Discontinuous Short Fibers Research Articles

Adhesion of individually formed fiber post adhesively luted with flowable short fiber composite

This laboratory study aimed to measure the push-out bond strength of individually formed fiber-reinforced composite (FRC) post luted with flowable short fiber-reinforced composite (SFRC) and to evaluate the influence of post coating with light-cured adhesive. Post spaces (Ø 1.7 mm) were drilled into 20 single-rooted decoronated premolar teeth. Post spaces were etched and treated with light-cured universal adhesive (G-Premio Bond). Individually formed FRC posts (Ø 1.5 mm, everStick) were luted either with light-cured SFRC (everX Flow) or conventional particulate-filled (PFC) dual-cure luting cement (G-CEM LinkForce). Half of the posts from each group were treated with dimethacrylate adhesive resin (Stick Resin) for 5 min before luting. After storage in water for two days, the roots were sectioned into 2 mm thick disks (n = 10/per group). Then, a push-out test-setup was used in a universal testing machine to measure the bond strength between post and dentin. The interface between post and SFRC was inspected using optical and scanning electron microscopy (SEM). Data were statistically analyzed using analysis of variance ANOVA (p = .05). Higher bond strength values (p < .05) were obtained when flowable SFRC was used as a post luting material. Resin coating of a post showed no significant effect (p > .05) on bond strength values. Light microscope images showed the ability of discontinuous short fibers in SFRC to penetrate into FRC posts. The use of flowable SFRC as luting material with individually formed FRC posts proved to be a promising method to improve the interface adhesion.

Fracture behavior of discontinuous fiber-reinforced composite inlay-retained fixed partial denture before and after fatigue aging.

To evaluate the fracture behavior of inlay-retained fixed partial dentures (IRFPDs) made of experimental short fiber-reinforced composite (SFRC) computer-aided design/computer-aided manufacturing (CAD/CAM) block before and after cyclic fatigue aging. Five groups (n=20/group) of three-unit posterior IRFPDs were fabricated. The first and second groups were CAD/CAM fabricated from experimental SFRC blocks or lithium-disilicate (IPS e.max CAD, IVOCLAR) materials, the third group comprised a three-dimensional-printed composite (Temp PRINT, GC), and the fourth and fifth groups comprised conventional laboratory flowable composite (Gradia Plus, GC) and commercial flowable SFRC (everX Flow, GC), respectively. All IRFPDs were luted into a metal jig with adhesive dual-cure resin cement (RelyX Ultimate, 3M ESPE). Half the IRFPDs per group (n=10) were subjected to fatigue aging for 10,000 cycles. The remaining half were statically loaded until fracture without fatigue aging. The load was applied vertically between triangular ridges of the buccal and lingual cusps. The fracture mode was visually examined using optical and scanning electron microscopy (SEM). Data were statistically analyzed using a two-way analysis of variance (ANOVA) followed by Tukey's HSD test. ANOVA revealed that IRFPDs made of experimental SFRC CAD/CAM had the highest (P<0.05) load-bearing capacity before (2624±463 N) and after (2775±297 N) aging among all groups. Cyclic fatigue aging decreased the load-bearing capacity (P>0.05) of all tested prostheses, except for the experimental SFRC CAD/CAM and conventional laboratory composite IRFPDs (P>0.05). SEM images showed the ability of discontinuous short fibers in the experimental SFRC CAD/CAM composite to redirect and hinder crack propagation. CAD/CAM-fabricated IRFPDs made of experimental SFRC blocks showed promising performance in clinical testing in terms of fracture behavior.

Multilevel Analysis of Strain Rate Effect on Visco-Damage Evolution in Short Random Fiber Reinforced Polymer Composites

Abstract In this study, the strain rate sensitivity of a discontinuous short fiber reinforced composite and the strain rate effect on the damage evolution are investigated. The studied material is a polymeric composite with a polyamide 6.6 matrix reinforced with oriented randomly short glass fibers at a 50% weigh ratio (PA6.6GF50). Tensile tests at low and high strain rate are conducted. In addition, interrupted tensile tests are carried out to quantify the damage at specific stress levels and strain rates. To perform the interrupted tensile tests, an intermediate fixture is realized via double notched mechanical fuses with different widths designed to break at suitable stress levels. The damage is estimated by the fraction of debonded fibers and matrix fractures. Based on the experimental observations, it is concluded that the ultimate stress and strain, and the damage threshold are mainly governed by the strain rate. Furthermore, it is established that the considered composite has a non-linear dynamic behavior with a viscous damage nature.

Mechanical characterization of particulated FRP composite pipes: A comprehensive experimental study

Particulated fiber reinforced polymer (FRP) composite pipes encompass unidirectional continuous glass fibers (hoop glass), resin (thermoset polymer vinylester) matrix, chop glass (discontinuous short fibers), and particulate reinforcement (sand) impregnated into resin. They are categorized based on their nominal diameter, pressure class, and stiffness class. Mechanical characteristics of this class of composite materials have not, to date, been comprehensively studied. As such, this paper presents a systematic approach toward comprehensive experimental investigation into their mechanical characterizations in terms of the axial and hoop tensile strengths. The particulated FRP composite pipes used in the current study have glass fibers reinforced along the hoop direction at approximately 89° angle. To assure the experimental data accuracy and reliability, three batches associated with each pipe category were selected which slightly differ in the composition of their constituents. Three specimens per batch were selected and two types of tests were conducted on each specimen. 18 tests (2 × 3 batches × 3 specimens)) were conducted per pipe category (9 tests for hoop and 9 tests for axial). Therefore, 648 tests were conducted in total on 36 pipe categories. Instron 5569A and Instron 8801 universal testing machines were utilized for the axial tensile tests and a split disc hydraulic testing machine for the hoop tensile tests. The mean tensile and the hoop axial stresses and their associated standard deviations were calculated based on the Population Standard Deviation (PSD) equation and then plotted against the material constituents. The results demonstrated that an increase in the composition of particulate reinforcement results in a decrease in the axial and the hoop tensile strengths. However, increasing the ratio of resin, chop glass, and glass fibers contributes to the enhancement of the axial and the hoop tensile strengths. This study provides comprehensive design guidelines for engineers and manufacturing industries.

