Crashworthiness of various random chopped carbon fiber reinforced epoxy composite materials and their strain rate dependence

The ACC (Automotive Composite Consortium) is interested in investigating the use of random chopped fiber reinforced composites as crash energy absorbers primarily because of the low costs involved in their manufacture thus making them cost effective for automotive applications. Although many scientists have investigated the energy absorption characteristics in various continuous fiber reinforced composite materials and their dependence on strain rate, there is very little literature available on the energy absorption and crushing characteristics of random chopped fiber reinforced composite materials and their strain rate dependence. Therefore, the primary goal was to determine the crashworthiness of various random chopped carbon fiber composite material systems. To meet this goal, first an experimental set up was developed for discerning the deformation behavior and damage mechanisms that occur during the progressive crushing of composite materials. The three different random chopped carbon reinforced epoxy composite material systems studied were P4, HexMC, and CCS100. Quasi‐static progressive crush tests were then performed on these random chopped carbon fiber composite plates to determine their crashworthiness. In addition, an attempt was made to investigate and characterize the strain rate effects on the energy absorption of a random chopped carbon fiber P4 composite. The specific energy absorption was found to increase with increasing loading rate from 15.2 to 762 cm/min. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1477–1486, 2006     

Improved strain sensing performance of glass fiber polymer composites with embedded pre-stretched polyvinyl alcohol–carbon nanotube fibers

Polyvinyl alcohol–carbon nanotube (PVA–CNT) fibers differing on their pre-stretching condition were embedded in glass fiber reinforced plastic (GFRP) composites and used as strain sensors for damage monitoring of the composite. Strain sensing of the composite was made by the in situ measurement of the embedded fiber’s electrical resistance change during the mechanical tests. Four glass fiber composite plates were manufactured; each one had embedded a different type of produced PVA–CNT fibers. The multi-functional materials were tested in monotonic tensile tests as well as in progressive damage accumulation tests. The electrical resistance readings of the PVA–CNT fibers were correlated with axial strain values, taking into account the induced damage of the composite. It has been demonstrated that increasing the fiber’s pre-stretching ratio, its electrical resistance response increases due to higher degree of the CNTs alignment in the PVA matrix. Higher fiber pre-stretching degree enables the better strain monitoring of the composite due to higher measured electrical resistance change values noticed for the same applied axial strain values. To this end, it enables for the better monitoring of the progressive damage accumulation inside the composite.     

Mechanical and interfacial properties of phenolic composites reinforced with treated cellulose fibers

Cellulose fiber‐reinforced phenolic composites were prepared and characterized by mechanical tests and morphological analysis in this study. First, preparation of the phenolic matrix was optimized using an experimental design. The variables studied were curing temperature and time. The responses measured were strength, elongation, modulus, and strain energy density, in tensile and flexural tests. After fixing the optimal curing conditions of the matrix at 75°C and 2.75 h, the effect of a latest drying stage was studied. Strengths in tensile and flexural tests of the matrix after the incorporation of the drying stage were 156 and 189% of the strengths of the undried matrix, and elastic moduli were three‐fold. Finally, cellulose fibers were incorporated as reinforcement. Alkali treatment of the fibers (1 and 5% NaOH), employment of silanes as coupling agents [(3‐aminopropyl) trimethoxysilane (APS) and 3‐(2‐aminoethylamino) propyltrimethoxysilane (AAPS)], and combined treatments alkali‐silane were tested. The AAPS silane treated cellulose fiber‐reinforced phenolic composite was the material with the best mechanical performance and adhesion fiber–matrix. The most significant improvements obtained with the AAPS silane treatment of the fibers were 25, 52, and 110% for tensile strength, elongation, and SED, respectively, in relation to the unreinforced material properties. POLYM. ENG. SCI., 54:2228–2238, 2014. © 2013 Society of Plastics Engineers     

Influence of PANI‐complex on the mechanical and electrical properties of carbon fiber reinforced polypropylene composites

