[SY-J4] Validation of analytical models for ply cracking of general symmetric composite laminates
Invited
Validation of analytical models for ply cracking of general symmetric composite laminates
Polymer matrix composites (PMCs) that have high specific strength and specific rigidity have been used in aerospace fields. Laminates made by stacking unidirectional fiber-reinforced lamina, which have predefined mechanical properties, are commonly used. Fiber-reinforced laminates have a specific fracture mode such as transverse cracking, delamination, and breakage of the fiber. Of these fracture modes, transverse cracking occurs in the earliest stage. In laminates with plies in different fiber orientations, transverse cracks can form from defect in a given ply, and grow traversing the thickness of the ply and running parallel to the fibers in that ply. The most direct effect of transverse cracking is reduction of the thermomechanical properties of the laminate, including changes in the effective values of Young's moduli, Poisson's ratios, and thermal expansion coefficients. Substantial transverse cracking may give rise to more deleterious forms of damage, or provide pathways for the entry of moisture and corrosive liquids. Thus, although this damage mode is not critical from a final fracture point of view, it can result in significant degradation in the properties of laminates. Therefore, it is necessary to understand the mechanical behavior of laminate including transverse cracks. The continuum damage mechanics (CDM) is considered to be a valid approach to this issue. This approach utilizes the internal state variable and damage variable to consider the effect of transverse cracks on the reduction of stiffness.
In this study, the three-dimensional local stress field (3-D LSF) model was formulated at first. Secondly, a Tohoku continuum damage mechanics (TCDM) model, which is an energy-based model of ply cracking of general composite laminates, was presented using the 3-D LSF model and the CDM approach. Especially, the damage variable d2 in the direction normal to the fiber was derived for the ply including transverse cracking as a function of transverse crack density using the 3-D LSF model. Finally, the validity of the TCDM model was estimated by comparing the NPL model and the experiment results.
Polymer matrix composites (PMCs) that have high specific strength and specific rigidity have been used in aerospace fields. Laminates made by stacking unidirectional fiber-reinforced lamina, which have predefined mechanical properties, are commonly used. Fiber-reinforced laminates have a specific fracture mode such as transverse cracking, delamination, and breakage of the fiber. Of these fracture modes, transverse cracking occurs in the earliest stage. In laminates with plies in different fiber orientations, transverse cracks can form from defect in a given ply, and grow traversing the thickness of the ply and running parallel to the fibers in that ply. The most direct effect of transverse cracking is reduction of the thermomechanical properties of the laminate, including changes in the effective values of Young's moduli, Poisson's ratios, and thermal expansion coefficients. Substantial transverse cracking may give rise to more deleterious forms of damage, or provide pathways for the entry of moisture and corrosive liquids. Thus, although this damage mode is not critical from a final fracture point of view, it can result in significant degradation in the properties of laminates. Therefore, it is necessary to understand the mechanical behavior of laminate including transverse cracks. The continuum damage mechanics (CDM) is considered to be a valid approach to this issue. This approach utilizes the internal state variable and damage variable to consider the effect of transverse cracks on the reduction of stiffness.
In this study, the three-dimensional local stress field (3-D LSF) model was formulated at first. Secondly, a Tohoku continuum damage mechanics (TCDM) model, which is an energy-based model of ply cracking of general composite laminates, was presented using the 3-D LSF model and the CDM approach. Especially, the damage variable d2 in the direction normal to the fiber was derived for the ply including transverse cracking as a function of transverse crack density using the 3-D LSF model. Finally, the validity of the TCDM model was estimated by comparing the NPL model and the experiment results.