Short Aramid Research Articles

Constructing flexible fiber bridging claws of micro/nano short aramid fiber at interlayer of basalt fiber reinforced polymer for improving compressive strength with and without impact

The high-performance Basalt Fiber Reinforced Polymer (BFRP) composites have been prepared by guiding Micro/Nano Short Aramid Fiber (MNSAF) into the interlayer to improve the resin-rich region and the interfacial transition region, and the flexible fiber bridging claws of MNSAF were constructed to grasp the adjacent layers for stronger interlaminar bond. The low-velocity impact results show that the MNSAF could improve the impact resistance of BFRP composites. The compression test results demonstrate that the compressive strength and the residual compressive strength after impact of MNSAF-reinforced BFRP composites were greater than those of unreinforced one, exhibiting the greatest 56.2% and 73.3% increments respectively for BFRP composites improved by 4wt% MNSAF. X-ray micro-computed tomography scanning results indicate that the “fiber bridging claws” contributed to better mechanical interlocking to inhibit the crack generation and propagation under impact and compression load, and the original delamination-dominated failure of unreinforced BFRP composites was altered into shear-dominated failure of MNSAF-reinforced BFRP composites. Overall, the MNSAF interleaving might be an effective method in manufacturing high-performance laminated fiber in industrial production.

Numerical and experimental investigation for flexural response of Kevlar short fiber tissue/carbon fiber belts toughened honeycomb sandwich plate

This paper investigates the flexural behavior of honeycomb sandwich panels with a toughened/untoughened interface using carbon fiber belt and short aramid fiber tissues. In the first part of the paper, bending response analysis of carbon fiber aluminum honeycomb sandwich plates with an untoughened interface is done using finite element-based first-order shear deformation theory. In the second part, experimental analysis is done to examine the effect of loading rates on the mechanical characteristics of plain and toughened sandwich panels using a three-point bending test. Four types of interface toughening are used as unidirectional and bi-directional stitches of carbon fiber belts, Kevlar short-fiber tissues, and carbon fiber belts combined with Kevlar short-fiber tissues. Experimental result shows that interface toughening improves the maximum load and energy absorbed by sandwich specimens for all loading rates. A scanning electron microscope is used to observe and analyze the failure mode and mechanism of strengthening the interface. It is observed that the stitch of the carbon fiber belt increases the adhesion contact between face sheets and core leading to prevent interfacial debonding. The peak load and energy absorptions of carbon fiber belts toughened interface sandwich are increased by 51 % and 42.5 %, respectively, compared with that of the plain sandwich by a small increment of weight (14%).

Interfacial toughening and bending performance of the CFRP/aluminum-honeycomb sandwich

CFRP / honeycomb sandwiches often fail prematurely due to interface debonding when subjected to bending loads. In this paper, three kinds of toughening interfaces were designed, and their effects on the sandwich’s three-point bending performances (including peak force and energy absorption) were studied. The results showed that the peak force and energy absorption of the sandwich were increased by 43.6% and 141.3%, respectively by adding a multi-scale toughening film (short aramid fiber (AF) film grafted with polydopamine (PDA) and graphene oxide (GO)) at the interface. The toughening interface affected the deformation process and failure mode of the sandwich by changing the competition mechanism between the facesheet, interface, and honeycomb strength. The short fibers of toughening film formed bridges at the toughened interface, and the crack propagation mechanism changed from interface debonding to a combination of interface debonding and matrix fracture. In addition, the test results revealed that the wettability, tensile strength, surface roughness, and specific surface area of the fiber could be significantly improved by treating with PDA and GO, which lead to crack deflection at the interface. Thus, the interface debonding is effectively delayed or prevented.