The aim of this work was to determine the influence of PANI‐complex on the mechanical and electrical properties of CF‐PP composites. As expected, an increase in tensile strength and modulus of the PP matrix could be achieved with an increasing fiber weight fraction. On the other hand, the PANI‐complex decreased the tensile strength and modulus of the fiber reinforced composites; however, these values remained on a better level than the value of the neat PP. Further, by using a long carbon fiber (LCF) reinforcement instead of short carbon fibers (SCF) the percolation threshold was moved towards a lower fiber weight content. In addition, a synergy effect between PANI‐complex and LCF in the PP‐matrix regarding the electrical properties occurred. In particular, an abrupt decrease in the surface resistivity could be avoided. Also, the surface resistivity of a blend is better when the blend consists of both PANI‐complex and LCF instead of only one of these fillers.     

Fabrication and mechanical properties of glass fiber‐reinforced wood plastic hybrid composites

To fully utilize the resource in the municipal solid waste (MSW) and improve the strength and toughness of wood plastic composites, glass fiber (GF)‐reinforced wood plastic hybrid composites (GWPCs) were prepared through compounding of recycled high‐density polyethylene (HDPE) from MSW, waste wood fibers, and chopped GF. Mechanical tests of GWPCs specimens with varying amounts of GF content were carried out and the impact fractured surface of GWPCs was observed through scanning electron microscope (SEM). The tensile strength of GWPCs and the efficiency coefficient values were predicted by Kelly‐Tyson method. The results indicated that the tensile strength and impact strength of GWPCs could be improved simultaneously by adding type L chopped GF (L‐GF), and would be dropped down when type S chopped GF (S‐GF) was included. The tensile strength of GWPCs was well accordant with the experimental result. The efficiency coefficient values of S‐GF and L‐GF are ?0.19 and 0.63, respectively. Inspection of SEM micrographs indicated that L‐GF had achieved full adhesion with the plastic matrix through addition of maleic anhydride‐g‐polyethylene. The main fracture modes of GWPCs included pullout of GF, broken of matrix, and interfacial debonding. Because of the synergistic effects between hybrid components in GF/wood fiber/HDPE hybrid system, a special 3D network microstructure was formed, which was the main contribution to the significant improvement in the tensile strength and impact strength of L‐GF‐reinforced hybrid composites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preferred orientation of chopped fibers in polymer-based composites processed by selective laser sintering and fused deposition modeling: Effects on mechanical properties

The orientation of reinforcing fibers in polymer-based composites greatly affects their mechanical features. It is known that different orientations of continuous fibers in the stacked layers of a laminate play a crucial role in providing an isotropic mechanical behavior, while the alignment of chopped fibers in injection molding of composites results in a degree of anisotropy. Recent additive manufacturing techniques have offered a way of controlling the fiber orientation. This article aims to investigate the effect of fiber orientation on the mechanical properties of polyamide/carbon fiber composites processed by fused deposition modeling and selective laser sintering. Tensile samples which had different fibers and layer interface with respect to the sample axis (and therefore to the tensile load) were produced. Tensile tests were performed at different strain rates; the tensile properties and the fracture surface morphology were correlated with the processing method and the sample microstructure. The best strength and stiffness were observed when the fibers and the layer interfaces were parallel to the sample axis.     

Unsaturated polyester‐toughened epoxy composites: Effect of sisal fiber on thermal and dynamic mechanical properties

