Effect of damage by hydroxyl generation on strength of silica fibers

Abstract

When water diffuses into silica glass, a chemical reaction between the water and the glass damages the ring structure of the glass, causing a reduction in the Young's modulus, a lowering of the intrinsic strength and a reduction in the crack‐growth resistance of the glass. In the absence of swelling of the glass within the water penetrated zone, the damage caused by hydroxyl group generation will have no effect on the strength of the glass fibers, provided the water‐affected surface zone is much thinner than the bulk material. In contrast, swelling stresses within the water penetrated zone at the fiber glass surface will increase the strength of the glass fibers.

Constitutive law of healthy gallbladder walls in passive state with damage effect

“…For linear materials, under the hypothesis of strain equivalence, scalar damage variable is related to the Young's moduli in undamaged/virgin and damaged states [9,16,30,31]. Particularly, once a brittle material is damaged, its Young's modulus must be degraded in comparison with its undamaged state, showing Young's modulus degradation or stress softening effect.…”

“…After pre-conditioning, GB walls exhibited a hyperelastic behaviour without any plastic characteristics [14,32], suggesting the GB walls with brittle damage. In this sense, the damage variable for isotropic, homogenous and brittle materials [3,9,16,30,31] was extended into anisotropic homogenous GB walls by introducing a scalar damage variable to the matrix and two families of fibres individually. Such an extension in damage variable for GB walls has not been declared in literature.…”

“…Damage effect is related to instant change in Young's modulus of a specimen during its uniaxial tensile tests [9,16,30,31]. To identify whether there is the damage effect in the…”

“…fibres, vir fl , in the virgin sate, then the equation in the virgin state is rewritten as Similarly, the Cauchy stress components in the tissue are divided into three parts: the first part is the stress in the matrix vir m due to vir m , the second part is the stress in the circumferential fibres vir fc and the third part is the stress in the longitudinal fibres vir fl , i.e. Likewise, the circumferential Young's moduli in total, in the matrix and in the fibres E dam c , E dam mc and E dam fc as well as the longitudinal Young's moduli in total, in the matrix and in the fibre E dam l , E dam ml and E dam fl are expressed asFor linear materials, the damage variable is related to the ratio of the Young's modulus in the damaged state to the modulus in the virgin state,[3,8,9,16,17,30,31], and written mathematically as For anisotropic, nonlinear GB walls, it is supposed that this definition is held for each pair of Young's moduli in Eq. (9) in the damaged state and those in Eq (12).…”

Molecular mechanism of the expansion of silica glass upon exposure to moisture

“…27 In either strength degradation or strength enhancement, one group assumes from IR data that surface structural/ stress relaxation is caused by the presence of molecular water, 25,[27][28][29]33 whereas another group concludes that expansion of silica occurs via formation of silanols (SiOHs) rather than molecular water in the glass. 26,32,34,35 The attribution of H 2 O molecules as the cause of strength enhancement is based on the difference in the depth of the high-frequency IR peak of the OH moiety on Si (SiOH) vs the depth of the change in the high-frequency IR peak of the asymmetric stretch of the Si-O-Si group indicative of a relaxation process. The latter continues to a greater depth than the former and is attributed to an undetectable amount of molecular water.…”