Moisture sorption of a three‐dimensional braided carbon fiber–epoxy composite under different media

A three‐dimensional braided carbon fiber–epoxy (C_3D/EP) composite was prepared by the vacuum‐assisted resin transfer molding (VARTM) technique. Its moisture absorption behavior under different media was characterized and compared with a unidirectional composite. Similar to the unidirectional composite, diffusion in the 3D composite obeys Fick's second law of diffusion when immersed in distilled water and phosphate‐buffered saline. In HCl and NaOH solutions, no Fickian behavior was observed. The similarity between the unidirectional and 3D composites suggests that fiber structure does not change diffusion pattern. However, the two composites showed different diffusion parameters (k, D, and M_e) in each medium studied. The 3D composite showed lower k, D, and M_e values because of its stronger hindrance effect to transport of moisture molecules. Diffusion in PBS is slower than that in distilled water because of the presence of heavy ions, but the diffusion pattern remains unchanged. In HCl, the diffusion behavior of the two composites cannot be described by Fick's law. In addition, the k value calculated from the initial linear part of the moisture sorption curve is much lower than that in distilled water. Diffusion in NaOH is unusual; the uptake initially increases rather rapidly but quickly drops, which is likely caused by the extensive solubility of the polymer matrix. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 507–512, 2005     

Impact resistant polymeric glasses using compressive pre‐stress

The application of an externally applied pre‐stress on impact properties is studied on polymethyl methacrylate (PMMA) organic glass. Samples are tested under equi‐biaxial compression, simple shear and a combination of biaxial compression and shear. Equi‐biaxial compression is shown to increase the threshold stress level for projectile penetration whereas shear pre‐stress has a large effect on the overall energy absorbed during an impact. There is also an apparent interaction observed between compression and shear to dramatically increase the threshold stress. Pre‐stressed laminates show an increase in damage area because of the unique formation of a secondary cone. Higher levels of compressive equi‐biaxial pre‐stress significantly increase the stress relaxation time because of the corresponding increase in hydrostatic stress. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Experimental and numerical study of distortion in flat,L‐shaped,and U‐shaped carbon fiber–epoxy composite parts

In this study, flat composite panels were fabricated to find the effect of different manufacturing parameters, including stacking sequence, part thickness, and tooling material, on distortion of carbon fiber‐epoxy composite parts. L‐shaped and U‐shaped panels were also made to investigate the effect of stacking sequence on spring‐in angle and warpage of the curved panels. Results showed that distortion of the flat panels caused by asymmetry in the stacking sequence was an order of magnitude greater than distortion of the panels with an unbalanced stacking sequence; whereas in the curved panels, the panel with an asymmetric stacking sequence showed the least spring‐in angle, and the largest angle was observed in the symmetric panel. MSC Marc was used to predict distortion of the panels, and the simulation results were compared with the experimental results for several stacking sequences of the flat and the L‐shaped panels. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40439.     

Enhancement of interlaminar fracture toughness of carbon fiber–epoxy composites using polyamide‐6,6 electrospun nanofibers

In this study, carbon fiber–epoxy composites are interleaved with electrospun polyamide‐6,6 (PA 66) nanofibers to improve their Mode‐I fracture toughness. These nanofibers are directly deposited onto carbon fabrics before composite manufacturing via vacuum infusion. Three‐point bending, tensile, compression, interlaminar shear strength, Charpy impact, and double cantilever beam tests are performed on the reference and PA 66 interleaved specimens to evaluate the effects of PA 66 nanofibers on the mechanical properties of composites. To investigate the effect of nanofiber areal weight density (AWD), nanointerlayers with various AWD are prepared by changing the electrospinning duration. It is found that the electrospun PA 66 nanofibers are very effective in improving Mode‐I toughness and impact resistance, compressive strength, flexural modulus, and strength of the composites. However, these nanofibers cause a decrease in the tensile strength of the composites. The glass‐transition temperature of the composites is not affected by the addition of PA 66 nanofibers. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45244.     

