Mixed-mode fracture behavior of glass fiber reinforced polymer concrete

Fracture toughness of chopped strand glass fiber reinforced particle-filled polymer composite beams was investigated in Mode I and Mode III loading conditions using three-point bend tests. Effects of crack angles on fracture behavior were also studied. The specimens, which have inclined crack at an angle θ to the axis of the specimens, were used to carry out the tests. The specimens were tested with inclination angles 30°, 45°, 60° and 75°. The results are compared with the values of K_IC obtained using conventional (θ=90° ) specimens. In addition, J integrals were also determined. J_IC increases continuously with increasing in crack angle from θ=30° to θ=90°. In contrast, J_IIIC decreases with the crack inclination angle θ from 30° to 90°.     

Effect of glass fiber surface chemistry on the mechanical properties of glass fiber reinforced, rubber-toughened nylon 6

The mechanical properties of nylon 6 and its blends with maleated ethylene-propylene rubber (EPR-g-MA) plus glass fibers were examined as a function of the chemical functionality of the silane surface treatment applied to the glass fibers. Three reactive silane coupling agents, with anhydride, epoxy, or amine functionality, were used and found to have little effect on the mechanical properties when no EPR-g-MA is present. When 20 wt% EPR-g-MA is used as a rubber toughener, however, the yield strength and Izod impact strength were lowest for the amine functional silane and highest for the anhydride silane, while the epoxy silane fell in-between. These results were attributed to the differences in reactivity of the three reactive silanes. An unreactive silane (octyl groups) was used as a release agent on the glass fibers and compared with the anhydride functional silane. The octyl silane did not improve the ductility of the composite, as may have been speculated, and had poor yield strength and impact resistance when compared to the anhydride silane. Both octyl and anhydride treated glass fibers improve the heat distortion temperature such that most of the high temperature stiffness that is lost on addition of EPR-g-MA is regained by adding glass fibers.     

Morphology and mechanical properties of glass fiber reinforced Nylon 6 nanocomposites

Nylon 6 composites containing both an organoclay and glass fibers as fillers were prepared by melt processing. The aspect ratios of the glass fibers and the clay platelets were determined by electron microscopy techniques. The aspect ratio of each type of filler decreased as filler loading increased. A two particle population model for the tensile modulus was constructed based on the Mori-Tanaka composite theory. The experimental levels of reinforcement appear to be reasonably consistent with model predictions when changes in particle aspect ratios are accounted for. The tensile strength increases and elongation at break decreases as the content of either filler increases according to expected trends. Izod impact strength increased with glass fiber content but decreased with clay content.     

Fracture energy and softening behavior of high-strength concrete

An experimental investigation on the fracture properties of high-strength concrete (HSC) is reported. Three-point bend beam specimens of size 100×100×500 mm were used as per RILEM-FMC 50 recommendations. The influence of maximum size of coarse aggregate on fracture energy, fracture toughness, and characteristic length of concrete has been studied. The compressive strength of concrete ranged between 40 and 75 MPa. Relatively brittle fracture behavior was observed with the increase in compressive strength. The load-CMOD relationship is linear in the ascending portion and gradually drops off after the peak value in the descending portion. The length of the tail end portion of the softening curve increases as the size of coarse aggregate increases. The fracture energy increases as the maximum size of coarse aggregate and compressive strength of concrete increase. The characteristic length of concrete increases with the maximum size of coarse aggregate and decreases as the compressive strength increases.     

Fracture behavior of carbon/epoxy laminated composite reinforced by iron powder

The fracture behaviors of a newly developed iron-powder reinforced carbon/epoxy laminated composite are investigated in this paper. Three kinds of DCB (double cantilever beam) specimens (without iron powder, with iron powder and with iron powder in a magnetic field) were prepared by the ASTM D 5528-94a. For the third DCB specimen, the unidirectional laminas were stacked with iron powder spread evenly on each lamina’s surface. This process was performed in a magnetic field to keep the iron powder standing along the out-plane direction. From the test data of Instron 5567, the fracture toughness, G _I , was calculated by using the compliance calibration method for each of the three kinds of specimens. The calculated fracture toughness shows that the iron powder effectively disturbs the progress of fiber branching between the laminates and provides a good stitching to the in-plane laminates during the fracture.     

