Mesoscale Process Modeling of a Thick Pultruded Composite with Variability in Fiber Volume Fraction

Abstract

Pultruded fiber-reinforced polymer composites are susceptible to microstructural nonuniformity such as variability in fiber volume fraction (Vf), which can have a profound effect on process-induced residual stress. Until now, this effect of non-uniform Vf distribution has been hardly addressed in the process models. In the present study, we characterized the Vf distribution and accompanying nonuniformity in a unidirectional fiber-reinforced pultruded profile using optical light microscopy. The identified nonuniformity in Vf was subsequently implemented in a mesoscale thermal–chemical–mechanical process model, developed explicitly for the pultrusion process. In our process model, the constitutive material behavior was defined locally with respect to the corresponding fiber volume fraction value in different-sized representative volume elements. The effect of nonuniformity on the temperature and cure degree evolution, and residual stress was analyzed in depth. The results show that the nonuniformity in fiber volume fraction across the cross-section increased the absolute magnitude of the predicted residual stress, leading to a more scattered residual stress distribution. The observed Vf gradient promotes tensile residual stress at the core and compressive residual stress at the outer regions. Consequently, it is concluded that it is essential to take the effects of nonuniformity in fiber distribution into account for residual stress estimations, and the proposed numerical framework was found to be an efficient tool to study this aspect.

Modeling Spring-In of L-Shaped Structural Profiles Pultruded at Different Pulling Speeds

“…It is also necessary to conduct multicriteria optimization of manufacturing conditions to maximize the pulling speed and minimize cure-induced residual stresses, spring-in, and formation of matrix cracks/delaminations, as was already done for other processes [ 73 , 106 ]. The effect of fiber volume fraction variability on the development of residual stresses and, therefore, on spring-in occurrence is to be investigated as well [ 30 ]. The authors also intend to simulate the formation of process-induced defects (spring-in, matrix cracks, delaminations) and their influence on the structural performance of other standard [ 107 , 108 , 109 ], curved [ 20 ], and new types of profiles designed using topology optimization methods [ 110 ].…”

“…Spring-in is the primary contributor [ 26 ] to the distortion of a profile, which may require costly and time-consuming shimming operations during assembly [ 27 , 28 ]. Residual stresses developing during the production and assembly stages are detrimental to the final mechanical performance of a structure [ 29 , 30 ]. Thus, the ability to predict, control, and compensate for process-induced deformations is crucial for the effective design and assembly of composite structures [ 31 , 32 ].…”

Cost-efficient, automated, and sustainable composite profile manufacture: A review of the state of the art, innovations, and future of pultrusion technologies

“…For resin-injection pultrusion, in particular, where analyses of the impregnation flow is essential to ensure saturation [15,[38][39][40]55,56], studies have considered geometrical configurations of the injection chamber [57][58][59][60][61] as well as other process parameters such as the profile-advancing pulling speed [62], resin viscosity [63], and fibre permeability [64]. Using thermo-chemical-mechanical analyses, numerous studies have also looked into process-induced stresses and deformation of thermoset pultrusion [17,[65][66][67][68][69][70][71][72]. Clearly, extensive efforts have been invested in advancing the fundamental understanding of the governing physics of pultrusion.…”

Failure mechanism of unidirectional basalt fiber‐reinforced polymer composites with pretension of fiber yarns

“…The strength and stiffness of FRPs with higher fiber volume fraction were higher than that of the lower counterparts. [28,29] Alternatively, it needed large pulling force to manufacture pultruded FRP composite products of high fiber volume fraction and high strength.…”