Chemical shrinkage characterization techniques for thermoset resins and associated composites

Abstract

International audienceControl and optimization of curing process is very important for the production of high quality composite parts. Crosslinking of molecules of thermoset resin occurs in this phase, which involves exothermy of reaction, chemical shrinkage (Sh) and development of thermo-physical and thermo-mechanical properties. Exact knowledge of the evolution of all these parameters is required for the better understanding and improvement of the fabrication process. Sh is one such property of thermoset matrix, which is difficult to characterize due to its coupling with thermal expansion/contraction. A number of techniques have been used to determine volume Sh of thermoset matrix, which later on has been used to find tensor of Sh for the simulation of residual stresses and shape distortion of composite part, etc. Direct characterization of volume Sh of composites has also been made by some authors. Though not much, but some work has also been reported to determine the Sh of composite part in a specific direction. In this article, all the techniques used in the literature for the characterization of Sh of resin and composite are reported briefly with their respective advantages, disadvantage and important results

Digital image correlation measurement of resin chemical and thermal shrinkage after gelation

“…Volume dilatometry methods: capillary type dilatometer [3], plunger type dilatometer [4,5], and gravimetric method [6] Non-volume dilatometric methods: prepreg warpage [7], ultrasonic methods [8], curing thermoset films on the metal substrate [9], density gradient column technique [10], optical extensometer [11], and modified rheology method [12] A detailed review of the different techniques for shrinkage measurement can be found in the work by Nawab et al [13]. For the non-volume dilatometric methods, the polymer deformation is constrained during cure, so the knowledge of polymer modulus development is required to interpret shrinkage strains.…”

In situ characterization of direction-dependent cure-induced shrinkage in thermoset composite laminates with fiber-optic sensors embedded in through-thickness and in-plane directions

“…capillary dilatometer, gravimetric method, rheometer, and thermo-mechanical analyzer) have been proposed and utilized to characterize and model cure shrinkage of thermoset resins and their composites. 4 However, most of the instruments work under conditions that do not match practical processes (e.g. in a high-pressure autoclave).…”

“…[4][5][6] Optical-fiber sensors are highly sensitive and very thin (diameter less than 150 mm), and thus can be embedded in composite materials in a minimally invasive manner and without significant effects on the global mechanical behavior of the host material. Several studies utilized fiber-optic sensors for in situ process monitoring of thermosetting resins 7-10 and their composites.…”

Bulk modulus evolution of thermoset resins during crosslinking: Is a direct and accurate measurement possible?

“…As no precise value was available in the literature, average values were chosen from the different studies concerning the development of mechanical properties of epoxy resins during cure. 3,[6][7][8][9][10][11][12][13][14]16,[24][25][26][27][28][29] Also, the different mechanical properties generally depend on the temperature, which is due to a modification of the molecular agitation as the temperature changes. As will be shown later, the chemical reaction happens during an isothermal step.…”