An official website of the United States government
As a next generation composite material, carbon fiber reinforced polymer (CFRP) has great potential to be widely used in manufacturing industries due to its outstanding mechanical properties. The high strength to weight ratio, and high stiffness inherent to CFRPs make them a desired material in various kinds of applications. CFRPs frequently experience bending loads while in use for such things as aircraft, automobiles, bridges, etc. Anisotropic behavior and limited in through thickness properties are major concerns which affect the performance of CFRPs. Moreover, in the interlaminar region, traditional CFRPs are often vulnerable to matrix sensitive damage such as compressive failure, delamination, and shear failure due to the absence of enough strength in through thickness direction. The tensile and compressive stress generated by the bending loads can weaken the interlaminar shear properties due to the absence of fibers in through thickness and ultimately can lead to catastrophic failure. This study introduces a novel approach with z-threaded CFRP (ZT-CFRP), which incorporates electrically aligned z-threaded carbon nanofibers (CNFs) as reinforcement. Flexural test using 3-point bending was performed on both control CFRP and ZT-CFRP samples reinforced with 1.0 wt.% carbon nanofiber z-threads. The results showed a 15% improvement in the flexural strength and about 36% linear elastic range increase for the ZT-CFRP laminates compared to the unmodified CFRP laminates, and validated the effectiveness of nanofiber Z-threading strategy in strengthening composite materials against flexural loading.
more »
« less
This content will become publicly available on May 19, 2026
INVESTIGATE THE IN-PLANE SHEAR PROPERTIES IMPROVEMENT OF CARBON FIBER REINFORCED POLYMER LAMINATE ENHANCED WITH CARBON NANOFIBER Z-THREADS BY USING DIGITAL IMAGE CORRELATION SYSTEM
In-plane shear strength is an important issue for the structural integrity of carbon fiber reinforced polymers (CFRP). In this study [± 45°]4s in-plane shear test was performed for both Z-threaded CFRP (ZT-CFRP) and traditional CFRP. A newly developed proprietary Bisphenol-F based epoxy blend was used in this study. A significant improvement of +24% in the in-plane shear strength for ZT-CFRP was observed. There was a notable difference found in the failure modes between control CFRP and ZT-CFRP samples. Intralaminar and interlaminar delamination modes were noticed in control CFRP samples spreading to all plies whereas the ZT-CFRP samples experienced a confined failure in the interlaminar region. Digital image correlation (DIC) showed more uniform stress distribution and higher strain in ZT-CFRP, which suggested ZT-CFRP was stronger and tougher under the in-plane shear testing. Microscopic analysis of failure mode indicated that the z-threaded CNFs act as effective nano-structural reinforcement between and inside the laminas to keep the interlaminar/intralaminar bonding stronger.
more »
« less
- PAR ID:
- 10655018
- Publisher / Repository:
- Society for the Advancement of Material and Process Engineering
- Date Published:
- Subject(s) / Keyword(s):
- Carbon Fiber-Reinforced Polymer (CFRP), In-Plane Shear Stress, Shear Modulus
- Format(s):
- Medium: X
- Location:
- Indianapolis, IN, USA
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Previous studies have provided evidence that reinforcement of epoxy adhesives with nanostructures such as carbon nanofibers (CNFs) produces higher strength bonded joints between carbon fiber reinforced polymer (CFRP) laminates and shifts bond-line failure modes from the adhesive into the laminate. Despite this, there has been no research dedicated to applying reinforced adhesives to the bonding of nano-reinforced CFRP such as CNF z-threaded carbon fiber reinforced polymer (ZT-CFRP) laminates, which have been proven to exhibit increased interlaminar shear strength, mode-I delamination toughness, and compressive strength over traditional CFRP. This study examined the effectiveness of using CNF reinforced epoxy adhesives for unidirectional ZT-CFRP laminate bonding through single-lap shear tests using the ASTM D5868-01 standard. Unidirectional CFRP laminate samples bonded with both epoxy adhesive and CNF reinforced epoxy adhesive were also tested for comparison. It was found that the average shear strength observed for ZT-CFRP samples bonded with CNF reinforced epoxy adhesive was approximately 44% and 26 % higher than that of CFRP samples bonded with epoxy adhesive and CNF reinforced epoxy adhesive, respectively. Microscopic image analysis was performed to examine the mode of bond failure. The roles of nanomaterials in the fracture mechanism of the adhesives and the composite laminates are also discussed.more » « less
