What type of discontinuity could be considered service induced?

The term "service induced discontinuity" refers to flaws or imperfections that develop in a material as a result of its use in service rather than during its manufacturing process. Fatigue cracks are a common example of such discontinuities. They typically develop over time due to repetitive loading and unloading conditions, which can lead to the gradual deterioration of the material's structure. As a component experiences cyclical stress during its operational life, microscopic cracks can form and expand, ultimately leading to a significant breakage.

Fatigue cracks are particularly relevant in applications involving metals and structural materials, where repeated stress can create conditions conducive to crack formation. Recognizing that these cracks are not present from the outset but rather emerge due to ongoing use captures the essence of "service induced" discontinuities.

In contrast, porosity and machining tears are generally associated with the manufacturing process. Porosity results from issues during casting or forging, while machining tears arise from inadequate finishing methods. Lap discontinuity occurs due to improper fusion during welding and typically reflects a flaw in the joining process rather than during service use. Thus, these options do not align with the definition of service-induced discontinuities.