In the present study, the mechanical and thermal properties of sisal fiber‐reinforced unsaturated polyester (UP)‐toughened epoxy composites were investigated. The sisal fibers were chemically treated with alkali (NaOH) and silane solutions in order to improve the interfacial interaction between fibers and matrix. The chemical composition of resins and fibers was identified by using Fourier‐transform infrared spectroscopy. The UP‐toughened epoxy blends were obtained by mixing UP (5, 10, and 15 wt%) into the epoxy resin. The fiber‐reinforced composites were prepared by incorporating sisal fibers (10, 20, and 30 wt%) within the optimized UP‐toughened epoxy blend. Scanning electron microscopy was used to analyze the morphological changes of the fibers and the adhesion between the fibers and the UP‐toughened epoxy system. The results showed that the tensile and flexural strength of (alkali‐silane)‐treated fiber (30 wt%) ‐reinforced composites increased by 83% and 55%, respectively, as compared with that of UP‐toughened epoxy blend. Moreover, thermogravimetric analysis revealed that the (alkali‐silane)‐treated fiber and its composite exhibited higher thermal stability than the untreated and alkali‐treated fiber systems. An increase in storage modulus and glass transition temperature was observed for the UP‐toughened epoxy matrix on reinforcement with treated fibers. The water uptake behavior of both alkali and alkali‐silane‐treated fiber‐reinforced composites is found to be less as compared with the untreated fiber‐reinforced composite. J. VINYL ADDIT. TECHNOL., 23:188–199, 2017. © 2015 Society of Plastics Engineers     

Natural rubber composites reinforced with sisal/oil palm hybrid fibers: Tensile and cure characteristics

Natural rubber was reinforced with untreated sisal and oil palm fibers chopped to different fiber lengths. The influence of fiber length on the mechanical properties of the hybrid composites was determined. Increasing the fiber length resulted in a decrease in the properties. The effects of concentration on the rubber composites reinforced with sisal/oil palm hybrid fibers were studied. Increasing the concentration of fibers resulted in a reduction in the tensile strength properties and tear strength but an increase in the modulus of the composites. Fiber breakage analysis was evaluated. The vulcanization parameters, processability characteristics, and stress–strain properties of these composites were analyzed. The extent of fiber alignment and the strength of the fiber–rubber interface adhesion were analyzed from the anisotropic swelling measurements. Scanning electron microscopy studies were performed to analyze the fiber/matrix interactions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2305–2312, 2004     

Synthesis of glass fiber‐multiwall carbon nanotube hybrid structures for high‐performance conductive composites

The conductive polyamide 66 (PA66)/carbon nanotube (CNT) composites reinforced with glass fiber‐multiwall CNT (GF‐MWCNT) hybrids were prepared by melt mixing. Electrostactic adsorption was utilized for the deposition of MWCNTs on the surfaces of glass fibers (GFs) to construct hybrid reinforcement with high‐electrical conductivity. The fabricated PA66/CNT composites reinforced with GF‐MWCNT hybrids showed enhanced electrical conductivity and mechanical properties as compared to those of PA66/CNT or PA66/GF/CNT composites. A significant reduction in percolation threshold was found for PA66/GF‐MWCNT/CNT composite (only 0.70 vol%). The morphological investigation demonstrated that MWCNT coating on the surfaces of the GFs improved load transfer between the GFs and the matrix. The presence of MWCNTs in the matrix‐rich interfacial regions enhanced the tensile modulus of the composite by about 10% than that of PA66/GF/CNT composite at the same CNT loading, which shows a promising route to build up high‐performance conductive composites. POLYM. COMPOS. 34:1313–1320, 2013. © 2013 Society of Plastics Engineers     

Caulis spatholobi residue fiber reinforced biodegradable poly (propylene carbonate) composites: The effect of fiber content on mechanical and morphological properties

Adding caulis spatholobi residue fiber (CSRF) to reinforce biodegradable poly (propylene carbonate) (PPC) as a reinforcement was investigated. The morphology of CSRF before and after continuous steam explosion, the mechanical and morphological properties of PPC/CSRF bio‐composites with different fiber content were investigated using scanning electron microscopy (SEM), mechanical tests and infrared spectroscopy. The tensile strength and modulus, and impact strength of the bio‐composites increased as the content of fiber increased in composites, the elongation at break declined. It was found that a small stay‐segment in the stress–strain curves and pulled‐out fibers on fractured surfaces of the composites. Infrared spectra result showed esterification and formation of hydrogen bonds between the matrix and CSRF. The fractured surface of the composites addressed a promotion of the interfacial interactions. POLYM. COMPOS., 35:208–216, 2014. © 2013 Society of Plastics Engineers     

