Micromechanics for fiber volume percent with a photocure vinyl ester composite

Micromechanics for fiber volume percent (V_f) from 0.0V_f to 54.0 V_f were conducted using (3 mm long × 9 μm diameter) high‐purity quartz fibers in a visible‐light vinyl ester particulate‐filled photocure resin. MTS fully articulated four‐point bend fixtures were used with a 40 mm test span and 50 × 2 × 2 mm³ sample dimensions. Specimens were tested following the combined modified ASTM standards for advanced ceramics ASTM‐C‐1161–94 and polymers ASTM‐D‐6272–00 for modulus, flexural strength, and yield strength. Experimental data provided reliable statistical support for the dominant fiber contribution expressed through the rule‐of‐mixtures theory as a valid representation of micromechanical physics. The rule‐of‐mixtures micromechanics described by V_f could explain 92, 85, and 78% of the variability related to modulus, flexural strength, and yield strength respectively. Statistically significant improvements with fiber addition began at 10.3V_f for modulus, 5.4V_f for flexural strength, and 10.3V_f for yield strength, p < 0.05. In addition, correlation matrix analysis was performed for all mechanical test data. An increase in V_f correlated significantly with increases in modulus, flexural strength, and yield strength as measured by the four‐point bending test, p < 10⁻¹⁰. All mechanical properties in turn correlated highly significantly with one another, p < 10⁻⁹. POLYM. COMPOS., 28:294–310, 2007. © 2007 Society of Plastics Engineers     

Interfacial adhesion in jute‐polyolefin composites

The interfacial adhesion between four different forms of jute fibers (sliver, bleached, mercerized and untreated) and polyolefinic matrices (LDPE and PP) was studied, as a critical factor affecting the mechanical behavior of these composites. The fiber‐matrix adhesion was estimated by means of the critical fiber length (l_c) and the stress transfer ability parameter (τ); such parameters were obtained by Single Fiber Composite (SFC) tests. Tests were carried out to evaluate the mean tensile strength of the fibers, the mean critical fiber lengths and the stress transfer ability parameter for every fiber‐matrix combination, according to Weibull's statistical method. Thermal‐mechanical characterization of the fibers was also carried out to evaluate the resistance to processing conditions. A limited degradation of strength was observed, which, however, does not preclude the use of jute fibers as reinforcing means in polyolefin based composites. It was found that the adhesion was better in PP‐jute composites than in LDPE‐jute composites. In both cases the results showed that the sliver jute and the untreated jute had better adhesion to both matrices than had the bleached and the mercerized fibers. With both matrices the interface adhesion was in the order: mercerized < bleached < untreated = sliver.     

Carbon fiber‐reinforced gelatin composites. I. Preparation and mechanical properties

Composites were made from carbon fibers and gelatin using a solvent‐casting or solution‐impregnation technique. Relationships between the fiber volume fraction (Vf), glycerol (plasticizer) content, gelatin content, fiber form, and mechanical properties (tensile strength and modulus, elongation at break, and shear strength) of the composites were investigated. In long carbon fiber gelatin composite (C_L/Gel), tensile strength, modulus, and shear strength increased steadily with the Vf. In the case of a short carbon fiber gelatin composite (C_S/Gel), an initial improvement in tensile strength and modulus was followed by a reduction, whereas the shear strength improved with the Vf and then reached a constant value. The elongation decreased with the Vf for both composites. It is shown that C_L/Gel had higher values of strength, modulus, and elongation than did C_S/Gel at any Vf level. The effects of glycerol and gelatin contents on the mechanical properties of the composites were found to be much less significant as compared to the Vf. According to scanning electron microscopic observation of the fracture surfaces, the fibers were uniformly distributed in the gelatin matrix, but the interfacial adhesion between the gelatin matrix and the carbon fibers was not very good for both composites. Fiber surface modification would be necessary to further improve the mechanical properties of the two composites. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 987–993, 2000     

Study on effects of short glass fiber reinforcement on the mechanical and thermal properties of PC/ABS composites

This article mainly investigated the length distributions of the alkali‐free short glass fibers in specimens and their effect on the mechanical and thermal properties of the composites. The results show that the initial length, addition level and feed way of the fibers have obvious effects on the length distributions of fibers in specimens, and thereby the mechanical and thermal properties of the composites. The main‐direction feed way has an intense shear action on the fibers in specimens. With the increase of the fiber content, the reinforcing effect of fibers on the tensile strength, flexural strength and flexural modulus of the composites is increased, while the impact strength is decreased first and then tends to be stable, and the strength factor (F) of the tensile strength to weld line is significantly reduced. The longer the fiber lengths in specimens are, the more obvious the reinforcing and toughening effects are. To some extent, with the increase of the fiber content, the storage modulus (E′) and loss modulus (E′′) of the specimens are increased, but the loss factor (Tan δ) is reduced. The effect of the fiber initial lengths on the heat‐degradation of composites is smaller than that of the fiber content. Meanwhile, adding fibers can improve the thermal stability of the composites, and this law is also confirmed by the heat deflection temperature (HDT) test. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40697.     

