Aramid composites

Brown, J.R., P.J.C. Chappell, Z. Mathys (1991), Plasma surface modification of advanced organic fibers part I. Effects on the mechanical, fracture and ballistic properties of aramid/aramid composites. J. Mater. Sci. 26. 4172 178,... 

Figures 9.19 and 9.20 present a survey of the mechanical properties of some (unidirectional) composites, in comparison with some other materials. In Figure 9.19 the values of modulus and strength are plotted as such, while in Figure 9.20 these values have been divided by the specific mass. From Figure 9.20 the enormous advantage of composites with respect to stiffness and strength per unit weight, in comparison to metals, is clearly visible. The modem carbon and aramide composites are superior to those based on glass fibres, for the specific stiffness even by a factor between 4 and 5.

Jeong YG, Jeon GW. Microstructure and performance of multiwalled carbon nanotube/ m-aramid composite films as electric heating elements. ACS Appl Mater Interface 2013 5(14) 6527-34. 

I Carbon composite I Aluminum Aramid composite SPFDB titanium... 

Aramid composites are very difficult to machine because of the extreme toughness of the aramid fiber. Special cutting and machining techniques and equipment are required. Information on the processes required for aramid composites is available from Du Pont, the producers of Kevlar, an aramid fiber, conunonly used in high-strength, low-weight advanced composites. 

Figure 1. 3-point short-beam shear strength of aramid composites... 

Usually aramid composites yield somewhat in compression in a bending test before they finally fracture in shear. This also has a more pronounced negative effect on the SBS values of composites with treated than on those with untreated fibres. Application of the compression correction as mentioned in [7] reduces the intercept of eq. (5) further and leads to an even closer agreement with eqs. (1) and (3). Compressive yielding, and hence the correction for this effect is less for beams with... 

The 3p-SBS of untreated aramid composites decreases with increasing V-. The absolute shear strength is much lower than for carbon or glass. This must be caused by the weak aramid-epoxy interface, since the SCF is very low for aramid in epoxy. On the assumption of a weak interface this decrease may also be explained by the rule of mixtures, with the exception of the strong fall at =80 %. This sharp decrease is a good indication that fracture occurs at the interface. 

The transverse tensile strength TTS of aramid composites shows a similar dependence on V as the bundle pull-out shear strength BPS. The nearly linear relation between TTS and (3-point) SBS for treated and untreated aramid composites in figure 3 is described by ... 

The recent work of Kim et al. [96] discloses the structure and the electrical properties of PPTA/multiwalled carbon nanotubes (MWCNT) composites obtained by in situ polymerization. These composites exhibited improved electrical conductivity. Ground PPTA/MWCN particles were shown to behave as electrorheological (ER) material. It seems that preparing of such less usual all-aramid composites or using PPTA as matrix to be reinforced by CNT may be an interesting pathway toward composite materials, requiring, however, improved manufacturing processes. 

Manufacturing of p-aramid composites with thermoset matrices... 

The discussion on the preparation and properties of p-aramid FRP composites should not omit the most famous application of these materials in ballistic protection. A great deal of the freely available information in this area is included in numerous patents and technical publications. Significantly less in number are the scientific articles, most frequently dealing with modeling studies. Even a brief overview on the p-aramid composites in ballistics would probably require a separate chapter. Due to space limitations, we wUl only mention here a recently reported phenomenon with big potential for more flexible and better protecting body armor in the future. 

Ilio, A.D., Tagliaferri, V. and Veniali, F. (1991) Cutting mechanisms in drilling of aramid composites, Int J Mach Tools Manuf, 31 155-65. 

These fibres are representative of the high performance aramid products currently available. The anisotropy of unidirectional composites is apparent as is the poor compression strength of aramid composites. The composite densities are extremely low. 

The Charpy impact strength for 60 v/o epoxy Kevlar 49 unidirectional composite is 240-3lOkJ/m, similar to the figures recorded for unidirectional GRP. Usually information for aramid composites refers to... 

The change in the laminates mass describes the loss/gain of moisture and this varies from the higher water absorbency of aramid composites to lower capacities of glass and carbon composites (Figure 9.5). Saturation of a composite is achieved far more easily in boiling water than in a humid atmosphere at room temperature. 

The effect of such preconditioning is to decrease the tensile properties (Table 9.2). The change is minimal for carbon and noticeable for aramid composites. Whereas glass composites are only slightly affected by a high relative humidity, boiling has a drastic effect. 

Interlaminar shear strength is however increased by exposure to a humid atmosphere (Table 9.3). Boiling does not affect aramid composites whilst the glass composite is weakened by 10% and the carbon composite s shear strength is increased by c.20%. 

Subsequent fatigue studies on twisted strands show that carbon and aramid composite strands had better fatigue resistance than roping steel. 

The aramid fibers are most often used in composites having polymer matrices common matrix materials are the epoxies and polyesters. Because the fibers are relatively flexible and somewhat ductile, they may be processed by most common textile operations. Typical apphcations of these aramid composites are in balhstic products (bulletproof... 

Treatment of the aramid fibres with polymers has been found to be an efficient way of increasing the flexural properties of the composite. Walton and Majumdar [118] had found that the tensile strength of the aramid composite was only 70% of the expected value, and suggested that this was the result of poor bonding. Wang et at. [80] determined the average bond strength to be 2.75 MPa, with a critical... 

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