Fracture of glass fiber reinforced cement

Fracture patterns produced when a crack advancing from a notch in cement paste intersected a Cem FIL-2 glass fiber strand placed perpendicular to it were studied. The specimens were small notched compact tension specimens that could be wedge loaded in the scanning electron microscope chamber using a wet cell. Four distinct cracking patterns were identified. In most cases the fiber caused a shift in the crack path and in some specimens, microcracking and separation of the crack into 2 to 4 branches were observed. The filaments maintained their continuity and bridged over the track. Similar tests with E-glass fibers after accelerated curing revealed brittle behavior in which the crack path was straight and many filaments were broken.     

Fracture resistance of partially pyrolysed polysiloxane preceramic polymer matrix composites reinforced by unidirectional basalt fibres

Two kinds of composite materials reinforced by long unidirectional basalt fibres varying in the matrix type were studied. The first type of matrix material was prepared by application of partial pyrolysis of polysiloxane preceramic resin at a temperature of 650 °C. The second type of matrix material was utilised from cured only polysiloxane and/or epoxy resin and served as reference materials. The advantages of partially pyrolysed composites at elevated temperatures were described recently but the direct comparison with generally used polymer-based composites was not explored deeply. Therefore, both representative materials were characterised with the aim to determine similarities and differences in the fracture processes. The microstructural, elastic and fracture properties were also examined. The fracture resistance was obtained in two typical directions, i.e. along and across the fibres. The fractographic analysis together with fracture characteristics revealed strong and weak aspects of both types of composite materials.     

Long jute fiber‐reinforced polypropylene composite: Effects of jute fiber bundle and glass fiber hybridization

Two types of long jute fiber pellet consisting of twisted‐jute yarn (LFT‐JF/PP) and untwisted‐jute yarn (UT‐JF/PP) pellets are used to prepare jute fiber–reinforced polypropylene (JF/PP) composites. The mechanical properties of both long fiber composites are compared with that of re‐pelletized pellet (RP‐JF/PP) of LFT‐JF/PP pellet, which is re‐compounded by extrusion compounding. High stiffness and high impact strength of JF/PP composites are as a result of using long fiber. However, the longer fiber bundle consequently affects the distribution of jute fiber. The incorporation of 10 wt % glass fibers is found to improve mechanical properties of JF/PP composites. Increasing mechanical properties of hybrid composites is dependent on the type of JF/PP pellets, which directly affect the fiber length and fiber orientation of glass fiber within hybrid composites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41819.     

Shear test method for and mechanical characteristics of short basalt fiber reinforced polymer composite materials

In this work, an experimental study was performed to investigate the shearing mechanical properties of short basalt fiber‐reinforced polymer composite materials (SBFRP), and an optimized test method was developed. The following findings were obtained: (1) The optimized V‐notched rail shear device and test method are reliable and valid, enabling the effective shear testing of samples similar to those tested in this study in the future. (2) The shearing failure cracks of SBFRPs can be classified into three types, namely, main cracks, coupling cracks, and micro‐cracks. The micro‐cracks, which originate from micro‐slippage at the interfaces between the short fibers and the epoxy resin, initiate prior to the main cracks. (3) The existence of a critical value of the fiber volume fraction is proposed, above which a sample possesses a nonlinear deformation capacity by virtue of the initial micro‐slippage at the fiber/matrix interfaces. Furthermore, a higher fiber volume fraction gives rise to a stronger nonlinear deformation capacity. (4) The shearing mechanical properties and other basic material attributes of SBFRPs with a fiber length of 3 mm are presented, thereby establishing a foundation for the theoretical study, finite‐element analysis, and application and dissemination of SBFRPs. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46078.     

玻璃纤维增强聚丙烯复合材料的研究进展

综述了长、短玻璃纤维增强聚丙烯（GFRPP）复合材料的研究进展，总结出纤维含量、纤维长度及分布、纤维取向及分布、纤维与基体界面结合和改性等均为影响GFRPP性能的因素。在复合材料中，长度大于临界长度的玻璃纤维对材料的强度才有作用；增强玻璃纤维与聚丙烯的界面结合也是提高增强效果的有效手段。     