Tensile and compressive behavior of poly(p-phenylene benzobisthiazole) fibers

Heat treated poly(p-phenylene benzobisthiazole) (PBZT) fibers tested in tension result in two types of failure modes. In failure mode I, the fiber exhibits a relatively sharp break; mode II is characterized by significant axial fiber splitting. Approximately 20% of the fibers failed in mode II when tested at 2.54, 7.62, and 12.7 cm gage lengths. At 1.25 cm gage length all the fibers failed in mode I. Tensile strength decreased from the 1.25 to 7.62 cm gage length, but tensile strength of the fibers tested at 7.62 and 12.7 cm gage lengths were similar. The two failure mode observation is supported by the Weibull statistical distribution. Fiber tensile properties were also measured at 150°C. Axial compressive strength of the PBZT fibers as determined from the recoil test is also reported and is found to be independent of fiber tensile modulus and fiber diameter. As-received heat-treated fibers were post heat treated between 700 and 775°C. Structural changes in the fiber were studied using infrared spectroscopy, small and wide angle x-ray scattering, and swelling studies. © 1995 John Wiley & Sons, Inc.     

Mechanical properties of injection molded long fiber polypropylene composites,Part 1: Tensile and flexural properties

Innovative polymers and composites are broadening the range of applications and commercial production of thermoplastics. Long fiber‐reinforced thermoplastics have received much attention due to their processability by conventional technologies. This study describes the development of long fiber reinforced polypropylene (LFPP) composites and the effect of fiber length and compatibilizer content on their mechanical properties. LFPP pellets of different sizes were prepared by extrusion process using a specially designed radial impregnation die and these pellets were injection molded to develop LFPP composites. Maleic‐anhydride grafted polypropylene (MA‐g‐PP) was chosen as a compatibilizer and its content was optimized by determining the interfacial properties through fiber pullout test. Critical fiber length was calculated using interfacial shear strength. Fiber length distributions were analyzed using profile projector and image analyzer software system. Fiber aspect ratio of more than 100 was achieved after injection molding. The results of the tensile and flexural properties of injection molded long glass fiber reinforced polypropylene with a glass fiber volume fraction of 0.18 are presented. It was found that the differences in pellet sizes improve the mechanical properties by 3–8%. Efforts are made to theoretically predict the tensile strength and modulus using the Kelly‐Tyson and Halpin‐Tsai model, respectively. POLYM. COMPOS., 28:259–266, 2007. © 2007 Society of Plastic Engineers     

Influence of varying fiber lengths on mechanical,thermal, and morphological properties of MA‐g‐PP compatibilized and chemically modified short pineapple leaf fiber reinforced polypropylene composites

Environmentally benign, low cost and abundantly available short pineapple leaf fibers (PALF), found mostly in the Tropical rain forest climates are ideal materials for manufacture of thermoplastic polymer‐matrix composites. Here, mechanical and thermal properties of composites of maleic anhydride grafted polypropylene (MA‐g‐PP) and chemically modified short PALF are studied as a function of different fiber lengths at 10 vol % fibers loading with fiber orientation in the longitudinal direction. The effects of fiber lengths and fiber loading on the morphological properties are assessed via observations by scanning electron microscopy. Fiber length of 6 mm oriented longitudinally at 10 vol % fibers loading in PP is the optimum and recommended composition, where 73% increase in impact properties, 37% increase in the flexural modulus, 33% increase in flexural strength, and 14% increase in vicat softening temperature are observed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Mechanical and thermal characterization of native brazilian coir fiber

Coir fiber native to the Brazilian northeast coast has been characterized by mechanical, thermal, and microscopy techniques. The tensile strength, initial modulus, and elongation at break were evaluated for untreated and alkaline‐treated fibers. The results showed an enhancement of mechanical properties after 48‐h soaking in 5 wt % NaOH. The thermal stability slightly decreased after this alkaline treatment. A thermal event was observed between 28 and 38°C. The heat capacity, C_p, as a function of temperature curves between −70 and 150°C, were obtained for the untreated and alkaline‐treated coir fibers. The morphologies of the coir‐fiber surfaces and cross sections were observed by scanning electron microscopy. The properties and the morphologies were discussed, comparing the native Brazilian coir fiber with the more extensively studied native Indian coir fiber. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1197–1206, 2000     