Interlaminar fracture toughness of carbon/epoxy composites laminates toughened by short carbon fiber

AbstractIn this paper, short carbon fiber (SCF) interlaminar toughened carbon fiber reinforced epoxy resin (CF/EP) composite laminates were prepared. The effect of SCF content on the mode II interlaminar fracture toughness (GIIC) and flexural properties of CF/EP composites was investigated. It was shown that the addition of SCF between the plies had an effect on the GIIC of the composites. When the SCF content was 10 g/m2, the GIIC increased from 1506.62 J/m2 to 1995.6 J/m2, which improved by about 32.46%. When the content of SCF was 5 g/m2, the flexural strength and flexural modulus increased by 36.92% and 98.48%, respectively, showing the best performance. The toughening mechanism of SCF was observed by SEM images as SCF debonding and pulling out from the resin and SCF fracture. The present study was also compared with our previous study on short aramid fiber interlaminar toughened CF/EP composites, and the test data and SEM images of the two experiments were compared to analyze the effect of different short fibers on the interlaminar toughening effect, which provides some reference for the selection of interlaminar toughening materials.

Comparative evaluation of mechanical properties of short aramid fiber on thermoplastic polymers

Abstract This study investigated the mechanical performance of short aramid fiber on polypropylene, polyethylene, polyamide 6, and polyamide 12. Extrusion, press molding, and CNC cutting methods were used in the production of composite samples. Tensile, three-point bending, drop weight and hardness tests of the composites were carried out. As the fiber volume fractions increased, the mechanical properties of the composites improved, but the most efficient fiber fractions for each matrix changed. To analyze the performance of the fibers in the matrix on the composites, scanning electron microscope (SEM) images of the fractured surfaces as a result of tensile and drop weight tests were examined. As the fiber volume fractions increased, the fiber deformation increased, and as a result, the mechanical performance of the composites was adversely affected. Analysis of variance (ANOVA) and F test were performed using signal/noise values to analyze in detail the effect of experimental parameters on output values. Finally, the results of a regression equation model were compared with the experimental readings. It was found to be in good agreement with the model and the results of the experiment.

Short aramid fiber reinforced thermotropic liquid crystalline polyester composites: Fabrication, thermal, and mechanical properties

We conducted a study to analyze the impact of short aramid fibers (AFs) on the melt-rheological behavior, thermal transition, thermal stability, and mechanical durability of thermotropic liquid crystal polyesters (TLCPs). By using different AF loading contents ranging from 3–15 wt%, we produced TLCP matrix composites through masterbatch-based melt-compounding and injection-molding. The SEM images and FT-IR spectra demonstrate that the AFs are dispersed in the TLCP matrix with a microfibrillar structure through good interfacial adhesion caused by specific intermolecular interactions between the TLCP and AFs. As a result, the complex viscosity, shear storage/loss moduli, and thermal transition (melt-crystallization, glass transition, and melting) temperatures of the composites increase with increasing AF filler content. However, the melt-crystallization and melting enthalpies increase only at low AF loading contents of 3–5 wt%. At high AF contents of 7–15wt%, the enthalpies decrease owing to the partial aggregation of AF fillers. The thermogravimetric analysis proves that the thermal stability of TLCP/AF composites improves when the AF filler is introduced. The dynamic mechanical analysis using the stepped isothermal method shows that the addition of 5 wt% AF to the TLCP leads to an approximately 150% improvement in elastic moduli and long-term mechanical durability at elevated temperatures.

Strain softening of natural rubber composites filled with carbon black and aramid fiber

Engineered rubber vulcanizates may contain a low content of short fibers and a high content of nanoparticles while the effects of the different fillers on the softening behavior are not yet explored. Herein, influences of carbon black (CB) and short aramid fiber (AF) on the Payne and Mullins effects of natural rubber composites are investigated for the first time by creating master curves of dynamic modulus or dissipation energy with respect to the straining responses of the matrix. It is revealed that the composite vulcanizates demonstrate the Payne effect characterized by decay of storage modulus, weak overshoot of loss modulus, and very weak high-order harmonics; this effect is mainly dominated by the rubber matrix experiencing microscopic strain amplitude enlarged by the filler. The composite vulcanizates exhibit the Mullins effect that becomes increasingly marked with increasing filler loading and is partially recovered by thermal annealing at relatively high temperatures. The energy dissipation during cyclic tensions is rooted in the viscoelastic deformation of the matrix and the filler-rubber interfacial debonding. The former is marked at room temperature where the rubber phase undergoes a crystallization-melting process during loading-unloading. The latter being marked in the presence of a small content of AF causes yieldinglike deformation for the virgin composites at low tensile strains, and its contribution to the softening is not recoverable during thermal annealing. The results show that the viscoelastic matrix is of importance in controlling the softening of the composite vulcanizates, which will be of guiding significance to conduct research studies on high-performance rubber composites products.

