Fracture Mechanics Lab Report

The objective of the lab was to learn about fracture mechanics. Fracture mechanics is the branch of structural mechanics that deals with mechanical behaviors of bodies containing flaws. Some important attributes of flaws are size, shape, and location/orientation relative to the stress field.

Procedure:

The primary tools for the lab consisted of 10 ceramic tiles and a Instron machine. The Instron machine was initially set up for 3-point bending by a technician. The base and thickness of the tile was then measured. Following that the length of the ______ was measured. Next, the Instron machine was set to 50 lb/min and 5 tiles was tested using 3 point bending. The max load to fracture in lb was recorded for each tile. Then, the Instron machine was set up for 4
This was expected as the max moment acts on the middle of the specimen, which is used to get stress. The stress is larger with a greater moment and stress is what breaks a beam.

Figure 2: 3 Point Bending Ceramic Tile Specimen Fracture Profile

For the 4 point bending test, the location of fracture varied more as shown in Figure 3, which depicts fracture at the mid left location of the tile. This was variation was expected as with 4 point bending more of the material is experiencing a high load more throughout and therefore there is a chance of a flaw causing fracture.

Figure 3: 4 Point Bending Ceramic Tile Specimen Fracture Profile

Discussion:

Overall, the average max stress of the four point bending test was 771 psi less than that of the three point bending test. This was expected due to four point bending having a more spread out max moment compared to three point bending. This creates a larger chance of a flaw causing fracture. For three point bending the max force is at the center resulting in less of a chance that a flaw would cause fracture unless it was near the