Effect Of Fiber Length Distribution Research Articles

A two‐stage analysis for the role of fiber size in terms of length distribution on the performance under accelerated weathering tests of oil palm empty fruit bunch fiber‐reinforced vinyl acrylic composites

AbstractThe performance of natural fiber‐reinforced polymer composites (NFRPCs) can be markedly affected by fiber length, to the extent that a sole mean value and standard deviation fail to accurately represent its overall dispersion. Hence, measuring the variability of fiber length is crucial to comprehend its influence on the properties of the resulting composites. Unfortunately, few studies have been conducted on this topic. This work consisted of two research stages: the first related to the effect of both fiber length distribution and processing temperature on the properties of oil palm empty fruit bunch (OPEFB) fiber‐reinforced vinyl acrylic composites, while the second stage analyzed the influence of the fiber length distribution on the material performance under accelerated weathering tests. Broadly, composites were characterized by tensile mechanical testing, optical microscopy and SEM, FTIR spectroscopy, TGA, and microbiological analysis. The key results showed that processing the material at temperatures surpassing 75°C did not lead to a homogenous phase between the components, rendering it unworthy of consideration. Furthermore, composites containing the longest OPEFB fibers exhibited the lowest elongation‐at‐break values. Regarding the incidence of aging treatments, pronounced effects were observed in those composites exposed to UV radiation and salt fog. In detail, the elongation at break decreased by up to 34%, while the tensile strength increased by up to 1 MPa, and Young's modulus rose by up to 17%. Finally, two fungal genera, Fusarium sp. and Rhizophydium sp., were identified on the OPEFB fibers; nevertheless, no fungal growth was observed on the composites.Highlights Natural reinforcement/filler size measured as fiber length distribution. Effect of fiber length distribution on composite performance. Composite performance after accelerated weathering tests.

Modeling and simulation of fiber movement in the drafting zone based on the iterative method

A model using the iterative method is introduced in this paper to simulate the drafting process, including roller drafting and apron drafting. This proven model is established based on the relationship between the controlling force and the guiding force on a single fiber at different positions in the drafting zone. Through simulation, the effects of fiber length distribution, roller gauge and draft ratio on fiber accelerated points are discussed. The result proves that the accelerated point of a fiber is related to its own length, but has nothing to do with the lengths of other fibers in the sliver. The smaller the roller gauge, the closer the fiber accelerated point is to the front-roller nip and the more concentrated the accelerated-point distribution. Under the condition that a sliver can be drafted, the draft ratio only affects the fiber accelerated points slightly. The distribution of all accelerated points and distributions of different types of fibers in the drafting zone can also be obtained, including floating fibers and fibers that are controlled by the front and back rollers. The model can be applied not only to the roller drafting system, but also to the apron drafting system as a theoretical guide for practice.

Processing and mechanical characterization of short carbon fiber-reinforced epoxy composites for material extrusion additive manufacturing

Fiber-reinforced polymer composites have been extensively utilized in recent years as feedstock materials for material extrusion additive manufacturing (AM) processes to improve strength, stiffness, and functionality of printed parts over unfilled printed polymers. However, the widespread adoption of AM of fiber-reinforced polymer composites requires a deeper understanding of the process-structure-property relationships in printed components, and such relationships are not well understood yet. Fiber length is critically important to the mechanical performance of short fiber composites, but very few studies to-date have focused on how the fiber length distribution (FLD) evolves during processing of composite feedstocks and how this evolution affects printing behavior and mechanical properties in 3D-printed composites. In this work, FLD is measured for carbon fiber reinforced epoxy composites over a wide range of ink compositions and shear mixing times, and the distributions are fit with a Weibull-type distribution function. The effects of FLD on the tradeoff between ink processability, ink rheology, printing behavior and mechanical properties are investigated. Furthermore, the effects of printing parameters (nozzle size and print speed) on mechanical anisotropy and fiber orientation distribution (FOD) in printed composites are explored. Mechanical properties of printed composites are characterized via 3 pt-flexural testing, and microstructure is investigated using optical and scanning electron microscopy (SEM), and x-ray computed tomography. Finally, the fitted Weibull parameters are fed into a composite model that incorporates FLD and FOD, and model predictions are found to be in excellent agreement with experimental observations.

The effect of fiber length distribution of fiber-reinforced polypropylene composites injection-molded on the mechanical properties

The effect of fiber length distribution of fiber-reinforced polypropylene composites injection-molded on the mechanical properties

Effects of fiber length distribution on flow property and internal microstructure of an injection molded part

Internal microstructures of micro-injection molded connectors were investigated to figure out the relationship between flow properties in the micro-channel and fiber length distributions (FLD). Micro-CT and image processing techniques were performed to convert the images obtained by Micro-CT into 3D structures and visualize the fiber length distributions. It was verified by both experimental and numerical analyses that the fiber length distribution affects significantly the processability and flowability of the composite melt for injection molding of microconnectors since a large amount of glass fibers within the material worsen the rheological properties and long fibers hinder flowability at narrow junctions and micro scale channels. Open image in new window

Statistical modeling of effective elastic modulus for multiphased hybrid composites

We explored the effective elastic moduli of hybrid composites by using different statistical models to understand and analyze the effect of fiber length distribution (FLD) on the mechanical properties. Micro-CT was used to investigate the internal structure of the hybrid composites, and FLD was calculated via image-processing for the composite samples. The interaction between inclusions and matrix was considered using a perturbed stress-strain theory. Statistical modeling with the Weibull, Log-normal and Generalized Extreme Value (GEV) functions was carried out to understand the role of skewness. The results show that different skewness and FLD have significant impacts on the effective elastic moduli of the hybrid composites, which demonstrates the practical importance of statistical modeling when evaluating and analyzing the their mechanical properties.

