4 KiB
Effect of interleaving on the impact of a UD carbon-epoxy
1995 #vem online ref Effect_of_interleaving_on_the_impact_of_a_UD_composite.pdf
Study of a drop-weight Impact-Shock-Collision response. The Viscoelasticity is poly(ethylene-co-acrylic acid) (PEAA) : high-strain low-modulus. improvement of PCLD damping follow Ross-Kerwin-Ungar (RKU) theory for sandwich of isotropic layers, and Ni-Adams (NA) theory for fibrous composite. for symmetric angle-ply laminate : RKU/NA + something else (attributed to additional shear deformation of the sandwiched layer induced by bending the outer layers). Interleaving changed the Composite Failure Modes from compressive fracture of base laminate to tensile fracture.
Optimal position needed (too much can lead to adverse compressive properties, and weigh penalties (because lower modulus)). Suggested of locations of premature failure or where there are stress concentrations (where discontinuities).
This paper showed a great increase in energy absorption of the drop-weight Impact-Shock-Collision.
Key point : suppression of propagation of the compressive crack + differences in stress redistribution.
Experimental optimization of impact absorption of carbon-epoxy laminate
2008 #perforated online ref Experimental_optimization_of_impact_absorption_of_carbon-epoxy_laminate.pdf
Aims to optimize the impact energy absorption of carbon-epoxy laminate. Interleaved with poly(ethylene-terephtalate) (PET), with d=1 mm circular holes at several densities.
ductility index (for Charpy impact test): ratio between the propagation and the initiation energies
5 basic failure modes in composite (see Composite Failure Modes) : (i) fibre fracture (for aramids, defibrilation) (ii) resin crazing, micro-cracking and gross fracture (iii) debonding between fibre and matrix (iv) fiber pull out from the matrix (v) delamination of adjacent plies
Elastic modulus practically independent of the level of interlaminar adhesion, while bending strength decreased as the interlaminar Fracture Toughness decreased.
While initiation energy increases, the propagation energy decreases with the interlaminar Fracture Toughness. ->The total fracture energy passes through a maximum for a given interlaminar Fracture Toughness (total impact energy increases is 1.8 higher than non interleaved)
Optimization method of composite laminates with a viscoelastic layer
2009 #perforated #vem Optimization_of_composite_laminate_with_viscoelastic_layer.pdf
This paper develops a method to transform a multi objective (damping and stiffness) into a single one, to facilitate optimization.
The Viscoelasticity layer is perforated, and the sandwich is Co-curing, so the resin flows through the VE layer and couples the structure. More stiffness, less damping => need optimizing (where holes, which size).
Co-curing means the viscoelastic material within the composite laminate undergo the temperature and pressure cycle needed to cure the composite material.
To make the single-objective, an evaluation function is constructed. This function is a liner weigh sum of two sub objective functions (loss factor and bending stiffness).
The variable in this function is the ratio of the perforation area to the total area.
The variation of stiffness and damping (here they chose the loss factor) depend a lot on the ratio's value and not just the change (ie 95%->100% see more change than 50%->55%). So a power function was chosen to approximate the objective function. (confidence of 0.95)
The calculation of the weigh are very interesting (but more complex than I can synthesize properly for now)
Result : < 5% of perforation