Longitudinal Compressive Properties

Natural Polymer Fibers (including regenerated fibers)  

Source Kumar, S., Indian Journal of Fiber and Textile Research, 16, 52-64, 1991.  

The Euler s equation then ean be rearranged to obtain the critical compres-sional stress (ct that is needed for a fiber to buckle  

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SMS Madhukar and L T Drzal, Effect of fiber-matrix adhesion on the longitudinal compressive properties of graphite/epoxy composites . Proceedings Fifth Technical Conference American Society for Composites, 1990, pp 849-858. 

Longitudinal tensile properties are excellent, longitudinal compressive properties very good, but anisotropy needs to be watched. 

Table 5.20 Effect of test method on the longitudinal compressive properties of carbon fibre composites...

In addition to longitudinal compressive properties, transverse compressive properties also are important. Fibers in composites need have sufficient transverse compressive modulus and strength since the external force sometimes is applied in the transverse direction to the fiber axis (Figure 15.27B). In both woven and nonwoven fabrics, fibers also may experience transverse compressive forces while in use. 

Static mechanical properties of aerogels have been measured mainly by the three-point flexure test [54] or by direct longitudinal compression [55]. The... 

Fibers and films possess anisotropic mechanical properties. Hence a discussion of this subject should include tensile and compression properties in at least two different directions, viz. in longitudinal and transverse direction to the filament axis. However, in general little is known of the transverse properties of fibers and films. 

Technical composites are multiphased, anisotrqiic bodies. Efficient and reliable use of such materials necessitates optimization of a laminated composite with respect to all of its directional properties (particularly, transverse tensile, shear, and longitudinal compression, as well as the earlier emphasis upon longitudinal properties). 

These values are for individual lamina or for a unidirectional composite, and they represent the theoretical maximum (for that fiber volume) for longitudinal in-plane properties. Transverse, shear, and compression properties will show maximums at different fiber volumes and for different fibers, depending on how the matrix and fiber interact. These properties are not reflected in strand data. These values may also be used to calculate the properties of a laminate that has fibers oriented in several directions. Using the techniques shown in Sec. 4.5.1, the methods of description for ply orientation must be introduced. 

Madhukar, M.S. and Drzal, L.T., Fiber-matrix adhesion and its effect on composite mechanical properties, II. Longitudinal (0°) and transverse (90°) tensile and flexure behavior of graphite/epoxy composites. J. Compos. Mater., 25, 958-991 (1991). Madhukar, M.S. and Drzal, L.T., Fiber-matrix adhesion and its effect on composite mechanical properties. III. Longitudinal (0°) compressive properties of graphite/epoxy composites. J. Compos. Mater., 26, 310-333 (1992). 

The longitudinal compressive modulus and strength, although markedly affected by the properties of the fibre, can also be strongly influenced by the type and behaviour of the matrix because of the lateral support that the latter gives to the fibre. 

This chapter is concerned with the short-term mechanical properties — moduli and strengths — of glass, aramid and carbon fibres in a thermosetting resin matrix. A little information on reinforced thermoplastic matrix systems is also included. The data mainly refer to the room temperature properties of 55-65 v/o fibre, unidirectional, systems. The effects of the variation in fibre volume loading, method of test and instantaneous and long term exposure to temperature are briefly mentioned. Longitudinal properties tend to be fibre dominated, and so are compressive properties to some extent for glass and carbon fibres. The anisotropy of unidirectional materials is noticeable. 

Notes The first subscript 1 or t refers to directions longitudinal and transverse to the fibre. The second subscript, t, f or c, refers to tensile, flexural and compressive properties. For example, is the transverse tensile modulus. 

Applications of ultrasonic techniques to solid-gas systems rely on the fact that velocity and attenuation of US-waves in porous materials is closely related to pore size, porosity, tortuosity, permeability and flux resistivity. Thus, the flux resistivity of acoustic absorbents oan be related to US attenuation [118,119], while the velocity of slow longitudinal US is related to pore tortuosity and diffusion, and transport properties, of other porous materials [120]. Ultrasound attenuation is very sensitive to the presence of an external agent suoh as moisture in the pore space [121] and has been used to monitor wetting and drying prooesses [122] on the other hand, US velocity has been used to measure the elastic coefficients of different types of paper and correlate them with properties such as tensile breaking strength, compressive strength, etc. [123]. 

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