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     

Effect of fiber length on processing and properties of extruded wood‐fiber/HDPE composites

Fiber length and distribution play important roles in the processing and mechanical performance of fiber‐based products such as paper and fiberboard. In the case of wood–plastic composites (WPC), the production of WPC with long fibers has been neglected, because they are difficult to handle with current production equipment. This study provides a better understanding of the effect of fiber length on WPC processing and properties. The objectives of this study were therefore to determine the role of fiber length in the formation process and property development of WPC. Three chemithermomechanical pulps (CTMP) with different lengths, distributions, and length‐to‐diameter ratios (L/D) were obtained by mechanical refining. Length, shape, and distribution were characterized using a fiber quality analyzer (FQA). The rheometer torque properties of high‐density polyethylene (HDPE) filled with the pulps at different loads were studied. Variations in fiber load and length distribution resulted in significant variations in melting properties and torque characteristics. Composites from the three length distributions were successfully processed using extrusion. Physical and mechanical properties of the obtained composites varied with both length distribution and additive type. Mechanical properties increased with increasing fiber length, whereas performance in water immersion tests decreased. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Investigation of basalt fiber composite aging behavior for applications in transportation

New materials such as basalt fiber offer the promise of innovative applications in transportation because of documented strengths (V. Ramakrishnan, N.S. Tolmare, and V. Brik, “NCHRP‐IDEA Program Project Final Report, ” Transportation Research Board, Washington, DC, (1998)). Previously, we found that mechanical properties of basalt twill fabric‐reinforced polymer composites were comparable to composites reinforced with glass fabrics of similar structures [Q. Liu, M.T. Shaw, R.S. Parnas, and A.M. McDonnell, Polymer Composites, 27(1), 41 (2006)]. Use in transportation also requires knowledge of environmental durability. This study reports the tolerance of basalt‐fiber‐reinforced polymer composites to salt water immersion, moisture absorption, temperature, and moisture cycling. Parallel tests were conducted for the corresponding glass‐reinforced polymer composites. Aging for 240 days in salt water or water decreased the Young's modulus and tensile strength of basalt composites slightly but significantly (p < 0.05). Freeze‐thaw cycling up to 199 cycles did not change the shear strength significantly, but aging in hot (40°C) salt water or water did decrease the shear strength of basalt composites (p < 0.05). The aging results indicate that the interfacial region in basalt composites may be more vulnerable to damage than that in glass composites. POLYM. COMPOS., 27:475–483, 2006. © 2006 Society of Plastics Engineers     

Mechanical and thermal shock properties of Cf/SiBCN composite: Effect of sintering densification and fiber coating

In this work, resin-derived carbon coating was prepared on carbon fibers by polymer impregnation pyrolysis method, then silicoboron carbonitride powder was prepared by mechanical alloying, and finally carbon fiber-reinforced silicoboron carbonitride composites were prepared by hot-pressing process. The effects of sintering densification and fiber coating on microstructure, mechanical properties, thermal shock resistance, and failure mechanisms of the composites were studied. Fiber bridging hinders the sintering densification, causing more defects in fiber-dense area and lower strength. However, higher sintering temperature (1800–2000°C) can improve mechanical properties significantly, including bending strength, vickers hardness, and elastic module, because further sintering densification enhances matrix strength and fiber/matrix bonding strength, while the change of fracture toughness is not obvious (2.24–2.38 MPa·m^1/2) due to counteraction of higher debonding resistance and less pull-out length. However, fiber coating improves fracture toughness greatly via protecting carbon fibers from chemical corrosion and damage of thermal stress and external stress. Due to lower coefficient of thermal expansion, lower fiber loading ratio, less stress concentration at the fiber/matrix interface, and better defect healing effect, lower sintering temperature favors thermal shock resistance of composites, and thermal shock recession mechanisms are the damage of interface.     

