Carbon Fiber-reinforced Polypropylene Research Articles

Study on the effect of fiber orientation on the elastic constants of carbon fiber reinforced polypropylene composites

In order to predict the effects of different fiber orientations on the elastic constants of composites, this paper takes carbon fiber reinforced polypropylene composites as an example, and adopts the Mori-Tanaka method to establish the Random Volume Element (RVE) model of fiber composites with five different fiber orientations, namely, 0 °, 30 °, 45 °, 60 °, and 90 °, and investigates the effects of the fiber The effects of fiber orientation and fiber volume fraction on their elastic constants were investigated to obtain the required data by this method instead of experiment. By improving the Halpin-Tsai model, the value of the orientation factor was determined on the basis of the random orientation factor, and the original shape factor was modified to an exponential shape factor, the orientation degree factor was introduced, and finally, the relationship equations between the modified exponential shape factor and the volume fraction and orientation degree were obtained. The results show that for the same fiber orientation and volume fraction, the smaller the value of shape factor, the higher the elastic modulus. The fitting errors of the four values of elastic constants were also analyzed, and it was found that the improved Halpin-Tsai model could be used to predict the elastic constants of carbon fiber-reinforced polypropylene composites in a certain range, thus providing a method to study the prediction of the elastic constants of composites by fiber orientation.

Effects of different types of functionalized polypropylenes on the tensile strength of short carbon fiber-reinforced polypropylene composites

In this study, the effects of various functionalized polypropylenes (PPs) with different types and contents of functional groups and crystallinities on the tensile strength of short carbon fiber (SCF)-reinforced plastics (SCFRPs) prepared by injection molding were evaluated. The tensile strengths of SCFRPs were significantly influenced by interfacial adhesion. The types and contents of functional groups introduced into functionalized PP were the dominant factors impacting the development of interfacial adhesion. In particular, near the surface where SCF and PP were highly oriented in parallel, functionalized PP with more functional groups added to side chains exhibited higher interfacial adhesion than that with fewer functional groups. These results suggested that PP molecular chain orientations resulting from the shear flow of injection molding were among the key factors affecting the interfacial adhesion of the PP matrix.

Infrared-thermography measurement of temperature distribution in carbon fiber–reinforced polypropylene during ultrasonic welding

Herein, the temperature distribution during ultrasonic welding of carbon fiber–reinforced polypropylene (CF/PP) was investigated. The temperature distribution was assessed using a thermographic camera that specifically targeted the lateral aspect of the welded section of the adherend in the lap joint. In addition, single lap shear tests were performed on the resulting welded joints. The welding experiments confirmed that the amplitude of the sonotrode impacts both the temperature distribution during welding and the quality of the joint, eventually affecting the mode of failure. By applying the half-width method to the measured temperature distribution in the thickness direction of the adherend, we assessed the spread of the high-temperature region centered on the welding interface. In this study, at a small amplitude (36 μm), the half-width of the maximum temperature showed approximately twice higher slope than at other amplitudes, indicating a wider high-temperature range even at the same interface temperature.

Line width prediction and mechanical properties of 3D printed continuous fiber reinforced polypropylene composites

A novel 3D printing process was used to fabricate continuous carbon fiber-reinforced polypropylene (CCF/PP) composites. In this study, a prediction model for the line width of 3D printed CCF/PP composites was developed based on the material conservation principle. According to this model, the correspondence rule between the process parameters and the fiber volume fraction of the sample was established. The accuracy of the prediction model was verified by monofilament printing experiments, and the maximum error of line width was 9.72%. Furthermore, the effects of process parameters on the flexural properties, tensile properties and interlaminar shear strength (ILSS) of 3D printed CCF/PP composites were investigated. The flexural strength of the sample reached 99.94 MPa and the flexural modulus reached 14.91 GPa. The maximum ILSS of the sample was 9.78 MPa, and the maximum tensile strength and modulus were 402.86 MPa and 43.64 GPa. The advantages of this process in terms of low manufacturing cost and trajectory flexibility could make it a good prospect for its application.

