Kevin Hoos

Static strength prediction in laminated composites by using discrete damage modeling

Discrete Damage Modeling of complex local failure patterns in laminated composites including matrix cracking, delamination, and fiber failure was performed. Discrete Damage Modeling uses the Regularized eXtended Finite Element Method for the simulation of matrix cracking at initially unknown locations and directions independent of the mesh orientation. Cohesive interface model is used both for Mesh Independent Cracking as well as delamination propagation. The fiber failure mode is modeled by two different methods in tension and compression. Tensile failure is predicted by Critical Failure Volume criterion, which takes into account volumetric scaling of tensile strength. Compression fiber failure is simulated with a single parameter continuum damage mechanics model with non-compressibility condition in the failed region. Ply level characterization input data were used for prediction of notched and unnotched laminate strength. All input data required for model application is directly measured by ASTM tests except tensile fiber scaling parameter and compression fiber failure fracture toughness, which were taken from literature sources. The model contains no internal calibration parameters. Tensile and compressive strength of unnotched and open hole composite laminates IM7/977-3 has been predicted and compared with experimental data. Three different layups, [0/45/90/−45]2S, [30/60/90/−60/−30]2S, and the [60/0/−60]3S, were modeled and tested and showed good agreement with experiment in the case of tensile loading, whereas the compressive strength was generally under predicted for unnotched laminates and overpredicted for open hole laminates.

Simulation of Mode I Fracture at the Micro-Level in Polymer Matrix Composite Laminate Plies

A technique for simulating evolving matrix damage through a polymer matrix composite ply was developed. This method simulates disbonding between fiber and matrix and cracking within the matrix at the micro-scale. The aim of the study is to develop a methodology whereby the mode I traction-separation law (cohesive zone) for a given lamina could be obtained by simulation only using the fiber and matrix constituent properties as inputs. The results obtained with randomly spaced fibers representing approximately 1/3 of a ply thickness are encouraging.

Mesh dependence of the discrete damage modeling in laminated composites

The present paper addresses the issue of direct simulation of complex local failure patterns in laminated composites including matrix cracking, delamination, and fiber failure. The analytical technique uses the Regularized eXtended Finite Element Method (Rx-FEM) for the simulation of matrix crack initiation and propagation at initially unknown locations; cohesive interface model for delamination and continuum damage mechanics model for fiber failure. An important feature of the technique is that it uses independently measured standard ply-level mechanical properties of the unidirectional composite (stiffness, strength, fracture toughness). Failure simulations of composites containing open holes are presented. Mesh and parameter sensitivity of the strength values is investigated.