Failure modes mechanical degradation

This report provides an aging assessment of electric motors and was conducted under the auspices of the USNRC NPAR. Pertinent failure-related information was derived from LERs, IPRDS, NPRDS, and NPE including failure modes, mechanisms, and causes for motor problems. In addition, motor design and materials of construction were reviewed to identify age-sensitive components. The study included consideration of the seismic susceptibility of age-degraded motor components to externally-induced vibrational effects. 

The check valves 03VH and 05VH are also identical, but they can degrade due to only one degradation mechanism and fail due to a unique failure mode. Three degradation states are considered for this degradation mechanism. The probability density functions of the transition times have the following forms ... 

Plastics. Part of the trend to substitute plastic and composite substrates for metals can be attributed to a desire to avoid the process of metallic corrosion and subsequent failure. Relatively little attention has been called to the possible failure modes of plastics under environments considered corrosive to metals. More extensive work should be conducted on the durability and life expectancy of plastic and composite materials under end-use environments. A further consideration is the potential for polymer degradation by the products of metal corrosion in hybrid structures comprising metal and polymer components. Since it is expected that coatings will continue to be used to protect plastic and composite substrates, ancillary programs need to be conducted on the mechanisms by which coatings can protect such substrates. 

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. 

In a different battery test with a simulated EV load pattern, a SWP-7 cell with an assembly pressure of 60 kPa achieved 450 cycles versus 270 cycles for an AGM cell with 73 kPa. The failure mode was found not to be the expansion of positive plate but, rather, sulfation of the negative plate. This led to the conclusion that the favourable mechanical properties of SWP-type separators suppress degradation of the positive active-material. 

Although cyclic environmental chamber test procedures may suffice for failure processes Involving, for example, mechanical stress, kinetic controlled processes dependent upon time and temperature such as oxidation and diffusion do not lend themselves to adequate Identification and analysis based solely on number of cycles. Thus Sandia National Laboratories developed an accelerated aging protocol for environmental testing which (1) identifies material incompatibilities and subsequent failure modes in Phase I and (2) proceeds with kinetic analysis of the Arrhenius type of failure mode processes which allow extrapolation necessary for lifetime prediction of components in Phase II. Thus two phases are necessary in a complete analysis to accurately predict system lifetimes. The accelerated aging protocol requires the Identification of the stresses that are most likely to damage the performance of the component under test. However, data is frequently not available on the performance of a system under a particular stress. When this is the case, it becomes necessary to make predictions of those stresses most likely to cause degradation and then test to see if the stresses selected are dominant. 

In addition to facilitating the acceptance of CMCs by designers, field tests will also determine CMC component degradation mechanisms and life-failure modes in operational environments. On the basis of these tests, promising composite systems can be refined, and less viable CMCs can be vetted. 

Thomas, S., Gupta, B. R., De, S. K., Mechanical properties, surface morphology and failure mode of gamma-ray irradiated blends of polypropylene and ethylene-vinyl acetate rubber. Polymer Degradation and Stability 1987,18(3), 189-212. 

Notice that the superscripts and subscripts of the failure rate, Xj previously introduced have been omitted since only one component with one degradation mechanism and one failure mode is considered. 

Let us consider the generic /-th component of the system characterized by nf(i) different failure modes and nfi) different degradation mechanisms, the y -th of which has associated degradation states, y =... 

In test case C2 corrective maintenance, inspections and preventive maintenance are performed on a two-unit system in a cold standby configuration. Each unit is affected by two degradation mechanisms and can fail due to two different failure modes. 

Pirmps 03PO and 05PO are identical, with two degradation mechanisms and two failure modes each. Three degradation states are considered for each degradation mechanism. The probabihty density functions of... 

Corrective maintenance (CM) repair action undertaken after a failure. Immediately after a failure mode occurrence, the component becomes unavailable and the repair task begins. After the corrective maintenance, the component is as good as new, i.e., all its degradation mechanisms are in state 1. The duration of this action is much longer than those of the preventive maintenance, since it is completely unscheduled. 

Like mechanically fastened metal structures, composites exhibit failure modes in tension, shear and bearing but, because of the complex failure mechanisms of composites, two further modes are possible, namely cleavage and puUout. Environmental degradation of a bolted joint, after exposure to hot, wet environment is most likely to occur in the shear and bearing strength properties. The evidence shows that for fiber reinforced epoxies, temperature has a more significant effect than moisture, but in the presence of both at 127°C, a strength loss of up to 40 percent is possible. 

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