Effect of fiber length distribution and fineness on theoretical unevenness of yarn

Fiber length distribution and fineness exert considerable influence on fiber random alignment and yarn unevenness. This study, based on early works by other researchers, presents the number of fibers in the cross‐section of the yarn in terms of fiber length distribution and fiber end density. By employing the non‐parametric kernel estimate of probability density function of fiber length, the computation of theoretical yarn unevenness is facilitated. Compared with the results from Martindale’s and Suh’s theory, the change trend of the calculated unevenness from the new expression is the same as that of the tested uneveness.

The analysis of the influence of fiber length distribution on the theoretical and additional unevenness of yarn

Fiber length distribution has an impact not only on the theoretical unevenness of yarn caused by random fiber alignment, but also upon the additional unevenness caused during processing, especially in drafting. For a given fiber length distribution, there is a discrepancy between the theoretical unevenness of yarn which is calculated with Martindale’s equation and the actual unevenness tested by instrument. In order to reflect the effect of fiber length distribution on the theoretical unevenness of yarn, in this research, a kernel function was used to estimate the probability density function of fiber length, therefore, calculation of Suh’s model for theoretical unevenness was realized. On this basis, the theoretical and additional unevenness of yarn were calculated. The statistical influence of fiber length parameters on yarn unevenness was discussed. It can be concluded that decreasing the values of effective length, length irregularity and 16 mm SFC by weight would improve the uniformity of yarn.

Continuum Micro-mechanics of Estimating Interfacial Shear Strength in Short Fiber Composites

A new continuum approach to micro-mechanics of short fiber composites yielded two separate methods of estimating the apparent interfacial shear strength and fiber orientation efficiency. The methods exploit the compilation of the effects of fiber length distribution and interfacial shear strength on strengthening efficiency into a function of strain. The In-Built Method derives a unique combination of apparent interfacial shear strength and fiber orientation efficiency being able to reproduce the experimental stress–strain curve of a short fiber reinforced composite with a very low residual standard deviation. The Boundary Method accomplishes rapid interfacial shear strength screening in materials selection by constructing and utilizing the proposed selection chart.

Strength of short fiber reinforced polymers: Effect of fiber length distribution

AbstractIn this study, the prediction of mechanical strength of short fiber reinforced plastics (SFRPs) is made possible by obtaining a Fiber Length Distribution (FLD) efficiency factor, ηFLD, from the formerly known twofold discrete strengthening equation of Kelly–Tyson. The unified parameter ηFLD is developed involving both the effects of fiber breakage and resulting distribution, fiber volume fraction and fiber and interface properties, so that they can be incorporated into modified rule of mixtures (MROM). This procedure helps to clarify the experimentally observed loss in strengthening rate with increasing fiber fraction. By adapting a few experimentally determined distributions to a Weibull type function, the analytical solutions described in this study establish the exploration of the strength of SFRPs in the entire fiber content range or can reveal the interfacial bond strength. After investigating the effects of fiber and interface parameters on strengthening efficiency, it is found that common fiber‐matrix combinations possessing intermediate critical fiber lengths show a significant decrease in strengthening efficiency with increasing fiber content at low fiber loadings. On the contrary, higher and lower critical fiber lengths yield less significant losses. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers

Microstructure and Strength of Injection Molded Natural Fiber Composites

Injection molded short natural fiber composites (NFC) are studied in this article. Micromechanical models are employed to investigate effects of fiber length distribution, fiber orientation, and fiber/matrix adhesion on mechanical performance of NFCs. A parametric study showed that length/diameter ratio strongly affects the composite strength, whereas fiber strength has very little influence on strength of the composites when fiber/matrix adhesion is poor. In order to verify conclusions based on theoretical predictions, modeling results are compared with experimental results of wood powder-, flax-, pulp-, and glass fiber composites. Recommendations on improvement of strength of NFC through change of the internal structure of the materials are formulated based on results of this investigation.

