**2.1 Erosion mechanism**

There have been a lot of studies on the solid particle erosion mechanism. Researchers found that under the action of sand and dust in complex environment, multiple erosion failure mechanisms are coupled, and a single erosion theory cannot meet the requirements of revealing the erosion phenomenon. At present, there are mainly the following erosion wear theories.

In 1985, the micro cutting theory came out. Subsequently, the erosion theory, secondary erosion theory, adiabatic shear and local deformation wear theory of plastic/brittle materials have developed successively. From the current erosion theory, micro cutting theory [8, 9] (as shown in **Figure 2a**) has analyzed the cutting action in

**Figure 2.** *Erosion mechanism (a) low angle, and (b) high angle.*

the erosion process under the condition of small angle of attack (small angle), but there is a large error in explaining the erosion behavior at large angle of attack (large angle). The deformation and wear theory [10] revealed the deformation process and energy change analysis of samples after multiple impact angle erosion. The theoretical model believed that the micro cutting effect of particles was not obvious during large angle erosion, and the wear of materials was mainly related to the deformation caused by impact, which made the materials crack and fall off. The elastoplastic indentation fracture theory [11] analyzed the erosion of brittle materials by sand dust under the condition of high angle of attack (**Figure 2b**). The secondary erosion theory [12] provides a good explanation for the complex process of erosion process, namely, brittle particle fragmentation and re erosion of materials.
