When inevitable, failure in composite laminates is preferred to occur gracefully to avoid loss of property and possibly life. While the inherent inhomogeneity of composites leads to slow dissipation of damage-related energy, overall failure is predominantly fiber-dominated and occurs in a rather brittle manner. This is affected to a certain extent by the laminate layup where multidirectional plies give in general a more ductile response as measured by ultimate deformation. Additionally, overall stiffness and strength as well as cost are important factors to consider in designing composite laminates. It is desirable then to optimize for high performance in terms of mechanical properties and low cost while keeping failure modes as graceful as can possibly be achieved.

Designing composite laminates with hybrid systems and creation of layups which permit gradual energy dissipation caused by damage are two ways proposed in this work to optimize for mechanical properties while avoiding catastrophic failure. In the hybrid system design, combining the less expensive glass reinforced plies with carbon reinforced plies offers a cost-effective product where change in the mechanical properties is marginal while energy dissipation past onset of internal damage follows the profile of a ductile material. The glass fiber core plies were embedded between two skin layers of carbon fiber mats forming a hybrid system. The skin layers comprised of one or two mats of 3k 43200 TWILL 2/2 carbon fibers textile. Two different glass fiber textiles are employed in the core layers namely (0^o^) UNI1050M50 and (0/±45^o^) ETXL1200-SBIL glass fiber mats.

Hybrid glass/carbon composite laminates subjected to three-point bending showed strain to failure which is double that measured for carbon composite specimens, without affecting the ultimate load. The carbon/glass hybrid system can also serves as a strengthening technique for glass fiber composites with tolerant  increase in thickness.

Energy dissipation mechanisms were also created by building laminates from unidirectional composites which were intentionally made discontinuous. In several bending tests performed of carbon-reinforced laminates, cuts across the fibers were introduced into the interior plies. These cut were located at different span fractions while keeping the outer skin of the laminate continuous. This created a longer path for damage progression and dissipated strain energy gradually before cutting through the next ply. This technique also doubled the strain to failure compared to specimens with intact plies while the reduction in ultimate load was marginal. The effect of fiber discontinuity in terms of spacing and distribution are among the factors considered for improving the ductile response and maintaining high strength.


Designing Composites for Graceful Failure

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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