What are 'smart materials' known for in engineering?

Smart materials are distinctive in engineering for their ability to change properties in response to external stimuli such as temperature, pressure, moisture, or electric and magnetic fields. This characteristic allows them to exhibit behaviors like shape-shifting, self-healing, or adapting their stiffness and damping properties, making them highly versatile in various applications.

For instance, shape memory alloys can return to a predetermined shape when heated, and piezoelectric materials can generate an electrical charge in response to applied mechanical stress. This responsiveness to stimuli is what sets smart materials apart from traditional materials, which typically remain unchanged under varying conditions.

The other options do not accurately define smart materials; remaining unchanged or merging with traditional materials does not capture the essence of their unique behaviors, and their application is not limited to high-temperature scenarios. Instead, smart materials span a wide range of temperatures and environments, broadening their potential uses in modern engineering designs.