Effect of fiber length distribution on gas holdup in a cocurrent air–water–fiber bubble column

An experimental investigation is reported on the effect of fiber length distribution on gas holdup in a cocurrent air–water–fiber bubble column. Different combinations of 1 and 3 mm Rayon fibers are used to simulate different fiber length distributions. At a constant total fiber mass fraction, gas holdup generally decreases with increasing mass fraction of the 3 mm Rayon fiber while other conditions remain constant. Crowding factors estimated using four different methods ( N c = N c , A , N c * , N c , L , and N c , M ) and the parameters N c , L N f 0.2 0.8 and N c , M N f 0.2 0.8 are tested on their performance to quantify the overall effects of fiber mass fraction and fiber length and its distribution on gas holdup. N c , L N f 0.2 0.8 and N c , M N f 0.2 0.8 provide the best characterization of the fiber effects on gas holdup in the cocurrent air–water–fiber bubble column. The crowding factor estimated using the model-based average fiber length ( N c , M ) also provides a good characterization and is better than the other crowding factor definitions.

EFFECTS OF FIBER LENGTH AND ORIENTATION DISTRIBUTIONS ON THE MECHANICAL PROPERTIES OF SHORT-FIBER-REINFORCED POLYMERS

Extrusion compounding and injection molding processes are frequently employed to fabricate short-fiber-reinforced polymers. During extrusion compounding and injection molding processing, considerable shear-induced fiber breakage takes place and results in a fiber length distribution (FLD) in final short-fiber-reinforced polymer (SFRP) composites. Also, during compounding and molding processing, progressive and continuous changes in fiber orientation occur and lead to a fiber orientation distribution (FOD) in final composites. Both FLD and FOD are governed by a number of design and fabrication factors including original fiber length, fiber content, mold geometry and processing conditions. The mechanical properties such as strength, stiffness and fracture toughness or specific work of fracture (WOF) of SFRP composites have been shown to depend critically on FLD and FOD. The present paper reviews previous research work on the effects of design/fabrication factors on FLD and FOD and the effects of FLD and FOD on the strength, stiffness and toughness or WOF of SFRP composites. Conclusions which can be drawn from the literature are presented with discussions of areas in which further research is required.

Tensile Properties and Static Fatigue Behavior of Cotton Warp Yams

Warp yams under a state of dynamic loading on a loom have to withstand cumulative damage caused by tensile fatigue at relatively low loads coupled with the abrasive action of the machine parts. To evaluate the fatigue phenomenon of sized cotton yams and its correlation with performance on a loom, one must first understand basic mechanical properties of yams in terms of fiber properties and fiber length distribution. The first section of this paper reports on the effect of fiber length distribution on tensile properties of yams at various tensile strain rates, and the second section presents the . fatigue behavior of 100% cotton yams. Fiber length and its distribution in cotton yams seem to influence the tensile behavior of both sized and unsized yams at all strain rates, but strain rates do not play a significant role in determining the properties of sized yams. Adding size tends to mask the effect of fiber length variation, particularly at higher size loading. The tensile properties of sized cotton yams are also influenced by the size type, such as polyester, carboxymethyl cellulose, and polyvinyl alcohol, at all add-on levels. The fatigue behavior of 100% cotton unsized and sized yam is eval uated using a Sulzer-Ruti Webtester. The mechanism of yam failure due to fatigue/ abrasion for unsized yam is affected by short fiber content. The base tension has the largest overall effect. Unsized yam containing 10% comber noil has an optimum bal ance of short and long fibers, making the yam structure more resistant to fatigue / abrasion. In sized yam, the effect of short fibers is partly masked by the properties and compatibility of size materials with the substrate. Polyester size has poor com patibility with cotton fibers; carboxymethyl cellulose and partially hydrolyzed polyvinyl alcohol tend to produce very highly increased resistance to fatigue and abrasion. Rep resenting fatigue /abrasion data in terms of mean or average lifetimes is questionable due to contradictory evidence. Representing fatigue data in terms of a three-parameter Weibull distribution leads to realistic interpretations.

Compounding of glass fiber‐reinforced polypropylene and investigation of its mechanical properties under simple and complex loading

AbstractPolypropylene is one of the important thermoplastics that has been reinforced with glass fibers to give a reasonably good engineering plastic. Because of its inert nature, it does not easily adhere to the glass surface and hence some improvement in mechanical properties. In the present study a vinyltriethoxysilane coupling agent in polymeric form has been tried and seen to improve the properties. Tests have been carried out at (a) constant strain rate (in the Instron testing machine), and (b)constant stress rate (water loading on a biaxial testing machine). Under constant strain rate only tensile properties have been studied while under constant stress rate, the tensile, torsional and combined tensile‐torsional tests have been carried out. In each of the above cases, a considerable improvement in elastic modulus has been observed. The Tensile strength is improved to the extent of about 25 percent. There is only a slight improvement in torsional strength. Different fiber volume contents were used and their effect studied on modulus and strength. The mechanical data for reinforced‐polypropylene samples have been discussed in terms of the fiber‐length distribution in the composite. Detailed analysis of tensile data suggests that at low strains, when the critical length is relatively low, the fibers contribute to a high modulus. With increasing strain the critical length increases and the load carrying capacity of the fibers is reduced. Consequently the gain in strength is relatively less. The effect of fiber length distribution in torsion and combined tension‐torsion tests would be expected to be similar and the results seem to confirm this.