Experimental study on the mechanical behavior and failure mechanism of 3d MWK carbon/epoxy composites under quasi‐static loading

Quasi‐static tensile, out‐of compression, in‐plane compression, three‐point‐bending and shear tests were conducted to reveal the mechanical behavior and failure mechanisms of three‐dimensional (3D) multiaxial warp‐knitted (MWK) carbon/epoxy composites. The characterization of the failure process and deformation analysis is supported by high‐speed camera system and Digital Image Correlation. The results show that tensile, bending, out‐of‐plane compression, in‐plane compression stress–strain response exhibit obvious linear elastic feature and brittle fracture characteristics, whereas the shear response exhibits a distinct nonlinear behavior and gradual damage process. Meanwhile, 3D MWK carbon/epoxy composites have good mechanical properties, which can be widely used in the fields of engineering. In addition, the failure for tension behaves as interlayer delaminating, 90/+45/−45° interface debonding and tensile breakage of 0° fibers; the damage for out‐of‐plane compression is mainly interlaminar shear dislocation together with local buckling and shear fracture of fibers; the failure pattern for in‐plane compression is 90° fiber separating along fiber/matrix interface as well as 0/+45/−45° fiber shear fracture in the shear plane. The main failure for bending is fiber/matrix interface debonding and fibers tearing on the compression surface, 0° fibers breakage on the tension surface as well as fiber layers delaminating. Although the shear behavior is characterized by a gradually growing shear matrix damage, 90/+45/−45° interface debonding, +45/−45° fibers shear fracture, and final 0° fiber compression failure. POLYM. COMPOS., 37:3486–3498, 2016. © 2015 Society of Plastics Engineers     

Performance of fibers embedded in a cementitious matrix

Reinforcement of cementitious materials with short fibers has been proved to be an economical and effective way to convert these brittle materials to ductile products. Many fibers with different geometries have been used as reinforcement materials. Fibers bonding to cementitious materials play an important role in mechanical performance of these composites. This article describes the performance of (homemade) fibers as reinforcement in cement‐based materials by investigation on bonding characteristic of fiber to cement matrix. To this end, the fibers (glass, polypropylene, polyacrylonitrile (PAN), and high strength nylon 66 (N66)) are characterized using microscopy analysis, tensile strength, and alkali attack tests. The fibers embedded in the cement matrix, then, pulled‐out to evaluate their bonding to cementitious materials. SEM analysis is used to study fiber/cement interfacial transition zone. The results show that PAN fibers have the advantages of preparing for cementitious reinforcement. It was found that the reinforcing efficiency of fibers‐reinforced cementitious composites was strongly depending on interfacial contact area in fiber/matrix interface and chemical/physical properties of fibers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

玻璃短纤维对多层多轴向经编复合材料层间撕裂性能影响

以玻璃纤维多轴向经编针织物为增强体,以环氧树脂为基体,将玻璃短纤维添加到玻纤织物增强体层之间,制备层间含有玻璃短纤维的多层多轴向经编复合材料。利用万能力学材料试验机对复合材料的层间撕裂性能进行测试和电镜扫描,对撕裂后的复合材料层间形态进行了观察,研究了玻璃短纤维对复合材料层间性能的影响。结果表明,玻璃短纤维增韧处理的复合材料层间撕裂性能明显增强,载荷-位移曲线初始斜率大,复合材料不易被以撕裂形式为主的载荷破坏。     

Polyester composites reinforced with noncrimp stitched carbon fabrics: Mechanical characterization of composites and investigation on the interaction between polyester and carbon fiber