Preparation and properties of T300 carbon fiber‐reinforced thermoplastic polyimide composites

In this study, a series of T300 carbon fiber‐reinforced polyimide (CFRPI) composites were prepared by laminating premolding polyimide (PI) films with unidirectional carbon fiber (CF) layers. On the basis of PI systems design, the effect of CF volume fraction, processing conditions, and PI molecular structure on the properties of CFRPI composites was studied in detail. In addition, two kinds of nano‐particles, including carbon nano‐tube (CNT) and SiO₂ were filled into the premolding PI films with different concentrations. And the effect of nano‐particles on the properties of CFRPI composites was also investigated. The surface characteristic of T300 CF was measured by X‐ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The properties of premolding PI film and CFRPI composites were measured by dynamic mechanical analysis (DMTA), SANS testing machine, scanning electron microscopy (SEM), and so forth. These experimental results showed that the properties of CFRPI composites were mainly affected by the premolding PI film and molding condition. The change of CF volume fraction from 55% to 65% took little effect on the mechanical properties of CFRPI composites. In addition, the incorporation of nano‐particle SiO₂ could further improve the properties of CFRPI composites, but CNT hardly improved the properties of CFRPI composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 646–654, 2006     

Freeze–thaw resistance of unidirectional‐fiber‐reinforced epoxy composites

The freeze–thaw resistance of unidirectional glass‐, carbon‐, and basalt‐fiber‐reinforced polymer (GFRPs, CFRPs, and BFRPs, respectively) epoxy wet layups was investigated from ?30 to 30°C in dry air. Embedded optic‐fiber Bragg grating sensors were applied to monitor the variation of the internal strain during the freeze–thaw cycles, with which the coefficient of thermal expansion (CTE) was estimated. With the CTE values, the stresses developed in the matrix of the FRPs were calculated, and CFRPs were slightly higher than in the BFRP and GFRP cases. The freeze–thaw cycle showed a negligible effect on the tensile properties of both GFRP and BFRP but exhibited an adverse effect on CFRP, causing a reduction of 16% in the strength and 18% in the modulus after 90 freeze–thaw cycles. The susceptibility of the bonding between the carbon fibers and epoxy to the freeze–thaw cycles was assigned to the deterioration of CFRP. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Impact response of carbon‐epoxy laminates containing buffer‐strip layers

This work looks at the dynamic behavior of laminated carbon‐epoxy (C‐E) composites with inserted interleaf polytetrafluoroethylene (PTFE)‐coated material. Instrumented impact tests performed on the interleaved test samples showed significant differences in the energy absorption characteristics that could be correlated with the failure mode. It was inferred that with the introduction of small amounts of less adherent layers of material at specific locations, the load‐carrying ability decreased while the energy‐absorbing capability was found to improve considerably. These and other experimental observations are discussed in this article. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 752–761, 2002     

Barrier properties for short‐fiber‐reinforced epoxy foams

The barrier properties of short‐fiber‐reinforced epoxy foam are characterized and compared with unreinforced epoxy foam in terms of moisture absorption, flammability properties, and impact properties. Compression and shear properties are also included to place in perspective the mechanical behavior of these materials. Compared with conventional epoxy foam, foam reinforced with aramid fibers exhibits higher moisture absorption and lower diffusion, while glass‐fiber‐reinforced foam is significantly stiffer and stronger. In addition, the polymeric foam composites studied present superior fire‐resistance compared with conventional epoxy foam systems. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3266–3272, 2006     

Surface modification and physical properties of various UHMWPE‐fiber‐reinforced modified epoxy composites

Two surface modification methods—plasma surface treatment and chemical agent treatment—were used to investigate their effects on the surface properties of ultrahigh‐molecular‐weight polyethylene (UHMWPE) fibers. In the analyses, performed using electron spectroscopy for chemical analysis, changes in weight, and scanning electron microscope observations, demonstrated that the two fiber‐surface‐modified composites formed between UHMWPE fiber and epoxy matrix exhibited improved interfacial adhesion and slight improvements in tensile strengths, but notable decreases in elongation, relative to those properties of the composites reinforced with the untreated UHMWPE fibers. In addition, three kinds of epoxy resins—neat DGEBA, polyurethane‐crosslinked DGEBA, and BHHBP‐DGEBA—were used as resin matrices to examine the tensile and elongation properties of their UHMWPE fiber‐reinforced composites. From stress/strain measurements and scanning electron microscope observations, the resin matrix improved the tensile strength apparently, but did not affect the elongation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 655–665, 2007     