长玻璃纤维增强聚丙烯复合材料的韧性

以玻璃纤维和聚丙烯为原料,制备了长玻璃纤维增强聚丙烯(LFT-PP)复合材料,研究了基体韧性、纤维长度和界面相容剂对LFT-PP韧性的影响。结果表明LFT-PP韧性随基体韧性增加而增加;当玻璃纤维长度从2.06mm增加到4.66mm时,LFT-PP的悬臂梁缺口冲击强度从134.4J/m提高到238.0J/m,增加了约80%;添加界面改性剂降低了LFT-PP悬臂梁缺口冲击强度,从311.4J/m降为181.8J/m。     

Scratch behavior of glass fiber reinforced polyester matrix composite after solid particle erosion

In current study, the tested material is a glass fiber reinforced polyester matrix composite with one stacking sequence namely [0/90]_s. First of all, the solid particle erosion behavior of composite samples was investigated under various impingement angles (15°, 30°, 45°, 60°, 75°, and 90°, respectively). Eroded composite samples were examined by non‐contact optical profilometer and 3D surface roughness maps were obtained. From optical profilometer results, it was clearly shown that values of erosion crater hole volumes were well suited with erosion rate values versus impingement angles. Maximum and minimum erosion crater hole volumes observed at 60° and 15° impingement angles due to semi‐ductile characteristic of the target material, respectively. After erosion tests, the scratch behavior of composite samples was examined. The results showed that the coefficient of friction was decreased by the increase in impingement angles of 45° and 60°. The maximum scratch hardness value was determined at 60° impingement angle. Scratch damage morphologies were determined by using optical microscope and scanning electron microscope. It was observed that low (15° and 30°) and high (75° and 90°) impingement angles result in remarkably severe surface deformation on the samples. POLYM. COMPOS., 36:1958–1966, 2015. © 2014 Society of Plastics Engineer     

短玻纤增强ABS复合材料的研制

介绍短玻纤维增强ABS复合材料的生产工艺,实验对比了处理玻纤用偶联剂种类和加入量、玻纤含量、ABS种类及抗冲改性剂加入量对复合材料性能的影响,结果表明,玻纤用质量分数为1.5%的偶联剂KH550处理,可增强9715A ABS,同时加入质量分数为2%抗冲改性剂的可得到综合性能较好的复合材料。     

Residual stress and fracture toughness of sintered body of ZrO2-GO composite ceramics material

Zirconia ceramics and carbon-based materials are widely adopted in medical and dental applications due to their excellent biocompatibility and aesthetics. However, fracture toughness of ceramic materials limits their application in clinical dentistry because of the existence of residual stress. In this study, zirconia/graphene oxide (ZrO₂-GO) composite ceramics were fabricated by hot-press sintering. Residual stresses developed on the surface of ZrO₂-GO composite ceramics were evaluated by X-ray residual stress analysis and indentation techniques. The variation of surface residual stress with GO content was evaluated, and found to be consistent with that of fracture toughness. The generation of residual stress was found to be directly related to fracture toughness. Residual stress calculated by theoretical formula of indentation method was consistent with that measured by X-ray diffraction in line with the content of GO. Based on above results, it is concluded that 0.1–0.15 wt% GO composite ceramics possessed better mechanical properties.     

Fracture toughness of injection molded glass fiber reinforced polypropylene

The fracture behavior of polypropylene reinforced with 30% by weight of short glass fibers was studied using single and double feed plaque moldings. Plaques were injection molded using several gate types and gate positions. Fracture toughness K_c, was calculated at different positions in the plaque moldings using single edge notched tension specimens. Fracture toughness was assessed in the directions parallel and perpendicular to the mold fill direction through measurements of the load to produce complete fracture. Results indicated that the value of fracture toughness is affected by the type of gate as well by size of gate. Position of the specimen also affected fracture toughness. Generally, specimens taken from positions near cavity walls gave higher toughness values than those taken from the center of the moldings. Furthermore, fracture toughness in the transverse direction was consistently higher than in the melt flow direction. Finally, in the case o double feed moldings, a much higher fracture toughness was obtained when the initial crack was perpendicular to the weld line than when it was placed inside the weld line.     

Methodology for characterisation of glass fibre composite architecture

Abstract

The present study outlines a methodology for microstructural characterisation of fibre reinforced composites containing circular fibres. Digital micrographs of polished cross-sections are used as input to a numerical image processing tool that determines spatial mapping and radii detection of the fibres. The information is used for different analyses to investigate and characterise the fibre architecture. As an example, the methodology is applied to glass fibre reinforced composites with varying fibre contents. The different fibre volume fractions (FVFs) affect the number of contact points per fibre, the communal fibre distance and the local FVF. The fibre diameter distribution and packing pattern remain somewhat similar for the considered materials. The methodology is a step towards a better understanding of the composite microstructure and can be used to evaluate the interconnection between fibre architecture and composite properties.     

