Stress corrosion cracking is primarily caused by what factors?

Stress corrosion cracking is primarily caused by the combination of constant tensile stress and a corrosive environment. This phenomenon occurs when a material, typically a metal, is subjected to sustained tensile stress while simultaneously being exposed to specific corrosive agents. The interaction between the mechanical stress and the corrosive environment leads to the deterioration of the material over time, ultimately resulting in cracking.

This type of failure is particularly relevant in various industrial and naval applications where components are not only under load but also subject to corrosive conditions, such as seawater or chemical exposure. The tensile stress can come from various sources, including mechanical loads, residual stresses from welding processes, or manufacturing imperfections. When these factors converge, they significantly reduce the material's ability to withstand tensile loads, leading to the formation and propagation of cracks.

The other options highlight important factors related to material failure but don't address the specific mechanics of stress corrosion cracking as accurately. High temperatures and low pH levels can affect corrosion rates, but they don't encapsulate the tensile stress component crucial to stress corrosion cracking. Similarly, fatigue and high humidity may contribute to other forms of corrosion or failure, while physical impacts and thermal cycling can influence stress levels but do not directly correlate with the specific mechanism of stress corrosion cracking.