Three‐dimensionally braided carbon fiber–epoxy composites,a new type of materials for osteosynthesis devices. II. Influence of fiber surface treatment

Interfacial adhesion between carbon fiber and epoxy resin plays an important role in determining performance of carbon–epoxy composites. The objective of this research is to determine the effect of fiber surface treatment (oxidization in air) on the mechanical properties (flexural strength and modulus, shear and impact strengths) of three‐dimensionally (3D) braided carbon‐fiber‐reinforced epoxy (C_3D/EP) composites. Carbon fibers were air‐treated under various conditions to improve fiber–matrix adhesion. It is found that excessive oxidation will cause formation of micropits. These micropits are preferably formed in crevices of fiber surfaces. The micropits formed on fiber surfaces produce strengthened fiber–matrix bond, but cause great loss of fiber strength and is probably harmful to the overall performance of the corresponding composites. A trade‐off between the fiber–matrix bond and fiber strength loss should be considered. The effectiveness of fiber surface treatment on performance improvement of the C_3D/EP composites was compared with that of the unidirectional carbon fiber–epoxy composites. In addition, the effects of fiber volume fraction (V_f) and braiding angle on relative performance improvements were determined. Results reveal obvious effects of V_f and braiding angle. A mechanism was proposed to explain the experimental phenomena. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1040–1046, 2002     

Study on time‐dependent resistance of carbon black‐loaded high‐density polyethylene composites during the isothermal course

Carbon black (CB)‐loaded high‐density polyethylene composites were prepared using conventional blending. The resistance and temperature (R‐T) relations under constant heating rates and the resistance and time (R‐t) relations at different isothermal temperatures have been studied. The results of the R‐T and differential scanning calorimetry (DSC) curve demonstrated a correlation between the positive temperature coefficient/negative temperature coefficient transition and the melting course. At isothermal temperatures below T_PTC/NTC, the resistance displayed a sharp increase and thereafter a mild decrease with time. The time to reach the highest resistance became shorter with rise in the isothermal temperature. The ratio between highest resistance and initial resistance was maximum at T_peak of the DSC curve. When the isothermal temperature was higher than T_PTC/NTC, the resistance attenuated with time. The attenuation fits to a first order exponential decay function. The calculated time constant τ decreased with rise in isothermal temperature. The attenuation discrepancy under different isothermal temperatures reduced as the heating rate before the isothermal courses was higher. A model based on polymer chain diffusion and CB movements at high temperature is proposed. The model can explain the results obtained in R‐T and R‐t measurements. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2258–2263, 2001     

Investigation of mechanical properties of alumina nanoparticle‐loaded hybrid glass/carbon‐fiber‐reinforced epoxy composites

This research work investigates the tensile strength and elastic modulus of the alumina nanoparticles, glass fiber, and carbon fiber reinforced epoxy composites. The first type composites were made by adding 1–5 wt % (in the interval of 1%) of alumina to the epoxy matrix, whereas the second and third categories of composites were made by adding 1–5 wt % short glass, carbon fibers to the matrix. A fourth type of composite has also been synthesized by incorporating both alumina particles (2 wt %) and fibers to the epoxy. Results showed that the longitudinal modulus has significantly improved because of the filler additions. Both tensile strength and modulus are further better for hybrid composites consisting both alumina particles and glass fibers or carbon fibers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39749.     

