An official website of the United States government
Moisture is a known issue for carbon fiber reinforced polymer (CFRP) manufacturing. During the process, in which a CFRP prepreg is carefully thawed, cut, stacked, and cured into a laminate, any bad moisture control can cause voids, affect the curing, and degrade the laminate. Recent studies of carbon nanofiber z-threaded CFRP (i.e., ZT-CFRP) prepreg and its laminates showed significant multifunctional improvements in the mechanical strengths, toughness, thermal conductivity, and electrical conductivity. The carbon nanofibers zig-zag thread among the carbon fibers in the through-thickness direction (i.e., z-direction) and mechanically interlock the fiber system together to form an effective 3D-fiber-network reinforced laminate. This paper presents a preliminary experimental study on the ZT-CFRP prepreg when facing the moisture exposure during the prepreg handling and lamination process. Both the ZT-CFRP and traditional CFRP prepregs, subjected to different humidity conditions, will be cut, and cured into laminate samples. The samples will be tested for their interlaminar shear strengths (ILSS) and hardness. Microscope pictures of the samples' fracture patterns will be compared for explaining the combined impact of the moistures and the carbon nanofiber z-threading strategy on the laminates' interlaminar shear strength and curing state.
more »
« less
Three-dimensional modeling of frontal polymerization for rapid, efficient, and uniform thermoset composites manufacturing
Due to the incapability of one-dimensional (1D) and two-dimensional (2D) models in simulating the frontal polymerization (FP) process in laminated composites with multiple fiber angles (e.g., cross-ply, angle-ply), modeling a three-dimensional (3D) domain, which is more representative of practical applications, provides critical guidance in the control and optimization of the FP process. In this paper, subroutines are developed to achieve the 3D modeling of FP in unidirectional and cross-ply carbon fiber laminates with finite element analysis, which are validated against the experimental data. The 3D model is employed to study the effect of triggering direction in relevance to the fiber direction on the FP process, which cannot be studied using traditional 1D/2D models. Our findings suggest that triggering in the fiber direction leads to a higher front velocity, in comparison to cases where front was triggered in the direction perpendicular to the fiber. Moreover, the average front velocity in cross-ply laminates is on average 20~25% lower than that in unidirectional laminates. When triggered using two opposite fronts in the in-plane direction, the maximum temperature of the thermal spike in the cross-ply laminate, when two fronts merge, is about 100 °C lower than that in the unidirectional laminate. In cross-ply laminates, a sloped pattern forms across the thickness direction as the front propagates in the in-plane direction, as opposed to the traditionally observed uniform propagation pattern in unidirectional cases. Furthermore, the effect of thermal conductivity is studied using two additional composite laminates with glass (1.14 W/m·K) and Kevlar fibers (0.04 W/m·K). It is shown that the frontal velocity, degree of cure, and the thermal spike temperature decrease as the thermal conductivity reduces.
more »
« less
- Award ID(s):
- 2208130
- PAR ID:
- 10469083
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Composites Part B: Engineering
- Volume:
- 266
- Issue:
- C
- ISSN:
- 1359-8368
- Page Range / eLocation ID:
- 111029
- Subject(s) / Keyword(s):
- Frontal polymerization finite element analysis cross-ply laminate triggering direction efficient manufacturing
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Introducing auxeticity or negative Poisson’s ratio is one potential solution to mitigate the low velocity impact damage of fiber reinforced polymer matrix composites, which can be achieved by tailoring the layup of an anisotropic composite laminate. This study aims to investigate the effect of laminate-level in-plane negative Poisson’s ratio on the low velocity impact behavior of carbon fiber reinforced polymer (CFRP) matrix composites using numerical simulations. The layups of the auxetic composites that allow them to produce negative Poisson’s ratios are identified based on the Classical Lamination Theory and verified through fundamental coupon-level experimental tests. To ensure meaningful comparisons, the non-auxetic counterpart composites are designed by allowing them to produce positive in-plane Poisson’s ratio while closely matching the longitudinal effective modulus of the auxetic laminate. The simulation results indicate that the auxetic laminates suffer smaller (12.6% on average) delamination area in top and bottom interfaces, much smaller (38% on average) matrix compressive damage in the top and bottom plies, and smaller (14.6% on average) fiber tensile damage area in each ply of the laminate at relatively higher impact energies (5 and 8 J).more » « less
