Meaning
Geometric sum values of individual touching surface peaks determine the actual interface zone through which load, heat, and electricity flow. The micro contact area is much smaller than the apparent nominal surface area of the mating parts. Designers track this parameter to evaluate thermal joints and electric connectors in high capacity assemblies.
Miscalculating this area leads to overheating or high resistance in electrical switches during heavy duty cycles.
Real Contact
Asperity peaks deform elastically or plastically to support the applied normal load. The micro contact area grows as the squeezing force increases and flattens the tallest surface hills. Test rigs measure electrical resistance across the joint to estimate the sum of these contact spots.
When the applied force is too low, the joint lacks sufficient contact spots and acts as a barrier to heat transfer.
Plastic Flow
High local pressure on individual peaks forces the material to exceed its yield limit and deform permanently. Inside the micro contact area, the average contact pressure approaches the hardness of the softer material. Hardness tests on sample interfaces verify how these junctions flatten under heavy assembly forces.
When asperities flatten completely, the surface undergoes severe wear and can weld together.
Electrical Path
Electric current flows through these narrow metal junctions where the insulating oxide layers have broken down. The micro contact area determines the constriction resistance and the maximum current capacity of the contact.
