hardness self-excitation

例句：

1. 1.The material has a high hardness and is suitable for making tools.
   这种材料硬度高，适合制作工具。
2. 2. The metal was found to be very hardness, which made it difficult to work with.
   这种金属非常坚硬，使得加工起来很困难。
3. 3.The new car has a higher hardness than the old one, so it will last longer.
   这款新车比旧款更硬，所以使用寿命更长。