Effects of various fillers on CEM‐1 laminate punchability

The primary objective of this study is to emphasize the modification of the epoxy resin formulation by implementing falling weight test to discuss reduction of impact energy and apply the thesis to improve the punchability on the CEM‐1 copper clad laminate. Experimental results demonstrate that the core structure can be modified with different phenolic resin; when phenolic resin PF‐440 of a smaller molecular weight is used as the modified agent, the impact energy can be lowered by 17%. In addition, three kinds of inorganic fillers, such as TiO_2, Al(OH)_3, SiO_2, are added and the core and face structure were modified separately. Adding these fillers has a small effect on lowering the impact energy and no clear evidence of tendency, while the phenolic resin has significant effect. When 10 phr TiO₂ is added to face, the impact energy can be lowered around 60% and has a visible effect on improving the punchability improvement of CEM‐1 copper clad laminate. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3381–3386, 2006     

The effect of hydroxyl‐terminated polybutadiene‐grafted carbon fiber on the impact performance of carbon fiber–epoxy resin composites

Carbon fiber (CF) containing 1.4 and 2.1 mmol/g of —COOH and —OH groups, respectively, was functionalized by using an excess of tolylene‐2,4‐diisocyanate. The NCO‐modified CF was submitted to a graft reaction with hydroxyl‐terminated polybutadiene (HTPB). The HTPB‐grafted carbon fiber was employed as reinforcing agent for epoxy resin‐based composites. The presence of the flexible HTPB at the interface between the fiber and the matrix resulted in a substantial improvement on impact strength. Additional improvement on toughness was achieved by using epoxy matrix containing dispersed phase of HTPB. The composite morphology was also studied by scanning electron microscopy. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1424–1431, 1999     

Experimental characterization and computational simulations of the low‐velocity impact behaviour of polypropylene

The objective of this work is to validate predictive models for the simulation of the mechanical response of polypropylene undergoing impact situations. The transferability of material parameters deduced from a particular loading scenario (uniaxial loading) to a different loading situation (multiaxial loading) was studied. The material was modelled with a modified viscoplastic phenomenological model based on the G'Sell–Jonas equation. To perform the numerical simulations, a user‐material subroutine (VUMAT) was implemented in the ABAQUS/explicit finite element code. Constitutive parameters for the model were determined from isostrain rate uniaxial tensile impact test data using an inverse calibration technique. In addition, falling‐weight low‐energy impact tests were performed on disc‐shaped specimens at velocities in the range 0.7 to 3.13 m s^?1. The model predictions were evaluated by comparison of the experimental and finite element response of the falling‐weight impact tests. The G'Sell–Jonas model showed much better predictability than classical elastoplasticity models. It also showed excellent agreement with experimental curves, provided stress‐whitening damage observed experimentally was accounted for in the model using an element failure criterion. © 2013 Society of Chemical Industry     

Effect of deposited carbon nanotubes on interlaminar properties of carbon fiber‐reinforced epoxy composites using a developed spraying processing

Carbon fiber‐reinforced epoxy composites, with incorporated carboxylic multiwall carbon nanotubes (CNTs), were prepared using vacuum‐assisted resin infusion (VARI) molding, and the in‐plane and out‐of‐plane properties, including mode‐I (G_Ic) and mode‐II (G_IIc) interlaminar fracture toughness, interlaminar shear strength (ILSS), tensile, and flexural properties were measured. A novel spraying technique, which sprays a kind of epoxy resin E20 with high viscosity after spraying the CNTs, was adopted to deposit the CNTs on the surface of carbon fiber fabric. The E20 was used to anchor CNTs on the fabric surface, avoiding that the deposited CNTs were removed by the infusing resin during VARI process. The spraying processing, including spraying amount and spraying sequence, was optimized based on the distribution of CNTs on the fibers. After that, three composite specimen groups were fabricated using different carbon fiber fabrics, including as‐received, CNT‐deposited with E20, and CNT‐deposited without E20. The effects of CNTs on the processing quality and mechanical properties of carbon fiber‐reinforced polymer composites were studied. The experimental results show that all studied laminates have uniform thickness with designed values and no obvious defects form inside the laminates. Compared with the composite without CNTs, depositing CNTs with E20 increases by 24% in the average propagation G_Ic, by 11% in the propagation G_IIc and by 12% in the ILSS, while it preserves the in‐plane mechanical properties, However, depositing CNTs without E20 reduces interlaminar fracture toughness. These phenomena are attributed to the differences in the distribution of CNTs and the fiber/matrix interfacial bonding for different spraying processing. POLYM. COMPOS., 2013. © 2012 Society of Plastics Engineers     

