Shear strength reinforcement

The polysulfide base material contains 50—80% of the polyfunctional mercaptan, which is a clear, amber, sympy Hquid polymer with a viscosity at 25°C of 35, 000 Pa-s(= cP), an average mol wt of 4000, a pH range of 6—8, and a ntild, characteristic mercaptan odor. Fillers are added to extend, reinforce, harden, and color the base. They may iaclude siUca, calcium sulfate, ziac oxide, ziac sulfide [1314-98-3] alumina, titanium dioxide [13463-67-7] and calcium carbonate. The high shear strength of the Hquid polymer makes the compositions difficult to mix. The addition of limited amounts of diluents improves the mix without reduciag the set-mbber characteristics unduly, eg, dibutyl phthalate [84-74-2], tricresyl phosphate [1330-78-5], and tributyl citrate [77-94-1]. 

If the matrix in 3.7 was reinforced with the same volume fraction of glass but in the form of randomly oriented glass fibres rather than continuous filaments, what would be the tensile strength of the composite. The fibres are 15 mm long, have an aspect ratio of 1000 and produce a reinforcement efficiency of 0.25. The fibre strength is 2 GN/m and the shear strength of the interface is 4 MN/m". 

Tests by Roe et al. [63] with unidirectional jute fiber-reinforced UP resins show a linear relationship (analogous to the linear mixing rule) between the volume content of fiber and Young s modulus and tensile strength of the composite over a range of fiber content of 0-60%. Similar results are attained for the work of fracture and for the interlaminate shear strength (Fig. 20). Chawla et al. [64] found similar results for the flexural properties of jute fiber-UP composites. 

Figure 20 Influence of fiber content by volume on tensile strength. Youngs modulus, work of fracture, and interlaminate shear strength of one-dimensional jute fiber-reinforced UP resins [63].

The lap shear test involves measuring the adhesive shear strength between two surface fluorinated polyolefin sheet tokens that are adhesively secured with a reinforcement resin. The tokens are individually reinforced with steel backing plates to eliminate flexural distortion in the shear joint. Lap shear tests carried out with various reinforcing polyester-type resins, contrasting fluorination and oxyfluorination as surface treatment, are shown in Table 16.8. 

Chen, F. and Jones, F. R Injection moulding of glass fibre reinforced phenolic composites 1. Study of the critical fibre length and the interfacial shear strength, Plast.. Rubber Composites Proc. Appl., 23, 241 (1995). 

ISO 14130 1997 Fibre-reinforced plastic composites - Determination of apparent interlaminar shear strength by short-beam method ISO 15024 2001 Fibre-reinforced plastic composites - Determination of mode I interlaminar fracture toughness, GIC, for unidirectionally reinforced materials... 

ISO 3597-4 2003 Textile-glass-reinforced plastics - Determination of mechanical properties on rods made of roving-reinforced resin - Part 4 Determination of apparent interlaminar shear strength... 

Gilbert, A.H., Goldstein, B. and Marom, G. (1990), A liquid droplet measurement technique as a means of assessing the interlaminar shear strength of fiber reinforced composites. Composites 21. 408-414. 

ASTM D 3846 (1985). Test method for in-plane shear strength of reinforced plastics. 

Desaeger, M. and Verpoest, I. (1993). On the use of the microindentation test technique to measure the interfacial shear strength of fiber reinforced polymer composites. Composites Sci. Technol. 48, 215-226. 

Drzal, L.T., Rich, M.J., Camping, J.D. and Park, W.J. (1980). Interfacial shear strength and failure mechanisms in graphite fiber composites. In 35th Annual Tech. Conf., Reinforced Plast. Compo.sites Inst., SPI, Paper 20C. 

Fisher, S., Rosensaft, M. and Marom, G. (1986). Dependence of the interlaminar shear strength on the loading span-to-depth ratio in aramid fiber-reinforced beams. Composites Sci. Technol. 25, 69-73. 

Morscher, G, Pirouz, P. and Hener, A.H. (1990). Temperature dependence of interfacial shear strength in SiC-fiher-reinforced RBSN. J. Am. Ceram. Soc. 73, 713-720. 

Figure 5.107 Variation in toughness and shear strength for various surface treatments of continuous carbon fiber-reinforced composites. Reprinted, by permission, from T. L. Vigo and B. J. Kinzig, ed.. Composite Applications, p. 224. Copyright 1992 by VCH Publishing, Inc.

In (15.36) rm is the matrix fracture energy, t is the interfacial shear strength, and Ex is the axial modulus of the composite. In (15.37) e refers to the effective properties of the composite, which, for unidirectional fiber reinforcement, can be calculated with good approximation by the rule of mixtures. 

Recently Nishijima et al. investigated the radiation effects of three-dimensional glass-fabric reinforced plastics (3DFRP) mentioned in the preceding section, since the interlaminar shear strength of composites was expected to be greatly enhanced by the presence of Z-axis reinforcement [78]. Two kinds of 3DFRP were newly developed and named as ZI-003 and ZI-005 of which the matrices were epoxy and BT resins, respectively [28]. The compressive tests... 

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