Fundamental influences on quasistatic and cyclic material behavior of short glass fiber reinforced polyamide illustrated on microscopic scale

In this work, the influences of fiber orientation and weld lines on the morphological structures and the mechanical behavior of polyamide 6.6 (PA6.6‐GF35) are investigated. In quasistatic and fatigue tests tensile and 3‐point‐bending loads are applied. Test temperatures vary between RT and 150°C. Two different specimen types are produced by using injection moulding process to create different fiber orientations as well as weld lines. Fiber orientations are determined using computer tomography. Scanning electron microscopy is used to investigate fracture surfaces of tested specimens. Results show that mechanical properties and morphological structures depend highly on fiber orientation and temperature. Transversely oriented fibers in weld lines result in brittle failure mechanisms and decreased mechanical properties. Different stress distributions in the specimens under tensile and flexural loads have influence on the material behavior as well. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40842.     

Are dentin posts biomechanically intensive?: A laboratory and FEA study

The goal of this laboratory and finite elemental stress analysis (FEA) study was to compare fracture strength of dentin post (DP) with stainless steel and glass fiber posts. Single-rooted teeth were decoronated and restored with ParaPost (PP), i-TFC (TFC), and DPs (n = 10). Resin cores were created and loaded until failure (1.0 mm/min). The data were analyzed (ANOVA, Tukey, Chi-Square tests). Three-dimensional FEA models of the posts were created and the stress distributions were calculated using Solid Works/Cosmos works structural analysis program. A significant difference was found among the groups (p < 0.001). TFC group showed the highest and the DP group showed the lowest fracture resistance (p < 0.001). PP created more stress at the root dentin and inside the post. Restoration of roots with glass fiber and DPs may reduce stresses within the core material and the remaining root. However, a fracture-resistant restoration cannot be achieved by using a DP.     

Fiber hybrid polyimide‐based composites reinforced with carbon fiber and poly‐p‐phenylene benzobisthiazole fiber: Tribological behaviors under sea water lubrication

Fiber hybrid polyimide‐based (PI‐based) composites reinforced with carbon fiber (CF) and poly‐p‐phenylene benzobisthiazole (PBO) fiber of different volume fractions were fabricated by means of hot press molding technique, and their mechanical properties and tribological behaviors under sea water lubrication were systematically investigated in relation to the synergism of CF and PBO fiber. Results showed that the incorporation of CF or PBO fiber improved the tensile strength, hardness, and wear resistance of PI. More importantly, because of the synergistic enhancement effect between CF and PBO fiber on PI matrix, the combination of 10%CF and 5%PBO fiber reinforced PI‐based composite had the best mechanical and tribological properties, showing promising application in ocean environment. POLYM. COMPOS., 37:1650–1658, 2016. © 2014 Society of Plastics Engineers     

Preparation and mechanical performance of ductile Csf/Al2O3-BN composites,Part 1: Effects of fiber length and sintering temperature

Since its invention, alumina ceramics have been extensively investigated for potential various applications. However, their intrinsic brittle nature is still an insurmountable obstacle when they are applied as structural components. This paper provides a simple routs to prepare ductile alumina based composites with the addition of chopped carbon fiber (C_sf/Al₂O₃-BN). Effects of fiber length and sintering temperature on the microstructure, phase composition, mechanical properties together with fracture behavior were systematically investigated. The results showed that composites with mixed fiber lengths of 12 mm and 1 mm exhibited homogeneous microstructure and striking enhancement in mechanical performances compared with composites with other fiber length. With the increase in sintering temperature from 1500 °C to 1650 °C, interfacial bonding strength increased and interface state converted from mechanical interlocking at 1500 °C into chemical bonding at 1650 °C. Chemical reaction in the composites degraded carbon fiber properties, which resulted in the decrease in mechanical performance of the composites.     

The Effect of Resin Matrix Composition on Mechanical Properties of E-glass Fiber-Reinforced Composite for Dental Use

The effects of resin matrix composition including bis-phenol-A-diglycidyl dimethacrylate (bis-GMA)-methyl methacrylate (MMA) based or urethane dimethacrylate (UEDMA)-triethylene glycol dimethacrylate (TEGDMA) based composition and storage conditions on the mechanical properties of E-glass fiber-reinforced composites (FRCs) were studied. Three experimental groups ('Exper 1', 'Exper 2', 'Exper 3') with differing UEDMA to TEGDMA ratio in the matrix together with a control group ('Control') based on bis-GMA–MMA resin matrix were prepared by light-curing. The storage conditions for each group were dry storage at room temperature for 24 h and 30- and 60-day immersion in deionized (DI) water at 37°C, which further divided each group into three subgroups. For all the four composition groups, mechanical properties including hardness, flexural strength and modulus in both three-point and four-point bendings were tested (n = 6), together with water sorption and solubility study (n = 6) and fracture site scanning with a scanning electron microscope (SEM). The experimental specimens were relatively strong and stiff in three-point bending compared to previous research. The same specimens in three-point bending had a lower flexural modulus and fractured at higher flexural stress than in four-point bending. According to the SEM images after fracture, some resin matrix was still bound to the fiber surface, showing cohesive–interfacial fracture type and relatively stable matrix–fiber adhesion. According to comprehensive analysis, the control group showed superior mechanical performance in most of the tests.     