Three‐dimensionally braided carbon fiber–epoxy composites,a new type of material for osteosynthesis devices. I. Mechanical properties and moisture absorption behavior

In recent years, three‐dimensionally (3D) braided composites have attracted a great deal of attention because of their high‐impact damage tolerance and fatigue life, superior fracture toughness, and so forth, and have been used in aeronautics, military, and transportation. These advantages make them strong candidates for osteosynthesis devices. In this study, 3D braided carbon fiber–epoxy (C_3D/EP) composites were produced via a simple vacuum impregnation technique. The load‐deflection curve, mechanical properties, and influence of fiber volume fraction, braiding angle, and axial reinforcing fibers were examined to determine their suitability for internal fixation devices. It is found that the C_3D/EP composites have excellent toughness and do not show brittleness when fractured because of their relatively high void content. The flexural, shear, and impact strengths of the C_3D/EP composites are excellent. It was shown that a C_3D/EP composite with a stiffness similar to load‐bearing bones can be made while maintaining enough strength. It is concluded that a relatively higher void content and braiding angle is more suitable for the C_3D/EP composites from the viewpoint of requirements of fracture fixation materials. The moisture absorption behavior and changes in mechanical properties caused by moisture uptake were evaluated. Results show that absorbed moisture slightly decreases mechanical properties of the C_3D/EP composites. Contrary to the unreinforced epoxy, the moisture absorption behavior of the C_3D/EP composites cannot be described with Fick's law of diffusion, probably because of the presence of voids and/or 3D fiber structure. The exact mechanisms should be proposed in further investigations. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1031–1039, 2002     

TTT‐diagram for epoxy film adhesives using quasi‐isothermal scans with initial fast ramps

The characterization of film adhesives is challenging because they required freezer storage, contain an inseparable filler—thermoplastic knit or fiber‐reinforcement, and are heat activated systems with a pre‐cure and unknown chemistry. A testing protocol that eliminates these sources of error is proposed. This study presents a method to generate time–temperature‐transformation (TTT) diagrams of epoxy film adhesives via differential scanning calorimetry (DSC). Non‐isothermal and isothermal DSC scans are used to capture the reaction and the glass transition temperature. The use of an initial fast ramp—up to 500 K/min—in the isothermal scans is explored for the first time. This technique shows the potential to produce a quasi‐isothermal cycle, eliminating the loss of data in the initial stage of the reaction. The total heat released, the activation energy, and the fractional kinetic parameter, are estimated via model‐free methods. The Kamal–Sourour model and the formal kinetic model are fit to model the rate of cure. The simplest model that accurately captures the reaction, a parallel two‐step model, A , is outlined. The glass transition temperature is modeled via DiBenedetto's equation to include the diffusion‐controlled mechanism. The TTT‐diagrams of two commercial adhesives, DA 408 and DA 409, are shown with an analysis of processing optimization. The use of quasi‐isothermal scans with initial fast ramps combined with the correction for filler, moisture, and pre‐curing history can be applied to characterize fast curing thermosets, complex B‐stage resins, and thermosetting composites. The modeling results can also be used in numerical studies of residual stresses and dimensional stability in the manufacturing of thermosetting composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45791.     

Evaluation of tribological performance of surface‐treated carbon fiber‐reinforced thermoplastic polyimide composite

The effect of surface treatment [rare earth solution (RES) and air oxidation] of carbon fibers (CFs) on the mechanical and tribological properties of carbon fiber‐reinforced polyimide (CF/PI) composites was comparatively investigated. Experimental results revealed that surface treatment can effectively improve the interfacial adhesion between carbon fiber and PI matrix. Thus, the flexural strength and wear resistance were significantly improved. The RES surface treatment is superior to air oxidation treatment in promoting interfacial adhesion between carbon fiber and PI matrix. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008