Which of the following is a method of forming test specimens?

Vibration casting is a widely recognized method of forming test specimens, particularly in the context of refractory materials. This technique involves pouring the material into a mold and then applying vibrations to consolidate it. The vibrations help eliminate air pockets and ensure better density and structural integrity in the finished specimen. This method is crucial for achieving uniformity and consistency, which are essential for accurate testing results.

While other methods like 3D printing, wooden framing, and injection molding have their own applications, they may not be as relevant or widely used in the context of forming test specimens for refractory materials. 3D printing is emerging in various manufacturing fields but is not traditionally associated with traditional refractory specimen formation. Wooden framing may be useful for some construction applications, but it lacks the precision required for testing materials. Injection molding, while effective for certain plastics and similar materials, is generally not applicable to the refractory context, where heat resistance and thermal properties are critical.

Therefore, vibration casting is the preferred method due to its effectiveness in ensuring the quality and reliability of test specimens in the refractory industry.