Strength Degradation

A model for predicting the compressive strength degradation of FRP materials in fire was applied as proposed in Chapter 5. Similarly to the modeling for stiffness degradation, it assumes that an FRP material at a certain temperature can be 

It may seem surprising that the strength in the water-cooling cases decreased although temperatures remained clearly below the onset of the glass-transition temperature ofthe resin (77/65 °C for MCl/2-4 vs about 110 °C). However, 

In analogy with Eq. (7.10), the time-dependent ultimate load, P (t), can be obtained as follows  

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Strength degradation - ereep failure, fatigue, wear, eorrosion. 

Lawn B. R., Marshall D. B., 1978, Indentation fracture and strength degradation in... 

Gong, J.H., Guan, Z.D., Jiang. D.C. (1992), Analysis of strength degradation of indented specimens due to thermal shock , in Bradt, R.C., Hasselman, D.P.H., Munz, D., Sakai, M., Shevchenko, V.Y., Fracture Mechanics of Ceramics, Plenum Press, New York, 605-610. 

Wiederhorn, S.M. and Lawn, B.R. (1979), Strength degradation of glass impacted with sharp particles I, Annealed surfaces , J. Am. Ceram. Soc., 62(1-2), 66-70. 

Primers. Primers tend to hinder adhesive strength degradation in moist environments by providing corrosion protection to the adherend surface. A fluid primer that easily wets the interface presumably tends to fill in minor discontinuities on the surface. Qrganosilane, organotitanate, and phenolic primers have been found to improve the bond strength of many adhesive systems. 

Both benzoxazole hydrolysis and hydrolysis of intermediate products such as benzamide or benzoate potentially cause tensile strength degradation in PBO, by disrupting the conjugated rigid rod stmcture and by chain scission, respectively. The former mechanism appears to be the primary mode of degradation in the laboratory-aged armor the latter mechanism appears to be predominant in the case of the failed field body armor. 

Bhatt RT, Hull DR (1998) Strength-degrading mechanisms for chemically-vapor-deposited SCS-6 silicon carbide fibres in an argon environment. J Am Ceram Soc... 

Figure 11.19 (a) Functional dependence of fracture toughness on flaw size for a ceramic exhibiting R curve behavior (top curve) and one that does not (lower curve), (h) Effect of R curve behavior on strength degradation as flaw size increases. Ceramics exhibiting R curve behavior are more flaw-tolerant than those that do not. 

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