-
Auxetic materials are those that exhibit negative Poisson’s ratios. Such a unique property was shown to improve the indentation and impact resistances. Angle-ply composite laminates can be designed to produce negative Poisson’s ratio at the laminate level due to the large anisotropicity of the individual layer and the strain mismatch between adjacent layers. This paper investigates the effect of through-thickness negative Poisson’s ratio on the low velocity impact behaviors of carbon fiber reinforced polymer matrix composite laminates, including the global impact behaviors, as well as the delamination, and the fiber and matrix damage. Results from numerical investigations show consistently reduced fiber and matrix tensile damage in the auxetic laminate in all plies, in comparison to the non-auxetic counterpart laminates (up to 40% on average). However, the auxetic laminate does not present a clear advantage on mitigating the delamination damage or the matrix compressive damage.more » « less
-
This study experimentally and analytically examined the influence of carbon nanofiber (CNF) z-threads on the through-thickness (i.e., z-direction) thermal conductivity of unidirectional carbon fiber reinforced plastics (CFRPs). It was hypothesized that a network of CNF z-threads within CFRPs would provide a thermally conductive microstructure throughout the sample thickness that would increase the through-thickness thermal conductivity. The experiments showed that the through-thickness thermal conductivity of the CNF z-threaded CFRPs (9.85 W/m-K) was approximately 7.53 times greater than that of the control CFRPs (1.31 W/m-K) and 2.73 times greater than that of the unaligned CNF-modified CFRPs (3.61 W/m-K). Accordingly, the CNF z-threads were found to play a substantial role in increasing the through-thickness thermal conductivity of CFRPs. To better understand the role of the CNF z-threads in through-thickness thermal transport, simple logical models of the CFRPs were constructed and then compared with the experimental results. Through these analyses, it was determined that CNF z-threads substantially enhance the through-thickness thermal conductivity by creating carbon fiber-CNF linkages throughout the CFRP laminate; these linkages allow the heat flow to largely bypass the resistive resin that envelops the carbon fibers. In addition, thermal infrared tests illustrated that the increased through-thickness thermal conductivity of the CNF z-threaded CFRP enabled the location and visualization of defects within the laminate, which was not possible with the control CFRP.more » « less
-
Frontal polymerization (FP) is a promising alternative manufacturing method for thermoset-based fiber-reinforced polymer composites (FRP) in comparison with the traditional autoclave/oven-curing method, due to its rapid curing process, low energy consumption, and low cost. Optimizing the weight contents of initiators relative to the resin’s mass is needed to adjust the mechanical properties of FRPs in industrial applications. This study investigates the effect of varying the photo-initiator (PI) weight content on tensile properties and the frontal polymerization characteristics, including the front velocity, front temperature, and degree of cure, in the FP process of the epoxy resin. Specifically, a dual-initiator system, including PI and thermal-initiator (TI), is used to initiate the polymerization process by ultraviolent (UV) light. The weight content of the TI is fixed at 1 w%, and the relative PI concentration is varied from 0.2 w% to 0.5 wt%. Results show that increasing the PI amount from 0.2 wt% to 0.3 wt% significantly improves the front velocity and the degree of cure by about two times. Increasing the PI content from 0.3 wt% to 0.4 wt% results in 15% and 26% higher degree of cure and front velocity, respectively. Moreover, due to the different front velocity in the top and bottom regions of the specimen, the specimens with 0.4 wt% PI exhibited a curved shape. The specimen with 0.5 wt% PI is thermally degraded and foamed. By comparing tensile properties, it is found that increasing the PI concentration from 0.2 wt% to 0.3 wt% improves the tensile strength and Young’s modulus by 3.91% and 7%, respectively, while the tensile strength and the Young’s modulus of frontal polymerized specimens are on average 8% and 14% higher than traditionally oven-cured ones, respectively.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.compositesb.2023.111029
