Failure modes membrane

Much recent ongoing work has focused on the chemical degradation mechanisms and revealed that radical attack is the root cause of the membrane decomposition. However, there is still a lack of fundamental understanding of the mechanisms for the degradation of mechanical strength, which is related to the membrane failure mode responsible for the sudden death behavior of fuel cells. 

Based on our experience, the strength of membrane/MEA, particularly strain-to-failure, measured ex situ has the potential to serve as a metric/indicator for PEMFC life prediction and accelerated testing when the failure mode is membrane crossover. It is an... 

This section describes a methodical procedure that allows reliability issues to be approached efficiently. MEMS reveal specific reliability aspects, which differ considerably from the reliability issues of integrated circuits and macroscopic devices. A classification of typical MEMS-failure modes is given, as well as an overview of lifetime distribution models. The extraction of reliability parameters is a Tack of failures situation using accelerated aging and suitable models. In a case study, the implementation of the methodology is illustrated with a real-fife example of dynamic mechanical stress on a thin membrane in a hot-film mass-airflow sensor. 

Membrane failure modes have been discussed above, and the connection to module design has also been discussed. Poor design for cyclic durability will be measured by the customer - the operating costs will be adversely affected by the requirement to replace membranes prematurely. Although the cost of membrane replacement should be offset by a recycle credit, the cost of materials and labor, and potential lost productivity, is stQl likely to be significant. The credit for recy-cUng palladium alloy membranes may be as great as 95% of the market value of the palladium (for foil membranes, perhaps only 85% of the market value if the palladium alloy is deposited onto a porous substrate). Environmentally, recycle also offers benefits versus recovery and purification of palladium from ore. 

For stationary applications a PEM fuel cell is required to operate for 40,000 hours or longer. The major MEA failure modes that lead to a much shorter lifetime are the membrane breach and the electrode decay. The former will result in reactant crossover that causes a sudden and catastrophic failure. lonomer chemical structure and end-group modification, reinforcement of the membrane, incorporation of additives into the membrane, and use of a protective subgasket or full-gasket are effective methods to slow down the membrane breach process. The electrode decay causes gradual loss of the fuel cell performance and rarely causes catastrophic failures. The performance decay lowers the fuel cell efficiency and when the efficiency becomes lower than a predetermined value, the fuel cell reaches its end of life. In... 

The theoretical framework for the SPIF of polymers is only able to model the deformation mechanics associated with failure mode 1, which is the more likely to develop during incremental sheet forming. The framework is built upon the extension of the membrane analysis with bi-directional in-plane contact friction forces, which was developed by Silva et al. (2008a) for the SPIF of metals, in order to include pressure-sensitive yield surfaces that are commonly found in the cold forming of polymers. Figure 8.3 shows the essentials for a membrane analysis in rotational symmetric conditions. 

Guideline 1 establishes the relationship between the membrane and bending stresses and the associated failure modes. The failure modes of concern are collapse/gross distortion (Pm)/ plastic collapse (Pb), excessive plastic deformation (Pl -I- Pb)/ and ratcheting and lack of shakedown P + Q). 

To understand important aspects of membrane elecfrode assembly (MEA) integrity and the failure modes of PEM fuel cells, fhe following terms are useful ... 

Failure modes studied included fuel starvation and cell reversal, partial fuel starvation, carbon corrosion, membrane thinning and hole formation oxidant starvation excessive drying and flooding, air and fuel contamination, freeze-start and freeze-thaw degradation. 

The Petri-Net degradation model developed in this work is a comprehensive model of the interactions between the previously identified failure modes in a PEMFC of standard construction. The standard construction is such that there is a PTFE based membrane, Carbon/Pt catalyst, steel BIP and carbon GDL. The individual degradation modules range from relatively simple relationships with 2 3 places and a low number of transitions, to larger modules with 8 places and 8 transitions. It contains 21 separate modules that interact to both dehver a voltage degradation value, and further interact with other failure modes. 

The primary failure mode for membranes is hole formation, which can be caused by chemical degradation, material fatigue due to mechanical stresses, or a combination... 

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