The primary purpose of the study is to investigate the anisotropic behavior of different noncrimp stitched fabric (NCF) reinforced polyester composites. Carbon fiber composite laminates were manufactured by vacuum infusion of polyester resin into two commonly used advanced noncrimp stitched carbon fabric types, unidirectional and biaxial carbon fabric. The effects of geometric variables on composite structural integrity and strength were illustrated. Hence, tensile and three‐point bending flexural tests were conducted up to failure on specimens strengthened with different layouts of fibrous plies in NCF. In this article an important practical problem in fibrous composites, interlaminar shear strength as measured in short beam shear tests, is discussed. The fabric composites were tested in three directions: at 0°, 45°, and 90°. Extensive photomicrographs of multilayered composites resulting from a variety of uniaxial loading conditions were presented. It was observed that broken fibers recede within the matrix in composites with weak interfacial bond. Another aim of the present work was to investigate the interaction between carbon fiber and polyester matrix. The experiments, in conjunction with scanning electron photomicrographs of fractured surfaces of composites, were interpreted in an attempt to explain the instability of polyester‐resin–carbon‐fiber interfaces. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4554–4564, 2006     

Concentration effect of γ‐glycidoxypropyltrimethoxysilane on the mechanical properties of glass fiber–epoxy composites

In this study, glass fibers were modified using γ‐glycidoxypropyltrimethoxysilane of different concentrations to improve the interfacial adhesion at interfaces between fibers and matrix. Effects of γ‐glycidoxypropyltrimethoxysilane on mechanical properties and fracture behavior of glass fiber/epoxy composites were investigated experimentally. Mechanical properties of the composites have been investigated by tensile tests, short beam tests, and flexural tests. The short‐beam method was used to measure the interlaminar shear strength (ILSS) of laminates. The tensile and flexural properties of composites were characterized by tensile and three‐point bending tests, respectively. The fracture surfaces of the composites were observed with a scanning electron microscope. On comparing the results obtained for the different concentrations of silane solution, it was found that the 0.5% GPS silane treatment provided the best mechanical properties. The ILSS value of heat‐cleaned glass fiber reinforced composite is enhanced by ∼59% as a result of the glass fiber treatment with 0.5% γ‐GPS. Also, an improvement of about 37% in tensile strength, about 78% in flexural strength of the composite with the 0.5% γ‐GPS treatment of glass fibers was observed. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Novel ceramic matrix composites with tungsten and molybdenum fiber reinforcement

Ceramic matrix composites usually utilize carbon or ceramic fibers as reinforcements. However, such fibers often expose a low ductility during failure. In this work, we follow the idea of a reinforcement concept of a ceramic matrix reinforced by refractory metal fibers to reach pseudo ductile behavior during failure. Tungsten and molybdenum fibers were chosen as reinforcement in SiCN ceramic matrix composites manufactured by polymer infiltration and pyrolysis process. The composites were investigated with respect to microstructure, flexural- and tensile strength. The single fiber strengths for both tungsten and molybdenum were investigated and compared to the strength of the composites. Tensile strengths of 206 and 156 MPa as well as bending strengths of 427 and 312 MPa were achieved for W/SiCN and Mo/SiCN composites, respectively. The W fiber became brittle across the entire cross section, while the Mo fiber showed a superficial, brittle reaction zone but kept ductile on the inside.     

Thermal and mechanical properties of hybrid carbon/oxidized polyacrylonitrile fibers‐epoxy composites

Nowadays, hybrid composites are one of the important materials in industry due to their special properties. In this research, hybrid oxidized polyacrylonitrile (PAN) and carbon fibers reinforcement were used in epoxy matrix. The hybrid composites were fabricated using the hand lay‐up technique by placing the reinforcements in different layering sequences. Thermal and mechanical properties of these hybrid composites were investigated by thermal analysis, horizontal burning, tensile and bending tests. The tensile test results indicated that increasing oxidized polyacrylonitrile fibers (OPFs) to carbon fibers ratio decreased tensile strength and elastic modulus but increased failure strain. Hybrid oxidized PAN and carbon fibers reinforcement in composites led to decreasing flexural stress and modulus, and increasing flame retardancy. Thermal analysis results also showed that the maximum rate of mass loss in all composites was 370.6°C. It was also found that the maximum and minimum amounts of char residue at 900°C were related to the composites with four layers of carbon and OPFs, respectively. POLYM. COMPOS., 38:1412–1417, 2017. © 2015 Society of Plastics Engineers     

