Strength Degradation Behavior Research Articles

Activation Energy for Strength Degradation of Fused Silica Optical Fibers

AbstractThe strength degradation behavior of fused silica optical fiber is well known to be sensitive to the temperature and an apparent activation energy can be determined. In addition, it has been observed that the activation energy also depends on the applied stress and the nature of the environment. However, no consistent model for this behavior has emerged. We propose a chemical kinetics model which accounts for the temperature dependence of the dissociation of water which predicts that degradation should be faster in pH 7 buffer than in pure water. Static fatigue of fused silica fibers in both water and pH 7 buffer solution has been carefully studied as a function of temperature to test the model. The apparent activation energies are stress dependent, and, while the dependency is not clear, different environments give different dependencies. These observations support the proposed model.

Statistical Fatigue Life Prediction of Cross-Ply Composite Laminates

Within the framework of statistical models of residual strength and fatigue life established in previous work, a new model for determining the stress redistribution function is proposed to predict fatigue life of cross-ply laminates in terms of the principal fatigue mechanisms, i.e., progressive matrix cracking in 90° plies. The simple shear-lag analysis is applied to describe the cycle-number-dependent stress redistribution process and the stiffness reduction of laminates resulting from the progressive matrix cracking in transverse plies. From the strength degradation behaviour and the static strength distribution of 0° plies as well as the fatigue behaviour of 90° plies, the fatigue life of cross-ply laminates with various lay-ups can be calculated from the model. Predictions of fatigue life from the model are compared with experimental data for [0/902] s, [02/902] s and [0/904] s, graphite/epoxy cross-ply laminates, and good agreement indicates success of the approach.

Using An Extended Tersoff Interatomic Potential to Analyze The Static-Fatigue Strength of SiO<SUB>2</SUB> under Atmospheric Influence

Calculations of SiO2 static-fatigue strength are used to show that the strength-degradation behavior of the material under the influence of the ambient atmosphere can be analyzed using an interatomic potential which is based on the Tersoff potential but extended to take charge transfer effects into account. The force-elongation curves of the Si-O interatomic bonds of the SiO2 are calculated with and without H2O in the atmosphere. Based on these curves, crack propagation behavior is analyzed, and calculated results are shown to correspond well with experimental results. Moreover, the calculated values of the strength decrease caused by the H2O also show fair agreement with the experimental values.

Simulation of fatigue performance of cross-ply composite laminates

The fatigue life of cross-ply composite laminates was evaluated using a statistical model. A modified shear-lag analysis was applied to describe the cycle-number-dependent stiffness reduction and consequent stress redistribution processes in the laminates resulted from both progressive transverse matrix cracking in transverse plies and local delamination at tips of transverse cracks. From the strength degradation behaviour and the static strength distribution of 0° plies as well as the fatigue behaviour of 90° plies, the fatigue life of cross-ply laminates with various types of lay-up can be simulated from the model. Predictions of fatigue performance are compared with experimental data for [0/902]s, [02/902]s and [02/904]s graphite/epoxy cross-ply laminates: good agreements are obtained.

Loading Rate Effects During Static Indentation and Impact on Silicon Carbide with Small Sphere

In order to study the relationship between static and cynamic behaviors of silion caride, both quasi-static indentaiton and impact experiments of spherical particle have been conducted. The difference inmaterial behavior when using the two mehtods suggests a loading rate difference in the damate pattrern and fracture strength of silicon carbide. This investigation showed some difference in damage pattern according to particla property, especially inthe case of particle impact. There was no differences in deformation behaviors according to the loading rate when the crater profiles were compared with each other at the same contact radius. From the result of residual strength evaluation, it was found that the strength degradation began at the initiation of ring crack and its behavior was colsely related to morphologies of the damage developed which was also dependent upon the extent of deformation atthe loaidng point. In the case of static indentation, there didnot exist the particle property effects onthe strength degradation behavior.

Static Fatigue Strength Analysis of SiO2 under Atmospheric Influence Using Extended Tersoff Interatomic Potential.

It is shown from the calculation of SiO2 static fatigue strength that the strength degradation behavior under the influence of atmosphere can be analyzed using the interatomic potential which is based on the Tersoff potential and extended to take the charge transfer effects into account. The force-elongation curves of Si-O interatomic bonds of SiO2 with and without H2O in the atmosphere are calculated. Based on these curves, crack propagation behavior is analyzed. The calculated results correspond to the experimental results well. Moreover, the calculated values of the decrease of the strength caused by H2O show fair agreement with the experimental values.