Quantum mechanics endows terbium and dysprosium with an inherent, indestructible, inseparable coupling between magnetic and mechanical effects. Combining with iron yields an alloy, terfenol-d, that is a soft ferromagnet -- a permanent magnet will stick to it but terfenol-d itself cannot be either permanently polarized or permanently depolarized. Since its origin is atomic, magnetostriction:

• Is immune to magnetic fields beyond saturation.
  
  
• Cannot be fatigued by high mechanical output.
  
  
• Cannot be permanently destroyed by temperature. If heated but not melted, terfenol-d magnetostriction is restored below its Curie temperature of 357C.

Magnetic field from the energizing wire coil crosses a small gap between terfenol-d and wire. Since they are not in contact, strain differences cannot cause fatigue cracks.

Billions of energization cycles of individual terfenol-d rods inside actuators have been run without detectable degradation.

• Power ultrasonic actuators. Billions of ultrasonic cycles -- fast and durable.
  
  
• The Navy tested a high preload terfenol-d sonar projector to billions of cycles without performance degradation, confirming that the property of interest is indestructible.

Compression Fatigue

Stress Cycle: -250   250 MPa @ 10 Hz
Runout Point >1 10^6 Cycles

Source: Load Capacity of Giant Magnetostrictive Materials

Packaging the quantum mechanical effect into terfenol-d and then packaging that into a suitable actuator are why it will survive in a harsh environment such as an engine cylinder head or an oil well and why the words robust, durable, and survivable apply. Packaging is a matter of terfenol-d metallurgy and ordinary engineering.