Simultaneously improve the mode II interlaminar fracture toughness, flexural properties, and impact strength of CFRP composites with short aramid fiber interlaminar toughening

AbstractThis work mainly focuses on the mode II interlaminar fracture behavior of carbon fiber composite that was interlaminar toughened by short aramid fiber modified epoxy resin. The short fibers were first dispersed in the epoxy matrix and then in the laminate interlayer area during the lamination process. The ENF test evaluated the Mode II interlaminar fracture toughness of laminates. The results show that mode II interlaminar fracture toughness increases with the addition of short fibers. When the fiber content is 10 g/m2, the toughening effect is the best at 2437.72 J/m2, which is about 61.8% higher than the untoughened sample. The toughening mechanism of CFRP laminates by adding short fibers was observed by mode II fracture surface SEM images. In addition, flexural properties and Charpy impact properties of short fiber modified resin interlayer toughened laminates were also studied. The results showed that with this method, flexural properties and impact strength were improved to a certain extent, proving that this method is an effective interlaminar toughening method.

Mechanical and tribological behaviour of PA6 and short aramid fiber composites

This paper presents the results of mechanical and tribological characteristics for two composites: PA6 as matrix and 5% aramid whiskers as additive material and PA6 + 10% aramid whiskers, comparing them to those made of PA6 (polyamide 6). To improve the mechanical and thermal properties of polyamide (PA6), the composites were prepared via the Brabender lab mixer and mould forming under given pressure and temperature conditions. Test specimens made of pure PA6 and PA6 mixed with 5 wt.% and 10 wt.% aramid whiskers were subjected to mechanical tests (three-point bending and impact), thermo–mechanical test (HDT - heat deflection temperature), tribological test (block-on-ring) and analyzed from morpho-structural point of view. Compared to the PA6 samples, the mass concentrations of aramid whiskers improved the HDT deflection temperature values. In the case of samples with 5% aramid whiskers, the absorbed energy increased by 13% and for those with 10% aramid whiskers they increased by 30%. Aramid whiskers-doped materials performed much better on severe tribological testing as compared to PA6 samples. Increasing the deflection temperature, also improved their resistance from a tribological point of view.

Compression‐after‐impact properties of carbon fiber composites with interlays of Aramid pulp micro‐/nanofibers

AbstractThe inherent resin‐rich ply interfaces in laminar carbon fiber reinforced polymer (CFRP) composites are toughened by ultrathin interlays formed by Aramid pulp (AP) micro‐/nanofibers, to show that stronger and more impact‐resistant CFRP can be manufactured with minimum disruption to the current composite forming process. Flexible nonwoven AP micro‐/nano‐fibers, less than 1 mm in length, can conveniently fit in the uneven surface profiles or microresin‐rich areas between carbon fiber plies and form in situ quasi‐Z‐directional fiber‐bridging across the ply interfaces. CFRPs with multiple interfacial AP interlays estimated to be around 3 and 6 g/m2 were tested before and after low energy impact. Ultrathin resin‐rich ply‐interface layers in plain CFRP were transformed into ultrathin “Short Aramid Fiber Epoxy” layers by the AP interlays (20–50 μm in thickness), leading to enhanced compressive energy absorption and up to 86.7% increase in Compression‐After‐Impact Strength. Keeping the interlay thin (around 30 μm or thinner if possible), even the compressive strength (without impact) is not compromised, and the energy absorption under compressive loading (without impact) is 130% higher. The distinctly different compressive failure mechanisms, delamination failure of the plain CFRP was transformed into matrix shear failure in AP‐toughened CFRP, as identified by nondestructive X‐ray microcomputed tomography scans. Scanning electron microscopy was performed on the failure surface to inspect the microscopic toughening mechanisms.

