Abstract
The ability of a material to display two equilibrium states, called bistability, has been previously observed in carbon fiber reinforced polymers (CFRPs). For bistability to occur, the laminate must consist of an unsymmetric layup about its midplane which generates internal residual stress from thermal contraction. Prior studies have observed bistability in CFRPs with small-scale rectangular geometries where all sides were less than 250 mm. The aim of this paper is to demonstrate the existence of bistability in large-scale CFRPs with rectangular and non-rectangular geometries. Experiments and finite element analyses were conducted to determine the viability of bistability in large-scale CFRPs where at least one length aspect of the specimen was greater than or equal to 304.8 mm.
Specimens whose shapes included rectangles, deltoids, triangles, and circles, were fabricated and tested to determine the presence of bistability and the associated curvature for each cured equilibrium state. Rectangular specimens had a side length of 914.4 mm and widths that varied from 177.8 to 457.2 mm. For the deltoids, triangles, and circles, one length aspect (i.e. the height, hypotenuse, and diameter, respectively) equaled 304.8 mm. Finite element models were created to compare the equilibrium shapes’ curvatures and displacements with the experimental laminates; the existence of bistability was also examined using a nondimensionalized bifurcation plot.
Experimentally, bistability was found to occur for the fabricated laminates up to six plies. As the studied laminates could be considered thin, they displayed cylindrical cured shapes. The non-traditional shaped CFRPs followed bistability trends found for traditional, small-scale, rectangular laminates. An inverse relationship between the ply count and curvature was exhibited for the large-scale, rectangular laminates; curvature decreased as the number of plies in the laminate increased.
A structural chemistry look at composites recycling
