Assembly process Failure mechanisms

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. 

Nanocomposites with carbon nanotubes have been an area of considerable R D ever since the excellent electrical and mechanical properties of carbon nanotubes were demonstrated. However, attempts to prepare carbon nanotube RPs often result in phase separation of the CNT and polymer phases causing premature material failure. Researchers at Nomadic Inc. and Oklahoma State University developed a layer-by-layer (LBL) assembly process that permits preparing polyelectrolyte/CNT RP with a CNT loading greater than 50 wt%. The excellent mechanical properties of these materials can be improved further by additional chemical action crosslinking of the CNT and polymer phases and by parallel alignment of the CNTs. The LBL method has been used to prepare various types of RPs. 

Reliability of electronic assemblies is a complex subject.This chapter has touched on only one aspect of the problem understanding the primary failure mechanisms of printed circuit boards and the interconnects between these boards and the electronic components mounted on them. This approach provides the basis for analyzing the impact of design and materials choices and manufacturing processes on printed circuit assembly reliabihty. It also provides the foundation for developing accelerated testing schemes to determine reliability. It is hoped that the fundamental approach will enable the reader to apply this methodology to new problems not yet addressed in mainstream literature. 

Non-routine operations during aseptic process Assembly of sterile equipment prior to use Mechanical failure Inadequate or improper sanitization Transfer of materials within APA Routine operations during aseptic process Airborne contaminants Surface contaminants Failure of sterilizing filter Failure of HEPA filter Inadequate or improper sterilization From most to least likely. (From Ref. I)... 

Collagen molecules undergo self-assembly by lateral associations into fibrils and fibers and are able, therefore, along with other biological functions, to ensure the mechanical support of the connective tissue. Collagen also plays an important role in many bioadhesion processes. Collagen molecules bound to implant materials enhance adhesion of epidermal cells to the surfaces of biomaterials and prevent implant failure. 

The reliability of an adhesive and its impact on the performance of an electronic assembly should be considered in the initial selection of the adhesive and the design of the system. The function that the adhesive must perform for a specific application, the environment it is expected to encounter, and its duration are all important. Various approaches may be used to predict and assure reliability. Key among these approaches is a basic understanding of possible failure modes and mechanisms. Most failure modes attributed to adhesives are now well understood and documented so that they can be avoided in the initial selection and qualification of the adhesive and in its processing. 

Manufacturing Improvements for precision engineering new processes, and tools to manipulate matter at the atomic level nanopowders that are sintered into bulk materials with special properties that may include sensors to detect incipient failures and actuators to repair problems chemical-mechanical polishing with nanoparticles, self-assembling of structures from molecules bioinspired materials and biostructures... 

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