Improved mechanical performances of short aramid fiber‐reinforced polypropylene composites by Ti3C2 Mxene nanosheets

AbstractFiber‐reinforced polypropylene (PP) composites are widely used for structural bearing because of their excellent mechanical property. So, it is necessary to improve the mechanical property of fiber‐reinforced PP composites. In this present, two‐dimensional Ti3C2 Mxene nanosheets were bound to short aramid fiber (SAF), forming Ti3C2 nanosheets‐modified SAF (Ti3C2/SAF), aiming to improve PP mechanical property. The Ti3C2 nanosheets were obtained after hydrofluoric acid etching and ultrasonically delamination procedure, followed by chemically bound to the surface of H3PO4 solution‐treated SAF to form Ti3C2/SAF. The Ti3C2/SAF‐reinforced PP (Ti3C2/SAF/PP) composites were prepared by a melt blending method. Scanning electron microscopy images showed that the Ti3C2/SAF modified with different concentration of Ti3C2 nanosheets solution presented the distinct morphologies, with the 0.3 mg/ml Ti3C2/SAF formed a relatively uniform Ti3C2 nanosheets coating on the SAF surface. Test results of mechanical performance indicated that the tensile and impact strength of Ti3C2/SAF/PP composites were significantly improved. Especially, the maximum tensile and impact strength of 0.3 Ti3C2/SAF/PP composite at 5 wt% reached to 37.8 MPa and 14.0 kJ/m2, which was increased by 11.5% (or 28.1%) in tensile strength and 12.9% (or 38.6%) in impact strength, compared with that of SAF/PP composite (or PP matrix). This can be attributed that Ti3C2 nanosheets binding to SAF improved the interfacial bonding strength between SAF and PP. This work provides a promising strategy for improving the mechanical properties of fiber‐reinforced PP composites.

Three-point bending properties of carbon fiber/honeycomb sandwich panels with short-fiber tissue and carbon-fiber belt interfacial toughening at different loading rate

The bending performances at different loading rate are studied for carbon fiber/honeycomb sandwich panels toughened by short aramid fiber tissues and carbon fiber belts. The carbon fiber belts are stitched cross the pores of honeycomb core for interfacial improvements. Three-point bending tests at different loading rates are carried out to investigate the effect of short aramid fiber tissue and carbon fiber belt on mechanical properties of carbon fiber/honeycomb sandwich specimens. Experimental results firstly indicate that the short-aramid-fiber interfacial toughening and carbon fiber belts toughening could both enhance the energy absorption and peak load of sandwich specimens at loading rates ranging from 2 mm/min to 500 mm/min. The failure modes and microstructures of toughened specimens are observed to analyse and explain the underlying mechanism of enhancing effect. It is illustrated that crack isolation phenomenon is found to be the main mechanism for avoiding interfacial damage of the sandwich specimen.

Stubble resistance of rubber vulcanizates: Influence of short fiber and resin

Stubble resistance of tread rubber vulcanizate of a tyre is crucial, especially for the off-the road (OTR) tyres. However, it has not been vividly discussed in the literature. Here, we developed a test method for stubble resistance, and studied the effect of short aramid fibre and two different types of resins on the stubble resistance of a conventional tire tread recipe with a view to its improvement. Resin filled compositions, being flexible, showed better cut initiation resistance, as compared to aramid fibre filled stiffer compositions, by dissipating the stress through chain orientation. During penetration, both cut growth and frictional force were important. For the aramid fibre composition, the frictional force dominated, whereas the cut growth was predominant for the resin filled vulcanizates. How the different energies associated with the fracture, e.g. cut initiation and growth energies, frictional energy and total fracture energy, altered with respect to the modulus or elongation at break of the rubber vulcanizates has also been discussed. At 4–6 phr of aramid filler concentration, stubble resistance drastically improved. On the other hand, the resin at 4 phr concentration exhibited an overall improvement in stubble resistance as compared to the conventional recipe. In summary, the present work contributed to the effect of different parameters on the stubble resistance of a tire tread rubber vulcanizate using an inhouse developed new test method.

