Non-Destructive Testing (NDT) Practice Test

What is a characteristic of shear waves in ultrasonic testing?

1. They travel faster than longitudinal waves

2. They cannot propagate through liquids

3. They penetrate further than longitudinal waves

4. They are used to inspect only specific materials

The correct answer is: They cannot propagate through liquids

Shear waves, also known as S-waves, are indeed characterized by their inability to propagate through fluids, which distinguishes them from longitudinal waves. In the context of ultrasonic testing, this characteristic is crucial because shear waves move through solids by causing shear strain in the material. This type of motion is not possible in fluids, where the particles can only support longitudinal stress. Understanding this aspect of shear waves is essential, particularly in applications such as inspecting structures made of solid materials (like metals and composites) where the detection of flaws or integrity evaluation requires the shear wave's unique propagation characteristics. The fact that they are ineffective in liquids makes them particularly valuable in testing solid materials since it allows for an assessment of defects or discontinuities that may be missed by longitudinal waves, which can propagate through both solids and fluids. Other options do not align with the fundamental properties of shear waves. For example, shear waves do not travel faster than longitudinal waves; in fact, they generally have a slower velocity in solids compared to longitudinal waves. Moreover, they do not penetrate further than longitudinal waves either; longitudinal waves typically have greater penetration due to their ability to travel through liquids and solids. Lastly, while shear waves are often used for specific materials, they are not limited to just a