Study of moisture absorption in natural fiber plastic composites

In this work, the variation of mechanical properties such as tensile, flexural, and impact strengths of roselle and sisal fibers hybrid polyester composite at dry and wet conditions were studied. The composites of roselle/sisal polyester-based hybrid composites with different weight% of fibers were prepared. Roselle and sisal fibers at a ratio of 1:1 had been incorporated in unsaturated polyester resin at various fiber lengths. When the fiber content and length of the roselle and sisal fibers were increased, the tensile and flexural strength of the composite increased. When the samples were subjected to moisture environment, decrease in tensile and flexural strength was observed. The maximum percentage of strength reductions in tensile and flexural strength were observed for the composites having the fiber length of 150 mm and 30 wt% fiber content. For impact strength, it was with the composites of 20 wt% and 150 mm at wet conditions compared to dry conditions. The percentage of strength reductions increased with fiber content and length in wet conditions. A scatter in the impact strength values was identified on both the conditions. The moisture absorption characteristics of the natural fibers are very important to produce the natural fiber hybrid composite materials with the positive hybrid effect. The experimental results are compared with theoretical and empirical or statistical results and found to be in good agreement.

Effect of moisture absorption on the mechanical properties of randomly oriented natural fibers/polyester hybrid composite

Environmental concern has resulted in a renewed interest in bio-based materials. Among them, plant fibers are perceived as an environmentally friendly substitute to glass fibers for the reinforcement of composites, particularly in automotive engineering. Due to their wide availability, low cost, low density, high-specific mechanical properties, and eco-friendly image, they are increasingly being employed as reinforcements in polymer matrix composites. Indeed, their complex microstructure as a composite material makes plant fiber a really interesting and challenging subject to study. Research subjects about such fibers are abundant because there are always some issues to prevent their use at large scale (poor adhesion, variability, low thermal resistance, hydrophilic behavior). The choice of natural fibers rather than glass fibers as filler yields a change of the final properties of the composite. One of the most relevant differences between the two kinds of fiber is their response to humidity. Actually, glass fibers are considered as hydrophobic whereas plant fibers have a pronounced hydrophilic behavior. Composite materials are often submitted to variable climatic conditions during their lifetime, including unsteady hygroscopic conditions. However, in humid conditions, strong hydrophilic behavior of such reinforcing fibers leads to high level of moisture absorption in wet environments. This results in the structural modification of the fibers and an evolution of their mechanical properties together with the composites in which they are fitted in. Thereby, the understanding of these moisture absorption mechanisms as well as the influence of water on the final properties of these fibers and their composites is of great interest to get a better control of such new biomaterials. This is the topic of this review paper.

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The hygroscopic behavior of plant fibers: a review

Objective: To determine the presence of chronic traumatic brain injury in professional soccer players. Methods: Fifty-three active professional soccer players from several professional Dutch soccer clubs were compared with a control group of 27 elite noncontact sport athletes. All participants underwent neuropsychological examination. The main outcome measures were neuropsychological tests proven to be sensitive to cognitive changes incurred during contact and collision sports. Results: The professional soccer players exhibited impaired performances in memory, planning, and visuoperceptual processing when compared with control subjects. Among professional soccer players, performance on memory, planning, and visuoperceptual tasks were inversely related to the number of concussions incurred in soccer and the frequency of \"heading\" the ball. Performance on neuropsychological testing also varied according to field position, with forward and defensive players exhibiting more impairment. Conclusion: Participation in professional soccer may affect adversely some aspects of cognitive functioning (i.e., memory, planning, and visuoperceptual processing).

Braced for impact: Reducing military paratroopers' ankle sprains using outside-the-boot braces

Textile composite is one of the important materials used in industry and is made from textile substrates embedded in the matrices of different materials (see ref. 1 ). However, due to its complicated microstructure, understanding of mechanical properties of textile composite materials is still in its infant stage (see refs 2.3 ). Recently, many researchers have contributed to develop finite element analysis (FEA) and theoretical analysis models for predicting mechanical properties of textile composites, and to study the variation trends of mechanical property with major architectural parameters. In this paper, a review of recent developments and results in predicting mechanical properties of textile composites using finite element analysis and theoretical analysis methods, focusing on elastic behaviour for woven fabric composites, is presented. The predictive capability of various models, including earlier one-dimensional (1D) ‘mosaic model’ and more recent three-dimensional (3D) models, are discussed in this review.

