Copyright Goodheart-Willcox Co., Inc. 595 Chapter 17 ∣ Final Drives metal into a casting) will not have chevron-shaped marks. A brittle fracture that follows the grain boundaries leaves a darker, rough surface. A brittle fracture that occurs through the grains has a sparkled appearance when a light shines on the surface. See Figure 17-42. A combination fracture, as its name implies, occurs to a component as the result of a combination of fatigue fracture, impact fracture, ductile fracture, or brittle fracture. Distortion Shafts, bolts, rods, and other ductile materials can distort. Examples of distortion are tor- sional twisting or bending. A distortion failure differs from a fracture because the compo- nent distorts but does not fracture into two or more pieces. See Figure 17-43. Corrosion Water and other contaminants can cause components to corrode. The corrosion can result in wear, distortion, or fractures. Corrective actions include preventing the intrusion of moisture and the use of proper lubricants. Ratchet mark Beach marks Fatigue zone Final fast fracture Goodheart-Willcox Publisher Figure 17-39. A shaft failure exhibiting multiple ratchet marks. Goodheart-Willcox Publisher Figure 17-40. This shaft has a torsional stress fracture, as evidenced by the 45° line at the initial point of fracture. Goodheart-Willcox Publisher Figure 17-41. A ductile fracture causes the component to deform. Shown here is one half of a piston connector-rod bolt that was over- heated, resulting in a ductile fracture. Goodheart-Willcox Publisher Figure 17-42. The threaded shaft of this clevis is fractured. The iron- based fracture leaves behind a rough, “woody” surface texture. Goodheart-Willcox Publisher Figure 17-43. This bolt exhibits distortion due to being tightened beyond its yield strength. As a result, the bolt is stretched and narrowed. Goodheart-Willcox Publisher Figure 17-38. The fatigue failure depicted in this drawing originated at the single ratchet mark and radiated outward, as shown by the beach marks. The fatigue zone is an area of slow crack growth. The final fast fracture is at the bottom.