What are the units of toughness in a material?

• A. Joules per cubic meter
• B. Joules per square meter
• C. Pascals
• D. Joules

Answer: (A)

Toughness is the amount of energy a material can absorb before it fractures, normalized by its volume. Since energy is measured in joules and volume in cubic meters, the proper unit is joules per cubic meter, an energy density that reflects how much energy the material can take per unit volume. This comes from toughness being the area under the stress–strain curve, which has units of energy per volume. The other options don’t fit: joules per square meter would be energy per area (not a volume-based property), pascals are pressure (energy per volume times a factor gives stress, but not toughness), and joules alone is total energy that depends on specimen size, not a material property.