-
Previously reported vertical UL-94 testing results showed that carbon nanofiber z-threaded carbon fiber-reinforced polymer (ZT-CFRP) laminates have significantly improved flame resistance capabilities compared to traditional carbon fiber-reinforced (CFRP) laminates. Shorter flame self-extinguishing times and no flame propagation were reported. These characteristics provided evidence that ZT-CFRP’s unique microstructure, combined with its inherent strengthened mechanical, thermal, and electrical properties, has the potential to have more favorable high-temperature applications than traditional CFRP. This study examined the interlaminar shear strength (ILSS) enhancement of ZT-CFRP laminates, in comparison to traditional CFRP, when exposed to gradually increased temperatures. This was accomplished through the use of a furnace and an in-house constructed three-point bending apparatus capable of supplying static loading to determine the temperature at which failure occurred. The apparatus was loaded with a specimen and then placed inside the furnace where the temperature was allowed to increase based upon a consistent heating schedule. It was observed that ZT-CFRP samples had an approximately 30 ˚C improvement in temperature handling capabilities while exposed to an interlaminar shear load when compared to CFRP samples. Microscopic image analysis was also performed to observe how CNF z-threads contributed to the improved performance observed for ZT-CFRP at extreme elevated temperatures.more » « less
-
In this study, unidirectional carbon fiber prepregs that contain long carbon nanofiber (CNF) z threads as a through-thickness (z-directional) reinforcement were manufactured. The CNF z threads are long enough to thread through multiple carbon fiber (CF) arrays, which creates a multi-scale CNF/CF/resin-composite. The CNF z-threaded prepregs were manufactured using an electric-field aligned flow-transferring process. It was hypothesized that the CNF z-threads with the zig-zag threading pattern reinforces the interlaminar and intralaminar regions of the CFRP laminate thus improve the compressive strength by reducing the chance of carbon fiber buckling. Compressive testing was performed per modified version of ASTM D695 (i.e., SACMA SRM 1R 94) to evaluate the compressive strength of the CNF z-threaded CFRP (ZT-CFRP) laminates. The samples were manufactured using AS4 carbon fibers, EPON 862/Epikure-W resin and a 1wt% CNF content. ZT-CFRP testing results were compared with unaligned CNF-modified CFRP (UA-CFRP) and unmodified CFRP samples to investigate the impact of the CNF z-threads on the compressive strength. Results showed an increase of ~15% for the compressive strength of ZT CFRPs, whereas the UA-CFRPs experienced a decrease of ~8% when compared to unmodified CFRPs. It was concluded that CNF/carbon fiber interlocking stops and delays crack growth, and helps to stabilize carbon fibers from further buckling.more » « less
-
The matrix sensitive weaknesses of Carbon Fiber Reinforced Polymer (CFRP) laminates are usually magnified by mainstream additive manufacturing (AM) methods due to the AM-process-induced voids and defects. In this paper, a novel Magnetic Compaction Force Assisted-Additive Manufacturing (MCFA-AM) method is used to print Carbon Nanofibers (CNF) Z-threaded CFRP (i.e., ZT-CFRP) composite laminates. The MCFA-AM method utilizes a magnetic force to simultaneously support, deposit, and compact Continuous Carbon Fiber Reinforced Polymer (C-CFRP) composites in free space and quickly solidifies the CFRP part without any mold; it effectively reduces the voids. Past research proved that the zig-zag threading pattern of the CNF z-threads reinforces the interlaminar and intralaminar regions in the ZT-CFRP laminates manufactured by the traditional Out of Autoclave-Vacuum Bag Only (OOA-VBO) method, and enhances the matrix sensitive mechanical, thermal, and electrical properties. In this study, the longitudinal compressive test (ASTM D695, i.e., SACMA SRM 1R-94) was performed on the MCFA-AM printed ZT-CFRP laminate. The results were compared with unaligned CNF-modified CFRP (UA-CFRP), control CFRP, and no-pressure CFRP samples’ data to investigate the impact of the CNF z-threads and MCFA-AM process on the CFRP’s performance. The 0.5-bar MCFA-AM printed ZT-CFRP showed comparable longitudinal compressive strength with the 1-bar OOA-VBO cured CFRP.more » « less
