A. James Clark School of Engineering

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The collections in this community comprise faculty research works, as well as graduate theses and dissertations.

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    Analysis of Manufacturing-Induced Defects and Structural Deformations in Lithium-Ion Batteries Using Computed Tomography
    (MDPI, 2018-04-13) Wu, Yi; Saxena, Saurabh; Xing, Yinjiao; Wang, Youren; Li, Chuan; Yung, Winco K. C.; Pecht, Michael
    Premature battery drain, swelling and fires/explosions in lithium-ion batteries have caused wide-scale customer concerns, product recalls, and huge financial losses in a wide range of products including smartphones, laptops, e-cigarettes, hoverboards, cars, and commercial aircraft. Most of these problems are caused by defects which are difficult to detect using conventional nondestructive electrical methods and disassembly-based destructive analysis. This paper develops an effective computed tomography (CT)-based nondestructive approach to assess battery quality and identify manufacturing-induced defects and structural deformations in batteries. Several unique case studies from commercial e-cigarette and smartphone applications are presented to show where CT analysis methods work.
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    EFFECTS OF GLASS/EPOXY INTERPHASES ON ELECTRO-CHEMICAL FAILURES IN PRINTED CIRCUIT BOARDS
    (2018) Sood, Bhanu Pratap; Pecht, Michael G; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Reduction in printed circuit board line spacing and via diameters and the increased density of vias with higher aspect ratios (ratio between the thickness of the board and the size of the drilled hole before plating) are making electronic products increasingly more susceptible to material and manufacturing defects. One failure mechanism of particular concern is conductive anodic filament formation, which typically occurs in two steps: degradation of the resin/glass fiber bond followed by an electrochemical reaction. The glass-resin bond degradation provides a path along which electrodeposition occurs due to electrochemical reactions. Once a path is formed, an aqueous layer, which enables the electrochemical reactions to take place, can develop through the adsorption, absorption, and capillary action of moisture at the resin/fiber interphase. This study describes the experimental and analytical work undertaken to understand the glass-resin delamination and the methods used for analyzing this critical interphase. This study shows that a smaller conductor spacing in reduces the time to failure due to conductive anodic filament formation and that the plated-through-hole to plated-through-hole conductor geometry is more susceptible to conductive anodic filament-induced failures than plated through hole to plane geometries. The results also show that laminates with similar materials and geometries with a 45-degree angle of weave demonstrate a higher resistance to conductive anodic filament formation compared with a 90-degree angle of weave. The study is the first of its kind conducted on FR-4 printed circuit board materials where the pathway formation due to breakage of the organosilane bonds at the glass/resin interphase was evaluated. Using techniques such as force spectroscopy, micro-Fourier transform infrared spectroscopy, scanning quantum interface device microscopy and focused ion beam, evidence of bond breakage and a pathway formation was revealed, poor glass treatment, hydrolysis of the silane glass finish (adsorption of water at the glass fiber/epoxy resin interphase) or repeated thermal cycling contribute to the bond breakage. The technique of applying in-situ resistance measurements during cross-sectioning analysis of printed circuit boards suspected of conductive anodic filament is the first time this method is described in the open literature. This solution addresses the potential problem in destructive physical analysis of grinding away the evidence of the CAF filament and ultimately loosing evidence at the failure site. By applying a subset of the evaluation criteria described in this research, an upfront evaluation of printed circuit board materials can be performed for susceptibility to electro-chemical migration and other failure causes in PCBs that are attributable to the glass/resin interfacial adhesion. Manufacturers can identify board suppliers based on answers to and validation of a series of questions. These questions focus on the necessary requirements of reliable board material manufacturing and are independent of the specifications of the product.
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    FAILURE MECHANISMS OF PEDIATRIC GROWING ROD CONSTRUCTS
    (2017) Hill, Genevieve A-L.; Fisher, John P; Dreher, Maureen L; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Early onset scoliosis (EOS) affects a vulnerable population of young children, and occurs at critical ages when the spine and thorax are developing. Children suffering with EOS have higher mortality rates due to cardiopulmonary complications; therefore, treatment for these patients can be life-saving. Pediatric growing rod constructs are an important treatment option for young patients with severe and progressive spinal deformities because they encourage growth and correction of the spinal curvature through successive lengthening procedures. However, growing rod constructs suffer from complication rates as high as 72%, which often lead to unplanned reoperations. To help prevent future failures of the same root cause, the failure mode and mechanism must be identified, which tell us how and why the devices failed respectively. This research included the first study to examine multiple, retrieved pediatric growing rod constructs from various sites to systematically investigate these significant items. The retrieval study revealed that rod fracture (failure mode) was due to bending fatigue (failure mechanism), and stress concentrations play an important role in rod fractures. The information obtained from the retrieval study enhanced the understanding of in vivo loading conditions experienced by the device and established clinically-relevant parameters for a mechanical bench model. This research also included the development and validation of a novel mechanical bench model that successfully replicated rod fracture due to bending fatigue. A mechanical bench model that is predicated on clinical outcomes can serve as a tool for engineers and researchers who are looking to improve pediatric growing rod constructs as it will enable them to make relevant predictions about the device’s resistance to failure. For example, the model was used in this research to investigate how the unique characteristics of pediatric growing rod constructs such as construct configuration and lengthening affect mechanical performance of the device. Key recommendations regarding surgical technique were identified in the retrieval study and verified through bench testing. The data obtained during this research can ultimately be used to reduce failure rates and unplanned revisions in this patient population.