Effects of different types of maleic anhydride-modified polypropylene on the interfacial shear strengths of carbon fiber-reinforced polypropylene composites

Effects of different types of maleic anhydride-modified polypropylene on the interfacial shear strengths of carbon fiber-reinforced polypropylene composites

Effect of de-sizing on the structural and mechanical properties of carbon fiber reinforced polypropylene composites molded by the novel direct fiber feeding injection molding technology

Carbon fiber reinforced thermoplastic composites are rapidly emerging as alternative materials for auto parts due to recyclability, excellent stiffness, and strength to weight ratio. In the present study, the influence of carbon fiber de-sizing on the structural and mechanical properties of the sized and de-sized Carbon Fiber Reinforced Polypropylene (CFPP) composites molded by the recently developed novel Direct Fiber Feeding Injection Molding technology was studied. The effect of carbon fiber de-sizing on the structural properties was studied from the fiber dispersion status, fiber orientation factor, fiber volume fraction, and the fiber length. The surface morphology of the sized and de-sized carbon fibers was studied from the Scanning Electron Microscopy (SEM) and Atomic Force Microscope images. The static mechanical properties were studied based on the tensile tests at different loading rate and temperature. The Dynamic Mechanical Analysis tests were conducted to analyze the dynamic viscoelastic behavior of the sized and de-sized CFPP composites. The SEM images were used to observe the failure mechanism. The preliminary results indicated that de-sized composites had better fiber dispersion as compared to the sized CFPP composites. It was found that de-sizing the carbon fiber surface does not significantly affect the carbon fiber length, fiber volume fraction, and fiber orientation in the CFPP composites. Also, the de-sized composites showed better static and thermodynamic mechanical properties caused by the enhanced fiber matrix interaction in CFPP composites as compared to the sized CFPP composites. [Formula: see text]

Design optimization of bioinspired helicoidal CFRPP/GFRPP hybrid composites for multiple low-velocity impact loads

Low-velocity impact (LVI) on continuous fiber reinforced thermoplastics (CoFRTPs) has been extensively studied with a focus on single material. Impact characteristics and optimal design of hybrid CoFRTPs have not been well addressed even though they are of considerable advantages in balancing cost and performance. This study aims to develop design optimization of bio-inspired hybrid CoFRTPs to resist multiple impact loads. In this study, the LVI behaviors of carbon fiber reinforced polypropylene (CFRPP) and glass fiber reinforced polypropylene (GFRPP) composites were first characterized experimentally, respectively. Three typical failure modes were identified in both the CFRPP and GFRPP specimens, and GFRPP exhibited better impact toughness than CFRPP. Second, a progressive failure model (PFM) was developed for finite element analysis, and numerical results in LVI damage modes and force-displacement curves agreed quite well with the corresponding experimental data. Third, parametric studies indicated that peak energy absorptions of CFRPP and GFRPP specimens respectively decreased by 20.9% and 25.5% with impact angles varying from 0° to 30°, and design of helicoidal stacking configuration can effectively enhance the LVI resistances for both the CFRPP and GFRPP specimens. Hybridization of CFRPP and GFRPP enables to improve LVI resistances and reduce the material costs. Finally, a multiobjective optimization was performed to optimize material cost and LVI resistance of helicoidal CFRPP/GFRPP hybrid composites accounting for multiple impact loads, which increased the peak energy absorption by 31.0% and reduced material cost by 33.4% compared with the baseline design. This study is anticipated to introduce an optimum configuration of hybrid composites for bearing multiple low-velocity impact loads.

The influence of the addition position of cellulose nanofibers on the crystalline and mechanical properties of carbon fiber-reinforced polypropylene composites

ABSTRACT The introduction of nanofillers into conventional microsized fiber-reinforced plastic composites has great potential to improve the fracture toughness and crystalline properties of composites, especially for semicrystalline thermoplastic polymers. Although the selective reinforcement is possible by nanofiller addition, the influence of the addition position of nanofillers on the mechanical properties and crystalline properties still has not been revealed. In this work, the cellulose nanofibers (CNFs) as the secondary filler were added (i) into a polypropylene (PP) matrix by a melt-mixing process and (ii) onto a carbon fiber (CF) surface by a dip-coating process in a CF-reinforced PP composite. By focusing on the transcrystals surrounding CFs, which enable improvement of the interfacial strength, the crystalline properties and mechanical properties were investigated through polarized optical microscopy, differential scanning calorimetry, X-ray diffraction, and 3-point bending tests in this study. We revealed that (i) CNF addition into the PP matrix disturbed the transcrystallization surrounding CFs and that the mechanical properties slightly decreased. Conversely, (ii) CNF addition onto the CF surface promoted transcrystallization surrounding the CF, and the flexural yield strength and modulus significantly improved by a maximum of 30% and 63%, respectively.