Modelling for predicting the mechanical properties of textile composites : A review

This study considers laminate warpage (or spring-in) associated with the curing of reinforced thermoset composites. This processing induced spring-in shows up in flat parts as well as those with curved geometry, and is most prevalent with parts that do not have a closed cross section. Three contributions to spring-in were considered, namely: thickness cure shrinkage, mold expansion, and fiber volume fraction gradients. These effects were combined into a predictive finite element model (FEM). Mold stretching and thickness shrinkage were described through a modified in-and out-of-plane material thermal expansion, respectively, while fiber volume fraction gradients were accounted for by scaling the thermal and elastic properties of the composite through the thickness with the fiber volume fraction. For thin parts ( 2 mm) spring-in was dominated by thickness cure shrinkage. The FEM was able to acco...

Isolating Components of Processing Induced Warpage in Laminated Composites

The effects of simulated marine environments on the performance of wood/thermoplastic composites under quasi-static and fatigue loading is investigated. The material under consideration consists of wood flour embedded in a thermoplastic matrix. The effects of additives and processing methods were included in the durability study. Moisture sorption studies are presented for these formulations and are found to compare favorably with a linear Fickian diffusion model. Qualitative and quantitative evidence of hygrothermal damage was nevertheless consistently observed. The combination of Fickian diffusion and damage is explained from moisture-induced swelling considerations of the constituents. The influence of marine environments on fatigue response was examined by immersing the coupons in seawater during the fatigue test. The synergistic effects of moisture and fatigue are discussed.

Effects of Moisture on the Durability of a Wood/Thermoplastic Composite

Manufacturing processes for laminated composites often produce parts whose dimensions do not match the mold from which they were made. This distortion is commonly referred to as ‘spring-in’. The amount of spring-in can depend on many factors including the manufacturing process (cure temperature, resin bleed, and applied pressure), the part (geometry, material, thickness, cure shrinkage, thermal expansion and layup sequence), and the tool (surface, thickness and thermal expansion). Much of the current work devoted to spring-in relies on extensive resin characterization. While this approach has been reasonably successful, it does little to assist the designer using material systems that have not been fully characterized (which is not always possible or feasible). This study considers the ability of a linear elastic finite element model to describe and quantify many of the factors contributing to spring-in. The aim of this study is to show that spring-in can be accurately predicted without a complete resin characterization. Numerical predictions based on relatively simple mechanical tests were observed to compare favorably with experimental measurements. Spring-in was dominated by thickness shrinkage, which contributed approximately 3/4 of the measured distortion. The mold stretching contribution diminished with thickness and was negligible for parts thicker than 2.5 mm (0.1 in.). While the material system at hand did not exhibit a fiber volume fraction gradient, its effects were included in the formulation of the model. For materials that have reported a gradient, it was found to account for approximately 10% of the part spring-in.

A linear finite element model to predict processing-induced distortion in FRP laminates

The effect of sea water on carbon/epoxy cross ply specimens is studied by consideration of fatigue data and failure modes. Tests were conducted using dry and saturated coupons fatigued in air, as well as pre-saturated coupons fatigued while immersed in sea water. The saturated coupons fatigued in air had the longest fatigue life, which was attributed to stress relief from sorption induced swelling. Saturated coupons fatigued in an immersed environment exhibited the shortest fatigue life, and also experienced significant deliminations prior to failure. Water trapped inside the transverse cracks during the load cycle provides a physical mechanism explaining this behavior. Analytical and numerical analyses are presented which show how moisture inside the transverse cracks can alter the coupon stress state and enhance delimination.

Lloyd V. Smith

Papers

Isolating Components of Processing Induced Warpage in Laminated Composites

Effects of Moisture on the Durability of a Wood/Thermoplastic Composite

A linear finite element model to predict processing-induced distortion in FRP laminates

The immersed fatigue response of polymer composites

Performance assessment of wood, metal and composite baseball bats