# Contact Resistance Modeling Under Complex Wear Conditions Based on Fractal Theory

## TL;DR

This paper models contact resistance in electromagnetic rail launchers under extreme wear conditions using fractal theory.

## Contribution

A novel static contact resistance model based on fractal theory is developed to analyze wear effects in electromagnetic launchers.

## Key findings

- Rail surface wear transitions from mechanical to electrical wear along the launch direction.
- Surface roughness decreases with wear, affecting contact resistance sensitivity to external load.
- Fractal theory helps model how wear influences static contact resistance evolution.

## Abstract

The muzzle velocity of electromagnetic rail launchers approaches 1550 m/s, exhibiting typical hypervelocity electrical contact characteristics. During the electromagnetic launching process, extreme conditions, such as high current density, high temperature rise, and strong strain can cause wear on the surfaces of the armature and rail. Electromagnetic launch tests are conducted to study the wear conditions of the rail surface and the relationship between the wear state and contact resistance. After the rail is abraded by hundreds of launching armatures, its surface 2D profile and morphological characteristics are measured and analyzed. Based on fractal theory, the static contact resistance model is developed. Concurrently, the contact resistance at various positions is measured to reveal the evolution of the static contact resistance between the armature and the rail under wear. The research results show that along the direction of the armature launch, the rail surface wear transitions from mechanical wear to electrical wear, the fluctuation range of the 2D profile becomes smoother, and the roughness of the rail surface shows a decreasing trend. When the roughness is greater, the contact resistance is more sensitive to changes in external load.