Experimental investigation on strength properties of Recron fibre with fly ash in concrete

In recent years, Self-Compacting Concrete has been widely used for placing concrete in congested reinforced concrete structure for difficult casting condition. For such applications the fresh concrete must possess high fluidity and good cohesiveness. The main objective is to determine the properties of concrete by adding Recron Fiber and replacing cement by fly ash in certain% and compare with the Conventional Concrete. Recron Fiber is a discontinuous short fiber that can be used in concrete to control and arrest cracks. The variation of Recron Fiber by 0%, 0.25%, 0.5%, 0.75%, 1% and fly ash by 25% in concrete was studied. The mix designs with strengths of 30 N/mm2 were considered by Nan Su method. The project reports on a comprehensive study on the strength of Self Compacting Concrete containing Recron Fiber and Fly ash. The study includes workability of fresh concrete, compressive strength, splitting tensile strength, flexural strength for hardened concrete. The test was conducted in 7 days and 28 days on the specimen and the result are compared with the conventional concrete. The experimental results shown that Recron Fiber gave maximum strength in 0.75% of Recron Fiber and also Fly ash gave maximum strength in 25% of replacement of cement. It has no resistance to acid and sulphate attack. The ultimate load carrying capacity of F25R0.75 Self Compacting Concrete Reinforced beam is higher than the Conventional Concrete is found in this experimental research.

Determination of shear modulus in bamboo fibers composite in torsion tests

Natural Fibers, when employed as reinforced in composites, contribute to the reduction of environmental impacts, moreover, its use decreases costs and reduces the weight of components. Several studies are carried out for the application of these materials in the automobile industry. Some mechanical behaviors such as elasticity moduli have already been experienced in these types of composites. However, for the use of these materials in quality and safety products, more mechanical information is required. The purpose of this study is to determine the shear moduli G13 and G23 of composites with vegetable fibers. Torsion tests were performed on epoxy resin composites with bamboo fibers without chemical treatment: one with 280-mm unidirectional long fibers and another one with 25-mm discontinuous short fibers. The torsion test was based on the variation of the base/height ratio (b/h) of the test specimen and at each base reduction a new torsion test was carried out. All tests featured a linear relationship between the torsional angle and the torque. On the experimental points plotted, the Saint-Venant equation modified to orthotropic material was interpolated, thus allowing the determination of the shear modulus G13 and G23 for the two composites. The shear moduli for long fiber composites presented the following values: G13 = 1.441 GPa, G23 = 1.726 GPa, and for short fibers G13 = 1.889 GPa, G23 = 1.290 GPa. The results showed that the composites are orthotropic for shear modulus due to the compression molding process.

The Behavior of Pseudo Strain-Hardening Cementitious Composite (PSH2C) Using Synthetic Fibers under Uniaxial Tensile Loading

The application of pseudo strain-hardening cement composites (PSH2C) to structural systems depends primarily on the tensile response of the materials, which is a direct function of fiber and matrix characteristics, the fiber content or volume fraction. In general, improved response of material is observed with an increase in the fiber volume fraction, as long as the fiber content does not impede mixing. This paper addresses the direct tensile response of pseudo strain hardening cement composites (PSH2C) reinforced with PET fibers, which belongs to a class of discontinuous short fiber reinforced cement based composites characterized by a strain hardening and multiple cracking responses under direct tensile loading. The variables are different types of fibers (PET, PET+PE, PET+PVA).

Prediction of the Elastic Properties of Short Basalt Fiber Reinforced Al Alloy Metal Matrix Composites

In this paper, a micro-mechanical model is implemented in software for the prediction of local mechanical properties of discontinuous short fiber reinforced composites. The model, based on the Mori and Tanaka method, shear-lag, computational model, Nielsen-Chen model and Miwa’s model is used to predict the elastic behaviour of basalt short fiber reinforced with Al alloy composites. The Al/basalt Metal Matrix Composites (MMCs) contain basalt short fiber from 2.5% to 10% in steps of 2.5 wt.% and are fabricated using squeeze infiltration technique. The effects of fiber length and orientation on elastic properties of Al/basalt MMCs are investigated. A comparison between the experimental data and the theoretical data based on physical models is made, and the significance of the findings is discussed. The results show that as short basalt fiber content was increased from 2.5% to 10% by wt.%, an improvement in Young’s modulus of 13.26% has been observed. Optical microscopy was used to examine the general microstructure and fiber distribution in the composite produced. Scanning Electron Microscopy (SEM) was performed on the fractured surface to understand the failure mechanisms.

Toughening of high strength cementitious matrix reinforced by discontinuous short fibers

High strength cementitious materials are more brittle than conventional cement-based materials. The brittleness of high strength cementitious materials can be reduced by using fibers. Toughening of high strength cementitious matrices reinforced by discontinuous short fibers is studied in this paper using nonlinear fracture mechanics. An R-curve-based approach is proposed to describe the matrix toughening due to fiber reinforcement. The effect of fiber bridging is modeled by a closing pressure which depends on length, diameter, and volume fraction of fibers, and the fiber-matrix interfacial bond. Results predicted by the proposed R-curve approach match quite well with experimental data from different studies. It is found that use of fibers in relatively high volume fractions not only reduces the brittle natuer of high strength cemenitious matrices, but also increases the maximum matrix strength.