results show the successful application of a micromechanics based progressive failure constitutive model for crush analysis of composite tubes made of different laminate and material compositions.
Progressive crush for tube with [±45/0/±45/0/±45/0/±45] laminate.
1- GENOA4.3 Volume 1 User Manual, Alpha STAR Corp., Long Beach, CA, 2008.
2- Lemaitre, J., A Course on Damage Mechanics, Springer, Berlin, 1992.
3- MD Nastran R3 Quick Reference Guide, MSC.Software Corporation, Santa Ana, CA, 2008.