Investigation of impact resistance performance of carbon fiber reinforced polypropylene composites with different lamination to applicate fender parts

Thermoplastic composites are rapidly emerging as alternative materials for auto parts owing to recyclability as well as excellent stiffness- and strength-to weight ratios. In this study, an optimal stacking sequence using twill-weave carbon fiber-reinforced polypropylene (CF/PP) prepregs and random fiber-reinforced polypropylene (RFP) sheets were investigated for the fabrication of an automobile fender. The lamination consisting of CF/PP only incurred imperfect resin impregnation. RFP insertion between CF/PP layers improved the resin impregnation. The hybrid stacking sequence not only reduced internal void contents but also increased the flexural and impact strength of the composite laminate. Using the optimal stacking sequence, a real-scale composite fender was fabricated and impact tests were performed. The test results were compared with the ones from an existing steel fender. In case of the steel fender, permanent deformation was observed even in one attempt, while no visible damage was found from the composite fender even after five consecutive impact tests.

Effect of microstructure induced by microcellular injection molding on electromagnetic interference shielding properties

AbstractPreparing lightweight and versatile products is the unremitting goal of industry to save resources and energy. Lightweight carbon fiber reinforced polypropylene (CF/PP) composite foams with high‐performance electromagnetic interference (EMI) shielding materials were fabricated by microcellular injection molding (MIM) technology. The average length and distribution of CF in CF/PP composite foams were examined. Thanks to the introduction of foaming process, the average CF length of composite foams was 33.98% longer than that of solids, which effectively enhanced the electrical conductivity and EMI shielding properties. The effect of shot size, gas content, and injection rate on the electrical conductivity and EMI properties was investigated. With melt shot size of 2/3 of the cavity volume, gas content of 0.5 wt% N2 and injection rate of 100 mm/s, optimal cellular structure of the composite material was obtained. The EMI shielding effectiveness (SE) reaches 36.94 dB, which is the highest value achieved by using MIM technology to the best of the authors' knowledge. In addition, the mechanical properties of cellular structure can still maintain good values, with the tensile strength and impact strength improved by 15.3% and 14.03%, respectively.

Experimental investigation into stamping of woven CF/PP laminates: Influences of molding temperature on thermal, mesoscopic and macroscopic properties

This study aimed to investigate the influences of stamping temperature (or molding temperature) on thermal properties of matrix, mesoscopic structures of fabric and effective macroscopic mechanical properties of composite materials through experimental characterization. The plain woven carbon fiber/polypropylene composite laminates were prepared by hot stamping at 190 °C, 220 °C and 250 °C, respectively. Thermal study was performed using differential scanning calorimeter and thermogravimetric analysis. The mesoscopic properties were characterized through microscope and scanning electron microscope (SEM). Tensile test and short beam shear test were conducted to evaluate macroscopic properties of the material. Effects of fabric structure on the crack initiation and propagation as well as local strain concentration of thermoplastic composite were investigated in detail using digital image correlation (DIC) technique. Relationships of process parameters, thermal characteristics, mesoscopic fabric structures and macroscopic mechanical properties of the carbon fiber reinforced polypropylene (CF/PP) materials were explored under different stamping temperatures. The experimental results revealed that with increase in processing temperature, the crystallinity of polypropylene (PP) matrix increased, and the interfacial adhesion between fiber and resin became strong, leading to increase in tensile modulus. Due to the change of resin viscosity, the aspect ratio, crimp angle and gap size of the fiber bundles also vary. The interfacial debonding was a main failure mode in CF/PP composites. This study is anticipated to provide fundamental understanding in how to tailor effective properties of composites through manufacturing process.

Effects of Processing Variables of Extrusion-Pultrusion Method on the Impregnation Quality of Thermoplastic Composite Filaments.

Carbon fibre-reinforced polypropylene composite filaments were fabricated via the extrusion–pultrusion method. One of the important factors influencing composites’ filament processability and structural properties is the impregnation quality, which can be represented by interfacial adhesion between the matrix and fibre. To improve the interfacial shear strength (IFSS) of the filament, four processing variables—melt temperature, pulling speed, number of pins in the impregnation die and fibre treatment—have been optimised using the Box–Behnken response surface methodology (RSM). Analysis of variance (ANOVA) was conducted to evaluate the linearity of the response surface models. Three levels were set for each independent variable. The melt temperature was varied at levels 190, 210 and 230 °C, while the pulling speed was set at three levels, namely, 40, 47 and 50 cm/min. The number of spreader pins was varied at 1, 2 and 3 pins, and there were three variations of the fibre treatment, namely, vinyltrimethoxysilane (VTMS), γ-aminopropyltriethoxy silane (APTS) and liquid nitrogen. Twenty-seven experimental runs were conducted, and a significant regression for the coefficient between the variables was obtained. The filament IFSS was measured by a customised pull-out test, and its surface morphology was characterised using a scanning electron microscope. ANOVA showed that fibre treatment significantly affected the IFSS due to their surface roughness, followed by pulling speed and melt temperature in quadratic order. Liquid nitrogen is recommended for carbon fibre treatment because of the high surface roughness, thereby providing a better matrix–fibre bonding effect. The results demonstrated that a melt temperature of 190 °C, pulling speed of 40 cm/min, three spreader pins and treatment of the fibre with liquid nitrogen afforded the optimum impregnation quality. It is important to keep a reasonable low processing temperature to obtain the geometrical stability of the product.

