Experimental determination of fiber properties

Experimental determination of the properties of any material is very important. This is particularly true in the case of fibrous materials because general insufficient data are available for them. Fibers have one very long dimension and the other two extremely small. This makes determination of their properties, physical and mechanical, far from trivial. In particular determination of their transverse properties, i.e. in the direction of the fiber diameter, can be difiicult. In this chapter we describe experimental techniques to determine some physical and mechanical properties of fibers. 

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The theory behind the experimental determination of the dynamic mechanical properties of solids has much in common with that of the dynamic mechanical analysis of melts. Samples in the form of strips, beams, fibers, or rods may be used. Such specimens may be subjected to oscillatory deformation in the form of tension, torsion, and—if they are sufficiently thick—fiexion and compression. 

While direct, this method is the most difficult experimentally due to the diminutive nature of fiber diameters and the uncertainty involved with contact angle measurements and hysteresis. The value i ) can also be measured on flat sheets of the fiber material but due to fabric finishes and different surface properties incurred during manufacture, the surface energetics of the sheet and fiber may be very dissimilar. Therefore, the value of co8i i was determined in the following manner from detergency data. The Kubelka-Munk Equation (12-13),... 

Microcomposite tests including fiber pull-out tests are aimed at generating useful information regarding the interface quality in absolute terms, or at least in comparative terms between different composite systems. In this regard, theoretical models should provide a systematic means for data reduction to determine the relevant properties with reasonable accuracy from the experimental results. The data reduction scheme must not rely on the trial and error method. Although there are several methods of micromechanical analysis available, little attempt in the past has been put into providing such a means in a unified format. A systematic procedure is presented here to generate the fiber pull-out parameters and ultimately the relevant fiber-matrix interface properties. 

Our study is outlined in five parts, (a) Two polystyrene plastics were reinforced at different fiber contents alternately with polyester, asbestos, and glass fibers, (b) The mechanical/physical properties of the resultant monofiber-reinforced plastics were determined and compared, (c) Combinations of fibers were then used to fabricate multifiber-rein-forced structures to exploit simultaneously the particular advantages of the different reinforcements, (d) The effect of each fabrication stage on the molecular weight and molecular weight distribution of the matrix plastics was established and (e) a linear mathematical model was formulated to predict the properties of multifiber structures and forecasted values compared with corresponding values experimentally obtained from (c) above. 

Evaluation of Fiber and Fabric Properties. Breaking strengths of the control and treated fabrics were determined according to ASTM D 1682, ravelled strip method (24) using an Instron model 1130 equipped with a 1,000 pound load cell and a gear ratio of 1 1. Five conditioned warp strips from each of two replicates were tested for each experimental condition. 

One of the most difficult experimental studies in cardiac mechanics is the determination of the mechanical properties of the myocardium and the associated wall stress distributions. In light of this fact it would appear more important to focus on the experimental aspects of this problem rather than pursuing the development of more complex models. However, in recent years the incorporation of fiber angle distribution into models have yielded some interesting results (Arts, 1979 Feit, 1979 Chadwick, 1982 Tozeren, 1983) and their approach should be further explored. 

Composite materials owe their exceptional mechanical and other useful properties to the existence of an extensive interface fraction localized at the phase boundary between filler and bulk resin. The larger the fractional interface (i.e., the smaller the particle or fiber dimension), the more pronounced will be its influence on the properties of the composite. With a compatible filler material the interface is more complex than a simple two-dimensional contact region between the particle and polymer. The interface layer formed around the particle has a finite thickness, and within it the material properties are very different from those in the bulk (Pukanszky 2005). These properties depend on interactions that are specific to the polymer/ filler system. Experimentally determined thicknesses of the polymer/inor-ganic filler interface typically range from 0.004 to 0.16 jLm (Pukanszky 2005). Therefore, the use of nanoparticle fillers with high specific surface area (as opposed to conventional fillers) that maximize the fractional interface area is particularly desirable in the design of composites. 

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