Effect of molecular rigidity and hydrogen bond interaction on mechanical properties of polyimide fibers

Six kinds of polyimide (PI) fibers with different molecular rigidity and hydrogen bond interactions were designed and prepared in order to investigate the relationship between structure and mechanical properties. The rigidity, aggregation structure, fracture morphology, hydrogen bond, and charge transfer (CT) interactions were investigated in detail. Conformational rigidity of six PI fibers were simulated and measured by D‐values of energy barrier and bottom in potential energy curves of PI units. Rigid rod‐like PI macromolecules tend to pack in order and show better mechanical properties. However, with the increase of D‐values, fracture mechanisms change from ductile fracture to brittle fracture. Brittle fracture resulting from high conformational rigidity is adverse to improvement of mechanical properties of PI fibers. Besides, strength of hydrogen bond and CT interactions are characterized by infrared spectroscopy and ultraviolet absorption spectra, respectively. The results indicate that higher interactions lead to higher tensile strength and initial modulus. Finally, PI fibers, which possess moderate conformational rigidity and strong hydrogen bond interactions, exhibit highest tensile strength (1.82 GPa) and initial modulus (85.7 GPa) in six kinds of PI fibers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43677.     

Long fiber reinforcement of polypropylene/polystyrene blends

The recycling of inseparable polymer mixtures usually results in blends with poor mechanical properties. A mixture of PP and PS was taken as a model compound for a recyclate. The effect of adding glass fibers to a mixture of PP/PS (70/30) was studied, with special attention to long glass fiber reinforcement. Test specimens were made in three different ways: by dry blending (direct injection molding), mild compounding with a single screw extruder, and compounding with a twin screw extruder. The fiber concentration was varied from 0 to 30 wt%. The fiber lengths were determined to investigate fiber attrition. The fiber lengths in the samples were 1.09 mm for dry blending, 0.72 mm for single screw compounding, and 0.33 mm for twin screw compounding. The mechanical behavior was studied by unnotched and notched Izod impact and tensile tests. The PP/PS blend had a low fracture strain and low unnotched Izod impact strength compared with a PP homopolymer. With an increasing fiber concentration and fiber length, the modulus, tensile strength, and particularly the impact strength increased. With a 30 wt% glass fiber of the long fiber compound (dry blended), the modulus was raised by a factor of 3.5, the fracture stress by a factor of 2.5 and the unnotched Izod impact strength by a factor of 10. The product quality as judged by the scatter of the data was best for the twin screw compound and poorest for the dry blend. Compounding with a single screw extruder gave fairly constant injection molding product properties, combined with excellent mechanical properties.     

Bond strength of fiber posts and short fiber-reinforced composite to root canal dentin following cyclic loading*

The aim of this study was to evaluate the effect of cyclic loading on the bond strength of fiber posts and short fiber-reinforced composite (FRC) to root canal. One hundred single-rooted teeth were divided into two groups according to the material used for luting fiber posts: (1) Resin-core material (Gradia Core, GC Corp.) and (2) Short FRC (EverX Posterior, GC Corp.). Then the specimens were randomly assigned into three sub-groups according to the post material and the groups are indicated as follows: (1) Short FRC (EverX Posterior) used instead of post and core, (2) Fiber post (GC post, GC Corp.) cemented with resin-core (Gradia Core), (3) Fiber post (GC post, GC Corp.) cemented with short FRC (EverX Posterior), (4) Experimental fiber post cemented with resin-core (Gradia Core, GC Corp), (5) Experimental fiber post cemented with short FRC (EverX Posterior). Then the specimens were subdivided into a further two groups in accordance with the storage condition (cyclic loading and 24 h water storage-control group) (n = 10/per group). The micropush-out bond strength between root dentin and posts was measured. Data were analyzed using three-way ANOVA and Tukey HSD tests (α = 0.05). Micropush-out bond strength of the posts to dentin was significantly affected by the type of post material (p < 0.05). However, the load cycling and the resin-based luting agent used had no effect on bond strength values (p = 0.706 and p = 0.346, respectively).