Assembly process Mechanically induced

Mechanical stresses exist in the MEA as a combination of built-in stresses, assembly stresses, and operation stresses. The cell/stack fabrication and assembly process result in the built-in and the assembly stresses. During operation, stresses can be induced by the change of water content in the membrane. There are possibly other sources of stresses due to various off design conditions. 

This paper presents results from a study of assemblies composed of glass fibre reinforced epoxy composites. First, tests performed to produce mixed mode fracture envelopes are presented. Then results from tests on lap shear and L-stiffener specimens are given. These enabled failure mechanisms to be examined in more detail using an image analysis technique to quantify local strain fields. Finally the application of a fracture-mechanics-based analysis to predict the failure loads of top-hat stiffeners with and without implanted bond-line defects is described. Correlation between test results and predictions is reasonable, but special attention is needed to account for size effects and micro-structural variations induced by the assembly process. 

Mechanically Induced Failures. PCBs may be mechanically loaded by test fixtures or processing equipment, when PCAs are loaded into card cages or fixtured into place with brackets, or when the assembly experiences mechanical shock or vibration in use. In general, once the PCA has been assembled, the interconnects to the components are the weak links in mechanical loading situations, not the boards themselves. 

The amount of TiO was varied, and the assembly was tested for its photocata-lytic activity using degradation of 2,4-xylidine as test reaction probe. The decrease in the concentration of xylidine and the corresponding increase in oxalate concentration were monitored through HPLC. A pseudo-first order kinetics was ob served in the photodegradation process based on the Langmuir-Hinshelwood mechanism. An inverse correlation was observed between the kinetic rate constant and the obtained Light-Induced Optoacoustic Spectroscopy (LIOAS) frequency maxima. 

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