A Systematic Characterization Approach for Vacuum Bag Only Prepregs towards an Accurate Process Design

Aerospace-grade composite parts can be manufactured using Vacuum Bag Only prepregs through an accurate process design. Quality in the desired part can be realized by following process modeling, process optimization, and validation, which strongly depend on a primary and systematic material characterization methodology of the prepreg system and material constitutive behavior. The present study introduces a systematic characterization approach of a Vacuum Bag Only prepreg by covering the relevant material properties in an integrated manner with the process mechanisms of fluid flow, consolidation, and heat transfer. The characterization recipe is practiced under the categories of (i) resin system, (ii) fiber architecture, and (iii) thermal behavior. First, empirical models are successively developed for the cure-kinetics, glass transition temperature, and viscosity for the resin system. Then, the fiber architecture of the uncured prepreg system is identified with X-ray tomography to obtain the air permeability. Finally, the thermal characteristics of the prepreg and its constituents are experimentally characterized by adopting a novel specimen preparation technique for the specific heat capacity and thermal conductivity. Thus, this systematic approach is designed to provide the material data to process modeling with the motivation of a robust and integrated Vacuum Bag Only process design.

The Curing Kinetics of Multiscale [Ni(EDTA)]-2 Intercalated Zn-Al Layered Double Hydroxides: Glass Fiber–Epoxy Composite Prepreg

In the present research, the effect of Zn2Al layered double hydroxides (LDH) and nickel (II)-EDTA complex intercalated LDH (LDH-[Ni(EDTA)]-2) on the cure kinetics of glass fiber/epoxy prepreg (GEP) was explored using nonisothermal differential scanning calorimetry (DSC). The results showed that LDH caused a shift in the cure temperature toward lower temperatures while accelerating the curing of epoxy prepregs. The use of LDH-[Ni(EDTA)]-2 more profoundly influenced the acceleration of the curing process. The curing kinetics of prepregs was assessed through the differential isoconversional Friedman (FR) technique and the integration method of Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS). A decrease was detected in the E α value of glass fiber/LDH-[Ni(EDTA)]-2/epoxy (GELP) and glass fiber/LDH-[Ni(EDTA)]-2/epoxy (GELNiP) prepregs at small cure degrees relative to GEP, suggesting the catalytic effect of LDH or LDH-[Ni(EDTA)]-2 on the initial epoxy/amine reaction. Furthermore, LDH-[Ni(EDTA)]-2 performed better due to the catalyst role of nickel (II). Moreover, the activation energy exhibited lower reliance on the degree of conversion in the cases of GELP and GELNiP rather than pure epoxy prepregs. An autocatalytic model was used to evaluate the curing behavior of the system. Based on the results, the curing reaction of the epoxy prepreg can be described by the autocatalytic Šesták-Berggren model even after the incorporation of LDH or LDH-[Ni(EDTA)]-2. The kinetic parameters of the autocatalytic model (such as E α , A , m , n ) and the equations explaining the curing behavior of prepregs were introduced as well whose predictions were in line with the experimental findings.

A new cure kinetics model to simulate thermomechanical behavior of polymeric sealants for automotive applications

Accurate prediction of the cure level of thermoset polymers is essential to simulate the thermomechanical behavior of polymeric thermoset sealants, which is strongly dependent on cure level. Conventional cure kinetics models, however, fail to accurately predict the cure levels of thermoset sealants subjected to a complex temperature program. Herein, we propose a new cure kinetics model that greatly enhances cure level predictability by considering temperature derivatives. The validity of our model was verified by simulating the thermomechanical behavior of a polymeric sealant using a user material subroutine (UMAT) of ABAQUS software. Experimental results from an appropriately designed thermomechanical test were compared with simulation results obtained from the UMAT.

Cure Kinetics of Samarium-doped Fe3O4/Epoxy Nanocomposites

There was a question on “how lanthanides doping in iron oxide affects cure kinetics of epoxy-based nanocomposites?” To answer, we synthesized samarium (Sm)-doped Fe3O4 nanoparticles via electrochemical method and characterized it using FTIR, XRD, FE-SEM, EDX, TEM, and XPS analyses. The magnetic particles were uniformly dispersed in epoxy resin to increase the curability of the epoxy/amine system. The effect of the lanthanide dopant on the curing reaction of epoxy with amine was explored by modeling DSC experimental data based on model-free methodology. It was found that Sm3+ in the structure of Fe3O4 crystal participates in cross-linking of epoxy by catalyzing the reaction between epoxide rings and amine groups of curing agents. In addition, the etherification reaction of active OH groups on the surface of nanoparticles reacts with epoxy rings which prolongs the reaction time at the late stage of reaction where diffusion is the dominant mechanism.

A UNIQUE APPROACH TO EXPERIMENTAL CHARACTERIZATION OF A THERMOSETTING POLYMER MATRIX FOR ICME FRAMEWORKS

A novel approach for characterization of thermosetting epoxy resins as a function of the degree of cure is presented. Density, cure kinetics, tensile strength, and Young’s modulus are experimentally characterized across four mixing ratios of DGEBF/DETDA epoxy. Dynamic differential scanning calorimetry (DSC) is used to characterize parameters for a Prout-Thompkins kinetic model unique to each mixing ratio case through a data fitting procedure. Tensile strength and Young’s modulus are then characterized using stress-strain data extracted from quasi-static, uniaxial tension tests at room temperature. Strains are measured with the 2-D digital image correlation (DIC) optical strain measurement technique. Strength tends to increase as amine content use in the formulation increases. The converse trend is observed for Young’s modulus. Density measurements also reveal an inverse relationship with amine content.