Ductile to Brittle Transition of Short Carbon Fiber-Reinforced Polypropylene Composites

In this work, the ductile to brittle transition behavior of short carbon fiber (SCF)-reinforced polypropylene (PP) composite is studied. Initially, the SCF-reinforced PP composites with a varying composition of SCF in the range of 0–40 wt% loading were first melt-mixed in a twin-screw extruder and later injection-molded to produce the testing samples. The experimental results indicate that with an increase in SCF loading, an increase in the tensile modulus and strength was observed along with a rapid decrease in the values of strain at break. A sudden decrease in strain at break was observed in composites in the range of 10–15 wt% SCF. To further study the sudden decrease in strain at break, an investigation was performed on composites that contained 10–15 wt% of SCF loading, starting from 10 wt% with a 1% increment to 15 wt% of SCF. The results of this study show that a decrease in strain at break was not linear; on the contrary, it was accompanied by a ductile to brittle transition, which specifically occurred in the range of 12–13 wt% of SCF loading and then continued to decrease with an increase in SCF loading.

A novel failure criterion based upon forming limit curve for thermoplastic composites

This study aims to explore failure mechanism and failure criteria of carbon fiber reinforced polypropylene (CFRPP) by presenting a novel notch-shaped design of specimens with two different fiber orientations (0/90)4 and (+45/-45)4 subject to stamping process under room temperature. Two forming limit curves/diagrams (FLCs/FLDs) were established based upon the minor strain and major strain, as well as the developed equivalent fiber strain combined with a ratio of minor to major strain (SR), respectively. A novel notch-shaped design enables to minimize the influence of fiber orientation on failure modes and FLC of CFRPP effectively. Not only did the equivalent fiber strain based FLC reflect the failure mode in terms of a certain SR value, but also showed the failure strain on fiber bundles quantitatively. Finite element (FE) models involving the new failure criteria (FLC) were developed on the basis of the experimental results. It was found that such a new FE model is able to better predict the results than those with the conventional maximum strain or maximum stress failure criteria. The difference in failure behaviors among these three failure criteria (i.e. FLC, maximum strain and maximum stress) was compared. The history of failure evolution and potential damage status of typical specimens were further analyzed through the FE model. The results indicated that the new FLC failure criteria can be used for the failure assessment in CFRPP structures. This study is anticipated to provide a guideline for further investigation into failure mechanism and failure criteria of thermoplastic composites under different service conditions.

Delamination Analysis in Drilling of Carbon Fiber Reinforced Polypropylene (CFR-PP) Composite Materials

Abstract Carbon Fiber Reinforced Polymeric (CFRP) composite materials are widely used in the fabrication of major structural parts in aerospace engineering application owing to their specific stiffness and high strength to weight ratio. The drilling process is often used machining operation in order to assemble the parts made by Fiber Reinforced Polymeric (FRP) composite materials. In this work the effect of drilling process variables such as spindle speed and drill feed rate on the drilling induced delamination at exit during drilling of Carbon Fiber Reinforced Polypropylene (CFR-PP) thermoplastic composite is studied in detail. For this study, CFR-PP laminates are fabricated using hot compression molding machine with film stacking technique. The fabricated laminates are tested for physical and various mechanical properties as per the relevant ASTM standards. To analyze the machining performances, the drilling experiments are conducted on a CNC Vertical Machining Center (VMC) using three type of twist drill made with high speed steel (HSS), tipped carbide (TC) and solid carbide (SC) of 6mm diameter. The main objective of this work is to analyze the influence of spindle speed and drill feed rate with respect to drilling induced delamination of drilled hole in CFR-PP composite materials. The empirical relation between machining variables and process responses are developed to predict the process outcome. The observations indicted that the developed regression model is highly suitable to predict the process responses during drilling of CFR-PP composite material. The developed mathematical model may be helpful to reduce the delamination damage which is the most significant undesirable failure during the drilling of CFR-PP material. The influence of machining parameters and their interactions are examined. The significance role of tool materials on the machining characteristic is also discussed in detail.