Effect of polymer modification of the paste–aggregate interface on the mechanical properties of concretes

We investigated the effect of thin viscoelastic polymer coatings around aggregate particles on the mechanical properties of “micro-concretes” with a maximum aggregate diameter of 10 mm. Aggregate particles > 5 mm were pre-treated with a latex at dosages of up to 2% by mass and dried prior to using the treated aggregate in the micro-concrete mix. Cured prisms were tested in flexion. The results show that thin polymer coatings on aggregates have a significant effect on micro-concrete cracking behaviour at much lower polymer dosages than are commonly used in polymer-modified mortars. We observed a significant improvement in post-peak energy absorption relative to the use of the same amount of polymer dispersed in the bulk paste. But, under the conditions tested here, reductions in the strengths and moduli of the composites due to the polymer additions appear to have more than outweighed the observed positive effects of increases in fracture energy and characteristic length.     

Fracture behavior of glass bead filled epoxies: Cleaning process of glass beads

Inorganic particles are commonly cleaned with solvents such as alcohols before being incorporated into thermoset polymers as fillers or tougheners, but the role of the cleaning process has never been examined. In this study, the effect of the cleaning process on the fracture behavior of particulate composites is investigated using glass bead filled epoxies as model systems. The cleaning process is shown to be a simple method to strengthen the interface between the glass beads and the epoxy matrix. Although the chemistry of the glass bead surface is unlikely to be altered by the cleaning process, submicron particles that exist on the glass bead surfaces are removed by cleaning with distilled water or ultrasonic vibration. The removal of submicron particles increases the interfacial strength between the glass beads and the matrix and changes the tensile strength of the composites. However, the modulus and fracture toughness of the composites is not significantly dependent on the cleaning process. Thus, it may be the case that debonding of the glass beads is not one of the major energy dissipating mechanisms in the fracture of glass bead filled thermoset systems. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1371–1383, 2001     

氧化铝纤维增强红柱石基复合材料的制备与性能

在南非进口红柱石细粉中分别加入 5 %、10 %、15 %和 2 0 %的氧化铝纤维 ,研究了纤维加入量对材料显气孔率、体积密度、力学性能及显微结构的影响。结果表明 :当氧化铝纤维加入量为 5 %～ 10 %时 ,材料的体积密度大 ,力学性能好 ,超过 10 %后材料的性能显著下降     

Compressive behavior of fiber reinforced high-performance concrete subjected to elevated temperatures

In this paper, the effects of elevated temperatures on the compressive strength stress–strain relationship (stiffness) and energy absorption capacities (toughness) of concretes are presented. High-performance concretes (HPCs) were prepared in three series, with different cementitious material constitutions using plain ordinary Portland cement (PC), with and without metakaolin (MK) and silica fume (SF) separate replacements. Each series comprised a concrete mix, prepared without any fibers, and concrete mixes reinforced with either or both steel fibers and polypropylene (PP) fibers. The results showed that after exposure to 600 and 800 °C, the concrete mixes retained, respectively, 45% and 23% of their compressive strength, on average. The results also show that after the concrete was exposed to the elevated temperatures, the loss of stiffness was much quicker than the loss in compressive strength, but the loss of energy absorption capacity was relatively slower. A 20% replacement of the cement by MK resulted in a higher compressive strength but a lower specific toughness, as compared with the concrete prepared with 10% replacement of cement by SF. The MK concrete also showed quicker losses in the compressive strength, elastic modulus and energy absorption capacity after exposure to the elevated temperatures. Steel fibers approximately doubled the energy absorption capacity of the unheated concrete. They were effective in minimizing the degradation of compressive strength for the concrete after exposure to the elevated temperatures. The steel-fiber-reinforced concretes also showed the highest energy absorption capacity after the high-temperature exposure, although they suffered a quick loss of this capacity. In comparison, using PP fibers reduced the energy absorption capacity of the concrete after exposure to 800 °C, although it had a minor beneficial effect on the energy absorption capacity of the concrete before heating.