Fatigue of three advanced SiC/SiC ceramic matrix composites at 1200°C in air and in steam

High‐temperature mechanical properties and tension‐tension fatigue behavior of three advanced SiC/SiC composites are discussed. The effects of steam on high‐temperature fatigue performance of the ceramic‐matrix composites are evaluated. The three composites consist of a SiC matrix reinforced with laminated, woven SiC (Hi‐Nicalon?) fibers. Composite 1 was processed by chemical vapor infiltration (CVI) of SiC into the Hi‐Nicalon? fiber preforms coated with boron nitride (BN) fiber coating. Composite 2 had an oxidation inhibited matrix consisting of alternating layers of silicon carbide and boron carbide and was also processed by CVI. Fiber preforms had pyrolytic carbon fiber coating with boron carbon overlay applied. Composite 3 had a melt‐infiltrated (MI) matrix consolidated by combining CVI‐SiC with SiC particulate slurry and molten silicon infiltration. Fiber preforms had a CVI BN fiber coating applied. Tensile stress‐strain behavior of the three composites was investigated and the tensile properties measured at 1200°C. Tension‐tension fatigue behavior was studied for fatigue stresses ranging from 80 to 160 MPa in air and from 60 to 140 MPa in steam. Fatigue run‐out was defined as 2 × 10⁵ cycles. Presence of steam significantly degraded the fatigue performance of the CVI SiC/SiC composite 1 and of the MI SiC/SiC composite 3, but had little influence on the fatigue performance of the SiC/SiC composite 2 with the oxidation inhibited matrix. The retained tensile properties of all specimens that achieved fatigue run‐out were characterized. Composite microstructure, as well as damage and failure mechanisms were investigated.     

Multiwalled carbon nanotube polymer composites: Synthesis and characterization of thin films

The aim of this article was to elucidate the basic relationships between processing conditions and the mechanical and electrical properties of multiwalled carbon nanotube reinforced polymer composites. In conventional chopped fiber reinforced polymer composites, uniform distributions of fibers throughout the matrix are critical to producing materials with superior physical properties. Previous methods have dispersed carbon nanotubes by aggressive chemical modification of the nanotubes or by the use of a surfactant prior to dispersion. 1 , 2 Here, ultrasonic energy was used to uniformly disperse multiwalled nanotubes (MWNTs) in solutions and to incorporate them into composites without chemical pretreatment. Polystyrene (PS) solutions containing MWNTs were cast and spun to yield thin film MWNT composites. The rheology of PS/MWNT suspensions was modeled using the Carreau equation. MWNTs were found to align at the shear rates generated by the spin casting process. The tensile modulus and strain to failure of samples compared well to classical micromechanical models, increasing with MWNT loading. The composite films showed lower strains at the yield stress than neat PS films. The presence of MWNTs at 2.5 vol % fraction approximately doubles the tensile modulus, and transforms the film from insulating to conductive (surface resistivity, ρ, approaching 10³ Ω/□). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2660–2669, 2002     

Multiple percolation in a carbon‐filled polymer composites via foaming

This article describes an investigation into the effects of foaming on the electrical conductivity for a carbon‐filled cyclic olefin copolymer (COC) composite incorporating both chopped carbon fibers (cCF) and carbon black (CB). Foamed and solid samples were injection molded and then analyzed for cell size, fiber length, fiber orientation, and electrical conductivity. Foamed samples exhibited higher electrical conductivity in the through‐plane direction for materials containing only CB or composites containing both filler types, and reduced electrical conductivity in the cCF‐filled composites. The increased electrical property gained by foaming was attributed to multiple percolation with CB aggregates forming more effective conductive clusters and networks in the continuous polymer phase during growth of the gas domains. A mechanism for the phenomenon was proposed based on these experimental observations. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010