Optimization and sensitivity analysis of drilling parameters for sustainable machining of carbon fiber–reinforced polypropylene composites

Machining processes face two major challenges: sustainability and cleaner production. However, the effective utilization of tool and methods of lubrication system in sustainable machining have been dealt in depth in earlier investigations. This work aims to optimize sustainable machining parameters in drilling process for recyclable carbon fiber-reinforced polypropylene (CFR-PP) composites. This work is focused on modeling and optimization of drilling parameters for sustainable machining with respect to thrust force and torque for CFR-PP composites. The response surface method based on D-optimal design of experiments is used for modeling and optimization with variables such as drill spindle speed and drill feed rate as numerical factors, which includes different drill material as the categorical factor. The influences of tool materials on the sustainable machining are also discussed in detail. Further, the sensitivity analysis is applied to compare the relative impact of control parameters (spindle speed, feed rate, and drill materials) on thrust force and torque. The scanning electron microscope images are used for analyzing the morphologies of drilled surfaces.

Trial Fabrication of Carbon Fiber-Reinforced Thermoplastic Honeycomb Sandwich Materials

This paper deals with a new fabrication technique of carbon fiber-reinforced thermoplastic (CFRTP) honeycomb cores and all-CFRTP honeycomb sandwich panels. The CFRTP core was made of plane woven carbon fiber-reinforced polypropylene prepreg sheets. The stacked CFRTP prepreg sheets were periodically hot-pressed at the node locations, and then expanded to form an all-CFRP honeycomb core. The resultant CFRTP honeycomb cores were glued with the same polypropylene-based plain-woven CFRTP skin plates. The mechanical performance of the all-CFRTP honeycomb sandwich panels was evaluated by flexural tests. The experimental results showed the effectiveness of proposed all-CFRTP sandwich panels.

Long discontinuous carbon fibre/polypropylene composites for high volume structural applications

A processing route is presented to manufacture discontinuous carbon fibre-reinforced polypropylene composites, using much longer fibre lengths (25 mm) and higher volume fractions (up to 45%) than previously reported in the literature. Carbon fibre tows are coated with different ratios of polypropylene, blended with a maleic anhydride coupling agent, to investigate the influence of the interfacial shear strength at the microscale on the macroscale composite properties. Improvements in the tensile performance at the macroscale (70% increase) are not as high as those reported for the interfacial shear strength at the microscale (300%), following the addition of the coupling agent. Consequently, the tensile strength of the carbon fibre-reinforced polypropylene material is only 45% of values reported for carbon fibre/epoxy systems, however, the tensile stiffness is comparable. This demonstrates the potential for using carbon fibre-reinforced polypropylene for structural applications, following further process optimisation to overcome the current high levels of porosity (3.3% at 0.45 Vf) to improve the tensile strength.

Prediction of fiber-directional flexural strength of carbon fiber-reinforced polypropylene based on time–temperature superposition principle

This study verified that the time–temperature superposition principle for fiber-directional flexural strength can be applied to thermoplastic composites undergoing instantaneous fast phenomena such as impact failure and long-term phenomena such as creep failure, by constructing the time- and temperature-dependent master curve of relaxation modulus of thermoplastic resin. The master curve could be transformed to another master curve that predicts fiber-directional flexural strength of carbon fiber-reinforced thermoplastic composites based on the micro-buckling failure theory expressed mainly by the resin’s elastic modulus. The experimental results obtained from high-speed bending test, static bending test at various temperatures, and creep bending test demonstrated that kink band failure occurred on the compressive surface of the specimen at every test condition. This validation and verification related to thermoplastic composites made it possible to predict static and dynamic flexural strengths at arbitrary temperature and creep flexural strength.

Influence of void content on the flexural fracture behaviour of carbon fiber reinforced polypropylene

In order to investigate the influence of void content on the fracture behaviour of carbon fiber reinforced polypropylene (CF/PP), we investigated the relationship between the mechanical properties of carbon fiber reinforced thermoplastics and their void content using CF/PP prepreg sheet and partially impregnated sheet. Two types of flexural properties of cross-ply (CP) plates and chopped carbon fiber tape reinforced thermoplastic (CTT) plates with different void contents were measured by three-point bending tests. The flexural strength of CP specimens decreased drastically when their void content became higher than 1%, whereas the flexural strength of the CTT specimens decreased gradually with an increase in void content. Un-impregnated regions in the composites resulted in small dotted defects under loading conditions, although they were only found on the tape along the longitudinal direction in the case of CTT. In addition, a larger number of defects was observed on CP and CTT specimens with lower strengths. Therefore, cyclic loading tests were conducted to observe flexural fracture behaviour in more detail to elucidate the reason behind voids causing a decrease in strength. During these tests, the dotted defects in the CP specimens were shown to be connected along the in-plane transverse direction, while those in the CTT specimen propagated along the second layered tape.