Scope:

ASTM C368 test method is used to predict whether ceramic tableware will shatter under impact.

This test method covers the following tests: 

1. Impact tests at the center of both flatware and hollowware and the rim of hollowware, and 
2. Chipping tests at the rim of flatware. Specimens may be either glazed or unglazed.

Test Procedure:

The following test procedures are described in ASTM C368:

• Procedure for Impact Testing of Flatware at Center:

The cylindrical tube is mounted on the backstop and set at a height such that the three ball bearings mounted at the end of the cylindrical tube are in contact and symmetrical with the central portion of the specimen. The hammer can be used to strike either the face or the back of the specimen. Usually, there are fewer failures when the face is struck. The backstop is adjusted so that the spherical surface of the tup just touches the surface of the specimen when the tup is hanging free. The two wing nuts are tightened at the base of the backstop. The positioning arms are held in a retracted position using their cotter keys so that the forward edges of the sleeve coincide with the clamp. The clamps on the vertical posts are adjusted to grip the specimen at the same height that the pendulum will strike it. The arms are positioned so that the rubber-covered surface will contact the rim of the sample. The cotter keys are removed to allow the positioning arms to hold the specimen against the cylindrical tube. The pendulum support bar is positioned and locked in position using the handwheels so that the tup strikes the center of the specimen. Once the preliminary adjustments are completed, the specimens are subjected to a schedule of impact force gradually increasing at a constant rate until the initial fracture.

• Procedure for Impact Testing of Hollowware at Center:

The same procedure is followed for this ASTM C368 test as described for flatware except for the cylindrical tube and the two triangular castings forming the V are removed to permit the rim of the specimen to be in contact with the surface of the backstop. The specimens are struck at the center of the back, and the positioning arms are allowed to contact the specimen at the foot rather than at the rim.

• Procedure for Chipping Test:  

Once the preliminary adjustments are completed the rolled-edge specimens are repeatedly struck on the edge with the cylindrical end of the hammer with blows of increasing force until failure occurs, beginning with an initial blow and increasing the force of each succeeding blow in given increments. 

Video 01: ASTM C368 Ceramic impact tester

Specimen size:

In ASTM C368, the specimens should be representative of the lot being sampled. Impact tests require a minimum of ten specimens and chipping tests require at least five specimens. Specimens should be inspected for soundness and obvious physical defects before testing.

Data:

The strength factor for flatware is calculated and reported. 

Conclusion:

ASTM C368 test method is used to predict whether ceramic tableware will shatter under impact.