hardening rule

例句：

1. 1.The hardening rule for the material is to be followed strictly.
   材料硬化规则必须严格遵循。
2. 2.The engineers are required to follow the hardening rule when designing the structure.
   工程师在设计结构时必须遵循硬化规则。
3. 3.The hardening rule is crucial in determining the strength of the material.
   硬化规则对于确定材料的强度至关重要。