Mode I interlaminar fracture toughness of CFRP laminates reinforced with short aramid fibers

Adhesive bonding has been applied successfully in many technologies. The short aramid fibers can be effectively embedded in interface layer wit adhesive-rich regions of the CFRP fabrics with carbon fibers oriented at 0° and 90° to form a strong pulling resistance. In this paper, the interface toughness of carbon fiber composite reinforced by aramid short fiber is studied based on the mode I crack growth test of double cantilever beam. The effort of the length and density of aramid short fiber on the interface toughness of carbon fiber composite are discussed. The test result shows that the best bonding strength is obtained at the condition of the aramid fibers with the length of 3 mm at the density of 24 g/m2. The ultimate load and the Mode I interlaminar fracture toughness are improved by 292.87% and 168.59%, respectively. The crack propagation path and fracture effect are analyzed and compared by Scanning Electron Microscopy (SEM) observations.

Effects of resin pre-coating on interfacial bond strength and toughness of laminar CFRP with and without short aramid fibre toughening

The brittle adhesive layer in carbon fiber-reinforced polymer (CFRP) laminates was strengthened by using short aramid fibers in this study. To ensure the feasibility and effectiveness of short aramid fiber interfacial toughening at the interface between the carbon-fiber face sheets, the self-prepared short aramid fibre tissue and the wettability treatment technology with resin pre-coating were applied to enable short aramid fibres to be well embedded in the uneven regions in the CFRP fabrics with fibres oriented at 0° and 90° to form a strong pulling resistance. The ultimate load and the mode I interlaminar fracture toughness have been improved by 75% and 103.9% from the double cantilever beam mode I crack propagation tests, respectively. The reinforcing mechanisms within the “composite adhesive layer” as a result of short aramid fibres are discussed together with detailed scanning electron microscopy observations and comparison test results.

Flexure and flexure-after-impact properties of carbon fibre composites interleaved with ultra-thin non-woven aramid fibre veils

Laminar carbon fibre reinforced polymer (CFRP) composites contain inherent weak ply interfaces due to the lack of through-thickness fibre reinforcement. In this study, all ply interfaces were interleaved with ultra-thin (13 μm) non-woven short aramid fibre (SAF) veils to generate across ply fibre bridging, formed in-situ by movements of free fibre ends during the composite forming process. The toughening effect of ultra-thin SAF veils (13 μm and 29 μm in thickness) before and after impact was measured and compared. It was found that the 13 μm SAF veils increased the bulk flexural strength and modulus of CFRP by 16.9% and 19.8% prior to impact, challenging the common belief that interleaving with micro-length or short fibres is only beneficial to post-impact properties. X-ray micro-computed tomography and cross-section microscopy examinations were used to explain the mechanisms for improved flexural properties before and after low-velocity impact.

Influence of thermal oxidation and maleinized liquid polybutadiene on dynamic and static performance of short aramid fiber‐reinforced carbon black‐ethylene propylene diene monomer composites

