Failure, contact

A loading contact of hard surfaces, for example, by static or dynamic impingement of bodies, can lead to cracking if the stresses exceed critical values. Such damage typically occurs in one of two modes (i) local area loading or blunt contact and point loading or sharp contact.  

An interesting variant of contact failure occurs if the contact is near an edge, as the crack may not stop there and an edge flake may break out [33-36]. Such edge flaking can often be observed in ceramic components used, for example, in classical ceramic 

Although frequently optically displeasing, contact damage does not always cause immediate failure, but may serve as the origin of some delayed failure caused by the subsequent steady or fast growth of cracks. The possible damage mechanisms will be discussed in Section 12.3. 

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One other long-term condition that takes place with relatively low level DC fields in the presence of moisture is the migration of the metal of the conductor into the plastic. This was discovered to be a common thing in the past with silver conductors and phenolic insulators. The first instance of field failures were discovered in telephone equipment. The problem can occur with other metals with phenolic and also conceivably with other plastics that are moisture sensitive and can have a solvating action on the conductor metals that they contact. Most of these type plastics should be avoided inside hermetically sealed containers with movable contacts. Vapors released from the organic plastic deposit on the contacts to produce an insulation layer leading to contact failure. 

Mechanisms of Failure. The causes of connector contact failure can be of a thermal, chemical, or mechanical nature, in addition to misapplication and physical abuse. 

Summary Applications of silicone elastomers for electrical and electronic fields are described. Applications are separated into five categories which involve applications concerning the volume resistivity, coating materials, technology and materials of transparency, other applications for these fields and issues of contact failure with low molecular weight siloxane. 

The contact failure appears within a limited current and voltage range [14]. It is well known that there is a relationship between silicone vapor concentration and the relay life. To get the long life of switching cycles, a reduction of the low molecular weight siloxane included in products is needed. 

Surface contact - failure to remove contamination, coatings or to wet... 

If too much pressure is applied to metal-filled polymer contacts, they can deform and flow over time, lessening contact pressure, and result in open or intermittent contact failures. 

Fretting corrosion, as it applies to tin and solder alloys, is the continuous formation and flaking of tin oxide from mated surfaces due to microscopic motion of one contact with respect to the other (see Fig. 9-11) (Antler, 1985). Motion induced by ordinary vibrations is sufficient to produce enough oxide debris to cause contact failure due to... 

PARTICLE CONTACT FAILURE AND COHESIVE POWDER FLOW CRITERIA... 

Figure 10(a) is a plot of the stress intensity factor K as a function of crack extension. The results indicate that crack propagation will be arrested when a certain extension size is reached. This may explain why the rolling contact failure mode of silicon nitride is non-catastrophic. The computations are based on an assumed crack path derived from the equations (3) to (5). The contact stress is 5.58GPa, and friction coefficient/= -0.05. The aim is to relate the stress intensity factors to crack propagation. The calculation of stress intensity factors presented here, while approximately in the plane of = 0°, may be useful in fatigue life prediction. 

These curves, based on experimental gear failure results, establish the specific lubricant film thickness A) for which the probability of tooth contact failure is 5% and 80%, as a function of the gear pitch line velocity. 

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