Metal, is considered to be strong material in most of time during human history. They are heavy, they are strong and they are hard. However, after WW2, new technology created weapons far more powerful than we ever had and traditional metal materials are no longer strong enough. What’s more, metals are too heavy and they are not the ideal material for ballistic protection personal armor.
Kevlar, a very strong synthesized fiber could make cloths that could not be penetrate by pistol bullet or knife. However, the Kevlar cloth is soft and human tissues would be badly injured still. Recently people started to use ultra-high molecular weight polyethylene, even carbon fiber, to replace Kevlar. Although the new fiber might be even stronger, none of them is considered to be hard. These kinds of material alone can protect a person from being killed, but he may still get some bones broken. In order to enhance the protection people put hard plates, such as steel, inside those fiber vests. Those composite designs work well but still are too heavy. Magnesium alloys is lighter but they are not that effective against bullets. Ceramics are extremely hard and light weighted compared with steel. Thus, they are considered to be the best replacement so far. And scientists are trying their best to develop better ceramics, harder, lighter and not that brittle. Today, carbide ceramics are widely used as ballistic proof materials those carbide plates, work together with the strong fibers, saved a lot solders lives.
Tungsten is extremely heavy and hard compared to other metals. Therefore, it is well-known as an ideal material to make armor piercing shells to destroy enemy tanks and armored vehicles after World War II. Combined with the new designs, those shells, with a long and thin tungsten rod as the core, piece the steel armor like there is nothing. To develop better armor, the engineers considered ceramics again and various designs of composite armors were developed. Those composite materials have a sandwich structure, and people use alloys and ceramics to build it. As different layers of these armors have different hardness, the AP shells can even break into several pieces and lost the power when they penetrating the armor. Recently, some countries started to try hang ceramic plates outside of the vehicle to protect the main armor.