AbstractShort aramid fiber (AF)‐reinforced rubber composites (SFRRs) possess better mechanical performance than carbon black‐filled rubber in many respects. However, the performance of an SFRR depends on interfacial adhesion to a large extent. In this article, AF was treated by thermal oxidation and then used to prepare AF‐reinforced carbon black‐ethylene propylene diene monomer (CB‐EPDM) composites in the presence of maleinized liquid polybutadiene rubber as the compatibilizer. The interfacial adhesion between the AF and matrix was evaluated by means of the relative debonding energy (RDE), and the corresponding dynamic and static performance was studied. The interfacial adhesion could be improved by a combination of fiber surface treatment and rubber compatibility, and the RDE was increased. Compared with those of the unmodified AF‐reinforced CB‐EPDM, the tensile moduli at 100% and 300% elongation and the tear strength increased by 27.4%, 16.7%, and 22.9%, respectively, and the stress‐controlled fatigue life of the notched sample increased by 140%. The results showed that the RDE decreased gradually with increasing average deformation after strain‐controlled fatigue for 30 000 cycles, and the RDE remained at a higher level in the AF‐reinforced CB‐EPDM when better interfacial adhesion was formed.

Role of Carbon Black for Enhancing the Mechanical Properties of Short Aramid Fiber Reinforced Ethylene-Acrylic Rubber

Composites based on ethylene-acrylic rubber and 1 mm short aramid fibers (AF) were developed by varying the fiber content from 3 to 40 phr. At 10 phr short fiber loading, the tensile modulus (10 % modulus) of the neat matrix was around 11 times increased. However, its breaking elongation was decreased from 408 to 58 %. This drastic reduction in the breaking elongation even at a 10 phr fiber loading leads to a brittle failure with inferior toughness. The tensile-fractured surface of the fiber-filled composite showed an intact matrix with no plastic deformation during fiber pulled-out. To solve this problem, carbon black (CB) was used as a toughening agent. Surprisingly, the addition of 20 phr CB onto a 10 phr AF-filled composite enhanced its 10 % modulus in the longitudinal direction by 70 % and also enhanced its breaking elongation from 58 to 351 %. From the morphological analysis, it has been presumed that the addition of CB enhanced the friction between the fiber and the matrix at a very low strain and also facilitate the matrix for a plastic deformation at a higher strain. This enhanced friction between the fiber and the matrix is considered as the improved low strain modulus and the subsequent plastic deformation at a higher strain is responsible for the improved toughness.

Mode-II fracture properties of CFRP/steel composite structure reinforced by short aramid fibers

To obtain a good bonding strength of steel/CFRP adhesive joint, the steel surface was machined by grooving process. Short aramid fibers were mixed into the adhesive layer to achieve the further adhesion strength. In the pressing process of steel/CFRP specimen preparation, short aramid fibers with the diameter of several micrometers could be embedded in the grooved gap and the rough surface of CFRP. The higher strength aramid fibers had been not only improved interfacial strength of steel/epoxy and CFRP/epoxy, but also reinforced the adhesive layer due to the bridging activities of aramid fibers. In this study, Mode II fracture strength of grooved-steel/CFRP adhesive joints was investigated by end-notch bending test. The ultimate load and fracture energy of specimens have been improved by 15.7 and 6.8%, in comparison to specimens with smooth steel surface, respectively. The reinforcing mechanisms of CFRP/steel bonding joint as a result of short aramid fibers were discussed according to the failure modes of specimens, and scanning electron microscopy observation and experimental results were carried out.

A Numerical Model to Predict the Anisotropy of Polymer Composites Reinforced with High-Aspect-Ratio Short Aramid Fibers

Some fiber types have a high aspect ratio and it is very difficult to predict their composites using traditional finite element (FE) modeling. In this study, an FE model was developed to predict the anisotropy of composites reinforced by short aramid fibers. Three fiber distribution types were studied as follows: perfectly aligned, normally distributed, and randomly distributed fibers. The elastic constants were obtained, and, for different alignment angles and parameters in the fiber orientation distribution function, their numerical results were compared to those of the Mori–Tanaka model. Good agreement was obtained; thus, the employed FE model is an excellent and simple method to predict the isotropy and anisotropy of a composite with high-aspect-ratio fibers. Therefore, the FE model was employed to predict the orientation distribution of a composite fiber with a nonlinear matrix. The predicted and experimental results agree well.